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pthread: Avoid spurious wakeups

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pthread_wait_cond can wake up unexpectedly (Wikipedia: Spurious_wakeup).

The FF_THREAD_SLICE thread mechanism could spontaneously execute
jobs or allow the caller of avctx->execute to return before all
jobs were complete.

Test both cases to ensure the wakeup is real.

Signed-off-by: Ben Jackson <ben@ben.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit 311583e779)
This commit is contained in:
Ben Jackson 2013-10-18 15:28:50 +01:00 • committed by Luca Barbato
parent 48d57650f1
commit 1123870879
1 changed files with 7 additions and 2 deletions
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9
libavcodec/pthread.c
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@ -75,6 +75,7 @@ typedef struct ThreadContext {
pthread_cond_t last_job_cond;
pthread_cond_t current_job_cond;
pthread_mutex_t current_job_lock;
unsigned current_execute;
int current_job;
int done;
} ThreadContext;
@ -195,6 +196,7 @@ static void* attribute_align_arg worker(void *v)
{
AVCodecContext *avctx = v;
ThreadContext *c = avctx->thread_opaque;
unsigned last_execute = 0;
int our_job = c->job_count;
int thread_count = avctx->thread_count;
int self_id;
@ -206,8 +208,9 @@ static void* attribute_align_arg worker(void *v)
if (c->current_job == thread_count + c->job_count)
pthread_cond_signal(&c->last_job_cond);
if (!c->done)
while (last_execute == c->current_execute && !c->done)
pthread_cond_wait(&c->current_job_cond, &c->current_job_lock);
last_execute = c->current_execute;
our_job = self_id;
if (c->done) {
@ -227,7 +230,8 @@ static void* attribute_align_arg worker(void *v)
static av_always_inline void avcodec_thread_park_workers(ThreadContext *c, int thread_count)
{
pthread_cond_wait(&c->last_job_cond, &c->current_job_lock);
while (c->current_job != thread_count + c->job_count)
pthread_cond_wait(&c->last_job_cond, &c->current_job_lock);
pthread_mutex_unlock(&c->current_job_lock);
}
@ -276,6 +280,7 @@ static int avcodec_thread_execute(AVCodecContext *avctx, action_func* func, void
c->rets = &dummy_ret;
c->rets_count = 1;
}
c->current_execute++;
pthread_cond_broadcast(&c->current_job_cond);
avcodec_thread_park_workers(c, avctx->thread_count);