<!--$Id: lock_get.so,v 10.41 2002/08/18 21:16:36 bostic Exp $--> <!--Copyright 1997-2002 by Sleepycat Software, Inc.--> <!--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,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table width="100%"><tr valign=top> <td> <h1>DbEnv::lock_get</h1> </td> <td align=right> <a href="../../db4-devel-4.1.25/api_cxx/c_index.html"><img src="../../db4-4.1.25/images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../../db4-4.1.25/images/ref.gif" alt="Ref"></a> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> #include <db_cxx.h> <p> int DbEnv::lock_get(u_int32_t locker, u_int32_t flags, const Dbt *obj, const db_lockmode_t lock_mode, DbLock *lock); </pre></h3> <h1>Description</h1> <p>The DbEnv::lock_get method acquires a lock from the lock table, returning information about it in the <b>lock</b> argument. <p>The <b>locker</b> argument specified to DbEnv::lock_get is an unsigned 32-bit integer quantity. It represents the entity requesting or releasing the lock. <p>The <b>flags</b> value must be set to 0 or the following value: <p><dl compact> <p><dt><a name="DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a><dd>If a lock cannot be granted because the requested lock conflicts with an existing lock, return DB_LOCK_NOTGRANTED or throw a <a href="../../db4-devel-4.1.25/api_cxx/lockng_class.html">DbLockNotGrantedException</a> immediately instead of waiting for the lock to become available. </dl> <p>The <b>obj</b> argument is an untyped byte string that specifies the object to be locked or released. 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="../../db4-devel-4.1.25/ref/lock/am_conv.html">Access method locking conventions</a> for more information. <p>The <b>mode</b> argument is used as an index into the environment's lock conflict matrix. When using the default lock conflict matrix, <b>mode</b> must be set to one of the following values: <p><dl compact> <dt>DB_LOCK_READ<dd>read (shared) <dt>DB_LOCK_WRITE<dd>write (exclusive) <dt>DB_LOCK_IWRITE<dd>intention to write (shared) <dt>DB_LOCK_IREAD<dd>intention to read (shared) <dt>DB_LOCK_IWR<dd>intention to read and write (shared) </dl> <p>See <a href="../../db4-devel-4.1.25/api_cxx/env_set_lk_conflicts.html">DbEnv::set_lk_conflicts</a> and <a href="../../db4-devel-4.1.25/ref/lock/stdmode.html">Standard Lock Modes</a> for more information on the lock conflict matrix. <p> Otherwise, 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. <h1>Errors</h1> <p>The DbEnv::lock_get method may fail and throw an exception or return a non-zero error for the following conditions: <p><dl compact> <p><dt>EINVAL<dd>An invalid flag value or parameter was specified. </dl> <p><dl compact> <p><dt>ENOMEM<dd>The maximum number of locks has been reached. </dl> <p>If the operation was selected to resolve a deadlock, the DbEnv::lock_get method will fail and and either return <a href="../../db4-devel-4.1.25/ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or throw a <a href="../../db4-devel-4.1.25/api_cxx/deadlock_class.html">DbDeadlockException</a> exception. <p>The DbEnv::lock_get method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the DbEnv::lock_get method may fail and either return <a href="../../db4-devel-4.1.25/ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw a <a href="../../db4-devel-4.1.25/api_cxx/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls will fail in the same way. <h1>Class</h1> <a href="../../db4-devel-4.1.25/api_cxx/env_class.html">DbEnv</a>, <a href="../../db4-devel-4.1.25/api_cxx/lock_class.html">DbLock</a> <h1>See Also</h1> <a href="../../db4-devel-4.1.25/api_cxx/lock_list.html">Locking Subsystem and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../../db4-devel-4.1.25/api_cxx/c_index.html"><img src="../../db4-4.1.25/images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../../db4-4.1.25/images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> </body> </html>