Re: Visual C++ STL - is there a possibility to use spin count CRTs ?

From:

peter koch <peter.koch.larsen@gmail.com>

Newsgroups:

microsoft.public.vc.stl

Date:

Sat, 10 Nov 2007 07:38:02 -0800

Message-ID:

<1194709082.716193.302080@o38g2000hse.googlegroups.com>

On 10 Nov., 13:58, Andre Kaufmann <andre.kaufmann_re_mo...@t-
online.de> wrote:

When I profile our Visual C++ applications from time to time I always
see a high number of context switches, caused by 2 or more threads
iterating through STL vectors.
The context switches are caused by a global critical section used for
example in the vector .end() function. Besides that the number of
context switch can be reduced by storing the vectors end() before
iterating in a local variable, I think it would be anyways better to let
the developer choose, how the globally used critical section is
initialized.

I would for example prefer to use InitializeCriticalSectionAndSpinCount
instead, since most vector operations are using the critical section
only for a short time. This may be different for other applications.
Another option would be to disable synchronization anyways and let the
code using the vector

Offers the Visual C++ STL any possibility to choose the synchronization
method in a multi threaded application on a single vector instance basis ?

At least I've found no such method. Since the number or cores increases
steadily it would be best to offer any user defined synchronization
method, since the likelihood of collisions will rise with the number of
cores.

Andre

I was at first quite surprised to hear that something like
std::vector::end should call a synchronisation primitive in the first
place, but you are right - under certain circumstances it could do so.
But looking at the code, it is obvious that it only does so in order
to assist in debugging. Turning off debugging (at least if you
remember to define _SECURE_STL or whatever the switch is) will remove
the locking completely and also speed your application up in other
areas.

/Peter