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SIGVEC(3B)							    SIGVEC(3B)

NAME    [Toc]    [Back]

     sigvec - 4.3BSD software signal facilities

SYNOPSIS    [Toc]    [Back]

     #include <signal.h>

     struct sigvec {
	  int  (*sv_handler)(int, int);
	  int  sv_mask;
	  int  sv_flags;

     int sigvec(int sig, struct	sigvec *vec, struct sigvec *ovec);

     To	use any	of the BSD signal routines (kill(3B), killpg(3B),
     sigblock(3B), signal(3B), sigpause(3B), sigsetmask(3B), sigstack(2B),
     sigvec(3B)) you must either

     1)	#define	_BSD_SIGNALS or	_BSD_COMPAT before including <signal.h>, or

     2)	specify	one of them in the compile command or makefile:

	  cc -D_BSD_SIGNALS -o prog prog.c

DESCRIPTION    [Toc]    [Back]

     sigvec specifies and reports on the way individual	signals	are to be
     handled in	the calling process.  If vec is	non-zero, it alters the	way
     the signal	will be	treated	- default behavior, ignored, or	handled	via a
     routine - and the signal mask to be used when delivering the signal if a
     handler is	installed.  If ovec is non-zero, the previous handling
     information for the signal	is returned to the user.  In this way (a NULL
     vec and a non-NULL	ovec) the user can inquire as to the current handling
     of	a signal without changing it.  If both vec and ovec are	NULL, sigvec
     will return -1 and	set errno to EINVAL if sig is an invalid signal	(else
     0), allowing an application to dynamically	determine the set of signals
     supported by the system.

     The system	defines	a set of signals that may be delivered to a process.
     Signal delivery resembles the occurrence of a hardware interrupt:	the
     signal is blocked from further occurrence,	the current process context is
     saved, and	a new one is built.  A process may specify a handler to	which
     a signal is delivered, or specify that a signal is	to be blocked or
     ignored.  A process may also specify that a default action	is to be taken
     by	the system when	a signal occurs.

     All signals have the same priority.  Signal routines execute with the
     signal that caused	their invocation blocked, but other signals may	yet
     occur.  A global signal mask defines the set of signals currently blocked
     from delivery to a	process.  The signal mask for a	process	is initialized
     from that of its parent (normally 0).  It may be changed with a
 call, or when a signal is delivered	to the

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SIGVEC(3B)							    SIGVEC(3B)


     When a signal condition arises for	a process, the signal is added to a
     set of signals pending for	the process.  If the signal is not currently
     blocked by	the process then it is delivered to the	process.  When a
     signal is delivered, the current state of the process is saved, a new
     signal mask is calculated (as described below), and the signal handler is
     invoked.  The call	to the handler is arranged so that if the signal
     handling routine returns normally the process will	resume execution in
     the context from before the signal's delivery.  If	the process wishes to
     resume in a different context, then it must arrange to restore the
     previous context itself.

     When a signal is delivered	to a process a new signal mask is installed
     for the duration of the process' signal handler (or until a sigblock or
     sigsetmask	call is	made).	This mask is formed by taking the current
     signal mask, adding the signal to be delivered, and or'ing	in the signal
     mask associated with the handler to be invoked.

     Sigvec assigns a handler for a specific signal.  If vec is	non-zero, it
     specifies a handler routine and mask to be	used when delivering the
     specified signal.	Further, if the	SV_ONSTACK bit is set in sv_flags, the
     system will deliver the signal to the process on a	signal stack,
     specified with sigstack(2b).

     For a list	of valid signal	numbers	and a general description of the
     signal mechanism, please see signal(5).

     Once a signal handler is installed, it remains installed until another
     sigvec call is made, or an	execve(2) is performed.	 The default action
     for a signal may be reinstated by setting sv_handler to SIG_DFL; this
     default is	termination with a core	image for signals marked [1].  If
     sv_handler	is SIG_IGN the signal is subsequently ignored, and pending
     instances of the signal are discarded.

     SIGKILL will immediately terminate	a process, regardless of its state.
     Processes which are stopped via job control (typically <ctrl>-Z) will not
     act upon any delivered signals other than SIGKILL until the job is
     restarted.	 Processes which are blocked via a blockproc(2)	system call
     will unblock if they receive a signal which is fatal (i.e., a non-jobcontrol
 signal which they are NOT catching), but will still be stopped if
     the job of	which they are a part is stopped.  Only	upon restart will they
     die.  Any non-fatal signals received by a blocked process will NOT	cause
     the process to be unblocked (a call to unblockproc(2) or
     unblockprocall(2) is necessary).

     After a fork(2) the child inherits	all handlers, the signal stack and the
     signal masks, but not the set of the pending signals.

     The exec(2) routines reset	all caught signals to default action , clear
     all handler masks and reset all signals to	be caught on the user stack.
     Ignored signals remain ignored; the blocked signal	mask is	unchanged and

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SIGVEC(3B)							    SIGVEC(3B)

     pending signals remain pending.

     The mask specified	in vec is not allowed to block SIGKILL,	SIGSTOP, or
     SIGCONT.  This is enforced	silently by the	system.

RETURN VALUE    [Toc]    [Back]

     A 0 value indicated that the call succeeded.  A -1	return value indicates
     an	error occurred and errno is set	to indicate the	reason.

ERRORS    [Toc]    [Back]

     sigvec is a library routine (executing in user space): if either vec or
     ovec points to memory that	is not a valid part of the process address
     space, the	process	will receive a memory fault (SIGSEGV) signal and
     terminate (unless it has installed	a handler for SIGSEGV).	 If the
     invalid pointer is	the result of using a REFERENCE	instead	of a POINTER,
     the compiler will issue a warning.

     sigvec will fail and no new signal	handler	will be	installed if one of
     the following occurs:

     [EINVAL]	    Sig	is not a valid signal number.

     [EINVAL]	    An attempt is made to ignore or supply a handler for

     [EINVAL]	    An attempt is made to ignore SIGCONT (by default SIGCONT
		    is ignored).

SEE ALSO    [Toc]    [Back]

     kill(3B), sigblock(3B), sigsetmask(3B), sigpause(3B), sigvec(3B),
     setjmp(3),	blockproc(2), signal(5).

     4.2BSD attempts to	restart	system calls which are interrupted by signal
     receipt; 4.3BSD gives the programmer a choice of restart or failedreturn-with-error
 via the SV_INTERRUPT flag in sigvec or use of the
     siginterrupt library routine.  IRIX provides only the fail-with-error
     option.  The affected system calls	are read(2), write(2), open(2),
     ioctl(2), and wait(2).  Refer to the sigset(2) man	page for more a
     detailed description of the behavior.

     The 4.3BSD	and System V signal facilities have different semantics.
     Using both	facilities in the same program is strongly discouraged and
     will result in unpredictable behavior.

									PPPPaaaaggggeeee 3333
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