'\" t
.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH pthread_sigmask 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
pthread_sigmask \- examine and change mask of blocked signals
.SH LIBRARY
POSIX threads library
.RI ( libpthread ", " \-lpthread )
.SH SYNOPSIS
.nf
.B #include <signal.h>
.PP
.BI "int pthread_sigmask(int " how ", const sigset_t *" set \
", sigset_t *" oldset );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR pthread_sigmask ():
.nf
    _POSIX_C_SOURCE >= 199506L || _XOPEN_SOURCE >= 500
.fi
.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).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR pthread_sigmask ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.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 EXAMPLES
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
\&
.\" SRC BEGIN (pthread_sigmask.c)
.EX
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/* Simple error handling functions */

#define handle_error_en(en, msg) \e
        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\en", sig);
    }
}

int
main(void)
{
    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, &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
.\" SRC END
.SH SEE ALSO
.BR sigaction (2),
.BR sigpending (2),
.BR sigprocmask (2),
.BR pthread_attr_setsigmask_np (3),
.BR pthread_create (3),
.BR pthread_kill (3),
.BR sigsetops (3),
.BR pthreads (7),
.BR signal (7)