pthread_sigmask (3) - Linux Manuals

pthread_sigmask: examine and change mask of blocked signals


pthread_sigmask - examine and change mask of blocked signals


#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)):


_POSIX_C_SOURCE >= 199506L || _XOPEN_SOURCE >= 500


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).
pthread_sigmask() Thread safetyMT-Safe


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


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.


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. */

    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 */ }


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