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authorRickard Green <[email protected]>2013-02-20 17:13:45 +0100
committerRickard Green <[email protected]>2013-02-21 01:08:10 +0100
commit9ccc56b450cef0fce8b0ed976e91d3dee13ee3b9 (patch)
treea0abfcfcc3cf2ea04f73ab8d766122ce94c493e5
parentdf40b0b99810121d9630730d6f58cf96bfea70e8 (diff)
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Fix lost enqueue notification
-rw-r--r--erts/emulator/beam/erl_thr_queue.c79
1 files changed, 44 insertions, 35 deletions
diff --git a/erts/emulator/beam/erl_thr_queue.c b/erts/emulator/beam/erl_thr_queue.c
index acadc5d4cd..ee2ff765e0 100644
--- a/erts/emulator/beam/erl_thr_queue.c
+++ b/erts/emulator/beam/erl_thr_queue.c
@@ -301,7 +301,7 @@ element_free(ErtsThrQ_t *q, ErtsThrQElement_t *el)
#ifdef USE_THREADS
static ERTS_INLINE ErtsThrQElement_t *
-enqueue_managed(ErtsThrQ_t *q, ErtsThrQElement_t *this, int want_last)
+enqueue_managed(ErtsThrQ_t *q, ErtsThrQElement_t *this)
{
erts_aint_t ilast, itmp;
@@ -321,28 +321,53 @@ enqueue_managed(ErtsThrQ_t *q, ErtsThrQElement_t *this, int want_last)
/* Move last pointer forward... */
while (1) {
- if (want_last) {
- if (erts_atomic_read_rb(&this->next) != ERTS_AINT_NULL) {
- /* Someone else will move it forward */
- ilast = erts_atomic_read_rb(&q->tail.data.last);
- return (ErtsThrQElement_t *) ilast;
- }
- }
- else {
- if (erts_atomic_read_nob(&this->next) != ERTS_AINT_NULL) {
- /* Someone else will move it forward */
- return NULL;
- }
+ if (erts_atomic_read_rb(&this->next) != ERTS_AINT_NULL) {
+ /* Someone else will move it forward */
+ ilast = erts_atomic_read_rb(&q->tail.data.last);
+ return (ErtsThrQElement_t *) ilast;
}
itmp = erts_atomic_cmpxchg_mb(&q->tail.data.last,
(erts_aint_t) this,
ilast);
if (ilast == itmp)
- return want_last ? this : NULL;
+ return this;
ilast = itmp;
}
}
+static ERTS_INLINE ErtsThrQElement_t *
+enqueue_marker(ErtsThrQ_t *q, ErtsThrQElement_t **headp)
+{
+ int maybe_notify;
+ erts_aint_t inext;
+ ErtsThrQElement_t *last, *head;
+
+ if (headp)
+ head = *headp;
+ else
+ head = ErtsThrQDirtyReadEl(&q->head.head);
+
+ ASSERT(!q->head.used_marker);
+ q->head.used_marker = 1;
+ last = enqueue_managed(q, &q->tail.data.marker);
+ maybe_notify = &q->tail.data.marker == last;
+ inext = erts_atomic_read_acqb(&head->next);
+ if (inext == (erts_aint_t) &q->tail.data.marker) {
+ ErtsThrQDirtySetEl(&q->head.head, &q->tail.data.marker);
+ if (headp)
+ *headp = &q->tail.data.marker;
+ }
+ else if (maybe_notify) {
+ /*
+ * We need to notify; otherwise, we might loose a notification
+ * for a concurrently inserted element.
+ */
+ q->head.notify(q->head.arg);
+ }
+ return last;
+}
+
+
static ErtsThrQCleanState_t
clean(ErtsThrQ_t *q, int max_ops, int do_notify)
{
@@ -409,20 +434,8 @@ clean(ErtsThrQ_t *q, int max_ops, int do_notify)
q->head.unref_end = q->head.next.unref_end;
if (!q->head.used_marker
- && q->head.unref_end == (ErtsThrQElement_t *) ilast) {
- q->head.used_marker = 1;
- ilast = (erts_aint_t) enqueue_managed(q,
- &q->tail.data.marker,
- 1);
- head = ErtsThrQDirtyReadEl(&q->head.head);
- if (head == q->head.unref_end) {
- ErtsThrQElement_t *next;
- next = ((ErtsThrQElement_t *)
- erts_atomic_read_acqb(&head->next));
- if (next == &q->tail.data.marker)
- ErtsThrQDirtySetEl(&q->head.head, &q->tail.data.marker);
- }
- }
+ && q->head.unref_end == (ErtsThrQElement_t *) ilast)
+ ilast = (erts_aint_t) enqueue_marker(q, NULL);
if (q->head.unref_end == (ErtsThrQElement_t *) ilast)
ERTS_SMP_MEMORY_BARRIER;
@@ -450,13 +463,9 @@ clean(ErtsThrQ_t *q, int max_ops, int do_notify)
erts_aint_t inext;
inext = erts_atomic_read_acqb(&head->next);
if (inext == ERTS_AINT_NULL) {
- q->head.used_marker = 1;
- (void) enqueue_managed(q, &q->tail.data.marker, 0);
- inext = erts_atomic_read_acqb(&head->next);
- if (inext == (erts_aint_t) &q->tail.data.marker) {
- ErtsThrQDirtySetEl(&q->head.head, &q->tail.data.marker);
+ enqueue_marker(q, &head);
+ if (head == &q->tail.data.marker)
goto check_thr_progress;
- }
}
}
@@ -603,7 +612,7 @@ enqueue(ErtsThrQ_t *q, void *data, ErtsThrQElement_t *this)
}
}
- notify = this == enqueue_managed(q, this, 1);
+ notify = this == enqueue_managed(q, this);
#ifdef ERTS_SMP