Re: [cxx-mem-model] Atomic C++ header file changes

[Andrew MacLeod <amacleod@redhat.com>]

On 08/19/2011 12:48 PM, Torvald Riegel wrote:
>
>> The problem with issuing a warning is that anytime the compiler creates
>> a C++ atomic class and you use a method with a memory order, it usually
>> leaves an externally call-able method which has to take a runtime
>> value... so you'd see the warning on basically every compilation...
>> which in turn defeats the purpose of the warning.
>>      
> Hmm. I would have assumed that the check that would raise warnings would
> be for actual calls, not for the instantiations. But that would probably
> require special handling of calls to the atomics class for all the
> integers and pointers (can atomic<T*>  be handled as one thing?). So, if
> that's too much work, at least document the constraint somewhere?
>
>    

I'd definitely document the constraint.

To be honest, I think its a pretty useless thing, bordering on moronic.  
The whole point of the memory model is to be able to generate more 
efficient code when you don't need SEQ_CST and really know what you are 
doing.

Even if you *DO* want to make that kind of a call, you have to expect 
the overhead of a runtime library call.  And if you are using SEQ_CST 
mode, its going to be that much slower again due to the call.    I think 
inlining it to be SEQ_CST will provide smaller code size always, and I'd 
be surpised if it *ever* became a performance issue.  And I do mean *ever*.

Andrew