Re: [Boost-users] mutexes : Is this thread-safe ?

From: Kevin Heifner (heifner_k_at_[hidden])
Date: 2006-02-20 15:33:41

Tom Widmer wrote:
> That particular re-ordering is illegal. Remember, when a mutex is 
> locked, no memory access or code that happens after the mutex is locked 
> (in this case the assignment to lk) can be moved to before the mutex was 
> locked (in other words, a mutex emits an appropriate memory barrier), so 
> lk will not be assigned until after global_mutex is locked.

[...]

> This is different from DCL, where one of the paths does *not* lock the 
> mutex - in the OP's code, all paths lock the mutex before accessing 
> shared data, so there's no problem.

Right. The mutex is acquired in the constructor and therefore 
provides the memory barrier needed.  It looks wrong to my eyes 
since I would never use raw new/delete in this context.  Sorry 
for the noise.

KevinH
-- 
Kevin Heifner  heifner @ ociweb.com  http://heifner.blogspot.com
           Object Computing, Inc. (OCI) www.ociweb.com