[x264-devel] [PATCH] Fix race condition in win32 threading init

[Andrey Turkin]

x264_threading_init must not return until threading is fully initialized. The code is mostly borrowed from FFmpeg codebase and adapted to handle init failure case.

---
 common/osdep.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 51 insertions(+), 13 deletions(-)

diff --git a/common/osdep.c b/common/osdep.c
index 9bc926a1..f07d446a 100644
--- a/common/osdep.c
+++ b/common/osdep.c
@@ -40,6 +40,12 @@
 #endif
 #include <time.h>
 
+#if _WIN32_WINNT < 0x0600 && defined(__MINGW32__)
+#undef MemoryBarrier
+#define MemoryBarrier __sync_synchronize
+#endif
+
+
 #if PTW32_STATIC_LIB
 /* this is a global in pthread-win32 to indicate if it has been initialized or not */
 extern int ptw32_processInitialized;
@@ -74,23 +80,55 @@ static void x264_threading_destroy( void )
 
 int x264_threading_init( void )
 {
-    /* if already init, then do nothing */
-    if( InterlockedCompareExchange( &x264_threading_is_init, 1, 0 ) )
-        return 0;
+    switch( InterlockedCompareExchange( &x264_threading_is_init, 1, 0 ) )
+    {
+    case 0:
+        /* this thread has to initialize threading */
 #if PTW32_STATIC_LIB
-    /* if static pthread-win32 is already initialized, then do nothing */
-    if( ptw32_processInitialized )
-        return 0;
-    if( !pthread_win32_process_attach_np() )
-        return -1;
+        /* if static pthread-win32 is already initialized, then do nothing */
+        if( !ptw32_processInitialized )
+        {
+            if( !pthread_win32_process_attach_np() )
+            {
+                InterlockedExchange( &x264_threading_is_init, 3 );
+                return -1;
+            }
+            /* register cleanup to run at process termination */
+            atexit( x264_threading_destroy );
+        }
 #else
-    if( x264_win32_threading_init() )
-        return -1;
+        if( x264_win32_threading_init() )
+        {
+            InterlockedExchange( &x264_threading_is_init, 3 );
+            return -1;
+        }
+        /* register cleanup to run at process termination */
+        atexit( x264_threading_destroy );
 #endif
-    /* register cleanup to run at process termination */
-    atexit( x264_threading_destroy );
+        InterlockedExchange( &x264_threading_is_init, 2 );
+        return 0;
 
-    return 0;
+    case 1:
+        /* other thread is running init */
+        for( ;; )
+        {
+            MemoryBarrier();
+            if( x264_threading_is_init == 2 )
+                return  0;
+            if( x264_threading_is_init == 3 )
+                return  -1;
+            Sleep( 0 );
+        }
+
+    case 2:
+        /* already initialized */
+        return 0;
+
+    case 3:
+        /* initialize failed */
+    default:
+        return -1;
+    }
 }
 #endif
 
-- 
2.11.0