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SIGWAIT(3P) POSIX Programmer's Manual SIGWAIT(3P)
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.
sigwait — wait for queued signals
#include <signal.h>
int sigwait(const sigset_t *restrict set, int *restrict sig);
The sigwait() function shall select a pending signal from set,
atomically clear it from the system's set of pending signals, and
return that signal number in the location referenced by sig. If
prior to the call to sigwait() there are multiple pending instances
of a single signal number, it is implementation-defined whether upon
successful return there are any remaining pending signals for that
signal number. If the implementation supports queued signals and
there are multiple signals queued for the signal number selected, the
first such queued signal shall cause a return from sigwait() and the
remainder shall remain queued. If no signal in set is pending at the
time of the call, the thread shall be suspended until one or more
becomes pending. The signals defined by set shall have been blocked
at the time of the call to sigwait(); otherwise, the behavior is
undefined. The effect of sigwait() on the signal actions for the
signals in set is unspecified.
If more than one thread is using sigwait() to wait for the same
signal, no more than one of these threads shall return from sigwait()
with the signal number. If more than a single thread is blocked in
sigwait() for a signal when that signal is generated for the process,
it is unspecified which of the waiting threads returns from
sigwait(). If the signal is generated for a specific thread, as by
pthread_kill(), only that thread shall return.
Should any of the multiple pending signals in the range SIGRTMIN to
SIGRTMAX be selected, it shall be the lowest numbered one. The
selection order between realtime and non-realtime signals, or between
multiple pending non-realtime signals, is unspecified.
Upon successful completion, sigwait() shall store the signal number
of the received signal at the location referenced by sig and return
zero. Otherwise, an error number shall be returned to indicate the
error.
The sigwait() function may fail if:
EINVAL The set argument contains an invalid or unsupported signal
number.
The following sections are informative.
None.
None.
To provide a convenient way for a thread to wait for a signal, this
volume of POSIX.1‐2008 provides the sigwait() function. For most
cases where a thread has to wait for a signal, the sigwait() function
should be quite convenient, efficient, and adequate.
However, requests were made for a lower-level primitive than
sigwait() and for semaphores that could be used by threads. After
some consideration, threads were allowed to use semaphores and
sem_post() was defined to be async-signal-safe.
In summary, when it is necessary for code run in response to an
asynchronous signal to notify a thread, sigwait() should be used to
handle the signal. Alternatively, if the implementation provides
semaphores, they also can be used, either following sigwait() or from
within a signal handling routine previously registered with
sigaction().
None.
Section 2.4, Signal Concepts, Section 2.8.1, Realtime Signals,
pause(3p), pthread_sigmask(3p), sigaction(3p), sigpending(3p),
sigsuspend(3p), sigtimedwait(3p)
The Base Definitions volume of POSIX.1‐2008, signal.h(0p), time.h(0p)
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 .
IEEE/The Open Group 2013 SIGWAIT(3P)
Pages that refer to this page: signal.h(0p), sigtimedwait(3p)
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