421 lines
11 KiB
HTML
421 lines
11 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>sem_open()--Open Named Semaphore</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 html 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>sem_open()--Open Named Semaphore</h2>
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<div class="box" style="width: 80%;">
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<br>
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Syntax
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<pre>
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#include <semaphore.h>
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sem_t * sem_open(const char *<em>name</em>, int <em>oflag</em>, ...);
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</pre>
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<br>
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Service Program Name: QP0ZPSEM<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>sem_open()</strong> function opens a named semaphore, returning
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a semaphore pointer that may be used on subsequent calls to <strong>
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sem_post()</strong>, <strong>sem_post_np()</strong>, <strong>
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sem_wait()</strong>, <strong>sem_wait_np()</strong>, <strong>
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sem_trywait()</strong>, <strong>sem_getvalue()</strong>, and <strong>
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sem_close()</strong>. When a semaphore is being created, the parameters <em>
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mode</em> and <em>value</em> must be specified on the call to <strong>
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sem_open()</strong>. If a semaphore is created, then the maximum value of the
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semaphore is set to SEM_VALUE_MAX and the title of the semaphore is set to the
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last 16 characters of the name.</p>
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<p>If <strong>sem_open()</strong> is called multiple times within the same
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process using the same name, <strong>sem_open()</strong> will return a pointer
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to the same semaphore, as long as another process has not used <strong>
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sem_unlink()</strong> to unlink the semaphore.</p>
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<p>If <strong>sem_open()</strong> is called from a program using data model
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LLP64, the returned semaphore pointer must be declared as a <samp>sem_t
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*__ptr128</samp>.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>name</strong></dt>
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<dd>(Input) A pointer to the null-terminated name of the semaphore to be
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opened. The name should begin with a slash ('/') character. If the name does
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not begin with a slash ('/') character, the system adds a slash to the
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beginning of the name.
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<p>This parameter is assumed to be represented in the CCSID (coded character
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set identifier) currently in effect for the job. If the CCSID of the job is
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65535, this parameter is assumed to be represented in the default CCSID of the
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job.</p>
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<p>The name is added to a set of names that is used only by named semaphores.
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The name has no relationship to any file system path names. The maximum length
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of the name is SEM_NAME_MAX.</p>
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<p>See <a href="ipcsemou.htm">QlgSem_open()</a>--Open Named Semaphore (using
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NLS-enabled path name) for a description and an example of supplying the <em>
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name</em> in any CCSID.</p>
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</dd>
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<dt><strong>oflag</strong></dt>
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<dd>(Input) Option flags.
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<p>The <em>oflag</em> parameter value is either zero or is obtained by
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performing an OR operation on one or more of the following constants:</p>
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<table cellpadding="5">
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<!-- cols="25 75" -->
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<tr>
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<td align="left" valign="top"><em>'0x0008' or O_CREAT</em></td>
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<td align="left" valign="top">Creates the named semaphore if it does not
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already exist.<br>
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<br>
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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>'0x0010' or O_EXCL</em></td>
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<td align="left" valign="top">Causes <strong>sem_open()</strong> to fail if
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O_CREAT is also set and the named semaphore already exists.</td>
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</tr>
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</table>
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<br>
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</dd>
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<dt><strong>mode</strong></dt>
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<dd>(input) Permission flags.
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<p>The <em>mode</em> parameter value is either zero or is obtained by
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performing an OR operation on one or more of the following list of constants.
