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sigwaitinfo.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:27:05 2020 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
p { margin-top: 0; margin-bottom: 0; vertical-align: top }
pre { margin-top: 0; margin-bottom: 0; vertical-align: top }
table { margin-top: 0; margin-bottom: 0; vertical-align: top }
h1 { text-align: center }
</style>
<title>SIGWAITINFO</title>
</head>
<body>
<h1 align="center">SIGWAITINFO</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#RETURN VALUE">RETURN VALUE</a><br>
<a href="#ERRORS">ERRORS</a><br>
<a href="#CONFORMING TO">CONFORMING TO</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#COLOPHON">COLOPHON</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">sigwaitinfo,
sigtimedwait, rt_sigtimedwait - synchronously wait for
queued signals</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>#include
<signal.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
sigwaitinfo(const sigset_t *</b><i>set</i><b>, siginfo_t
*</b><i>info</i><b>);</b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
sigtimedwait(const sigset_t *</b><i>set</i><b>, siginfo_t
*</b><i>info</i><b>, <br>
const struct timespec *</b><i>timeout</i><b>);</b></p>
<p style="margin-left:5%; margin-top: 1em">Feature Test
Macro Requirements for glibc (see
<b>feature_test_macros</b>(7)):</p>
<p style="margin-left:11%; margin-top: 1em"><b>sigwaitinfo</b>(),
<b>sigtimedwait</b>():
_POSIX_C_SOURCE >= 199309L</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>sigwaitinfo</b>()
suspends execution of the calling thread until one of the
signals in <i>set</i> is pending (If one of the signals in
<i>set</i> is already pending for the calling thread,
<b>sigwaitinfo</b>() will return immediately.)</p>
<p style="margin-left:11%; margin-top: 1em"><b>sigwaitinfo</b>()
removes the signal from the set of pending signals and
returns the signal number as its function result. If the
<i>info</i> argument is not NULL, then the buffer that it
points to is used to return a structure of type
<i>siginfo_t</i> (see <b>sigaction</b>(2)) containing
information about the signal.</p>
<p style="margin-left:11%; margin-top: 1em">If multiple
signals in <i>set</i> are pending for the caller, the signal
that is retrieved by <b>sigwaitinfo</b>() is determined
according to the usual ordering rules; see <b>signal</b>(7)
for further details.</p>
<p style="margin-left:11%; margin-top: 1em"><b>sigtimedwait</b>()
operates in exactly the same way as <b>sigwaitinfo</b>()
except that it has an additional argument, <i>timeout</i>,
which specifies the interval for which the thread is
suspended waiting for a signal. (This interval will be
rounded up to the system clock granularity, and kernel
scheduling delays mean that the interval may overrun by a
small amount.) This argument is of the following type:</p>
<p style="margin-left:17%; margin-top: 1em">struct timespec
{ <br>
long tv_sec; /* seconds */ <br>
long tv_nsec; /* nanoseconds */ <br>
}</p>
<p style="margin-left:11%; margin-top: 1em">If both fields
of this structure are specified as 0, a poll is performed:
<b>sigtimedwait</b>() returns immediately, either with
information about a signal that was pending for the caller,
or with an error if none of the signals in <i>set</i> was
pending.</p>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">On success,
both <b>sigwaitinfo</b>() and <b>sigtimedwait</b>() return a
signal number (i.e., a value greater than zero). On failure
both calls return -1, with <i>errno</i> set to indicate the
error.</p>
<h2>ERRORS
<a name="ERRORS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>EAGAIN</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em">No signal in <i>set</i> was
became pending within the <i>timeout</i> period specified to
<b>sigtimedwait</b>().</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>EINTR</b></p></td>
<td width="2%"></td>
<td width="78%">
<p>The wait was interrupted by a signal handler; see
<b>signal</b>(7). (This handler was for a signal other than
one of those in <i>set</i>.)</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>EINVAL</b></p></td>
