pthread_setschedparam(3) — Linux manual page


pthread_...chedparam(3) Library Functions Manual pthread_...chedparam(3)

NAME         top

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

LIBRARY         top

       POSIX threads library (libpthread, -lpthread)

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 *restrict policy,
                                 struct sched_param *restrict param);

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 pthread_mutexattr_setprotocol(3)).

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 pthread_setschedparam().

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ pthread_setschedparam(),            │ Thread safety │ MT-Safe │
       │ pthread_getschedparam()             │               │         │

STANDARDS         top


HISTORY         top

       glibc 2.0 POSIX.1-2001.

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 sched(7).

EXAMPLES         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

           # ./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 <errno.h>
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.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))
                   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)
                   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);

               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)

Linux man-pages (unreleased)     (date)          pthread_...chedparam(3)

Pages that refer to this page: sched_setattr(2)sched_setscheduler(2)pthread_attr_setinheritsched(3)pthread_attr_setschedparam(3)pthread_attr_setschedpolicy(3)pthread_setschedprio(3)aio(7)sched(7)