Section (3) pthread_sigmask

Linux manual pages Section 3  


pthread_sigmask — examine and change mask of blocked signals


#include <signal.h>
int pthread_sigmask( int how,
  const sigset_t *set,
  sigset_t *oldset);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_POSIX_C_SOURCE >= 199506L || _XOPEN_SOURCE >= 500
[Note] Note

Compile and link with −pthread.


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).


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


See sigprocmask(2).


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

Interface Attribute Value
pthread_sigmask() Thread safety MT-Safe


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


A new thread inherits a copy of its creator_zsingle_quotesz_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.


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
, sig);

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. */

    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 */


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


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