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


     #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.


     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
         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-


     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  also documents an ENOTSUP ("attempt was made to set the policy
     or  scheduling  parameters  to  an  unsupported   value")   error   for


     For   an   explanation   of   the  terms  used  in  this  section,  see
     allbox;  lbw24   lb   lb   l   l   l.    Interface Attribute Value   T{
     pthread_setschedparam(),       pthread_getschedparam()      T}   Thread
     safety  MT-Safe


     POSIX.1-2001, POSIX.1-2008.


     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
         Password:  #  ./a.out  -mf10  -ar20 -i e Scheduler settings of main
             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|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;
         } }
     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 (-m)\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");
         /* 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, &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" :
         /* 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 */
         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); }


     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)


     This page is part of release 4.16 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


/data/webs/external/dokuwiki/data/pages/man/pthread_getschedparam.txt · Last modified: 2019/05/17 09:47 by

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