aboutsummaryrefslogtreecommitdiffstats
path: root/erts/emulator/beam/erl_time_sup.c
blob: bf9dca499267fee8cdad17c1b3b6bb79a2c0aee2 (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
/*
 * %CopyrightBegin%
 *
 * Copyright Ericsson AB 1999-2011. All Rights Reserved.
 *
 * The contents of this file are subject to the Erlang Public License,
 * Version 1.1, (the "License"); you may not use this file except in
 * compliance with the License. You should have received a copy of the
 * Erlang Public License along with this software. If not, it can be
 * retrieved online at http://www.erlang.org/.
 *
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
 * the License for the specific language governing rights and limitations
 * under the License.
 *
 * %CopyrightEnd%
 */

/*
** Support routines for the timer wheel
**
** This code contains two strategies for dealing with 
** date/time changes in the system. 
** If the system has some kind of high resolution timer (HAVE_GETHRTIME),
** the high resolution timer is used to correct the time-of-day and the
** timeouts, the base source is the hrtimer, but at certain intervals the 
** OS time-of-day is checked and if it is not within certain bounds, the 
** delivered time gets slowly adjusted for each call until
** it corresponds to the system time (built-in adjtime...). 
** The call gethrtime() is detected by autoconf on Unix, but other 
** platforms may define it in erl_*_sys.h and implement 
** their own high resolution timer. The high resolution timer
** strategy is (probably) best on all systems where the timer have 
** a resolution higher or equal to gettimeofday (or what's implemented
** is sys_gettimeofday()). The actual resolution is the interesting thing,
** not the unit's thats used (i.e. on VxWorks, nanoseconds can be
** retrieved in terms of units, but the actual resolution is the same as 
** for the clock ticks).
** If the systems best timer routine is kernel ticks returned from 
** sys_times(), and the actual resolution of sys_gettimeofday() is
** better (like most unixes that does not have any realtime extensions), 
** another strategy is used. The tolerant gettimeofday() corrects 
** the value with respect to uptime (sys_times() return value) and checks 
** for correction both when delivering timeticks and delivering nowtime.
** this strategy is slower, but accurate on systems without better timer 
** routines. The kernel tick resolution is not enough to implement
** a gethrtime routine. On Linux and other non solaris unix-boxes the second 
** strategy is used, on all other platforms we use the first.
** 
** The following is expected (from sys.[ch] and erl_*_sys.h):
**
** 64 bit integers. So it is, and so it will be.
**
** sys_init_time(), will return the clock resolution in MS and
** that's about it. More could be added of course
** If the clock-rate is constant (i.e. 1 ms) one can define 
** SYS_CLOCK_RESOLUTION (to 1),
** which makes erts_deliver_time/erts_time_remaining a bit faster.
**
** if HAVE_GETHRTIME is defined:
**    sys_gethrtime() will return a SysHrTime (long long) representing 
**    nanoseconds, sys_init_hrtime() will do any initialization.
** else
**    a long (64bit) integer type called Sint64 should be defined.
**
** sys_times() will return clock_ticks since start and 
**    fill in a SysTimes structure (struct tms). Instead of CLK_TCK, 
**    SYS_CLK_TCK is used to determine the resolution of kernel ticks.
**
** sys_gettimeofday() will take a SysTimeval (a struct timeval) as parameter
**    and fill it in as gettimeofday(X,NULL).
**
*/

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "sys.h"
#include "erl_vm.h"
#include "global.h"

static erts_smp_mtx_t erts_timeofday_mtx;

static SysTimeval inittv; /* Used everywhere, the initial time-of-day */

static SysTimes t_start; /* Used in elapsed_time_both */
static SysTimeval gtv; /* Used in wall_clock_elapsed_time_both */
static SysTimeval then; /* Used in get_now */
static SysTimeval last_emu_time; /* Used in erts_get_emu_time() */
SysTimeval erts_first_emu_time; /* Used in erts_get_emu_time() */

union {
    erts_smp_atomic_t time;
    char align[ERTS_CACHE_LINE_SIZE];
} approx erts_align_attribute(ERTS_CACHE_LINE_SIZE);

static void
init_approx_time(void)
{
    erts_smp_atomic_init_nob(&approx.time, 0);
}

static ERTS_INLINE erts_approx_time_t
get_approx_time(void)
{
    return (erts_approx_time_t) erts_smp_atomic_read_nob(&approx.time);
}

static ERTS_INLINE void
update_approx_time(SysTimeval *tv)
{
    erts_approx_time_t new_secs = (erts_approx_time_t) tv->tv_sec;
    erts_approx_time_t old_secs = get_approx_time();
    if (old_secs != new_secs)
	erts_smp_atomic_set_nob(&approx.time, new_secs);
}

