sighold.3p (6530B)
- '\" et
- .TH SIGHOLD "3P" 2017 "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 \-1 and set
- .IR errno
- to
- .BR [EINTR] .
- .P
- For all other functions, upon successful completion, 0 shall be returned.
- Otherwise, \-1 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\(hy2017,
- .IR "\fB<signal.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, 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 .
- .PP
- 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 .