RE: [boost] Re: Threads: New Win32 Implementation

From: Bill Wade (bill.wade_at_[hidden])
Date: 2000-09-08 10:06:01

> From: William Kempf [mailto:sirwillard_at_[hidden]]

> > > Uhmmm... I'd have to see a concrete example.  Other than a slight
> > > performance hit I can think of no reason why the locks must
> overlap
> > > this way.

Suppose I want to implement wait()?  To paraphrase, the current windows
sample code has:

wait(Lock& lock)
{
  ...
  lock.mutex.unlock()
  ...
  lock.mutex.lock();
  ...
}

Strictly speaking there is no overlap involved here.  However, I believe
that you're suggesting that if I want to write wait() using the boost
interface I should use something like

wait(auto_ptr<Lock>& lock, Mutex& mutex)
{
  ...
  lock.release();
  ...
  lock.reset(new Lock(mutex));
  ...
}

Not only does this version of the code have a "slight performance hit", but
the exception safety may also be compromised.  It is plausible that the
first version always succeeds.  Clearly the second version may fail because
of a failure to allocate memory.  The second version might also change the
dynamic type of *lock (say from a LoggingLock to a plain old Lock).