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364 lines
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HTML
364 lines
14 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DbEnv::lock_get()</title>
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<link rel="stylesheet" href="apiReference.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
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<link rel="up" href="lock.html" title="Chapter 7. The DbLock Handle" />
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<link rel="prev" href="lockdetect.html" title="DbEnv::lock_detect()" />
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<link rel="next" href="lockid.html" title="DbEnv::lock_id()" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DbEnv::lock_get()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="lockdetect.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7.
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The DbLock Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="lockid.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="lockget"></a>DbEnv::lock_get()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db_cxx.h>
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int
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DbEnv::lock_get(u_int32_t locker, u_int32_t flags,
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const Dbt *object, const db_lockmode_t lock_mode, DbLock *lock);</pre>
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<p>
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The <code class="methodname">DbEnv::lock_get()</code> method acquires a lock from the lock table,
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returning information about it in the <span class="bold"><strong>lock</strong></span> parameter.
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</p>
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<p>
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The <code class="methodname">DbEnv::lock_get()</code> <span>
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<span>
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method either returns a non-zero error value or throws an
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exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3633660"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3633416"></a>locker</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>locker</strong></span> parameter is an unsigned
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32-bit integer quantity. It represents the entity requesting the
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lock.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3633746"></a>flags</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
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or the following value:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="get_DB_LOCK_NOWAIT"></a>
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<code class="literal">DB_LOCK_NOWAIT</code>
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</p>
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<p>
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If a lock cannot be granted because the requested lock conflicts with
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an existing lock, return DB_LOCK_NOTGRANTED immediately instead of
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waiting for the lock to become available.
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</p>
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</li>
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</ul>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634119"></a>object</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>object</strong></span> parameter is an untyped
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byte string that specifies the object to be locked. Applications
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using the locking subsystem directly while also doing locking via the
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Berkeley DB access methods must take care not to inadvertently lock
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objects that happen to be equal to the unique file IDs used to lock
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files. See <a href="../../programmer_reference/lock_am_conv.html" class="olink">Access method
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locking conventions</a> in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>
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for more information.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634123"></a>lock_mode</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>lock_mode</strong></span> parameter is used as an
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index into the environment's lock conflict matrix. When using the
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default lock conflict matrix, <span class="bold"><strong>lock_mode</strong></span> must be set to one of the following
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values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">DB_LOCK_READ</code>
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</p>
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<p>
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read (shared)
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</p>
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</li>
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<li>
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<p>
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<code class="literal">DB_LOCK_WRITE</code>
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</p>
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<p>
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write (exclusive)
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</p>
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</li>
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<li>
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<p>
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<code class="literal">DB_LOCK_IWRITE</code>
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</p>
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<p>
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intention to write (shared)
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</p>
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</li>
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<li>
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<p>
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<code class="literal">DB_LOCK_IREAD</code>
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</p>
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<p>
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intention to read (shared)
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</p>
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</li>
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<li>
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<p>
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<code class="literal">DB_LOCK_IWR</code>
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</p>
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<p>
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intention to read and write (shared)
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</p>
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</li>
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</ul>
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</div>
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<p>
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See <a class="xref" href="envset_lk_conflicts.html" title="DbEnv::set_lk_conflicts()">DbEnv::set_lk_conflicts()</a>
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and <a href="../../programmer_reference/lock_stdmode.html" class="olink">Standard Lock Modes</a>
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for more information on the lock conflict matrix.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634208"></a>lock</h4>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DbEnv::lock_get()</code>
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method returns the lock information in <span class="bold"><strong>lock</strong></span>.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3634295"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DbEnv::lock_get()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634103"></a><span>DbDeadlockException or </span>DB_LOCK_DEADLOCK</h4>
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</div>
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</div>
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</div>
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<p>
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A transactional database environment operation was selected to resolve
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a deadlock.
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</p>
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<p>
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<a class="xref" href="dbdeadlock.html" title="DbDeadlockException">DbDeadlockException</a> is thrown if
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_LOCK_DEADLOCK</code> is returned.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634179"></a><span>DbLockNotGrantedException or </span>DB_LOCK_NOTGRANTED</h4>
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</div>
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</div>
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</div>
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<p>
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A Berkeley DB Concurrent Data Store database environment configured
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for lock timeouts was unable to grant a lock in the allowed time.
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</p>
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<p>
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<a class="xref" href="dblocknotgranted.html" title="DbLockNotGrantedException">DbLockNotGrantedException</a> is thrown if
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_LOCK_NOTGRANTED</code> is returned.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3633762"></a><span>DbLockNotGrantedException or </span>DB_LOCK_NOTGRANTED</h4>
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</div>
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</div>
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</div>
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<p>
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The <a class="link" href="lockvec.html#vec_DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a>
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flag or lock timers were configured and the lock could not be granted
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before the wait-time expired.
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</p>
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<p>
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<a class="xref" href="dblocknotgranted.html" title="DbLockNotGrantedException">DbLockNotGrantedException</a> is thrown if
|
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_LOCK_NOTGRANTED</code> is returned.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634349"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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An invalid flag value or parameter was specified.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634489"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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The method was called on an environment which had been
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opened without being configured for locking.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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|||
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3634497"></a>ENOMEM</h4>
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</div>
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</div>
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</div>
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<p>
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The maximum number of locks has been reached.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3634333"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
|
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|
|
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>,
|
|||
|
|
<a class="link" href="lock.html" title="Chapter 7. The DbLock Handle">DbLock</a>
|
|||
|
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</p>
|
|||
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</div>
|
|||
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<div class="sect2" lang="en" xml:lang="en">
|
|||
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<div class="titlepage">
|
|||
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<div>
|
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<div>
|
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<h3 class="title"><a id="id3634252"></a>See Also</h3>
|
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|
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</div>
|
|||
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</div>
|
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</div>
|
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<p>
|
|||
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<a class="xref" href="lock.html#locklist" title="Locking Subsystem and Related Methods">Locking Subsystem and Related Methods</a>
|
|||
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
|
|||
|
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<td width="40%" align="left"><a accesskey="p" href="lockdetect.html">Prev</a> </td>
|
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<td width="20%" align="center">
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<a accesskey="u" href="lock.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="lockid.html">Next</a></td>
|
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|
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</tr>
|
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<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">DbEnv::lock_detect() </td>
|
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|
|
<td width="20%" align="center">
|
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|
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<a accesskey="h" href="index.html">Home</a>
|
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|
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</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> DbEnv::lock_id()</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
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|
</body>
|
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</html>
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