From d14d103a0c786e895fa6a801587ed5d807df6da4 Mon Sep 17 00:00:00 2001
From: Ian Romanick <idr@us.ibm.com>
Date: Fri, 2 Jul 2004 00:01:09 +0000
Subject: [PATCH] Fix a potential race condition.  Fix a couple of places where
 _glapi_DispatchTSD wasn't properly handled.

---
 src/mesa/glapi/glapi.c | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/src/mesa/glapi/glapi.c b/src/mesa/glapi/glapi.c
index 2a083949fe0..1f640e3e10e 100644
--- a/src/mesa/glapi/glapi.c
+++ b/src/mesa/glapi/glapi.c
@@ -155,10 +155,15 @@ static int NoOpUnused(void)
  * static dispatch functions to call \c _glapi_get_dispatch to get the real
  * dispatch table.
  * 
- * Throughout the code \c _glapi_DispatchTSD == \c NULL is used to determine
- * whether or not the application is multi-threaded.
+ * There is a race condition in setting \c _glapi_DispatchTSD to \c NULL.
+ * It is possible for the original thread to be setting it at the same instant
+ * a new thread, perhaps running on a different processor, is clearing it.
+ * Because of that, \c ThreadSafe, which can only ever be changed to
+ * \c GL_FALSE, is used to determin whether or not the application is
+ * multithreaded.
  */
 /*@{*/
+static GLboolean ThreadSafe = GL_FALSE;  /**< In thread-safe mode? */
 _glthread_TSD _gl_DispatchTSD;           /**< Per-thread dispatch pointer */
 static _glthread_TSD RealDispatchTSD;    /**< only when using override */
 static _glthread_TSD ContextTSD;         /**< Per-thread context pointer */
@@ -184,9 +189,12 @@ static int glUnused(void)
 
 
 struct _glapi_table *_glapi_Dispatch = (struct _glapi_table *) __glapi_noop_table;
+#if defined( THREADS )
 struct _glapi_table *_glapi_DispatchTSD = (struct _glapi_table *) __glapi_noop_table;
+#endif
 struct _glapi_table *_glapi_RealDispatch = (struct _glapi_table *) __glapi_noop_table;
 
+
 /* Used when thread safety disabled */
 void *_glapi_Context = NULL;
 
@@ -219,7 +227,7 @@ void
 _glapi_check_multithread(void)
 {
 #if defined(THREADS)
-   if ( _glapi_DispatchTSD != NULL ) {
+   if (!ThreadSafe) {
       static unsigned long knownID;
       static GLboolean firstCall = GL_TRUE;
       if (firstCall) {
@@ -227,6 +235,7 @@ _glapi_check_multithread(void)
          firstCall = GL_FALSE;
       }
       else if (knownID != _glthread_GetID()) {
+         ThreadSafe = GL_TRUE;
          _glapi_set_dispatch(NULL);
       }
    }
@@ -249,7 +258,7 @@ _glapi_set_context(void *context)
 {
 #if defined(THREADS)
    _glthread_SetTSD(&ContextTSD, context);
-   _glapi_Context = (_glapi_DispatchTSD == NULL) ? NULL : context;
+   _glapi_Context = (ThreadSafe) ? NULL : context;
 #else
    _glapi_Context = context;
 #endif
@@ -266,7 +275,7 @@ void *
 _glapi_get_context(void)
 {
 #if defined(THREADS)
-   if ( _glapi_DispatchTSD == NULL ) {
+   if (ThreadSafe) {
       return _glthread_GetTSD(&ContextTSD);
    }
    else {
@@ -303,7 +312,7 @@ _glapi_set_dispatch(struct _glapi_table *dispatch)
 #if defined(THREADS)
    if (DispatchOverride) {
       _glthread_SetTSD(&RealDispatchTSD, (void *) old_style_dispatch);
-      if ( dispatch == NULL )
+      if (ThreadSafe)
          _glapi_RealDispatch = (struct _glapi_table*) __glapi_threadsafe_table;
       else
          _glapi_RealDispatch = dispatch;
@@ -311,11 +320,14 @@ _glapi_set_dispatch(struct _glapi_table *dispatch)
    else {
       /* normal operation */
       _glthread_SetTSD(&_gl_DispatchTSD, (void *) old_style_dispatch);
-      _glapi_DispatchTSD = dispatch;
-
-      _glapi_Dispatch = (dispatch == NULL)
-	  ? (struct _glapi_table *) __glapi_threadsafe_table
-	  : old_style_dispatch;
+      if (ThreadSafe) {
+	 _glapi_Dispatch = (struct _glapi_table *) __glapi_threadsafe_table;
+	 _glapi_DispatchTSD = NULL;
+      }
+      else {
+	 _glapi_Dispatch = old_style_dispatch;
+	 _glapi_DispatchTSD = dispatch;
+      }
    }
 #else /*THREADS*/
    if (DispatchOverride) {
@@ -336,7 +348,7 @@ struct _glapi_table *
 _glapi_get_dispatch(void)
 {
 #if defined(THREADS)
-   if ( _glapi_DispatchTSD == NULL ) {
+   if (ThreadSafe) {
       if (DispatchOverride) {
          return (struct _glapi_table *) _glthread_GetTSD(&RealDispatchTSD);
       }
@@ -394,8 +406,9 @@ _glapi_begin_dispatch_override(struct _glapi_table *override)
 
 #if defined(THREADS)
    _glthread_SetTSD(&_gl_DispatchTSD, (void *) override);
-   if ( _glapi_DispatchTSD == NULL ) {
+   if ( ThreadSafe ) {
       _glapi_Dispatch = (struct _glapi_table *) __glapi_threadsafe_table;
+      _glapi_DispatchTSD = NULL;
    }
    else {
       _glapi_Dispatch = override;
-- 
2.30.2