How to get thread priorities?

Question

linux

Hello!
There is a task:

Write a program that creates two or three threads and reports the priorities of these threads.

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#include <pthread.h>

void * thread_func(void *arg) {
    int loc_id = * (int *) arg;

    for (int i = 0; i < 1; i++) {
        printf("Thread %i is running\n", loc_id);
        sleep(1);
    } 
}

int main(int argc, char * argv[]) {

    int id1, id2, result;
    pthread_t thread1, thread2;

    struct sched_param param1, param2;
    int priority1, priority2;
    int policy1, policy2;
    int res1, res2;

    id1 = 1; 
    result = pthread_create(&thread1, NULL, thread_func, &id1);

    if (result != 0) {
        perror("Creating the first thread");
        return EXIT_FAILURE;
    }

    res1 = pthread_getschedparam(thread1, &policy1, &param1);
    priority1 = param1.sched_priority;
    printf("pr1 = %d\n", priority1);

    id2 = 2;
    result = pthread_create(&thread2, NULL, thread_func, &id2);

    if (result != 0) {
        perror("Creating the second thread");
        return EXIT_FAILURE;
    }

    res2 = pthread_getschedparam(thread2, &policy2, &param2);
    priority2 = param2.sched_priority;
    printf("pr2 = %d\n", priority2);

    result = pthread_join(thread1, NULL);

    if (result != 0) {
        perror("Joining the first thread");
        return EXIT_FAILURE;
    }

    result = pthread_join(thread2, NULL);

    if (result != 0) {
        perror("Joining the second thread");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

With the help of lines

res1 = pthread_getschedparam(thread1, &policy1, &param1);
priority1 = param1.sched_priority;
printf("pr1 = %d\n", priority1);

res2 = pthread_getschedparam(thread2, &policy2, &param2);
priority2 = param2.sched_priority;
printf("pr2 = %d\n", priority2);

I'm trying to get the priorities of the first and second thread, respectively, but I get zero values.
Could you tell me how to correctly create several threads and display their priorities, which will differ from zero.

Answer 1

You seem to be doing everything right, although you need to call a function to set the thread priorities, and only then can you display them. Read more here: man7.org/linux/man-pages/man3/pthread_setschedpara...