Re: one last boost conversion question: notify_one

From: Christopher Currie (Christopher_at_[hidden])
Date: 2003-05-22 14:24:33

Mark,

The problem is that your "get" waits on the condition before it checks 
if the condition has already been met. So if you call "get" after the 
producer has already "post"ed, you'll sit on the condition forever. The 
canonical form of waiting on a condition looks like this:

> MSG mqueue::get();
> {
>   MSG msgResult;
>   { boost::mutex::scoped_lock lockQueue( _mutexQueue );
>     while ( _queueOut.empty() )
 >       _conditionMessageReady.wait( lockQueue );
>     
 >     msgResult = _queueOut.front();
>     _queueOut.pop(); 
>   }
>   return msgResult;
> }

Now if you call get and there's something in the queue, there's no need 
to wait on the condition.

> P.S. The lockQueue is locked when the condition is done waiting, right?

Yes, the lock is automatically released when entering wait, and acquired 
before exiting it.

Hope this helps!

Christopher