Re: SetThreadIdealProcessor()?

From:
Tom Handal <tom.handal@gmail.com>
Newsgroups:
microsoft.public.vc.language
Date:
Mon, 14 Jun 2010 22:54:50 -0700 (PDT)
Message-ID:
<4b9e551c-0cb0-4b0c-8003-70b913b0b235@u3g2000prl.googlegroups.com>
On Jun 13, 4:32 pm, Vincent Fatica <vi...@blackholespam.net> wrote:

On Sun, 13 Jun 2010 23:01:19 +0100, Stephen Wolstenholme

<st...@tropheus.demon.co.uk> wrote:

|On 13 Jun 2010 12:43:54 -0400, Vincent Fatica|<vi...@blackholespam.net> =

wrote:

|
|>of SetThreadIdealProcessor(), the docs say:
|>
|>>dwIdealProcessor [in]
|>
|>>The number of the preferred processor for the thread. This value is ze=

ro-based. If this parameter is MAXIMUM_PROCESSORS, the function returns the=
 current ideal processor without changing it.

|>
|>>Return Value
|>
|>>If the function succeeds, the return value is the previous preferred p=

rocessor.

|>
|>But this code (VC9, XPSP3) gives the results below it:
|>
|>>for ( INT i=0; i<10; i++ )
|>> wprintf(L"%u ", SetThreadIdealProcessor(GetCurrentThread(=

), MAXIMUM_PROCESSORS));

|>
|>1 0 3 2 1 0 3 2 1 0 [yes, they cycle]
|>
|>What's up with that?
|
|It suggests you are starting multiple threads on a four processor
|machine.
|
|I start eight threads on a two processor machine and get returns 0 1 0
|1 0 1 0 1.

It's a 4-processor machine, but I'm not starting any threads.

#include <windows.h>
#include <stdio.h>
INT wmain ( INT argc, WCHAR **argv )
{
        for ( INT i=0; i<10; i++ )
                wprintf(L"%u ", SetThreadIdealProcessor(G=

etCurrentThread(),

MAXIMUM_PROCESSORS));
        return 0;

}

g:\projects\test\release> test.exe
0 3 2 1 0 3 2 1 0 3
--
 - Vince


Windows uses a round-robin scheduling algorithm. My guess is that
each time you call this function, the thread is being re-assigned to
the next available processor. Since the scheduler works in a round-
robin fashion, you see this effect. This is my educated guess :-)

http://www.installsetupconfig.com/win32programming/threadprocesssynchroniza=
tionapis11_45.html

http://msdn.microsoft.com/en-us/library/ms685100(VS.85).aspx

Hope this helps...

Tom Handal

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