/*
 * erts_get_approx_time() returns an *approximate* time
 * in seconds. NOTE that this time may jump backwards!!!
 */
erts_approx_time_t
erts_get_approx_time(void)
{
    return get_approx_time();
}

#ifdef HAVE_GETHRTIME

int erts_disable_tolerant_timeofday;

static SysHrTime hr_init_time, hr_last_correction_check, 
    hr_correction, hr_last_time;

static void init_tolerant_timeofday(void)
{
    /* Should be in sys.c */
#if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_CONF)
    if (sysconf(_SC_NPROCESSORS_CONF) > 1) {
	char b[1024];
	int maj,min,build;
	os_flavor(b,1024);
	os_version(&maj,&min,&build);
	if (!strcmp(b,"sunos") && maj <= 5 && min <= 7) {
	    erts_disable_tolerant_timeofday = 1;
	}
    }
#endif
    hr_init_time = sys_gethrtime();
    hr_last_correction_check = hr_last_time = hr_init_time;
    hr_correction = 0;
}

static void get_tolerant_timeofday(SysTimeval *tv)
{
    SysHrTime diff_time, curr;

    if (erts_disable_tolerant_timeofday) {
	sys_gettimeofday(tv);
	return;
    }
    *tv = inittv;
    diff_time = ((curr = sys_gethrtime()) + hr_correction - hr_init_time) / 1000; 

    if (curr < hr_init_time) {
	erl_exit(1,"Unexpected behaviour from operating system high "
		 "resolution timer");
    }

    if ((curr - hr_last_correction_check) / 1000 > 1000000) {
	/* Check the correction need */
	SysHrTime tv_diff, diffdiff;
	SysTimeval tmp;
	int done = 0;

	sys_gettimeofday(&tmp);
	tv_diff = ((SysHrTime) tmp.tv_sec) * 1000000 + tmp.tv_usec;
	tv_diff -= ((SysHrTime) inittv.tv_sec) * 1000000 + inittv.tv_usec;
	diffdiff = diff_time - tv_diff;
	if (diffdiff > 10000) {
	    SysHrTime corr = (curr - hr_last_time) / 100;
	    if (corr / 1000 >= diffdiff) {
		++done;
		hr_correction -= ((SysHrTime)diffdiff) * 1000;
	    } else {
		hr_correction -= corr;
	    }
	    diff_time = (curr + hr_correction - hr_init_time) / 1000; 
	} else if (diffdiff < -10000) {
	    SysHrTime corr = (curr - hr_last_time) / 100;
	    if (corr / 1000 >= -diffdiff) {
		++done;
		hr_correction -= ((SysHrTime)diffdiff) * 1000;
	    } else {
		hr_correction += corr;
	    }
	    diff_time = (curr + hr_correction - hr_init_time) / 1000; 
	} else {
	    ++done;
	}
	if (done) {
	    hr_last_correction_check = curr;
	}
    }
    tv->tv_sec += (int) (diff_time / ((SysHrTime) 1000000));
    tv->tv_usec += (int) (diff_time % ((SysHrTime) 1000000));
    if (tv->tv_usec >= 1000000) {
	tv->tv_usec -= 1000000;
	tv->tv_sec += 1;
    }
    hr_last_time = curr;
}

#define correction (hr_correction/1000000)

#else /* !HAVE_GETHRTIME */
#if !defined(CORRECT_USING_TIMES) 
#define init_tolerant_timeofday() 
#define get_tolerant_timeofday(tvp) sys_gettimeofday(tvp)
#else

typedef Sint64 Milli;

static clock_t init_ct;
static Sint64 ct_wrap;
static Milli init_tv_m;
static Milli correction_supress; 
static Milli last_ct_diff;
static Milli last_cc; 
static clock_t last_ct;

