pthread multithreading with priority

freeindy · 09-08-2011, 10:02 AM

Hi,

I'm trying to run a multi-threading process (under my ubuntu) with different priorities but can't make it to work. The program is:

Code:

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

pthread_t task_2_id;

void* task_2(void* arg)
{
    int type;
    struct sched_param sch_params;
    pthread_getschedparam(task_2_id, &type, &sch_params);
    while(1)
    {
        printf("TASK 2 priority: %d\n", sch_params.sched_priority);
        sleep(1);
    }
}

int main(void)
{
    int type;
    int status;
    pthread_attr_t attr;
    struct sched_param sch_params;

    pthread_attr_init(&attr);
    pthread_attr_getschedparam(&attr, &sch_params);
    sch_params.sched_priority = 100;
    pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
    pthread_attr_setschedparam(&attr,&sch_params);

    /* Main task with priority */
    status = pthread_create(&task_2_id,
                            &attr,
                            task_2,
                            NULL);

    printf("Status: %d\n", status);

    pthread_getschedparam(pthread_self(), &type, &sch_params);

    while(1)
    {
        printf("Maint task priority: %d\n", sch_params.sched_priority);
        sleep(1);
    }

    exit(0);
}

But at my out in the console is:

Code:

$ ./my_app 
Status: 0
Maint task priority: 0
TASK 2 priority: 0
Maint task priority: 0
TASK 2 priority: 0
Maint task priority: 0
TASK 2 priority: 0

I thought I could set a priority (100-140) to a task under linux. Or Am I wrong? Or simply, is there is something wrong with my code?

Thanks in advance,
Indy

dwhitney67 · 09-08-2011, 11:09 AM

Check the value that is returned by these two functions, and report back whether they indicate the call was successful.

Code:

pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
pthread_attr_setschedparam(&attr,&sch_params);

freeindy · 09-09-2011, 05:03 AM

Sorry. Silly of me. I should have checked.
There were problems setting schedule parameters. So I changed the code to the following in main:

Code:

printf("Priority (min-max): %d-%d\n",
           sched_get_priority_min(sch_type),
           sched_get_priority_max(sch_type));


    pthread_attr_init(&attr);
    status = pthread_attr_getschedparam(&attr, &sch_params);
    printf("getschedparam status: %d\n", status);
    sch_params.sched_priority = 50;
    status = pthread_attr_setschedpolicy(&attr, SCHED_RR);
    printf("setschedpolicy status: %d\n", status);
    status = pthread_attr_setschedparam(&attr,&sch_params);
    printf("setschedparam status: %d\n", status);

    /* Main task with priority */
    status = pthread_create(&task_2_id,
                            &attr,
                            task_2,
                            NULL);
    printf("pthread_create status: %d\n", status);

And the output is:

Code:

$ ./my_app 
Priority (min-max): 1-99
getschedparam status: 0
setschedpolicy status: 0
setschedparam status: 0
pthread_create status: 0
Maint task priority: 0
TASK 2 priority: 0
Maint task priority: 0
TASK 2 priority: 0
Maint task priority: 0
TASK 2 priority: 0

So even though my priority is 50 (between 1-99), I still don't get the priority I want. One thing is concerning me is that I'm running latest Ubuntu without real-time kernel patch. Does that have any affect? I have also tried to run the binary as normal user and sudo but without any success, i.e same result.

Thanks again,
Indy

archieval · 09-09-2011, 05:11 AM

Check this old post:
http://www.linuxquestions.org/questi...hreads-459117/

Regards,
archieval