SIGNAL(3C) Standard C Library Functions SIGNAL(3C)
NAME
signal, sigset, sighold, sigrelse, sigignore, sigpause - simplified
signal management for application processes
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.h(3HEAD) for an explanation of general signal
concepts.
The
signal() and
sigset() functions modify signal dispositions. The
sig argument specifies the signal, which may be any signal except
SIGKILL and
SIGSTOP. The
disp argument 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.
The
sighold() function adds
sig to the calling process's signal mask.
The
sigrelse() function removes
sig from the calling process's signal
mask.
The
sigignore() function sets the disposition of
sig to
SIG_IGN. The
sigpause() function removes
sig from the calling process's signal
mask and suspends the calling process until a signal is received.
RETURN VALUES
Upon successful completion,
signal() returns the signal's previous
disposition. Otherwise, it returns
SIG_ERR and sets
errno to
indicate the error.
Upon successful completion,
sigset() returns
SIG_HOLD if the signal
had been blocked or the signal's previous disposition if it had not
been blocked. Otherwise, it returns
SIG_ERR and sets
errno to
indicate the error.
Upon successful completion,
sighold(),
sigrelse(),
sigignore(), and
sigpause(), return
0. Otherwise, they return
-1 and set
errno to
indicate the error.
ERRORS
These functions fail if:
EINTR A signal was caught during the execution
sigpause().
EINVAL The value of the
sig argument is not a valid signal or is
equal to
SIGKILL or
SIGSTOP.
USAGE
The
sighold() function used 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
-1 with
errno set to
ECHILD (see
wait(3C) and
waitid(2)).
The system guarantees that if more than one instance of the same
signal is generated to a process, at least one signal will be
received. It does not guarantee the reception of every generated
signal.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
exit(2),
kill(2),
pause(2),
sigaction(2),
sigsend(2),
waitid(2),
wait(3C),
signal.h(3HEAD),
attributes(7),
standards(7) September 6, 2007 SIGNAL(3C)
