Ubuntu Manpage: cache::async - Asynchronous in-memory cache

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?

_________________________________________________________________________________________________

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  Trackers
       [http://core.tcl.tk/tcllib/reportlist].  Please also report any ideas for enhancements you
       may have for either package and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the output of diff -u.

       Note further that attachments are strongly preferred over inlined patches. Attachments can
       be made by going to the Edit form of the ticket immediately after its creation,  and  then
       using the left-most button in the secondary navigation bar.

KEYWORDS

       asynchronous, cache, callback, synchronous

COPYRIGHT

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