Re: [boost] Re: [shared_ptr] Interlocked* - possible bug?

From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-09-30 15:31:10

Alexander Terekhov wrote:
> Peter Dimov wrote:
>> 
>> Alexander Terekhov wrote:
>>> Peter Dimov wrote:
>>>> 
>>>> Alexander Terekhov wrote:
>>>>>> No, it's not; C++ behavior _is defined in terms of_ volatile (and
>>>>>> I/O calls), not the other way around.
>>>>> 
>>>>> As if rule. And C++ says nothing about mutiple threads.
>>>> 
>>>> Nope. "As if" is defined in terms of observable behavior, and
>>>> "observable behavior" is defined in terms of volatile and I/O.
>>> 
>>> int main() {
>>>  volatile int a = 1;
>>>  return --a;
>>> }
>>> 
>>> prove that it can't be transformed to
>>> 
>>> int main() {
>>> }
>> 
>> The observable behavior is
>> 
>> write volatile @a 1
> 
>  nop
> 
>> read volatile @a x
> 
>  nop
> 
>> write volatile @a x-1
> 
>  nop
> 
>> exit(x-1)
> 
>  push    0
>  call    _exit
> 
>> 
>> in the first case, and
> 
> Happy now (debugger notwithstanding)?

No. A conforming compiler is not allowed to do that.

> C'mon, volatile is brain-dead.

Nobody's arguing otherwise. ;-) But a nop it isn't.