wpe: Fix race condition on teardown

There was a race when going to PAUSED while pushing a buffer to the
pipeline process (where we weren't even cancelling anything).

This rework base all the cancellation around the GCancellable
"cancelled" signal trying to ensure that the streaming thread will not
block once a cancel operation happens.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2504>

1 files changed, 37 insertions, 4 deletions

diff --git a/ext/wpe/wpe-extension/gstwpeaudiosink.c b/ext/wpe/wpe-extension/gstwpeaudiosink.c
index d5d8a944a..66a6c4d93 100644
--- a/ext/wpe/wpe-extension/gstwpeaudiosink.c
+++ b/ext/wpe/wpe-extension/gstwpeaudiosink.c
@@ -186,11 +186,28 @@ unlock (GstBaseSink * sink)
   GstWpeAudioSink *self = GST_WPE_AUDIO_SINK (sink);
 
   g_cancellable_cancel (self->cancellable);
+
+  return TRUE;
+}
+
+static gboolean
+unlock_stop (GstBaseSink * sink)
+{
+  GstWpeAudioSink *self = GST_WPE_AUDIO_SINK (sink);
+  GCancellable *cancellable = self->cancellable;
+
+  self->cancellable = g_cancellable_new ();
+  g_object_unref (cancellable);
+
+  return TRUE;
+}
+
+static void
+_cancelled_cb (GCancellable * _cancellable, GstWpeAudioSink * self)
+{
   g_mutex_lock (&self->buf_lock);
   g_cond_broadcast (&self->buf_cond);
   g_mutex_unlock (&self->buf_lock);
-
-  return TRUE;
 }
 
 static gboolean
@@ -205,7 +222,7 @@ stop (GstBaseSink * sink)
   }
 
   /* Stop processing and claim buffers back */
-  unlock (sink);
+  g_cancellable_cancel (self->cancellable);
 
   GST_DEBUG_OBJECT (sink, "Stopping %d", self->id);
   gst_wpe_extension_send_message (webkit_user_message_new ("gstwpe.stop",
@@ -220,9 +237,22 @@ change_state (GstElement * element, GstStateChange transition)
   GstWpeAudioSink *self = GST_WPE_AUDIO_SINK (element);
 
   switch (transition) {
+    case GST_STATE_CHANGE_PAUSED_TO_PLAYING:
+    {
+      if (g_cancellable_is_cancelled (self->cancellable)) {
+        GCancellable *cancellable = self->cancellable;
+        self->cancellable = g_cancellable_new ();
+
+        g_object_unref (cancellable);
+      }
+      break;
+    }
     case GST_STATE_CHANGE_PLAYING_TO_PAUSED:
+      g_cancellable_cancel (self->cancellable);
+
       gst_wpe_extension_send_message (webkit_user_message_new ("gstwpe.pause",
-              g_variant_new_uint32 (self->id)), self->cancellable, NULL, NULL);
+              g_variant_new_uint32 (self->id)), NULL, NULL, NULL);
+
       break;
     default:
       break;
@@ -250,6 +280,8 @@ gst_wpe_audio_sink_init (GstWpeAudioSink * self)
   g_return_if_fail (pad_template != NULL);
 
   self->cancellable = g_cancellable_new ();
+  g_cancellable_connect (self->cancellable,
+      G_CALLBACK (_cancelled_cb), self, NULL);
 }
 
 static void
@@ -273,6 +305,7 @@ gst_wpe_audio_sink_class_init (GstWpeAudioSinkClass * klass)
   gstelement_class->change_state = GST_DEBUG_FUNCPTR (change_state);
   gstbasesink_class->stop = GST_DEBUG_FUNCPTR (stop);
   gstbasesink_class->unlock = GST_DEBUG_FUNCPTR (unlock);
+  gstbasesink_class->unlock_stop = GST_DEBUG_FUNCPTR (unlock_stop);
   gstbasesink_class->render = GST_DEBUG_FUNCPTR (render);
   gstbasesink_class->set_caps = GST_DEBUG_FUNCPTR (set_caps);
 }