Subj : Re: Boost.Threads on its way to C++0x
To   : comp.programming.threads
From : gottlobfrege
Date : Wed Apr 27 2005 05:07 pm


Torsten Robitzki wrote:
> gottlobfrege@gmail.com wrote:
>
> >
> >    void ensure_initted()
> >    {
> >       if (!AtomicExchange(&started, true))
> >       {
> >          InitCriticalSection(&cs);
> >          AtomicExchange(&initted, true);
> > 	}
> > 	else
> > 	{
> >          // There's better ways to do this than spinning,
> >          // but this is make the example shorter.
> >          // In fact, this example has a starvation problem,
> >          // if this thread has a higher priority
> >          // than the init thread.
> >          // (ie may never get a chance to be initted)
> >
> >          while (!AtomicRead(&initted))
> >          {
> >              Sleep(1);
> >          }
> >       }
> >    }
>
> When a first thread executes the first call to AtomicExchange() every

> other thread will leave the function immediately after the call to
this
> function without ensuring that the first thread finished the call to
> InitCriticalSection(). So the call to EnterCriticalSection() can
operate
> on an unitialized cs.
>
> regards
> Torsten

I don't see that.  The first thread (sees started as 0 and) sets
*started* to true, and goes into the init code.

The next thread sees started as true, goes and waits for *initted* to
become true.

What am I missing?  It wasn't meant to be a good example, but I thought
at least that much worked.

.