188 lines
9.8 KiB
HTML
188 lines
9.8 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>sleep</title>
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<basefont size="3"> <a name="sleep"></a> <a name="tag_03_705"></a><!-- sleep -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_705_01"></a>NAME</h4>
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<blockquote>sleep - suspend execution for an interval of time</blockquote>
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<h4><a name="tag_03_705_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
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<br>
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unsigned sleep(unsigned</tt> <i>seconds</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_705_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sleep</i>() function shall cause the calling thread to be suspended from execution until either the number of realtime
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seconds specified by the argument <i>seconds</i> has elapsed or a signal is delivered to the calling thread and its action is to
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invoke a signal-catching function or to terminate the process. The suspension time may be longer than requested due to the
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scheduling of other activity by the system.</p>
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<p>If a SIGALRM signal is generated for the calling process during execution of <i>sleep</i>() and if the SIGALRM signal is being
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ignored or blocked from delivery, it is unspecified whether <i>sleep</i>() returns when the SIGALRM signal is scheduled. If the
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signal is being blocked, it is also unspecified whether it remains pending after <i>sleep</i>() returns or it is discarded.</p>
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<p>If a SIGALRM signal is generated for the calling process during execution of <i>sleep</i>(), except as a result of a prior call
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to <a href="../functions/alarm.html"><i>alarm</i>()</a>, and if the SIGALRM signal is not being ignored or blocked from delivery,
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it is unspecified whether that signal has any effect other than causing <i>sleep</i>() to return.</p>
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<p>If a signal-catching function interrupts <i>sleep</i>() and examines or changes either the time a SIGALRM is scheduled to be
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generated, the action associated with the SIGALRM signal, or whether the SIGALRM signal is blocked from delivery, the results are
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unspecified.</p>
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<p>If a signal-catching function interrupts <i>sleep</i>() and calls <a href="../functions/siglongjmp.html"><i>siglongjmp</i>()</a>
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or <a href="../functions/longjmp.html"><i>longjmp</i>()</a> to restore an environment saved prior to the <i>sleep</i>() call, the
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action associated with the SIGALRM signal and the time at which a SIGALRM signal is scheduled to be generated are unspecified. It
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is also unspecified whether the SIGALRM signal is blocked, unless the process' signal mask is restored as part of the
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environment.</p>
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<p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Interactions between <i>sleep</i>() and any of <a href="../functions/setitimer.html"><i>setitimer</i>()</a>, <a href=
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"../functions/ualarm.html"><i>ualarm</i>()</a>, or <a href="../functions/usleep.html"><i>usleep</i>()</a> are unspecified. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_705_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If <i>sleep</i>() returns because the requested time has elapsed, the value returned shall be 0. If <i>sleep</i>() returns due
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to delivery of a signal, the return value shall be the "unslept" amount (the requested time minus the time actually slept) in
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seconds.</p>
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</blockquote>
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<h4><a name="tag_03_705_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_705_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_705_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_705_08"></a>RATIONALE</h4>
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<blockquote>
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<p>There are two general approaches to the implementation of the <i>sleep</i>() function. One is to use the <a href=
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"../functions/alarm.html"><i>alarm</i>()</a> function to schedule a SIGALRM signal and then suspend the process waiting for that
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signal. The other is to implement an independent facility. This volume of IEEE Std 1003.1-2001 permits either
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approach.</p>
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<p>In order to comply with the requirement that no primitive shall change a process attribute unless explicitly described by this
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volume of IEEE Std 1003.1-2001, an implementation using SIGALRM must carefully take into account any SIGALRM signal
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scheduled by previous <a href="../functions/alarm.html"><i>alarm</i>()</a> calls, the action previously established for SIGALRM,
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and whether SIGALRM was blocked. If a SIGALRM has been scheduled before the <i>sleep</i>() would ordinarily complete, the
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<i>sleep</i>() must be shortened to that time and a SIGALRM generated (possibly simulated by direct invocation of the
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signal-catching function) before <i>sleep</i>() returns. If a SIGALRM has been scheduled after the <i>sleep</i>() would ordinarily
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complete, it must be rescheduled for the same time before <i>sleep</i>() returns. The action and blocking for SIGALRM must be saved
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and restored.</p>
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<p>Historical implementations often implement the SIGALRM-based version using <a href="../functions/alarm.html"><i>alarm</i>()</a>
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and <a href="../functions/pause.html"><i>pause</i>()</a>. One such implementation is prone to infinite hangups, as described in <a
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href="pause.html"><i>pause</i>()</a> . Another such implementation uses the C-language <a href=
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"../functions/setjmp.html"><i>setjmp</i>()</a> and <a href="../functions/longjmp.html"><i>longjmp</i>()</a> functions to avoid that
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window. That implementation introduces a different problem: when the SIGALRM signal interrupts a signal-catching function installed
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by the user to catch a different signal, the <a href="../functions/longjmp.html"><i>longjmp</i>()</a> aborts that signal-catching
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function. An implementation based on <a href="../functions/sigprocmask.html"><i>sigprocmask</i>()</a>, <a href=
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"../functions/alarm.html"><i>alarm</i>()</a>, and <a href="../functions/sigsuspend.html"><i>sigsuspend</i>()</a> can avoid these
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problems.</p>
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<p>Despite all reasonable care, there are several very subtle, but detectable and unavoidable, differences between the two types of
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implementations. These are the cases mentioned in this volume of IEEE Std 1003.1-2001 where some other activity relating
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to SIGALRM takes place, and the results are stated to be unspecified. All of these cases are sufficiently unusual as not to be of
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concern to most applications.</p>
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<p>See also the discussion of the term <i>realtime</i> in <a href="alarm.html"><i>alarm</i>()</a> .</p>
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<p>Since <i>sleep</i>() can be implemented using <a href="../functions/alarm.html"><i>alarm</i>()</a>, the discussion about alarms
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occurring early under <a href="../functions/alarm.html"><i>alarm</i>()</a> applies to <i>sleep</i>() as well.</p>
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<p>Application writers should note that the type of the argument <i>seconds</i> and the return value of <i>sleep</i>() is
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<b>unsigned</b>. That means that a Strictly Conforming POSIX System Interfaces Application cannot pass a value greater than the
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minimum guaranteed value for {UINT_MAX}, which the ISO C standard sets as 65535, and any application passing a larger value is
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restricting its portability. A different type was considered, but historical implementations, including those with a 16-bit
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<b>int</b> type, consistently use either <b>unsigned</b> or <b>int</b>.</p>
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<p>Scheduling delays may cause the process to return from the <i>sleep</i>() function significantly after the requested time. In
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such cases, the return value should be set to zero, since the formula (requested time minus the time actually spent) yields a
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negative number and <i>sleep</i>() returns an <b>unsigned</b>.</p>
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</blockquote>
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<h4><a name="tag_03_705_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_705_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="alarm.html"><i>alarm</i>()</a> , <a href="getitimer.html"><i>getitimer</i>()</a> , <a href=
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"nanosleep.html"><i>nanosleep</i>()</a> , <a href="pause.html"><i>pause</i>()</a> , <a href="sigaction.html"><i>sigaction</i>()</a>
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, <a href="sigsetjmp.html"><i>sigsetjmp</i>()</a> , <a href="ualarm.html"><i>ualarm</i>()</a> , <a href=
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"usleep.html"><i>usleep</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_705_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_705_12"></a>Issue 5</h4>
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<blockquote>
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<p>The DESCRIPTION is updated for alignment with the POSIX Threads Extension.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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