[boost] Re: Lock unification

From: Eric Niebler (eric_at_[hidden])
Date: 2004-07-15 18:11:29

David Abrahams wrote:
>"Eric Niebler" <eric_at_[hidden]> writes:
>>David Abrahams wrote:
>>>"Eric Niebler" <eric_at_[hidden]> writes:
>>>
>>>>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, 
>>>
>>>I'm not convinced it is.  It potentially puts information about the
>>>kind of locking being done very far from the actual call that does
>>>locking.  
>>
>>
>>True, but the other design under consideration doesn't help with
>>that. It requires two-step construction for some constructs which
>>could result in code like:
>>
>>   scoped_lock l( m, false );
>>   maybe_takes_the_lock_i_dont_know( l );
> 
> 
> I don't know what you're referring to.  I don't see any two-step
> construction going on there.  Links or examples, please?
> 

With the single c'tor approach that Peter D. has been championing, to 
get a try lock, you need two statements:

   scoped_lock l( m, false );
   if( l.try_lock() ) ...

That's all I was refering to. Perhaps "2-step construction" is 
misleading. My point was, it's just as easy to make the locking logic 
remote with this design as with mine.

> BTW, it just occurred to me that
> 
>      timed_lock(m, 0)
> 
> could potentially generate different code from
> 
>      timed_lock(m, some_int)
> 
> If we can detect literal zero... which I think is possible.
> 
> What about:
> 
>   scoped_lock l(m);               // block
>   scoped_lock l(m, 0);            // try
>   scoped_lock l(m, 33);           // timed
> 
>   scoped_lock l(m, deferred);     // deferred 
>   scoped_lock l(deferred(m));     // alternate
>  
> ??
> 

Interesting. That's workable.

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