[boost] Re: Lock unification

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-15 19:29:34

"Eric Niebler" <eric_at_[hidden]> writes:

> Eric Niebler wrote:
>> David Abrahams wrote:
>>> 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.
>> 
>
> On second thought, I think it's too subtle. You can detect literal
> zero, but you can't detect (at compile-time) an int with a value of
> zero. I'm not comfortable with this:
>
>    scoped_lock l(m, 0);
>
> meaning something different than:
>
>    int t = 0;
>    scoped_lock l(m, t);
>
> Perhaps it's really OK because the effect is the same, but the fact
> that they would execute different code paths sets off bells in my
> head.

I'm not too worried.  It really would be semantically identical and
the timed lock code could contain a branch for the zero case if you
want efficiency.

It might still be too cute, but as long as we're talking about
slimming the interface down we should discuss it.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com