Provided by: manpages-dev_3.35-0.1ubuntu1_all bug

NAME

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

SYNOPSIS

       #include <pthread.h>

       pthread_setschedparam(pthread_t thread, int policy,
                             const struct sched_param *param);
       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_setscheduler(2).

       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_setscheduler(2).

       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

       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.

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

       POSIX.1-2001  also documents an ENOTSUP ("attempt was made to set the policy or scheduling
       parameters to an unsupported value") error for pthread_setschedparam().

CONFORMING TO

       POSIX.1-2001.

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_setscheduler(2).

EXAMPLE

       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
           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 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|s}         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, 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)
               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 */

           if (main_sched_str != NULL) {
               if (!get_policy(main_sched_str[0], &policy))
                   usage(argv[0], "Bad policy for main thread (-s)\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");
           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);

               s = 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)
               handle_error_en(s, "pthread_create");

           /* Destroy unneeded thread attributes object */

           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),   sched_setscheduler(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)

COLOPHON

       This page is part of release 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.