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<?xml version="1.0" encoding="utf-8"?><!DOCTYPE html  PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN'  'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'><html lang="en" xmlns="http://www.w3.org/1999/xhtml">
  <head>
<title>Twisted Documentation: Managing Clients of Perspectives</title>
<link href="stylesheet.css" rel="stylesheet" type="text/css"/>
  <link href="http://twistedmatrix.com/users/acapnotic/" rel="author" title="Kevin Turner"/></head>

  <body bgcolor="white">
    <h1 class="title">Managing Clients of Perspectives</h1>
    <div class="toc"><ol><li><a href="#auto0">Overview</a></li><li><a href="#auto1">Managing Avatars</a></li><li><a href="#auto2">Managing Clients</a></li></ol></div>
    <div class="content">
<span/>

<h2>Overview<a name="auto0"/></h2>

<p>In all the <code class="API"><a href="http://twistedmatrix.com/documents/13.2.0/api/twisted.spread.pb.IPerspective.html" title="twisted.spread.pb.IPerspective">IPerspective</a></code> uses
we have shown so far, we ignored the <code>mind</code> argument and created
a new <code>Avatar</code> for every connection. This is usually an easy
design choice, and it works well for simple cases.</p>

<p>In more complicated cases, for example an <code>Avatar</code> that
represents a player object which is persistent in the game universe,
we will want connections from the same player to use the same 
<code>Avatar</code>.</p>

<p>Another thing which is necessary in more complicated scenarios
is notifying a player asynchronously. While it is possible, of
course, to allow a player to call 
<code>perspective_remoteListener(referencable)</code> that would
mean both duplication of code and a higher latency in logging in,
both bad.</p>

<p>In previous sections all realms looked to be identical.
In this one we will show the usefulness of realms in accomplishing
those two objectives.</p>

<h2>Managing Avatars<a name="auto1"/></h2>

<p>The simplest way to manage persistent avatars is to use a straight-forward
caching mechanism:</p>

<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">implements</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">SimpleAvatar</span>(<span class="py-src-parameter">pb</span>.<span class="py-src-parameter">Avatar</span>):
    <span class="py-src-variable">greetings</span> = <span class="py-src-number">0</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">name</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span> = <span class="py-src-variable">name</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">perspective_greet</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span> += <span class="py-src-number">1</span>
        <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&lt;%d&gt;hello %s&quot;</span> % (<span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span>)

<span class="py-src-keyword">class</span> <span class="py-src-identifier">CachingRealm</span>:
    <span class="py-src-variable">implements</span>(<span class="py-src-variable">portal</span>.<span class="py-src-variable">IRealm</span>)

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span> = {}

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">requestAvatar</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">avatarId</span>, <span class="py-src-parameter">mind</span>, *<span class="py-src-parameter">interfaces</span>):
        <span class="py-src-keyword">if</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">interfaces</span>: <span class="py-src-keyword">raise</span> <span class="py-src-variable">NotImplementedError</span>
        <span class="py-src-keyword">if</span> <span class="py-src-variable">avatarId</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>]
        <span class="py-src-keyword">else</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>] = <span class="py-src-variable">SimpleAvatar</span>(<span class="py-src-variable">avatarId</span>)
        <span class="py-src-keyword">return</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span>, <span class="py-src-variable">p</span>, <span class="py-src-keyword">lambda</span>:<span class="py-src-variable">None</span>
</pre>

<p>This gives us a perspective which counts the number of greetings it
sent its client. Implementing a caching strategy, as opposed to generating
a realm with the correct avatars already in it, is usually easier. This
makes adding new checkers to the portal, or adding new users to a checker
database, transparent. Otherwise, careful synchronization is needed between
the checker and avatar is needed (much like the synchronization between
UNIX's <code>/etc/shadow</code> and <code>/etc/passwd</code>).</p>

<p>Sometimes, however, an avatar will need enough per-connection state
that it would be easier to generate a new avatar and cache something
else. Here is an example of that:</p>

<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">implements</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">Greeter</span>:
    <span class="py-src-variable">greetings</span> = <span class="py-src-number">0</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">hello</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span> += <span class="py-src-number">1</span>
        <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&lt;%d&gt;hello&quot;</span> % (<span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span>)

