pthread_setschedparam

PTHREAD_SETSCHEDPARAM(3)   Linux Programmer's Manual  PTHREAD_SETSCHEDPARAM(3)



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

SYNOPSIS
       #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.

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(7).

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

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       ┌─────────────────────────┬───────────────┬─────────┐
       │Interface                Attribute     Value   │
       ├─────────────────────────┼───────────────┼─────────┤
       │pthread_setschedparam(), │ Thread safety │ MT-Safe │
       │pthread_getschedparam()  │               │         │
       └─────────────────────────┴───────────────┴─────────┘
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

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(7).

EXAMPLES
       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|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");
           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 */

           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);
       }

SEE ALSO
       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)

COLOPHON
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       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2020-06-09          PTHREAD_SETSCHEDPARAM(3)