Re: [boost] [thread] countdown_latch

Subject: Re: [boost] [thread] countdown_latch
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-05-14 01:46:01

Le 14/05/13 00:44, Gaetano Mendola a écrit :
>
> Unlocking as soon as possible is something it should happen whenever 
> is possible, but basically you are doing this kind of optimization:
>
> instead of
>
> void foo() {
>   boost::unique_lock<boost::mutex> lk(mutex_);
>   ....
>   return;
> }
>
> you are optimizing doing this:
>
> void foo() {
>   boost::unique_lock<boost::mutex> lk(mutex_);
>   ...
>   lk.unlock;
>   return;
> }
>
> and I'm asking, is it worth?  Do you have an evidence of it ?
> Having say that do whatever you believe is better in terms of clarity
> and correctness.
> I have seen also that in a couple of points the unique_lock can be
> replaced by a lock_guard (and possibly declared const).
>
>
>
Sorry Gaetano,

I have an uncommitted version where

     bool count_down(unique_lock<mutex> &lk)
     /// pre_condition (count_.value_ > 0)
     {
       BOOST_ASSERT(count_.value_ > 0);
       if (--count_.value_ == 0)
       {
         lk.unlock();
         count_.cond_.notify_all(); // unlocked !!!
         return true;
       }
       return false;
     }

Maybe I'm wrong and I'm doing premature optimization and it is better to 
use lock_guard and don't unlock before notifying.
As you point it is in any case clearer.

Measures would be needed :(

Thanks for your interest,
Vicente