pthread_sigmask(3)

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
", 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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