pthread_getattr_default_np(3)

NAME
pthread_getattr_default_np, pthread_setattr_default_np, - get or set default thread-creation attributes

LIBRARY
POSIX threads library (libpthread, -lpthread)

SYNOPSIS
#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <pthread.h>

int pthread_getattr_default_np(pthread_attr_t *attr);
int pthread_setattr_default_np(const pthread_attr_t *attr);

DESCRIPTION
The pthread_setattr_default_np() function sets the default attributes used for creation of a new thread—that is, the attributes that are used when pthread_create(3) is called with a second argument that is NULL. The default attributes are set using the attributes supplied in *attr, a previously initialized thread attributes object. Note the following details about the supplied attributes object:

•   The attribute settings in the object must be valid.

•   The stack address attribute must not be set in the object.

•   Setting the stack size attribute to zero means leave the default stack size unchanged.

The pthread_getattr_default_np() function initializes the thread attributes object referred to by attr so that it contains the default attributes used for thread creation.

ERRORS

EINVAL
    (pthread_setattr_default_np()) One of the attribute settings in attr is invalid, or the stack address attribute is set in attr.

ENOMEM
    (pthread_setattr_default_np()) Insufficient memory.

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe

STANDARDS
GNU; hence the suffix "_np" (nonportable) in their names.

HISTORY
glibc 2.18.

EXAMPLES
The program below uses pthread_getattr_default_np() to fetch the default thread-creation attributes and then displays various settings from the returned thread attributes object. When running the program, we see the following output:

    $ ./a.out
    Stack size:          8388608
    Guard size:          4096
    Scheduling policy:   SCHED_OTHER
    Scheduling priority: 0
    Detach state:        JOINABLE
    Inherit scheduler:   INHERIT

  Program source
    #define _GNU_SOURCE
    #include <err.h>
    #include <errno.h>
    #include <pthread.h>
    #include <stdio.h>
    #include <stdlib.h>

    static void
    display_pthread_attr(pthread_attr_t *attr)
    {
        int s;
        size_t stacksize;
        size_t guardsize;
        int policy;
        struct sched_param schedparam;
        int detachstate;
        int inheritsched;

        s = pthread_attr_getstacksize(attr, &stacksize);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getstacksize");
        printf("Stack size:          %zu\n", stacksize);

        s = pthread_attr_getguardsize(attr, &guardsize);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getguardsize");
        printf("Guard size:          %zu\n", guardsize);

        s = pthread_attr_getschedpolicy(attr, &policy);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getschedpolicy");
        printf("Scheduling policy:   %s\n",
               (policy == SCHED_FIFO) ? "SCHED_FIFO" :
               (policy == SCHED_RR) ? "SCHED_RR" :
               (policy == SCHED_OTHER) ? "SCHED_OTHER" : "[unknown]");

        s = pthread_attr_getschedparam(attr, &schedparam);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getschedparam");
        printf("Scheduling priority: %d\n", schedparam.sched_priority);

        s = pthread_attr_getdetachstate(attr, &detachstate);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getdetachstate");
        printf("Detach state:        %s\n",
               (detachstate == PTHREAD_CREATE_DETACHED) ? "DETACHED" :
               (detachstate == PTHREAD_CREATE_JOINABLE) ? "JOINABLE" :
               "???");

        s = pthread_attr_getinheritsched(attr, &inheritsched);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_attr_getinheritsched");
        printf("Inherit scheduler:   %s\n",
               (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
               (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
               "???");
    }

    int
    main(void)
    {
        int s;
        pthread_attr_t attr;

        s = pthread_getattr_default_np(&attr);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_getattr_default_np");

        display_pthread_attr(&attr);

        exit(EXIT_SUCCESS);
    }

SEE ALSO
pthread_attr_getaffinity_np(3), pthread_attr_getdetachstate(3), pthread_attr_getguardsize(3), pthread_attr_getinheritsched(3), pthread_attr_getschedparam(3), pthread_attr_getschedpolicy(3), pthread_attr_getscope(3), pthread_attr_getstack(3), pthread_attr_getstackaddr(3), pthread_attr_getstacksize(3), pthread_attr_init(3), pthread_create(3), pthreads(7)