<div class='fossil-doc' data-title='cache::async - In-memory caches'>
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<div class="doctools">
<h1 class="doctools_title">cache::async(n) 0.3 tcllib &quot;In-memory caches&quot;</h1>
<div id="name" class="doctools_section"><h2><a name="name">Name</a></h2>
<p>cache::async - Asynchronous in-memory cache</p>
</div>
<div id="toc" class="doctools_section"><h2><a name="toc">Table Of Contents</a></h2>
<ul class="doctools_toc">
<li class="doctools_section"><a href="#toc">Table Of Contents</a></li>
<li class="doctools_section"><a href="#synopsis">Synopsis</a></li>
<li class="doctools_section"><a href="#section1">Description</a></li>
<li class="doctools_section"><a href="#section2">API</a></li>
<li class="doctools_section"><a href="#section3">Bugs, Ideas, Feedback</a></li>
<li class="doctools_section"><a href="#keywords">Keywords</a></li>
<li class="doctools_section"><a href="#copyright">Copyright</a></li>
</ul>
</div>
<div id="synopsis" class="doctools_section"><h2><a name="synopsis">Synopsis</a></h2>
<div class="doctools_synopsis">
<ul class="doctools_requirements">
<li>package require <b class="pkgname">Tcl 8.4</b></li>
<li>package require <b class="pkgname">cache::async <span class="opt">?0.3?</span></b></li>
</ul>
<ul class="doctools_syntax">
<li><a href="#1"><b class="cmd">::cache::async</b> <i class="arg">objectName</i> <i class="arg">commandprefix</i> <span class="opt">?<i class="arg">options</i>...?</span></a></li>
<li><a href="#2"><i class="arg">objectName</i> <b class="method">get</b> <i class="arg">key</i> <i class="arg">donecmdprefix</i></a></li>
<li><a href="#3"><i class="arg">objectName</i> <b class="method">set</b> <i class="arg">key</i> <i class="arg">value</i></a></li>
<li><a href="#4"><i class="arg">objectName</i> <b class="method">unset</b> <i class="arg">key</i></a></li>
<li><a href="#5"><i class="arg">objectName</i> <b class="method">exists</b> <i class="arg">key</i></a></li>
<li><a href="#6"><i class="arg">objectName</i> <b class="method">clear</b> <span class="opt">?<i class="arg">key</i>?</span></a></li>
</ul>
</div>
</div>
<div id="section1" class="doctools_section"><h2><a name="section1">Description</a></h2>
<p>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.</p>
</div>
<div id="section2" class="doctools_section"><h2><a name="section2">API</a></h2>
<p>The package exports a class, <b class="class">cache::async</b>, as specified
below.</p>
<dl class="doctools_definitions">
<dt><a name="1"><b class="cmd">::cache::async</b> <i class="arg">objectName</i> <i class="arg">commandprefix</i> <span class="opt">?<i class="arg">options</i>...?</span></a></dt>
<dd><p>The command creates a new <i class="term"><a href="../../../../index.html#cache">cache</a></i> object with an associated
global Tcl command whose name is <i class="arg">objectName</i>.  This command may
be used to invoke various operations on the object.</p>
<p>The <i class="arg">commandprefix</i> 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
<b class="const">get</b>, 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.</p>
<p>The only supported option is</p>
<dl class="doctools_options">
<dt><b class="option">-full-async-results</b></dt>
<dd><p>This option defines the behaviour of the cache for when requested keys
are known to the cache at the time of <b class="method">get</b> request. By default
such requeste are responded to asynchronously as well. Setting this
option to <b class="const">false</b> forces the cache to respond to them
synchronuously, although still through the specified callback.</p></dd>
</dl></dd>
</dl>
<p>The object commands created by the class commands above have
the form:</p>
<dl class="doctools_definitions">
<dt><a name="2"><i class="arg">objectName</i> <b class="method">get</b> <i class="arg">key</i> <i class="arg">donecmdprefix</i></a></dt>
<dd><p>This method requests the data for the <i class="arg">key</i> 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.</p>
<p>Whenever the information is/becomes available the <i class="arg">donecmdprefix</i>
will be run to transfer the result to the caller. This command prefix
is invoked with either 2 or 3 arguments, i.e.</p>
<ol class="doctools_enumerated">
