diff options
Diffstat (limited to 'bdb/docs/ref/lock/intro.html')
| -rw-r--r-- | bdb/docs/ref/lock/intro.html | 89 |
1 files changed, 0 insertions, 89 deletions
diff --git a/bdb/docs/ref/lock/intro.html b/bdb/docs/ref/lock/intro.html deleted file mode 100644 index b5c85af05b0..00000000000 --- a/bdb/docs/ref/lock/intro.html +++ /dev/null @@ -1,89 +0,0 @@ -<!--$Id: intro.so,v 10.16 2000/03/18 21:43:14 bostic Exp $--> -<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.--> -<!--All rights reserved.--> -<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><tr valign=top> -<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Locking Subsystem</dl></h3></td> -<td width="1%"><a href="../../ref/program/runtime.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/lock/page.html"><img src="../../images/next.gif" alt="Next"></a> -</td></tr></table> -<p> -<h1 align=center>Berkeley DB and locking</h1> -<p>The lock subsystem provides interprocess and intraprocess concurrency -control mechanisms. While the locking system is used extensively by the -Berkeley DB access methods and transaction system, it may also be used as a -stand-alone 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">DBENV->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_detect.html">lock_detect</a> function provides the programmatic interface to -the Berkeley DB deadlock detector. Whenever two threads of control issue lock -requests that are not carefully ordered or that require upgrading locks -(obtaining write locks on objects that are already read-locked), the -possibility for deadlock arises. A deadlock occurs when two or more -threads of control are blocked, waiting for actions that another one of -these blocked threads must take. For example, assume that threads one -and two have each obtained read locks on object A. Now suppose that both -threads wish to obtain write locks on object A. Neither thread can be -granted its writelock (because of the other thread's readlock). 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">DBENV->set_lk_detect</a>) and forces it to return -the value DB_LOCK_DEADLOCK, which indicates that a deadlock occurred. -The thread receiving such an error should abort its current transaction, -or simply release all its locks if it is not running in a transaction, -and retry the operation. -<p>The <a href="../../api_c/lock_vec.html">lock_vec</a> interface is used to acquire and release locks. -<p>Two additional interfaces, <a href="../../api_c/lock_get.html">lock_get</a> and <a href="../../api_c/lock_put.html">lock_put</a>, are -provided. These interfaces are simpler front-ends to the <a href="../../api_c/lock_vec.html">lock_vec</a> -functionality, where <a href="../../api_c/lock_get.html">lock_get</a> acquires a lock, and -<a href="../../api_c/lock_put.html">lock_put</a> releases a lock that was acquired using <a href="../../api_c/lock_get.html">lock_get</a> -or <a href="../../api_c/lock_vec.html">lock_vec</a>. -<p>It is up to the application to specify lockers and objects appropriately. -When used with the Berkeley DB access methods, these 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 the 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">lock_id</a> function returns a unique ID which may safely be used -as the locker parameter to the <a href="../../api_c/lock_vec.html">lock_vec</a> interface. The access -methods use <a href="../../api_c/lock_id.html">lock_id</a> to generate unique lockers for the cursors -associated with a database. -<p>The <a href="../../api_c/lock_vec.html">lock_vec</a> function performs any number of lock operations -atomically. It also provides the ability 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 where 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 "lock-coupling"). Using <a href="../../api_c/lock_vec.html">lock_vec</a> -instead of separate calls to <a href="../../api_c/lock_put.html">lock_put</a> and <a href="../../api_c/lock_get.html">lock_get</a> reduces -the synchronization overhead between multiple threads or processes. -<p>The three interfaces, <a href="../../api_c/lock_get.html">lock_get</a>, <a href="../../api_c/lock_put.html">lock_put</a> and <a href="../../api_c/lock_vec.html">lock_vec</a>, -are fully compatible, and may be used interchangeably. -<p>All locks explicitly requested by an application should be released via -calls to <a href="../../api_c/lock_put.html">lock_put</a> or <a href="../../api_c/lock_vec.html">lock_vec</a>. -<p>The <a href="../../api_c/lock_stat.html">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">DBENV->close</a>. -<p>Finally, the entire locking subsystem may be discarded using the -<a href="../../api_c/env_remove.html">DBENV->remove</a> interface. -<table><tr><td><br></td><td width="1%"><a href="../../ref/program/runtime.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/lock/page.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> |