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/* pthreads_sched_test.c */
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
[[noreturn]]
static void
usage(char *prog_name, char *msg)
{


    if (msg != NULL)


        fputs(msg, stderr);


    fprintf(stderr, "Usage: %s [options]\n", prog_name);


    fprintf(stderr, "Options are:\n");
#define fpe(msg) fprintf(stderr, "\t%s", msg)          /* Shorter */


    fpe("-a<policy><prio> Set scheduling policy and priority in\n");


    fpe("                 thread attributes object\n");


    fpe("                 <policy> can be\n");


    fpe("                     f  SCHED_FIFO\n");


    fpe("                     r  SCHED_RR\n");


    fpe("                     o  SCHED_OTHER\n");


    fpe("-A               Use default thread attributes object\n");


    fpe("-i {e|i}         Set inherit scheduler attribute to\n");


    fpe("                 'explicit' or 'inherit'\n");


    fpe("-m<policy><prio> Set scheduling policy and priority on\n");


    fpe("                 main thread before pthread_create() call\n");


    exit(EXIT_FAILURE);
}
static int
get_policy(char p, int *policy)
{


    switch (p) {


    case 'f': *policy = SCHED_FIFO;     return 1;


    case 'r': *policy = SCHED_RR;       return 1;


    case 'o': *policy = SCHED_OTHER;    return 1;


    default:  return 0;


    }
}
static void
display_sched_attr(int policy, const struct sched_param *param)
{


    printf("    policy=%s, priority=%d\n",


           (policy == SCHED_FIFO)  ? "SCHED_FIFO" :


           (policy == SCHED_RR)    ? "SCHED_RR" :


           (policy == SCHED_OTHER) ? "SCHED_OTHER" :


           "???",


           param->sched_priority);
}
static void
display_thread_sched_attr(char *msg)
{


    int policy, s;


    struct sched_param param;


    s = pthread_getschedparam(pthread_self(), &policy, &param);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_getschedparam");


    printf("%s\n", msg);


    display_sched_attr(policy, &param);
}
static void *
thread_start(void *arg)
{


    display_thread_sched_attr("Scheduler attributes of new thread");


    return NULL;
}
int
main(int argc, char *argv[])
{


    int s, opt, inheritsched, use_null_attrib, policy;


    pthread_t thread;


    pthread_attr_t attr;


    pthread_attr_t *attrp;


    char *attr_sched_str, *main_sched_str, *inheritsched_str;


    struct sched_param param;


    /* Process command-line options.  */


    use_null_attrib = 0;


    attr_sched_str = NULL;


    main_sched_str = NULL;


    inheritsched_str = NULL;


    while ((opt = getopt(argc, argv, "a:Ai:m:")) != -1) {


        switch (opt) {


        case 'a': attr_sched_str = optarg;      break;


        case 'A': use_null_attrib = 1;          break;


        case 'i': inheritsched_str = optarg;    break;


        case 'm': main_sched_str = optarg;      break;


        default:  usage(argv[0], "Unrecognized option\n");


        }


    }


    if (use_null_attrib


        && (inheritsched_str != NULL || attr_sched_str != NULL))


    {


        usage(argv[0], "Can't specify -A with -i or -a\n");


    }


    /* Optionally set scheduling attributes of main thread,


       and display the attributes.  */


    if (main_sched_str != NULL) {


        if (!get_policy(main_sched_str[0], &policy))


            usage(argv[0], "Bad policy for main thread (-m)\n");


        param.sched_priority = strtol(&main_sched_str[1], NULL, 0);


        s = pthread_setschedparam(pthread_self(), policy, &param);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_setschedparam");


    }


    display_thread_sched_attr("Scheduler settings of main thread");


    printf("\n");


    /* Initialize thread attributes object according to options.  */


    attrp = NULL;


    if (!use_null_attrib) {


        s = pthread_attr_init(&attr);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_init");


        attrp = &attr;


    }


    if (inheritsched_str != NULL) {


        if (inheritsched_str[0] == 'e')


            inheritsched = PTHREAD_EXPLICIT_SCHED;


        else if (inheritsched_str[0] == 'i')


            inheritsched = PTHREAD_INHERIT_SCHED;


        else


            usage(argv[0], "Value for -i must be 'e' or 'i'\n");


        s = pthread_attr_setinheritsched(&attr, inheritsched);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setinheritsched");


    }


    if (attr_sched_str != NULL) {


        if (!get_policy(attr_sched_str[0], &policy))


            usage(argv[0], "Bad policy for 'attr' (-a)\n");


        param.sched_priority = strtol(&attr_sched_str[1], NULL, 0);


        s = pthread_attr_setschedpolicy(&attr, policy);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setschedpolicy");


        s = pthread_attr_setschedparam(&attr, &param);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setschedparam");


    }


    /* If we initialized a thread attributes object, display


       the scheduling attributes that were set in the object.  */


    if (attrp != NULL) {


        s = pthread_attr_getschedparam(&attr, &param);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_getschedparam");


        s = pthread_attr_getschedpolicy(&attr, &policy);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_getschedpolicy");


        printf("Scheduler settings in 'attr'\n");


        display_sched_attr(policy, &param);


        pthread_attr_getinheritsched(&attr, &inheritsched);


        printf("    inheritsched is %s\n",


               (inheritsched == PTHREAD_INHERIT_SCHED)  ? "INHERIT" :


               (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :


               "???");


        printf("\n");


    }


    /* Create a thread that will display its scheduling attributes.  */


    s = pthread_create(&thread, attrp, &thread_start, NULL);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_create");


    /* Destroy unneeded thread attributes object.  */


    if (!use_null_attrib) {


      s = pthread_attr_destroy(&attr);


      if (s != 0)


          errc(EXIT_FAILURE, s, "pthread_attr_destroy");


    }


    s = pthread_join(thread, NULL);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_join");


    exit(EXIT_SUCCESS);
}