Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : Alexander Terekhov
Date : Thu Aug 11 2005 06:51 pm


John Doug Reynolds wrote:
[...]
> I'm uncertain whether you are objecting to the apparently local nature
> of the Lock in my original transcription, or whether you are pointing
> to a more fundamental problem.  If so, could you explain your
> assertions more fully?

To begin with, even if compiler won't optimize-out your per-thread 
locks (which is perfectly legal), compiler and/or hardware can 
transform your

:         Singleton* tmp = new Singleton;
:         local.lock(); local.unlock(); // just a memory barrier
:         pInstance = tmp;

to (in effect):

 < pseudo-code; assume everything is throw()-nothing >

          local.lock();
          pInstance = Singleton::operator new();
          ::new(pInstance) Singleton(); 
          local.unlock(); 

regards,
alexander.

.