99 lines
4.4 KiB
HTML
99 lines
4.4 KiB
HTML
<!--$Id: lock_get.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: DB_ENV->lock_get</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>DB_ENV->lock_get</b>
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</td>
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<td align=right>
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<a href="../api_c/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.h>
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<p>
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int
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DB_ENV->lock_get(DB_ENV *env, u_int32_t locker,
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u_int32_t flags, const DBT *object,
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const db_lockmode_t lock_mode, DB_LOCK *lock);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB_ENV->lock_get</b>
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<p>The DB_ENV->lock_get method acquires a lock from the lock table, returning
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information about it in the <b>lock</b> parameter.</p>
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<p>The DB_ENV->lock_get method
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returns a non-zero error value on failure
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and 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or
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the following value:
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<br>
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<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
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existing lock,
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return DB_LOCK_NOTGRANTED immediately instead of waiting
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for the lock to become available.
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</ul>
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<br></ul>
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<b>lock_mode</b><ul compact><li>The <b>lock_mode</b> parameter is used as an index into the environment's
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lock conflict matrix. When using the default lock conflict matrix,
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<b>lock_mode</b> must be set to one of the following values:
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<br>
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<b>DB_LOCK_READ</b><ul compact><li>read (shared)</ul>
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<b>DB_LOCK_WRITE</b><ul compact><li>write (exclusive)</ul>
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<b>DB_LOCK_IWRITE</b><ul compact><li>intention to write (shared)</ul>
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<b>DB_LOCK_IREAD</b><ul compact><li>intention to read (shared)</ul>
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<b>DB_LOCK_IWR</b><ul compact><li>intention to read and write (shared)</ul>
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<br>
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<p>See <a href="../api_c/env_set_lk_conflicts.html">DB_ENV->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>
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<b>locker</b><ul compact><li>The <b>locker</b> parameter is an unsigned 32-bit integer quantity. It
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represents the entity requesting the lock.</ul>
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<b>object</b><ul compact><li>The <b>object</b> parameter is an untyped byte string that specifies the
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object to be locked. Applications using the locking subsystem directly
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while also doing locking via the Berkeley DB access methods must take care not
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to inadvertently lock objects that happen to be equal to the unique file
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IDs used to lock files. See
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<a href="../ref/lock/am_conv.html">Access method locking conventions</a>
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for more information.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DB_ENV->lock_get method
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may fail and return one of the following non-zero errors:</p>
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<br>
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<b>DB_LOCK_DEADLOCK</b><ul compact><li>A transactional database environment operation was selected to resolve
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a deadlock.</ul>
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<b>DB_LOCK_NOTGRANTED</b><ul compact><li>A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable
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to grant a lock in the allowed time.</ul>
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<br>
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<br>
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<b>DB_LOCK_NOTGRANTED</b><ul compact><li>The <a href="../api_c/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.</ul>
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<br>
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<br>
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<b>EINVAL</b><ul compact><li>An
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invalid flag value or parameter was specified.</ul>
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<br>
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<br>
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<b>ENOMEM</b><ul compact><li>The maximum number of locks has been reached.</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_c/env_class.html">DB_ENV</a>, <a href="../api_c/lock_class.html">DB_LOCK</a>
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<br><b>See Also</b>
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<a href="../api_c/lock_list.html">Locking Subsystem 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_c/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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</body>
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</html>
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