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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>timer_getoverrun</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="timer_getoverrun"></a> <a name="tag_03_778"></a><!-- timer_getoverrun --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_778_01"></a>NAME</h4><blockquote>timer_getoverrun, timer_gettime, timer_settime - per-process timers (<b>REALTIME</b>)</blockquote><h4><a name="tag_03_778_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('TMR')">TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/time.h.html">time.h</a>><br><br> int timer_getoverrun(timer_t</tt> <i>timerid</i><tt>);<br> int timer_gettime(timer_t</tt> <i>timerid</i><tt>, struct itimerspec *</tt><i>value</i><tt>);<br> int timer_settime(timer_t</tt> <i>timerid</i><tt>, int</tt> <i>flags</i><tt>,<br> const struct itimerspec *restrict</tt> <i>value</i><tt>,<br> struct itimerspec *restrict</tt> <i>ovalue</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_778_03"></a>DESCRIPTION</h4><blockquote><p>The <i>timer_gettime</i>() function shall store the amount of time until the specified timer, <i>timerid</i>, expires and thereload value of the timer into the space pointed to by the <i>value</i> argument. The <i>it_value</i> member of this structureshall contain the amount of time before the timer expires, or zero if the timer is disarmed. This value is returned as the intervaluntil timer expiration, even if the timer was armed with absolute time. The <i>it_interval</i> member of <i>value</i> shall containthe reload value last set by <i>timer_settime</i>().</p><p>The <i>timer_settime</i>() function shall set the time until the next expiration of the timer specified by <i>timerid</i> fromthe <i>it_value</i> member of the <i>value</i> argument and arm the timer if the <i>it_value</i> member of <i>value</i> isnon-zero. If the specified timer was already armed when <i>timer_settime</i>() is called, this call shall reset the time until nextexpiration to the <i>value</i> specified. If the <i>it_value</i> member of <i>value</i> is zero, the timer shall be disarmed. Theeffect of disarming or resetting a timer with pending expiration notifications is unspecified.</p><p>If the flag TIMER_ABSTIME is not set in the argument <i>flags</i>, <i>timer_settime</i>() shall behave as if the time until nextexpiration is set to be equal to the interval specified by the <i>it_value</i> member of <i>value</i>. That is, the timer shallexpire in <i>it_value</i> nanoseconds from when the call is made. If the flag TIMER_ABSTIME is set in the argument <i>flags</i>,<i>timer_settime</i>() shall behave as if the time until next expiration is set to be equal to the difference between the absolutetime specified by the <i>it_value</i> member of <i>value</i> and the current value of the clock associated with <i>timerid</i>.That is, the timer shall expire when the clock reaches the value specified by the <i>it_value</i> member of <i>value</i>. If thespecified time has already passed, the function shall succeed and the expiration notification shall be made.</p><p>The reload value of the timer shall be set to the value specified by the <i>it_interval</i> member of <i>value</i>. When a timeris armed with a non-zero <i>it_interval</i>, a periodic (or repetitive) timer is specified.</p><p>Time values that are between two consecutive non-negative integer multiples of the resolution of the specified timer shall berounded up to the larger multiple of the resolution. Quantization error shall not cause the timer to expire earlier than therounded time value.</p><p>If the argument <i>ovalue</i> is not NULL, the <i>timer_settime</i>() function shall store, in the location referenced by<i>ovalue</i>, a value representing the previous amount of time before the timer would have expired, or zero if the timer wasdisarmed, together with the previous timer reload value. Timers shall not expire before their scheduled time.</p><p>Only a single signal shall be queued to the process for a given timer at any point in time. When a timer for which a signal isstill pending expires, no signal shall be queued, and a timer overrun shall occur. <sup>[<a href="javascript:open_code('RTS')">RTS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> When a timerexpiration signal is delivered to or accepted by a process, if the implementation supports the Realtime Signals Extension, the<i>timer_getoverrun</i>() function shall return the timer expiration overrun count for the specified timer. The overrun countreturned contains the number of extra timer expirations that occurred between the time the signal was generated (queued) and whenit was delivered or accepted, up to but not including an implementation-defined maximum of {DELAYTIMER_MAX}. If the number of suchextra expirations is greater than or equal to {DELAYTIMER_MAX}, then the overrun count shall be set to {DELAYTIMER_MAX}. The valuereturned by <i>timer_getoverrun</i>() shall apply to the most recent expiration signal delivery or acceptance for the timer. <imgsrc="../images/opt-end.gif" alt="[Option End]" border="0"> If no expiration signal has been delivered for the timer, or if theRealtime Signals Extension is not supported, the return value of <i>timer_getoverrun</i>() is unspecified.