From 31db310be489e1fc83fa3f72366e2e5fdd2a00e7 Mon Sep 17 00:00:00 2001 From: Vinson Lee Date: Mon, 26 Apr 2010 00:25:30 -0700 Subject: os: Check for spurious wakeups in pipe_barrier_wait. The POSIX function pthread_cond_wait can have spurious wakeups when waiting on a condition variable. Add a 64-bit counter that is incremented whenever the barrier becomes full. A woken thread checks the counter. If the counter has not changed then it has been spuriously woken and goes back to sleep. If the counter has changed then it was properly signaled and exits the barrier. Tested on Mac OS X. This patch was based on ideas from Luca Barbieri. --- src/gallium/auxiliary/os/os_thread.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/src/gallium/auxiliary/os/os_thread.h b/src/gallium/auxiliary/os/os_thread.h index 07a4268fc0..c09e8a7a76 100644 --- a/src/gallium/auxiliary/os/os_thread.h +++ b/src/gallium/auxiliary/os/os_thread.h @@ -302,6 +302,7 @@ static INLINE void pipe_barrier_wait(pipe_barrier *barrier) typedef struct { unsigned count; unsigned waiters; + uint64_t sequence; pipe_mutex mutex; pipe_condvar condvar; } pipe_barrier; @@ -310,6 +311,7 @@ static INLINE void pipe_barrier_init(pipe_barrier *barrier, unsigned count) { barrier->count = count; barrier->waiters = 0; + barrier->sequence = 0; pipe_mutex_init(barrier->mutex); pipe_condvar_init(barrier->condvar); } @@ -329,9 +331,14 @@ static INLINE void pipe_barrier_wait(pipe_barrier *barrier) barrier->waiters++; if (barrier->waiters < barrier->count) { - pipe_condvar_wait(barrier->condvar, barrier->mutex); + uint64_t sequence = barrier->sequence; + + do { + pipe_condvar_wait(barrier->condvar, barrier->mutex); + } while (sequence == barrier->sequence); } else { barrier->waiters = 0; + barrier->sequence++; pipe_condvar_broadcast(barrier->condvar); } -- cgit v1.2.3