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.