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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Concurrent call to glClientWaitSync results in segfault in one of the waiters."
href="https://bugs.freedesktop.org/show_bug.cgi?id=98172#c42">Comment # 42</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Concurrent call to glClientWaitSync results in segfault in one of the waiters."
href="https://bugs.freedesktop.org/show_bug.cgi?id=98172">bug 98172</a>
from <span class="vcard"><a class="email" href="mailto:shinji.suzuki@gmail.com" title="Suzuki, Shinji <shinji.suzuki@gmail.com>"> <span class="fn">Suzuki, Shinji</span></a>
</span></b>
<pre>Sorry for the clutter. Timeout is not handled in the previous attempt.
(The use of the shared completion flag seems to have potential synchronization
problem because a waiter can see a successful wait as a result of unsuccessful
call to fence_finish() if another thread comes and completes a successful
fence_finish() call after the first thread completes unsuccessful
fence_finish() but before returns.)
static void st_client_wait_sync(struct gl_context *ctx,
struct gl_sync_object *obj,
GLbitfield flags, GLuint64 timeout)
{
struct pipe_screen *screen = st_context(ctx)->pipe->screen;
struct st_sync_object *so = (struct st_sync_object*)obj;
struct pipe_fence_handle *fence = NULL;
/* We don't care about GL_SYNC_FLUSH_COMMANDS_BIT, because flush is
* already called when creating a fence.
*/
/* Duplicate the reference so that the fence object is guaranteed to
* be alive at least until associated 'unref' below is executed.
* This is important because multiple threads have to execute
* fence_finish() concurrently even if they target same fence object
* in order to deal with potentially different time-out settings.
*/
screen->fence_reference(screen, &fence, so->fence);
if (fence) {
if(screen->fence_finish(screen, fence, timeout)) {
so->b.StatusFlag = GL_TRUE;
if( p_atomic_cmpxchg(&so->fence, fence, NULL) == fence ) {
/* Get done with 'so->object'. This is a 'unref' op.
* Borrow the value in 'fence' since so->fence is already
* set to NULL by the cmpxchg above.
*/
struct pipe_fence_handle * fence_copy = fence;
screen->fence_reference(screen, &fence_copy, NULL);
}
}
} // fence==0 means the fence has already reached
screen->fence_reference(screen, &fence, NULL);
}</pre>
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