380 lines
8.5 KiB
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380 lines
8.5 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of SIGWAITINFO</TITLE>
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</HEAD><BODY>
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<H1>SIGWAITINFO</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait
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for queued signals
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/signal.h">signal.h</A>></B>
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<B>int sigwaitinfo(const sigset_t *</B><I>set</I><B>, siginfo_t *</B><I>info</I><B>);</B>
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<B>int sigtimedwait(const sigset_t *</B><I>set</I><B>, siginfo_t *</B><I>info</I><B>, </B>
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<B> const struct timespec *</B><I>timeout</I><B>);</B>
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</PRE>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>sigwaitinfo</B>(),
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<B>sigtimedwait</B>():
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_POSIX_C_SOURCE >= 199309L
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>sigwaitinfo</B>()
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suspends execution of the calling thread until one of the signals in
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<I>set</I>
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is pending
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(If one of the signals in
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<I>set</I>
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is already pending for the calling thread,
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<B>sigwaitinfo</B>()
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will return immediately.)
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<P>
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<B>sigwaitinfo</B>()
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removes the signal from the set of pending
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signals and returns the signal number as its function result.
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If the
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<I>info</I>
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argument is not NULL,
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then the buffer that it points to is used to return a structure of type
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<I>siginfo_t</I>
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(see
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<B><A HREF="/cgi-bin/man/man2html?2+sigaction">sigaction</A></B>(2))
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containing information about the signal.
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<P>
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If multiple signals in
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<I>set</I>
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are pending for the caller, the signal that is retrieved by
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<B>sigwaitinfo</B>()
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is determined according to the usual ordering rules; see
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<B><A HREF="/cgi-bin/man/man2html?7+signal">signal</A></B>(7)
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for further details.
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<P>
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<B>sigtimedwait</B>()
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operates in exactly the same way as
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<B>sigwaitinfo</B>()
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except that it has an additional argument,
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<I>timeout</I>,
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which specifies the interval for which
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the thread is suspended waiting for a signal.
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(This interval will be rounded up to the system clock granularity,
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and kernel scheduling delays mean that the interval
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may overrun by a small amount.)
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This argument is of the following type:
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<P>
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struct timespec {
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<BR> long tv_sec; /* seconds */
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<BR> long tv_nsec; /* nanoseconds */
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}
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<P>
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If both fields of this structure are specified as 0, a poll is performed:
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<B>sigtimedwait</B>()
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returns immediately, either with information about a signal that
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was pending for the caller, or with an error
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if none of the signals in
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<I>set</I>
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was pending.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, both
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<B>sigwaitinfo</B>()
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and
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<B>sigtimedwait</B>()
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return a signal number (i.e., a value greater than zero).
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On failure both calls return -1, with
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<I>errno</I>
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set to indicate the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>EAGAIN</B>
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<DD>
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No signal in
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<I>set</I>
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was became pending within the
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<I>timeout</I>
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period specified to
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<B>sigtimedwait</B>().
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<DT id="2"><B>EINTR</B>
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<DD>
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The wait was interrupted by a signal handler; see
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<B><A HREF="/cgi-bin/man/man2html?7+signal">signal</A></B>(7).
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(This handler was for a signal other than one of those in
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<I>set</I>.)
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<DT id="3"><B>EINVAL</B>
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<DD>
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<I>timeout</I>
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was invalid.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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In normal usage, the calling program blocks the signals in
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<I>set</I>
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via a prior call to
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<B><A HREF="/cgi-bin/man/man2html?2+sigprocmask">sigprocmask</A></B>(2)
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(so that the default disposition for these signals does not occur if they
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become pending between successive calls to
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<B>sigwaitinfo</B>()
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or
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<B>sigtimedwait</B>())
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and does not establish handlers for these signals.
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In a multithreaded program,
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the signal should be blocked in all threads, in order to prevent
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the signal being treated according to its default disposition in
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a thread other than the one calling
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<B>sigwaitinfo</B>()
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or
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<B>sigtimedwait</B>()).
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<P>
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The set of signals that is pending for a given thread is the
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union of the set of signals that is pending specifically for that thread
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and the set of signals that is pending for the process as a whole (see
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<B><A HREF="/cgi-bin/man/man2html?7+signal">signal</A></B>(7)).
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<P>
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Attempts to wait for
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<B>SIGKILL</B>
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and
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<B>SIGSTOP</B>
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are silently ignored.
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<P>
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If multiple threads of a process are blocked
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waiting for the same signal(s) in
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<B>sigwaitinfo</B>()
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or
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<B>sigtimedwait</B>(),
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then exactly one of the threads will actually receive the
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signal if it becomes pending for the process as a whole;
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which of the threads receives the signal is indeterminate.
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<P>
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<B>sigwaitinfo</B>()
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or
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<B>sigtimedwait</B>(),
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can't be used to receive signals that
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are synchronously generated, such as the
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<B>SIGSEGV</B>
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signal that results from accessing an invalid memory address
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or the
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<B>SIGFPE</B>
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signal that results from an arithmetic error.
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Such signals can be caught only via signal handler.
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<P>
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POSIX leaves the meaning of a NULL value for the
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<I>timeout</I>
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argument of
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<B>sigtimedwait</B>()
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unspecified, permitting the possibility that this has the same meaning
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as a call to
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<B>sigwaitinfo</B>(),
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and indeed this is what is done on Linux.
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<A NAME="lbAI"> </A>
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<H3>C library/kernel differences</H3>
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On Linux,
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<B>sigwaitinfo</B>()
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is a library function implemented on top of
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<B>sigtimedwait</B>().
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<P>
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The glibc wrapper functions for
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<B>sigwaitinfo</B>()
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and
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<B>sigtimedwait</B>()
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silently ignore attempts to wait for the two real-time signals that
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are used internally by the NPTL threading implementation.
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See
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<B><A HREF="/cgi-bin/man/man2html?7+nptl">nptl</A></B>(7)
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for details.
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<P>
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The original Linux system call was named
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<B>sigtimedwait</B>().
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However, with the addition of real-time signals in Linux 2.2,
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the fixed-size, 32-bit
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<I>sigset_t</I>
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type supported by that system call was no longer fit for purpose.
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Consequently, a new system call,
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<B>rt_sigtimedwait</B>(),
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was added to support an enlarged
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<I>sigset_t</I>
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type.
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The new system call takes a fourth argument,
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<I>size_t sigsetsize</I>,
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which specifies the size in bytes of the signal set in
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<I>set</I>.
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This argument is currently required to have the value
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<I>sizeof(sigset_t)</I>
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(or the error
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<B>EINVAL</B>
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results).
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The glibc
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<B>sigtimedwait</B>()
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wrapper function hides these details from us, transparently calling
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<B>rt_sigtimedwait</B>()
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when the kernel provides it.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+kill">kill</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sigaction">sigaction</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+signal">signal</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+signalfd">signalfd</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sigpending">sigpending</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sigprocmask">sigprocmask</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+sigqueue">sigqueue</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sigsetops">sigsetops</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sigwait">sigwait</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+signal">signal</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+time">time</A></B>(7)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="4"><A HREF="#lbAB">NAME</A><DD>
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<DT id="5"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="6"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="7"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="8"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="9"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="10"><A HREF="#lbAH">NOTES</A><DD>
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<DL>
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<DT id="11"><A HREF="#lbAI">C library/kernel differences</A><DD>
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</DL>
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<DT id="12"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="13"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:34 GMT, March 31, 2021
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