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212 lines
9.3 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DB_ENV->set_thread_count()</title>
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<link rel="stylesheet" href="apiReference.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB C API Reference" />
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<link rel="up" href="env.html" title="Chapter 5. The DB_ENV Handle" />
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<link rel="prev" href="envset_shm_key.html" title="DB_ENV->set_shm_key()" />
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<body>
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<div xmlns="" class="navheader">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DB_ENV->set_thread_count()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="envset_shm_key.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5.
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The DB_ENV Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="envset_thread_id.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="envset_thread_count"></a>DB_ENV->set_thread_count()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB_ENV->set_thread_count(DB_ENV *dbenv, u_int32_t count); </pre>
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<p>
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Declare an approximate number of threads in the database
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environment. This method allocates resources in your environment
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for the threads your application will use. If you fail to properly
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estimate the number of threads your application will use, your
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application will run out of resources and errors will be returned
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when the application attempts to start one too many threads.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> method does not set the
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maximum number of threads but is used to determine memory sizing and
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the thread control block reclamation policy.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> method must be called
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prior to opening the database environment. In addition, this method must be
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used with the
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<a class="xref" href="envfailchk.html" title="DB_ENV->failchk()">DB_ENV->failchk()</a> method.
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</p>
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<p>
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If a process invokes this method without the use of
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<a class="xref" href="envfailchk.html" title="DB_ENV->failchk()">DB_ENV->failchk()</a>
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the program may be unable to allocate a thread
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control block. This is true of the standalone Berkeley DB utility
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programs.
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</p>
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<p>
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If a process has not configured an <span class="bold"><strong>is_alive</strong></span> function from the
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<a class="xref" href="envset_isalive.html" title="DB_ENV->set_isalive()">DB_ENV->set_isalive()</a>
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method, and then attempts to join a database environment configured
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for failure checking with the <a class="xref" href="envfailchk.html" title="DB_ENV->failchk()">DB_ENV->failchk()</a>,
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<a class="xref" href="envset_thread_id.html" title="DB_ENV->set_thread_id()">DB_ENV->set_thread_id()</a>,
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<a class="xref" href="envset_isalive.html" title="DB_ENV->set_isalive()">DB_ENV->set_isalive()</a> and
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<code class="methodname">DB_ENV->set_thread_count()</code> methods, the program may be unable to
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allocate a thread control block and fail to join the environment.
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<span class="bold"><strong>This is true of the standalone Berkeley DB
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utility programs.</strong></span> To avoid problems when using the
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standalone Berkeley DB utility programs with environments configured
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for failure checking, incorporate the utility's functionality directly
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in the application, or call the
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<a class="xref" href="envfailchk.html" title="DB_ENV->failchk()">DB_ENV->failchk()</a> method
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before running the utility.
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</p>
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<p>
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The database environment's thread count may also be configured
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using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The syntax of the entry
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in that file is a single line with the string "set_thread_count",
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one or more whitespace characters, and the thread count. Because
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the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is read when the database environment is
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opened, it will silently overrule configuration done before that
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time.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> method configures operations performed
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using the specified <a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a> handle, not all
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operations performed on the underlying database environment.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> method may not be called after the
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<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> method is
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called.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> <span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3897218"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3897226"></a>count</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>count</strong></span> parameter is an approximate
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thread count for the database environment.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3897382"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DB_ENV->set_thread_count()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3897653"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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If the method was called after <a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a>
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was called; or if an invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3897635"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3897690"></a>See Also</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a>
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="envset_shm_key.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="env.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="envset_thread_id.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">DB_ENV->set_shm_key() </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> DB_ENV->set_thread_id()</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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