From f504781a136b1992a1cee26a7da841892d796d91 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Wed, 21 Nov 2018 15:54:17 +0100
Subject: erts: Add counters:put/3

---
 erts/emulator/beam/erl_bif_counters.c | 50 ++++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 7 deletions(-)

(limited to 'erts/emulator/beam/erl_bif_counters.c')

diff --git a/erts/emulator/beam/erl_bif_counters.c b/erts/emulator/beam/erl_bif_counters.c
index a46b462225..001e643857 100644
--- a/erts/emulator/beam/erl_bif_counters.c
+++ b/erts/emulator/beam/erl_bif_counters.c
@@ -19,7 +19,7 @@
  */
 
 /*
- * Purpose:  High performance atomics.
+ * Purpose:  The implementation for 'counters' with 'write_concurrency'.
  */
 
 #ifdef HAVE_CONFIG_H
@@ -37,6 +37,15 @@
 #include "erl_bif_unique.h"
 #include "erl_map.h"
 
+/*
+ * Each logical counter consists of one 64-bit atomic instance per scheduler
+ * plus one instance for the "base value".
+ *
+ * get() reads all atomics for the counter and return the sum.
+ * add() reads and writes only its own scheduler specific atomic instance.
+ * put() reads all scheduler specific atomics and writes a new base value.
+ */
+#define ATOMICS_PER_COUNTER (erts_no_schedulers + 1)
 
 #define COUNTERS_PER_CACHE_LINE (ERTS_CACHE_LINE_SIZE / sizeof(erts_atomic64_t))
 
@@ -52,7 +61,7 @@ typedef struct
     } u[1];
 }CountersRef;
 
-static int counters_destructor(Binary *unused)
+static int counters_destructor(Binary *mbin)
 {
     return 1;
 }
@@ -76,10 +85,10 @@ BIF_RETTYPE erts_internal_counters_new_1(BIF_ALIST_1)
         BIF_ERROR(BIF_P, BADARG);
     }
 
-    if (cnt > (ERTS_UWORD_MAX / (sizeof(erts_atomic64_t)*2*erts_no_schedulers)))
+    if (cnt > (ERTS_UWORD_MAX / (sizeof(erts_atomic64_t)*2*ATOMICS_PER_COUNTER)))
         BIF_ERROR(BIF_P, SYSTEM_LIMIT);
 
-    cache_lines = erts_no_schedulers * div_ceil(cnt, COUNTERS_PER_CACHE_LINE);
+    cache_lines = ATOMICS_PER_COUNTER * div_ceil(cnt, COUNTERS_PER_CACHE_LINE);
     bytes = offsetof(CountersRef, u) + cache_lines * ERTS_CACHE_LINE_SIZE;
     mbin = erts_create_magic_binary_x(bytes,
                                       counters_destructor,
@@ -87,6 +96,7 @@ BIF_RETTYPE erts_internal_counters_new_1(BIF_ALIST_1)
                                       0);
     p = ERTS_MAGIC_BIN_DATA(mbin);
     p->arity = cnt;
+
 #ifdef DEBUG
     p->ulen = cache_lines;
 #endif
@@ -120,7 +130,7 @@ static ERTS_INLINE int get_ref_cnt(Eterm ref, Eterm index,
     UWord ix, ui, vi;
     if (!get_ref(ref, &p) || !term_to_UWord(index, &ix) || --ix >= p->arity)
         return 0;
-    ui = (ix / COUNTERS_PER_CACHE_LINE) * erts_no_schedulers + sched_ix;
+    ui = (ix / COUNTERS_PER_CACHE_LINE) * ATOMICS_PER_COUNTER;
     vi = ix % COUNTERS_PER_CACHE_LINE;
     ASSERT(ui < p->ulen);
     *pp = p;
@@ -134,7 +144,8 @@ static ERTS_INLINE int get_ref_my_cnt(Eterm ref, Eterm index,
 {
     ErtsSchedulerData *esdp = erts_get_scheduler_data();
     ASSERT(esdp && !ERTS_SCHEDULER_IS_DIRTY(esdp));
-    return get_ref_cnt(ref, index, pp, app, esdp->no - 1);
+    ASSERT(esdp->no > 0 && esdp->no < ATOMICS_PER_COUNTER);
+    return get_ref_cnt(ref, index, pp, app, esdp->no);
 }
 
 static ERTS_INLINE int get_ref_first_cnt(Eterm ref, Eterm index,
@@ -172,7 +183,7 @@ BIF_RETTYPE erts_internal_counters_get_2(BIF_ALIST_2)
     if (!get_ref_first_cnt(BIF_ARG_1, BIF_ARG_2, &p, &ap)) {
         BIF_ERROR(BIF_P, BADARG);
     }
-    for (j = erts_no_schedulers; j ; --j) {
+    for (j = ATOMICS_PER_COUNTER; j ; --j) {
         acc += erts_atomic64_read_nob(ap);
         ap = (erts_atomic64_t*) ((byte*)ap + ERTS_CACHE_LINE_SIZE);
     }
@@ -194,6 +205,31 @@ BIF_RETTYPE erts_internal_counters_add_3(BIF_ALIST_3)
     return am_ok;
 }
 
+BIF_RETTYPE erts_internal_counters_put_3(BIF_ALIST_3)
+{
+    CountersRef* p;
+    erts_atomic64_t* first_ap;
+    erts_atomic64_t* ap;
+    erts_aint64_t acc;
+    erts_aint64_t val;
+    int j;
+
+    if (!get_ref_first_cnt(BIF_ARG_1, BIF_ARG_2, &p, &first_ap)
+        || !term_to_Sint64(BIF_ARG_3, &val)) {
+        BIF_ERROR(BIF_P, BADARG);
+    }
+
+    ap = first_ap;
+    acc = 0;
+    j = ATOMICS_PER_COUNTER - 1;
+    do {
+        ap = (erts_atomic64_t*) ((byte*)ap + ERTS_CACHE_LINE_SIZE);
+        acc += erts_atomic64_read_nob(ap);
+    } while (--j);
+    erts_atomic64_set_nob(first_ap, val-acc);
+
+    return am_ok;
+}
 
 BIF_RETTYPE erts_internal_counters_info_1(BIF_ALIST_1)
 {
-- 
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