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<!--$Id: memp_register.so,v 10.23 2000/05/25 13:47:08 dda Exp $-->
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<h1>memp_register</h1>
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<h3><pre>
#include <db.h>
<p>
int
memp_register(DB_ENV *env, int ftype,
int (*pgin_fcn)(DB_ENV *, db_pgno_t pgno, void *pgaddr, DBT *pgcookie),
int (*pgout_fcn)(DB_ENV *, db_pgno_t pgno, void *pgaddr, DBT *pgcookie));
</pre></h3>
<h1>Description</h1>
<p>The memp_register function registers page-in and page-out
functions for files of type <b>ftype</b> in the specified pool.
<p>If the <b>pgin_fcn</b> function is non-NULL, it is called each time
a page is read into the memory pool from a file of type <b>ftype</b>, or
a page is created for a file of type <b>ftype</b> (see the
DB_MPOOL_CREATE flag for the <a href="../api_c/memp_fget.html">memp_fget</a> function).
<p>If the <b>pgout_fcn</b> function is non-NULL, it is called each time
a page is written to a file of type <b>ftype</b>.
<p>Both the <b>pgin_fcn</b> and <b>pgout_fcn</b> functions are called with
a reference to the current environment, the page number, a pointer to the
page being read or written, and any argument <b>pgcookie</b> that was
specified to the <a href="../api_c/memp_fopen.html">memp_fopen</a> function when the file was opened.
The <b>pgin_fcn</b> and <b>pgout_fcn</b> functions should return 0 on
success, and an applicable non-zero <b>errno</b> value on failure, in
which case the shared memory pool interface routine (and, by extension,
any Berkeley DB library function) calling it will also fail, returning that
<b>errno</b> value.
<p>The purpose of the memp_register function is to support processing
when pages are entered into, or flushed from, the pool. A file type must
be specified to make it possible for unrelated threads or processes, that
are sharing a pool, to evict each other's pages from the pool.
Applications should call memp_register, during initialization,
for each type of file requiring input or output processing that will be
sharing the underlying pool. (No registry is necessary for the standard
Berkeley DB access method types, as <a href="../api_c/db_open.html">DB->open</a> registers them
separately.)
<p>If a thread or process does not call memp_register for a file
type, it is impossible for it to evict pages for any file requiring input
or output processing from the pool. For this reason,
memp_register should always be called by each application sharing
a pool for each type of file included in the pool, regardless of whether
or not the application itself uses files of that type.
<p>There are no standard values for <b>ftype</b>, <b>pgin_fcn</b>,
<b>pgout_fcn</b> and <b>pgcookie</b>, except that the <b>ftype</b>
value for a file must be a non-zero positive number, as negative numbers
are reserved for internal use by the Berkeley DB library. For this reason,
applications sharing a pool must coordinate their values amongst
themselves.
<p>The memp_register function returns a non-zero error value on failure and 0 on success.
<h1>Errors</h1>
<p>The memp_register function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the memp_register function may fail and return
<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
in the same way.
<h1>See Also</h1>
<a href="../api_c/env_set_mp_mmapsize.html">DBENV->set_mp_mmapsize</a>,
<a href="../api_c/memp_fclose.html">memp_fclose</a>,
<a href="../api_c/memp_fget.html">memp_fget</a>,
<a href="../api_c/memp_fopen.html">memp_fopen</a>,
<a href="../api_c/memp_fput.html">memp_fput</a>,
<a href="../api_c/memp_fset.html">memp_fset</a>,
<a href="../api_c/memp_fsync.html">memp_fsync</a>,
<a href="../api_c/memp_register.html">memp_register</a>,
<a href="../api_c/memp_stat.html">memp_stat</a>,
<a href="../api_c/memp_sync.html">memp_sync</a>
and
<a href="../api_c/memp_trickle.html">memp_trickle</a>.
</tt>
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