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
              original 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
              construction 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
              prefix 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 distinct 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
              undefined.

              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)
