[glib/glib-2-28] GTimeZone: fix non-threadsafe refcounting

[Ryan Lortie <ryanl src gnome org>]

commit e781c26b2516d2131f9b830e174e5e2b41e91d81
Author: Ryan Lortie <desrt desrt ca>
Date:   Sat Apr 16 10:52:12 2011 -0400

    GTimeZone: fix non-threadsafe refcounting
    
    In the previous code, if the timezone was pulled out of the cache again
    just as the last reference was being dropped, the cache code will
    increase its refcount and return it while the unref code was freeing it.
    
    Protect against that.
    
    Note that this patch is not a straight cherry-pick of the one from
    master.  It follows closer to the solution that was originally
    recommended in the bug and holds the mutex during every unref operation.
    Because we don't have the GTimeZoneMonitor changes involved here, it's a
    little bit more elegant (due to no early exit condition).  Also, it's
    the stable release, and I have more confidence in it (even if it's
    probably slower).
    
    Closes #646435.

 glib/gtimezone.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/glib/gtimezone.c b/glib/gtimezone.c
index 902e2c3..e882682 100644
--- a/glib/gtimezone.c
+++ b/glib/gtimezone.c
@@ -164,11 +164,10 @@ g_time_zone_unref (GTimeZone *tz)
 {
   g_assert (tz->ref_count > 0);
 
+  G_LOCK(time_zones);
   if (g_atomic_int_dec_and_test (&tz->ref_count))
     {
-      G_LOCK(time_zones);
       g_hash_table_remove (time_zones, tz->name);
-      G_UNLOCK(time_zones);
 
       if (tz->zoneinfo)
         g_buffer_unref (tz->zoneinfo);
@@ -177,6 +176,7 @@ g_time_zone_unref (GTimeZone *tz)
 
       g_slice_free (GTimeZone, tz);
     }
+  G_UNLOCK(time_zones);
 }
 
 /**