/* sys_times() might need to be wrapped and the values shifted (right)
   a bit to cope with newer linux (2.5.*) kernels, this has to be taken care 
   of dynamically to start with, a special version that uses
   the times() return value as a high resolution timer can be made
   to fully utilize the faster ticks, like on windows, but for now, we'll
   settle with this silly workaround */
#ifdef ERTS_WRAP_SYS_TIMES 
#define KERNEL_TICKS() (sys_times_wrap() &  \
			((1UL << ((sizeof(clock_t) * 8) - 1)) - 1)) 
#else
SysTimes dummy_tms;

#define KERNEL_TICKS() (sys_times(&dummy_tms) &  \
			((1UL << ((sizeof(clock_t) * 8) - 1)) - 1)) 

#endif

static void init_tolerant_timeofday(void)
{
    last_ct = init_ct = KERNEL_TICKS();
    last_cc = 0;
    init_tv_m = (((Milli) inittv.tv_sec) * 1000) + 
	(inittv.tv_usec / 1000);
    ct_wrap = 0;
    correction_supress = 0;
}


static void get_tolerant_timeofday(SysTimeval *tvp)
{
    clock_t current_ct;
    SysTimeval current_tv;
    Milli ct_diff;
    Milli tv_diff;
    Milli current_correction;
    Milli act_correction;	/* long shown to be too small */
    Milli max_adjust;

    if (erts_disable_tolerant_timeofday) {
	sys_gettimeofday(tvp);
	return;
    }

#ifdef ERTS_WRAP_SYS_TIMES 
#define TICK_MS (1000 / SYS_CLK_TCK_WRAP)
#else
#define TICK_MS (1000 / SYS_CLK_TCK)
#endif
    current_ct = KERNEL_TICKS();
    sys_gettimeofday(&current_tv);

    /* I dont know if uptime can move some units backwards
       on some systems, but I allow for small backward 
       jumps to avoid such problems if they exist...*/
    if (last_ct > 100 && current_ct < (last_ct - 100)) {
	ct_wrap += ((Sint64) 1) << ((sizeof(clock_t) * 8) - 1);
    }
    last_ct = current_ct;
    ct_diff = ((ct_wrap + current_ct) - init_ct) * TICK_MS;

    /*
     * We will adjust the time in milliseconds and we allow for 1% 
     * adjustments, but if this function is called more often then every 100 
     * millisecond (which is obviously possible), we will never adjust, so 
     * we accumulate small times by setting last_ct_diff iff max_adjust > 0
     */
    if ((max_adjust = (ct_diff - last_ct_diff)/100) > 0)
	last_ct_diff = ct_diff;

    tv_diff = ((((Milli) current_tv.tv_sec) * 1000) + 
	       (current_tv.tv_usec / 1000)) - init_tv_m;

    current_correction = ((ct_diff - tv_diff) / TICK_MS) * TICK_MS; /* trunc */

    /* 
     * We allow the current_correction value to wobble a little, as it
     * suffers from the low resolution of the kernel ticks. 
     * if it hasn't changed more than one tick in either direction, 
     * we will keep the old value.
     */
    if ((last_cc > current_correction + TICK_MS) ||
	(last_cc < current_correction - TICK_MS)) {
	last_cc = current_correction;
    } else {
	current_correction = last_cc;
    }
    
    /*
     * As time goes, we try to get the actual correction to 0, 
     * that is, make erlangs time correspond to the systems dito.
     * The act correction is what we seem to need (current_correction)
     * minus the correction suppression. The correction supression
     * will change slowly (max 1% of elapsed time) but in millisecond steps.
     */
    act_correction = current_correction - correction_supress;
    if (max_adjust > 0) {
	/*
	 * Here we slowly adjust erlangs time to correspond with the 
	 * system time by changing the correction_supress variable.
	 * It can change max_adjust milliseconds which is 1% of elapsed time
	 */
	if (act_correction > 0) {
	    if (current_correction - correction_supress > max_adjust) {
		correction_supress += max_adjust;
	    } else {
		correction_supress = current_correction;
	    }
	    act_correction = current_correction - correction_supress;
	} else if (act_correction < 0) {
	    if (correction_supress - current_correction > max_adjust) {
		correction_supress -= max_adjust;
	    } else {
		correction_supress = current_correction;
	    }
	    act_correction = current_correction - correction_supress;
	}
    }
    /*
     * The actual correction will correct the timeval so that system 
     * time warps gets smothed down.
     */
    current_tv.tv_sec += act_correction / 1000;
    current_tv.tv_usec += (act_correction % 1000) * 1000;

    if (current_tv.tv_usec >= 1000000) {
	++current_tv.tv_sec ;
	current_tv.tv_usec -= 1000000;
    } else if (current_tv.tv_usec < 0) {
	--current_tv.tv_sec;
	current_tv.tv_usec += 1000000;
    }
    *tvp = current_tv;
#undef TICK_MS
}

