Re: [msysGit] Re: [PATCH/RFC] mingw: implement PTHREAD_MUTEX_INITIALIZER

On Wed, Oct 26, 2011 at 5:05 AM, Atsushi Nakagawa [off-list ref] wrote:

On Oct 25, 11:55 pm, Erik Faye-Lund [off-list ref] wrote:

quoted

[...]
+int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t
*attr)
+{
+       InitializeCriticalSection(&mutex->cs);
+       mutex->autoinit = 0;
+       return 0;
+}
+
+int pthread_mutex_lock(pthread_mutex_t *mutex)
+{
+       if (mutex->autoinit) {
+               if (InterlockedCompareExchange(&mutex->autoinit, -1, 1) !=
-1) {

I'm making the assumption that mutex->autoinit starts off as 1 before things
get multi-threaded..
I've only looked at what's in the patch so I could be missing vital
context..  Anyways, is there a reason why you made this
"InterlockedCompareExchange(..., -1, 1) != -1" and not
"InterlockedCompareExchange(..., -1, 1) == 1"?

No, not really.

It looks to me the former adds a race condition after "if (mutex->autoinit)
{".  e.g. A second thread could reinitialize mutex->cs after the first
thread has already entered EnterCriticalSection(...).

You are indeed correct, thanks for spotting :)