<span class="py-src-keyword">class</span> <span class="py-src-identifier">SimpleAvatar</span>(<span class="py-src-parameter">pb</span>.<span class="py-src-parameter">Avatar</span>):
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">name</span>, <span class="py-src-parameter">greeter</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span> = <span class="py-src-variable">name</span>
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greeter</span> = <span class="py-src-variable">greeter</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">perspective_greet</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-keyword">return</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">greeter</span>.<span class="py-src-variable">hello</span>()+<span class="py-src-string">' '</span>+<span class="py-src-variable">self</span>.<span class="py-src-variable">name</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">CachingRealm</span>:
    <span class="py-src-variable">implements</span>(<span class="py-src-variable">portal</span>.<span class="py-src-variable">IRealm</span>)

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greeters</span> = {}

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">requestAvatar</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">avatarId</span>, <span class="py-src-parameter">mind</span>, *<span class="py-src-parameter">interfaces</span>):
        <span class="py-src-keyword">if</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">interfaces</span>: <span class="py-src-keyword">raise</span> <span class="py-src-variable">NotImplementedError</span>
        <span class="py-src-keyword">if</span> <span class="py-src-variable">avatarId</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">greeters</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">greeters</span>[<span class="py-src-variable">avatarId</span>]
        <span class="py-src-keyword">else</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">greeters</span>[<span class="py-src-variable">avatarId</span>] = <span class="py-src-variable">Greeter</span>()
        <span class="py-src-keyword">return</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span>, <span class="py-src-variable">SimpleAvatar</span>(<span class="py-src-variable">avatarId</span>, <span class="py-src-variable">p</span>), <span class="py-src-keyword">lambda</span>:<span class="py-src-variable">None</span>
</pre>

<p>It might seem tempting to use this pattern to have an avatar which
is notified of new connections. However, the problems here are twofold:
it would lead to a thin class which needs to forward all of its methods,
and it would be impossible to know when disconnections occur. Luckily,
there is a better pattern:</p>

<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">implements</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">SimpleAvatar</span>(<span class="py-src-parameter">pb</span>.<span class="py-src-parameter">Avatar</span>):
    <span class="py-src-variable">greetings</span> = <span class="py-src-number">0</span>
    <span class="py-src-variable">connections</span> = <span class="py-src-number">0</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">name</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span> = <span class="py-src-variable">name</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">connect</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">connections</span> += <span class="py-src-number">1</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">disconnect</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">connections</span> -= <span class="py-src-number">1</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">perspective_greet</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span> += <span class="py-src-number">1</span>
        <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&lt;%d&gt;hello %s&quot;</span> % (<span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span>)

<span class="py-src-keyword">class</span> <span class="py-src-identifier">CachingRealm</span>:
    <span class="py-src-variable">implements</span>(<span class="py-src-variable">portal</span>.<span class="py-src-variable">IRealm</span>)

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span> = {}

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">requestAvatar</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">avatarId</span>, <span class="py-src-parameter">mind</span>, *<span class="py-src-parameter">interfaces</span>):
        <span class="py-src-keyword">if</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">interfaces</span>: <span class="py-src-keyword">raise</span> <span class="py-src-variable">NotImplementedError</span>
        <span class="py-src-keyword">if</span> <span class="py-src-variable">avatarId</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>]
        <span class="py-src-keyword">else</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>] = <span class="py-src-variable">SimpleAvatar</span>(<span class="py-src-variable">avatarId</span>)
        <span class="py-src-variable">p</span>.<span class="py-src-variable">connect</span>()
        <span class="py-src-keyword">return</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span>, <span class="py-src-variable">p</span>, <span class="py-src-variable">p</span>.<span class="py-src-variable">disconnect</span>
</pre>

<p>It is possible to use such a pattern to define an arbitrary limit for
the number of concurrent connections:</p>

<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">implements</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">SimpleAvatar</span>(<span class="py-src-parameter">pb</span>.<span class="py-src-parameter">Avatar</span>):
    <span class="py-src-variable">greetings</span> = <span class="py-src-number">0</span>
    <span class="py-src-variable">connections</span> = <span class="py-src-number">0</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">name</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span> = <span class="py-src-variable">name</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">connect</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">connections</span> += <span class="py-src-number">1</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">disconnect</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">connections</span> -= <span class="py-src-number">1</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">perspective_greet</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span> += <span class="py-src-number">1</span>
        <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;&lt;%d&gt;hello %s&quot;</span> % (<span class="py-src-variable">self</span>.<span class="py-src-variable">greetings</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">name</span>)

<span class="py-src-keyword">class</span> <span class="py-src-identifier">CachingRealm</span>:
    <span class="py-src-variable">implements</span>(<span class="py-src-variable">portal</span>.<span class="py-src-variable">IRealm</span>)

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">max</span>=<span class="py-src-number">1</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span> = {}
        <span class="py-src-variable">self</span>.<span class="py-src-variable">max</span> = <span class="py-src-variable">max</span>

