Subj : Re: Challenge: Multithreading & Synchronization
To   : comp.programming.threads
From : Uenal Mutlu
Date : Sat May 21 2005 02:49 am

"Uenal Mutlu" wrote
> "Uenal Mutlu" wrote
> > "David Schwartz" wrote
> > >
> > > "Uenal Mutlu" wrote in message
> > >
> > > > It depends on the situation.
> > > > In a time-critical application I usually do the following:
> > > >  while (!fMyFlag)
> > > >     MyYield();    // gives up the rest of the time slice, ie.
> > > > SwitchToOtherThread
> > > >  //...
> > >
> > >     And if there is no other thread?
> >
> > You don't know what's inside in my MyYield().
> > And: if there is no other thread then fMyFlag hardly can be set.
> > FYI/Hint: I don't use Sleep(0)
> >
> > > > in a non time critical situation I mostly do use something like that:
> > > >  while (!fMyFlag)
> > > >     MySleep(100);    // sleeps 100 ms
> > > >  //...
> > >
> > >     Hard to imagine a mutex in a non-time critical situation. Why
> > > deliberately write bad code?
> >
> > Sorry, I don't understand. The code above has not necessarily something
> > todo with mutex use at all. It is just a condition variable lookup from inside
> > application code.
> >
> > > > As said, in the examples above the variable fMyFlag is an atomic type,
> > > > because
> > > > it is accessed by at least 2 threads.
> > >
> > >     The use of an atomic type is insufficient. For platform-specific code,
> > > memory barriers or interlocked operations must be used. For portable code,
> > > mutexes must be used.
> >
> > You don't know how my atomic counter class actually is implemented.
> > And you also seem to have overlooked what I wrote in my prev posting:
> > "I personally do use an atomic flag (actually it is an atomic counter with the
> > possible values 0 and 1). I've this implemented in a class. Internally it uses
> > InterLockedXXX funcs of the Win32 API."
> >
> > >     Atomic operations are atomic with respect to a single processor only,
> > > that is, code cannot be interrupted or signalled during the operation. They
> > > have no special SMP or multi-threading semantics.
> >
> > I don't agree. If you use the InterLockedXXX then all this is handled automatically by them.
>
> See also this DOC of Micro$oft:
> http://www.microsoft.com/whdc/driver/kernel/locks.mspx
> (http://download.microsoft.com/download/e/b/a/eba1050f-a31d-436b-9281-92cdfeae4b45/Locks.doc)

Citation from the above DOC:

"InterlockedXxx Routines
The InterlockedXxx routines perform common arithmetic and logical operations atomically,
ensuring correct results on SMP systems. Whenever possible, drivers should use these routines.
Most of them are native processor instructions and therefore do not require a lock.
The InterlockedXxx routines can be used with pageable data. They are usually
implemented inline by the compiler and can be called at any IRQL."

.