aboutsummaryrefslogtreecommitdiffstats
path: root/erts/doc/src/erl_nif.xml
blob: 4ec5ab78d81f43b7969560dceca66d814c942a30 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE cref SYSTEM "cref.dtd">

<cref>
  <header>
    <copyright>
      <year>2001</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>erl_nif</title>
    <prepared>Sverker Eriksson</prepared>
    <responsible>Sverker Eriksson</responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>2009-11-17</date>
    <rev>PA1</rev>
    <file>erl_nif.xml</file>
  </header>
  <lib>erl_nif</lib>
  <libsummary>API functions for an Erlang NIF library.</libsummary>
  <description>
    <p>A NIF library contains native implementation of some functions
      of an Erlang module. The native implemented functions (NIFs) are
      called like any other functions without any difference to the
      caller. Each NIF must have an implementation in Erlang that
      is invoked if the function is called before the NIF library
      is successfully loaded. A typical such stub implementation
      is to throw an exception. But it can also be used as a fallback
      implementation if the NIF library is not implemented for some
      architecture.</p>

    <warning>
      <marker id="WARNING"/>
      <p><em>Use this functionality with extreme care.</em></p>
      <p>A native function is executed as a direct extension of the
        native code of the VM. Execution is not made in a safe environment.
        The VM <em>cannot</em> provide the same services as provided when
        executing Erlang code, such as pre-emptive scheduling or memory
        protection. If the native function does not behave well, the whole
        VM will misbehave.</p>
      <list type="bulleted">
        <item>
          <p>A native function that crash will crash the whole VM.</p>
        </item>
        <item>
          <p>An erroneously implemented native function can cause a VM
            internal state inconsistency, which can cause a crash of the VM,
            or miscellaneous misbehaviors of the VM at any point after the
            call to the native function.</p>
        </item>
        <item>
          <p>A native function doing <seealso marker="#lengthy_work">lengthy
            work</seealso> before returning degrades responsiveness of the VM,
            and can cause miscellaneous strange behaviors. Such strange
            behaviors include, but are not limited to, extreme memory usage,
            and bad load balancing between schedulers. Strange behaviors that
            can occur because of lengthy work can also vary between Erlang/OTP
            releases.</p>
        </item>
      </list>
    </warning>

    <p>A minimal example of a NIF library can look as follows:</p>

    <code type="none">
/* niftest.c */
#include "erl_nif.h"

static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
    return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1);
}

static ErlNifFunc nif_funcs[] =
{
    {"hello", 0, hello}
};

ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)</code>

    <p>The Erlang module can look as follows:</p>

    <code type="none">
-module(niftest).

-export([init/0, hello/0]).

init() ->
      erlang:load_nif("./niftest", 0).

hello() ->
      "NIF library not loaded".</code>

    <p>Compile and test can look as follows (on Linux):</p>

    <code type="none">
$> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
$> erl

1> c(niftest).
{ok,niftest}
2> niftest:hello().
"NIF library not loaded"
3> niftest:init().
ok
4> niftest:hello().
"Hello world!"</code>

    <p>A better solution for a real module is to take advantage of the new
      directive <c>on load</c> (see section
      <seealso marker="doc/reference_manual:code_loading#on_load">Running a
      Function When a Module is Loaded</seealso> in the Erlang Reference
      Manual) to load the NIF library automatically when the module is
      loaded.</p>

    <note>
      <p>A NIF does not have to be exported, it can be local to the module.
        However, unused local stub functions will be optimized
        away by the compiler, causing loading of the NIF library to fail.</p>
    </note>

    <p>A loaded NIF library is tied to the Erlang module code version
      that loaded it. If the module is upgraded with a new version, the
      new Erlang code need to load its own NIF library (or maybe choose not
      to). The new code version can, however, choose to load the
      same NIF library as the old code if it wants to. Sharing the
      dynamic library means that static data defined by the library
      is shared as well. To avoid unintentionally shared static
      data, each Erlang module code can keep its own private data. This
      private data can be set when the NIF library is loaded and
      then retrieved by calling <seealso marker="#enif_priv_data">
      <c>enif_priv_data</c></seealso>.</p>

    <p>A NIF library cannot be loaded explicitly. A library is
      automatically unloaded when the module code that it belongs to is purged
      by the code server.</p>
  </description>

  <section>
  <title>Functionality</title>
    <p>All functions that a NIF library needs to do with Erlang are
      performed through the NIF API functions. Functions exist
      for the following functionality:</p>

    <taglist>
      <tag>Read and write Erlang terms</tag>
      <item>
        <p>Any Erlang terms can be passed to a NIF as function arguments and
          be returned as function return values. The terms are of C-type
          <seealso marker="#ERL_NIF_TERM"><c>ERL_NIF_TERM</c></seealso> and can
          only be read or written using API functions. Most functions to read
          the content of a term are prefixed <c>enif_get_</c> and usually return
          <c>true</c> (or <c>false</c>) if the term is of the expected type (or
          not). The functions to write terms are all prefixed <c>enif_make_</c>
          and usually
          return the created <c>ERL_NIF_TERM</c>. There are also some functions
          to query terms, like <c>enif_is_atom</c>, <c>enif_is_identical</c>,
          and <c>enif_compare</c>.</p>
        <p>All terms of type <c>ERL_NIF_TERM</c> belong to an environment of
          type <seealso marker="#ErlNifEnv"><c>ErlNifEnv</c></seealso>. The
          lifetime of a term is controlled by the lifetime of its environment
          object. All API functions that read or write terms has the
          environment that the term belongs to as the first function
          argument.</p>
      </item>
      <tag>Binaries</tag>
      <item>
        <p>Terms of type binary are accessed with the help of struct type
          <seealso marker="#ErlNifBinary"><c>ErlNifBinary</c></seealso>,
          which contains a pointer (<c>data</c>) to the raw binary data and the
          length (<c>size</c>) of the data in bytes. Both <c>data</c> and
          <c>size</c> are read-only and are only to be written using calls to
          API functions. Instances of <c>ErlNifBinary</c> are, however, always
          allocated by the user (usually as local variables).</p>
        <p>The raw data pointed to by <c>data</c> is only mutable after a call
          to <seealso marker="#enif_alloc_binary">
          <c>enif_alloc_binary</c></seealso> or
          <seealso marker="#enif_realloc_binary">
          <c>enif_realloc_binary</c></seealso>. All other functions that
          operate on a binary leave the data as read-only.
          A mutable binary must in the end either be freed with
          <seealso marker="#enif_release_binary">
          <c>enif_release_binary</c></seealso>
          or made read-only by transferring it to an Erlang term with
          <seealso marker="#enif_make_binary"><c>enif_make_binary</c></seealso>.
          However, it does not have to occur in the same NIF call. Read-only
          binaries do not have to be released.</p>
        <p><seealso marker="#enif_make_new_binary">
          <c>enif_make_new_binary</c></seealso> can be used as a shortcut to
          allocate and return a binary in the same NIF call.</p>
        <p>Binaries are sequences of whole bytes. Bitstrings with an arbitrary
          bit length have no support yet.</p>
      </item>
      <tag>Resource objects</tag>
      <item>
        <p>The use of resource objects is a safe way to return pointers to
          native data structures from a NIF. A resource object is
          only a block of memory allocated with
          <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>.
          A handle ("safe pointer") to this memory block can then be returned
          to Erlang by the use of
          <seealso marker="#enif_make_resource">
          <c>enif_make_resource</c></seealso>.
          The term returned by <c>enif_make_resource</c> is opaque in nature.
          It can be stored and passed between processes on the same node, but
          the only real end usage is to pass it back as an argument to a NIF.
          The NIF can then call <seealso marker="#enif_get_resource">
          <c>enif_get_resource</c></seealso> and get back a pointer to the
          memory block, which is guaranteed to still be valid. A resource
          object is not deallocated until the last handle term
          is garbage collected by the VM and the resource is released with
          <seealso marker="#enif_release_resource">
          <c>enif_release_resource</c></seealso>
          (not necessarily in that order).</p>
        <p>All resource objects are created as instances of some <em>resource
          type</em>. This makes resources from different modules to be
          distinguishable. A resource type is created by calling
          <seealso marker="#enif_open_resource_type">
          <c>enif_open_resource_type</c></seealso> when a library is loaded.
          Objects of that resource type can then later be allocated and
          <c>enif_get_resource</c> verifies that the resource is of the
          expected type. A resource type can have a user-supplied destructor
          function, which is automatically called when resources of that type
          are released (by either the garbage collector or
          <c>enif_release_resource</c>). Resource types are uniquely identified
          by a supplied name string and the name of the implementing module.</p>
        <marker id="enif_resource_example"/>
        <p>The following is a template example of how to create and return a
          resource object.</p>
        <code type="none">
ERL_NIF_TERM term;
MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));

/* initialize struct ... */

term = enif_make_resource(env, obj);

