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gstbasesrc: Do not hold LIVE_LOCK while sending events

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An application that triggers a state transition from PLAYING to PAUSED
needs to acquire the LIVE_LOCK. Consequently the LIVE_LOCK must not be
taken while pushing anything on the pads because this operation might
get blocked by something that cannot be unblocked without the
application being able to proceed with the state transitions for other
elements in the pipeline. This commit extends the previous behaviour
where the live lock was released before pushing buffers (indirectly
through the unlock before subclass->create) to now also include
unlocking before pushing events.

The issue was discovered in a case for WebRTC where the application
tried to shut down a pipeline but an event originating from a video
source element (based on basesrc) was in the process of being pushed
down the pipeline when it got stuck on the STREAM_LOCK for the pad after
the rtpgccbwe element. This lock in turn was held by the rtcpgccbwe
element as it was in the process of pushing data down the pipeline but
was stuck on the blocking probes installed on dtlssrtpenc to prevent
data from flowing before dtls keys had been negotiated. What should have
happened here is that the blocking probes should be removed, but that
can only happen if the application may continue driving the state
transitions.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6671>
This commit is contained in:
Johan Sternerup 2024-04-16 14:30:24 +02:00 committed by GStreamer Marge Bot
parent 700c00eda3
commit a3f8f036fe
1 changed files with 10 additions and 4 deletions
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14
subprojects/gstreamer/libs/gst/base/gstbasesrc.c
View file

@ -2885,6 +2885,7 @@ gst_base_src_loop (GstPad * pad)
gboolean eos;
guint blocksize;
GList *pending_events = NULL, *tmp;
GstEvent *seg_event = NULL;
eos = FALSE;
@ -2973,14 +2974,15 @@ gst_base_src_loop (GstPad * pad)
/* push events to close/start our segment before we push the buffer. */
if (G_UNLIKELY (src->priv->segment_pending)) {
GstEvent *seg_event = gst_event_new_segment (&src->segment);
/* generate the event but do not send until outside of live_lock */
seg_event = gst_event_new_segment (&src->segment);
gst_event_set_seqnum (seg_event, src->priv->segment_seqnum);
src->priv->segment_seqnum = gst_util_seqnum_next ();
gst_pad_push_event (pad, seg_event);
src->priv->segment_pending = FALSE;
}
/* collect any pending events */
if (g_atomic_int_get (&src->priv->have_events)) {
GST_OBJECT_LOCK (src);
/* take the events */
@ -2989,8 +2991,13 @@ gst_base_src_loop (GstPad * pad)
g_atomic_int_set (&src->priv->have_events, FALSE);
GST_OBJECT_UNLOCK (src);
}
GST_LIVE_UNLOCK (src);
/* Push out pending events if any */
/* now outside the live_lock we can push the segment event */
if (G_UNLIKELY (seg_event))
gst_pad_push_event (pad, seg_event);
/* and the pending events if any */
if (G_UNLIKELY (pending_events != NULL)) {
for (tmp = pending_events; tmp; tmp = g_list_next (tmp)) {
GstEvent *ev = (GstEvent *) tmp->data;
@ -3070,7 +3077,6 @@ gst_base_src_loop (GstPad * pad)
GST_BUFFER_FLAG_SET (buf, GST_BUFFER_FLAG_DISCONT);
src->priv->discont = FALSE;
}
GST_LIVE_UNLOCK (src);
/* push buffer or buffer list */
if (src->priv->pending_bufferlist != NULL) {