[FFmpeg-cvslog] pthread: Avoid spurious wakeups
Ben Jackson
git at videolan.org
Thu Jan 16 23:36:19 CET 2014
ffmpeg | branch: release/0.10 | Ben Jackson <ben at ben.com> | Fri Oct 18 15:28:50 2013 +0100| [1123870879835be0948a184dfe5d71b48eb07240] | committer: Luca Barbato
pthread: Avoid spurious wakeups
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 at ben.com>
Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
Signed-off-by: Luca Barbato <lu_zero at gentoo.org>
(cherry picked from commit 311583e7798237be5cc531d672a9e37f8c729d83)
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1123870879835be0948a184dfe5d71b48eb07240
---
libavcodec/pthread.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/libavcodec/pthread.c b/libavcodec/pthread.c
index af1c945..65c6e2f 100644
--- a/libavcodec/pthread.c
+++ b/libavcodec/pthread.c
@@ -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);
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