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">requestAvatar</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">avatarId</span>, <span class="py-src-parameter">mind</span>, *<span class="py-src-parameter">interfaces</span>):
        <span class="py-src-keyword">if</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">interfaces</span>: <span class="py-src-keyword">raise</span> <span class="py-src-variable">NotImplementedError</span>
        <span class="py-src-keyword">if</span> <span class="py-src-variable">avatarId</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>]
        <span class="py-src-keyword">else</span>:
            <span class="py-src-variable">p</span> = <span class="py-src-variable">self</span>.<span class="py-src-variable">avatars</span>[<span class="py-src-variable">avatarId</span>] = <span class="py-src-variable">SimpleAvatar</span>(<span class="py-src-variable">avatarId</span>)
        <span class="py-src-keyword">if</span> <span class="py-src-variable">p</span>.<span class="py-src-variable">connections</span> &gt;= <span class="py-src-variable">self</span>.<span class="py-src-variable">max</span>:
            <span class="py-src-keyword">raise</span> <span class="py-src-variable">ValueError</span>(<span class="py-src-string">&quot;too many connections&quot;</span>)
        <span class="py-src-variable">p</span>.<span class="py-src-variable">connect</span>()
        <span class="py-src-keyword">return</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span>, <span class="py-src-variable">p</span>, <span class="py-src-variable">p</span>.<span class="py-src-variable">disconnect</span>
</pre>

<h2>Managing Clients<a name="auto2"/></h2>

<p>So far, all our realms have ignored the <code>mind</code> argument.
In the case of PB, the <code>mind</code> is an object supplied by
the remote login method -- usually, when it passes over the wire,
it becomes a <code>pb.RemoteReference</code>. This object allows
sending messages to the client as soon as the connection is established
and authenticated.</p>

<p>Here is a simple remote-clock application which shows the usefulness
of the <code>mind</code> argument:</p>

<pre class="python"><p class="py-linenumber"> 1
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</p><span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">implements</span>

<span class="py-src-keyword">class</span> <span class="py-src-identifier">SimpleAvatar</span>(<span class="py-src-parameter">pb</span>.<span class="py-src-parameter">Avatar</span>):
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">__init__</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">client</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TimerService</span>(<span class="py-src-number">1</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">telltime</span>)
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span>.<span class="py-src-variable">startService</span>()
        <span class="py-src-variable">self</span>.<span class="py-src-variable">client</span> = <span class="py-src-variable">client</span>
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">telltime</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">client</span>.<span class="py-src-variable">callRemote</span>(<span class="py-src-string">&quot;notifyTime&quot;</span>, <span class="py-src-variable">time</span>.<span class="py-src-variable">time</span>())
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">perspective_setperiod</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">period</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span>.<span class="py-src-variable">stopService</span>()
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span> = <span class="py-src-variable">internet</span>.<span class="py-src-variable">TimerService</span>(<span class="py-src-variable">period</span>, <span class="py-src-variable">self</span>.<span class="py-src-variable">telltime</span>)
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span>.<span class="py-src-variable">startService</span>()
    <span class="py-src-keyword">def</span> <span class="py-src-identifier">logout</span>(<span class="py-src-parameter">self</span>):
        <span class="py-src-variable">self</span>.<span class="py-src-variable">s</span>.<span class="py-src-variable">stopService</span>()

<span class="py-src-keyword">class</span> <span class="py-src-identifier">Realm</span>:
    <span class="py-src-variable">implements</span>(<span class="py-src-variable">portal</span>.<span class="py-src-variable">IRealm</span>)

    <span class="py-src-keyword">def</span> <span class="py-src-identifier">requestAvatar</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">avatarId</span>, <span class="py-src-parameter">mind</span>, *<span class="py-src-parameter">interfaces</span>):
        <span class="py-src-keyword">if</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span> <span class="py-src-keyword">not</span> <span class="py-src-keyword">in</span> <span class="py-src-variable">interfaces</span>: <span class="py-src-keyword">raise</span> <span class="py-src-variable">NotImplementedError</span>
        <span class="py-src-variable">p</span> = <span class="py-src-variable">SimpleAvatar</span>(<span class="py-src-variable">mind</span>)
        <span class="py-src-keyword">return</span> <span class="py-src-variable">pb</span>.<span class="py-src-variable">IPerspective</span>, <span class="py-src-variable">p</span>, <span class="py-src-variable">p</span>.<span class="py-src-variable">logout</span>
</pre>

<p>In more complicated situations, you might want to cache the avatars
and give each one a set of <q>current clients</q> or something similar.</p>

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