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For another process to open the semaphore, the process's effective UIDd must be
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able to open the semaphore in both read and write mode.</p>
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<table cellpadding="5">
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<!-- cols="25 75" -->
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<tr>
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<td align="left" valign="top"><em>'0x0100' or S_IRUSR</em></td>
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<td align="left" valign="top">Permits the creator of the named semaphore to
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open the semaphore in read mode.<br>
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<br>
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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>'0x0080' or S_IWUSR</em></td>
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<td align="left" valign="top">Permits the creator of the named semaphore to
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open the semaphore in write mode.<br>
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<br>
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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>'0x0020' or S_IRGRP</em></td>
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<td align="left" valign="top">Permits the group associated with the named
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semaphore to open the semaphore in read mode.<br>
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<br>
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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>'0x0010' or S_IWGRP</em></td>
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<td align="left" valign="top">Permits the group associated with the named
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semaphore to open the semaphore in write mode.<br>
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<br>
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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>'0x0004' or S_IROTH</em></td>
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<td align="left" valign="top">Permits others to open the named semaphore in
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read mode.<br>
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<br>
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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>'0x0002' or S_IWOTH</em></td>
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<td align="left" valign="top">Permits others to open the named semaphore in
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write mode.<br>
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<br>
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</td>
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</tr>
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</table>
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<br>
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</dd>
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<dt><strong>value</strong></dt>
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<dd>(Input) Initial value of the named semaphore.</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="TBLASEMO1">Authorization required for
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sem_open()</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">Named semaphore to be created</td>
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<td align="left" valign="top">None</td>
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<td align="left" valign="top">None</td>
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</tr>
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<tr>
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<td align="left" valign="top">Existing named semaphore to be accessed</td>
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<td align="left" valign="top">*RW</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="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>sem_open()</strong> was successful. The
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value returned is a pointer to the open named semaphore.<br>
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<br>
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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>SEM_FAILED</em></td>
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<td align="left" valign="top"><strong>sem_open()</strong> was not successful.
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The <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><a name="ecsemo">Error Conditions</a></h3>
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<p>If <strong>sem_open()</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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</dd>
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<dt><em>[EEXIST]</em></dt>
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<dd>
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<p>Semaphore exists.</p>
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<p>A named semaphore exists for the parameter <em>name</em>, but O_CREAT and
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O_EXCL are both set in <em>oflag</em>.</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>value</em> parameter is greater than SEM_VALUE_MAX.</p>
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</dd>
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<dt><em>[ENAMETOOLONG]</em></dt>
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<dd>
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<p>The name is too long. The name is longer than the SEM_NAME_MAX
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characters.</p>
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</dd>
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<dt><em>[ENOENT]</em></dt>
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<dd>
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<p>No such path or directory.</p>
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<p>The name specified on the <strong>sem_open()</strong> call does not refer to
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an existing named semaphore and O_CREAT was not set in <em>oflag</em>.</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 also could 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>System semaphore resources have been exhausted.</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><a name="risemo">Related Information</a></h3>
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<ul>
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<li>The <<strong>semaphore.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>
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</li>
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<li><a href="ipcsemou.htm">QlgSem_open()</a> Open Named Semaphore (using
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NLS-enabled path name)<br>
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<br>
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</li>
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<li><a href="ipcsemcl.htm">sem_close()</a>--Close Named Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemge.htm">sem_getvalue()</a>--Get Semaphore Value<br>
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<br>
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</li>
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<li><a href="ipcsemon.htm">sem_open_np()</a>--Open Named Semaphore with Maximum
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Value<br>
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<br>
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</li>
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<li><a href="ipcsemp.htm">sem_post()</a>--Post to Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsempn.htm">sem_post_np()</a>--Post Value to Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemtr.htm">sem_trywait()</a>--Try to Decrement Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemun.htm">sem_unlink()</a>--Unlink Named Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemw.htm">sem_wait()</a>--Wait for Semaphore<br>
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|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcsemwn.htm">sem_wait_np()</a>--Wait for Semaphore with
|
||
|
|
Timeout</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>The following example opens the named semaphore "/mysemaphore" and creates
|
||
|
|
the semaphore with an initial value of 10 if it does not already exist. If the
|
||
|
|
semaphore is created, the permissions are set such that only the current user
|
||
|
|
has access to the semaphore.</p>
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
#include <semaphore.h>
|
||
|
|
main() {
|
||
|
|
sem_t * my_semaphore;
|
||
|
|
int rc;
|
||
|
|
|
||
|
|
my_semaphore = sem_open("/mysemaphore",
|
||
|
|
O_CREAT, S_IRUSR | S_IWUSR, 10);
|
||
|
|
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<hr>
|
||
|
|
API introduced: V4R4
|
||
|
|
|
||
|
|
<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>
|
||
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|
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