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

#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);
Compile and link with -pthread.

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.

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

These functions are available in glibc since version 2.18.

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

These functions are nonstandard GNU extensions; hence the suffix "_np" (nonportable) in their names.

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

#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define errExitEN(en, msg) \
                        do { errno = en; perror(msg); \
                             exit(EXIT_FAILURE); } while (0)
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)
        errExitEN(s, "pthread_attr_getstacksize");
    printf("Stack size:          %zd\n", stacksize);
    s = pthread_attr_getguardsize(attr, &guardsize);
    if (s != 0)
        errExitEN(s, "pthread_attr_getguardsize");
    printf("Guard size:          %zd\n", guardsize);
    s = pthread_attr_getschedpolicy(attr, &policy);
    if (s != 0)
        errExitEN(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)
        errExitEN(s, "pthread_attr_getschedparam");
    printf("Scheduling priority: %d\n", schedparam.sched_priority);
    s = pthread_attr_getdetachstate(attr, &detachstate);
    if (s != 0)
        errExitEN(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)
        errExitEN(s, "pthread_attr_getinheritsched");
    printf("Inherit scheduler:   %s\n",
            (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
            (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
main(int argc, char *argv[])
    int s;
    pthread_attr_t attr;
    s = pthread_getattr_default_np(&attr);
    if (s != 0)
        errExitEN(s, "pthread_getattr_default_np");

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)

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