Mesa (master): Revert "glapi: Fix a possible race in getting current context/dispatch."
Brian Paul
brianp at kemper.freedesktop.org
Tue Aug 25 15:43:55 UTC 2009
Module: Mesa
Branch: master
Commit: a94d66e85748a6ac2b2d4700b6504cc89d1e1945
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=a94d66e85748a6ac2b2d4700b6504cc89d1e1945
Author: Brian Paul <brianp at vmware.com>
Date: Tue Aug 25 09:37:43 2009 -0600
Revert "glapi: Fix a possible race in getting current context/dispatch."
This reverts commit 17090cf3efb0db8fa01b502a9c0df27cbd1a67da.
We're reverting this because it causes ABI breakage with the X server.
Maybe re-attempt with another patch.
---
src/mesa/glapi/glapi.c | 75 +++++++++++++++++++++++---------------------
src/mesa/glapi/glapi.h | 5 +--
src/mesa/glapi/glthread.h | 2 +-
3 files changed, 41 insertions(+), 41 deletions(-)
diff --git a/src/mesa/glapi/glapi.c b/src/mesa/glapi/glapi.c
index 4bb10df..e36fccb 100644
--- a/src/mesa/glapi/glapi.c
+++ b/src/mesa/glapi/glapi.c
@@ -160,20 +160,26 @@ static GLint NoOpUnused(void)
* the variables \c _glapi_Dispatch and \c _glapi_Context are used for this
* purpose.
*
- * In the "normal" threaded case, the variable \c _glapi_SingleThreaded will be
- * \c GL_FALSE if an application is detected as being multithreaded.
- * Single-threaded applications will use \c _glapi_Dispatch and \c
- * _glapi_Context just like the case without any threading support. When \c
- * _glapi_SingleThreaded is \c GL_FALSE, the thread state data \c
- * _gl_DispatchTSD and \c ContextTSD are used. Drivers and the static dispatch
- * functions access these variables via \c _glapi_get_dispatch and \c
- * _glapi_get_context.
+ * In the "normal" threaded case, the variables \c _glapi_Dispatch and
+ * \c _glapi_Context will be \c NULL if an application is detected as being
+ * multithreaded. Single-threaded applications will use \c _glapi_Dispatch
+ * and \c _glapi_Context just like the case without any threading support.
+ * When \c _glapi_Dispatch and \c _glapi_Context are \c NULL, the thread state
+ * data \c _gl_DispatchTSD and \c ContextTSD are used. Drivers and the
+ * static dispatch functions access these variables via \c _glapi_get_dispatch
+ * and \c _glapi_get_context.
*
+ * There is a race condition in setting \c _glapi_Dispatch 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_TRUE, is
+ * used to determine whether or not the application is multithreaded.
+ *
* In the TLS case, the variables \c _glapi_Dispatch and \c _glapi_Context are
* hardcoded to \c NULL. Instead the TLS variables \c _glapi_tls_Dispatch and
- * \c _glapi_tls_Context are used. The variable \c _glapi_SingleThreaded,
- * though not used, is defined and hardcoded to \c GL_FALSE to maintain binary
- * compatability between TLS enabled loaders and non-TLS DRI drivers.
+ * \c _glapi_tls_Context are used. Having \c _glapi_Dispatch and
+ * \c _glapi_Context be hardcoded to \c NULL maintains binary compatability
+ * between TLS enabled loaders and non-TLS DRI drivers.
*/
/*@{*/
#if defined(GLX_USE_TLS)
@@ -188,9 +194,6 @@ PUBLIC __thread void * _glapi_tls_Context
PUBLIC const struct _glapi_table *_glapi_Dispatch = NULL;
PUBLIC const void *_glapi_Context = NULL;
-/* Unused, but maintain binary compatability with non-TLS DRI drivers */
-GLboolean _glapi_SingleThreaded = GL_FALSE;
-
#else
#if defined(THREADS)
@@ -205,9 +208,9 @@ _glthread_DECLARE_STATIC_MUTEX(ThreadCheckMutex);
#define CHECK_MULTITHREAD_UNLOCK() _glthread_UNLOCK_MUTEX(ThreadCheckMutex)
#endif
-GLboolean _glapi_SingleThreaded = GL_TRUE; /**< In single-thread mode? */
-_glthread_TSD _gl_DispatchTSD; /**< Per-thread dispatch pointer */
-static _glthread_TSD ContextTSD; /**< Per-thread context pointer */
+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 */
#if defined(WIN32_THREADS)
void FreeTSD(_glthread_TSD *p);
@@ -241,7 +244,7 @@ _glapi_check_multithread(void)
static unsigned long knownID;
static GLboolean firstCall = GL_TRUE;
- if (!_glapi_SingleThreaded)
+ if (ThreadSafe)
return;
CHECK_MULTITHREAD_LOCK();
@@ -254,12 +257,9 @@ _glapi_check_multithread(void)
firstCall = GL_FALSE;
}
else if (knownID != _glthread_GetID()) {
- /*
- * switch to thread-safe mode. _glapi_Context and _glapi_Dispatch are no
- * longer accessed after this point, except for raced by the first
- * thread. Because of the race, they cannot be reset to NULL.
