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diff --git a/libdb/docs/ref/lock/intro.html b/libdb/docs/ref/lock/intro.html deleted file mode 100644 index df90ae973..000000000 --- a/libdb/docs/ref/lock/intro.html +++ /dev/null @@ -1,107 +0,0 @@ -<!--$Id$--> -<!--Copyright 1997-2002 by Sleepycat Software, Inc.--> -<!--All rights reserved.--> -<!--See the file LICENSE for redistribution information.--> -<html> -<head> -<title>Berkeley DB Reference Guide: Berkeley DB and locking</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><h3><dl><dt>Berkeley DB Reference Guide:<dd>Locking Subsystem</dl></h3></td> -<td align=right><a href="../../ref/program/faq.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../reftoc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/lock/config.html"><img src="../../images/next.gif" alt="Next"></a> -</td></tr></table> -<p> -<h1 align=center>Berkeley DB and locking</h1> -<p>The locking subsystem provides interprocess and intraprocess concurrency -control mechanisms. Although the lock system is used extensively by -the Berkeley DB access methods and transaction system, it may also be used as -a standalone subsystem to provide concurrency control to any set of -designated resources. -<p>The Lock subsystem is created, initialized, and opened by calls to -<a href="../../api_c/env_open.html">DB_ENV->open</a> with the <a href="../../api_c/env_open.html#DB_INIT_LOCK">DB_INIT_LOCK</a> or <a href="../../api_c/env_open.html#DB_INIT_CDB">DB_INIT_CDB</a> -flags specified. -<p>The <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a> interface is used to acquire and release locks. -The <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a> function performs any number of lock operations -atomically. It also provides the capability to release all locks held -by a particular locker and release all the locks on a particular object. -(Performing multiple lock operations atomically is useful in performing -Btree traversals -- you want to acquire a lock on a child page and once -acquired, immediately release the lock on its parent. This is -traditionally referred to as <i>lock-coupling</i>). Two additional -interfaces, <a href="../../api_c/lock_get.html">DB_ENV->lock_get</a> and <a href="../../api_c/lock_put.html">DB_ENV->lock_put</a>, are provided. These -interfaces are simpler front-ends to the <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a> functionality, -where <a href="../../api_c/lock_get.html">DB_ENV->lock_get</a> acquires a lock, and <a href="../../api_c/lock_put.html">DB_ENV->lock_put</a> releases -a lock that was acquired using <a href="../../api_c/lock_get.html">DB_ENV->lock_get</a> or <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a>. -All locks explicitly requested by an application should be released via -calls to <a href="../../api_c/lock_put.html">DB_ENV->lock_put</a> or <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a>. Using <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a> -instead of separate calls to <a href="../../api_c/lock_put.html">DB_ENV->lock_put</a> and <a href="../../api_c/lock_get.html">DB_ENV->lock_get</a> also -reduces the synchronization overhead between multiple threads or -processes. The three interfaces are fully compatible, and may be used -interchangeably. -<p>Applications must specify lockers and lock objects appropriately. When -used with the Berkeley DB access methods, lockers and objects are handled -completely internally, but an application using the lock manager -directly must either use the same conventions as the access methods or -define its own convention to which it adheres. If an application is -using the access methods with locking at the same time that it is -calling the lock manager directly, the application must follow a -convention that is compatible with the access methods' use of the -locking subsystem. See <a href="../../ref/lock/am_conv.html">Access -method locking conventions</a> for more information. -<p>The <a href="../../api_c/lock_id.html">DB_ENV->lock_id</a> function returns a unique ID that may safely be used -as the locker parameter to the <a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a> interface. The access -methods