103 lines
5.2 KiB
HTML
103 lines
5.2 KiB
HTML
<!--$Id: env_set_alloc.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DbEnv::set_alloc</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>DbEnv::set_alloc</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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extern "C" {
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typedef void *(*db_malloc_fcn_type)(size_t);
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typedef void *(*db_realloc_fcn_type)(void *, size_t);
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typedef void *(*db_free_fcn_type)(void *);
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};
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<p>
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int
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DbEnv::set_alloc(db_malloc_fcn_type app_malloc,
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db_realloc_fcn_type app_realloc,
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db_free_fcn_type app_free);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbEnv::set_alloc</b>
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<p>Set the allocation functions used by the <a href="../api_cxx/env_class.html">DbEnv</a> and <a href="../api_cxx/db_class.html">Db</a>
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methods to allocate or free memory owned by the application.</p>
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<p>There are a number of interfaces in Berkeley DB where memory is allocated by
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the library and then given to the application. For example, the
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<a href="../api_cxx/dbt_class.html#DB_DBT_MALLOC">DB_DBT_MALLOC</a> flag, when specified in the <a href="../api_cxx/dbt_class.html">Dbt</a> object,
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will cause the <a href="../api_cxx/db_class.html">Db</a> methods to allocate and reallocate memory
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which then becomes the responsibility of the calling application. (See
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<a href="../api_cxx/dbt_class.html">Dbt</a> for more information.) Other examples are the Berkeley DB
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interfaces which return statistical information to the application:
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<a href="../api_cxx/db_stat.html">Db::stat</a>, <a href="../api_cxx/lock_stat.html">DbEnv::lock_stat</a>, <a href="../api_cxx/log_archive.html">DbEnv::log_archive</a>,
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<a href="../api_cxx/log_stat.html">DbEnv::log_stat</a>, <a href="../api_cxx/memp_stat.html">DbEnv::memp_stat</a>, and <a href="../api_cxx/txn_stat.html">DbEnv::txn_stat</a>. There is one
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method in Berkeley DB where memory is allocated by the application and then
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given to the library: <a href="../api_cxx/db_associate.html">Db::associate</a>.</p>
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<p>On systems in which there may be multiple library versions of the
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standard allocation routines (notably Windows NT), transferring memory
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between the library and the application will fail because the Berkeley DB
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library allocates memory from a different heap than the application uses
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to free it. To avoid this problem, the DbEnv::set_alloc and
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<a href="../api_cxx/db_set_alloc.html">Db::set_alloc</a> methods can be used to pass Berkeley DB references to the
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application's allocation routines.</p>
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<p>It is not an error to specify only one or two of the possible allocation
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function parameters to these interfaces; however, in that case the
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specified interfaces must be compatible with the standard library
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interfaces, as they will be used together. The functions specified must
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match the calling conventions of the ANSI C X3.159-1989 (ANSI C) library routines of
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the same name.</p>
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<p>The DbEnv::set_alloc method configures operations performed using the specified
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<a href="../api_cxx/env_class.html">DbEnv</a> handle, not all operations performed on the underlying
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database environment.</p>
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<p>The DbEnv::set_alloc method may not be called after the <a href="../api_cxx/env_open.html">DbEnv::open</a> method is
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called.
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</p>
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<p>The DbEnv::set_alloc method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>app_malloc</b><ul compact><li>The <b>app_malloc</b> parameter is the application-specified malloc
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function.</ul>
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<b>app_realloc</b><ul compact><li>The <b>app_realloc</b> parameter is the application-specified realloc
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function.</ul>
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<b>app_free</b><ul compact><li>The <b>app_free</b> parameter is the application-specified free function.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DbEnv::set_alloc method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_cxx/env_open.html">DbEnv::open</a> was called; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/env_class.html">DbEnv</a>
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<br><b>See Also</b>
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<a href="../api_cxx/env_list.html">Database Environments and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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