pthread_sigmask(3) Library Functions Manual pthread_sigmask(3)

pthread_sigmask - examine and change mask of blocked signals

POSIX threads library (libpthread, -lpthread)

#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)):


_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).

Interface Attribute Value
pthread_sigmask () Thread safety MT-Safe



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

#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) \

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(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. */
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 */ }

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

2023-07-20 Linux man-pages 6.05.01