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+'\" et
+.TH SIGWAIT "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
+sigwait
+\(em wait for queued signals
+.SH SYNOPSIS
+.LP
+.nf
+#include <signal.h>
+.P
+int sigwait(const sigset_t *restrict \fIset\fP, int *restrict \fIsig\fP);
+.fi
+.SH DESCRIPTION
+The
+\fIsigwait\fR()
+function shall select a pending signal from
+.IR set ,
+atomically clear it from the system's set of pending signals, and
+return that signal number in the location referenced by
+.IR sig .
+If prior to the call to
+\fIsigwait\fR()
+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
+\fIsigwait\fR()
+and the remainder shall remain queued. If no signal in
+.IR set
+is pending at the time of the call, the thread shall be suspended
+until one or more becomes pending. The signals defined by
+.IR set
+shall have been blocked at the time of the call to
+\fIsigwait\fR();
+otherwise, the behavior is undefined. The effect of
+\fIsigwait\fR()
+on the signal actions for the signals in
+.IR set
+is unspecified.
+.P
+If more than one thread is using
+\fIsigwait\fR()
+to wait for the same signal, no more than one of these threads shall
+return from
+\fIsigwait\fR()
+with the signal number. If more than a single thread is blocked in
+\fIsigwait\fR()
+for a signal when that signal is generated for the process, it is
+unspecified which of the waiting threads returns from
+\fIsigwait\fR().
+If the signal is generated for a specific thread, as by
+\fIpthread_kill\fR(),
+only that thread shall return.
+.P
+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.
+.SH "RETURN VALUE"
+Upon successful completion,
+\fIsigwait\fR()
+shall store the signal number of the received signal at the location
+referenced by
+.IR sig
+and return zero. Otherwise, an error number shall be returned to
+indicate the error.
+.SH ERRORS
+The
+\fIsigwait\fR()
+function may fail if:
+.TP
+.BR EINVAL
+The
+.IR set
+argument contains an invalid or unsupported signal number.
+.LP
+.IR "The following sections are informative."
+.SH EXAMPLES
+None.
+.SH "APPLICATION USAGE"
+None.
+.SH RATIONALE
+To provide a convenient way for a thread to wait for a signal, this volume of POSIX.1\(hy2017
+provides the
+\fIsigwait\fR()
+function. For most cases where a thread has to wait for a signal, the
+\fIsigwait\fR()
+function should be quite convenient, efficient, and adequate.
+.P
+However, requests were made for a lower-level primitive than
+\fIsigwait\fR()
+and for semaphores that could be used by threads. After some
+consideration, threads were allowed to use semaphores and
+\fIsem_post\fR()
+was defined to be async-signal-safe.
+.P
+In summary, when it is necessary for code run in response to an
+asynchronous signal to notify a thread,
+\fIsigwait\fR()
+should be used to handle the signal. Alternatively, if the
+implementation provides semaphores, they also can be used, either
+following
+\fIsigwait\fR()
+or from within a signal handling routine previously registered with
+\fIsigaction\fR().
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "Section 2.4" ", " "Signal Concepts",
+.IR "Section 2.8.1" ", " "Realtime Signals",
+.IR "\fIpause\fR\^(\|)",
+.IR "\fIpthread_sigmask\fR\^(\|)",
+.IR "\fIsigaction\fR\^(\|)",
+.IR "\fIsigpending\fR\^(\|)",
+.IR "\fIsigsuspend\fR\^(\|)",
+.IR "\fIsigtimedwait\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2017,
+.IR "\fB<signal.h>\fP",
+.IR "\fB<time.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 .