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playbin3: Add lock to protect buffering messages

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Fix a small race where a group can receive stream-start
and post a pending buffering message just as another
thread posts a different buffering message, causing them
to be received by the application out of order. In the
worst case, this leads the application receiving a
stale 99% buffering message and going back to buffering
right after the 100% buffering message.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1840>
This commit is contained in:
Jan Schmidt 2022-03-02 03:43:00 +11:00 committed by GStreamer Marge Bot
parent 1f3ca43c51
commit 17f11c2cda
1 changed files with 30 additions and 0 deletions
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30
subprojects/gst-plugins-base/gst/playback/gstplaybin3.c
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@ -518,6 +518,8 @@ struct _GstPlayBin3
guint64 ring_buffer_max_size; /* 0 means disabled */
gboolean is_live; /* Whether our current group is live */
GMutex buffering_post_lock; /* Protect serialisation of buffering messages. Must not acquire this while holding any SOURCE_GROUP lock */
};
struct _GstPlayBin3Class
@ -1326,6 +1328,8 @@ gst_play_bin3_init (GstPlayBin3 * playbin)
g_rec_mutex_init (&playbin->lock);
g_mutex_init (&playbin->dyn_lock);
g_mutex_init (&playbin->buffering_post_lock);
/* assume we can create an input-selector */
playbin->have_selector = TRUE;
@ -1431,6 +1435,8 @@ gst_play_bin3_finalize (GObject * object)
g_rec_mutex_clear (&playbin->activation_lock);
g_rec_mutex_clear (&playbin->lock);
g_mutex_clear (&playbin->buffering_post_lock);
g_mutex_clear (&playbin->dyn_lock);
g_mutex_clear (&playbin->elements_lock);
@ -2480,12 +2486,20 @@ gst_play_bin3_handle_message (GstBin * bin, GstMessage * msg)
playbin->curr_group = group;
playbin->next_group = other_group;
/* we may need to serialise a buffering
* message, and need to take that lock
* before any source group lock, so
* do that now */
g_mutex_lock (&playbin->buffering_post_lock);
GST_SOURCE_GROUP_LOCK (group);
if (group->playing == FALSE)
changed = TRUE;
group->playing = TRUE;
buffering_msg = group->pending_buffering_msg;
group->pending_buffering_msg = NULL;
GST_SOURCE_GROUP_UNLOCK (group);
GST_SOURCE_GROUP_LOCK (other_group);
@ -2498,9 +2512,13 @@ gst_play_bin3_handle_message (GstBin * bin, GstMessage * msg)
gst_play_bin3_check_group_status (playbin);
else
GST_DEBUG_OBJECT (bin, "Groups didn't changed");
/* If there was a pending buffering message to send, do it now */
if (buffering_msg)
GST_BIN_CLASS (parent_class)->handle_message (bin, buffering_msg);
g_mutex_unlock (&playbin->buffering_post_lock);
} else if (GST_MESSAGE_TYPE (msg) == GST_MESSAGE_BUFFERING) {
GstSourceGroup *group;
@ -2508,8 +2526,11 @@ gst_play_bin3_handle_message (GstBin * bin, GstMessage * msg)
GST_PLAY_BIN3_LOCK (playbin);
group = find_source_group_owner (playbin, msg->src);
if (group->active) {
g_mutex_lock (&playbin->buffering_post_lock);
GST_SOURCE_GROUP_LOCK (group);
GST_PLAY_BIN3_UNLOCK (playbin);
if (!group->playing) {
GST_DEBUG_OBJECT (playbin,
"Storing buffering message from pending group " "%p %"
@ -2517,8 +2538,17 @@ gst_play_bin3_handle_message (GstBin * bin, GstMessage * msg)
gst_message_replace (&group->pending_buffering_msg, msg);
gst_message_unref (msg);
msg = NULL;
} else {
/* Ensure there's no cached buffering message for this group */
gst_message_replace (&group->pending_buffering_msg, NULL);
}
GST_SOURCE_GROUP_UNLOCK (group);
if (msg != NULL) {
GST_BIN_CLASS (parent_class)->handle_message (bin, msg);
msg = NULL;
}
g_mutex_unlock (&playbin->buffering_post_lock);
} else {
GST_PLAY_BIN3_UNLOCK (playbin);
}