if (keep_a_reference_of_our_own) {
    /* store 'obj' in static variable, private data or other resource object */
}
else {
    enif_release_resource(obj);
    /* resource now only owned by "Erlang" */
}
return term;</code>
        <p>Notice that once <c>enif_make_resource</c> creates the term to
          return to Erlang, the code can choose to either keep its own
          native pointer to the allocated struct and release it later, or
          release it immediately and rely only on the garbage collector
          to deallocate the resource object eventually when it collects
          the term.</p> 
        <p>Another use of resource objects is to create binary terms with
          user-defined memory management.
          <seealso marker="#enif_make_resource_binary">
          <c>enif_make_resource_binary</c></seealso>
          creates a binary term that is connected to a resource object. The
          destructor of the resource is called when the binary is garbage
          collected, at which time the binary data can be released. An example
          of this can be a binary term consisting of data from a <c>mmap</c>'ed
          file. The destructor can then do <c>munmap</c> to release the memory
          region.</p>
        <p>Resource types support upgrade in runtime by allowing a loaded NIF
          library to take over an already existing resource type and by that
          "inherit" all existing objects of that type. The destructor of the
          new library is thereafter called for the inherited objects and the
          library with the old destructor function can be safely unloaded.
          Existing resource objects, of a module that is upgraded, must either
          be deleted or taken over by the new NIF library. The unloading of a
          library is postponed as long as there exist resource objects with a
          destructor function in the library.</p>
      </item>
      <tag>Threads and concurrency</tag>
      <item>
        <p>A NIF is thread-safe without any explicit synchronization as
          long as it acts as a pure function and only reads the supplied
          arguments. When you write to a shared state either through
          static variables or <seealso marker="#enif_priv_data">
          <c>enif_priv_data</c></seealso>, you need to supply your own explicit
          synchronization. This includes terms in process-independent
          environments that are shared between threads. Resource objects also
          require synchronization if you treat them as mutable.</p>
        <p>The library initialization callbacks <c>load</c>, <c>reload</c>, and
          <c>upgrade</c> are all thread-safe even for shared state data.</p>
      </item>
      <tag><marker id="version_management"/>Version Management</tag>
      <item>
        <p>When a NIF library is built, information about the NIF API version
          is compiled into the library. When a NIF library is loaded, the
          runtime system verifies that the library is of a compatible version.
          <c>erl_nif.h</c> defines the following:</p>
        <taglist>
          <tag><c>ERL_NIF_MAJOR_VERSION</c></tag>
          <item>
            <p>Incremented when NIF library incompatible changes are made to the
              Erlang runtime system. Normally it suffices to recompile the NIF
              library when the <c>ERL_NIF_MAJOR_VERSION</c> has changed, but it
              can, under rare circumstances, mean that NIF libraries must be
              slightly modified. If so, this will of course be documented.</p>
          </item>
          <tag><c>ERL_NIF_MINOR_VERSION</c></tag>
          <item>
            <p>Incremented when new features are added. The runtime system uses
              the minor version to determine what features to use.</p>
          </item>
        </taglist>
        <p>The runtime system normally refuses to load a NIF library if
          the major versions differ, or if the major versions are equal and
          the minor version used by the NIF library is greater than the one
          used by the runtime system. Old NIF libraries with lower major
          versions are, however, allowed after a bump of the major version
          during a transition period of two major releases. Such old NIF
          libraries can however fail if deprecated features are used.</p>
      </item>
      <tag><marker id="time_measurement"/>Time Measurement</tag>
      <item>
        <p>Support for time measurement in NIF libraries:</p>
        <list type="bulleted">
          <item><seealso marker="#ErlNifTime">
            <c>ErlNifTime</c></seealso></item>
          <item><seealso marker="#ErlNifTimeUnit">
            <c>ErlNifTimeUnit</c></seealso></item>
          <item><seealso marker="#enif_monotonic_time">
            <c>enif_monotonic_time()</c></seealso></item>
          <item><seealso marker="#enif_time_offset">
            <c>enif_time_offset()</c></seealso></item>
          <item><seealso marker="#enif_convert_time_unit">
            <c>enif_convert_time_unit()</c></seealso></item>
      </list>
      </item>
      <tag><marker id="lengthy_work"/>Long-running NIFs</tag>
      <item>
        <p>As mentioned in the <seealso marker="#WARNING">warning</seealso> text
          at the beginning of this manual page, it is of <em>vital
          importance</em> that a native function returns relatively fast. It is
          difficult to give an exact maximum amount of time that a native
          function is allowed to work, but usually a well-behaving native
          function is to return to its caller within 1 millisecond. This can be
          achieved using different approaches. If you have full control over the
          code to execute in the native function, the best approach is to
          divide the work into multiple chunks of work and call the native
          function multiple times. This is, however, not always possible, for
          example when calling third-party libraries.</p>
        <p>The <seealso marker="#enif_consume_timeslice">
          <c>enif_consume_timeslice()</c></seealso> function can be used to
          inform the runtime system about the length of the NIF call.
          It is typically always to be used unless the NIF executes very
          fast.</p>
        <p>If the NIF call is too lengthy, this must be handled in one of
          the following ways to avoid degraded responsiveness, scheduler load
          balancing problems, and other strange behaviors:</p>
        <taglist>
          <tag>Yielding NIF</tag>
          <item>
            <p>If the functionality of a long-running NIF can be split so that
              its work can be achieved through a series of shorter NIF calls,
              the application has two options:</p>
            <list type="bulleted">
              <item>
                <p>Make that series of NIF calls from the Erlang level.</p>
              </item>
              <item>
                <p>Call a NIF that first performs a chunk of the work, then
                  invokes the <seealso marker="#enif_schedule_nif">
                  <c>enif_schedule_nif</c></seealso> function to schedule
                  another NIF call to perform the next chunk. The final call
                  scheduled in this manner can then return the overall
                  result.</p>
              </item>
            </list>
            <p>Breaking up a long-running function in this manner enables the
              VM to regain control between calls to the NIFs.</p>
            <p>This approach is always preferred over the other alternatives
              described below. This both from a performance perspective and
              a system characteristics perspective.</p>
          </item>
          <tag>Threaded NIF</tag>
          <item>
            <p>This is accomplished by dispatching the work to another thread
              managed by the NIF library, return from the NIF, and wait for
              the result. The thread can send the result back to the Erlang
              process using <seealso marker="#enif_send">
              <c>enif_send</c></seealso>.
              Information about thread primitives is provided below.</p>
          </item>
          <tag><marker id="dirty_nifs"/>Dirty NIF</tag>
          <item>
            <note>
              <p><em>The dirty NIF functionality described here
                is experimental</em>. Dirty NIF support is available only when
                the emulator is configured with dirty schedulers enabled. This
                feature is disabled by default. The Erlang runtime
                without SMP support does not support dirty schedulers even when
                the dirty scheduler support is enabled. To check at runtime for
                the presence of dirty scheduler threads, code can use the
                <seealso marker="#enif_system_info">
                <c>enif_system_info()</c></seealso> API function.</p>
            </note>
            <p>A NIF that cannot be split and cannot execute in a millisecond
              or less is called a "dirty NIF", as it performs work that the
              ordinary schedulers of the Erlang runtime system cannot handle cleanly.
              Applications that make use of such functions must indicate to the
              runtime that the functions are dirty so they can be handled 
              specially. This is handled by executing dirty jobs on a separate
	      set of schedulers called dirty schedulers. A dirty NIF executing
	      on a dirty scheduler does not have the same duration restriction
	      as a normal NIF.
            </p>

            <p>
              It is important to classify the dirty job correct. An I/O bound
	      job should be classified as such, and a CPU bound job should be
	      classified as such. If you should classify CPU bound jobs
	      as I/O bound jobs, dirty I/O schedulers might starve ordinary
	      schedulers. I/O bound jobs are expected to either block waiting
	      for I/O, and/or spend a limited amount of time moving data.
            </p>

            <p>
              To schedule a dirty NIF for execution, the application has two options:</p>
            <list type="bulleted">
              <item>
                <p>Set the appropriate flags value for the dirty NIF in its
                  <seealso marker="#ErlNifFunc"> <c>ErlNifFunc</c></seealso>
                  entry.</p>
              </item>
              <item>
                <p>Call <seealso marker="#enif_schedule_nif">
                  <c>enif_schedule_nif</c></seealso>, pass to it a pointer
                  to the dirty NIF to be executed, and indicate with argument
                  <c>flags</c> whether it expects the operation to be CPU-bound
                  or I/O-bound.</p>
              </item>
            </list>
            <p>A job that alternates between I/O bound and CPU bound can be
              reclassified and rescheduled using <c>enif_schedule_nif</c> so
              that it executes on the correct type of dirty scheduler at all
              times. For more information see the documentation of the
              <c>erl(1)</c> command line arguments
              <seealso marker="erl#+SDcpu"><c>+SDcpu</c></seealso>,
              and <seealso marker="erl#+SDio"><c>+SDio</c></seealso>.</p>
            <p>While a process executes a dirty NIF, some operations that
              communicate with it can take a very long time to complete.
              Suspend or garbage collection of a process executing a dirty
              NIF cannot be done until the dirty NIF has returned. Thus, other
              processes waiting for such operations to complete might
              have to wait for a very long time. Blocking multi-scheduling, that
              is, calling <seealso marker="erlang#system_flag_multi_scheduling">
              <c>erlang:system_flag(multi_scheduling, block)</c></seealso>, can
              also take a very long time to complete. This becaue all ongoing
              dirty operations on all dirty schedulers must complete before
              the block operation can complete.</p>
            <p>Many operations communicating with a process executing a
              dirty NIF can, however, complete while it executes the
              dirty NIF. For example, retrieving information about it through
              <seealso marker="erlang:process_info/1">
              <c>erlang:process_info</c></seealso>, setting its group leader,
              register/unregister its name, and so on.</p>
            <p>Termination of a process executing a dirty NIF can only be
              completed up to a certain point while it executes the dirty NIF.
              All Erlang resources, such as its registered name and its <c>ets</c>
              tables, are released. All links and monitors are triggered. The
              execution of the NIF is, however, <em>not</em> stopped. The NIF
              can safely continue execution, allocate heap memory, and so on,
              but it is of course better to stop executing as soon as possible.
              The NIF can check whether a current process is alive using
              <seealso marker="#enif_is_current_process_alive">
              <c>enif_is_current_process_alive</c></seealso>. Communication
              using <seealso marker="#enif_send"><c>enif_send</c></seealso> and
              <seealso marker="#enif_port_command">
              <c>enif_port_command</c></seealso> is also dropped when the
              sending process is not alive. Deallocation of certain internal
              resources, such as process heap and process control block, is
              delayed until the dirty NIF has completed.</p>
          </item>
        </taglist>
      </item>
    </taglist>
  </section>

  <section>
    <title>Initialization</title>
    <taglist>
      <tag><marker id="ERL_NIF_INIT"/><c>ERL_NIF_INIT(MODULE,
        ErlNifFunc funcs[], load, reload, upgrade, unload)</c></tag>
      <item>
        <p>This is the magic macro to initialize a NIF library. It
          is to be evaluated in global file scope.</p>
        <p><c>MODULE</c> is the name of the Erlang module as an
          identifier without string quotations. It is stringified by
          the macro.</p>
        <p><c>funcs</c> is a static array of function descriptors for
          all the implemented NIFs in this library.</p>
        <p><c>load</c>, <c>reload</c>, <c>upgrade</c> and <c>unload</c>
          are pointers to functions. One of <c>load</c>, <c>reload</c>, or
          <c>upgrade</c> is called to initialize the library.
          <c>unload</c> is called to release the library. All are
          described individually below.</p>
        <p>If compiling a NIF for static inclusion through
          <c>--enable-static-nifs</c>, you must define <c>STATIC_ERLANG_NIF</c>
           before the <c>ERL_NIF_INIT</c> declaration.</p>
      </item>
      <tag><marker id="load"/><c>int (*load)(ErlNifEnv* env, void** priv_data,
        ERL_NIF_TERM load_info)</c></tag>
      <item>
        <p><c>load</c> is called when the NIF library is loaded
          and no previously loaded library exists for this module.</p>
        <p><c>*priv_data</c> can be set to point to some private data
          that the library needs to keep a state between NIF
          calls. <c>enif_priv_data</c> returns this pointer.
          <c>*priv_data</c> is initialized to <c>NULL</c> when <c>load</c> is
          called.</p> 
        <p><c>load_info</c> is the second argument to <seealso
          marker="erlang#load_nif-2"><c>erlang:load_nif/2</c></seealso>.</p>
        <p>The library fails to load if <c>load</c> returns
          anything other than <c>0</c>. <c>load</c> can be <c>NULL</c> if
          initialization is not needed.</p> 
      </item>
      <tag><marker id="upgrade"/><c>int (*upgrade)(ErlNifEnv* env, void**
        priv_data, void** old_priv_data, ERL_NIF_TERM load_info)</c></tag>
      <item>
        <p><c>upgrade</c> is called when the NIF library is loaded
          and there is old code of this module with a loaded NIF library.</p>
        <p>Works as <c>load</c>, except that <c>*old_priv_data</c> already
          contains the value set by the last call to <c>load</c> or
          <c>reload</c> for the old module code. <c>*priv_data</c> is
          initialized to <c>NULL</c> when <c>upgrade</c> is called. It is
          allowed to write to both <c>*priv_data</c> and
          <c>*old_priv_data.</c></p> 
        <p>The library fails to load if <c>upgrade</c> returns
           anything other than <c>0</c> or if <c>upgrade</c> is <c>NULL</c>.</p>
      </item>
      <tag><marker id="unload"/><c>void (*unload)(ErlNifEnv* env, void*
        priv_data)</c></tag>
      <item>
        <p><c>unload</c> is called when the module code that
          the NIF library belongs to is purged as old. New code of the same
          module may or may not exist. Notice that <c>unload</c> is not
          called for a replaced library as a consequence of <c>reload</c>.</p>
      </item>
      <tag><marker id="reload"/><c>int (*reload)(ErlNifEnv* env, void**
        priv_data, ERL_NIF_TERM load_info)</c></tag>
      <item>
        <note>
          <p><em>The reload mechanism is deprecated.</em> It was only intended
            as a development feature. Do not use it as an upgrade method for
            live production systems. It can be removed in future releases.
            Ensure to pass <c>reload</c> as <c>NULL</c> to
            <seealso marker="#ERL_NIF_INIT"><c>ERL_NIF_INIT</c></seealso>
            to disable it when not used.</p>
        </note>
        <p><c>reload</c> is called when the NIF library is loaded and a
          previously loaded library already exists for this module code.</p>
        <p>Works as <c>load</c>, except that
          <c>*priv_data</c> already contains the value set by the
          previous call to <c>load</c> or <c>reload</c>.</p>
        <p>The library fails to load if <c>reload</c> returns
          anything other than <c>0</c> or if <c>reload</c> is <c>NULL</c>.</p> 
      </item>
    </taglist>
  </section>

