SIGHOLD
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
sighold,
sigignore,
sigpause,
sigrelse,
sigset
- signal management
SYNOPSIS
#include <signal.h>
int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);
DESCRIPTION
Use of any of these functions is unspecified in a mult-threaded
process.
The
sighold(),
sigignore(),
sigpause(),
sigrelse(),
and
sigset()
functions provide simplified signal management.
The
sigset()
function shall 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
sigset()
is used, and
disp
is the address of a signal handler, the system shall add
sig
to the signal mask of the calling process before executing the signal
handler; when the signal handler returns, the system shall restore the
signal mask of the calling process to its state prior to the delivery
of the signal. In addition, if
sigset()
is used, and
disp
is equal to SIG_HOLD,
sig
shall be added to the
signal mask of the calling process and
sig's
disposition shall remain unchanged. If
sigset()
is used, and
disp
is not equal to SIG_HOLD,
sig
shall be removed from the signal mask of the calling process.
The
sighold()
function shall add
sig
to the signal mask of the calling process.
The
sigrelse()
function shall remove
sig
from the signal mask of the calling process.
The
sigignore()
function shall set the disposition of
sig
to SIG_IGN.
The
sigpause()
function shall remove
sig
from the signal mask of the calling process and suspend the calling process
until a signal is received. The
sigpause()
function shall restore the signal mask of the process to its original
state before returning.
If the action for the SIGCHLD signal is set to SIG_IGN, child processes
of the
calling processes shall not be transformed into zombie processes when
they terminate. If the calling process subsequently waits for its
children, and the process has no unwaite-for children that were
transformed into zombie processes, it shall block until all of its
children terminate, and
wait(),
waitid(),
and
waitpid()
shall fail and set
errno
to
[ECHILD].
RETURN VALUE
Upon successful completion,
sigset()
shall return SIG_HOLD if the signal had been blocked and the signal's
previous disposition if it had not been blocked. Otherwise, SIG_ERR
shall be returned and
errno
set to indicate the error.
The
sigpause()
function shall suspend execution of the thread until a signal is
received, whereupon it shall return -1 and set
errno
to
[EINTR].
For all other functions, upon successful completion, 0 shall be returned.
Otherwise, -1 shall be returned and
errno
set to indicate the error.
ERRORS
These functions shall fail if:
- EINVAL
-
The
sig
argument is an illegal signal number.
The
sigset()
and
sigignore()
functions shall fail if:
- EINVAL
-
An attempt is made to catch a signal that cannot be caught, or to
ignore a signal that cannot be ignored.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The
sigaction()
function provides a more comprehensive and reliable mechanism for
controlling signals; new applications should use the
sigaction()
function instead of the obsolescent
sigset()
function.
The
sighold()
function, 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. For broader
portability, the
pthread_sigmask()
or
sigprocmask()
functions should be used instead of the obsolescent
sighold()
and
sigrelse()
functions.
For broader portability, the
sigsuspend()
function should be used instead of the obsolescent
sigpause()
function.
RATIONALE
Each of these historic functions has a direct analog in the other
functions which are required to be pe-thread and threa-safe (aside
from
sigprocmask(),
which is replaced by
pthread_sigmask()).
The
sigset()
function can be implemented as a simple wrapper for
sigaction().
The
sighold()
function is equivalent to
sigprocmask()
or
pthread_sigmask()
with SIG_BLOCK set. The
sigignore()
function is equivalent to
sigaction()
with SIG_IGN set. The
sigpause()
function is equivalent to
sigsuspend().
The
sigrelse()
function is equivalent to
sigprocmask()
or
pthread_sigmask()
with SIG_UNBLOCK set.
FUTURE DIRECTIONS
These functions may be removed in a future version.
SEE ALSO
Section 2.4,
Signal Concepts,
exec,
pause(),
pthread_sigmask(),
sigaction(),
signal(),
sigsuspend(),
wait(),
waitid()
The Base Definitions volume of POSIX.1-2017,
<signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.-2017, Standard for Information Technology- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/ma-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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