NAME

sigblock, sigmask — block signals

SYNOPSIS

#include <signal.h>

int
sigblock(int mask);

int
sigmask(int signum);

DESCRIPTION

sigblock() adds the signals specified in mask to the set of signals currently being blocked from delivery. Signals are blocked if the corresponding bit in mask is a 1; the macro sigmask() is provided to construct the mask for a given signum.

It is not possible to block SIGKILL or SIGSTOP; this restriction is silently imposed by the system.

RETURN VALUES

The previous set of masked signals is returned.

EXAMPLES

The following example utilizing sigblock():

int omask;

omask = sigblock(sigmask(SIGINT) | sigmask(SIGHUP));

Becomes:

sigset_t set, oset;

sigemptyset(&set);
sigaddset(&set, SIGINT);
sigaddset(&set, SIGHUP);
sigprocmask(SIG_BLOCK, &set, &oset);

Another use of sigblock() is to get the current set of masked signals without changing what is actually blocked. Instead of:

int set;

set = sigblock(0);

Use the following:

sigset_t set;

sigprocmask(SIG_BLOCK, NULL, &set);

SEE ALSO

kill(2), sigaction(2), sigprocmask(2), sigaddset(3), sigsetmask(3)

HISTORY

A sigblock() system call first appeared in 4.2BSD. In 4.3BSD-Reno, it was reimplemented as a wrapper around sigprocmask(2). The old system call was kept for compatibility until OpenBSD 4.9.