Re: [PATCH/RFC] mingw: implement PTHREAD_MUTEX_INITIALIZER

[Atsushi Nakagawa <atnak@chejz.com>]

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On Oct 25, 11:55 pm, Erik Faye-Lund <kusmab...@gmail.com> wrote:
> [...]
> +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"?

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(...).

> +                       pthread_mutex_init(mutex, NULL);
> +                       mutex->autoinit = 0;
> +               } else
> +                       while (mutex->autoinit != 0)
> +                               ; /* wait for other thread */
> +       }
> +
> +       EnterCriticalSection(&mutex->cs);
> +       return 0;
> +}
> [...]

-- 
Atsushi Nakagawa


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