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v4l2bufferpool: Wait before polling if queue is empty

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In kernel before 3.17, polling during queue underrun would unblock right
away and trigger POLLERR. As we are not handling POLLERR, we would endup
blocking in DQBUF call, which won't be unblocked correctly when going
to NULL state. A deadlock at start caused by locking error in libv4l2 was
also seen before this patch. Instead, we wait until the queue is no longer
empty before polling.

https://bugzilla.gnome.org/show_bug.cgi?id=731015
This commit is contained in:
Nicolas Dufresne 2014-07-03 15:28:45 -04:00
parent db1d9444d6
commit 652ed3bceb
2 changed files with 25 additions and 1 deletions
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23
sys/v4l2/gstv4l2bufferpool.c
View file

@ -846,6 +846,11 @@ gst_v4l2_buffer_pool_flush_start (GstBufferPool * bpool)
gst_poll_set_flushing (pool->poll, TRUE);
GST_OBJECT_LOCK (pool);
pool->empty = FALSE;
g_cond_broadcast (&pool->empty_cond);
GST_OBJECT_UNLOCK (pool);
if (pool->other_pool)
gst_buffer_pool_set_flushing (pool->other_pool, TRUE);
}
@ -934,6 +939,11 @@ gst_v4l2_buffer_pool_poll (GstV4l2BufferPool * pool)
{
gint ret;
GST_OBJECT_LOCK (pool);
while (pool->empty)
g_cond_wait (&pool->empty_cond, GST_OBJECT_GET_LOCK (pool));
GST_OBJECT_UNLOCK (pool);
if (!pool->can_poll_device)
goto done;
@ -1001,6 +1011,11 @@ gst_v4l2_buffer_pool_qbuf (GstV4l2BufferPool * pool, GstBuffer * buf)
if (!gst_v4l2_allocator_qbuf (pool->vallocator, group))
goto queue_failed;
GST_OBJECT_LOCK (pool);
pool->empty = FALSE;
g_cond_signal (&pool->empty_cond);
GST_OBJECT_UNLOCK (pool);
return GST_FLOW_OK;
already_queued:
@ -1047,7 +1062,11 @@ gst_v4l2_buffer_pool_dqbuf (GstV4l2BufferPool * pool, GstBuffer ** buffer)
/* mark the buffer outstanding */
pool->buffers[group->buffer.index] = NULL;
g_atomic_int_add (&pool->num_queued, -1);
if (g_atomic_int_dec_and_test (&pool->num_queued)) {
GST_OBJECT_LOCK (pool);
pool->empty = TRUE;
GST_OBJECT_UNLOCK (pool);
}
timestamp = GST_TIMEVAL_TO_TIME (group->buffer.timestamp);
@ -1354,6 +1373,8 @@ gst_v4l2_buffer_pool_init (GstV4l2BufferPool * pool)
{
pool->poll = gst_poll_new (TRUE);
pool->can_poll_device = TRUE;
g_cond_init (&pool->empty_cond);
pool->empty = TRUE;
}
static void

3
sys/v4l2/gstv4l2bufferpool.h
View file

@ -53,6 +53,9 @@ struct _GstV4l2BufferPool
GstPoll *poll; /* a poll for video_fd */
gboolean can_poll_device;
gboolean empty;
GCond empty_cond;
GstV4l2Allocator *vallocator;
GstAllocator *allocator;
GstAllocationParams params;