Re: [RFT PATCH 2/2] win32: optimize pthread_cond_broadcast

[Johannes Sixt <j.sixt@viscovery.net>]

Am 07.06.2010 15:38, schrieb Paolo Bonzini:
> @@ -172,9 +172,10 @@ int pthread_cond_broadcast(pthread_cond_t *cond)
>   	 * 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)) {
> +	if (cond->waiters>  0) {
>   		BOOLEAN result;
> +		cond->was_broadcast = cond->waiters>  1;
> +

It is possible that you set was_broadcast to 1 here, while another thread 
still sees was_broadcast == 0 in cond_wait. As a consequence, this thread 
WaitsForSingleObject(), which will never arrive because the other thread 
does not call SetEvent(). But this is more a problem of your first patch, 
not of this one, so you better fix the first one first before you go 
further into this one.

That said, as long as this series buys performance only at the expense of 
clarity, I'm rather opposed to it because we do not call cond_wait and 
cond_broadcast in time-critical paths.

-- Hannes