  <section>
    <title>Data Types</title>
    <taglist>
      <tag><marker id="ERL_NIF_TERM"/><c>ERL_NIF_TERM</c></tag>
      <item>
        <p>Variables of type <c>ERL_NIF_TERM</c> can refer to any Erlang term.
          This is an opaque type and values of it can only by used either as
          arguments to API functions or as return values from NIFs. All
          <c>ERL_NIF_TERM</c>s belong to an environment
          (<seealso marker="#ErlNifEnv"><c>ErlNifEnv</c></seealso>).
          A term cannot be destructed individually, it is valid until its
          environment is destructed.</p>
      </item>
      <tag><marker id="ErlNifEnv"/><c>ErlNifEnv</c></tag>
      <item>
        <p><c>ErlNifEnv</c> represents an environment that can host Erlang
          terms. All terms in an environment are valid as long as the
          environment is valid. <c>ErlNifEnv</c> is an opaque type; pointers to
          it can only be passed on to API functions. Two types of environments
          exist:</p>
        <taglist>
          <tag>Process-bound environment</tag>
          <item>
            <p>Passed as the first argument to all NIFs. All function arguments
              passed to a NIF belong to that environment. The return value from
              a NIF must also be a term belonging to the same environment.</p>
            <p>A process-bound environment contains transient information
              about the calling Erlang process. The environment is only valid
              in the thread where it was supplied as argument until the NIF
              returns. It is thus useless and dangerous to store pointers to
              process-bound environments between NIF calls.</p>
          </item>
          <tag>Process-independent environment</tag>
          <item>
            <p>Created by calling <seealso marker="#enif_alloc_env">
              <c>enif_alloc_env</c></seealso>. This environment can be
              used to store terms between NIF calls and to send terms with
              <seealso marker="#enif_send"><c>enif_send</c></seealso>. A
              process-independent environment with all its terms is valid until
              you explicitly invalidate it with
              <seealso marker="#enif_free_env"><c>enif_free_env</c></seealso>
              or <c>enif_send</c>.</p>
          </item>
        </taglist>
        <p>All contained terms of a list/tuple/map must belong to the same
          environment as the list/tuple/map itself. Terms can be copied between
          environments with
          <seealso marker="#enif_make_copy"><c>enif_make_copy</c></seealso>.</p>
      </item>
      <tag><marker id="ErlNifFunc"/><c>ErlNifFunc</c></tag>
      <item>
        <code type="none">
typedef struct {
    const char* name;
    unsigned arity;
    ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
    unsigned flags;
} ErlNifFunc;</code>
        <p>Describes a NIF by its name, arity, and implementation.</p>
        <taglist>
          <tag><c>fptr</c></tag>
          <item>
            <p>A pointer to the function that implements the NIF.</p>
          </item>
          <tag><c>argv</c></tag>
          <item>
            <p>Contains the function arguments passed to the NIF.</p>
          </item>
          <tag><c>argc</c></tag>
          <item>
            <p>The array length, that is, the function arity. <c>argv[N-1]</c>
              thus denotes the Nth argument to the NIF. Notice that the argument
              <c>argc</c> allows for the same C function to implement several
              Erlang functions with different arity (but probably with the same
              name).</p>
          </item>
          <tag><c>flags</c></tag>
          <item>
            <p>Is <c>0</c> for a regular NIF (and so its value can be omitted
              for statically initialized <c>ErlNifFunc</c> instances).</p>
            <p><c>flags</c> can be used to indicate that the NIF is a
              <seealso marker="#dirty_nifs">dirty NIF</seealso> that is to be
              executed on a dirty scheduler thread.</p>
            <p><em>The dirty NIF functionality described here is
              experimental.</em> You have to enable support for dirty
              schedulers when building OTP to try out the functionality.</p>
            <p>If the dirty NIF is expected to be CPU-bound, its <c>flags</c>
              field is to be set to <c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c> or
              <c>ERL_NIF_DIRTY_JOB_IO_BOUND</c>.</p>
            <note>
              <p>If one of the <c>ERL_NIF_DIRTY_JOB_*_BOUND</c> flags is set,
                and the runtime system has no support for dirty schedulers,
                the runtime system refuses to load the NIF library.</p>
            </note>
          </item>
        </taglist>
      </item>
      <tag><marker id="ErlNifBinary"/><c>ErlNifBinary</c></tag>
      <item>
        <code type="none">
typedef struct {
    unsigned size;
    unsigned char* data;
} ErlNifBinary;</code>
        <p><c>ErlNifBinary</c> contains transient information about an
          inspected binary term. <c>data</c> is a pointer to a buffer
          of <c>size</c> bytes with the raw content of the binary.</p>
          <p>Notice that <c>ErlNifBinary</c> is a semi-opaque type and you are
          only allowed to read fields <c>size</c> and <c>data</c>.</p>
      </item>
      <tag><marker id="ErlNifBinaryToTerm"/><c>ErlNifBinaryToTerm</c></tag>
      <item>
        <p>An enumeration of the options that can be specified to
          <seealso marker="#enif_binary_to_term">
          <c>enif_binary_to_term</c></seealso>.
          For default behavior, use value <c>0</c>.</p>
        <p>When receiving data from untrusted sources, use option
          <c>ERL_NIF_BIN2TERM_SAFE</c>.</p>
      </item>
      <tag><marker id="ErlNifPid"/><c>ErlNifPid</c></tag>
      <item>
        <p>A process identifier (pid). In contrast to pid terms (instances of
          <c>ERL_NIF_TERM</c>), <c>ErlNifPid</c>s are self-contained and not
          bound to any <seealso marker="#ErlNifEnv">environment</seealso>.
          <c>ErlNifPid</c> is an opaque type.</p>
      </item>
      <tag><marker id="ErlNifPort"/><c>ErlNifPort</c></tag>
      <item>
        <p>A port identifier. In contrast to port ID terms (instances of
          <c>ERL_NIF_TERM</c>), <c>ErlNifPort</c>s are self-contained and not
          bound to any <seealso marker="#ErlNifEnv">environment</seealso>.
          <c>ErlNifPort</c> is an opaque type.</p>
      </item>
      <tag><marker id="ErlNifResourceType"/><c>ErlNifResourceType</c></tag>
      <item>
        <p>Each instance of <c>ErlNifResourceType</c> represents a class of
          memory-managed resource objects that can be garbage collected.
          Each resource type has a unique name and a destructor function that
          is called when objects of its type are released.</p>
      </item>
      <tag><marker id="ErlNifResourceDtor"/><c>ErlNifResourceDtor</c></tag>
      <item>
        <code type="none">
typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);</code>
        <p>The function prototype of a resource destructor function.</p>
      </item>
      <tag><marker id="ErlNifCharEncoding"/><c>ErlNifCharEncoding</c></tag>
      <item>
        <code type="none">
typedef enum {
    ERL_NIF_LATIN1
}ErlNifCharEncoding;</code>
        <p>The character encoding used in strings and atoms. The only
          supported encoding is <c>ERL_NIF_LATIN1</c> for
          ISO Latin-1 (8-bit ASCII).</p>
      </item>
      <tag><marker id="ErlNifSysInfo"/><c>ErlNifSysInfo</c></tag>
      <item>
        <p>Used by <seealso marker="#enif_system_info">
          <c>enif_system_info</c></seealso> to return information about the
          runtime system. Contains the same content as
          <seealso marker="erl_driver#ErlDrvSysInfo">
          <c>ErlDrvSysInfo</c></seealso>.</p>
      </item>
      <tag><marker id="ErlNifSInt64"/><c>ErlNifSInt64</c></tag>
      <item>
        <p>A native signed 64-bit integer type.</p>
      </item>
      <tag><marker id="ErlNifUInt64"/><c>ErlNifUInt64</c></tag>
      <item>
        <p>A native unsigned 64-bit integer type.</p>
      </item>
      <tag><marker id="ErlNifTime"/><c>ErlNifTime</c></tag>
      <item>
        <p>A signed 64-bit integer type for representation of time.</p>
      </item>
      <tag><marker id="ErlNifTimeUnit"/><c>ErlNifTimeUnit</c></tag>
      <item>
        <p>An enumeration of time units supported by the NIF API:</p>
        <taglist>
          <tag><c>ERL_NIF_SEC</c></tag>
          <item>Seconds</item>
          <tag><c>ERL_NIF_MSEC</c></tag>
          <item>Milliseconds</item>
          <tag><c>ERL_NIF_USEC</c></tag>
          <item>Microseconds</item>
          <tag><c>ERL_NIF_NSEC</c></tag>
          <item>Nanoseconds</item>
        </taglist>
      </item>
      <tag><marker id="ErlNifUniqueInteger"/><c>ErlNifUniqueInteger</c></tag>
      <item>
        <p>An enumeration of the properties that can be requested from
          <seealso marker="#enif_make_unique_integer">
          <c>enif_unique_integer</c></seealso>.
          For default properties, use value <c>0</c>.</p>
        <taglist>
          <tag><c>ERL_NIF_UNIQUE_POSITIVE</c></tag>
          <item>
            <p>Return only positive integers.</p>
          </item>
          <tag><c>ERL_NIF_UNIQUE_MONOTONIC</c></tag>
          <item>
            <p>Return only <seealso
              marker="time_correction#Strictly_Monotonically_Increasing">
              strictly monotonically increasing</seealso> integer corresponding
              to creation time.</p>
          </item>
        </taglist>
      </item>
    </taglist>
  </section>

  <funcs>
    <func>
      <name><ret>void *</ret><nametext>enif_alloc(size_t size)</nametext></name>
      <fsummary>Allocate dynamic memory.</fsummary>
      <desc>
        <p>Allocates memory of <c>size</c> bytes.</p>
        <p>Returns <c>NULL</c> if the allocation fails.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_alloc_binary(size_t size, ErlNifBinary* bin)</nametext>
      </name>
      <fsummary>Create a new binary.</fsummary>
      <desc>
        <p>Allocates a new binary of size <c>size</c> bytes.
          Initializes the structure pointed to by <c>bin</c> to
          refer to the allocated binary. The binary must either be released by
          <seealso marker="#enif_release_binary">
          <c>enif_release_binary</c></seealso> 
          or ownership transferred to an Erlang term with
          <seealso marker="#enif_make_binary"><c>enif_make_binary</c></seealso>.
          An allocated (and owned) <c>ErlNifBinary</c> can be kept between NIF
          calls.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if allocation
          fails.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifEnv *</ret><nametext>enif_alloc_env()</nametext></name>
      <fsummary>Create a new environment.</fsummary>
      <desc>
        <p>Allocates a new process-independent environment. The environment can
          be used to hold terms that are not bound to any process. Such terms
          can later be copied to a process environment with
          <seealso marker="#enif_make_copy"><c>enif_make_copy</c></seealso> or
          be sent to a process as a message with <seealso marker="#enif_send">
          <c>enif_send</c></seealso>.</p>
        <p>Returns pointer to the new environment.</p>
      </desc>
    </func>

