Re: [boost] [thread] best practice to lock multiple mutexes

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-02-29 13:38:01

Anthony Williams:
...

> Finally, though the BTS-based mutex is faster than the boost 1.35 one in 
> most
> cases, the CRITICAL_SECTION based version is actually very competitive, 
> and
> fastest in many cases. I found this surprising, because it didn't match my 
> prior
> experience, but might be a consequence of the (generally undesirable) 
> properties
> of CRITICAL_SECTIONS: some threads end up getting all the locks, and 
> running to
> completion very quickly, thus reducing the running thread count for the
> remainder of the test.

This is a general property of artificial benchmarks that do nothing outside 
of the critical region. In such a case running the same thread to completion 
is indeed the most efficient way to accomplish the overall task.

Sensible user code will generally try to keep its critical regions short and 
move as much of the code outside as possible (to increase the amount of 
available parallelism).