Re: [RFT PATCH 1/2] win32: optimize condition variable implementation

>   int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex)
>   {
> -	int last_waiter;
> +	int num_waiters;
>
> -	EnterCriticalSection(&cond->waiters_lock);
> +	/*
> +	 * This access is protected under the mutex.
> +	 */
>   	cond->waiters++;
> -	LeaveCriticalSection(&cond->waiters_lock);
>
>   	/*
>   	 * Unlock external mutex and wait for signal.
> @@ -105,17 +104,17 @@ int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex)
>   	WaitForSingleObject(cond->sema, INFINITE);
>
>   	/*
> -	 * Decrease waiters count. If we are the last waiter, then we must
> +	 * Decrease waiters count.  The mutex prevents concurrent increments,
> +	 * so doing this decrement atomically is enough.
> +	 */
> +	num_waiters = InterlockedDecrement(&cond->waiters);
> +
> +	/* If we are the last waiter, then we must
>   	 * notify the broadcasting thread that it can continue.
>   	 * But if we continued due to cond_signal, we do not have to do that
>   	 * because the signaling thread knows that only one waiter continued.
>   	 */
> -	EnterCriticalSection(&cond->waiters_lock);
> -	cond->waiters--;
> -	last_waiter = cond->was_broadcast&&  cond->waiters == 0;
> -	LeaveCriticalSection(&cond->waiters_lock);
> -
> -	if (last_waiter) {
> +	if (num_waiters == 0&&  cond->was_broadcast) {
>   		/*
>   		 * cond_broadcast was issued while mutex was held. This means
>   		 * that all other waiters have continued, but are contending

> @@ -168,12 +168,18 @@ int pthread_cond_signal(pthread_cond_t *cond)
>    */
>   int pthread_cond_broadcast(pthread_cond_t *cond)
>   {
> -	EnterCriticalSection(&cond->waiters_lock);
> +	/*
> +	 * As in pthread_cond_signal, access to cond->waiters and
> +	 * cond->was_broadcast is locked via the external mutex.
> +	 */
>
>   	if ((cond->was_broadcast = cond->waiters>  0)) {
> +		BOOLEAN result;
>   		/* wake up all waiters */
> -		ReleaseSemaphore(cond->sema, cond->waiters, NULL);
> -		LeaveCriticalSection(&cond->waiters_lock);
> +		result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
> +		if (!result)
> +			return err_win_to_posix(GetLastError());
> +
>   		/*
>   		 * At this point all waiters continue. Each one takes its
>   		 * slice of the semaphor. Now it's our turn to wait: Since