sigset(2)                 AT&T SYSTEM V                 sigset(2)



NAME
     sigset, sighold, sigrelse, sigignore, sigpause - signal
     management

SYNOPSIS
     #include <signal.h>

     void (*sigset (sig, func))()
     int sig;
     void (*func)();

     int sighold (sig)
     int sig;

     int sigrelse (sig)
     int sig;

     int sigignore (sig)
     int sig;

     int sigpause (sig)
     int sig;

DESCRIPTION
     These functions provide signal management for application
     processes.  See signal(5) for an explanation of general sig-
     nal concepts.

     sigset specifies the system signal action to be taken upon
     receipt of a signal.  sig specifies the signal, which may be
     any signal except SIGKILL and SIGSTOP.  func specifies the
     signal's disposition, which may be SIGDFL, SIGIGN,
     SIGHOLD, or the address of a signal handler.

     If func is SIGDFL, the default action for signal sig is
     reinstated; this default is usually termination [see sig-
     nal(5)].  If func is SIGIGN the signal is subsequently
     ignored and pending instances of the signal are discarded.
     If func is SIGHOLD the signal is held upon receipt (and its
     previous disposition is otherwise unaffected).  Any pending
     signal of this type remains held.  Only one signal of each
     type is held.  Otherwise, when the signal occurs further
     occurences of the signal are automatically blocked and func
     is called.

     For information on the signal handler interface, see sig-
     nal(5).

     When a signal handler function is specified for a signal
     being delivered, the system adds sig to the calling
     process's signal mask before executing the signal handler;
     when the signal handler returns, the system restores the



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sigset(2)                 AT&T SYSTEM V                 sigset(2)



     calling process's signal mask to its state prior to the
     delivery of the signal.  If a non-local goto (longjmp) is
     taken, then sigrelse must be called to restore the system
     signal action and release any held signal of this type.

     In general, upon return from the signal-catching handler,
     the receiving process will resume execution at the point it
     was interrupted.  However, when a signal is caught during a
     read(2), a write(2), an open(2), or an ioctl(2) system call
     on a slow device, during a pause(2) system call, or during a
     wait(2) system call that does not return immediately due to
     the existence of a previously stopped or zombie process, the
     signal-catching handler will be executed and then the inter-
     rupted system call may return a -1 to the calling process
     with errno set to EINTR.

     Unlike the signal(2) facilities, the handler func remains
     installed after a signal has been delivered.

     sighold and sigrelse are used to establish critical regions
     of code.  sighold adds sig to the calling process's signal
     mask; it is analogous to raising the priority level and
     deferring or holding a signal until the priority is lowered
     by sigrelse.  sigrelse removes sig from the calling
     process's signal mask, restoring the system signal action to
     that specified previously by sigset.

     sigignore sets the action for signal sig to SIGIGN (see
     above).

     sigpause suspends the calling process until it receives a
     signal, the same as pause(2).  However, if the signal sig
     had been received and held, it is released (removed from the
     current signal mask) and the system signal action taken.
     This system call is useful for testing variables that are
     changed on the occurrence of a signal.  The correct usage is
     to use sighold to block the signal first, then test the
     variables.  If they have not changed, then call sigpause to
     wait for the signal.  When the sigpause returns, the origi-
     nal signal mask is restored.

RETURN VALUE
     Upon successful completion, sigset returns the previous
     value of the system signal action for the specified signal
     sig, or SIGHOLD if it had been blocked.  Otherwise, a value
     of SIGERR is returned and errno is set to indicate the
     error.  SIGERR is defined in <signal.h>.

     For the other functions, upon successful completion, a value
     of 0 is returned.  Otherwise, a value of -1 is returned and
     errno is set to indicate the error.




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sigset(2)                 AT&T SYSTEM V                 sigset(2)



ERRORS
     These functions will fail if one or more of the following
     are true:

     [EINVAL]       sig is an illegal signal number (including
                    SIGKILL and SIGSTOP) or the default handling
                    of sig cannot be changed.

     [EINTR]        A signal was caught during the system call
                    sigpause.

SEE ALSO
     kill(2), pause(2), sigaction(2), signal(2), wait(2),
     setjmp(3C), signal(5).

NOTES
     If the disposition of SIGCHLD is set to a signal handler,
     SIGCHLD will not be sent when the calling process's children
     are stopped or continued.

     If the disposition of SIGCHLD is set to SIGIGN, the calling
     process's child processes will not create zombie processes
     when they terminate [see exit(2)].  If the calling process
     subsequently waits for its children, it blocks until all of
     its children terminate; it then returns a value of -1 with
     errno set to ECHILD [see wait(2), sigaction(2), signal(5)].

     The other signal management functions, signal(2) and
     pause(2), should not be used in conjunction with these rou-
     tines for a particular signal type.

























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