    <func>
      <name><ret>void *</ret><nametext>enif_alloc_resource(ErlNifResourceType*
        type, unsigned size)</nametext></name>
      <fsummary>Allocate a memory-managed resource object.</fsummary>
      <desc>
        <p>Allocates a memory-managed resource object of type <c>type</c> and
          size <c>size</c> bytes.</p>
      </desc>
    </func>

    <func>
      <name><ret>size_t</ret><nametext>enif_binary_to_term(ErlNifEnv *env,
        const unsigned char* data, size_t size, ERL_NIF_TERM *term,
        ErlNifBinaryToTerm opts)</nametext></name>
      <fsummary>Create a term from the external format.</fsummary>
      <desc>
        <p>Creates a term that is the result of decoding the binary data at
          <c>data</c>, which must be encoded according to the Erlang external
          term format. No more than <c>size</c> bytes are read from <c>data</c>.
          Argument <c>opts</c> corresponds to the second argument to
          <seealso marker="erlang#binary_to_term-2">
          <c>erlang:binary_to_term/2</c></seealso> and must be either <c>0</c>
          or <c>ERL_NIF_BIN2TERM_SAFE</c>.</p>
        <p>On success, stores the resulting term at <c>*term</c> and returns
          the number of bytes read. Returns <c>0</c> if decoding fails or if
          <c>opts</c> is invalid.</p>
        <p>See also <seealso marker="#ErlNifBinaryToTerm">
          <c>ErlNifBinaryToTerm</c></seealso>,
          <seealso marker="erlang#binary_to_term-2">
          <c>erlang:binary_to_term/2</c></seealso>, and
          <seealso marker="#enif_term_to_binary">
          <c>enif_term_to_binary</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret><nametext>enif_clear_env(ErlNifEnv* env)</nametext>
      </name>
      <fsummary>Clear an environment for reuse.</fsummary>
      <desc>
        <p>Frees all terms in an environment and clears it for reuse.
          The environment must have been allocated with
          <seealso marker="#enif_alloc_env"><c>enif_alloc_env</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)</nametext>
      </name>
      <fsummary>Compare two terms.</fsummary>
      <desc>
        <p>Returns an integer &lt; <c>0</c> if <c>lhs</c> &lt; <c>rhs</c>,
          <c>0</c> if <c>lhs</c> = <c>rhs</c>, and &gt; <c>0</c> if
          <c>lhs</c> &gt; <c>rhs</c>. Corresponds to the Erlang
          operators <c>==</c>, <c>/=</c>, <c>=&lt;</c>, <c>&lt;</c>,
          <c>&gt;=</c>, and <c>&gt;</c> (but <em>not</em> <c>=:=</c> or
          <c>=/=</c>).</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_cond_broadcast(ErlNifCond *cnd)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_cond_broadcast">
          <c>erl_drv_cond_broadcast</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifCond *</ret>
        <nametext>enif_cond_create(char *name)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_cond_create">
          <c>erl_drv_cond_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_cond_destroy(ErlNifCond *cnd)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_cond_destroy">
          <c>erl_drv_cond_destroy</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_cond_signal(ErlNifCond *cnd)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_cond_signal">
          <c>erl_drv_cond_signal</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)</nametext>
      </name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_cond_wait">
          <c>erl_drv_cond_wait</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_consume_timeslice(ErlNifEnv *env, int percent)</nametext>
      </name>
      <fsummary></fsummary>
      <desc>
        <p>Gives the runtime system a hint about how much CPU time the current
          NIF call has consumed since the last hint, or since the start of the
          NIF if no previous hint has been specified. The time is specified as a
          percent of the timeslice that a process is allowed to execute
          Erlang code until it can be suspended to give time for other runnable
          processes. The scheduling timeslice is not an exact entity, but can
          usually be approximated to about 1 millisecond.</p>
        <p>Notice that it is up to the runtime system to determine if and how
          to use this information. Implementations on some platforms can use
          other means to determine consumed CPU time. Lengthy NIFs should
          regardless of this frequently call <c>enif_consume_timeslice</c> to
          determine if it is allowed to continue execution.</p>
        <p>Argument <c>percent</c> must be an integer between 1 and 100. This
          function must only be called from a NIF-calling thread, and argument
          <c>env</c> must be the environment of the calling process.</p>
        <p>Returns <c>1</c> if the timeslice is exhausted, otherwise <c>0</c>.
          If <c>1</c> is returned, the NIF is to return as soon as possible in
          order for the process to yield.</p>
        <p>This function is provided to better support co-operative scheduling,
          improve system responsiveness, and make it easier to prevent
          misbehaviors of the VM because of a NIF monopolizing a scheduler
          thread. It can be used to divide <seealso marker="#lengthy_work">
          length work</seealso> into a number of repeated NIF calls without the
          need to create threads.</p>
        <p>See also the <seealso marker="#WARNING">warning</seealso> text at
          the beginning of this manual page.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifTime</ret><nametext>enif_convert_time_unit(ErlNifTime
        val, ErlNifTimeUnit from, ErlNifTimeUnit to)</nametext></name>
      <fsummary>Convert time unit of a time value.</fsummary>
      <desc>
        <marker id="enif_convert_time_unit"></marker>
        <p>Converts the <c>val</c> value of time unit <c>from</c> to
          the corresponding value of time unit <c>to</c>. The result is
          rounded using the floor function.</p>
        <taglist>
          <tag><c>val</c></tag>
          <item>Value to convert time unit for.</item>
          <tag><c>from</c></tag>
          <item>Time unit of <c>val</c>.</item>
          <tag><c>to</c></tag>
          <item>Time unit of returned value.</item>
        </taglist>
        <p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid
          time unit argument.</p>
        <p>See also <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso>
          and
          <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_cpu_time(ErlNifEnv *)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Returns the CPU time in the same format as
          <seealso marker="erlang#timestamp-0">
          <c>erlang:timestamp()</c></seealso>.
          The CPU time is the time the current logical CPU has spent executing
          since some arbitrary point in the past. If the OS does not support
          fetching this value, <c>enif_cpu_time</c> invokes
          <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)</nametext>
      </name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_equal_tids">
          <c>erl_drv_equal_tids</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret><nametext>enif_free(void* ptr)</nametext></name>
      <fsummary>Free dynamic memory.</fsummary>
      <desc>
        <p>Frees memory allocated by
          <seealso marker="#enif_alloc"><c>enif_alloc</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_free_env(ErlNifEnv* env)</nametext></name>
      <fsummary>Free an environment allocated with enif_alloc_env.</fsummary>
      <desc>
        <p>Frees an environment allocated with
          <seealso marker="#enif_alloc_env"><c>enif_alloc_env</c></seealso>.
          All terms created in the environment are freed as well.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_atom(ErlNifEnv* env, ERL_NIF_TERM
        term, char* buf, unsigned size, ErlNifCharEncoding encode)</nametext>
      </name>
      <fsummary>Get the text representation of an atom term.</fsummary>
      <desc>
        <p>Writes a <c>NULL</c>-terminated string in the buffer pointed to by
          <c>buf</c> of size <c>size</c>, consisting of the string
          representation of the atom <c>term</c> with encoding
          <seealso marker="#ErlNifCharEncoding">encode</seealso>.</p>
        <p>Returns the number of bytes written (including terminating
          <c>NULL</c> character) or <c>0</c> if <c>term</c> is not an atom with
           maximum length of <c>size-1</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_atom_length(ErlNifEnv* env,
        ERL_NIF_TERM term, unsigned* len, ErlNifCharEncoding encode)</nametext>
      </name>
      <fsummary>Get the length of atom <c>term</c>.</fsummary>
      <desc>
        <p>Sets <c>*len</c> to the length (number of bytes excluding
          terminating <c>NULL</c> character) of the atom <c>term</c> with
          encoding <c>encode</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is not
          an atom.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_double(ErlNifEnv* env,
        ERL_NIF_TERM term, double* dp)</nametext></name>
      <fsummary>Read a floating-point number term.</fsummary>
      <desc>
        <p>Sets <c>*dp</c> to the floating-point value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is not
          a float.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_int(ErlNifEnv* env, ERL_NIF_TERM
        term, int* ip)</nametext></name>
      <fsummary>Read an integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the integer value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is not
          an integer or is outside the bounds of type <c>int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_int64(ErlNifEnv* env, ERL_NIF_TERM
        term, ErlNifSInt64* ip)</nametext></name>
      <fsummary>Read a 64-bit integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the integer value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is not
          an integer or is outside the bounds of a signed 64-bit integer.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_local_pid(ErlNifEnv* env,
        ERL_NIF_TERM term, ErlNifPid* pid)</nametext></name>
      <fsummary>Read a local pid term.</fsummary>
      <desc>
        <p>If <c>term</c> is the pid of a node local process, this function
          initializes the pid variable <c>*pid</c> from it and returns
          <c>true</c>. Otherwise returns <c>false</c>. No check is done to see
          if the process is alive.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_local_port(ErlNifEnv* env,
        ERL_NIF_TERM term, ErlNifPort* port_id)</nametext></name>
      <fsummary>Read a local port term.</fsummary>
      <desc>
        <p>If <c>term</c> identifies a node local port, this function
          initializes the port variable <c>*port_id</c> from it and returns
          <c>true</c>. Otherwise returns <c>false</c>. No check is done to see
          if the port is alive.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_list_cell(ErlNifEnv* env,
        ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail)</nametext>
      </name>
      <fsummary>Get head and tail from a list.</fsummary>
      <desc>
        <p>Sets <c>*head</c> and <c>*tail</c> from list <c>list</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if it is
          not a list or the list is empty.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_list_length(ErlNifEnv* env,
        ERL_NIF_TERM term, unsigned* len)</nametext></name>
      <fsummary>Get the length of list <c>term</c>.</fsummary>
      <desc>
        <p>Sets <c>*len</c> to the length of list <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not a proper list.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_long(ErlNifEnv* env, ERL_NIF_TERM
        term, long int* ip)</nametext></name>
      <fsummary>Read a long integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the long integer value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not an integer or is outside the bounds of type <c>long int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_map_size(ErlNifEnv* env,
        ERL_NIF_TERM term, size_t *size)</nametext></name>
      <fsummary>Read the size of a map term.</fsummary>
      <desc>
        <p>Sets <c>*size</c> to the number of key-value pairs in the map
          <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not a map.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_map_value(ErlNifEnv* env,
        ERL_NIF_TERM map, ERL_NIF_TERM key, ERL_NIF_TERM* value)</nametext>
      </name>
      <fsummary>Get the value of a key in a map.</fsummary>
      <desc>
        <p>Sets <c>*value</c> to the value associated with <c>key</c> in the
          map <c>map</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>map</c> is not
          a map or if <c>map</c> does not contain <c>key</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_resource(ErlNifEnv* env,
        ERL_NIF_TERM term, ErlNifResourceType* type, void** objp)</nametext>
      </name>
      <fsummary>Get the pointer to a resource object.</fsummary>
      <desc>
        <p>Sets <c>*objp</c> to point to the resource object referred to by
          <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not a handle to a resource object of type <c>type</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_string(ErlNifEnv* env,
        ERL_NIF_TERM list, char* buf, unsigned size,
        ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Get a C-string from a list.</fsummary>
      <desc>
        <p>Writes a <c>NULL</c>-terminated string in the buffer pointed to by
          <c>buf</c> with size <c>size</c>, consisting of the characters
          in the string <c>list</c>. The characters are written using encoding
          <seealso marker="#ErlNifCharEncoding">encode</seealso>.</p>
        <p>Returns one of the following:</p>
        <list type="bulleted">
          <item>The number of bytes written (including terminating <c>NULL</c>
            character)</item>
