<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>DbEnv::set_thread_count()</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> <link rel="up" href="env.html" title="Chapter 5. The DbEnv Handle" /> <link rel="prev" href="envset_shm_key.html" title="DbEnv::set_shm_key()" /> <link rel="next" href="envset_thread_id.html" title="DbEnv::set_thread_id()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DbEnv::set_thread_count()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="envset_shm_key.html">Prev</a> </td> <th width="60%" align="center">Chapter 5. The DbEnv Handle </th> <td width="20%" align="right"> <a accesskey="n" href="envset_thread_id.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="envset_thread_count"></a>DbEnv::set_thread_count()</h2> </div> </div> </div> <pre class="programlisting">#include <db_cxx.h> int DbEnv::set_thread_count(u_int32_t count); </pre> <p> Declare an approximate number of threads in the database environment. The <code class="methodname">DbEnv::set_thread_count()</code> method must be called prior to opening the database environment if the <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> method will be used. The <code class="methodname">DbEnv::set_thread_count()</code> method does not set the maximum number of threads but is used to determine memory sizing and the thread control block reclamation policy. </p> <p> If a process has not configured an <span class="bold"><strong>is_alive</strong></span> function from the <a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a> method, and then attempts to join a database environment configured for failure checking with the <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a>, <a class="xref" href="envset_thread_id.html" title="DbEnv::set_thread_id()">DbEnv::set_thread_id()</a>, <a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a> and <code class="methodname">DbEnv::set_thread_count()</code> methods, the program may be unable to allocate a thread control block and fail to join the environment. <span class="bold"><strong>This is true of the standalone Berkeley DB utility programs.</strong></span> To avoid problems when using the standalone Berkeley DB utility programs with environments configured for failure checking, incorporate the utility's functionality directly in the application, or call the <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> method before running the utility. </p> <p> The database environment's thread count may also be configured 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 in that file is a single line with the string "set_thread_count", one or more whitespace characters, and the thread count. Because 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 opened, it will silently overrule configuration done before that time. </p> <p> The <code class="methodname">DbEnv::set_thread_count()</code> method configures operations performed using the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle, not all operations performed on the underlying database environment. </p> <p> The <code class="methodname">DbEnv::set_thread_count()</code> method may not be called after the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called. </p> <p> The <code class="methodname">DbEnv::set_thread_count()</code> <span> <span> method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1674565"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1674818"></a>count</h4> </div> </div> </div> <p> The <span class="bold"><strong>count</strong></span> parameter is an approximate thread count for the database environment. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1674967"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DbEnv::set_thread_count()</code> <span> <span> method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> exception, encapsulating one of the following non-zero errors, or return one of the following non-zero errors: </span> </span> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1674981"></a>EINVAL</h4> </div> </div> </div> <p> If the method was called after <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> was called; or if an invalid flag value or parameter was specified. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1674982"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1675050"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="envset_shm_key.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="env.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="envset_thread_id.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DbEnv::set_shm_key() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DbEnv::set_thread_id()</td> </tr> </table> </div> </body> </html>