pthread_setschedparam man page on Archlinux

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       pthread_setschedparam,  pthread_getschedparam - set/get scheduling pol‐
       icy and parameters of a thread

       #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

       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 spec‐
	      ified 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


       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 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
	   # ./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
	       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	prior‐
       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|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" :
		   (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, ¶m);
	   if (s != 0)
	       handle_error_en(s, "pthread_getschedparam");

	   printf("%s\n", msg);
	   display_sched_attr(policy, ¶m);

       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);

	       s = pthread_setschedparam(pthread_self(), policy, ¶m);
	       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))
			   "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, ¶m);
	       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, ¶m);
	       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, ¶m);

	       s = 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 */

	   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");


       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),

       This page is part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at

Linux				  2008-11-17	      PTHREAD_SETSCHEDPARAM(3)

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