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

.SH NAME

pthread_sigmask \- examine and change mask of blocked signals

.SH SYNOPSIS

.nf

.B #include <signal.h>

.PP

.BI "int pthread_sigmask(int " how ", const sigset_t *" set \

", sigset_t *" oldset );

.fi

.PP

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

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.ad l

.BR pthread_sigmask ():

.RS 4

_POSIX_C_SOURCE\ >=\ 199506L || _XOPEN_SOURCE\ >=\ 500

.RE

.ad b

.SH DESCRIPTION

The

.BR pthread_sigmask ()

function is just like

.BR sigprocmask (2),

with the difference that its use in multithreaded programs

is explicitly specified by POSIX.1.

Other differences are noted in this page.

.PP

For a description of the arguments and operation of this function, see

.BR sigprocmask (2).

.SH RETURN VALUE

On success,

.BR pthread_sigmask ()

returns 0;

on error, it returns an error number.

.SH ERRORS

See

.BR sigprocmask (2).

.SH ATTRIBUTES

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

.BR attributes (7).

.TS

allbox;

lb lb lb

l l l.

Interface	Attribute	Value

T{

.BR pthread_sigmask ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

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

.SH NOTES

A new thread inherits a copy of its creator's signal mask.

.PP

The glibc

.BR pthread_sigmask ()

function silently ignores attempts to block the two real-time signals that

are used internally by the NPTL threading implementation.

See

.BR nptl (7)

for details.

.SH EXAMPLE

The program below blocks some signals in the main thread,

and then creates a dedicated thread to fetch those signals via

.BR sigwait (3).

The following shell session demonstrates its use:

.PP

.in +4n

.EX

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

[1] 5423

.RB "$" " kill \-QUIT %1"

Signal handling thread got signal 3

.RB "$" " kill \-USR1 %1"

Signal handling thread got signal 10

.RB "$" " kill \-TERM %1"

[1]+  Terminated              ./a.out

.EE

.in

.SS Program source

\&

.EX

#include <pthread.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <signal.h>

#include <errno.h>

/* Simple error handling functions */

#define handle_error_en(en, msg) \\

        do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

static void *

sig_thread(void *arg)

{

    sigset_t *set = arg;

    int s, sig;

    for (;;) {

        s = sigwait(set, &sig);

        if (s != 0)

            handle_error_en(s, "sigwait");

        printf("Signal handling thread got signal %d\\n", sig);

    }

}

int

main(int argc, char *argv[])

{

    pthread_t thread;

    sigset_t set;

    int s;

    /* Block SIGQUIT and SIGUSR1; other threads created by main()

       will inherit a copy of the signal mask. */

    sigemptyset(&set);

    sigaddset(&set, SIGQUIT);

    sigaddset(&set, SIGUSR1);

    s = pthread_sigmask(SIG_BLOCK, &set, NULL);

    if (s != 0)

        handle_error_en(s, "pthread_sigmask");

    s = pthread_create(&thread, NULL, &sig_thread, (void *) &set);

    if (s != 0)

        handle_error_en(s, "pthread_create");

    /* Main thread carries on to create other threads and/or do

       other work */

    pause();            /* Dummy pause so we can test program */

}

.EE

.SH SEE ALSO

.BR sigaction (2),

.BR sigpending (2),

.BR sigprocmask (2),

.BR pthread_create (3),

.BR pthread_kill (3),

.BR sigsetops (3),

.BR pthreads (7),

.BR signal (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/.