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RE: how to get thread priorities to work

Dual core processor. 

-----Original Message-----
From: Lubashev, Igor [] 
Sent: Monday, May 02, 2011 5:51 PM
To: Burkhardt, Glenn;
Subject: RE: how to get thread priorities to work

Without looking too much into this, are you trying this on a multi-core
machine (either multiple cores or one hyperthreading core)?  

- Igor

-----Original Message-----
[] On Behalf Of Burkhardt,
Sent: Monday, May 02, 2011 5:43 PM
Subject: how to get thread priorities to work

I've been puzzling over this for way too long now.  I can't seem to get
thread priorities to work.  Any help will be appreciated.  

For the code that follows, I would expect that only one of the threads
would run, and the counter for the lower priority thread would never
increment.  But that's not the case, on both a WinXP and Win7 system
(built with MinGW 10/30/2010, gcc 4.5.2).  The counter values for the
two threads are close to being the same (e.g., 94686137, 99999999).


#include <math.h>
#include <windows.h>
#include <stdio.h>
#include <pthread.h>
#include <errno.h>

void sleep10(int *cnt) {
    double x;
    for (int i=0; i < 100000000; i++) {
        x = sin(1.0/(1.0+i));
        *cnt = i;

void printError() {
    char *msg;
    int errorCode = GetLastError();
                  | FORMAT_MESSAGE_FROM_SYSTEM
                  0, errorCode, 0, (LPTSTR)&msg, 0, 0);
    printf("error=%d: %s\n", errorCode, msg);

void *thread(void *count) {
    printf("%p: %d\n", count, GetThreadPriority(GetCurrentThread()));

    printf("%p exit\n", count);
    return 0;

int main() {
    struct sched_param spMax, spMin;
    pthread_attr_t attrMax, attrMin;
    pthread_t tMax, tMin;
    int minCount, maxCount;

    spMax.sched_priority = sched_get_priority_max(SCHED_OTHER);
    spMin.sched_priority = sched_get_priority_min(SCHED_OTHER);

    pthread_attr_setschedparam(&attrMax, &spMax);
    pthread_attr_setschedparam(&attrMin, &spMin);

    pthread_create(&tMax, &attrMax, thread, &maxCount);
    pthread_create(&tMin, &attrMin, thread, &minCount);

    printf("join %d\n", GetThreadPriority(GetCurrentThread()));
    pthread_join(tMax, 0);

    printf("%p: %d, %p: %d\n", &minCount, minCount, &maxCount,

    return 0;

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