use <a href="../../api_c/lock_id.html">DB_ENV->lock_id</a> to generate unique lockers for the cursors -associated with a database. -<p>The <a href="../../api_c/lock_detect.html">DB_ENV->lock_detect</a> function provides the programmatic interface to -the Berkeley DB deadlock detector. Whenever two threads of control issue lock -requests concurrently, the possibility for deadlock arises. A deadlock -occurs when two or more threads of control are blocked, waiting for -actions that another one of the blocked threads must take. For example, -assume that threads A and B have each obtained read locks on object X. -Now suppose that both threads want to obtain write locks on object X. -Neither thread can be granted its write lock (because of the other -thread's read lock). Both threads block and will never unblock because -the event for which they are waiting can never happen. -<p>The deadlock detector examines all the locks held in the environment, -and identifies situations where no thread can make forward progress. -It then selects one of the participants in the deadlock (according to -the argument that was specified to <a href="../../api_c/env_set_lk_detect.html">DB_ENV->set_lk_detect</a>), and -forces it to return the value <a href="../../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a>, which indicates -that a deadlock occurred. The thread receiving such an error must -release all of its locks and undo any incomplete modifications to the -locked resource. Locks are typically released, and modifications -undone, by closing any cursors involved in the operation and aborting -any transaction enclosing the operation. The operation may optionally -be retried. -<p>The <a href="../../api_c/lock_stat.html">DB_ENV->lock_stat</a> function returns information about the status of -the lock subsystem. It is the programmatic interface used by the -<a href="../../utility/db_stat.html">db_stat</a> utility. -<p>The locking subsystem is closed by the call to <a href="../../api_c/env_close.html">DB_ENV->close</a>. -<p>Finally, the entire locking subsystem may be discarded using the -<a href="../../api_c/env_remove.html">DB_ENV->remove</a> interface. -<!--$Id$--> -<p><table border=1 align=center> -<tr><th>Locking Subsystem and Related Methods</th><th>Description</th></tr> -<tr><td><a href="../../api_c/env_set_lk_conflicts.html">DB_ENV->set_lk_conflicts</a></td><td>Set lock conflicts matrix</td></tr> -<tr><td><a href="../../api_c/env_set_lk_detect.html">DB_ENV->set_lk_detect</a></td><td>Set automatic deadlock detection</td></tr> -<tr><td><a href="../../api_c/env_set_lk_max_lockers.html">DB_ENV->set_lk_max_lockers</a></td><td>Set maximum number of lockers</td></tr> -<tr><td><a href="../../api_c/env_set_lk_max_locks.html">DB_ENV->set_lk_max_locks</a></td><td>Set maximum number of locks</td></tr> -<tr><td><a href="../../api_c/env_set_lk_max_objects.html">DB_ENV->set_lk_max_objects</a></td><td>Set maximum number of lock objects</td></tr> -<tr><td><a href="../../api_c/env_set_timeout.html">DB_ENV->set_timeout</a></td><td>Set lock and transaction timeout</td></tr> -<tr><td><a href="../../api_c/lock_detect.html">DB_ENV->lock_detect</a></td><td>Perform deadlock detection</td></tr> -<tr><td><a href="../../api_c/lock_get.html">DB_ENV->lock_get</a></td><td>Acquire a lock</td></tr> -<tr><td><a href="../../api_c/lock_id.html">DB_ENV->lock_id</a></td><td>Acquire a locker ID</td></tr> -<tr><td><a href="../../api_c/lock_id_free.html">DB_ENV->lock_id_free</a></td><td>Release a locker ID</td></tr> -<tr><td><a href="../../api_c/lock_put.html">DB_ENV->lock_put</a></td><td>Release a lock</td></tr> -<tr><td><a href="../../api_c/lock_stat.html">DB_ENV->lock_stat</a></td><td>Return lock subsystem statistics</td></tr> -<tr><td><a href="../../api_c/lock_vec.html">DB_ENV->lock_vec</a></td><td>Acquire/release locks</td></tr> -</table> -<table width="100%"><tr><td><br></td><td align=right><a href="../../ref/program/faq.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../reftoc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/lock/config.html"><img src="../../images/next.gif" alt="Next"></a> -</td></tr></table> -<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> -</body> -</html> |