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402 lines
12 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>semop()-Perform Semaphore Operations on Semaphore Set</title>
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<!-- Begin Header Records ========================================== -->
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Change History: -->
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<!-- YYMMDD USERID Change description -->
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<!-- Direct1 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!-- This file has undergone html/error condition cleanup on 05/01/02 by JET -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!--End Header Records --><!-- Java sync-link -->
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>semop()--Perform Semaphore Operations on Semaphore Set</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax<br>
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<pre>
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#include <sys/sem.h>
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int semop(int <em>semid</em>, struct sembuf <em>*sops</em>,
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size_t <em>nsops</em>);
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</pre>
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<br>
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Service Program Name: QP0ZCPA<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>semop()</strong> function performs operations on semaphores in a
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semaphore set. These operations are supplied in a user-defined array of
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operations.</p>
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<p>Each semaphore operation specified by the <em>sops</em> array is
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performed on the semaphore set specified by <em>semid</em>. The entire array
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of operations is performed atomically; no other thread will operate on the
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semaphore set until all of the operations are done or it is determined that
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they cannot be done. If the entire set of operations cannot be performed, none
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of the operations are done, and the thread waits until all of the operations
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can be done.</p>
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<p>The members of the <samp>sembuf</samp> structure are as follows:</p>
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<table cellpadding="5">
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<!-- cols="15 85" -->
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<tr>
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<td align="left" valign="top"><em>unsigned short sem_num</em> </td>
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<td align="left" valign="top">The number of the semaphore in the semaphore set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>short sem_op</em> </td>
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<td align="left" valign="top">The operation to perform on the semaphore.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>short sem_flg</em> </td>
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<td align="left" valign="top">The operation flags.</td>
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</tr>
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</table>
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<p>The <strong>semop()</strong> function changes each semaphore specified by <em>
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sem_num</em> according to the value of <em>sem_op</em> as follows:</p>
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<br>
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<ul>
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<li>If <em>sem_op</em> is positive, <strong>semop()</strong> increments the
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value of the semaphore and wakes up any threads waiting for the semaphore to
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increase. This corresponds to releasing resources controlled by the
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semaphore.<br>
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<br>
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</li>
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<li>If <em>sem_op</em> is negative, <strong>semop()</strong> attempts to
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decrement the value of the semaphore. If the result would be negative, it waits
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for the semaphore value to increase. If the result would be positive, it
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decrements the semaphore. If the result would be zero, it decrements the
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semaphore and wakes up any threads waiting for the semaphore to be zero. This
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corresponds to the allocation of resources.<br>
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<br>
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</li>
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<li>If <em>sem_op</em> is zero, the thread waits for the semaphore's value to
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be zero.</li>
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</ul>
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<p>If IPC_NOWAIT is set in <em>sem_flg</em> and the operation cannot be completed, <strong>
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semop()</strong> returns with a return value of -1 and <em>errno</em> set to EAGAIN
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instead of causing the thread to wait.</p>
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<p>If SEM_UNDO is set in <em>sem_flg</em>, <strong>semop()</strong> causes IPC to reverse the
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effect of this semaphore operation when the thread ends, effectively releasing
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the resources or request for resources controlled by the semaphore. This value
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is known as the semaphore adjustment value.</p>
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<p>If the thread waits for the semaphore value to change, the calling thread suspends
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processing until one of the following occurs:</p>
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<ul>
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<li>The semaphore reaches the specified value.</li>
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<li>The semaphore set identifier <em>semid</em> is removed from the system.
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When this occurs, the <strong>semop()</strong> function returns with a return value of -1 and
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<em>errno</em> set to EIDRM.</li>
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<li>A signal is delivered to the calling thread. When this occurs, the <strong>semop</strong>
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function returns with a return value of -1 and <em>errno</em> set to EINTER.
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</li>
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</ul>
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<p>The system maintains status information about a semaphore set which can
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be retrieved with the <a href="ipcsemct.htm">semctl()</a> function. When a
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semaphore operation is successfully completed, the system sets the members of the
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<samp>semid_ds</samp> structure as follows:</p>
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<ul>
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<li><samp>shm_otime</samp> is set to the current time.</li>
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</ul>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong><em>semid</em></strong></dt>
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<dd>(Input) Semaphore set identifier, a positive integer. It is returned by the
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<a href="ipcsemgt.htm">semget()</a> function and used to identify the semaphore set on
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which to perform the control operation.<br>
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<br>
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</dd>
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<dt><strong><em>sops</em></strong></dt>
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<dd>(Input) Pointer to array of semaphore operation structures.<br>
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<br>
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</dd>
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<dt><strong><em>nsops</em></strong></dt>
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<dd>(Input) Number of <samp>sembuf</samp> structures in <em>sops</em> array.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p><strong><a name="TBLASOP1">Authorization Required for semop()</a></strong></p>
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<table border cellpadding="5">
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<!-- cols="60 20 20" -->
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<tr>
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<th align="left" valign="bottom">Object Referred to</th>
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<th align="left" valign="bottom">Authority Required</th>
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<th align="left" valign="bottom">errno</th>
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</tr>
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<tr>
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<td align="left" valign="top">Semaphore, <em>sem_op</em> is negative</td>
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<td align="left" valign="top">Write</td>
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<td align="left" valign="top">EACCES</td>
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</tr>
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<tr>
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<td align="left" valign="top">Semaphore, <em>sem_op</em> is positive</td>
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<td align="left" valign="top">Write</td>
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<td align="left" valign="top">EACCES</td>
