Manpage of PTHREAD_SETSCHEDPARAM

PTHREAD_SETSCHEDPARAM

Section: Linux Programmer's Manual (3)
Updated: 2015-08-08
Index
 

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.

policyspecifies the new scheduling policy for thread. The supported values for policy, and their semantics, are described in sched(7).

The structure pointed to by paramspecifies 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 policyand 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 threadare not changed.  

ERRORS

Both of these functions can fail with the following error:
ESRCH
No thread with the ID threadcould be found.

pthread_setschedparam() may additionally fail with the following errors:

EINVAL
policyis not a recognized policy, or paramdoes 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).
InterfaceAttributeValue
pthread_setschedparam(), pthread_getschedparam() Thread safetyMT-Safe
 

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).  

EXAMPLE

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_FIFOwith a priority of 10, and initializes a thread attributes object with a scheduling policy attribute of SCHED_RRand 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 eScheduler settings of main thread
    policy=SCHED_FIFO, priority=10

Scheduler settings in aqattraq
    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 iScheduler settings of main thread
    policy=SCHED_FIFO, priority=10

Scheduler settings in aqattraq
    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 ioption, the output would have been the same, since PTHREAD_INHERIT_SCHEDis 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("                 aqexplicitaq or aqinheritaq\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 aqfaq: *policy = SCHED_FIFO;     return 1;
    case aqraq: *policy = SCHED_RR;       return 1;
    case aqoaq: *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 aqaaq: attr_sched_str = optarg;      break;
        case aqAaq: use_null_attrib = 1;          break;
        case aqiaq: inheritsched_str = optarg;    break;
        case aqmaq: 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], "Canaqt 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] == aqeaq)
            inheritsched = PTHREAD_EXPLICIT_SCHED;
        else if (inheritsched_str[0] == aqiaq)
            inheritsched = PTHREAD_INHERIT_SCHED;
        else
            usage(argv[0], "Value for -i must be aqeaq or aqiaq\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 aqattraq (-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 aqattraq\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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
Program source
SEE ALSO

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