[glib] GMutex (linux): detect and report some errors

[Ryan Lortie <desrt src gnome org>]

commit ecf1359191b2f796a7d63288652dd1a93525417d
Author: Ryan Lortie <desrt desrt ca>
Date:   Sun Jun 29 17:47:10 2014 -0400

    GMutex (linux): detect and report some errors
    
    Detect the following two errors:
    
     - attempting to unlock a mutex that is not locked
    
     - attempting to clear a mutex that was not initialised or was
       initialised but is still locked
    
    Both of these are fatal errors.  We avoid using g_error() here because
    doing so would involve calls back into the GMutex code, and if things
    are going off the rails then we want to avoid that.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=731986

 glib/gthread-posix.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)
---
diff --git a/glib/gthread-posix.c b/glib/gthread-posix.c
index f7d5d8a..54ef769 100644
--- a/glib/gthread-posix.c
+++ b/glib/gthread-posix.c
@@ -1289,6 +1289,11 @@ g_mutex_init (GMutex *mutex)
 void
 g_mutex_clear (GMutex *mutex)
 {
+  if G_UNLIKELY (mutex->i[0] != 0)
+    {
+      fprintf (stderr, "g_mutex_clear() called on uninitialised or locked mutex\n");
+      abort ();
+    }
 }
 
 static void __attribute__((noinline))
@@ -1304,11 +1309,18 @@ g_mutex_lock_slowpath (GMutex *mutex)
 }
 
 static void __attribute__((noinline))
-g_mutex_unlock_slowpath (GMutex *mutex)
+g_mutex_unlock_slowpath (GMutex *mutex,
+                         guint   prev)
 {
   /* We seem to get better code for the uncontended case by splitting
-   * out this call...
+   * this out...
    */
+  if G_UNLIKELY (prev == 0)
+    {
+      fprintf (stderr, "Attempt to unlock mutex that was not locked\n");
+      abort ();
+    }
+
   syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAKE, (gsize) 1, NULL);
 }
 
@@ -1323,9 +1335,13 @@ g_mutex_lock (GMutex *mutex)
 void
 g_mutex_unlock (GMutex *mutex)
 {
+  guint prev;
+
+  prev = exchange_release (&mutex->i[0], 0);
+
   /* 1-> 0 and we're done.  Anything else and we need to signal... */
-  if G_UNLIKELY (exchange_release (&mutex->i[0], 0) != 1)
-    g_mutex_unlock_slowpath (mutex);
+  if G_UNLIKELY (prev != 1)
+    g_mutex_unlock_slowpath (mutex, prev);
 }
 
 gboolean