SIGHOLD(3P) POSIX Programmer's Manual SIGHOLD(3P)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 multi-threaded
process.
The sighold(), sigignore(), sigpause(), sigrelse(), and sigset() func‐
tions provide simplified signal management.
The sigset() function shall modify signal dispositions. The sig argu‐
ment 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 sys‐
tem shall add sig to the signal mask of the calling process before exe‐
cuting 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 unwaited-for children that were trans‐
formed 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 sig‐
nal 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 portabil‐
ity, 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 func‐
tions which are required to be per-thread and thread-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 sigac‐
tion() with SIG_IGN set. The sigpause() function is equivalent to sig‐
suspend(). 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(), sigac‐
tion(), signal(), sigsuspend(), wait(), waitid()
The Base Definitions volume of POSIX.1‐2008, <signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SIGHOLD(3P)
