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           #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.


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


           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.


           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


           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


           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 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
               # ./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
           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
           /* 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");
           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" :
               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 (-s)\n");
                   param.sched_priority = strtol(&main_sched_str[1], NULL, 0);
                   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" :
               s = pthread_join(thread, NULL);
               if (s != 0)
                   handle_error_en(s, "pthread_join");


           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),

    Linux 2008-11-17 PTHREAD_SETSCHEDPARAM(3)


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