pthread_setschedparam

       icy 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 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_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_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:
       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 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.

           # ./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

   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" :

               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);
               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");
           }

           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
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       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.



Linux                             2008-11-17          PTHREAD_SETSCHEDPARAM(3)
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