pthread_setschedparam

SYNOPSIS
       #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
       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  parame-
       ters 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_mutex-
       attr_setprotocol(3)).

RETURN VALUE
       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
       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
       errors:

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

       +-------------------------+---------------+---------+
       |Interface                | Attribute     | Value   |
       +-------------------------+---------------+---------+
       |pthread_setschedparam(), | Thread safety | MT-Safe |
       |pthread_getschedparam()  |               |         |
       +-------------------------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       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).

EXAMPLE
       The program below demonstrates the use of  pthread_setschedparam()  and
       pthread_getschedparam(), as well as the use of a number of other sched-
       uling-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 schedul-
       ing  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
           Password:
           # ./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 prior-
       ity 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.

       ity 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");
           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;
           }
       }

       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;
       }

       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 */

           printf("\n");

           /* 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;
               else
                   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);

               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");

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       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
       This page is part of release 4.04 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
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-08-08          PTHREAD_SETSCHEDPARAM(3)
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