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add comments for flags array

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Cloud Wu
2014-05-07 13:51:32 +08:00
parent 18c8a9d20c
commit 2d19b6cac1
1 changed files with 6 additions and 0 deletions
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6
skynet-src/skynet_mq.c
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@@ -31,6 +31,8 @@ struct global_queue {
uint32_t head; uint32_t head;
uint32_t tail; uint32_t tail;
struct message_queue ** queue; struct message_queue ** queue;
// We use a separated flag array to ensure the mq is pushed.
// See the comments below.
bool * flag; bool * flag;
}; };
@@ -47,6 +49,9 @@ skynet_globalmq_push(struct message_queue * queue) {
struct global_queue *q= Q; struct global_queue *q= Q;
uint32_t tail = GP(__sync_fetch_and_add(&q->tail,1)); uint32_t tail = GP(__sync_fetch_and_add(&q->tail,1));
// The thread would suspend here, and the q->queue[tail] is last version ,
// but the queue tail is increased.
// So we set q->flag[tail] after changing q->queue[tail].
q->queue[tail] = queue; q->queue[tail] = queue;
__sync_synchronize(); __sync_synchronize();
q->flag[tail] = true; q->flag[tail] = true;
@@ -61,6 +66,7 @@ skynet_globalmq_pop() {
return NULL; return NULL;
} }
// Check the flag first, if the flag is false, the pushing may not complete.
if(!q->flag[head_ptr]) { if(!q->flag[head_ptr]) {
return NULL; return NULL;
} }