How to do it...

In this recipe, we'll be writing a small program to get the round-robin timeslice by using the sched_rr_get_interval() function:

1. On a new shell, open a new file called schedGetInterval.cpp. We have to include <sched.h> for the scheduler capabilities, <iostream.h> to log to the standard output, and <string.h> to use the strerror function and translate the errno integer into a readable string:

#include <sched.h>
#include <iostream>
#include <string.h>

int main ()
{
    std::cout << "Starting ..." << std::endl;

2. To get the round-robin interval, we have to set the scheduler policy for our process:

    struct sched_param sched;
    sched.sched_priority = 8;
    if (sched_setscheduler(0, SCHED_RR, &sched) == -1)
        std::cout << "sched_setscheduler failed = "
            << strerror(errno) 
                  << std::endl;
    else
        std::cout << "sched_setscheduler, priority set to = " 
                  << sched.sched_priority << std::endl;

3. Now, we can get the interval with the sched_rr_get_interval() function:

    struct timespec tp;
    int retCode = sched_rr_get_interval(0, &tp);
    if (retCode == -1)
    {
        std::cout << "sched_rr_get_interval failed = " 
                  << strerror(errno) << std::endl;
        return 1;
    }    

    std::cout << "timespec sec = " << tp.tv_sec 
              << " nanosec = " << tp.tv_nsec << std::endl;
    std::cout << "End ..." << std::endl;
    return 0;
}

Let's see how this works under the hood.