SIGHOLD(3)                 POSIX Programmer's Manual                SIGHOLD(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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()
       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 unwaited-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 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 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 1003.1-2017, 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 .

       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 .



IEEE/The Open Group                  2017                           SIGHOLD(3)