          <item><c>-size</c> if the string was truncated because of buffer
            space</item>
          <item><c>0</c> if <c>list</c> is not a string that can be encoded
            with <c>encode</c> or if <c>size</c> was &lt; <c>1</c>.</item>
        </list>
        <p>The written string is always <c>NULL</c>-terminated, unless buffer
          <c>size</c> is &lt; <c>1</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM
        term, int* arity, const ERL_NIF_TERM** array)</nametext></name>
      <fsummary>Inspect the elements of a tuple.</fsummary>
      <desc>
        <p>If <c>term</c> is a tuple, this function sets <c>*array</c> to point
          to an array containing the elements of the tuple, and sets
          <c>*arity</c> to the number of elements. Notice that the array
          is read-only and <c>(*array)[N-1]</c> is the Nth element of
          the tuple. <c>*array</c> is undefined if the arity of the tuple
          is zero.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not a tuple.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_uint(ErlNifEnv* env, ERL_NIF_TERM
        term, unsigned int* ip)</nametext></name>
      <fsummary>Read an unsigned integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the unsigned integer value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not an unsigned integer or is outside the bounds of type
          <c>unsigned int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_uint64(ErlNifEnv* env,
        ERL_NIF_TERM term, ErlNifUInt64* ip)</nametext></name>
      <fsummary>Read an unsigned 64-bit integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the unsigned integer value of <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not an unsigned integer or is outside the bounds of an unsigned
          64-bit integer.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM
        term, unsigned long* ip)</nametext></name>
      <fsummary>Read an unsigned integer term.</fsummary>
      <desc>
        <p>Sets <c>*ip</c> to the unsigned long integer value of
          <c>term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>term</c> is
          not an unsigned integer or is outside the bounds of type
          <c>unsigned long</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_getenv(const char* key, char* value,
        size_t *value_size)</nametext></name>
      <fsummary>Get the value of an environment variable.</fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_getenv">
          <c>erl_drv_getenv</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_has_pending_exception(ErlNifEnv* env,
        ERL_NIF_TERM* reason)</nametext></name>
      <fsummary>Check if an exception has been raised.</fsummary>
      <desc>
        <p>Returns <c>true</c> if a pending exception is associated with the
          environment <c>env</c>. If <c>reason</c> is a <c>NULL</c> pointer,
          ignore it. Otherwise, if a pending exception associated with
          <c>env</c> exists, set <c>ERL_NIF_TERM</c> to which <c>reason</c>
          points to the value of the exception's term. For example, if
          <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso> is called to set a pending
          <c>badarg</c> exception, a later call to
          <c>enif_has_pending_exception(env, &amp;reason)</c> sets
          <c>reason</c> to the atom <c>badarg</c>, then return <c>true</c>.</p>
        <p>See also <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso> and
          <seealso marker="#enif_raise_exception">
          <c>enif_raise_exception</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_inspect_binary(ErlNifEnv* env,
        ERL_NIF_TERM bin_term, ErlNifBinary* bin)</nametext></name>
      <fsummary>Inspect the content of a binary.</fsummary>
      <desc>
        <p>Initializes the structure pointed to by <c>bin</c> with information
          about binary term <c>bin_term</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>bin_term</c>
          is not a binary.</p>
      </desc> 
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_inspect_iolist_as_binary(ErlNifEnv*
        env, ERL_NIF_TERM term, ErlNifBinary* bin)</nametext></name>
      <fsummary>Inspect the content of an iolist.</fsummary>
      <desc>
        <p>Initializes the structure pointed to by <c>bin</c> with a
          continuous buffer with the same byte content as <c>iolist</c>. As
          with <c>inspect_binary</c>, the data pointed to by <c>bin</c> is
          transient and does not need to be released.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>iolist</c> is
          not an iolist.</p>
      </desc> 
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is an atom.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is an atom.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a binary.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a binary.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_current_process_alive(ErlNifEnv* env)</nametext>
      </name>
      <fsummary>Determine if currently executing process is alive.</fsummary>
      <desc>
        <p>Returns <c>true</c> if the currently executing process is currently
          alive, otherwise <c>false</c>.</p>
        <p>This function can only be used from a NIF-calling thread, and with
          an environment corresponding to currently executing processes.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_empty_list(ErlNifEnv* env,
        ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an empty list.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is an empty list.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_exception(ErlNifEnv* env,
        ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an exception.</fsummary>
      <desc><marker id="enif_is_exception"/>
      <p>Return true if <c>term</c> is an exception.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM
        term)</nametext></name>
      <fsummary>Determine if a term is a fun.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a fun.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_identical(ERL_NIF_TERM lhs,
        ERL_NIF_TERM rhs)</nametext></name>
      <fsummary>Erlang operator =:=.</fsummary>
      <desc>
        <p>Returns <c>true</c> if the two terms are identical. Corresponds to
          the Erlang operators <c>=:=</c> and <c>=/=</c>.</p>
      </desc> 
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a list.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a list.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_map(ErlNifEnv* env, ERL_NIF_TERM
        term)</nametext></name>
      <fsummary>Determine if a term is a map.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a map, otherwise
          <c>false</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_number(ErlNifEnv* env, ERL_NIF_TERM
        term)</nametext></name>
      <fsummary>Determine if a term is a number (integer or float).</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a number.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a pid.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a pid.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a port.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a port.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_port_alive(ErlNifEnv* env,
        ErlNifPort *port_id)</nametext></name>
      <fsummary>Determine if a local port is alive.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>port_id</c> is alive.</p>
        <p>This function is only thread-safe when the emulator with SMP support
          is used. It can only be used in a non-SMP emulator from a NIF-calling
          thread.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_is_process_alive(ErlNifEnv* env,
        ErlNifPid *pid)</nametext></name>
      <fsummary>Determine if a local process is alive.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>pid</c> is alive.</p>
        <p>This function is only thread-safe when the emulator with SMP support
          is used. It can only be used in a non-SMP emulator from a NIF-calling
          thread.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a reference.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a reference.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)</nametext>
      </name>
      <fsummary>Determine if a term is a tuple.</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c>term</c> is a tuple.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_keep_resource(void* obj)</nametext>
      </name>
      <fsummary>Add a reference to a resource object.</fsummary>
      <desc>
        <p>Adds a reference to resource object <c>obj</c> obtained from
          <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>. Each call to
          <c>enif_keep_resource</c> for an object must be balanced by a call to
          <seealso marker="#enif_release_resource">
          <c>enif_release_resource</c></seealso>
          before the object is destructed.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_atom(ErlNifEnv* env, const char* name)</nametext>
      </name>
      <fsummary>Create an atom term.</fsummary>
      <desc>
        <p>Creates an atom term from the <c>NULL</c>-terminated C-string
          <c>name</c> with ISO Latin-1 encoding. If the length of <c>name</c>
          exceeds the maximum length allowed for an atom (255 characters),
          <c>enif_make_atom</c> invokes <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_atom_len(ErlNifEnv* env,
        const char* name, size_t len)</nametext></name>
      <fsummary>Create an atom term.</fsummary>
      <desc>
        <p>Create an atom term from the string <c>name</c> with length
          <c>len</c>. <c>NULL</c> characters are treated as any other
          characters. If <c>len</c> exceeds the maximum length
          allowed for an atom (255 characters), <c>enif_make_atom</c> invokes
          <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_badarg(ErlNifEnv* env)</nametext></name>
      <fsummary>Make a badarg exception.</fsummary>
      <desc>
        <p>Makes a <c>badarg</c> exception to be returned from a NIF, and
          associates it with environment <c>env</c>. Once a NIF or any function
          it calls invokes <c>enif_make_badarg</c>, the runtime ensures that a
          <c>badarg</c> exception is raised when the NIF returns, even if the
          NIF attempts to return a non-exception term instead.</p>
        <p>The return value from <c>enif_make_badarg</c> can be used only as
          the return value from the NIF that invoked it (directly or indirectly)
          or be passed to <seealso marker="#enif_is_exception">
          <c>enif_is_exception</c></seealso>, but not to any other NIF API
          function.</p>
        <p>See also <seealso marker="#enif_has_pending_exception">
          <c>enif_has_pending_exception</c></seealso> and
          <seealso marker="#enif_raise_exception">
          <c>enif_raise_exception</c></seealso>.</p>
        <note>
          <p>Before <c>ERTS</c> 7.0 (Erlang/OTP 18), the return value
            from <c>enif_make_badarg</c> had to be returned from the NIF. This
            requirement is now lifted as the return value from the NIF is
            ignored if <c>enif_make_badarg</c> has been invoked.</p>
        </note>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)</nametext>
      </name>
      <fsummary>Make a binary term.</fsummary>
      <desc>
        <p>Makes a binary term from <c>bin</c>. Any ownership of
          the binary data is transferred to the created term and
          <c>bin</c> is to be considered read-only for the rest of the NIF
          call and then as released.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_copy(ErlNifEnv* dst_env,
        ERL_NIF_TERM src_term)</nametext></name>
      <fsummary>Make a copy of a term.</fsummary>
      <desc>
        <p>Makes a copy of term <c>src_term</c>. The copy is created in
          environment <c>dst_env</c>. The source term can be located in any
          environment.</p>
      </desc>        
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_double(ErlNifEnv* env, double d)</nametext></name>
      <fsummary>Create a floating-point term.</fsummary>
      <desc>
        <p>Creates a floating-point term from a <c>double</c>. If argument
          <c>double</c> is not finite or is NaN, <c>enif_make_double</c>
          invokes <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_make_existing_atom(ErlNifEnv* env,
        const char* name, ERL_NIF_TERM* atom, ErlNifCharEncoding
        encode)</nametext></name>
      <fsummary>Create an existing atom term.</fsummary>
      <desc>
        <p>Tries to create the term of an already existing atom from
          the <c>NULL</c>-terminated C-string <c>name</c> with encoding
          <seealso marker="#ErlNifCharEncoding">encode</seealso>.</p>
        <p>If the atom already exists, this function stores the term in
          <c>*atom</c> and returns <c>true</c>, otherwise <c>false</c>.
          Also returns <c>false</c> if the length of <c>name</c> exceeds the
          maximum length allowed for an atom (255 characters).</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_make_existing_atom_len(ErlNifEnv* env,
        const char* name, size_t len, ERL_NIF_TERM* atom, ErlNifCharEncoding
        encoding)</nametext></name>
      <fsummary>Create an existing atom term.</fsummary>
      <desc>
        <p>Tries to create the term of an already existing atom from the
          string <c>name</c> with length <c>len</c> and encoding
          <seealso marker="#ErlNifCharEncoding">encode</seealso>. <c>NULL</c>
          characters are treated as any other characters.</p>
        <p>If the atom already exists, this function stores the term in
          <c>*atom</c> and returns <c>true</c>, otherwise <c>false</c>.
          Also returns <c>false</c> if <c>len</c> exceeds the maximum length
          allowed for an atom (255 characters).</p>
      </desc>
    </func>

