105 lines
5.1 KiB
HTML
105 lines
5.1 KiB
HTML
<!--$Id: lock_get.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
|
|
<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
|
|
<!--See the file LICENSE for redistribution information.-->
|
|
<html>
|
|
<head>
|
|
<title>Berkeley DB: DbEnv::lock_get</title>
|
|
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
|
|
<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
|
|
</head>
|
|
<body bgcolor=white>
|
|
<table width="100%"><tr valign=top>
|
|
<td>
|
|
<b>DbEnv::lock_get</b>
|
|
</td>
|
|
<td align=right>
|
|
<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></td>
|
|
</tr></table>
|
|
<hr size=1 noshade>
|
|
<tt>
|
|
<b><pre>
|
|
#include <db_cxx.h>
|
|
<p>
|
|
int
|
|
DbEnv::lock_get(u_int32_t locker, u_int32_t flags,
|
|
const Dbt *object, const db_lockmode_t lock_mode, DbLock *lock);
|
|
</pre></b>
|
|
<hr size=1 noshade>
|
|
<b>Description: DbEnv::lock_get</b>
|
|
<p>The DbEnv::lock_get method acquires a lock from the lock table, returning
|
|
information about it in the <b>lock</b> parameter.</p>
|
|
<p>The DbEnv::lock_get method
|
|
either returns a non-zero error value
|
|
or throws an exception that encapsulates a non-zero error value on
|
|
failure, and returns 0 on success.
|
|
</p>
|
|
<b>Parameters</b> <br>
|
|
<b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or
|
|
the following value:
|
|
<br>
|
|
<b><a name="DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a></b><ul compact><li>If a lock cannot be granted because the requested lock conflicts with an
|
|
existing lock,
|
|
return DB_LOCK_NOTGRANTED or throw a
|
|
<a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> immediately instead of waiting for
|
|
the lock to become available.</ul>
|
|
<br></ul>
|
|
<b>lock_mode</b><ul compact><li>The <b>lock_mode</b> parameter is used as an index into the environment's
|
|
lock conflict matrix. When using the default lock conflict matrix,
|
|
<b>lock_mode</b> must be set to one of the following values:
|
|
<br>
|
|
<b>DB_LOCK_READ</b><ul compact><li>read (shared)</ul>
|
|
<b>DB_LOCK_WRITE</b><ul compact><li>write (exclusive)</ul>
|
|
<b>DB_LOCK_IWRITE</b><ul compact><li>intention to write (shared)</ul>
|
|
<b>DB_LOCK_IREAD</b><ul compact><li>intention to read (shared)</ul>
|
|
<b>DB_LOCK_IWR</b><ul compact><li>intention to read and write (shared)</ul>
|
|
<br>
|
|
<p>See <a href="../api_cxx/env_set_lk_conflicts.html">DbEnv::set_lk_conflicts</a> and <a href="../ref/lock/stdmode.html">Standard Lock Modes</a> for more information on the lock conflict matrix.</p></ul>
|
|
<b>locker</b><ul compact><li>The <b>locker</b> parameter is an unsigned 32-bit integer quantity. It
|
|
represents the entity requesting the lock.</ul>
|
|
<b>object</b><ul compact><li>The <b>object</b> parameter is an untyped byte string that specifies the
|
|
object to be locked. Applications using the locking subsystem directly
|
|
while also doing locking via the Berkeley DB access methods must take care not
|
|
to inadvertently lock objects that happen to be equal to the unique file
|
|
IDs used to lock files. See
|
|
<a href="../ref/lock/am_conv.html">Access method locking conventions</a>
|
|
for more information.</ul>
|
|
<br>
|
|
<br><b>Errors</b>
|
|
<p>The DbEnv::lock_get method
|
|
may fail and throw
|
|
<a href="../api_cxx/except_class.html">DbException</a>,
|
|
encapsulating one of the following non-zero errors, or return one of
|
|
the following non-zero errors:</p>
|
|
<br>
|
|
<b>EINVAL</b><ul compact><li>An
|
|
invalid flag value or parameter was specified.</ul>
|
|
<br>
|
|
<p>If a transactional database environment operation was selected to
|
|
resolve a deadlock, the DbEnv::lock_get method will fail and
|
|
either return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or
|
|
throw a <a href="../api_cxx/deadlock_class.html">DbDeadlockException</a> exception.</p>
|
|
<p>If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable
|
|
to grant a lock in the allowed time, the DbEnv::lock_get method will fail and
|
|
either return <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or
|
|
throw a <a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p>
|
|
<p>If the <a href="../api_cxx/lock_vec.html#DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a> flag or lock timers were configured and the lock could not be granted before the wait-time expired,
|
|
the DbEnv::lock_get method will fail and
|
|
either return DB_LOCK_NOTGRANTED or
|
|
throw a <a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p>
|
|
<p>If the maximum number of locks has been reached, the DbEnv::lock_get method will fail and
|
|
either return ENOMEM or
|
|
throw a DbMemoryException.</p>
|
|
<hr size=1 noshade>
|
|
<br><b>Class</b>
|
|
<a href="../api_cxx/env_class.html">DbEnv</a>, <a href="../api_cxx/lock_class.html">DbLock</a>
|
|
<br><b>See Also</b>
|
|
<a href="../api_cxx/lock_list.html">Locking Subsystem and Related Methods</a>
|
|
</tt>
|
|
<table width="100%"><tr><td><br></td><td align=right>
|
|
<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>
|
|
</td></tr></table>
|
|
<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
|
|
</body>
|
|
</html>
|