561 lines
17 KiB
HTML
561 lines
17 KiB
HTML
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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>semctl()-Perform Semaphore Control Operations</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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<!-- Edited by Kersten Feb 02 -->
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<!-- This file has undergone 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 -->
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<!-- 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>semctl()--Perform Semaphore Control Operations</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 semctl(int <em>semid</em>, int <em>semnum</em>, int <em>cmd</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>semctl()</strong> function allows the caller to control the
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semaphore set specified by the <em>semid</em> parameter.</p>
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<p>A semaphore set is controlled by setting the <em>cmd</em> parameter
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to one of the following values:
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<dl>
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<dt><strong>IPC_RMID (0x00000000)</strong></dt>
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<dd>Remove the semaphore set identifier <em>semid</em> from the system and
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destroy the set of semaphores. Any threads that are waiting in
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<strong>semop()</strong> are woken up and <strong>semop()</strong> returns with a
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return value of -1 and <em>errno</em> set to EIDRM.
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<p>The IPC_RMID command can be run
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only by a thread with appropriate privileges or one that has an effective user
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ID equal to the user ID of the owner or the user ID of the creator of the
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semaphore set.
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<p></dd>
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<dt><strong>IPC_SET (0x00000001)</strong></dt>
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<dd>Set the user ID of the owner, the group ID of the owner, and the permissions
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for the semaphore set to the values in the
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<samp>sem_perm.uid</samp>, <samp>sem_perm.gid</samp>, and
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<samp>sem_perm.mode</samp> members of the
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<samp>semid_ds</samp> data structure pointed to by the fourth parameter.
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<p>The IPC_SET command can be run only by a thread with appropriate privileges or one that
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has an effective user ID equal to the user ID of the owner or the user ID
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of the creator of the semaphore set.</p>
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<p></dd>
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<dt><strong>IPC_STAT (0x00000002)</strong></dt>
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<dd>Store the current value of each member of the
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<samp>semid_ds</samp> data structure into the
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structure pointed to by the fourth parameter. The IPC_STAT
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command requires read permission to the semaphore set.
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<p></dd>
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<dt><strong>GETNCNT (0x00000003)</strong></dt>
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<dd>Return the number of threads waiting for the value of semaphore
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<em>semnum</em> to increase. This value is the <samp>semncnt</samp> value in the
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<samp>semaphore_t</samp> data structure associated with the specified
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semaphore. The GETNCNT command requires read permission to the semaphore set.
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<p></dd>
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<dt><strong>GETPID (0x00000004)</strong></dt>
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<dd>Return the process ID of the last thread to operate on semaphore <em>semnum</em>.
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This value is the <samp>sempid</samp> value in the
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<samp>semaphore_t</samp> data structure associated with the specified
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semaphore. The GETPID command requires read permission to the semaphore set.
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<p></dd>
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<dt><strong>GETVAL (0x00000005)</strong></dt>
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<dd>Return the current value of semaphore <em>semnum</em>.
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This value is the <samp>semval</samp> value in the
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<samp>semaphore_t</samp> data structure associated with the specified
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semaphore. The GETVAL command requires read permission to the semaphore set.
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<p></dd>
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<dt><strong>GETALL (0x00000006)</strong></dt>
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<dd>Return the values of each semaphore in the semaphore set into the array pointed
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to by the fourth parameter, which is a pointer to an array of type <samp>unsigned short</samp>.
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The values are the <samp>semval</samp> value in the
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<samp>semaphore_t</samp> data structure associated with each semaphore in the
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semaphore set. The GETALL command requires read
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permission to the semaphore set.
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<p></dd>
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<dt><strong>GETZCNT (0x00000007)</strong></dt>
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<dd>Return the number of threads waiting for the value of semaphore <em>semnum</em>
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to reach zero. This value is the <samp>semzcnt</samp> value in the
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<samp>semaphore_t</samp> data structure associated with the specified
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semaphore. The GETZCNT command requires read permission to the semaphore set.
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<p></dd>
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<dt><strong>SETVAL (0x00000008)</strong></dt>
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<dd>Set the value of semaphore <em>semnum</em> to the integer value of type
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<samp>int</samp> specified in the fourth parameter and clear the associated
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per-thread semaphore adjustment value.
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The SETVAL command requires write permission to the semaphore set.
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<p></dd>
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<dt><strong>SETALL (0x00000009)</strong></dt>
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<dd>Set the values of each semaphore in the semaphore set to the values
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contained in the array pointed to by the fourth parameter, which is a
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pointer to an array of type <samp>unsigned short</samp>.
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In addition, the associated per-thread
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semaphore-adjustment value is cleared for each semaphore. The SETALL command requires
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write permission to the semaphore set.
