Re: [boost] [thread] countdown_latch

Subject: Re: [boost] [thread] countdown_latch
From: Gaetano Mendola (mendola_at_[hidden])
Date: 2013-05-11 17:25:19

On 27/04/2013 09.05, Vicente J. Botet Escriba wrote:
> The change set is  https://svn.boost.org/trac/boost/changeset/84055. To
> see the sources, you would need to update the trunk or to take a look at
> https://svn.boost.org/svn/boost/trunk/boost/thread/
>
> Please let me know what do you think.

Is the explicit lk.unlock() inside the

bool count_down(unique_lock<mutex> &lk);

needed ?

I see the two places where it's called are:

void count_down()
{
   boost::unique_lock<boost::mutex> lk(mutex_);
   count_down(lk);
}

and

void count_down_and_wait()
{
   boost::unique_lock<boost::mutex> lk(mutex_);
   if (count_down(lk))
   {
     return;
   }
   count_.cond_.wait(lk, detail::counter_is_zero(count_));
}

in both cases the unique_lock does the job, or I'm missing
something?

Also I would add a new method to boost::detail::counter

   bool dec_and_notify_all_if_value(const std::size a_value)
   {
     if (--value_ == a_value)
     {
       cond_.notify_all();
       return true;
     }
     return false;
   }

This way you can further simplify the count_down(unique_lock<mutex> &lk)
method:

     //lk is here only to assure it's a thread safe call
     bool count_down(unique_lock<mutex> &lk)
     /// pre_condition (count_.value_ > 0)
     {
       BOOST_ASSERT(count_.value_ > 0);
       return count_.dec_and_notify_all_if_value(0);
     }

Regards
Gaetano Mendola