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.TH SIGHOLD "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

sighold,

sigignore,

sigpause,

sigrelse,

sigset

\(em signal management

.SH SYNOPSIS

.LP

.nf

#include <signal.h>

.P

int sighold(int \fIsig\fP);

int sigignore(int \fIsig\fP);

int sigpause(int \fIsig\fP);

int sigrelse(int \fIsig\fP);

void (*sigset(int \fIsig\fP, void (*\fIdisp\fP)(int)))(int);

.fi

.SH DESCRIPTION

Use of any of these functions is unspecified in a multi-threaded

process.

.P

The

\fIsighold\fR(),

\fIsigignore\fR(),

\fIsigpause\fR(),

\fIsigrelse\fR(),

and

\fIsigset\fR()

functions provide simplified signal management.

.P

The

\fIsigset\fR()

function shall modify signal dispositions. The

.IR sig

argument specifies the signal, which may be any signal except SIGKILL

and SIGSTOP. The

.IR disp

argument specifies the signal's disposition, which may be SIG_DFL,

SIG_IGN, or the address of a signal handler. If

\fIsigset\fR()

is used, and

.IR disp

is the address of a signal handler, the system shall add

.IR 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

\fIsigset\fR()

is used, and

.IR disp

is equal to SIG_HOLD,

.IR sig

shall be added to the

signal mask of the calling process and

.IR sig 's

disposition shall remain unchanged. If

\fIsigset\fR()

is used, and

.IR disp

is not equal to SIG_HOLD,

.IR sig

shall be removed from the signal mask of the calling process.

.P

The

\fIsighold\fR()

function shall add

.IR sig

to the signal mask of the calling process.

.P

The

\fIsigrelse\fR()

function shall remove

.IR sig

from the signal mask of the calling process.

.P

The

\fIsigignore\fR()

function shall set the disposition of

.IR sig

to SIG_IGN.

.P

The

\fIsigpause\fR()

function shall remove

.IR sig

from the signal mask of the calling process and suspend the calling process

until a signal is received. The

\fIsigpause\fR()

function shall restore the signal mask of the process to its original

state before returning.

.P

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

transformed into zombie processes, it shall block until all of its

children terminate, and

\fIwait\fR(),

\fIwaitid\fR(),

and

\fIwaitpid\fR()

shall fail and set

.IR errno

to

.BR [ECHILD] .

.SH "RETURN VALUE"

Upon successful completion,

\fIsigset\fR()

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

.IR errno

set to indicate the error.

.P

The

\fIsigpause\fR()

function shall suspend execution of the thread until a signal is

received, whereupon it shall return \(mi1 and set

.IR errno

to

.BR [EINTR] .

.P

For all other functions, upon successful completion, 0 shall be returned.

Otherwise, \(mi1 shall be returned and

.IR errno

set to indicate the error.

.SH ERRORS

These functions shall fail if:

.TP

.BR EINVAL

The

.IR sig

argument is an illegal signal number.

.P

The

\fIsigset\fR()

and

\fIsigignore\fR()

functions shall fail if:

.TP

.BR EINVAL

An attempt is made to catch a signal that cannot be caught, or to

ignore a signal that cannot be ignored.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

The

\fIsigaction\fR()

function provides a more comprehensive and reliable mechanism for

controlling signals; new applications should use the

\fIsigaction\fR()

function instead of the obsolescent

\fIsigset\fR()

function.

.P

The

\fIsighold\fR()

function, in conjunction with

\fIsigrelse\fR()

or

\fIsigpause\fR(),

may be used to establish critical regions of code that require the

delivery of a signal to be temporarily deferred. For broader

portability, the

\fIpthread_sigmask\fR()

or

\fIsigprocmask\fR()

functions should be used instead of the obsolescent

\fIsighold\fR()

and

\fIsigrelse\fR()

functions.

.P

For broader portability, the

\fIsigsuspend\fR()

function should be used instead of the obsolescent

\fIsigpause\fR()

function.

.SH RATIONALE

Each of these historic functions has a direct analog in the other

functions which are required to be per-thread and thread-safe (aside

from

\fIsigprocmask\fR(),

which is replaced by

\fIpthread_sigmask\fR()).

The

\fIsigset\fR()

function can be implemented as a simple wrapper for

\fIsigaction\fR().

The

\fIsighold\fR()

function is equivalent to

\fIsigprocmask\fR()

or

\fIpthread_sigmask\fR()

with SIG_BLOCK set. The

\fIsigignore\fR()

function is equivalent to

\fIsigaction\fR()

with SIG_IGN set. The

\fIsigpause\fR()

function is equivalent to

\fIsigsuspend\fR().

The

\fIsigrelse\fR()

function is equivalent to

\fIsigprocmask\fR()

or

\fIpthread_sigmask\fR()

with SIG_UNBLOCK set.

.SH "FUTURE DIRECTIONS"

These functions may be removed in a future version.

.SH "SEE ALSO"

.IR "Section 2.4" ", " "Signal Concepts",

.IR "\fIexec\fR\^",

.IR "\fIpause\fR\^(\|)",

.IR "\fIpthread_sigmask\fR\^(\|)",

.IR "\fIsigaction\fR\^(\|)",

.IR "\fIsignal\fR\^(\|)",

.IR "\fIsigsuspend\fR\^(\|)",

.IR "\fIwait\fR\^(\|)",

.IR "\fIwaitid\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<signal.h>\fP"

.SH 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

Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .