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 calling process' signal mask before
executing the signal handler; when the signal handler returns, the system
shall restore the calling process' signal mask 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 calling
process' signal mask 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 calling process' signal mask.
The sighold() function shall add sig to the calling process'
The sigrelse() function shall remove sig from the calling process'
The sigignore() function shall set the disposition of sig to
The sigpause() function shall remove sig from the calling process'
signal mask and suspend the calling process until a signal is received. The
sigpause() function shall restore the process' signal mask 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].
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 sigpause() function shall suspend execution of the thread until a
signal is received, whereupon it shall return -1 and set errno to
For all other functions, upon successful completion, 0 shall be returned.
Otherwise, -1 shall be returned and errno set to indicate the error.
The sigaction() function provides a more comprehensive and reliable
mechanism for controlling signals; new applications should use
sigaction() rather than sigset().
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.
The sigsuspend() function should be used in preference to
sigpause() for broader portability.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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