PTHREAD_SIGMASK

Section: Linux Programmer's Manual (3)
Updated: 2020-11-01
Page Index

NAME

pthread_sigmask - examine and change mask of blocked signals

SYNOPSIS

#include <signal.h>

int pthread_sigmask(int how, const sigset_t *set, sigset_t *oldset);

Compile and link with -pthread.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

pthread_sigmask():

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

DESCRIPTION

The pthread_sigmask() function is just like sigprocmask(2), with the difference that its use in multithreaded programs is explicitly specified by POSIX.1. Other differences are noted in this page.

For a description of the arguments and operation of this function, see sigprocmask(2).

RETURN VALUE

On success, pthread_sigmask() returns 0; on error, it returns an error number.

ERRORS

See sigprocmask(2).

ATTRIBUTES

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

Interface	Attribute	Value
pthread_sigmask()	Thread safety	MT-Safe

CONFORMING TO

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

NOTES

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

The glibc pthread_sigmask() function silently ignores attempts to block the two real-time signals that are used internally by the NPTL threading implementation. See nptl(7) for details.

EXAMPLES

The program below blocks some signals in the main thread, and then creates a dedicated thread to fetch those signals via sigwait(3). The following shell session demonstrates its use:

$ ./a.out & [1] 5423 $ kill -QUIT %1 Signal handling thread got signal 3 $ kill -USR1 %1 Signal handling thread got signal 10 $ kill -TERM %1 [1]+ Terminated ./a.out

Program source

#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, &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 */ }

COLOPHON

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