async_mutex has is used in a very strange but intentional way: it is
locked by default, and unlocked only in regions that can be run
concurrently.
If the user was calling API functions to the same context from different
threads (in a safe way), this could unintentionally unlock the mutex on
a different thread than the previous lock operation. It's not allowed by
the pthread API.
Fix this by emulating a binary semaphore using a mutex and condition
variable. (Posix semaphores are not available on all platforms.)
---
libavcodec/pthread_frame.c | 41 +++++++++++++++++++++++++++++++----------
1 file changed, 31 insertions(+), 10 deletions(-)
diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index 65a04d8e90..9ca7a766df 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -119,6 +119,8 @@ typedef struct FrameThreadContext {
*/
pthread_mutex_t hwaccel_mutex;
pthread_mutex_t async_mutex;
+ pthread_cond_t async_cond;
+ int async_lock;
int next_decoding; ///< The next context to submit a packet to.
int next_finished; ///< The next context to return output from.
@@ -129,6 +131,24 @@ typedef struct FrameThreadContext {
*/
} FrameThreadContext;
+static void async_lock(FrameThreadContext *fctx)
+{
+ pthread_mutex_lock(&fctx->async_mutex);
+ while (fctx->async_lock)
+ pthread_cond_wait(&fctx->async_cond, &fctx->async_mutex);
+ fctx->async_lock = 1;
+ pthread_mutex_unlock(&fctx->async_mutex);
+}
+
+static void async_unlock(FrameThreadContext *fctx)
+{
+ pthread_mutex_lock(&fctx->async_mutex);
+ av_assert0(fctx->async_lock);
+ fctx->async_lock = 0;
+ pthread_cond_broadcast(&fctx->async_cond);
+ pthread_mutex_unlock(&fctx->async_mutex);
+}
+
/**
* Codec worker thread.
*
@@ -196,7 +216,8 @@ static attribute_align_arg void *frame_worker_thread(void
*arg)
if (p->async_serializing) {
p->async_serializing = 0;
- pthread_mutex_unlock(&p->parent->async_mutex);
+
+ async_unlock(p->parent);
}
atomic_store(&p->state, STATE_INPUT_READY);
@@ -428,7 +449,7 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
/* release the async lock, permitting blocked hwaccel threads to
* go forward while we are in this function */
- pthread_mutex_unlock(&fctx->async_mutex);
+ async_unlock(fctx);
/*
* Submit a packet to the next decoding thread.
@@ -497,7 +518,7 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
/* return the size of the consumed packet if no error occurred */
ret = (p->result >= 0) ? avpkt->size : p->result;
finish:
- pthread_mutex_lock(&fctx->async_mutex);
+ async_lock(fctx);
if (err < 0)
return err;
return ret;
@@ -559,7 +580,8 @@ void ff_thread_finish_setup(AVCodecContext *avctx) {
if (avctx->hwaccel &&
!(avctx->hwaccel->caps_internal & HWACCEL_CAP_ASYNC_SAFE)) {
p->async_serializing = 1;
- pthread_mutex_lock(&p->parent->async_mutex);
+
+ async_lock(p->parent);
}
pthread_mutex_lock(&p->progress_mutex);
@@ -575,7 +597,7 @@ static void park_frame_worker_threads(FrameThreadContext
*fctx, int thread_count
{
int i;
- pthread_mutex_unlock(&fctx->async_mutex);
+ async_unlock(fctx);
for (i = 0; i < thread_count; i++) {
PerThreadContext *p = &fctx->threads[i];
@@ -588,7 +610,7 @@ static void park_frame_worker_threads(FrameThreadContext
*fctx, int thread_count
}
}
- pthread_mutex_lock(&fctx->async_mutex);
+ async_lock(fctx);
}
void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
@@ -647,9 +669,8 @@ void ff_frame_thread_free(AVCodecContext *avctx, int
thread_count)
av_freep(&fctx->threads);
pthread_mutex_destroy(&fctx->buffer_mutex);
pthread_mutex_destroy(&fctx->hwaccel_mutex);
-
- pthread_mutex_unlock(&fctx->async_mutex);
pthread_mutex_destroy(&fctx->async_mutex);
+ pthread_cond_destroy(&fctx->async_cond);
av_freep(&avctx->internal->thread_ctx);
}
@@ -693,10 +714,10 @@ int ff_frame_thread_init(AVCodecContext *avctx)
pthread_mutex_init(&fctx->buffer_mutex, NULL);
pthread_mutex_init(&fctx->hwaccel_mutex, NULL);
-
pthread_mutex_init(&fctx->async_mutex, NULL);
- pthread_mutex_lock(&fctx->async_mutex);
+ pthread_cond_init(&fctx->async_cond, NULL);
+ fctx->async_lock = 1;
fctx->delaying = 1;
for (i = 0; i < thread_count; i++) {
--
2.11.0
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