Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.

@(#)sigset.3 4.1 (Berkeley) 05/15/85

C 4 sigset, signal, sighold, sigignore, sigrelse, sigpause - manage signals

 #include <signal.h>  void action();  int sig; 

 sigset(sig, action)  signal(sig, action) 

 sighold(sig)  sigignore(sig)  sigrelse(sig) 

 sigpause(sig) 

cc ... -ljobs

 DESCRIPTION
This is a package of signal management functions to manage the signals
as described in
 sigsys (2). These functions are available only in this version of UNIX, and should
not be used when the mechanisms of
 signal (2) would suffice, as they would then impair portability.
These functions are contained in the jobs library, obtained by
specifying the loader option -ljobs.

 Sigset is used to provide a default signal handler for signal
 sig. This function is remembered across subsequent calls to the other
functions, and need not be specified again.
After
 sigset instances of
 sig will cause an interrupt to be taken at
 func, with the signal then held so that recursive trapping due to
the signal will not occur. During normal return from
 func, the routines arrange for the signal action to be restored so that
subsequent signals will also trap to
 func. If a non-local exit is to be taken, then
 sigrelse must be called to un-hold the signal action, restoring the
original catch.
 Func may also be specified as
SIG_DFL, SIG_IGN or SIG_HOLD, as described in
 sigsys (2). The value specified on the previous call to
 sigset is returned; if
 sigset has never been called, then the default action inherited from the
system is returned.

 Signal is like
 sigset, but the signal will not be held when the action routine is called;
rather it will have reverted to SIG_DFL.
This is generally unsafe, but is included for backwards compatibility
to the old signal mechanism.
It should not be used.

 Sighold and
 sigrelse may be used to block off
 sig in a piece of code where it cannot be tolerated.
After
 sigrelse the catch initially set with
 sigset will be restored.

 Sigignore can be used to temporarily set the action for
 sig to ignore the signal. If the signal had been held before
the call to
 sigignore, any pending instance of the signal will be discarded.

 Sigpause may be used by a routine which wishes to check for some condition
produced at interrupt level by the
 sig signal, and then to pause waiting for the condition to arise with
the catch of the signal enabled.
In correct usage it must be preceded by an instance of
 sighold to block the signal.
 Sigpause is like
 pause in that it will return after
 any signal is processed.
The usual thing to do then is to reenable the hold with
 sighold, check the condition
again, and
 sigpause again if the condition has not arisen.
 "SEE ALSO"
sigsys(2), signal(2), jobs(3), tty(4)
 BUGS
 Sighold and
 sigrelse do not nest; the first
 sigrelse restores the default catch.

These functions store information in data space. You thus
 must call
 sigsys (2) rather than any of
 sigset or
 signal after a
 vfork (2) in the child which is to then
 exec (2).