From f22390e46e52ef52f2854acd7ef198d708d14e98 Mon Sep 17 00:00:00 2001
From: Matthew Waters <matthew@centricular.com>
Date: Mon, 28 Nov 2016 14:19:18 +1100
Subject: [PATCH] glcontext: fix race between creation/shutdown

626bcccff96f624f59c5212b3e21e472240171fd removed some locks that
allowed the main loop quit to occur before the context was fully
created.

2776cef25d2a98668b73272aecfe77e684e6627e attempted to readd them but
missed the scop of the quit() call.

Also remove the use of g_thread_join() as that's not safe to use when
it's possible to lose the last reference from the GL thread.

https://bugzilla.gnome.org/show_bug.cgi?id=775171
---
 gst-libs/gst/gl/gstglcontext.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/gst-libs/gst/gl/gstglcontext.c b/gst-libs/gst/gl/gstglcontext.c
index 3f43325568..899c121c5c 100644
--- a/gst-libs/gst/gl/gstglcontext.c
+++ b/gst-libs/gst/gl/gstglcontext.c
@@ -204,6 +204,7 @@ struct _GstGLContextPrivate
   /* conditions */
   GMutex render_lock;
   GCond create_cond;
+  GCond destroy_cond;
 
   gboolean created;
   gboolean alive;
@@ -275,6 +276,7 @@ gst_gl_context_init (GstGLContext * context)
   g_mutex_init (&context->priv->render_lock);
 
   g_cond_init (&context->priv->create_cond);
+  g_cond_init (&context->priv->destroy_cond);
   context->priv->created = FALSE;
 
   g_weak_ref_init (&context->priv->other_context_ref, NULL);
@@ -661,22 +663,20 @@ gst_gl_context_finalize (GObject * object)
     gst_gl_window_set_resize_callback (context->window, NULL, NULL, NULL);
     gst_gl_window_set_draw_callback (context->window, NULL, NULL, NULL);
 
+    g_mutex_lock (&context->priv->render_lock);
     if (context->priv->alive) {
       GST_INFO_OBJECT (context, "send quit gl window loop");
       gst_gl_window_quit (context->window);
 
       GST_INFO_OBJECT (context, "joining gl thread");
-      g_mutex_lock (&context->priv->render_lock);
-      if (context->priv->alive) {
-        GThread *t = context->priv->gl_thread;
-        g_mutex_unlock (&context->priv->render_lock);
-        g_thread_join (t);
-      } else {
-        g_mutex_unlock (&context->priv->render_lock);
-      }
+      while (context->priv->alive)
+        g_cond_wait (&context->priv->destroy_cond, &context->priv->render_lock);
       GST_INFO_OBJECT (context, "gl thread joined");
+
+      g_thread_unref (context->priv->gl_thread);
       context->priv->gl_thread = NULL;
     }
+    g_mutex_unlock (&context->priv->render_lock);
 
     gst_gl_window_set_close_callback (context->window, NULL, NULL, NULL);
     gst_object_unref (context->window);
@@ -695,6 +695,7 @@ gst_gl_context_finalize (GObject * object)
   g_mutex_clear (&context->priv->render_lock);
 
   g_cond_clear (&context->priv->create_cond);
+  g_cond_clear (&context->priv->destroy_cond);
 
   g_free (context->priv->gl_exts);
   g_weak_ref_clear (&context->priv->other_context_ref);
@@ -1291,6 +1292,7 @@ gst_gl_context_create_thread (GstGLContext * context)
   }
 
   context->priv->created = FALSE;
+  g_cond_signal (&context->priv->destroy_cond);
   g_mutex_unlock (&context->priv->render_lock);
 
   return NULL;