SIGBLOCK(3)

NAME
sigblock, sigmask - block signals

SYNOPSIS
#include <signal.h>
int
sigblock(int mask);
int
sigmask(int signum);

DESCRIPTION
This interface is made obsolete by: sigprocmask(2).

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), sigsetmask(3), sigsetops(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.