Get/Set the pthread scheduling policy in Linux

The code below is a sample provided by the book in my Operating Systems course. When compiling it I get the error shown below it.

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5

int main(int argc, char *argv[])
{
    int i, policy;
    pthread_t tid[NUM_THREADS];
    pthread_attr_t attr;

    pthread_attr_init(&attr);

    if(pthread_attr_getschedpolicy(&attr, &policy) != 0)
        fprintf(stderr, "Unable to get policy.n");
    else{
        if(policy == SCHED_OTHER)
            printf("SCHED_OTHERn");
        else if(policy == SCHED_RR)
            printf("SCHED_RRn");
        else if(policy == SCHED_FIFO)
            printf("SCHED_FIFOn");
    }

    if(pthread_attr_setschedpolicy(&attr, SCHED_FIFO) != 0)
        fprintf(stderr, "Unable to set policy.n");
    /* create the threads */
    for(i = 0; i < NUM_THREADS; i++)
        pthread_create(&tid[i], &attr, runner, NULL);
    /* now join on each thread */
    for(i = 0; i < NUM_THREADS; i++)
        pthread_join(tid[i], NULL);
}

/* Each thread will begin control in this function */
void *runner(void *param)
{
    /* do some work... */

    pthread_exit(0);
}

I compiled it using this command…

gcc linux_scheduling.c -o scheduling

However, I get this error.

linux_scheduling.c:32:34: error: 'runner' undeclared (first use in this function)   
pthread_create(&tid[i], &attr, runner, NULL);
                               ^
linux_scheduling.c:32:34: note: each undeclared identifier is report only once for each function it appears in

I tried adding -pthread:

gcc linux_scheduling.c -o scheduling -pthread

but the error remains.

Thanks for your help!

Answer

You have the correct compiling command:

gcc linux_scheduling.c -o scheduling -pthread

but you need to put:

void *runner(void *param);

ahead of the start of main to declare it:

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5

void *runner(void *param);

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