[boost] Re: Boost.Threads: Do we need all those mutexes?

From: Michael Glassford (glassfordm_at_[hidden])
Date: 2004-07-07 23:23:35

Eric Niebler wrote:
> Peter Dimov wrote:
> 
>> compare:
>>
>>     TryLock l( m, unlocked );
>>
>>     if( l.try_lock() )
>>     {
>>     }
>>
>> with:
>>
>>     TryLock l( m, non_blocking );
>>
>>     if( l.locked() )
>>     {
>>     }
>>
> 
> (Jumping late, forgive me if this has been discussed already.)
> 
> How about:
> 
> if( ScopedLock l = try_lock( m ) )
> {
> }
> 
> where try_lock is function that returns a simple wrapper class:
> 
> template< Mutex > struct try_locker
> {
>     Mutex & m;
>     ...
> };
> 
> template< Mutex > try_locker< Mutex > try_lock( Mutex & m )
> {
>     return try_locker< Mutex >( m );
> };
> 
> and ScopedLock is some lockable type which has a constructor that 
> accepts a try_locker. (It would also need a bool-ish conversion to allow 
> the lock to be declared in the "if" statement, but that's not relevant 
> to this discussion.)

Interesting idea. I suppose you could even do this:

    if (ScopedLock l(m, locker()))
    {
    }

where locker() is a function object that defines

    operator()(LockType& l)

which the lock calls in the constructor, passing *this. You could have
locker(), try_locker(), timed_locker(t), etc.

Mike