pthread_ge...default_np(3)

✨ pthread_ge...default_np(3) ✨

okay bestie so you found a very niche corner of the Library Functions Manual (section 3, the library-calls girlies 💅) and honestly? you ate. this page is about pthread_getattr_default_np and pthread_setattr_default_np, which — no cap — are about the default vibe your threads get born with 🍼✨

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🌸 NAME 🌸

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

(yes there is a lil trailing comma situation in the original name line, we don't talk about her 🫶)

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📚 LIBRARY 📚

POSIX threads library — that's libpthread, linked with -lpthread 🧵

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🧚 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);

so slay, we got two functions, both returning int, both living in <pthread.h>. and yeah, you need that _GNU_SOURCE define up top or she simply will not appear ✨

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💅 DESCRIPTION 💅

so here's the tea, bestie ☕

pthread_setattr_default_np() sets the default attributes used when a brand new thread gets created — like, the attributes that get used when pthread_create(3) is called with a second argument that is NULL 🫶. it's literally the "what happens if you don't specify anything" of thread creation.

you set those defaults using the attributes you hand over in *attr, which has to be a thread attributes object you already initialized. and now, the important details about that object you're passing in, lowkey:

• 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 😌

meanwhile, pthread_getattr_default_np() initializes the thread attributes object pointed to by attr so it contains the default attributes used for thread creation. it's giving "show me the receipts" 🔍

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💀 ERRORS 💀

• EINVAL (pthread_setattr_default_np()) — one of the attribute settings in attr is invalid, or the stack address attribute is set in attr. nope, not today ✋
• ENOMEM (pthread_setattr_default_np()) — insufficient memory. the memory said "no ❤️"

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👑 ATTRIBUTES 👑

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

• pthread_getattr_default_np(), pthread_setattr_default_np() — Thread safety: MT-Safe 🦋

(the original puts this in a table, but tables are not the vibe here, so: MT-Safe, periodt)

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🌈 STANDARDS 🌈

GNU. hence the suffix "_np" (nonportable) in their names — it's literally in the name that she doesn't travel well, iykyk 💀

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🎀 HISTORY 🎀

glibc 2.18. a classic, honestly ✨

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🍓 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 you run it, you see this:

$ ./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 <pthread.h>
#include <sched.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);
}

not me noticing every single error check in this example is errc(EXIT_FAILURE, ...) 💀 it's called being thorough bestie, we love a defensive queen 🫶

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💜 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) 🌈

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and that's the whole page, bestie ✨ this one's from Linux man-pages 6.20, dated 2026-02-08, and it's giving very much "pthread_ge...default_np(3) but make it cute". go forth and set your defaults, you icon 👑🦋💖