    <func><name><ret>ERL_NIF_TERM</ret>
      <nametext>enif_make_int(ErlNifEnv* env, int i)</nametext></name>
      <fsummary>Create an integer term.</fsummary>
      <desc>
        <p>Creates an integer term.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i)</nametext>
      </name>
      <fsummary>Create an integer term.</fsummary>
      <desc>
        <p>Creates an integer term from a signed 64-bit integer.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_list(ErlNifEnv* env, unsigned cnt, ...)</nametext>
      </name>
      <fsummary>Create a list term.</fsummary>
      <desc>
        <p>Creates an ordinary list term of length <c>cnt</c>. Expects
          <c>cnt</c> number of arguments (after <c>cnt</c>) of type
          <c>ERL_NIF_TERM</c> as the elements of the list.</p>
        <p>Returns an empty list if <c>cnt</c> is 0.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1)</nametext>
      </name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list2(ErlNifEnv* env,
        ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list3(ErlNifEnv* env,
        ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list4(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list5(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list6(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list7(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list8(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list9(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a list term.</fsummary>
      <desc>
        <p>Creates an ordinary list term with length indicated by the
          function name. Prefer these functions (macros) over the variadic
          <c>enif_make_list</c> to get a compile-time error if the number of
          arguments does not match.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list_cell(ErlNifEnv*
        env, ERL_NIF_TERM head, ERL_NIF_TERM tail)</nametext></name>
      <fsummary>Create a list cell.</fsummary>
      <desc>
        <p>Creates a list cell <c>[head | tail]</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_list_from_array(ErlNifEnv* env, const ERL_NIF_TERM
          arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a list term from an array.</fsummary>
      <desc>
        <p>Creates an ordinary list containing the elements of array <c>arr</c>
          of length <c>cnt</c>.</p>
        <p>Returns an empty list if <c>cnt</c> is 0.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_long(ErlNifEnv* env, long int i)</nametext></name>
      <fsummary>Create an integer term from a long int.</fsummary>
      <desc>
        <p>Creates an integer term from a <c>long int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_make_map_put(ErlNifEnv* env,
        ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM value,
        ERL_NIF_TERM* map_out)</nametext></name>
      <fsummary>Insert key-value pair in map.</fsummary>
      <desc>
        <p>Makes a copy of map <c>map_in</c> and inserts <c>key</c> with
          <c>value</c>. If <c>key</c> already exists in <c>map_in</c>, the old
          associated value is replaced by <c>value</c>.</p>
        <p>If successful, this function sets <c>*map_out</c> to the new map and
          returns <c>true</c>. Returns <c>false</c> if <c>map_in</c> is not a
          map.</p>
        <p>The <c>map_in</c> term must belong to environment <c>env</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_make_map_remove(ErlNifEnv* env,
        ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM* map_out)</nametext>
      </name>
      <fsummary>Remove key from map.</fsummary>
      <desc>
        <p>If map <c>map_in</c> contains <c>key</c>, this function makes a copy
          of <c>map_in</c> in <c>*map_out</c>, and removes <c>key</c> and the
          associated value. If map <c>map_in</c> does not contain <c>key</c>,
          <c>*map_out</c> is set to <c>map_in</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if <c>map_in</c> is
          not a map.</p>
        <p>The <c>map_in</c> term must belong to environment <c>env</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_make_map_update(ErlNifEnv* env,
        ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM new_value,
        ERL_NIF_TERM* map_out)</nametext></name>
      <fsummary>Replace value for key in map.</fsummary>
      <desc>
        <p>Makes a copy of map <c>map_in</c> and replace the old associated
          value for <c>key</c> with <c>new_value</c>.</p>
        <p>If successful, this function sets <c>*map_out</c> to the new map and
          returns <c>true</c>. Returns <c>false</c> if <c>map_in</c> is not a
          map or if it does not contain <c>key</c>.</p>
        <p>The <c>map_in</c> term must belong to environment <c>env</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>unsigned char *</ret><nametext>enif_make_new_binary(ErlNifEnv*
        env, size_t size, ERL_NIF_TERM* termp)</nametext></name>
      <fsummary>Allocate and create a new binary term.</fsummary>
      <desc>
        <p>Allocates a binary of size <c>size</c> bytes and creates an owning
          term. The binary data is mutable until the calling NIF returns.
          This is a quick way to create a new binary without having to use
          <seealso marker="#ErlNifBinary"><c>ErlNifBinary</c></seealso>.
          The drawbacks are that the binary cannot be kept between NIF calls
          and it cannot be reallocated.</p>
        <p>Returns a pointer to the raw binary data and sets
          <c>*termp</c> to the binary term.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_new_map(ErlNifEnv* env)</nametext></name>
      <fsummary>Make an empty map term.</fsummary>
      <desc>
        <p>Makes an empty map term.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_pid(ErlNifEnv* env, const ErlNifPid* pid)</nametext>
      </name>
      <fsummary>Make a pid term.</fsummary>
      <desc>
        <p>Makes a pid term from <c>*pid</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_ref(ErlNifEnv* env)</nametext></name>
      <fsummary>Create a reference.</fsummary>
      <desc>
        <p>Creates a reference like <seealso marker="erlang#make_ref-0">
          <c>erlang:make_ref/0</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_resource(ErlNifEnv* env, void* obj)</nametext>
      </name>
      <fsummary>Create an opaque handle to a resource object.</fsummary>
      <desc>
        <p>Creates an opaque handle to a memory-managed resource object
          obtained by <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>. No ownership transfer is done,
          as the resource object still needs to be released by
          <seealso marker="#enif_release_resource">
          <c>enif_release_resource</c></seealso>. However, notice that the call
          to <c>enif_release_resource</c> can occur immediately after obtaining
          the term from <c>enif_make_resource</c>, in which case the resource
          object is deallocated when the term is garbage collected. For more
          details, see the <seealso marker="#enif_resource_example">example of
          creating and returning a resource object</seealso> in the User's
          Guide.</p>
        <p>Notice that the only defined behavior of using a resource term in
          an Erlang program is to store it and send it between processes on the
          same node. Other operations, such as matching or
          <c>term_to_binary</c>, have unpredictable (but harmless) results.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_resource_binary(ErlNifEnv* env, void* obj, const
        void* data, size_t size)</nametext></name>
      <fsummary>Create a custom binary term.</fsummary>
      <desc>
        <p>Creates a binary term that is memory-managed by a resource object
          <c>obj</c> obtained by <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>. The returned binary term
          consists of <c>size</c> bytes pointed to by <c>data</c>. This raw
          binary data must be kept readable and unchanged until the destructor
          of the resource is called. The binary data can be stored external to
          the resource object, in which case the destructor is responsible
          for releasing the data.</p>
        <p>Several binary terms can be managed by the same resource object. The
          destructor is not called until the last binary is garbage collected.
          This can be useful to return different parts of a larger binary
          buffer.</p>
        <p>As with <seealso marker="#enif_make_resource">
          <c>enif_make_resource</c></seealso>, no ownership transfer is done.
          The resource still needs to be released with
          <seealso marker="#enif_release_resource">
          <c>enif_release_resource</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM list_in,
        ERL_NIF_TERM *list_out)</nametext></name>
      <fsummary>Create the reverse of a list.</fsummary>
      <desc>
        <p>Sets <c>*list_out</c> to the reverse list of the list <c>list_in</c>
          and returns <c>true</c>, or returns <c>false</c> if <c>list_in</c> is
          not a list.</p>
        <p>This function is only to be used on short lists, as a copy is
          created of the list, which is not released until after the NIF
          returns.</p>
        <p>The <c>list_in</c> term must belong to environment <c>env</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string(ErlNifEnv* env,
        const char* string, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create a string.</fsummary>
      <desc>
        <p>Creates a list containing the characters of the
          <c>NULL</c>-terminated string <c>string</c> with encoding
          <seealso marker="#ErlNifCharEncoding">encoding</seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string_len(ErlNifEnv*
        env, const char* string, size_t len, ErlNifCharEncoding
        encoding)</nametext></name>
      <fsummary>Create a string.</fsummary>
      <desc>
        <p>Creates a list containing the characters of the string <c>string</c>
          with length <c>len</c> and encoding
          <seealso marker="#ErlNifCharEncoding">encoding</seealso>.
          <c>NULL</c> characters are treated as any other characters.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_sub_binary(ErlNifEnv*
        env, ERL_NIF_TERM bin_term, size_t pos, size_t size)</nametext></name>
      <fsummary>Make a subbinary term.</fsummary>
      <desc>
        <p>Makes a subbinary of binary <c>bin_term</c>, starting at
          zero-based position <c>pos</c> with a length of <c>size</c> bytes.
          <c>bin_term</c> must be a binary or bitstring. <c>pos+size</c> must
          be less or equal to the number of whole bytes in <c>bin_term</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple(ErlNifEnv* env,
        unsigned cnt, ...)</nametext></name>
      <fsummary>Creates a tuple term.</fsummary>
      <desc>
        <p>Creates a tuple term of arity <c>cnt</c>. Expects <c>cnt</c> number
          of arguments (after <c>cnt</c>) of type <c>ERL_NIF_TERM</c> as the
          elements of the tuple.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple1(ErlNifEnv* env,
        ERL_NIF_TERM e1)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple2(ErlNifEnv* env,
        ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple3(ErlNifEnv* env,
        ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple4(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple5(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple6(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple7(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple8(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple9(ErlNifEnv* env,
        ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a tuple term.</fsummary>
      <desc>
        <p>Creates a tuple term with length indicated by the
          function name. Prefer these functions (macros) over the variadic
          <c>enif_make_tuple</c> to get a compile-time error if the number of
          arguments does not match.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_tuple_from_array(ErlNifEnv* env, const ERL_NIF_TERM
        arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a tuple term from an array.</fsummary>
      <desc>
        <p>Creates a tuple containing the elements of array <c>arr</c>
          of length <c>cnt</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_uint(ErlNifEnv* env, unsigned int i)</nametext>
      </name>
      <fsummary>Create an unsigned integer term.</fsummary>
      <desc>
        <p>Creates an integer term from an <c>unsigned int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i)</nametext>
      </name>
      <fsummary>Create an unsigned integer term.</fsummary>
      <desc>
        <p>Creates an integer term from an unsigned 64-bit integer.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_make_ulong(ErlNifEnv* env, unsigned long i)</nametext>
      </name>
      <fsummary>Create an integer term from an unsigned long int.</fsummary>
      <desc>
        <p>Creates an integer term from an <c>unsigned long int</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_unique_integer(ErlNifEnv
        *env, ErlNifUniqueInteger properties)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Returns a unique integer with the same properties as specified by
          <seealso marker="erlang#unique_integer-1">
          <c>erlang:unique_integer/1</c></seealso>.</p>
        <p><c>env</c> is the environment to create the integer in.</p>
        <p><c>ERL_NIF_UNIQUE_POSITIVE</c> and <c>ERL_NIF_UNIQUE_MONOTONIC</c>
          can be passed as the second argument to change the properties of the
          integer returned. They can be combined by OR:ing the two values
          together.</p>
        <p>See also <seealso marker="#ErlNifUniqueInteger">
          <c>ErlNifUniqueInteger</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_create(ErlNifEnv *env,
        ERL_NIF_TERM map, ErlNifMapIterator *iter, ErlNifMapIteratorEntry
        entry)</nametext></name>
      <fsummary>Create a map iterator.</fsummary>
      <desc>
        <p>Creates an iterator for the map <c>map</c> by initializing the
          structure pointed to by <c>iter</c>. Argument <c>entry</c> determines
          the start position of the iterator: <c>ERL_NIF_MAP_ITERATOR_FIRST</c>
          or <c>ERL_NIF_MAP_ITERATOR_LAST</c>.</p>
        <p>Returns <c>true</c> on success, or false if <c>map</c> is not a
          map.</p>
        <p>A map iterator is only useful during the lifetime of environment
          <c>env</c> that the <c>map</c> belongs to. The iterator must be
          destroyed by calling <seealso marker="#enif_map_iterator_destroy">
          <c>enif_map_iterator_destroy</c></seealso>:</p>
        <code type="none">
ERL_NIF_TERM key, value;
ErlNifMapIterator iter;
enif_map_iterator_create(env, my_map, &amp;iter, ERL_NIF_MAP_ITERATOR_FIRST);

