[clutter] main: Do not release the lock if it hasn't been acquired

[Emmanuele Bassi <ebassi src gnome org>]

commit 0da0e5122e7526ada688beef22684bb0ed54a367
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Sep 26 09:45:46 2012 +0100

    main: Do not release the lock if it hasn't been acquired
    
    On various systems, trying to release a mutex that hasn't been acquired
    will result in a run-time error.
    
    In order to avoid this, we trylock() the Big Clutter Lockâ and
    immediately unlock() it, regardless of the result; if the lock was
    already acquired, trylock() will immediately fail, and we can release
    it; if the lock was not acquired, trylock() will succeed, and we can
    release the lock immediately.
    
    This is necessary to maintain binary compatibility and invariants for
    Clutter applications doing:
    
      clutter_init()
      clutter_threads_enter()
      ...
      clutter_main()
      ...
      clutter_threads_leave()
    
    instead of the correct:
    
      clutter_init()
      clutter_threads_enter()
      ...
      clutter_threads_leave()
      clutter_main()
      clutter_threads_enter()
      ...
      clutter_threads_leave()
    
    With Clutter â 1.12, the idiomatic form is:
    
      clutter_init()
      ...
      clutter_main()
    
    given that the public Big Clutter Lockâ acquire/release API has been
    deprecated, and nobody should take the lock outside of Clutter itself.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=679439

 clutter/clutter-main.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/clutter/clutter-main.c b/clutter/clutter-main.c
index 7e8fe95..089dc5a 100644
--- a/clutter/clutter-main.c
+++ b/clutter/clutter-main.c
@@ -226,6 +226,16 @@ clutter_threads_impl_lock (void)
 static void
 clutter_threads_impl_unlock (void)
 {
+  /* we need to trylock here, in case the lock hasn't been acquired; on
+   * various systems trying to release a mutex that hasn't been acquired
+   * will cause a run-time error. trylock() will either fail, in which
+   * case we can release the lock we own; or it will succeeds, in which
+   * case we need to release the lock we just acquired. so we ignore the
+   * returned value.
+   *
+   * see: https://bugs.gnome.org/679439
+   */
+  g_mutex_trylock (&clutter_threads_mutex);
   g_mutex_unlock (&clutter_threads_mutex);
 }