pthread_sigmask(3)

NAME
pthread_sigmask - examine and change mask of blocked signals

LIBRARY
POSIX threads library (libpthread, -lpthread)

SYNOPSIS
#include <signal.h>

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

    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
 | Thread safety | MT-Safe

STANDARDS
POSIX.1-2008.

HISTORY
POSIX.1-2001.

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 <err.h>
    #include <errno.h>
    #include <pthread.h>
    #include <signal.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>

    /* Simple error handling functions */

    static void *
    sig_thread(void *arg)
    {
        sigset_t *set = arg;
        int s, sig;

        for (;;) {
            s = sigwait(set, &sig);
            if (s != 0)
                errc(EXIT_FAILURE, s, "sigwait");
            printf("Signal handling thread got signal %d\n", 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)
            errc(EXIT_FAILURE, s, "pthread_sigmask");

        s = pthread_create(&thread, NULL, &sig_thread, &set);
        if (s != 0)
            errc(EXIT_FAILURE, s, "pthread_create");

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

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

SEE ALSO
sigaction(2), sigpending(2), sigprocmask(2), pthread_attr_setsigmask_np(3), pthread_create(3), pthread_kill(3), sigsetops(3), pthreads(7), signal(7)