#endif /* CORRECT_USING_TIMES */
#endif /* !HAVE_GETHRTIME */

/*
** Why this? Well, most platforms have a constant clock resolution of 1,
** we dont want the deliver_time/time_remaining routines to waste 
** time dividing and multiplying by/with a variable that's always one.
** so the return value of sys_init_time is ignored on those platforms.
*/
 
#ifndef SYS_CLOCK_RESOLUTION
static int clock_resolution;
#define CLOCK_RESOLUTION clock_resolution
#else
#define CLOCK_RESOLUTION SYS_CLOCK_RESOLUTION
#endif

/*
** The clock resolution should really be the resolution of the 
** time function in use, which on most platforms 
** is 1. On VxWorks the resolution should be
** the number of ticks per second (or 1, which would work nicely to).
**
** Setting lower resolutions is mostly interesting when timers are used
** instead of something like select.
*/

static SysTimeval last_delivered; 

static void init_erts_deliver_time(const SysTimeval *inittv)
{
    /* We set the initial values for deliver_time here */
    last_delivered = *inittv;
    last_delivered.tv_usec = 1000 * (last_delivered.tv_usec / 1000); 
                                                   /* ms resolution */
}

static void do_erts_deliver_time(const SysTimeval *current)
{
    SysTimeval cur_time;
    erts_time_t elapsed;
    
    /* calculate and deliver appropriate number of ticks */
    cur_time = *current;
    cur_time.tv_usec = 1000 * (cur_time.tv_usec / 1000); /* ms resolution */
    elapsed = (1000 * (cur_time.tv_sec - last_delivered.tv_sec) +
	       (cur_time.tv_usec - last_delivered.tv_usec) / 1000) / 
	CLOCK_RESOLUTION;

    /* Sometimes the time jump backwards,
       resulting in a negative elapsed time. We compensate for
       this by simply pretend as if the time stood still. :) */

    if (elapsed > 0) {

	ASSERT(elapsed < ((erts_time_t) ERTS_SHORT_TIME_T_MAX));

	erts_do_time_add((erts_short_time_t) elapsed);
	last_delivered = cur_time;
    }
}

int 
erts_init_time_sup(void)
{
    erts_smp_mtx_init(&erts_timeofday_mtx, "timeofday");

    init_approx_time();

    last_emu_time.tv_sec = 0;
    last_emu_time.tv_usec = 0;

#ifndef SYS_CLOCK_RESOLUTION
    clock_resolution = sys_init_time();
#else
    (void) sys_init_time();
#endif
    sys_gettimeofday(&inittv);
    
#ifdef HAVE_GETHRTIME
    sys_init_hrtime();
#endif
    init_tolerant_timeofday();

    init_erts_deliver_time(&inittv);
    gtv = inittv;
    then.tv_sec = then.tv_usec = 0;

    erts_deliver_time();

    return CLOCK_RESOLUTION;
}    
/* info functions */

void 
elapsed_time_both(UWord *ms_user, UWord *ms_sys, 
		  UWord *ms_user_diff, UWord *ms_sys_diff)
{
    UWord prev_total_user, prev_total_sys;
    UWord total_user, total_sys;
    SysTimes now;

    sys_times(&now);
    total_user = (now.tms_utime * 1000) / SYS_CLK_TCK;
    total_sys = (now.tms_stime * 1000) / SYS_CLK_TCK;

    if (ms_user != NULL)
	*ms_user = total_user;
    if (ms_sys != NULL)
	*ms_sys = total_sys;

    erts_smp_mtx_lock(&erts_timeofday_mtx);
    
    prev_total_user = (t_start.tms_utime * 1000) / SYS_CLK_TCK;
    prev_total_sys = (t_start.tms_stime * 1000) / SYS_CLK_TCK;
    t_start = now;
    
    erts_smp_mtx_unlock(&erts_timeofday_mtx);

    if (ms_user_diff != NULL)
	*ms_user_diff = total_user - prev_total_user;
	  
    if (ms_sys_diff != NULL)
	*ms_sys_diff = total_sys - prev_total_sys;
}


/* wall clock routines */

void 
wall_clock_elapsed_time_both(UWord *ms_total, UWord *ms_diff)
{
    UWord prev_total;
    SysTimeval tv;

    erts_smp_mtx_lock(&erts_timeofday_mtx);

    get_tolerant_timeofday(&tv);

