signal(2) signal(2)
NAME
signal, sigset, sighold, sigrelse, sigignore, sigpause -
simplified signal management
SYNOPSIS
#include <signal.h>
void (*signal(int sig, void (*disp)(int)))(int);
void (*sigset(int sig, void (*disp)(int)))(int);
int sighold(int sig);
int sigrelse(int sig);
int sigignore(int sig);
int sigpause(int sig);
DESCRIPTION
These functions provide simplified signal management for
application processes. See signal(5) for an explanation of
general signal concepts.
signal and sigset are used to modify signal dispositions. sig
specifies the signal, which may be any signal except SIGKILL
and SIGSTOP. disp specifies the signal's disposition, which
may be SIG_DFL, SIG_IGN, or the address of a signal handler.
If signal is used, disp is the address of a signal handler,
and sig is not SIGILL, SIGTRAP, or SIGPWR, the system first
sets the signal's disposition to SIG_DFL before executing the
signal handler. If sigset is used and disp is the address of
a signal handler, 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 calling
process's signal mask to its state prior to the delivery of
the signal. In addition, if sigset is used and disp is equal
to SIG_HOLD, sig is added to the calling process's signal mask
and the signal's disposition remains unchanged. However, if
sigset is used and disp is not equal to SIG_HOLD, sig will be
removed from the calling process's signal mask.
sighold adds sig to the calling process's signal mask.
sigrelse removes sig from the calling process's signal mask.
sigignore sets the disposition of sig to SIG_IGN.
sigpause removes sig from the calling process's signal mask
and suspends the calling process until a signal is received.
Copyright 1994 Novell, Inc. Page 1
signal(2) signal(2)
Return Values
On success, signal returns the signal's previous disposition.
On failure, signal returns SIG_ERR and sets errno to identify
the error.
On success, sigset returns SIG_HOLD if the signal had been
blocked or the signal's previous disposition if it had not
been blocked. On failure, sigset returns SIG_ERR and sets
errno to identify the error.
All other functions return zero on success. On failure, they
return -1 and set errno to identify the error.
Errors
In the following conditions, these functions fail and set
errno to:
EINVAL The value of the sig argument is not a valid
signal or is equal to SIGKILL or SIGSTOP.
EINTR A signal was caught during the system call
sigpause.
USAGE
sighold in conjunction with sigrelse or sigpause may be used
to establish critical regions of code that require the
delivery of a signal to be temporarily deferred.
If signal or sigset is used to set SIGCHLD's disposition to a
signal handler, SIGCHLD will not be sent when the calling
process's children are stopped or continued.
If any of the above functions are used to set SIGCHLD's
disposition to SIG_IGN, 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), waitid(2)].
REFERENCES
kill(2), pause(2), sigaction(2), signal(5), sigsend(2),
wait(2), waitid(2)
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signal(2) signal(2)
NOTICES
Considerations for Threads Programming
Signal dispositions (that is, default/ignore/handler) are a
process attribute and are shared by all threads. Signal
masks, on the other hand, are maintained independently per
thread.
See signal(5) for further details.
Considerations for Lightweight Processes
Each LWP has a its own signal mask. The Threads Library
maintains a separate signal mask per thread and adjusts (if
necessary) the LWP's mask before a thread begins executing.
Copyright 1994 Novell, Inc. Page 3