Subj : Re: Optimization to Jeffrey Richter's COptex (Windows)?
To   : comp.programming.threads
From : Alexander Terekhov
Date : Thu Jan 27 2005 02:41 am


Joseph Seigh wrote:
[...]
> BOOL CoptexTryEnter(coptex_t *lock) {
> 
>         CoptexSpin(lock);
>         if (InterlockedCompareExchange(&(lock->m_lLockCount), 1, 0) == 0) {
>                 lock->m_dwThreadId = GetCurrentThreadId();
>                 lock->m_lRecurseCount = 1;
>                 return TRUE;
>         }
> 
>         else if (lock->m_dwThreadId == GetCurrentThreadId()) {
>                 lock->m_lRecurseCount++;
>                 return TRUE;
>         }
> 
>         return FALSE;
> }
> 
> I'm assuming GetCurrentThreadId or an equivalent intrinsic is very
> efficient.  With an unconditional increment of the lockcount you
> end up with the threadid final check after a memory barrier anyway
> so paranoids like Alexander should be happy. :)

Paranoids like me know that according to the MS docu, 
InterlockedCompareExchange() performs nothing ("no operation") if 
the Destination value is NOT equal to the Comperand value. 

I can imagine reasonable implementation for XBOX Next that would 
have neither trailing "isync" (for acquire msync) nor leading 
"sync" (for release msync) instructions on that path.

regards,
alexander.

.