[boost] Re: Threads

From: jsiek_at_[hidden]
Date: 2000-08-21 09:16:07

Looks like we'll need to do some more research to figure out:

1. Can CV's be implemented portably without the lock during notify()
  restriction? (yes for pthreads, maybe for Win32?)
2. Are there any performance trade-offs?
   (no lock is better with pthreads, Win32?)
3. Should the boost CV interface require lock during notify()?

William Kempf writes:
 > I'm not an expert on pthreads.  Everything that I do know comes from 
 > Pthreads Programming, O'Reilly & Associates, Inc. (a Nutshell book).  
 > To quote them, from page 82:
 > 
 > "It all sounds complicated, but what if the mutex and the condition 
 > variable weren't linked?  If the condition were signaled without a 
 > mutex, the signaling thread might signal the condition before the 
 > waiting thread begins waiting for it -- in which case the waiting 
 > thread would never wake up."
 > 
 > > Perhaps the problem came from how you were implementing CVs
 > > on Win32?
 > 
 > The implementation I have is based on the implementation designed by 
 > Douglas Schmidt (sp?) for the ACE framework.  He's one of the leading 
 > authorities on this subject.  There is a definate race condition in 
 > this implementation if the external mutex isn't locked during the 
 > call to notify().
 > 
 > Sounds like this is a non-issue for pthreads, at least according to 
 > the quote you gave from the standard.  I must admit to be confused on 
 > this subject now, though.  :(