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188 lines
7.1 KiB
HTML
188 lines
7.1 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.08 [en] (X11; I; FreeBSD 2.2.8-19990120-SNAP i386) [Netscape]">
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</HEAD>
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<BODY>
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<H2>
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<A NAME="Locking Commands"></A>Locking Commands</H2>
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Most locking commands work with the environment handle. However,
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when a user gets a lock we create a new lock handle that they then use
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with in a similar manner to all the other handles to release the lock.
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We present the general locking functions first, and then those that manipulate
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locks.
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<P><B>> <env> lock_detect [-lock_conflict] [default|oldest|youngest|random]</B>
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<P>This command runs the deadlock detector. It directly translates
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to the <A HREF="../../docs/api_c/lock_detect.html">lock_detect</A> DB call.
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It returns either a 0 (for success), a DB error message or it throws a
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Tcl error with a system message. The first argument sets the policy
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for deadlock as follows:
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<UL>
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<LI>
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<B>default</B> selects the DB_LOCK_DEFAULT policy for default detection
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(default if not specified)</LI>
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<LI>
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<B>oldest </B>selects DB_LOCK_OLDEST to abort the oldest locker on a deadlock</LI>
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<LI>
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<B>random</B> selects DB_LOCK_RANDOM to abort a random locker on a deadlock</LI>
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<LI>
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<B>youngest</B> selects DB_LOCK_YOUNGEST to abort the youngest locker on
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a deadlock</LI>
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</UL>
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The second argument, <B>-lock_conflict</B>, selects the DB_LOCK_CONFLICT
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flag to only run the detector if a lock conflict has occurred since the
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last time the detector was run.
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<HR WIDTH="100%">
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<BR><B>> <env> lock_stat</B>
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<P>This command returns a list of name/value pairs where the names correspond
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to the C-structure field names of DB_LOCK_STAT and the values are the data
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returned. This command is a direct translation of the <A HREF="../../docs/api_c/lock_stat.html">lock_stat</A>
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DB call.
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<HR WIDTH="100%">
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<BR><A NAME="> <env> lock_id"></A><B>> <env> lock_id</B>
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<P>This command returns a unique locker ID value. It directly translates
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to the <A HREF="../../docs/api_c/lock_id.html">lock_id</A> DB call.
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<HR WIDTH="100%">
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<BR><A NAME="> <env> lock_get"></A><B>> <env> lock_get [-nowait]<I>lockmode
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locker obj</I></B>
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<P>This command gets a lock. It will invoke the <A HREF="../../docs/api_c/lock_get.html">lock_get</A>
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function. After it successfully gets a handle to a lock, we bind
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it to a new Tcl command of the form <B><I>$env.lockX</I></B>, where X is
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an integer starting at 0 (e.g. <B>$env.lock0, $env.lock1, </B>etc).
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We use the <I>Tcl_CreateObjCommand()</I> to create the top level locking
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command function. It is through this handle that the user can release
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the lock. Internally, the handle we get back from DB will be stored
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as the <I>ClientData</I> portion of the new command set so that future
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locking calls will have that handle readily available.
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<P>The arguments are:
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<UL>
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<LI>
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<B><I>locker</I></B> specifies the locker ID returned from the <A HREF="#> <env> lock_id">lock_id</A>
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command</LI>
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<LI>
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<B><I>obj</I></B> specifies an object to lock</LI>
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<LI>
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the <B><I>lock mode</I></B> is specified as one of the following:</LI>
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<UL>
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<LI>
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<B>ng </B>specifies DB_LOCK_NG for not granted (always 0)</LI>
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<LI>
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<B>read</B> specifies DB_LOCK_READ for a read (shared) lock</LI>
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<LI>
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<B>write</B> specifies DB_LOCK_WRITE for an exclusive write lock</LI>
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<LI>
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<B>iwrite </B>specifies DB_LOCK_IWRITE for intent for exclusive write lock</LI>
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<LI>
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<B>iread </B>specifies DB_LOCK_IREAD for intent for shared read lock</LI>
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<LI>
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<B>iwr </B>specifies DB_LOCK_IWR for intent for eread and write lock</LI>
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</UL>
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<LI>
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<B>-nowait</B> selects the DB_LOCK_NOWAIT to indicate that we do not want
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to wait on the lock</LI>
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</UL>
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<HR WIDTH="100%">
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<BR><B>> <lock> put</B>
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<P>This command releases the lock referenced by the command. It is
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a direct translation of the <A HREF="../../docs/api_c/lock_put.html">lock_put</A>
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function. It returns either a 0 (for success), a DB error message
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or it throws a Tcl error with a system message. Additionally, since
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the handle is no longer valid, we will call
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<I>Tcl_DeleteCommand()
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</I>so
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that further uses of the handle will be dealt with properly by Tcl itself.
