1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Environment FAQ</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> 10 <link rel="up" href="env.html" title="Chapter��9.�� The Berkeley DB Environment" /> 11 <link rel="prev" href="env_remote.html" title="Remote filesystems" /> 12 <link rel="next" href="cam.html" title="Chapter��10.�� Berkeley DB Concurrent Data Store Applications" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Environment FAQ</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="env_remote.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��9.�� 23 The Berkeley DB Environment 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="cam.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="env_faq"></a>Environment FAQ</h2> 35 </div> 36 </div> 37 </div> 38 <div class="orderedlist"> 39 <ol type="1"> 40 <li> 41 <p> 42 <span class="bold"><strong>I'm using multiple processes to access an Berkeley DB database 43 environment; is there any way to ensure that two processes don't run transactional 44 recovery at the same time, or that all processes have exited the database 45 environment so that recovery can be run?</strong></span> 46 </p> 47 <p> 48 See <a class="xref" href="transapp_fail.html" title="Handling failure in Transactional Data Store applications">Handling failure in Transactional Data Store applications</a> and 49 <a class="xref" href="transapp_app.html" title="Architecting Transactional Data Store applications">Architecting Transactional Data Store applications</a> for a full 50 discussion of this topic. 51 </p> 52 </li> 53 <li> 54 <p> 55 <span class="bold"><strong>How can I associate application information with a <a href="../api_reference/C/db.html" class="olink">DB</a> or 56 <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> handle?</strong></span> 57 </p> 58 <p> 59 In the C API, the <a href="../api_reference/C/db.html" class="olink">DB</a> and <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> structures each contain an "app_private" field intended 60 to be used to reference application-specific information. See the <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a> and 61 <a href="../api_reference/C/envcreate.html" class="olink">db_env_create()</a> documentation for more information. 62 </p> 63 <p> 64 In the C++ or Java APIs, the easiest way to associate application-specific data with a 65 handle is to subclass the <a href="../api_reference/CXX/db.html" class="olink">Db</a> or <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a>, for example subclassing 66 <a href="../api_reference/CXX/db.html" class="olink">Db</a> to get MyDb. Objects of type MyDb will still have the Berkeley DB API 67 methods available on them, and you can put any extra data or methods you want into the 68 MyDb class. If you are using "callback" APIs that take <a href="../api_reference/CXX/db.html" class="olink">Db</a> or 69 <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a> arguments (for example, 70 <a href="../api_reference/CXX/dbset_bt_compare.html" class="olink">Db::set_bt_compare()</a>) 71 these will always be called with the <a href="../api_reference/CXX/db.html" class="olink">Db</a> or <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a> objects you 72 create. So if you always use MyDb objects, you will be able to take the first argument 73 to the callback function and cast it to a MyDb (in C++, cast it to (MyDb*)). That will 74 allow you to access your data members or methods. 75 </p> 76 </li> 77 </ol> 78 </div> 79 </div> 80 <div class="navfooter"> 81 <hr /> 82 <table width="100%" summary="Navigation footer"> 83 <tr> 84 <td width="40%" align="left"><a accesskey="p" href="env_remote.html">Prev</a>��</td> 85 <td width="20%" align="center"> 86 <a accesskey="u" href="env.html">Up</a> 87 </td> 88 <td width="40%" align="right">��<a accesskey="n" href="cam.html">Next</a></td> 89 </tr> 90 <tr> 91 <td width="40%" align="left" valign="top">Remote filesystems��</td> 92 <td width="20%" align="center"> 93 <a accesskey="h" href="index.html">Home</a> 94 </td> 95 <td width="40%" align="right" valign="top">��Chapter��10.�� 96 Berkeley DB Concurrent Data Store Applications 97 </td> 98 </tr> 99 </table> 100 </div> 101 </body> 102</html> 103