<?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. This method allocates resources in your environment for the threads your application will use. If you fail to properly estimate the number of threads your application will use, your application will run out of resources and errors will be returned when the application attempts to start one too many threads. </p> <p> 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> The <code class="methodname">DbEnv::set_thread_count()</code> method must be called prior to opening the database environment. In addition, this method must be used with the <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> method. </p> <p> If a process invokes this method without the use of <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> the program may be unable to allocate a thread control block. This is true of the standalone Berkeley DB utility programs. </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="id3507305"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id3507303"></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="id3507127"></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="id3507525"></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="id3507548"></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="id3507188"></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>