From 9e208ba0b6bea2372f55746c7b4a38161f27480d Mon Sep 17 00:00:00 2001
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Date: Fri, 24 Nov 2017 16:58:21 -0500
Subject: [PATCH] sdlshare2: Fix race conditions

The client-draw callback is running on the GL Thread, which will
be required to map the buffer. Map early, and pass the mapped
frame instead. On top of that, make sure to signal any pending
draw before trying to push EOS, as some pad locks might be taken.
This is the cost of using the same thread to control GStreamer and
to render GL.
---
 tests/examples/gl/sdl/sdlshare2.c | 66 ++++++++++++++++++++-----------
 1 file changed, 42 insertions(+), 24 deletions(-)

diff --git a/tests/examples/gl/sdl/sdlshare2.c b/tests/examples/gl/sdl/sdlshare2.c
index b616a8797e..b9ce10876d 100644
--- a/tests/examples/gl/sdl/sdlshare2.c
+++ b/tests/examples/gl/sdl/sdlshare2.c
@@ -66,13 +66,9 @@ InitGL (int Width, int Height)  // We call this right after our OpenGL window is
 
 /* The main drawing function. */
 static void
-DrawGLScene (GstSample * sample)
+DrawGLScene (GstVideoFrame * v_frame)
 {
-  GstVideoFrame v_frame;
-  GstVideoInfo v_info;
   guint texture = 0;
-  GstBuffer *buf = gst_sample_get_buffer (sample);
-  GstCaps *caps = gst_sample_get_caps (sample);
 
 #ifdef WIN32
   if (!wglGetCurrentContext ())
@@ -82,14 +78,7 @@ DrawGLScene (GstSample * sample)
     return;
 #endif
 
-  gst_video_info_from_caps (&v_info, caps);
-
-  if (!gst_video_frame_map (&v_frame, &v_info, buf, GST_MAP_READ | GST_MAP_GL)) {
-    g_warning ("Failed to map the video buffer");
-    return;
-  }
-
-  texture = *(guint *) v_frame.data[0];
+  texture = *(guint *) v_frame->data[0];
 
   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth Buffer
   glLoadIdentity ();            // Reset The View
@@ -139,8 +128,21 @@ DrawGLScene (GstSample * sample)
 
   // swap buffers to display, since we're double buffered.
   SDL_GL_SwapBuffers ();
+}
 
-  gst_video_frame_unmap (&v_frame);
+static GMutex app_lock;
+static GCond app_cond;
+static gboolean app_rendered = FALSE;
+static gboolean app_quit = FALSE;
+
+static void
+stop_pipeline (GstElement * pipeline)
+{
+  g_mutex_lock (&app_lock);
+  app_quit = TRUE;
+  g_cond_signal (&app_cond);
+  g_mutex_unlock (&app_lock);
+  gst_element_send_event (pipeline, gst_event_new_eos ());
 }
 
 static gboolean
@@ -151,12 +153,12 @@ update_sdl_scene (gpointer data)
 
   while (SDL_PollEvent (&event)) {
     if (event.type == SDL_QUIT) {
-      gst_element_send_event (GST_ELEMENT (pipeline), gst_event_new_eos ());
+      stop_pipeline (pipeline);
       return FALSE;
     }
     if (event.type == SDL_KEYDOWN) {
       if (event.key.keysym.sym == SDLK_ESCAPE) {
-        gst_element_send_event (GST_ELEMENT (pipeline), gst_event_new_eos ());
+        stop_pipeline (pipeline);
         return FALSE;
       }
     }
@@ -165,18 +167,15 @@ update_sdl_scene (gpointer data)
   return TRUE;
 }
 
-static GMutex app_lock;
-static GCond app_cond;
-
 static gboolean
 executeCallback (gpointer data)
 {
-  GstSample *sample = (GstSample *) data;
-
   g_mutex_lock (&app_lock);
 
-  DrawGLScene (sample);
+  if (!app_quit)
+    DrawGLScene (data);
 
+  app_rendered = TRUE;
   g_cond_signal (&app_cond);
   g_mutex_unlock (&app_lock);
 
@@ -187,12 +186,31 @@ static gboolean
 on_client_draw (GstElement * glsink, GstGLContext * context, GstSample * sample,
     gpointer data)
 {
+  GstBuffer *buf = gst_sample_get_buffer (sample);
+  GstCaps *caps = gst_sample_get_caps (sample);
+  GstVideoFrame v_frame;
+  GstVideoInfo v_info;
+
+  /* FIXME don't do that every frame */
+  gst_video_info_from_caps (&v_info, caps);
+
+  if (!gst_video_frame_map (&v_frame, &v_info, buf, GST_MAP_READ | GST_MAP_GL)) {
+    g_warning ("Failed to map the video buffer");
+    return TRUE;
+  }
+
   g_mutex_lock (&app_lock);
 
-  g_idle_add_full (G_PRIORITY_HIGH, executeCallback, sample, NULL);
-  g_cond_wait (&app_cond, &app_lock);
+  app_rendered = FALSE;
+  g_idle_add_full (G_PRIORITY_HIGH, executeCallback, &v_frame, NULL);
+
+  while (!app_rendered && !app_quit)
+    g_cond_wait (&app_cond, &app_lock);
+
   g_mutex_unlock (&app_lock);
 
+  gst_video_frame_unmap (&v_frame);
+
   return TRUE;
 }