Re: [PATCH] threaded pack-objects: Use condition variables for thread communication.

From: David Brown <git@davidb.org>
Date: Dec 16, 2007, 19:18 UTC
Message-ID: <20071216191828.GA5446@old.davidb.org>
In-Reply-To: <200712161941.38109.johannes.sixt@telecom.at>

On Sun, Dec 16, 2007 at 07:41:37PM +0100, Johannes Sixt wrote:

Show 14 quoted lines

>On Sunday 16 December 2007 13:05, Peter Baumann wrote:
>> On Sun, Dec 16, 2007 at 12:18:53AM +0100, Johannes Sixt wrote:
>> > +
>> > +		progress_lock();
>> > +		me->working = 0;
>> > +		progress_unlock();
>> > +		pthread_cond_signal(&progress_cond);
>>
>> Shouldn't the pthread_cond_signal be inside the lock?
>> e.g. swap progress_unlock() with pthread_cond_signal(&progress_cond)
>
>No, that's not necessary. Both ways are correct, but if it's outside the lock 
>there is less contention on the mutex (because the waiting thread must 
>acquire the mutex lock before it can return from pthread_cond_wait).

The signal needs to be before the unlock if is more than one signaller. Since normal usage has the signal inside of the lock, most implementations should do this efficiently.

Dave