Re: [Boost-Users] Re: A Quick Question about Threads

From: Richard Howells (Richard_at_[hidden])
Date: 2003-07-31 17:48:30

Maybe it's a terminology thing. In Win32 the difference between a critical
section and a mutex is that a mutex is a system wide object (ie it is known
in other processes) and a critical section is only available to the threads
of one process.

A critical section can only block those threads that choose to Enter it in
the same way as a mutex can only block those threads that choose to Wait on
it.

I have not done any performance testing but one would expect critical
sections to perform better because they are (mostly) non-kernel code.

Best - Richard

----- Original Message ----- 
From: "Mark Sizer" <yg-boost-users_at_[hidden]>
To: <boost-users_at_[hidden]>
Sent: Thursday, July 31, 2003 10:42 PM
Subject: [Boost-Users] Re: A Quick Question about Threads

> Generically, the difference between critical sections and mutexes is
> immense. In terms of implementation, one never knows.
>
> A critical section blocks EVERYTHING else in the process. A mutex only
> blocks things that are waiting on that particular mutex.
>
> If one is actually getting parallel processing (i.e. multi-processor
> machine), mutexes can be far more performant because only stuff that
> needs to block does - everything else keeps going. Critical sections are
> much easier to manage - in a way they're like a single global mutex.
> Deadlocks are much more difficult.
>
> Back in the day (NT 3.51), Windows was much more (two orders of
> magnitude) efficient with critical sections than with mutexes. That may
> no longer be true (I hope not, I'm using boost mutexes, now). Threading
> under Windows is not such a good idea anyway, with the exception of
> things that block anyway (e.g. I/O, client/server RPC, etc...). Windows
> doesn't deal well with more than two processors, so what's the point of
> having dozens of threads? They won't run in parallel anyway. State-based
> event engines tend to perform better than multithreading, although I
> find them nightmarish to debug.
>
> I have no clue what any other platform does. I'm hoping Linux scales to
> multiprocessor systems better, but while I've ported the code, I haven't
> run any tests, yet. Anyone have an 8-processor Linux box they want to
> loan me?
>
> - Mark
>
> Paul Grenyer wrote:
>
> > On Thu, 2003-07-31 at 19:48, Jason Winnebeck wrote:
> >
> > Hi
> >
> >
> >>How do you think mutex and CS differ?  From what I understand they
> >>perform the same purpose.  Win32 CS's are recursive lockable, I believe
> >>that is an option or an ability of the boost mutex as well.  I wouldn't
> >>be surprised if it was implemented as CS's in Win32.
> >>
> >
> > I'm wasn't sure there was a difference. I've used Critical Sections
> > before by not mutexes. If they're the same (or similar) so much the
> > better!
> >
> >
>
>
>
>
>
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