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<p></dd>
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</dl>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>semid</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>semnum</strong></dt>
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<dd>(Input) Semaphore number, a non-negative integer. It identifies a semaphore
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within the semaphore set on which to perform the control operation.<br>
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<br>
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</dd>
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<dt><strong>cmd</strong></dt>
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<dd>(Input) Command, the control operation to perform on the semaphore set. Valid
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values are listed above.<br>
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<br>
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</dd>
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<dt><strong>...</strong></dt>
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<dd>(Input/output) An optional fourth parameter whose type depends on the value
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of <em>cmd</em>. For the <em>cmd</em> SETVAL, this parameter must be an
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integer of type <samp>int</samp>. For the <em>cmd</em> IPC_STAT or IPC_SET, this parameter must
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be a pointer to a <samp>semid_ds</samp> structure. For the <em>cmd</em>
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GETALL or SETALL, this parameter must be a pointer to an array of type <samp>
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unsigned short</samp>. For all other values of <em>cmd</em>, this parameter is
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not required.
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<p>The members of the <samp>semid_ds</samp> structure are as follows:</p>
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</dd>
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</dl>
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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>struct ipc_perm sem_perm</em> </td>
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<td align="left" valign="top">The members of the <samp>ipc_perm</samp> structure
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are as follows:
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<table cellpadding="5">
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<tr>
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<td align="left" valign="top"><em>uid_t uid</em> </td>
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<td align="left" valign="top">The user ID of the owner of the semaphore set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>gid_t gid</em> </td>
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<td align="left" valign="top">The group ID of the owner of the semaphore set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>uid_t cuid</em> </td>
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<td align="left" valign="top">The user ID of the creator of the semaphore set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>gid_t cgid</em> </td>
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<td align="left" valign="top">The group ID of the creator of the semaphore set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>mode_t mode</em> </td>
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<td align="left" valign="top">The permissions for the semaphore set.</td>
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</tr>
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</table>
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</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>unsigned short sem_nsems</em> </td>
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<td align="left" valign="top">The number of semaphores in the set.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t sem_otime</em> </td>
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<td align="left" valign="top">The time the last thread operated on the semaphore set
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using <strong>semop()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t sem_ctime</em> </td>
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<td align="left" valign="top">The time the last thread changed the semaphore set
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using <strong>semctl()</strong>.</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>Authorities</h3>
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<p><strong><a name="TBLASCTL1">Authorization Required for
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semctl()</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, get the value of (<em>cmd</em> =
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GETVAL)</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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<tr>
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<td align="left" valign="top">Semaphore, set the value of (<em>cmd</em> =
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SETVAL)</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, get last process to operate on
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(<em>cmd</em> = GETPID)</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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<tr>
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<td align="left" valign="top">Semaphore, get number of threads waiting for
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value to increase (<em>cmd</em> = GETNCNT)</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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<tr>
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<td align="left" valign="top">Semaphore, get number of threads waiting for
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value to reach zero (<em>cmd</em> = GETZCNT)</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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<tr>
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<td align="left" valign="top">Semaphore set, get value of each semaphore
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(<em>cmd</em> = GETALL)</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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<tr>
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<td align="left" valign="top">Semaphore set, set value of each semaphore
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(<em>cmd</em> = SETALL)</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 set, retrieve state information
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(<em>cmd</em> = IPC_STAT)</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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<tr>
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<td align="left" valign="top">Semaphore set, set state information
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(<em>cmd</em> = IPC_SET)</td>
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<td align="left" valign="top">See Note</td>
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<td align="left" valign="top">EPERM</td>
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</tr>
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<tr>
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<td align="left" valign="top">Semaphore set, remove (<em>cmd</em> =
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IPC_RMID)</td>
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<td align="left" valign="top">See Note</td>
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<td align="left" valign="top">EPERM</td>
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</tr>
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</table>
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<p><strong>Note:</strong> To set semaphore set information or to remove a
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semaphore set, the thread must be the owner or creator of the semaphore set, or
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have appropriate privileges.</p>
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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="15 85" -->
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<tr>
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<td align="left" valign="top"><em>value</em></td>
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<td align="left" valign="top"><strong>semctl()</strong> was successful.
