Re: A Quick Question about Threads

From: Mark Sizer (yg-boost-users_at_[hidden])
Date: 2003-07-31 16:42:59

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!
> 
>