Subj : Re: stl & threads
To   : comp.programming.threads
From : Uenal Mutlu
Date : Wed May 25 2005 06:10 am

"David Schwartz" wrote
>
> "Uenal Mutlu" wrote
>
> [snip]
>
> >      bool   IsLockedByAny() const { return cLocked > 0; }
> >      bool   IsLockedByMe()  const { return cLocked > 0 && dwThrId ==
> > GetCurrentThreadId(); }
>
> [snip]
>
> >    private:
> >      CRITICAL_SECTION cs;
> >      size_t           cLocked;
> >      DWORD            dwThrId;
> >      const bool       fRecursiveMutex;
> >  };
>
> [snip]
>
>     Suppose I write code like this:
>
>  while(IsLockedByAny() && !IsLockedByMe()) i++;
>
>     What guarantees that the compiler doesn't optimize away the repeated
> reads of 'cLocked' and spin forever? I admit that it's dumb to do something
> like that, but it's also bad for a mutex class to contain errors.

Yeah, a good argument.
The solution is to make them volatile:
  volatile size_t           cLocked;
  volatile DWORD            dwThrId;

.