while (enif_map_iterator_get_pair(env, &amp;iter, &amp;key, &amp;value)) {
    do_something(key,value);
    enif_map_iterator_next(env, &amp;iter);
}
enif_map_iterator_destroy(env, &amp;iter);</code>
        <note>
          <p>The key-value pairs of a map have no defined iteration order.
            The only guarantee is that the iteration order of a single map
            instance is preserved during the lifetime of the environment that
            the map belongs to.</p>
        </note>
      </desc>
    </func>

    <func>
      <name><ret>void</ret><nametext>enif_map_iterator_destroy(ErlNifEnv *env,
        ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Destroy a map iterator.</fsummary>
      <desc>
        <p>Destroys a map iterator created by
          <seealso marker="#enif_map_iterator_create">
          <c>enif_map_iterator_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_get_pair(ErlNifEnv *env,
        ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM
        *value)</nametext></name>
      <fsummary>Get key and value at current map iterator position.</fsummary>
      <desc>
        <p>Gets key and value terms at the current map iterator position.</p>
        <p>On success, sets <c>*key</c> and <c>*value</c> and returns
          <c>true</c>. Returns <c>false</c> if the iterator is positioned at
          head (before first entry) or tail (beyond last entry).</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_is_head(ErlNifEnv *env,
        ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Check if map iterator is positioned before first.</fsummary>
      <desc>
        <p>Returns <c>true</c> if map iterator <c>iter</c> is positioned
          before the first entry.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_is_tail(ErlNifEnv *env,
        ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Check if map iterator is positioned after last.</fsummary>
      <desc>
        <p>Returns <c>true</c> if map iterator <c>iter</c> is positioned
          after the last entry.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_next(ErlNifEnv *env,
        ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Increment map iterator to point to next entry.</fsummary>
      <desc>
        <p>Increments map iterator to point to the next key-value entry.</p>
        <p>Returns <c>true</c> if the iterator is now positioned at a valid
          key-value entry, or <c>false</c> if the iterator is positioned at
          the tail (beyond the last entry).</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_map_iterator_prev(ErlNifEnv *env,
        ErlNifMapIterator *iter)</nametext></name>
      <fsummary>Decrement map iterator to point to previous entry.</fsummary>
      <desc>
        <p>Decrements map iterator to point to the previous key-value entry.</p>
        <p>Returns <c>true</c> if the iterator is now positioned at a valid
          key-value entry, or <c>false</c> if the iterator is positioned at
          the head (before the first entry).</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifTime</ret>
        <nametext>enif_monotonic_time(ErlNifTimeUnit time_unit)</nametext>
      </name>
      <fsummary>Get Erlang monotonic time.</fsummary>
      <desc>
        <marker id="enif_monotonic_time"></marker>
        <p>Returns the current
          <seealso marker="time_correction#Erlang_Monotonic_Time">
          Erlang monotonic time</seealso>. Notice that it is not uncommon with
          negative values.</p>
        <p><c>time_unit</c> is the time unit of the returned value.</p>
        <p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid time
          unit argument, or if called from a thread that is not a scheduler
          thread.</p>
        <p>See also <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso>
          and <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.
        </p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifMutex *</ret>
        <nametext>enif_mutex_create(char *name)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_mutex_create">
          <c>erl_drv_mutex_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_mutex_destroy(ErlNifMutex *mtx)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_mutex_destroy">
          <c>erl_drv_mutex_destroy</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_mutex_lock(ErlNifMutex *mtx)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_mutex_lock">
          <c>erl_drv_mutex_lock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
      <nametext>enif_mutex_trylock(ErlNifMutex *mtx)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_mutex_trylock">
          <c>erl_drv_mutex_trylock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_mutex_unlock(ErlNifMutex *mtx)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_mutex_unlock">
          <c>erl_drv_mutex_unlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret>
        <nametext>enif_now_time(ErlNifEnv *env)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Returns an <seealso marker="erlang#now-0">
          <c>erlang:now()</c></seealso> time stamp.</p>
        <p><em>This function is deprecated.</em></p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifResourceType *</ret>
        <nametext>enif_open_resource_type(ErlNifEnv* env, const char*
        module_str, const char* name, ErlNifResourceDtor* dtor,
        ErlNifResourceFlags flags, ErlNifResourceFlags* tried)</nametext>
      </name>
      <fsummary>Create or takeover a resource type.</fsummary>
      <desc>
        <p>Creates or takes over a resource type identified by the string
          <c>name</c> and gives it the destructor function pointed to by
          <seealso marker="#ErlNifResourceDtor"><c>dtor</c></seealso>.
          Argument <c>flags</c> can have the following values:</p>
        <taglist>
          <tag><c>ERL_NIF_RT_CREATE</c></tag>
          <item>Creates a new resource type that does not already exist.</item>
          <tag><c>ERL_NIF_RT_TAKEOVER</c></tag>
          <item>Opens an existing resource type and takes over ownership of all
            its instances. The supplied destructor <c>dtor</c> is called both
            for existing instances and new instances not yet created by the
            calling NIF library.</item>
        </taglist>
        <p>The two flag values can be combined with bitwise OR. The resource
          type name is local to the calling module. Argument <c>module_str</c>
          is not (yet) used and must be <c>NULL</c>. <c>dtor</c> can be
          <c>NULL</c> if no destructor is needed.</p>
        <p>On success, the function returns a pointer to the resource type and
          <c>*tried</c> is set to either <c>ERL_NIF_RT_CREATE</c> or
          <c>ERL_NIF_RT_TAKEOVER</c> to indicate what was done. On failure,
          returns <c>NULL</c> and sets <c>*tried</c> to <c>flags</c>.
          It is allowed to set <c>tried</c> to <c>NULL</c>.</p>
        <p>Notice that <c>enif_open_resource_type</c> is only allowed to be
          called in the three callbacks
          <seealso marker="#load"><c>load</c></seealso>,
          <seealso marker="#reload"><c>reload</c></seealso>, and
          <seealso marker="#upgrade"><c>upgrade</c></seealso>.</p>
      </desc>
    </func>

