[Mesa-dev] [PATCH 1/2] c11/threads: implement thrd_current on Windows

[Emil Velikov]

From: Emil Velikov <emil.velikov at collabora.com>

Earlier commit removed the implementation due to a subtle bug, in the
existing code. Namely:

One was comparing directly the thread handle/IDs rather than using
thrd_equal(). As the pseudo-handles never matched things went south.

That bug was resolved with commit 458c7490c29 "mapi: rewrite
u_current_init() function without u_thread_self()" thus we can bring the
thrd_current implementation back, whist preserving the correct
thrd_equal implementation as-is.

With this in place, we can remove a handful of the remaining pthread vs
WIN32 specifics.

Cc: Brian Paul <brianp at vmware.com>
Cc: José Fonseca <jfonseca at vmware.com>
Signed-off-by: Emil Velikov <emil.l.velikov at gmail.com>
---
 include/c11/threads_win32.h | 35 ++++++-----------------------------
 1 file changed, 6 insertions(+), 29 deletions(-)

diff --git a/include/c11/threads_win32.h b/include/c11/threads_win32.h
index d017c31c34e..f0eb5c77c60 100644
--- a/include/c11/threads_win32.h
+++ b/include/c11/threads_win32.h
@@ -494,42 +494,19 @@ thrd_create(thrd_t *thr, thrd_start_t func, void *arg)
     return thrd_success;
 }
 
-#if 0
 // 7.25.5.2
 static inline thrd_t
 thrd_current(void)
 {
-    HANDLE hCurrentThread;
-    BOOL bRet;
-
-    /* GetCurrentThread() returns a pseudo-handle, which is useless.  We need
-     * to call DuplicateHandle to get a real handle.  However the handle value
-     * will not match the one returned by thread_create.
-     *
-     * Other potential solutions would be:
-     * - define thrd_t as a thread Ids, but this would mean we'd need to OpenThread for many operations
-     * - use malloc'ed memory for thrd_t. This would imply using TLS for current thread.
-     *
-     * Neither is particularly nice.
+    /* GetCurrentThread() returns a pseudo-handle, which will not match the
+     * one returned by thread_create.
      *
-     * Life would be much easier if C11 threads had different abstractions for
-     * threads and thread IDs, just like C++11 threads does...
+     * At the same time, the only way that one should compare thread handle
+     * and/or IDs is via thrd_equal. That in itself attributes for the above
+     * situation.
      */
-
-    bRet = DuplicateHandle(GetCurrentProcess(), // source process (pseudo) handle
-                           GetCurrentThread(), // source (pseudo) handle
-                           GetCurrentProcess(), // target process
-                           &hCurrentThread, // target handle
-                           0,
-                           FALSE,
-                           DUPLICATE_SAME_ACCESS);
-    assert(bRet);
-    if (!bRet) {
-	hCurrentThread = GetCurrentThread();
-    }
-    return hCurrentThread;
+    return GetCurrentThread();
 }
-#endif
 
 // 7.25.5.3
 static inline int
-- 
2.12.2