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<BR>
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<HR WIDTH="100%">
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<BR><A NAME="> <env> lock_vec"></A><B>> <env> lock_vec [-nowait] <I>locker
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</I>{get|put|put_all|put_obj
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[<I>obj</I>] [<I>lockmode</I>] [<I>lock</I>]} ...</B>
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<P>This command performs a series of lock calls. It is a direct translation
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of the <A HREF="../../docs/api_c/lock_vec.html">lock_vec</A> function.
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This command will return a list of the return values from each operation
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specified in the argument list. For the 'put' operations the entry
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in the return value list is either a 0 (for success) or an error.
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For the 'get' operation, the entry is the lock widget handle, <B>$env.lockN</B>
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(as described above in <A HREF="#> <env> lock_get"><env> lock_get</A>)
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or an error. If an error occurs, the return list will contain the
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return values for all the successful operations up the erroneous one and
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the error code for that operation. Subsequent operations will be
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ignored.
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<P>As for the other operations, if we are doing a 'get' we will create
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the commands and if we are doing a 'put' we will have to delete the commands.
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Additionally, we will have to do this after the call to the DB lock_vec
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and iterate over the results, creating and/or deleting Tcl commands.
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It is possible that we may return a lock widget from a get operation that
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is considered invalid, if, for instance, there was a <B>put_all</B> operation
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performed later in the vector of operations. The arguments are:
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<UL>
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<LI>
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<B><I>locker</I></B> specifies the locker ID returned from the <A HREF="#> <env> lock_id">lock_id</A>
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command</LI>
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<LI>
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<B>-nowait</B> selects the DB_LOCK_NOWAIT to indicate that we do not want
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to wait on the lock</LI>
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<LI>
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the lock vectors are tuple consisting of {an operation, lock object, lock
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mode, lock handle} where what is required is based on the operation desired:</LI>
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<UL>
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<LI>
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<B>get</B> specifes DB_LOCK_GET to get a lock. Requires a tuple <B>{get
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<I>obj</I>
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<I>mode</I>}
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</B>where
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<B><I>mode</I></B>
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is:</LI>
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<UL>
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<LI>
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<B>ng </B>specifies DB_LOCK_NG for not granted (always 0)</LI>
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<LI>
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<B>read</B> specifies DB_LOCK_READ for a read (shared) lock</LI>
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<LI>
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<B>write</B> specifies DB_LOCK_WRITE for an exclusive write lock</LI>
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<LI>
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<B>iwrite </B>specifies DB_LOCK_IWRITE for intent for exclusive write lock</LI>
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<LI>
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<B>iread </B>specifies DB_LOCK_IREAD for intent for shared read lock</LI>
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<LI>
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<B>iwr </B>specifies DB_LOCK_IWR for intent for eread and write lock</LI>
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</UL>
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<LI>
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<B>put</B> specifies DB_LOCK_PUT to release a <B><I>lock</I></B>.
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Requires a tuple <B>{put <I>lock}</I></B></LI>
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<LI>
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<B>put_all </B>specifies DB_LOCK_PUT_ALL to release all locks held by <B><I>locker</I></B>.
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Requires a tuple <B>{put_all}</B></LI>
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<LI>
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<B>put_obj</B> specifies DB_LOCK_PUT_OBJ to release all locks held by <B><I>locker</I></B>
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associated with the given <B><I>obj</I></B>. Requires a tuple <B>{put_obj
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<I>obj</I>}</B></LI>
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</UL>
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</UL>
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