alphacombine: De-couple flush-start/stop events handling

There is no guarantee that any FLUSH_STOP event is preceded by a FLUSH_START. The element now stops flushing once it has received a FLUSH_STOP on all its sink pads.

Fixes #4174 (closed)

subprojects/gst-plugins-bad/gst/codecalpha/gstalphacombine.c

@@ -174,6 +174,31 @@ pad_blocked (GstPad * pad, GstPadProbeInfo * info, gpointer user_data)
   return GST_PAD_PROBE_OK;
 }
 
+/* Has to be called with buffer_lock held */
+static void
+gst_alpha_combine_clear_sink_pad_probe (GstAlphaCombine * self)
+{
+  if (!self->pad_block_id)
+    return;
+
+  g_assert (self->blocked_pad);
+  gst_pad_remove_probe (self->blocked_pad, self->pad_block_id);
+  self->pad_block_id = 0;
+  self->blocked_pad = NULL;
+}
+
+/* Has to be called with buffer_lock held */
+static void
+gst_alpha_combine_unlock_reset_flushing_state (GstAlphaCombine * self)
+{
+  self->flushing = FALSE;
+  self->flush_stops = 0;
+
+  /* Reset the format cookies to ensure they are equal */
+  self->sink_format_cookie = 0;
+  self->alpha_format_cookie = 0;
+}
+
 static void
 gst_alpha_combine_unlock_stop (GstAlphaCombine * self, GstPad * pad)
 {
@@ -185,11 +210,7 @@ gst_alpha_combine_unlock_stop (GstAlphaCombine * self, GstPad * pad)
     if (self->flush_stops == 2) {
       GST_DEBUG_OBJECT (self,
           "Both sink pads received FLUSH_STOP, unblocking them");
-      g_assert (self->pad_block_id);
-      g_assert (self->blocked_pad);
-      gst_pad_remove_probe (self->blocked_pad, self->pad_block_id);
-      self->pad_block_id = 0;
-      self->blocked_pad = NULL;
+      gst_alpha_combine_clear_sink_pad_probe (self);
     } else {
       GST_DEBUG_OBJECT (pad, "FLUSH_STOP received, blocking");
       g_assert (!self->pad_block_id);
@@ -203,22 +224,19 @@ gst_alpha_combine_unlock_stop (GstAlphaCombine * self, GstPad * pad)
     }
   }
 
-  self->flushing = FALSE;
-  self->flush_stops = 0;
-
-  /* Reset the format cookies to ensure they are equal */
-  self->sink_format_cookie = 0;
-  self->alpha_format_cookie = 0;
-
+  gst_alpha_combine_unlock_reset_flushing_state (self);
   g_mutex_unlock (&self->buffer_lock);
 }
 
 static void
 gst_alpha_combine_reset (GstAlphaCombine * self)
 {
+  g_mutex_lock (&self->buffer_lock);
+  gst_alpha_combine_clear_sink_pad_probe (self);
   gst_buffer_replace (&self->alpha_buffer, NULL);
   gst_buffer_replace (&self->last_alpha_buffer, NULL);
   self->last_flow_ret = GST_FLOW_OK;
+  g_mutex_unlock (&self->buffer_lock);
 }
 
 /*
@@ -627,7 +645,9 @@ gst_alpha_combine_change_state (GstElement * element, GstStateChange transition)
 
   switch (transition) {
     case GST_STATE_CHANGE_READY_TO_PAUSED:
-      gst_alpha_combine_unlock_stop (self, NULL);
+      g_mutex_lock (&self->buffer_lock);
+      gst_alpha_combine_unlock_reset_flushing_state (self);
+      g_mutex_unlock (&self->buffer_lock);
       break;
     case GST_STATE_CHANGE_PAUSED_TO_READY:
       gst_alpha_combine_unlock (self);