cache::async(n) 						 In-memory caches						   cache::async(n)

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NAME

       cache::async - Asynchronous in-memory cache

SYNOPSIS

       package require Tcl  8.4

       package require cache::async  ?0.3?

       ::cache::async objectName commandprefix ?options...?

       objectName get key donecmdprefix

       objectName set key value

       objectName unset key

       objectName exists key

       objectName clear ?key?

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DESCRIPTION

       This  package provides objects which cache data in memory, and operate asynchronously with regard to request and responses. The objects are
       agnostic with regard to cache keys and values, and unknown methods are delegated to the provider of cached data. These two properties  make
       it easy to use caches as a facade for any data provider.

API

       The package exports a class, cache::async, as specified below.

       ::cache::async objectName commandprefix ?options...?
	      The  command creates a new cache object with an associated global Tcl command whose name is objectName.  This command may be used to
	      invoke various operations on the object.

	      The commandprefix is the action to perform when an user asks for data in the cache and the cache doesn't yet  know  about  the  key.
	      When  run  the commandprefix is given three additional arguments, the string get, the key requested, and the cache object itself, in
	      the form of its object command, in this order. The execution of the action is done in an idle-handler, decoupling it from the origi-
	      nal request.

	      The only supported option is

	      -full-async-results
		     This  option defines the behaviour of the cache for when requested keys are known to the cache at the time of get request. By
		     default such requeste are responded to asynchronously as well. Setting this option to false forces the cache  to  respond	to
		     them synchronuously, although still through the specified callback.

       The object commands created by the class commands above have the form:

       objectName get key donecmdprefix
	      This method requests the data for the key from the cache. If the data is not yet known the command prefix specified during construc-
	      tion of the cache object is used to ask for this information.

	      Whenever the information is/becomes available the donecmdprefix will be run to transfer the result to the caller. This command  pre-
	      fix is invoked with either 2 or 3 arguments, i.e.

	      [1]    The string set, the key, and the value.

	      [2]    The string unset, and the key.
       These  two  possibilities  are used to either signal the value for the key, or that the key has no value defined for it. The latter is dis-
       tinct from the cache not knowing about the key.

       For a cache object configured to be fully asynchronous (default) the donecmdprefix is always run in an idle-handler, decoupling it from the
       request. Otherwise the callback will be invoked synchronously when the key is known to the cache at the time of the invokation.

       Another	important  part  of the cache's behaviour, as it is asynchronous it is possible that multiple get requests are issued for the same
       key before it can respond. In that case the cache will issue only one data request to the provider, for the first of these, and suspend the
       others, and then notify all of them when the data becomes available.

       objectName set key value

       objectName unset key
	      These  two  methods  are provided to allow users of the cache to make keys known to the cache, as either having a value, or as unde-
	      fined.

	      It is expected that the data provider (see commandprefix of the constructor) uses them in response  to  data  requests  for  unknown
	      keys.

	      Note  how this matches the cache's own API towards its caller, calling the donecmd of get-requests issued to itself with either "set
	      key value" or "unset key", versus issuing get-requests to its own provider with itself in the place of the donecmd, expecting to	be
	      called with either "set key value" or "unset key".

	      This also means that these methods invoke the donecmd of all get-requests waiting for information about the modified key.

       objectName exists key
	      This  method  queries the cache for knowledge about the key and returns a boolean value. The result is true if the key is known, and
	      false otherwise.

       objectName clear ?key?
	      This method resets the state of either the specified key or of all keys known to the cache, making it  unkown.  This  forces  future
	      get-requests to reload the information from the provider.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category cache of
       the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you  may  have  for
       either package and/or documentation.

KEYWORDS

       asynchronous, cache, callback, synchronous

COPYRIGHT

       Copyright (c) 2008 Andreas Kupries <andreas_kupries@users.sourceforge.net>

cache									0.3							   cache::async(n)