glapi: Protect _glapi_check_multithread by a mutex.

Multiple threads might call _glapi_check_multithread at roughly the same
time.  It is possbile that all of them are wrongly regarded as firstCall
if there is no mutex.  This bug causes xeglthreads to crash sometimes.

Acked-by: Ian Romanick <[email protected]>
Signed-off-by: Chia-I Wu <[email protected]>

1 files changed, 15 insertions, 14 deletions

diff --git a/src/mesa/glapi/glapi.c b/src/mesa/glapi/glapi.c
index 2b105d0f17d..30aec209e7d 100644
--- a/src/mesa/glapi/glapi.c
+++ b/src/mesa/glapi/glapi.c
@@ -198,6 +198,7 @@ PUBLIC const void *_glapi_Context = NULL;
 
 #if defined(THREADS)
 
+_glthread_DECLARE_STATIC_MUTEX(ThreadCheckMutex);
 static GLboolean ThreadSafe = GL_FALSE;  /**< In thread-safe mode? */
 _glthread_TSD _gl_DispatchTSD;           /**< Per-thread dispatch pointer */
 static _glthread_TSD ContextTSD;         /**< Per-thread context pointer */
@@ -231,23 +232,23 @@ void
 _glapi_check_multithread(void)
 {
 #if defined(THREADS) && !defined(GLX_USE_TLS)
-   if (!ThreadSafe) {
-      static unsigned long knownID;
-      static GLboolean firstCall = GL_TRUE;
-      if (firstCall) {
-         knownID = _glthread_GetID();
-         firstCall = GL_FALSE;
-      }
-      else if (knownID != _glthread_GetID()) {
-         ThreadSafe = GL_TRUE;
-         _glapi_set_dispatch(NULL);
-         _glapi_set_context(NULL);
-      }
+   static unsigned long knownID;
+   static GLboolean firstCall = GL_TRUE;
+
+   if (ThreadSafe)
+      return;
+
+   _glthread_LOCK_MUTEX(ThreadCheckMutex);
+   if (firstCall) {
+      knownID = _glthread_GetID();
+      firstCall = GL_FALSE;
    }
-   else if (!_glapi_get_dispatch()) {
-      /* make sure that this thread's dispatch pointer isn't null */
+   else if (knownID != _glthread_GetID()) {
+      ThreadSafe = GL_TRUE;
       _glapi_set_dispatch(NULL);
+      _glapi_set_context(NULL);
    }
+   _glthread_UNLOCK_MUTEX(ThreadCheckMutex);
 #endif
 }