    <func>
     <name><ret>int</ret><nametext>enif_port_command(ErlNifEnv* env, const
       ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg)</nametext>
     </name>
     <fsummary>Send a port_command to to_port.</fsummary>
     <desc>
       <p>Works as <seealso marker="erlang#port_command-2">
         <c>erlang:port_command/2</c></seealso>,
         except that it is always completely asynchronous.</p>
       <taglist>
         <tag><c>env</c></tag>
         <item>The environment of the calling process. Must not be
           <c>NULL</c>.</item>
         <tag><c>*to_port</c></tag>
         <item>The port ID of the receiving port. The port ID is to refer to a
           port on the local node.</item>
         <tag><c>msg_env</c></tag>
         <item>The environment of the message term. Can be a process-independent
           environment allocated with <seealso marker="#enif_alloc_env">
           <c>enif_alloc_env</c></seealso> or <c>NULL</c>.</item>
         <tag><c>msg</c></tag>
         <item>The message term to send. The same limitations apply as on the
           payload to <seealso marker="erlang#port_command-2">
           <c>erlang:port_command/2</c></seealso>.</item>
       </taglist>
       <p>Using a <c>msg_env</c> of <c>NULL</c> is an optimization, which
         groups together calls to <c>enif_alloc_env</c>, <c>enif_make_copy</c>,
         <c>enif_port_command</c>, and <c>enif_free_env</c> into one call.
         This optimization is only useful when a majority of the terms are to
         be copied from <c>env</c> to <c>msg_env</c>.</p>
       <p>Returns <c>true</c> if the command is successfully sent. Returns
         <c>false</c> if the command fails, for example:</p>
       <list type="bulleted">
         <item><c>*to_port</c> does not refer to a local port.</item>
         <item>The currently executing process (that is, the sender) is not
           alive.</item>
         <item><c>msg</c> is invalid.</item>
       </list>
       <p>See also <seealso marker="#enif_get_local_port">
         <c>enif_get_local_port</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void *</ret>
        <nametext>enif_priv_data(ErlNifEnv* env)</nametext></name>
      <fsummary>Get the private data of a NIF library.</fsummary>
      <desc>
        <p>Returns the pointer to the private data that was set by
          <seealso marker="#load"><c>load</c></seealso>,
          <seealso marker="#reload"><c>reload</c></seealso>, or
          <seealso marker="#upgrade"><c>upgrade</c></seealso>.</p>
        <p>Was previously named <c>enif_get_data</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_raise_exception(ErlNifEnv*
        env, ERL_NIF_TERM reason)</nametext></name>
      <fsummary>Raise a NIF error exception.</fsummary>
      <desc>
        <p>Creates an error exception with the term <c>reason</c> to be
          returned from a NIF, and associates it with environment <c>env</c>.
          Once a NIF or any function it calls invokes
          <c>enif_raise_exception</c>, the runtime ensures that the exception
          it creates is raised when the NIF returns, even if the NIF attempts
          to return a non-exception term instead.</p>
        <p>The return value from <c>enif_raise_exception</c> can only be used
          as the return value from the NIF that invoked it (directly or
          indirectly) or be passed to <seealso marker="#enif_is_exception">
          <c>enif_is_exception</c></seealso>, but not to any other NIF API
          function.</p>
        <p>See also <seealso marker="#enif_has_pending_exception">
          <c>enif_has_pending_exception</c></seealso> and
          <seealso marker="#enif_make_badarg">
          <c>enif_make_badarg</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_realloc_binary(ErlNifBinary* bin, size_t size)</nametext>
      </name>
      <fsummary>Change the size of a binary.</fsummary>
      <desc>
        <p>Changes the size of a binary <c>bin</c>. The source binary
          can be read-only, in which case it is left untouched and
          a mutable copy is allocated and assigned to <c>*bin</c>.</p>
        <p>Returns <c>true</c> on success, or <c>false</c> if memory allocation
          failed.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_release_binary(ErlNifBinary* bin)</nametext></name>
      <fsummary>Release a binary.</fsummary>
      <desc>
        <p>Releases a binary obtained from
          <seealso marker="#enif_alloc_binary">
          <c>enif_alloc_binary</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_release_resource(void* obj)</nametext></name>
      <fsummary>Release a resource object.</fsummary>
      <desc>
        <p>Removes a reference to resource object <c>obj</c>obtained from
          <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>.
          The resource object is destructed when the last reference is removed.
          Each call to <c>enif_release_resource</c> must correspond to a
          previous call to <c>enif_alloc_resource</c> or
          <seealso marker="#enif_keep_resource">
          <c>enif_keep_resource</c></seealso>.
          References made by <seealso marker="#enif_make_resource">
          <c>enif_make_resource</c></seealso>
          can only be removed by the garbage collector.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifRWLock *</ret>
        <nametext>enif_rwlock_create(char *name)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_create">
          <c>erl_drv_rwlock_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_rwlock_destroy(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_destroy">
          <c>erl_drv_rwlock_destroy</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_rwlock_rlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rlock">
          <c>erl_drv_rwlock_rlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_rwlock_runlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_runlock">
          <c>erl_drv_rwlock_runlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_rwlock_rwlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwlock">
          <c>erl_drv_rwlock_rwlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_rwlock_rwunlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwunlock">
          <c>erl_drv_rwlock_rwunlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_rwlock_tryrlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrlock">
          <c>erl_drv_rwlock_tryrlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrwlock">
          <c>erl_drv_rwlock_tryrwlock</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ERL_NIF_TERM</ret><nametext>enif_schedule_nif(ErlNifEnv* env,
        const char* fun_name, int flags, ERL_NIF_TERM (*fp)(ErlNifEnv* env, int
        argc, const ERL_NIF_TERM argv[]), int argc, const ERL_NIF_TERM
        argv[])</nametext></name>
      <fsummary>Schedule a NIF for execution.</fsummary>
      <desc>
        <p>Schedules NIF <c>fp</c> to execute. This function allows an
          application to break up long-running work into multiple regular NIF
          calls or to schedule a <seealso marker="#dirty_nifs">
          dirty NIF</seealso> to execute on a dirty scheduler thread.</p>
        <p><em>The dirty NIF functionality described here is
          experimental.</em> You have to enable support for dirty
          schedulers when building OTP to try out the functionality.</p>
        <taglist>
          <tag><c>fun_name</c></tag>
          <item>
            <p>Provides a name for the NIF that is scheduled for execution.
              If it cannot be converted to an atom, <c>enif_schedule_nif</c>
              returns a <c>badarg</c> exception.</p>
          </item>
          <tag><c>flags</c></tag>
          <item>
            <p>Must be set to <c>0</c> for a regular NIF. If the emulator was
              built with the experimental dirty scheduler support enabled,
              <c>flags</c> can be set to either
              <c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c> if the job is expected to be
              CPU-bound, or <c>ERL_NIF_DIRTY_JOB_IO_BOUND</c> for
              jobs that will be I/O-bound. If dirty scheduler threads are not
              available in the emulator, an attempt to schedule such a job
              results in a <c>badarg</c> exception.</p>
          </item>
          <tag><c>argc</c> and <c>argv</c></tag>
          <item>
            <p>Can either be the originals passed into the calling NIF,
              or can be values created by the calling NIF.</p>
          </item>
        </taglist>
        <p>The calling NIF must use the return value of
          <c>enif_schedule_nif</c> as its own return value.</p>
        <p>Be aware that <c>enif_schedule_nif</c>, as its name implies, only
          schedules the NIF for future execution. The calling NIF does not
          block waiting for the scheduled NIF to execute and return. This means
          that the calling NIF cannot expect to receive the scheduled NIF
          return value and use it for further operations.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifPid *</ret>
        <nametext>enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)</nametext>
      </name>
      <fsummary>Get the pid of the calling process.</fsummary>
      <desc>
        <p>Initializes the pid variable <c>*pid</c> to represent the
          calling process.</p>
        <p>Returns <c>pid</c>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_send(ErlNifEnv* env, ErlNifPid* to_pid,
        ErlNifEnv* msg_env, ERL_NIF_TERM msg)</nametext></name>
      <fsummary>Send a message to a process.</fsummary>
      <desc>
        <p>Sends a message to a process.</p>
        <taglist>
          <tag><c>env</c></tag>
          <item>The environment of the calling process. Must be <c>NULL</c>
            only if calling from a created thread.</item>
          <tag><c>*to_pid</c></tag>
          <item>The pid of the receiving process. The pid is to refer to a
            process on the local node.</item>
          <tag><c>msg_env</c></tag>
          <item>The environment of the message term. Must be a
            process-independent environment allocated with
            <seealso marker="#enif_alloc_env"><c>enif_alloc_env</c></seealso>
            or NULL.</item>
          <tag><c>msg</c></tag>
          <item>The message term to send.</item>
        </taglist>
        <p>Returns <c>true</c> if the message is successfully sent. Returns
          <c>false</c> if the send operation fails, that is:</p>
        <list type="bulleted">
          <item><c>*to_pid</c> does not refer to an alive local process.</item>
          <item>The currently executing process (that is, the sender) is not
           alive.</item>
        </list>
        <p>The message environment <c>msg_env</c> with all its terms (including
          <c>msg</c>) is invalidated by a successful call to <c>enif_send</c>.
          The environment is to either be freed with
          <seealso marker="#enif_free_env">
          <c>enif_free_env</c></seealso> of cleared for reuse with
          <seealso marker="#enif_clear_env"><c>enif_clear_env</c></seealso>.</p>
        <p>If <c>msg_env</c> is set to <c>NULL</c>, the <c>msg</c> term is
          copied and the original term and its environemt is still valid after
          the call.</p>
        <p>This function is only thread-safe when the emulator with SMP support
          is used. It can only be used in a non-SMP emulator from a NIF-calling
          thread.</p>
        <note>
          <p>Passing <c>msg_env</c> as <c>NULL</c> is only supported as from
            <c>ERTS</c> 8.0 (Erlang/OTP 19).</p>
        </note>
      </desc>
    </func>

    <func>
      <name><ret>unsigned</ret>
        <nametext>enif_sizeof_resource(void* obj)</nametext></name>
      <fsummary>Get the byte size of a resource object.</fsummary>
      <desc>
        <p>Gets the byte size of resource object <c>obj</c> obtained by
          <seealso marker="#enif_alloc_resource">
          <c>enif_alloc_resource</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_snprintf(char *str, size_t size, const
        char *format, ...)</nametext></name>
      <fsummary>Format strings and Erlang terms.</fsummary>
      <desc>
        <p>Similar to <c>snprintf</c> but this format string also accepts
          <c>"%T"</c>, which formats Erlang terms.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret><nametext>enif_system_info(ErlNifSysInfo
        *sys_info_ptr, size_t size)</nametext></name>
      <fsummary>Get information about the Erlang runtime system.</fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#driver_system_info">
          <c>driver_system_info</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret><nametext>enif_term_to_binary(ErlNifEnv *env,
        ERL_NIF_TERM term, ErlNifBinary *bin)</nametext></name>
      <fsummary>Convert a term to the external format.</fsummary>
      <desc>
        <p>Allocates a new binary with <seealso marker="#enif_alloc_binary">
          <c>enif_alloc_binary</c></seealso> and stores the result of encoding
          <c>term</c> according to the Erlang external term format.</p>
      <p>Returns <c>true</c> on success, or <c>false</c> if the allocation
        fails.</p>
      <p>See also <seealso marker="erlang#term_to_binary-1">
        <c>erlang:term_to_binary/1</c></seealso> and
        <seealso marker="#enif_binary_to_term">
        <c>enif_binary_to_term</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_thread_create(char *name,ErlNifTid
        *tid,void * (*func)(void *),void *args,ErlNifThreadOpts
        *opts)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_create">
          <c>erl_drv_thread_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_thread_exit(void *resp)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_exit">
          <c>erl_drv_thread_exit</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_thread_join(ErlNifTid, void **respp)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_join">
          <c>erl_drv_thread_join</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifThreadOpts *</ret>
        <nametext>enif_thread_opts_create(char *name)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_create">
          <c>erl_drv_thread_opts_create</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_thread_opts_destroy(ErlNifThreadOpts *opts)</nametext>
      </name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_destroy">
          <c>erl_drv_thread_opts_destroy</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifTid</ret>
        <nametext>enif_thread_self(void)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_thread_self">
          <c>erl_drv_thread_self</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
      <nametext>enif_thread_type(void)</nametext></name>
      <fsummary>Determine type of current thread</fsummary>
      <desc>
        <p>Determine the type of currently executing thread. A positive value
        indicates a scheduler thread while a negative value or zero indicates
        another type of thread. Currently the following specific types exist
        (which may be extended in the future):</p>
        <taglist>
          <tag><c>ERL_NIF_THR_UNDEFINED</c></tag>
          <item><p>Undefined thread that is not a scheduler thread.</p></item>
          <tag><c>ERL_NIF_THR_NORMAL_SCHEDULER</c></tag>
          <item><p>A normal scheduler thread.</p></item>
          <tag><c>ERL_NIF_THR_DIRTY_CPU_SCHEDULER</c></tag>
          <item><p>A dirty CPU scheduler thread.</p></item>
          <tag><c>ERL_NIF_THR_DIRTY_IO_SCHEDULER</c></tag>
          <item><p>A dirty I/O scheduler thread.</p></item>
        </taglist>
      </desc>
    </func>

    <func>
      <name><ret>ErlNifTime</ret>
        <nametext>enif_time_offset(ErlNifTimeUnit time_unit)</nametext></name>
      <fsummary>Get current time offset.</fsummary>
      <desc>
        <marker id="enif_time_offset"></marker>
        <p>Returns the current time offset between
          <seealso marker="time_correction#Erlang_Monotonic_Time">
          Erlang monotonic time</seealso> and
          <seealso marker="time_correction#Erlang_System_Time">
          Erlang system time</seealso>
          converted into the <c>time_unit</c> passed as argument.</p>
        <p><c>time_unit</c> is the time unit of the returned value.</p>
        <p>Returns <c>ERL_NIF_TIME_ERROR</c> if called with an invalid
          time unit argument or if called from a thread that is not a
          scheduler thread.</p>
        <p>See also <seealso marker="#ErlNifTime"><c>ErlNifTime</c></seealso>
          and
          <seealso marker="#ErlNifTimeUnit"><c>ErlNifTimeUnit</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void *</ret>
        <nametext>enif_tsd_get(ErlNifTSDKey key)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_tsd_get">
          <c>erl_drv_tsd_get</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>int</ret>
        <nametext>enif_tsd_key_create(char *name, ErlNifTSDKey *key)</nametext>
      </name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_create">
          <c>erl_drv_tsd_key_create</c></seealso>.</p>
    </desc>
   </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_tsd_key_destroy(ErlNifTSDKey key)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_destroy">
          <c>erl_drv_tsd_key_destroy</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name><ret>void</ret>
        <nametext>enif_tsd_set(ErlNifTSDKey key, void *data)</nametext></name>
      <fsummary></fsummary>
      <desc>
        <p>Same as <seealso marker="erl_driver#erl_drv_tsd_set">
          <c>erl_drv_tsd_set</c></seealso>.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>See Also</title>
    <p><seealso marker="erlang#load_nif-2">
      <c>erlang:load_nif/2</c></seealso></p>
  </section>
</cref>