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Depending on the control operation specified in <em>cmd</em>, <strong>
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semctl()</strong> returns the following values:<br>
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|
|
|
||
|
|
|
||
|
|
<table cellpadding="5">
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>GETVAL</em></td>
|
||
|
|
<td align="left" valign="top">The value of the specified semaphore.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>GETPID</em></td>
|
||
|
|
<td align="left" valign="top">The process ID of the last thread that performed
|
||
|
|
a semaphore operation on the specified semaphore.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>GETNCNT</em></td>
|
||
|
|
<td align="left" valign="top">The number of threads waiting for the value of
|
||
|
|
the specified semaphore to increase.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>GETZCNT</em></td>
|
||
|
|
<td align="left" valign="top">The number of threads waiting for the value of
|
||
|
|
the specified semaphore to reach zero.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>For all other values of</em> cmd:</td>
|
||
|
|
<td align="left" valign="top">The value is 0.</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top"><em>-1</em></td>
|
||
|
|
<td align="left" valign="top"><strong>semctl()</strong> was not successful. The
|
||
|
|
<em>errno</em> variable is set to indicate the error.</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h3>Error Conditions</h3>
|
||
|
|
|
||
|
|
<p>If <strong>semctl()</strong> is not successful, <em>errno</em> usually
|
||
|
|
indicates one of the following errors. Under some conditions, <em>errno</em>
|
||
|
|
could indicate an error other than those listed here.</p>
|
||
|
|
|
||
|
|
<dl compact>
|
||
|
|
<dt><em>[EACCES]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>Permission denied.</p>
|
||
|
|
|
||
|
|
<p>An attempt was made to access an object in a way forbidden by its object
|
||
|
|
access permissions.</p>
|
||
|
|
|
||
|
|
<p>The thread does not have access to the specified file, directory, component,
|
||
|
|
or path.</p>
|
||
|
|
|
||
|
|
<p>The <em>cmd</em> parameter is IPC_STAT, GETVAL, GETPID, GETNCNT, GETZCNT, or
|
||
|
|
GETALL and the calling thread does not have read permission to the semaphore set.</p>
|
||
|
|
|
||
|
|
<p>The <em>cmd</em> parameter is SETVAL, or SETALL and the calling thread does
|
||
|
|
not have write permission to the semaphore set.</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EDAMAGE]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>A damaged object was encountered.</p>
|
||
|
|
|
||
|
|
<p>A referenced object is damaged. The object cannot be used.</p>
|
||
|
|
|
||
|
|
<p>The semaphore set has been damaged by a previous semaphore operation.</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EFAULT]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>The address used for an argument is not correct.</p>
|
||
|
|
|
||
|
|
<p>In attempting to use an argument in a call, the system detected an address
|
||
|
|
that is not valid.</p>
|
||
|
|
|
||
|
|
<p>While attempting to access a parameter passed to this function, the system
|
||
|
|
detected an address that is not valid.</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EINVAL]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>The value specified for the argument is not correct.</p>
|
||
|
|
|
||
|
|
<p>A function was passed incorrect argument values, or an operation was
|
||
|
|
attempted on an object and the operation specified is not supported for that
|
||
|
|
type of object.</p>
|
||
|
|
|
||
|
|
<p>An argument value is not valid, out of range, or NULL.</p>
|
||
|
|
|
||
|
|
<p>One of the following has occurred:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>The <em>semid</em> parameter is not a valid semaphore identifier.</li>
|
||
|
|
|
||
|
|
<li>The <em>semnum</em> parameter is less than zero or greater than or equal to
|
||
|
|
<samp>sem_nsems</samp>.</li>
|
||
|
|
|
||
|
|
<li>The <em>cmd</em> parameter is not a valid command.<p></li>
|
||
|
|
</ul>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EPERM]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>Operation not permitted.</p>
|
||
|
|
|
||
|
|
<p>You must have appropriate privileges or be the owner of the object or other
|
||
|
|
resource to do the requested operation.</p>
|
||
|
|
|
||
|
|
<p>The <em>cmd</em> parameter is IPC_RMID or IPC_SET and both of the
|
||
|
|
following are true:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>the calling thread does not have appropriate privileges.</li>
|
||
|
|
|
||
|
|
<li>the effective user ID of the calling thread is not equal to the user ID of the
|
||
|
|
owner or the user ID of the creator of the semaphore set.</li>
|
||
|
|
</ul>
|
||
|
|
<p></dd>
|
||
|
|
|
||
|
|
<dt><em>[ERANGE]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>A range error occurred.</p>
|
||
|
|
|
||
|
|
<p>The value of an argument is too small, or a result too large.</p>
|
||
|
|
|
||
|
|
<p>The <em>cmd</em> parameter is SETVAL, and the value to which <samp>
|
||
|
|
semval</samp> is to be set is greater than the system-imposed maximum.</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EUNKNOWN]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>Unknown system state.</p>
|
||
|
|
|
||
|
|
<p>The operation failed because of an unknown system state. See any messages in
|
||
|
|
the job log and correct any errors that are indicated, then retry the
|
||
|
|
operation.</p>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Error Messages</h3>
|
||
|
|
|
||
|
|
<p>None.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3><a name="USAGE_NOTES">Usage Notes</a></h3>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>"Appropriate privileges" is defined to be *ALLOBJ special authority. If the
|
||
|
|
user profile under which the thread is running does not have *ALLOBJ special
|
||
|
|
authority, the thread does not have appropriate privileges.<p></li>
|
||
|
|
|
||
|
|
<li>Take care when using a union for the optional fourth parameter. If the
|
||
|
|
optional fourth parameter is an integer, <strong>semctl()</strong> expects it to
|
||
|
|
directly follow the third parameter in storage. But a union that contains a
|
||
|
|
pointer is aligned on a 16-byte boundary, which might not directly follow the
|
||
|
|
third parameter. Therefore, the value used by <strong>semctl()</strong> for the
|
||
|
|
fourth parameter might not be the value intended by the caller,
|
||
|
|
and unexpected results could occur.<p></li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
|
||
|
|
|
||
|
|
<h3>Related Information</h3>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>The <<strong>sys/sem.h</strong>> file (see <a href="unix13.htm">
|
||
|
|
Header Files for UNIX-Type Functions</a>)<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcsemgt.htm">semget()</a>--Get Semaphore Set with Key<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcsemop.htm">semop()</a>--Perform Semaphore Operations on
|
||
|
|
Semaphore Set</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>
|
||
|
|
|