219 lines
5.9 KiB
HTML
219 lines
5.9 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of TIMER_GETOVERRUN</TITLE>
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</HEAD><BODY>
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<H1>TIMER_GETOVERRUN</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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timer_getoverrun - get overrun count for a POSIX per-process timer
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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/time.h">time.h</A>></B>
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<B>int timer_getoverrun(timer_t </B><I>timerid</I><B>);</B>
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</PRE>
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<P>
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Link with <I>-lrt</I>.
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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>timer_getoverrun</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>timer_getoverrun</B>()
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returns the "overrun count" for the timer referred to by
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<I>timerid</I>.
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An application can use the overrun count to accurately calculate the number
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of timer expirations that would have occurred over a given time interval.
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Timer overruns can occur both when receiving expiration notifications
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via signals
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(<B>SIGEV_SIGNAL</B>),
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and via threads
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(<B>SIGEV_THREAD</B>).
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<P>
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When expiration notifications are delivered via a signal,
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overruns can occur as follows.
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Regardless of whether or not a real-time signal is used for
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timer notifications,
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the system queues at most one signal per timer.
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(This is the behavior specified by POSIX.1.
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The alternative, queuing one signal for each timer expiration,
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could easily result in overflowing the allowed limits for
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queued signals on the system.)
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Because of system scheduling delays,
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or because the signal may be temporarily blocked,
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there can be a delay between the time when the notification
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signal is generated and the time when it
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is delivered (e.g., caught by a signal handler) or accepted (e.g., using
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<B><A HREF="/cgi-bin/man/man2html?2+sigwaitinfo">sigwaitinfo</A></B>(2)).
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In this interval, further timer expirations may occur.
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The timer overrun count is the number of additional
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timer expirations that occurred between the time when the signal
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was generated and when it was delivered or accepted.
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<P>
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Timer overruns can also occur when expiration notifications
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are delivered via invocation of a thread,
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since there may be an arbitrary delay between an expiration of the timer
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and the invocation of the notification thread,
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and in that delay interval, additional timer expirations may occur.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>timer_getoverrun</B>()
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returns the overrun count of the specified timer;
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this count may be 0 if no overruns have occurred.
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On failure, -1 is returned, and
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<I>errno</I>
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is 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>EINVAL</B>
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<DD>
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<I>timerid</I>
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is not a valid timer ID.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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This system call is available since Linux 2.6.
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<A NAME="lbAH"> </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="lbAI"> </A>
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<H2>NOTES</H2>
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When timer notifications are delivered via signals
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(<B>SIGEV_SIGNAL</B>),
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on Linux it is also possible to obtain the overrun count via the
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<I>si_overrun</I>
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field of the
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<I>siginfo_t</I>
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structure (see
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<B><A HREF="/cgi-bin/man/man2html?2+sigaction">sigaction</A></B>(2)).
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This allows an application to avoid the overhead of making
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a system call to obtain the overrun count,
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but is a nonportable extension to POSIX.1.
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<P>
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POSIX.1 discusses timer overruns only in the context of
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timer notifications using signals.
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<A NAME="lbAJ"> </A>
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<H2>BUGS</H2>
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POSIX.1 specifies that if the timer overrun count
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is equal to or greater than an implementation-defined maximum,
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<B>DELAYTIMER_MAX</B>,
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then
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<B>timer_getoverrun</B>()
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should return
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<B>DELAYTIMER_MAX</B>.
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However, Linux does not implement this feature: instead,
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if the timer overrun value exceeds the maximum representable integer,
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the counter cycles, starting once more from low values.
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<A NAME="lbAK"> </A>
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<H2>EXAMPLE</H2>
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See
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<B><A HREF="/cgi-bin/man/man2html?2+timer_create">timer_create</A></B>(2).
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+clock_gettime">clock_gettime</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+signalfd">signalfd</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sigwaitinfo">sigwaitinfo</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+timer_create">timer_create</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+timer_delete">timer_delete</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+timer_settime">timer_settime</A></B>(2),
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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="lbAM"> </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="2"><A HREF="#lbAB">NAME</A><DD>
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<DT id="3"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="4"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="5"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="6"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="7"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="8"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="9"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="10"><A HREF="#lbAJ">BUGS</A><DD>
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<DT id="11"><A HREF="#lbAK">EXAMPLE</A><DD>
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<DT id="12"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="13"><A HREF="#lbAM">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: 00:05:35 GMT, March 31, 2021
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</BODY>
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</HTML>
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