NAME         top

       pthread_setschedparam,  pthread_getschedparam  -  set/get  scheduling
       policy and parameters of a thread

SYNOPSIS         top

       #include <pthread.h>

       int pthread_setschedparam(pthread_t thread, int policy,
                                 const struct sched_param *param);
       int pthread_getschedparam(pthread_t thread, int *policy,
                                 struct sched_param *param);

       Compile and link with -pthread.

DESCRIPTION         top

       The pthread_setschedparam() function sets the scheduling policy and
       parameters of the thread thread.

       policy specifies the new scheduling policy for thread.  The supported
       values for policy, and their semantics, are described in sched(7).

       The structure pointed to by param specifies the new scheduling
       parameters for thread.  Scheduling parameters are maintained in the
       following structure:

           struct sched_param {
               int sched_priority;     /* Scheduling priority */

       As can be seen, only one scheduling parameter is supported.  For
       details of the permitted ranges for scheduling priorities in each
       scheduling policy, see sched(7).

       The pthread_getschedparam() function returns the scheduling policy
       and parameters of the thread thread, in the buffers pointed to by
       policy and param, respectively.  The returned priority value is that
       set by the most recent pthread_setschedparam(),
       pthread_setschedprio(3), or pthread_create(3) call that affected
       thread.  The returned priority does not reflect any temporary
       priority adjustments as a result of calls to any priority inheritance
       or priority ceiling functions (see, for example,
       pthread_mutexattr_setprioceiling(3) and

RETURN VALUE         top

       On success, these functions return 0; on error, they return a nonzero
       error number.  If pthread_setschedparam() fails, the scheduling
       policy and parameters of thread are not changed.

ERRORS         top

       Both of these functions can fail with the following error:

       ESRCH  No thread with the ID thread could be found.

       pthread_setschedparam() may additionally fail with the following

       EINVAL policy is not a recognized policy, or param does not make
              sense for the policy.

       EPERM  The caller does not have appropriate privileges to set the
              specified scheduling policy and parameters.

       POSIX.1 also documents an ENOTSUP ("attempt was made to set the
       policy or scheduling parameters to an unsupported value") error for

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                Attribute     Value   │
       │pthread_setschedparam(), │ Thread safety │ MT-Safe │
       │pthread_getschedparam()  │               │         │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       For a description of the permissions required to, and the effect of,
       changing a thread's scheduling policy and priority, and details of
       the permitted ranges for priorities in each scheduling policy, see

EXAMPLE         top

       The program below demonstrates the use of pthread_setschedparam() and
       pthread_getschedparam(), as well as the use of a number of other
       scheduling-related pthreads functions.

       In the following run, the main thread sets its scheduling policy to
       SCHED_FIFO with a priority of 10, and initializes a thread attributes
       object with a scheduling policy attribute of SCHED_RR and a
       scheduling priority attribute of 20.  The program then sets (using
       pthread_attr_setinheritsched(3)) the inherit scheduler attribute of
       the thread attributes object to PTHREAD_EXPLICIT_SCHED, meaning that
       threads created using this attributes object should take their
       scheduling attributes from the thread attributes object.  The program
       then creates a thread using the thread attributes object, and that
       thread displays its scheduling policy and priority.

           $ su      # Need privilege to set real-time scheduling policies
           # ./a.out -mf10 -ar20 -i e
           Scheduler settings of main thread
               policy=SCHED_FIFO, priority=10

           Scheduler settings in 'attr'
               policy=SCHED_RR, priority=20
               inheritsched is EXPLICIT

           Scheduler attributes of new thread
               policy=SCHED_RR, priority=20

       In the above output, one can see that the scheduling policy and
       priority were taken from the values specified in the thread
       attributes object.

       The next run is the same as the previous, except that the inherit
       scheduler attribute is set to PTHREAD_INHERIT_SCHED, meaning that
       threads created using the thread attributes object should ignore the
       scheduling attributes specified in the attributes object and instead
       take their scheduling attributes from the creating thread.

           # ./a.out -mf10 -ar20 -i i
           Scheduler settings of main thread
               policy=SCHED_FIFO, priority=10

           Scheduler settings in 'attr'
               policy=SCHED_RR, priority=20
               inheritsched is INHERIT

           Scheduler attributes of new thread
               policy=SCHED_FIFO, priority=10

       In the above output, one can see that the scheduling policy and
       priority were taken from the creating thread, rather than the thread
       attributes object.

       Note that if we had omitted the -i i option, the output would have
       been the same, since PTHREAD_INHERIT_SCHED is the default for the
       inherit scheduler attribute.

   Program source

       /* pthreads_sched_test.c */

       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
               do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       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");

       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, 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" :

       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)
               handle_error_en(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;

       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)
                   handle_error_en(s, "pthread_setschedparam");

           display_thread_sched_attr("Scheduler settings of main thread");

           /* Initialize thread attributes object according to options */

           attrp = NULL;

           if (!use_null_attrib) {
               s = pthread_attr_init(&attr);
               if (s != 0)
                   handle_error_en(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;
                   usage(argv[0], "Value for -i must be 'e' or 'i'\n");

               s = pthread_attr_setinheritsched(&attr, inheritsched);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setinheritsched");

           if (attr_sched_str != NULL) {
               if (!get_policy(attr_sched_str[0], &policy))
                           "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)
                   handle_error_en(s, "pthread_attr_setschedpolicy");
               s = pthread_attr_setschedparam(&attr, &param);
               if (s != 0)
                   handle_error_en(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)
                   handle_error_en(s, "pthread_attr_getschedparam");
               s = pthread_attr_getschedpolicy(&attr, &policy);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_getschedpolicy");

               printf("Scheduler settings in 'attr'\n");
               display_sched_attr(policy, &param);

               s = pthread_attr_getinheritsched(&attr, &inheritsched);
               printf("    inheritsched is %s\n",
                       (inheritsched == PTHREAD_INHERIT_SCHED)  ? "INHERIT" :
                       (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :

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

           s = pthread_create(&thread, attrp, &thread_start, NULL);
           if (s != 0)
               handle_error_en(s, "pthread_create");

           /* Destroy unneeded thread attributes object */

           if (!use_null_attrib) {
             s = pthread_attr_destroy(&attr);
             if (s != 0)
                 handle_error_en(s, "pthread_attr_destroy");

           s = pthread_join(thread, NULL);
           if (s != 0)
               handle_error_en(s, "pthread_join");


SEE ALSO         top

       getrlimit(2), sched_get_priority_min(2), pthread_attr_init(3),
       pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3),
       pthread_attr_setschedpolicy(3), pthread_create(3), pthread_self(3),
       pthread_setschedprio(3), pthreads(7), sched(7)

COLOPHON         top

       This page is part of release 4.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2015-08-08         PTHREAD_SETSCHEDPARAM(3)