pthread_attr_getinheritsched example c c++

NAME

pthread_attr_getinheritsched, pthread_attr_setinheritsched - get and set the inheritsched attribute (REALTIME THREADS)

SYNOPSIS

#include <pthread.h>

int pthread_attr_getinheritsched(const pthread_attr_t *restrict attr,
       int *restrict inheritsched);
int pthread_attr_setinheritsched(pthread_attr_t *attr,
       int inheritsched); 

DESCRIPTION

The pthread_attr_getinheritsched(), and pthread_attr_setinheritsched() functions, respectively, shall get and set the inheritsched attribute in the attr argument.
When the attributes objects are used by pthread_create(), the inheritsched attribute determines how the other scheduling attributes of the created thread shall be set.
The supported values of inheritsched shall be:

PTHREAD_INHERIT_SCHED

Specifies that the thread scheduling attributes shall be inherited from the creating thread, and the scheduling attributes in this attrargument shall be ignored.

PTHREAD_EXPLICIT_SCHED

Specifies that the thread scheduling attributes shall be set to the corresponding values from this attributes object.

The symbols PTHREAD_INHERIT_SCHED and PTHREAD_EXPLICIT_SCHED are defined in the <pthread.h> header. (pthread_attr_getinheritsched, pthread_attr_setinheritsched)
The following thread scheduling attributes defined by IEEE Std 1003.1-2001 are affected by the inheritsched attribute: scheduling policy (schedpolicy), scheduling parameters ( schedparam), and scheduling contention scope ( contentionscope).

RETURN VALUE

If successful, the pthread_attr_getinheritsched() and pthread_attr_setinheritsched() functions shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The pthread_attr_getinheritsched() function may fail if:

[EINVAL]

The value specified by attr does not refer to an initialized thread attribute object.

The pthread_attr_setinheritsched() function may fail if:

[EINVAL]

The value of inheritsched is not valid.

[EINVAL]

The value specified by attr does not refer to an initialized thread attribute object.

[ENOTSUP]

An attempt was made to set the attribute to an unsupported value.

These functions shall not return an error code of [EINTR].

Example of (pthread_attr_getinheritsched, pthread_attr_setinheritsched)

#define _GNU_SOURCE     /* To get pthread_getattr_np() declaration */
#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
display_pthread_attr(pthread_attr_t *attr, char *prefix)
{
    int s, i;
    size_t v;
    void *stkaddr;
    struct sched_param sp;

   s = pthread_attr_getdetachstate(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getdetachstate");
    printf("%sDetach state        = %s\n", prefix,
            (i == PTHREAD_CREATE_DETACHED) ? "PTHREAD_CREATE_DETACHED" :
            (i == PTHREAD_CREATE_JOINABLE) ? "PTHREAD_CREATE_JOINABLE" :
            "???");

   s = pthread_attr_getscope(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getscope");
    printf("%sScope               = %s\n", prefix,
            (i == PTHREAD_SCOPE_SYSTEM)  ? "PTHREAD_SCOPE_SYSTEM" :
            (i == PTHREAD_SCOPE_PROCESS) ? "PTHREAD_SCOPE_PROCESS" :
            "???");

   s = pthread_attr_getinheritsched(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getinheritsched");
    printf("%sInherit scheduler   = %s\n", prefix,
            (i == PTHREAD_INHERIT_SCHED)  ? "PTHREAD_INHERIT_SCHED" :
            (i == PTHREAD_EXPLICIT_SCHED) ? "PTHREAD_EXPLICIT_SCHED" :
            "???");

   s = pthread_attr_getschedpolicy(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getschedpolicy");
    printf("%sScheduling policy   = %s\n", prefix,
            (i == SCHED_OTHER) ? "SCHED_OTHER" :
            (i == SCHED_FIFO)  ? "SCHED_FIFO" :
            (i == SCHED_RR)    ? "SCHED_RR" :
            "???");

   s = pthread_attr_getschedparam(attr, &sp);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getschedparam");
    printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

   s = pthread_attr_getguardsize(attr, &v);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getguardsize");
    printf("%sGuard size          = %d bytes\n", prefix, v);

   s = pthread_attr_getstack(attr, &stkaddr, &v);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getstack");
    printf("%sStack address       = %p\n", prefix, stkaddr);
    printf("%sStack size          = 0x%x bytes\n", prefix, v);
}

static void *
thread_start(void *arg)
{
    int s;
    pthread_attr_t gattr;

   /* pthread_getattr_np() is a non-standard GNU extension that
       retrieves the attributes of the thread specified in its
       first argument */

   s = pthread_getattr_np(pthread_self(), &gattr);
    if (s != 0)
        handle_error_en(s, "pthread_getattr_np");

   printf("Thread attributes:\n");
    display_pthread_attr(&gattr, "\t");

   exit(EXIT_SUCCESS);         /* Terminate all threads */
}

int
main(int argc, char *argv[])
{
    pthread_t thr;
    pthread_attr_t attr;
    pthread_attr_t *attrp;      /* NULL or &attr */
    int s;

   attrp = NULL;

   /* If a command-line argument was supplied, use it to set the
       stack-size attribute and set a few other thread attributes,
       and set attrp pointing to thread attributes object */

   if (argc > 1) {
        int stack_size;
        void *sp;

       attrp = &attr;

       s = pthread_attr_init(&attr);
        if (s != 0)
            handle_error_en(s, "pthread_attr_init");

       s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setdetachstate");

       s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setinheritsched");

       stack_size = strtoul(argv[1], NULL, 0);

       s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
        if (s != 0)
            handle_error_en(s, "posix_memalign");

       printf("posix_memalign() allocated at %p\n", sp);

       s = pthread_attr_setstack(&attr, sp, stack_size);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setstack");
    }

   s = pthread_create(&thr, attrp, &thread_start, NULL);
    if (s != 0)
        handle_error_en(s, "pthread_create");

   if (attrp != NULL) {
        s = pthread_attr_destroy(attrp);
        if (s != 0)
            handle_error_en(s, "pthread_attr_destroy");
    }

   pause();    /* Terminates when other thread calls exit() */
}