.TH SIGSET 3J
.UC
.SH NAME
sigset, signal, sighold, sigignore, sigrelse, sigpause \- manage signals
.SH SYNOPSIS
.nf
.B #include <signal.h>
.B void action();
.BI "int action();" " (if void is not supported)"
.B int sig;
.PP
.B sigset(sig, action)
.B signal(sig, action)
.PP
.B sighold(sig)
.B sigignore(sig)
.B sigrelse(sig)
.PP
.B sigpause(sig)
.PP
.fi
.B cc ... \-ljobs
.nf
.SH DESCRIPTION
This is a package of signal management functions to manage the signals
as described in
.IR sigsys (2J).
These functions are not available in most versions of UNIX, and should
not be used when the mechanisms of
.IR signal (2)
would suffice, as they would then impair portability.
These functions are contained in the \fIjobs\fP library, obtained by
specifying the loader option \fB\-ljobs\fP.
.PP
.I Sigset
is used to provide a default signal handler for signal
.I sig.
This function is remembered across subsequent calls to the other
functions, and need not be specified again.
After
.I sigset
instances of
.I sig
will cause an interrupt to be taken at
.I func,
with the signal then held so that recursive trapping due to
the signal will not occur.  During normal return from
.I func,
the routines arrange for the signal action to be restored so that
subsequent signals will also trap to
.I func.
If a non-local exit is to be taken, then
.I sigrelse
must be called to un-hold the signal action, restoring the
original catch.
.I Func
may also be specified as
SIG_DFL, SIG_IGN or SIG_HOLD, as described in
.IR sigsys (2J).
The value specified on the previous call to
.I sigset
is returned; if
.I sigset
has never been called, then the default action inherited from the
system is returned.
.PP
.I Signal
is like
.I 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.
.PP
.I Sighold
and
.I sigrelse
may be used to block off
.I sig
in a piece of code where it cannot be tolerated.
After
.I sigrelse
the catch initially set with
.I sigset
will be restored.
.PP
.I Sigignore
can be used to temporarily set the action for
.I sig
to ignore the signal.  If the signal had been held before
the call to
.I sigignore,
any pending instance of the signal will be discarded.
.PP
.I Sigpause
may be used by a routine which wishes to check for some condition
produced at interrupt level by the
.I 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
.I sighold
to block the signal.
.I Sigpause
is like
.I pause
in that it will return after
.I any
signal is processed.
The usual thing to do then is to reenable the hold with
.I sighold,
check the condition
again, and
.I sigpause
again if the condition has not arisen.
.SH "SEE ALSO"
signal(2), sigsys(2J), intro(3J), tty(4)
.SH BUGS
.I Sighold
and
.I sigrelse
do not nest; the first
.I sigrelse
restores the default catch.
.PP
These functions store information in data space.  You thus
.B must
call
.IR sigsys (2J)
rather than any of
.I sigset
or
.I signal
after a
.IR vfork (2)
in the child which is to then
.IR exec .