Re: [Boost-users] [Threads] Conditions and avoiding lengthy mutexlocks (background loading for a game)

From: Peter Mackay (mackay.pete+gmane_at_[hidden])
Date: 2006-04-28 05:22:59

Hello,

Thomas, Thank you very much for your detailed reply.

> You usually don't hold the mutex guarding the state indicating
> variables for a long time.
> You usually hold it just enough to update the variables to indicate
> the new state you have transitioned to.

Ah, so even though I pass the mutex into the condition when waiting, I don't 
have to leave the mutex locked while handling the request.

> That is you hold it while you pick up the request from the queue and
> transfer it to local variables in the thread (or somehow mark it in
> the queue) as being processed, then you release the lock and go off
> and handle request.

That sounds exactly like what I want to do. Thanks.

> After you are done processing you grab the lock
> again and update state or lock for new requests and then repeat. If
> there are no requests then you block on condition while holding the
> mutex and the blocking wait releases and reacquires  the lock for you
> when the condition is signaled. You will be holding the mutex lock
> for very little time unless popping/marking queue elements is quite
> expensive.

I'm planning on just copying the requests to a local variable in the thread 
function, so this should be okay.

> Also, it often a little more efficient to signal the condition
> variable while not holding the mutex. It can avoid needless context
> ping ponging.

Ah, I didn't realise I could do that.

Thanks again, you've really helped me out.

Peter