<li><p>The string <b class="const">set</b>, the <i class="arg">key</i>, and the value.</p></li>
<li><p>The string <b class="const">unset</b>, and the <i class="arg">key</i>.</p></li>
</ol>
<p>These two possibilities are used to either signal the value for the
<i class="arg">key</i>, or that the <i class="arg">key</i> has no value defined for it. The
latter is distinct from the cache not knowing about the <i class="arg">key</i>.</p>
<p>For a cache object configured to be fully asynchronous (default) the
<i class="arg">donecmdprefix</i> is always run in an idle-handler, decoupling it
from the request. Otherwise the callback will be invoked synchronously
when the <i class="arg">key</i> is known to the cache at the time of the
invokation.</p>
<p>Another important part of the cache's behaviour, as it is asynchronous
it is possible that multiple <b class="method">get</b> requests are issued for the
same <i class="arg">key</i> 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.</p></dd>
<dt><a name="3"><i class="arg">objectName</i> <b class="method">set</b> <i class="arg">key</i> <i class="arg">value</i></a></dt>
<dd></dd>
<dt><a name="4"><i class="arg">objectName</i> <b class="method">unset</b> <i class="arg">key</i></a></dt>
<dd><p>These two methods are provided to allow users of the cache to make
keys known to the cache, as either having a <i class="arg">value</i>, or as
undefined.</p>
<p>It is expected that the data provider (see <i class="arg">commandprefix</i> of the
constructor) uses them in response to data requests for unknown keys.</p>
<p>Note how this matches the cache's own API towards its caller, calling
the <i class="arg">donecmd</i> of <b class="method">get</b>-requests issued to itself with
either &quot;set key value&quot; or &quot;unset key&quot;, versus issuing
<b class="method">get</b>-requests to its own provider with itself in the place of
the <i class="arg">donecmd</i>, expecting to be called with either &quot;set key value&quot;
or &quot;unset key&quot;.</p>
<p>This also means that these methods invoke the <i class="arg">donecmd</i> of all
<b class="method">get</b>-requests waiting for information about the modified
<i class="arg">key</i>.</p></dd>
<dt><a name="5"><i class="arg">objectName</i> <b class="method">exists</b> <i class="arg">key</i></a></dt>
<dd><p>This method queries the cache for knowledge about the <i class="arg">key</i> and
returns a boolean value. The result is <b class="const">true</b> if the key is
known, and <b class="const">false</b> otherwise.</p></dd>
<dt><a name="6"><i class="arg">objectName</i> <b class="method">clear</b> <span class="opt">?<i class="arg">key</i>?</span></a></dt>
<dd><p>This method resets the state of either the specified <i class="arg">key</i> or of
all keys known to the cache, making it unkown. This forces future
<b class="method">get</b>-requests to reload the information from the provider.</p></dd>
</dl>
</div>
<div id="section3" class="doctools_section"><h2><a name="section3">Bugs, Ideas, Feedback</a></h2>
<p>This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category <em>cache</em> of the
<a href="http://core.tcl.tk/tcllib/reportlist">Tcllib Trackers</a>.
Please also report any ideas for enhancements you may have for either
package and/or documentation.</p>
<p>When proposing code changes, please provide <em>unified diffs</em>,
i.e the output of <b class="const">diff -u</b>.</p>
<p>Note further that <em>attachments</em> are strongly preferred over
inlined patches. Attachments can be made by going to the <b class="const">Edit</b>
form of the ticket immediately after its creation, and then using the
left-most button in the secondary navigation bar.</p>
</div>
<div id="keywords" class="doctools_section"><h2><a name="keywords">Keywords</a></h2>
<p><a href="../../../../index.html#asynchronous">asynchronous</a>, <a href="../../../../index.html#cache">cache</a>, <a href="../../../../index.html#callback">callback</a>, <a href="../../../../index.html#synchronous">synchronous</a></p>
</div>
<div id="copyright" class="doctools_section"><h2><a name="copyright">Copyright</a></h2>
<p>Copyright &copy; 2008 Andreas Kupries &lt;andreas_kupries@users.sourceforge.net&gt;</p>
</div>
</div>
