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Thread pools: memory barriers in task completion notifications.

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The ngx_thread_pool_done object isn't volatile, and at least some
compilers assume that it is permitted to reorder modifications of
volatile and non-volatile objects.  Added appropriate ngx_memory_barrier()
calls to make sure all modifications will happen before the lock is released.

Reported by Mindaugas Rasiukevicius,
http://mailman.nginx.org/pipermail/nginx-devel/2016-April/008160.html.
This commit is contained in:
Maxim Dounin 2016-04-19 17:18:28 +03:00
parent eb38cbda2f
commit eeb72127cf
1 changed files with 4 additions and 0 deletions
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4
src/core/ngx_thread_pool.c
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@ -345,6 +345,8 @@ ngx_thread_pool_cycle(void *data)
*ngx_thread_pool_done.last = task; *ngx_thread_pool_done.last = task;
ngx_thread_pool_done.last = &task->next; ngx_thread_pool_done.last = &task->next;
ngx_memory_barrier();
ngx_unlock(&ngx_thread_pool_done_lock); ngx_unlock(&ngx_thread_pool_done_lock);
(void) ngx_notify(ngx_thread_pool_handler); (void) ngx_notify(ngx_thread_pool_handler);
@ -366,6 +368,8 @@ ngx_thread_pool_handler(ngx_event_t *ev)
ngx_thread_pool_done.first = NULL; ngx_thread_pool_done.first = NULL;
ngx_thread_pool_done.last = &ngx_thread_pool_done.first; ngx_thread_pool_done.last = &ngx_thread_pool_done.first;
ngx_memory_barrier();
ngx_unlock(&ngx_thread_pool_done_lock); ngx_unlock(&ngx_thread_pool_done_lock);
while (task) { while (task) {