Re: [boost] [threads] win32 mutex and read-write mutex

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2006-10-09 04:55:52

"Peter Dimov" <pdimov_at_[hidden]> writes:

> Anthony Williams wrote:
>
>> "Cory Nelson" <phrosty_at_[hidden]> writes:
>>
>>> 2) It doesn't spin at all - giving an app a chance to stay away from
>>> WaitForSingleObject on multithreaded systems will be a good boost to
>>> scalability under typical use.  Win32 critical sections have a
>>> default spin count of 4000 on multithreaded systems.  With
>>> multi-core getting more and more common I think this is an important
>>> aspect to consider.
>>
>> Yes, it's worth considering. I would be intrigued to see what
>> difference it made. I have a dual-core system and a single-core
>> system, so I could see how it performed on both with/without
>> spinning. Any ideas for how to construct a benchmark?
>
> I would advise against spinning. Spinning is a bit of a gamble; it may or 
> may not be a win depending on several factors (average critical section 
> length, spin count, whether other threads in ready state can make better use 
> of the CPU time, context switch performance) and the optimal spin count is 
> very application-dependent.
>
> It isn't a problem if the user gambles with his own money, so to speak, i.e. 
> spins manually with try_lock. However it can be a problem if the 
> implementation gambles with the user's money and loses, since there is no 
> way to make it not spin. IOW, you can easily turn a non-spinning mutex into 
> a spinning mutex, but not vice versa.

How about a try_lock(spin_count) call? or even a lock(spin_count)? Would that
be superfluous?

Anthony
-- 
Anthony Williams
Software Developer
Just Software Solutions Ltd
http://www.justsoftwaresolutions.co.uk