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.TH PTHREAD_ATTR_INIT 3 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

pthread_attr_init, pthread_attr_destroy \- initialize and destroy

thread attributes object

.SH SYNOPSIS

.nf

.B #include <pthread.h>

.PP

.BI "int pthread_attr_init(pthread_attr_t *" attr );

.BI "int pthread_attr_destroy(pthread_attr_t *" attr );

.PP

Compile and link with \fI\-pthread\fP.

.fi

.SH DESCRIPTION

The

.BR pthread_attr_init ()

function initializes the thread attributes object pointed to by

.IR attr

with default attribute values.

After this call, individual attributes of the object can be set

using various related functions (listed under SEE ALSO),

and then the object can be used in one or more

.BR pthread_create (3)

calls that create threads.

.PP

Calling

.BR pthread_attr_init ()

on a thread attributes object that has already been initialized

results in undefined behavior.

.PP

When a thread attributes object is no longer required,

it should be destroyed using the

.BR pthread_attr_destroy ()

function.

Destroying a thread attributes object has no effect

on threads that were created using that object.

.PP

Once a thread attributes object has been destroyed,

it can be reinitialized using

.BR pthread_attr_init ().

Any other use of a destroyed thread attributes object

has undefined results.

.SH RETURN VALUE

On success, these functions return 0;

on error, they return a nonzero error number.

.SH ERRORS

POSIX.1 documents an

.B ENOMEM

error for

.BR pthread_attr_init ();

on Linux these functions always succeed

(but portable and future-proof applications should nevertheless

handle a possible error return).

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.ad l

.TS

allbox;

lbw22 lb lb

l l l.

Interface	Attribute	Value

T{

.BR pthread_attr_init (),

.BR pthread_attr_destroy ()

T}	Thread safety	MT-Safe

.TE

.ad

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

.SH NOTES

The

.I pthread_attr_t

type should be treated as opaque:

any access to the object other than via pthreads functions

is nonportable and produces undefined results.

.SH EXAMPLE

The program below optionally makes use of

.BR pthread_attr_init ()

and various related functions to initialize a thread attributes

object that is used to create a single thread.

Once created, the thread uses the

.BR pthread_getattr_np (3)

function (a nonstandard GNU extension) to retrieve the thread's

attributes, and then displays those attributes.

.PP

If the program is run with no command-line argument,

then it passes NULL as the

.I attr

argument of

.BR pthread_create (3),

so that the thread is created with default attributes.

Running the program on Linux/x86-32 with the NPTL threading implementation,

we see the following:

.PP

.in +4n

.EX

.\" Results from glibc 2.8, SUSE 11.0; Oct 2008

.RB "$" " ulimit \-s" "       # No stack limit ==> default stack size is 2 MB"

unlimited

.RB "$" " ./a.out"

Thread attributes:

        Detach state        = PTHREAD_CREATE_JOINABLE

        Scope               = PTHREAD_SCOPE_SYSTEM

        Inherit scheduler   = PTHREAD_INHERIT_SCHED

        Scheduling policy   = SCHED_OTHER

        Scheduling priority = 0

        Guard size          = 4096 bytes

        Stack address       = 0x40196000

        Stack size          = 0x201000 bytes

.EE

.in

.PP

When we supply a stack size as a command-line argument,

the program initializes a thread attributes object,

sets various attributes in that object,

and passes a pointer to the object in the call to

.BR pthread_create (3).

Running the program on Linux/x86-32 with the NPTL threading implementation,

we see the following:

.PP

.in +4n

.EX

.\" Results from glibc 2.8, SUSE 11.0; Oct 2008

.RB "$" " ./a.out 0x3000000"

posix_memalign() allocated at 0x40197000

Thread attributes:

        Detach state        = PTHREAD_CREATE_DETACHED

        Scope               = PTHREAD_SCOPE_SYSTEM

        Inherit scheduler   = PTHREAD_EXPLICIT_SCHED

        Scheduling policy   = SCHED_OTHER

        Scheduling priority = 0

        Guard size          = 0 bytes

        Stack address       = 0x40197000

        Stack size          = 0x3000000 bytes

.EE

.in

.SS Program source

\&

.EX

#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%zx 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 = &att;;

        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() */

}

.EE

.SH SEE ALSO

.ad l

.nh

.BR pthread_attr_setaffinity_np (3),

.BR pthread_attr_setdetachstate (3),

.BR pthread_attr_setguardsize (3),

.BR pthread_attr_setinheritsched (3),

.BR pthread_attr_setschedparam (3),

.BR pthread_attr_setschedpolicy (3),

.BR pthread_attr_setscope (3),

.BR pthread_attr_setstack (3),

.BR pthread_attr_setstackaddr (3),

.BR pthread_attr_setstacksize (3),

.BR pthread_create (3),

.BR pthread_getattr_np (3),

.BR pthread_setattr_default_np (3),

.BR pthreads (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.