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</tr>
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<tr>
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<td align="left" valign="top">Semaphore, <em>sem_op</em> is zero</td>
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<td align="left" valign="top">Read</td>
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<td align="left" valign="top">EACCES</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="5 95" -->
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<tr>
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<td align="left" valign="top"><em>0</em></td>
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<td align="left" valign="top"><strong>semop()</strong> was successful.</td>
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</tr>
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<tr>
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<td align="left" valign="top" nowrap><em>-1</em></td>
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<td align="left" valign="top"><strong>semop()</strong> was not successful. The
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<em>errno</em> variable is set to indicate the error.</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>semop()</strong> is not successful, <em>errno</em> usually
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indicates one of the following errors. Under some conditions, <em>errno</em>
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could indicate an error other than those listed here.</p>
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<dl>
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<dt><em>[EACCES]</em></dt>
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<dd>
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<p>Permission denied.</p>
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<p>An attempt was made to access an object in a way forbidden by its object
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access permissions.</p>
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<p>The thread does not have access to the specified file, directory, component,
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or path.</p>
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<p>The <em>sem_op</em> value is negative or positive and the calling thread does
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not have write permisstion to the semaphore set.</p>
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<p>The <em>sem_op</em> value is zero and the calling thread does
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not have read permisstion to the semaphore set.</p>
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</dd>
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<dt><em>[EAGAIN]</em></dt>
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<dd>
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<p>Operation would have caused the process to be suspended.</p>
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<p>The operation would result in the calling thread waiting and
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the IPC_NOWAIT flag is set in the <em>sem_flg</em> member.</p>
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</dd>
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<dt><em>[EDAMAGE]</em></dt>
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<dd>
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<p>A damaged object was encountered.</p>
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<p>A referenced object is damaged. The object cannot be used.</p>
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<p>The semaphore set has been damaged by a previous semaphore operation.</p>
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</dd>
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<dt><em>[EFAULT]</em></dt>
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<dd>
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<p>The address used for an argument is not correct.</p>
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<p>In attempting to use an argument in a call, the system detected an address
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that is not valid.</p>
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<p>While attempting to access a parameter passed to this function, the system
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detected an address that is not valid.</p>
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</dd>
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<dt><em>[EFBIG]</em></dt>
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<dd>
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<p>Object is too large.</p>
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<p>The size of the object would exceed the system allowed maximum size.</p>
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<p>The <em>sem_num</em> parameter is less than zero or greater than or equal to the
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number of semaphores in the set associated with <em>semid</em>.</p>
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</dd>
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<dt><em>[EIDRM]</em></dt>
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<dd>
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<p>ID has been removed.</p>
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<p>The semaphore identifier <em>semid</em> has been removed from the
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system.</p>
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</dd>
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<dt><em>[EINTR]</em></dt>
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<dd>
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<p>Interrupted function call.</p>
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<p>The <em>semop()</em> function was interrupted by a signal.</p>
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</dd>
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<dt><em>[EINVAL]</em></dt>
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<dd>
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<p>The value specified for the argument is not correct.</p>
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<p>A function was passed incorrect argument values, or an operation was
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attempted on an object and the operation specified is not supported for that
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type of object.</p>
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<p>An argument value is not valid, out of range, or NULL.</p>
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<p>The <em>semid</em> parameter is not a valid semaphore identifier.</p>
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</dd>
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<dt><em>[ENOSPC]</em></dt>
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<dd>
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<p>No space available.</p>
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<p>The requested operations required additional space on the device and there
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is no space left. This could also be caused by exceeding the user profile
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storage limit when creating or transferring ownership of an object.</p>
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<p>Insufficient space remains to hold the intended file, directory, or
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link.</p>
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<p>The limit on the number of individual threads requesting a SEM_UNDO would be
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exceeded.</p>
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</dd>
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<dt><em>[ERANGE]</em></dt>
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<dd>
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<p>A range error occurred.</p>
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<p>The value of an argument is too small, or a result too large.</p>
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<p>An operation would cause a <em>semval</em> to overflow the system-imposed
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limit, or an operation would cause a semaphore adjustment value to overflow the
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system-imposed limit.</p>
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</dd>
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<dt><em>[EUNKNOWN]</em></dt>
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<dd>
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<p>Unknown system state.</p>
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<p>The operation failed because of an unknown system state. See any messages in
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the job log and correct any errors that are indicated, then retry the
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operation.</p>
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</dd>
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</dl>
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<br>
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<h3>Error Messages</h3>
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<p>None.</p>
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<br>
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<h3>Related Information</h3>
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||
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<ul>
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<li>The <<strong>sys/sem.h</strong>> file (see <a href="unix13.htm">
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Header Files for UNIX-Type Functions</a>)<br>
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<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcsemgt.htm">semget()</a>--Get Semaphore Set with Key<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcsemct.htm">semctl()</a>--Perform Semaphore Control
|
||
|
|
Operations</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Example</h3>
|
||
|
|
|
||
|
|
<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
|
||
|
|
for information pertaining to code examples.</p>
|
||
|
|
|
||
|
|
<p>For an example of using this function, see <a href="../apiref/apiexusmem.htm">
|
||
|
|
Using Semaphores and Shared Memory</a> in Examples: APIs.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<hr>
|
||
|
|
API introduced: V3R6
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<center>
|
||
|
|
<table cellpadding="2" cellspacing="2">
|
||
|
|
<tr align="center">
|
||
|
|
<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
|
||
|
|
"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</center>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|