</p></blockquote><h4><a name="tag_03_778_04"></a>RETURN VALUE</h4><blockquote><p>If the <i>timer_getoverrun</i>() function succeeds, it shall return the timer expiration overrun count as explained above.</p><p>If the <i>timer_gettime</i>() or <i>timer_settime</i>() functions succeed, a value of 0 shall be returned.</p><p>If an error occurs for any of these functions, the value -1 shall be returned, and <i>errno</i> set to indicate the error.</p></blockquote><h4><a name="tag_03_778_05"></a>ERRORS</h4><blockquote><p>The <i>timer_getoverrun</i>(), <i>timer_gettime</i>(), and <i>timer_settime</i>() functions shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The <i>timerid</i> argument does not correspond to an ID returned by <a href="../functions/timer_create.html"><i>timer_create</i>()</a> but not yet deleted by <a href="../functions/timer_delete.html"><i>timer_delete</i>()</a>.</dd></dl><p>The <i>timer_settime</i>() function shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>A <i>value</i> structure specified a nanosecond value less than zero or greater than or equal to 1000 million, and the<i>it_value</i> member of that structure did not specify zero seconds and nanoseconds.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_778_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_778_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_778_08"></a>RATIONALE</h4><blockquote><p>Practical clocks tick at a finite rate, with rates of 100 hertz and 1000 hertz being common. The inverse of this tick rate isthe clock resolution, also called the clock granularity, which in either case is expressed as a time duration, being 10milliseconds and 1 millisecond respectively for these common rates. The granularity of practical clocks implies that if one reads agiven clock twice in rapid succession, one may get the same time value twice; and that timers must wait for the next clock tickafter the theoretical expiration time, to ensure that a timer never returns too soon. Note also that the granularity of the clockmay be significantly coarser than the resolution of the data format used to set and get time and interval values. Also note thatsome implementations may choose to adjust time and/or interval values to exactly match the ticks of the underlying clock.</p><p>This volume of IEEE Std 1003.1-2001 defines functions that allow an application to determine theimplementation-supported resolution for the clocks and requires an implementation to document the resolution supported for timersand <a href="../functions/nanosleep.html"><i>nanosleep</i>()</a> if they differ from the supported clock resolution. This is moreof a procurement issue than a runtime application issue.</p></blockquote><h4><a name="tag_03_778_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_778_10"></a>SEE ALSO</h4><blockquote><p><a href="clock_getres.html"><i>clock_getres</i>()</a> , <a href="timer_create.html"><i>timer_create</i>()</a> , the BaseDefinitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/time.h.html"><i><time.h></i></a></p></blockquote><h4><a name="tag_03_778_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 5. Included for alignment with the POSIX Realtime Extension.</p></blockquote><h4><a name="tag_03_778_12"></a>Issue 6</h4><blockquote><p>The <i>timer_getoverrun</i>(), <i>timer_gettime</i>(), and <i>timer_settime</i>() functions are marked as part of the Timersoption.</p><p>The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Timersoption.</p><p>The [EINVAL] error condition is updated to include the following: "and the <i>it_value</i> member of that structure did notspecify zero seconds and nanoseconds." This change is for IEEE PASC Interpretation 1003.1 #89.</p><p>The DESCRIPTION for <i>timer_getoverrun</i>() is updated to clarify that "If no expiration signal has been delivered for thetimer, or if the Realtime Signals Extension is not supported, the return value of <i>timer_getoverrun</i>() is unspecified".</p><p>The <b>restrict</b> keyword is added to the <i>timer_settime</i>() prototype for alignment with the ISO/IEC 9899:1999standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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