    *ms_total = 1000 * (tv.tv_sec - inittv.tv_sec) +
	(tv.tv_usec - inittv.tv_usec) / 1000;

    prev_total = 1000 * (gtv.tv_sec - inittv.tv_sec) +
	(gtv.tv_usec - inittv.tv_usec) / 1000;
    *ms_diff = *ms_total - prev_total;
    gtv = tv;

    /* must sync the machine's idea of time here */
    do_erts_deliver_time(&tv);

    erts_smp_mtx_unlock(&erts_timeofday_mtx);
}

/* get current time */
void 
get_time(int *hour, int *minute, int *second)
{
    time_t the_clock;
    struct tm *tm;
#ifdef HAVE_LOCALTIME_R
    struct tm tmbuf;
#endif
    
    the_clock = time((time_t *)0);
#ifdef HAVE_LOCALTIME_R
    tm = localtime_r(&the_clock, &tmbuf);
#else
    tm = localtime(&the_clock);
#endif
    *hour = tm->tm_hour;
    *minute = tm->tm_min;
    *second = tm->tm_sec;
}

/* get current date */
void 
get_date(int *year, int *month, int *day)
{
    time_t the_clock;
    struct tm *tm;
#ifdef HAVE_LOCALTIME_R
    struct tm tmbuf;
#endif


    the_clock = time((time_t *)0);
#ifdef HAVE_LOCALTIME_R
    tm = localtime_r(&the_clock, &tmbuf);
#else
    tm = localtime(&the_clock);
#endif
    *year = tm->tm_year + 1900;
    *month = tm->tm_mon +1;
    *day = tm->tm_mday;
}

/* get localtime */
void 
get_localtime(int *year, int *month, int *day, 
	      int *hour, int *minute, int *second)
{
    time_t the_clock;
    struct tm *tm;
#ifdef HAVE_LOCALTIME_R
    struct tm tmbuf;
#endif

    the_clock = time((time_t *)0);
#ifdef HAVE_LOCALTIME_R
    localtime_r(&the_clock, (tm = &tmbuf));
#else
    tm = localtime(&the_clock);
#endif
    *year = tm->tm_year + 1900;
    *month = tm->tm_mon +1;
    *day = tm->tm_mday;
    *hour = tm->tm_hour;
    *minute = tm->tm_min;
    *second = tm->tm_sec;
}


/* get universaltime */
void 
get_universaltime(int *year, int *month, int *day, 
		  int *hour, int *minute, int *second)
{
    time_t the_clock;
    struct tm *tm;
#ifdef HAVE_GMTIME_R
    struct tm tmbuf;
#endif

    the_clock = time((time_t *)0);
#ifdef HAVE_GMTIME_R
    gmtime_r(&the_clock, (tm = &tmbuf));
#else
    tm = gmtime(&the_clock);
#endif
    *year = tm->tm_year + 1900;
    *month = tm->tm_mon +1;
    *day = tm->tm_mday;
    *hour = tm->tm_hour;
    *minute = tm->tm_min;
    *second = tm->tm_sec;
}


/* days in month = 1, 2, ..., 12 */
static const int mdays[14] = {0, 31, 28, 31, 30, 31, 30,
                                 31, 31, 30, 31, 30, 31};

#define  IN_RANGE(a,x,b)  (((a) <= (x)) && ((x) <= (b)))
#define  is_leap_year(y)  (((((y) % 4) == 0) && \
                            (((y) % 100) != 0)) || \
                           (((y) % 400) == 0))

/* This is the earliest year we are sure to be able to handle
   on all platforms w/o problems */
#define  BASEYEAR       1902 