<td width="2%"></td>
<td width="78%">
<p><i>timeout</i> was invalid.</p></td></tr>
</table>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">POSIX.1-2001,
POSIX.1-2008.</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">In normal
usage, the calling program blocks the signals in <i>set</i>
via a prior call to <b>sigprocmask</b>(2) (so that the
default disposition for these signals does not occur if they
become pending between successive calls to
<b>sigwaitinfo</b>() or <b>sigtimedwait</b>()) and does not
establish handlers for these signals. In a multithreaded
program, the signal should be blocked in all threads, in
order to prevent the signal being treated according to its
default disposition in a thread other than the one calling
<b>sigwaitinfo</b>() or <b>sigtimedwait</b>()).</p>
<p style="margin-left:11%; margin-top: 1em">The set of
signals that is pending for a given thread is the union of
the set of signals that is pending specifically for that
thread and the set of signals that is pending for the
process as a whole (see <b>signal</b>(7)).</p>
<p style="margin-left:11%; margin-top: 1em">Attempts to
wait for <b>SIGKILL</b> and <b>SIGSTOP</b> are silently
ignored.</p>
<p style="margin-left:11%; margin-top: 1em">If multiple
threads of a process are blocked waiting for the same
signal(s) in <b>sigwaitinfo</b>() or <b>sigtimedwait</b>(),
then exactly one of the threads will actually receive the
signal if it becomes pending for the process as a whole;
which of the threads receives the signal is
indeterminate.</p>
<p style="margin-left:11%; margin-top: 1em"><b>sigwaitinfo</b>()
or <b>sigtimedwait</b>(), can’t be used to receive
signals that are synchronously generated, such as the
<b>SIGSEGV</b> signal that results from accessing an invalid
memory address or the <b>SIGFPE</b> signal that results from
an arithmetic error. Such signals can be caught only via
signal handler.</p>
<p style="margin-left:11%; margin-top: 1em">POSIX leaves
the meaning of a NULL value for the <i>timeout</i> argument
of <b>sigtimedwait</b>() unspecified, permitting the
possibility that this has the same meaning as a call to
<b>sigwaitinfo</b>(), and indeed this is what is done on
Linux.</p>
<p style="margin-left:11%; margin-top: 1em"><b>C
library/kernel differences</b> <br>
On Linux, <b>sigwaitinfo</b>() is a library function
implemented on top of <b>sigtimedwait</b>().</p>
<p style="margin-left:11%; margin-top: 1em">The glibc
wrapper functions for <b>sigwaitinfo</b>() and
<b>sigtimedwait</b>() silently ignore attempts to wait for
the two real-time signals that are used internally by the
NPTL threading implementation. See <b>nptl</b>(7) for
details.</p>
<p style="margin-left:11%; margin-top: 1em">The original
Linux system call was named <b>sigtimedwait</b>(). However,
with the addition of real-time signals in Linux 2.2, the
fixed-size, 32-bit <i>sigset_t</i> type supported by that
system call was no longer fit for purpose. Consequently, a
new system call, <b>rt_sigtimedwait</b>(), was added to
support an enlarged <i>sigset_t</i> type. The new system
call takes a fourth argument, <i>size_t sigsetsize</i>,
which specifies the size in bytes of the signal set in
<i>set</i>. This argument is currently required to have the
value <i>sizeof(sigset_t)</i> (or the error <b>EINVAL</b>
results). The glibc <b>sigtimedwait</b>() wrapper function
hides these details from us, transparently calling
<b>rt_sigtimedwait</b>() when the kernel provides it.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>kill</b>(2),
<b>sigaction</b>(2), <b>signal</b>(2), <b>signalfd</b>(2),
<b>sigpending</b>(2), <b>sigprocmask</b>(2),
<b>sigqueue</b>(3), <b>sigsetops</b>(3), <b>sigwait</b>(3),
<b>signal</b>(7), <b>time</b>(7)</p>
<h2>COLOPHON
<a name="COLOPHON"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This page is
part of release 5.02 of the Linux <i>man-pages</i> project.
A description of the project, information about reporting
bugs, and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.</p>
<hr>
</body>
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