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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017 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.1‐2017, signal.h(0p),
time.h(0p)
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 SIGWAIT(3P)
Pages that refer to this page: signal.h(0p), sigtimedwait(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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