freebsd man page for sigblock

SIGSETMASK(2)						      BSD System Calls Manual						     SIGSETMASK(2)

NAME
     sigsetmask, sigblock -- manipulate current signal mask

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <signal.h>

     int
     sigsetmask(int mask);

     int
     sigblock(int mask);

     int
     sigmask(int signum);

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

     The sigsetmask() function sets the current signal mask to the specified mask.  Signals are blocked from delivery if the corresponding bit in
     mask is a 1.  The sigblock() function adds the signals in the specified mask to the current signal mask, rather than overwriting it as
     sigsetmask() does.  The macro sigmask() is provided to construct the mask for a given signum.

     The system quietly disallows SIGKILL or SIGSTOP to be blocked.

RETURN VALUES
     The sigblock() and sigsetmask() functions return the previous set of masked signals.

SEE ALSO
     kill(2), sigaction(2), sigprocmask(2), sigsuspend(2), sigvec(2), sigsetops(3)

HISTORY
     The sigsetmask() and sigblock() functions first appeared in 4.2BSD and have been deprecated.

BSD
								   June 2, 1993 							       BSD