amcvideodec: set our data pointer in java to NULL on close

The frame available callback can be called after deconfiguring the amc codec.
Guard against this by setting the back pointer to NULL on close() and ignoring
any NULL data pointer.

https://bugzilla.gnome.org/show_bug.cgi?id=761014

sys/androidmedia/gstamcvideodec.c

@@ -485,6 +485,21 @@ gst_amc_video_dec_close (GstVideoDecoder * decoder)
     self->surface = NULL;
   }
 
+  if (self->listener) {
+    JNIEnv *env = gst_amc_jni_get_env ();
+    GError *err = NULL;
+
+    if (!gst_amc_jni_call_void_method (env, &err, self->listener,
+          self->set_context_id, GST_AMC_VIDEO_DEC_TO_JLONG (NULL))) {
+      GST_ERROR_OBJECT (self, "Failed to unset back pointer on the listener. "
+          "crashes/hangs may ensue: %s", err ? err->message : "Unknown");
+      GST_ELEMENT_ERROR_FROM_ERROR (self, err);
+    }
+
+    gst_amc_jni_object_unref (env, self->listener);
+  }
+  self->listener = NULL;
+
   if (self->codec) {
     GError *err = NULL;
 
@@ -1683,7 +1698,6 @@ gst_amc_video_dec_new_on_frame_available_listener (GstAmcVideoDec * decoder,
   jobject listener = NULL;
   jclass listener_cls = NULL;
   jmethodID constructor_id = 0;
-  jmethodID set_context_id = 0;
 
   JNINativeMethod amcOnFrameAvailableListener = {
     "native_onFrameAvailable",
@@ -1711,9 +1725,9 @@ gst_amc_video_dec_new_on_frame_available_listener (GstAmcVideoDec * decoder,
     goto done;
   }
 
-  set_context_id =
+  decoder->set_context_id =
       gst_amc_jni_get_method_id (env, err, listener_cls, "setContext", "(J)V");
-  if (!set_context_id) {
+  if (!decoder->set_context_id) {
     goto done;
   }
 
@@ -1724,7 +1738,7 @@ gst_amc_video_dec_new_on_frame_available_listener (GstAmcVideoDec * decoder,
   }
 
   if (!gst_amc_jni_call_void_method (env, err, listener,
-          set_context_id, GST_AMC_VIDEO_DEC_TO_JLONG (decoder))) {
+          decoder->set_context_id, GST_AMC_VIDEO_DEC_TO_JLONG (decoder))) {
     gst_amc_jni_object_unref (env, listener);
     listener = NULL;
   }
@@ -1943,7 +1957,6 @@ gst_amc_video_dec_set_format (GstVideoDecoder * decoder,
   } else if (self->downstream_supports_gl && !self->surface) {
     int ret = TRUE;
     JNIEnv *env = NULL;
-    jobject listener = NULL;
     GstAmcSurfaceTexture *surface_texture = NULL;
 
     env = gst_amc_jni_get_env ();
@@ -1953,15 +1966,24 @@ gst_amc_video_dec_set_format (GstVideoDecoder * decoder,
       return FALSE;
     }
 
-    listener =
+    if (self->listener) {
+      if (!gst_amc_jni_call_void_method (env, &err, self->listener,
+            self->set_context_id, GST_AMC_VIDEO_DEC_TO_JLONG (NULL))) {
+        ret = FALSE;
+        goto done;
+      }
+
+      gst_amc_jni_object_unref (env, self->listener);
+    }
+    self->listener =
         gst_amc_video_dec_new_on_frame_available_listener (self, env, &err);
-    if (!listener) {
+    if (!self->listener) {
       ret = FALSE;
       goto done;
     }
 
     if (!gst_amc_surface_texture_set_on_frame_available_listener
-        (surface_texture, listener, &err)) {
+        (surface_texture, self->listener, &err)) {
       ret = FALSE;
       goto done;
     }
@@ -1971,7 +1993,6 @@ gst_amc_video_dec_set_format (GstVideoDecoder * decoder,
 
   done:
     g_object_unref (surface_texture);
-    gst_amc_jni_object_unref (env, listener);
     if (!ret) {
       GST_ELEMENT_ERROR_FROM_ERROR (self, err);
       return FALSE;
@@ -2511,6 +2532,10 @@ gst_amc_video_dec_on_frame_available (JNIEnv * env, jobject thiz,
 {
   GstAmcVideoDec *self = JLONG_TO_GST_AMC_VIDEO_DEC (context);
 
+  /* apparently we can be called after the decoder has been closed */
+  if (!self)
+    return;
+
   g_mutex_lock (&self->gl_lock);
   self->gl_ready_frame_count++;
   GST_LOG_OBJECT (self, "frame %u available", self->gl_ready_frame_count);

sys/androidmedia/gstamcvideodec.h

@@ -100,6 +100,9 @@ struct _GstAmcVideoDec
   gboolean downstream_supports_gl;
   GstFlowReturn downstream_flow_ret;
 
+  jobject listener;
+  jmethodID set_context_id;
+
   gboolean gl_mem_attached;
   GstGLMemory *oes_mem;
   GError *gl_error;

sys/androidmedia/org/freedesktop/gstreamer/androidmedia/GstAmcOnFrameAvailableListener.java

@@ -31,11 +31,11 @@ public class GstAmcOnFrameAvailableListener implements OnFrameAvailableListener
         native_onFrameAvailable(context, surfaceTexture);
     }
 
-    public long getContext () {
+    public synchronized long getContext () {
         return context;
     }
 
-    public void setContext (long c) {
+    public synchronized void setContext (long c) {
         context = c;
     }