- */
- _glapi_SingleThreaded = GL_FALSE;
+ ThreadSafe = GL_TRUE;
+ _glapi_set_dispatch(NULL);
+ _glapi_set_context(NULL);
}
CHECK_MULTITHREAD_UNLOCK();
#endif
@@ -279,10 +279,8 @@ _glapi_set_context(void *context)
#if defined(GLX_USE_TLS)
_glapi_tls_Context = context;
#elif defined(THREADS)
- if (_glapi_SingleThreaded)
- _glapi_Context = context;
- /* always update TSD because we might switch to it at any time */
_glthread_SetTSD(&ContextTSD, context);
+ _glapi_Context = (ThreadSafe) ? NULL : context;
#else
_glapi_Context = context;
#endif
@@ -301,8 +299,12 @@ _glapi_get_context(void)
#if defined(GLX_USE_TLS)
return _glapi_tls_Context;
#elif defined(THREADS)
- return (_glapi_SingleThreaded)
- ? _glapi_Context : _glthread_GetTSD(&ContextTSD);
+ if (ThreadSafe) {
+ return _glthread_GetTSD(&ContextTSD);
+ }
+ else {
+ return _glapi_Context;
+ }
#else
return _glapi_Context;
#endif
@@ -517,9 +519,8 @@ _glapi_set_dispatch(struct _glapi_table *dispatch)
#if defined(GLX_USE_TLS)
_glapi_tls_Dispatch = dispatch;
#elif defined(THREADS)
- if (_glapi_SingleThreaded)
- _glapi_Dispatch = dispatch;
_glthread_SetTSD(&_gl_DispatchTSD, (void *) dispatch);
+ _glapi_Dispatch = (ThreadSafe) ? NULL : dispatch;
#else /*THREADS*/
_glapi_Dispatch = dispatch;
#endif /*THREADS*/
@@ -533,15 +534,17 @@ _glapi_set_dispatch(struct _glapi_table *dispatch)
PUBLIC struct _glapi_table *
_glapi_get_dispatch(void)
{
+ struct _glapi_table * api;
#if defined(GLX_USE_TLS)
- return _glapi_tls_Dispatch;
+ api = _glapi_tls_Dispatch;
#elif defined(THREADS)
- return (_glapi_SingleThreaded)
- ? _glapi_Dispatch
- : (struct _glapi_table *) _glthread_GetTSD(&_gl_DispatchTSD);
+ api = (ThreadSafe)
+ ? (struct _glapi_table *) _glthread_GetTSD(&_gl_DispatchTSD)
+ : _glapi_Dispatch;
#else
- return _glapi_Dispatch;
+ api = _glapi_Dispatch;
#endif
+ return api;
}
diff --git a/src/mesa/glapi/glapi.h b/src/mesa/glapi/glapi.h
index b2a1fe6..8f2cf66 100644
--- a/src/mesa/glapi/glapi.h
+++ b/src/mesa/glapi/glapi.h
@@ -94,10 +94,7 @@ extern void *_glapi_Context;
extern struct _glapi_table *_glapi_Dispatch;
# ifdef THREADS
-/* this variable is here only for quick access to current context/dispatch */
-extern GLboolean _glapi_SingleThreaded;
-# define GET_CURRENT_CONTEXT(C) GLcontext *C = (GLcontext *) \
- ((_glapi_SingleThreaded) ? _glapi_Context : _glapi_get_context())
+# define GET_CURRENT_CONTEXT(C) GLcontext *C = (GLcontext *) (_glapi_Context ? _glapi_Context : _glapi_get_context())
# else
# define GET_CURRENT_CONTEXT(C) GLcontext *C = (GLcontext *) _glapi_Context
# endif
diff --git a/src/mesa/glapi/glthread.h b/src/mesa/glapi/glthread.h
index a36bea7..8ec933a 100644
--- a/src/mesa/glapi/glthread.h
+++ b/src/mesa/glapi/glthread.h
@@ -322,7 +322,7 @@ extern __thread struct _glapi_table * _glapi_tls_Dispatch
#elif !defined(GL_CALL)
# if defined(THREADS)
# define GET_DISPATCH() \
- ((__builtin_expect(_glapi_SingleThreaded, 1)) \
+ ((__builtin_expect( _glapi_Dispatch != NULL, 1 )) \
? _glapi_Dispatch : _glapi_get_dispatch())
# else
# define GET_DISPATCH() _glapi_Dispatch
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