/* A more "clever" mktime
 * return  1, if successful
 * return -1, if not successful
 */

static int erl_mktime(time_t *c, struct tm *tm) {
    time_t clock;

    clock = mktime(tm);

    if (clock != -1) {
	*c = clock;
	return 1;
    }

    /* in rare occasions mktime returns -1
     * when a correct value has been entered
     *
     * decrease seconds with one second
     * if the result is -2, epochs should be -1
     */

    tm->tm_sec = tm->tm_sec - 1;
    clock = mktime(tm);
    tm->tm_sec = tm->tm_sec + 1;

    *c = -1;

    if (clock == -2) {
	return 1;
    }

    return -1;
}

/*
 * gregday
 *
 * Returns the number of days since Jan 1, 1600, if year is
 * greater of equal to 1600 , and month [1-12] and day [1-31] 
 * are within range. Otherwise it returns -1.
 */
static time_t gregday(int year, int month, int day)
{
  Sint ndays = 0;
  Sint gyear, pyear, m;
  
  /* number of days in previous years */
  gyear = year - 1600;
  if (gyear > 0) {
    pyear = gyear - 1;
    ndays = (pyear/4) - (pyear/100) + (pyear/400) + pyear*365 + 366;
  }
  /* number of days in all months preceeding month */
  for (m = 1; m < month; m++)
    ndays += mdays[m];
  /* Extra day if leap year and March or later */
  if (is_leap_year(year) && (month > 2))
    ndays++;
  ndays += day - 1;
  return (time_t) (ndays - 135140);        /* 135140 = Jan 1, 1970 */
}

#define SECONDS_PER_MINUTE  (60)
#define SECONDS_PER_HOUR    (60 * SECONDS_PER_MINUTE)
#define SECONDS_PER_DAY     (24 * SECONDS_PER_HOUR)

int seconds_to_univ(Sint64 time, Sint *year, Sint *month, Sint *day, 
	Sint *hour, Sint *minute, Sint *second) {

    Sint y,mi;
    Sint days = time / SECONDS_PER_DAY;
    Sint secs = time % SECONDS_PER_DAY;
    Sint tmp;

    if (secs < 0) {
	days--;
	secs += SECONDS_PER_DAY;
    }
    
    tmp     = secs % SECONDS_PER_HOUR;

    *hour   = secs / SECONDS_PER_HOUR;
    *minute = tmp  / SECONDS_PER_MINUTE;
    *second = tmp  % SECONDS_PER_MINUTE;

    days   += 719468;
    y       = (10000*((Sint64)days) + 14780) / 3652425; 
    tmp     = days - (365 * y + y/4 - y/100 + y/400);

    if (tmp < 0) {
	y--;
	tmp = days - (365*y + y/4 - y/100 + y/400);
    }
    mi = (100 * tmp + 52)/3060;
    *month = (mi + 2) % 12 + 1;
    *year  = y + (mi + 2) / 12;
    *day   = tmp - (mi * 306 + 5)/10 + 1;

    return 1;
}

int univ_to_seconds(Sint year, Sint month, Sint day, Sint hour, Sint minute, Sint second, Sint64 *time) {
    Sint days;

    if (!(IN_RANGE(1600, year, INT_MAX - 1) &&
          IN_RANGE(1, month, 12) &&
          IN_RANGE(1, day, (mdays[month] + 
                             (month == 2 
                              && (year % 4 == 0) 
                              && (year % 100 != 0 || year % 400 == 0)))) &&
          IN_RANGE(0, hour, 23) &&
          IN_RANGE(0, minute, 59) &&
          IN_RANGE(0, second, 59))) {
      return 0;
    }
 
    days   = gregday(year, month, day);
    *time  = SECONDS_PER_DAY;
    *time *= days;             /* don't try overflow it, it hurts */
    *time += SECONDS_PER_HOUR * hour;
    *time += SECONDS_PER_MINUTE * minute;
    *time += second;

    return 1;
}

#if defined(HAVE_TIME2POSIX) && defined(HAVE_DECL_TIME2POSIX) && \
    !HAVE_DECL_TIME2POSIX
extern time_t time2posix(time_t);
#endif

int 
local_to_univ(Sint *year, Sint *month, Sint *day, 
	      Sint *hour, Sint *minute, Sint *second, int isdst)
{
    time_t the_clock;
    struct tm *tm, t;
#ifdef HAVE_GMTIME_R
    struct tm tmbuf;
#endif
    
