[boost] Re: Lock unification

From: Eric Niebler (eric_at_[hidden])
Date: 2004-07-15 11:34:01

Peter Dimov wrote:
> 
> 
> The "unified" timed lock case is
> 
> {
>     scoped_lock l( m, false );
> 
>     if( l.timed_lock( t ) )
>     {
>         // do stuff
>     }
>     else
>     {
>         // what do we do here? presumably either:
> 
>         // setup for unbounded wait
>         l.lock();
>         // do stuff
> 
>         // or signal failure
>     }
> }
> 
> The scoped_timed_lock use case also needs to eventually contain an if( l )
> statement; you can't do much if you don't know whether your timed lock
> succeeded. One might also argue that a separate scoped_timed_lock makes
> accidentally omitting the if() statement more likely and harder to spot.
> 
> But it's hard to tell without real use cases.
> 

I continue to believe that a better interface for a unified lock 
involves descriptively named helper functions:

scoped_lock l1( m );                 // lock unconditionally
scoped_lock l1 = defer_lock( m );    // don't lock
scoped_lock l2 = try_lock( m );      // try lock
scoped_lock l3 = timed_lock( m, t ); // timed lock

It's just as clear as you could hope for, and it's extensible. I feel 
that the single lock c'tor with a bool arg is less readable and rather 
inflexible.

Earlier I posted code demonstrating how this interface could be made to 
work.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com