procpri/t_setpriority.c

/* t_setpriority.c

   Demonstrate the use of setpriority(2) and getpriority(2) to change and
   retrieve a process's nice value.

   Usage: t_setpriority {p|g|u} id priority
*/
#include <sys/time.h>
#include <sys/resource.h>
#include "tlpi_hdr.h"

int
main(int argc, char *argv[])
{
    int which, prio;
    id_t who;

    if (argc != 4 || strchr("pgu", argv[1][0]) == NULL)
        usageErr("%s {p|g|u} who priority\n"
                "    set priority of: p=process; g=process group; "
                "u=processes for user\n", argv[0]);

    /* Set nice value according to command-line arguments */

    which = (argv[1][0] == 'p') ? PRIO_PROCESS :
                (argv[1][0] == 'g') ? PRIO_PGRP : PRIO_USER;
    who = getLong(argv[2], 0, "who");
    prio = getInt(argv[3], 0, "prio");

    if (setpriority(which, who, prio) == -1)
        errExit("setpriority");

    /* Retrieve nice value to check the change */

    errno = 0;                  /* Because successful call may return -1 */
    prio = getpriority(which, who);
    if (prio == -1 && errno != 0)
        errExit("getpriority");

    printf("Nice value = %d\n", prio);

    exit(EXIT_SUCCESS);
}