1<!--$Id: memp_register.so,v 10.38 2004/08/13 03:38:58 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: DbEnv::memp_register</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>DbEnv::memp_register</b> 14</td> 15<td align=right> 16<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a> 17<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db_cxx.h> 23<p> 24extern "C" { 25 typedef int (*pgin_fcn_type)(DB_ENV *dbenv, 26 db_pgno_t pgno, void *pgaddr, DBT *pgcookie); 27 typedef int (*pgout_fcn_type)(DB_ENV *dbenv, 28 db_pgno_t pgno, void *pgaddr, DBT *pgcookie); 29}; 30int 31DbEnv::memp_register(int ftype, 32 pgin_fcn_type pgin_fcn, pgout_fcn_type pgout_fcn); 33</pre></b> 34<hr size=1 noshade> 35<b>Description: DbEnv::memp_register</b> 36<p>The DbEnv::memp_register method registers page-in and page-out 37functions for files of type <b>ftype</b> in the specified pool.</p> 38<p>If the <b>pgin_fcn</b> function is non-NULL, it is called each time 39a page is read into the memory pool from a file of type <b>ftype</b>, or 40a page is created for a file of type <b>ftype</b> (see the 41DB_MPOOL_CREATE flag for the <a href="../api_cxx/memp_fget.html">DbMpoolFile::get</a> method).</p> 42<p>If the <b>pgout_fcn</b> function is non-NULL, it is called each time 43a page is written to a file of type <b>ftype</b>.</p> 44<p>The purpose of the DbEnv::memp_register function is to support processing 45when pages are entered into, or flushed from, the pool. For example, this 46functionality might be used to do byte-endian conversion as pages are read 47from, or written to, the underlying file.</p> 48<p>A file type must be specified to make it possible for unrelated threads 49or processes that are sharing a pool, to evict each other's pages from 50the pool. During initialization, applications should call 51DbEnv::memp_register for each type of file requiring input or output 52processing that will be sharing the underlying pool. (No registry is 53necessary for the standard Berkeley DB access method types because 54<a href="../api_cxx/db_open.html">Db::open</a> registers them separately.)</p> 55<p>If a thread or process does not call DbEnv::memp_register for a file 56type, it is impossible for it to evict pages for any file requiring input 57or output processing from the pool. For this reason, 58DbEnv::memp_register should always be called by each application sharing 59a pool for each type of file included in the pool, regardless of whether 60or not the application itself uses files of that type.</p> 61<p>The DbEnv::memp_register method 62either returns a non-zero error value 63or throws an exception that encapsulates a non-zero error value on 64failure, and returns 0 on success. 65</p> 66<b>Parameters</b> <br> 67 <b>ftype</b><ul compact><li>The <b>ftype</b> parameter specifies the type of file for which the 68page-in and page-out functions will be called. 69<p>The <b>ftype</b> value for a file must be a non-zero positive number 70less than 128 (0 and negative numbers are reserved for internal use by 71the Berkeley DB library).</p></ul> 72 <b>pgin_fcn, pgout_fcn</b><ul compact><li>The page-in and page-out functions. 73<p>The <b>pgin_fcn</b> and <b>pgout_fcn</b> functions are called with a 74reference to the current database environment, the page number being 75read or written, a pointer to the page being read or written, and any 76parameter <b>pgcookie</b> that was specified to the 77<a href="../api_cxx/memp_set_pgcookie.html">DbMpoolFile::set_pgcookie</a> method.</p> 78<p>The <b>pgin_fcn</b> and <b>pgout_fcn</b> functions should return 0 on 79success, and a non-zero value on failure, in which case the shared Berkeley DB 80library function calling it will also fail, returning that non-zero 81value. The non-zero value should be selected from values outside of the 82Berkeley DB library namespace.</p></ul> 83<br> 84<hr size=1 noshade> 85<br><b>Class</b> 86<a href="../api_cxx/env_class.html">DbEnv</a>, <a href="../api_cxx/mempfile_class.html">DbMpoolFile</a> 87<br><b>See Also</b> 88<a href="../api_cxx/memp_list.html">Memory Pools and Related Methods</a> 89</tt> 90<table width="100%"><tr><td><br></td><td align=right> 91<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> 92</td></tr></table> 93<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 94</body> 95</html> 96