    if (!(IN_RANGE(BASEYEAR, *year, INT_MAX - 1) &&
          IN_RANGE(1, *month, 12) &&
          IN_RANGE(1, *day, (mdays[*month] + 
                             (*month == 2 
                              && (*year % 4 == 0) 
                              && (*year % 100 != 0 || *year % 400 == 0)))) &&
          IN_RANGE(0, *hour, 23) &&
          IN_RANGE(0, *minute, 59) &&
          IN_RANGE(0, *second, 59))) {
      return 0;
    }
    
    t.tm_year = *year - 1900;
    t.tm_mon = *month - 1;
    t.tm_mday = *day;
    t.tm_hour = *hour;
    t.tm_min = *minute;
    t.tm_sec = *second;
    t.tm_isdst = isdst;

    /* the nature of mktime makes this a bit interesting,
     * up to four mktime calls could happen here
     */

    if (erl_mktime(&the_clock, &t) < 0) {
	if (isdst) {
	    /* If this is a timezone without DST and the OS (correctly)
	       refuses to give us a DST time, we simulate the Linux/Solaris
	       behaviour of giving the same data as if is_dst was not set. */
	    t.tm_isdst = 0;
	    if (erl_mktime(&the_clock, &t) < 0) {
		/* Failed anyway, something else is bad - will be a badarg */
		return 0;
	    }
	} else {
	    /* Something else is the matter, badarg. */
	    return 0;
	}
    }

#ifdef HAVE_TIME2POSIX
    the_clock = time2posix(the_clock);
#endif

#ifdef HAVE_GMTIME_R
    tm = gmtime_r(&the_clock, &tmbuf);
#else
    tm = gmtime(&the_clock);
#endif
    if (!tm) {
      return 0;
    }
    *year = tm->tm_year + 1900;
    *month = tm->tm_mon +1;
    *day = tm->tm_mday;
    *hour = tm->tm_hour;
    *minute = tm->tm_min;
    *second = tm->tm_sec;
    return 1;
}
#if defined(HAVE_POSIX2TIME) && defined(HAVE_DECL_POSIX2TIME) && \
    !HAVE_DECL_POSIX2TIME
extern time_t posix2time(time_t);
#endif

int 
univ_to_local(Sint *year, Sint *month, Sint *day, 
	      Sint *hour, Sint *minute, Sint *second)
{
    time_t the_clock;
    struct tm *tm;
#ifdef HAVE_LOCALTIME_R
    struct tm tmbuf;
#endif
    
    if (!(IN_RANGE(BASEYEAR, *year, INT_MAX - 1) &&
          IN_RANGE(1, *month, 12) &&
          IN_RANGE(1, *day, (mdays[*month] + 
                             (*month == 2 
                              && (*year % 4 == 0) 
                              && (*year % 100 != 0 || *year % 400 == 0)))) &&
          IN_RANGE(0, *hour, 23) &&
          IN_RANGE(0, *minute, 59) &&
          IN_RANGE(0, *second, 59))) {
      return 0;
    }
    
    the_clock = *second + 60 * (*minute + 60 * (*hour + 24 *
                                            gregday(*year, *month, *day)));
#ifdef HAVE_POSIX2TIME
    /*
     * Addition from OpenSource - affects FreeBSD.
     * No valid test case /PaN
     *
     * leap-second correction performed
     * if system is configured so;
     * do nothing if not
     * See FreeBSD 6.x and 7.x
     * /usr/src/lib/libc/stdtime/localtime.c
     * for the details
     */
    the_clock = posix2time(the_clock);
#endif

#ifdef HAVE_LOCALTIME_R
    tm = localtime_r(&the_clock, &tmbuf);
#else
    tm = localtime(&the_clock);
#endif
    if (tm) {
	*year   = tm->tm_year + 1900;
	*month  = tm->tm_mon +1;
	*day    = tm->tm_mday;
	*hour   = tm->tm_hour;
	*minute = tm->tm_min;
	*second = tm->tm_sec;
	return 1;
    }
    return 0;
}


/* get a timestamp */
void
get_now(Uint* megasec, Uint* sec, Uint* microsec)
{
    SysTimeval now;
    
    erts_smp_mtx_lock(&erts_timeofday_mtx);
    
    get_tolerant_timeofday(&now);
    do_erts_deliver_time(&now);

