Subj : Re: Memory Barriers, Compiler Optimizations, etc.
To   : comp.programming.threads
From : Neill Clift [MSFT]
Date : Mon Feb 07 2005 01:11 pm

"SenderX" <xxx@xxx.com> wrote in message 
news:v5GdnRpcBK9IXJrfRVn-vA@comcast.com...
>> > Here are some questions that need clarification in your documentation:
>> >
>> > 1. Can external data depend on the return value from a failed CAS?
>>
>> I don't undestand what your asking.
>
> static CMyData my_data;
> static volatile LONG flag = 0;
>
>
> my_data.setup();
> InterlockedCompareExchange( &flag, 1, 0 );
>
>
> AnotherConcurrentThread
> ------------------
>
> while ( ! InterlockedCompareExchange( &flag, 0, 0 ) ) { Sleep( 0 ); _asm
> pause; }
> // flag is set
> my_data.use();
>
>
>
> Is this safe?
>

Yes. As another poster mentions a less contrived example
would be using say InterlockedCompareExchange to do
one time initialization and if the call fails using the return
as the initialized value.
I would consider it a bug if we didn't honour this and push
for it to be fixed in current platforms.

.