I reread http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf and
is not explicit.
But I checked C11 threads.h implementation and thrd_current also uses
DuplicateHandle.
So C11/threads_win32.h is correct. And ISO C11 standard commited
screwed up here. Maybe they'll introduce thread ids at some point
(MSVC's implementation has a non-standard _Thrd_id() function), and we
can use it, but until then, it's better not pretend that thrd_current
meets our needs because it doesn't.
Jose
On 21/04/17 15:06, Jose Fonseca wrote:
No, I'm afraid the problem is still there AFAICS.
GetCurrentThread returns a magic constant (-2 if I'm not mistaken). So
it is (and always will be) useless for thrd_current.
Imagine that:
- thread #1 invokes thrd_current() and gets -2
- thread #2 invokes thrd_current() and gets -2
- a thread (#1, #2 or another thrad) receives invokes thread_equal(-2, -2)
The only way this would work is if it would be forbidden to pass the
value of thrd_current to other threads. I'll need to re-read the specs,
but my guess is that it would be pretty useless.
I also doubt the way mapi uses would work.
Furthermore map really wants a fast thread id. It doesn't need actual
thread handles, just some way of telling threads apart, any id.
Jose
On 20/04/17 15:15, Emil Velikov wrote:
From: Emil Velikov <emil.veli...@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 <bri...@vmware.com>
Cc: José Fonseca <jfons...@vmware.com>
Signed-off-by: Emil Velikov <emil.l.veli...@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
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