    /* Make sure time is later than last */
    if (then.tv_sec > now.tv_sec ||
	(then.tv_sec == now.tv_sec && then.tv_usec >= now.tv_usec)) {
	now = then;
	now.tv_usec++;
    }
    /* Check for carry from above + general reasonability */
    if (now.tv_usec >= 1000000) {
	now.tv_usec = 0;
	now.tv_sec++;
    }
    then = now;
    
    erts_smp_mtx_unlock(&erts_timeofday_mtx);
    
    *megasec = (Uint) (now.tv_sec / 1000000);
    *sec = (Uint) (now.tv_sec % 1000000);
    *microsec = (Uint) (now.tv_usec);

    update_approx_time(&now);
}

void
get_sys_now(Uint* megasec, Uint* sec, Uint* microsec)
{
    SysTimeval now;
    
    sys_gettimeofday(&now);
    
    *megasec = (Uint) (now.tv_sec / 1000000);
    *sec = (Uint) (now.tv_sec % 1000000);
    *microsec = (Uint) (now.tv_usec);

    update_approx_time(&now);
}


/* deliver elapsed *ticks* to the machine - takes a pointer
   to a struct timeval representing current time (to save
   a gettimeofday() where possible) or NULL */

void erts_deliver_time(void) {
    SysTimeval now;
    
    erts_smp_mtx_lock(&erts_timeofday_mtx);
    
    get_tolerant_timeofday(&now);
    do_erts_deliver_time(&now);
    
    erts_smp_mtx_unlock(&erts_timeofday_mtx);

    update_approx_time(&now);
}

/* get *real* time (not ticks) remaining until next timeout - if there
   isn't one, give a "long" time, that is guaranteed
   to not cause overflow when we report elapsed time later on */

void erts_time_remaining(SysTimeval *rem_time)
{
    erts_time_t ticks;
    SysTimeval cur_time;
    erts_time_t elapsed;

    /* erts_next_time() returns no of ticks to next timeout or -1 if none */

    ticks = (erts_time_t) erts_next_time();
    if (ticks == (erts_time_t) -1) {
	/* timer queue empty */
	/* this will cause at most 100000000 ticks */
	rem_time->tv_sec = 100000;
	rem_time->tv_usec = 0;
    } else {
	/* next timeout after ticks ticks */
	ticks *= CLOCK_RESOLUTION;
	
	erts_smp_mtx_lock(&erts_timeofday_mtx);
	
	get_tolerant_timeofday(&cur_time);
	cur_time.tv_usec = 1000 * 
	    (cur_time.tv_usec / 1000);/* ms resolution*/
	elapsed = 1000 * (cur_time.tv_sec - last_delivered.tv_sec) +
	    (cur_time.tv_usec - last_delivered.tv_usec) / 1000;
	
	erts_smp_mtx_unlock(&erts_timeofday_mtx);
	
	if (ticks <= elapsed) { /* Ooops, better hurry */
	    rem_time->tv_sec = rem_time->tv_usec = 0;
	    return;
	}
	rem_time->tv_sec = (ticks - elapsed) / 1000;
	rem_time->tv_usec = 1000 * ((ticks - elapsed) % 1000);
    }
}

void erts_get_timeval(SysTimeval *tv)
{
    erts_smp_mtx_lock(&erts_timeofday_mtx);
    get_tolerant_timeofday(tv);
    erts_smp_mtx_unlock(&erts_timeofday_mtx);
    update_approx_time(tv);
}

erts_time_t
erts_get_time(void)
{
    SysTimeval sys_tv;
    
    erts_smp_mtx_lock(&erts_timeofday_mtx);
    
    get_tolerant_timeofday(&sys_tv);
    
    erts_smp_mtx_unlock(&erts_timeofday_mtx);

    update_approx_time(&sys_tv);

    return sys_tv.tv_sec;
}

#ifdef HAVE_ERTS_NOW_CPU
void erts_get_now_cpu(Uint* megasec, Uint* sec, Uint* microsec) {
  SysCpuTime t;
  SysTimespec tp;

  sys_get_proc_cputime(t, tp);
  *microsec = (Uint)(tp.tv_nsec / 1000);
  t = (tp.tv_sec / 1000000);
  *megasec = (Uint)(t % 1000000);
  *sec = (Uint)(tp.tv_sec % 1000000);
}
#endif