1<!--$Id: lock_get.so,v 10.54 2007/10/26 15:01:06 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: DbEnv::lock_get</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>DbEnv::lock_get</b> 14</td> 15<td align=right> 16<a href="/api_cxx/api_core.html"><img src="/images/api.gif" alt="API"></a> 17<a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db_cxx.h> 23<p> 24int 25DbEnv::lock_get(u_int32_t locker, u_int32_t flags, 26 const Dbt *object, const db_lockmode_t lock_mode, DbLock *lock); 27</pre></b> 28<hr size=1 noshade> 29<b>Description: DbEnv::lock_get</b> 30<p>The DbEnv::lock_get method acquires a lock from the lock table, returning 31information about it in the <b>lock</b> parameter.</p> 32<p>The DbEnv::lock_get method 33either returns a non-zero error value 34or throws an exception that encapsulates a non-zero error value on 35failure, and returns 0 on success. 36</p> 37<b>Parameters</b> <br> 38 <b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or 39the following value: 40<br> 41<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 42existing lock, 43return DB_LOCK_NOTGRANTED or throw a 44<a href="/api_cxx/lockng_class.html">DbLockNotGrantedException</a> immediately instead of waiting for 45the lock to become available.</ul> 46<br></ul> 47 <b>lock_mode</b><ul compact><li>The <b>lock_mode</b> parameter is used as an index into the environment's 48lock conflict matrix. When using the default lock conflict matrix, 49<b>lock_mode</b> must be set to one of the following values: 50<br> 51<b>DB_LOCK_READ</b><ul compact><li>read (shared)</ul> 52<b>DB_LOCK_WRITE</b><ul compact><li>write (exclusive)</ul> 53<b>DB_LOCK_IWRITE</b><ul compact><li>intention to write (shared)</ul> 54<b>DB_LOCK_IREAD</b><ul compact><li>intention to read (shared)</ul> 55<b>DB_LOCK_IWR</b><ul compact><li>intention to read and write (shared)</ul> 56<br> 57<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> 58 <b>locker</b><ul compact><li>The <b>locker</b> parameter is an unsigned 32-bit integer quantity. It 59represents the entity requesting the lock.</ul> 60 <b>object</b><ul compact><li>The <b>object</b> parameter is an untyped byte string that specifies the 61object to be locked. Applications using the locking subsystem directly 62while also doing locking via the Berkeley DB access methods must take care not 63to inadvertently lock objects that happen to be equal to the unique file 64IDs used to lock files. See 65<a href="/ref/lock/am_conv.html">Access method locking conventions</a> 66for more information.</ul> 67<br> 68<br><b>Errors</b> 69<p>The DbEnv::lock_get method 70may fail and throw 71<a href="/api_cxx/except_class.html">DbException</a>, 72encapsulating one of the following non-zero errors, or return one of 73the following non-zero errors:</p> 74<br> 75<b>EINVAL</b><ul compact><li>An 76invalid flag value or parameter was specified.</ul> 77<br> 78<p>If a transactional database environment operation was selected to 79resolve a deadlock, the DbEnv::lock_get method will fail and 80either return <a href="/ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or 81throw a <a href="/api_cxx/deadlock_class.html">DbDeadlockException</a> exception.</p> 82<p>If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable 83to grant a lock in the allowed time, the DbEnv::lock_get method will fail and 84either return <a href="/ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or 85throw a <a href="/api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p> 86<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, 87the DbEnv::lock_get method will fail and 88either return DB_LOCK_NOTGRANTED or 89throw a <a href="/api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p> 90<p>If the maximum number of locks has been reached, the DbEnv::lock_get method will fail and 91either return ENOMEM or 92throw a DbMemoryException.</p> 93<hr size=1 noshade> 94<br><b>Class</b> 95<a href="/api_cxx/env_class.html">DbEnv</a>, <a href="/api_cxx/lock_class.html">DbLock</a> 96<br><b>See Also</b> 97<a href="/api_cxx/lock_list.html">Locking Subsystem and Related Methods</a> 98</tt> 99<table width="100%"><tr><td><br></td><td align=right> 100<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> 101</td></tr></table> 102<p><font size=1>Copyright (c) 1996,2008 Oracle. 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