~justin-fathomdb/nova/justinsb-openstack-api-volumes

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<title>Twisted Documentation: The Basics</title>

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<h1 class="title">The Basics</h1>

<div class="toc"><ol><li><a href="#auto0">Application</a></li><li><a href="#auto1">twistd</a></li><li><a href="#auto2">tap2deb</a></li><li><a href="#auto3">tap2rpm</a></li></ol></div>

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

<p>Twisted programs usually work with

<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.application.service.Application.html" title="twisted.application.service.Application">twisted.application.service.Application</a></code>.

This class usually holds all persistent configuration of

a running server -- ports to bind to, places where connections

to must be kept or attempted, periodic actions to do and almost

everything else. It is the root object in a tree of services implementing

<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.application.service.IService.html" title="twisted.application.service.IService">IService</a></code>.</p>

<p>Other HOWTOs describe how to write custom code for Applications,

but this one describes how to use already written code (which can be

part of Twisted or from a third-party Twisted plugin developer). The

Twisted distribution comes with an important tool to deal with

Applications, <code>twistd</code>.</p>

<p><code>Application</code>s are just Python objects, which can

be created and manipulated in the same ways as any other object.

</p>

<h2>twistd<a name="auto1"/></h2><a name="twistd" shape="rect"/>

<p>The Twisted Daemon is a program that knows how to run Applications.

This program

is <code class="shell">twistd(1)</code>. Strictly

speaking, <code class="shell">twistd</code> is not necessary --

fetching the application, getting the <code>IService</code> component,

calling <code>startService</code>, scheduling <code>stopService</code> when

the reactor shuts down, and then calling <code>reactor.run()</code> could be

done manually. <code class="shell">twistd(1)</code>, however, supplies

many options which are highly useful for program set up.</p>

<p><code class="shell">twistd</code> supports choosing a reactor (for more on

reactors, see <a href="choosing-reactor.html" shape="rect">Choosing a Reactor</a>), logging

to a logfile, daemonizing and more. <code class="shell">twistd</code> supports all

Applications mentioned above -- and an additional one. Sometimes

it is convenient to write the code for building a class in straight

Python. One big source of such Python files is the <code>doc/examples</code>

directory. When a straight Python file which defines an <code>Application</code>

object called <code>application</code> is used, use the <code class="shell">-y</code>

option.</p>

<p>When <code class="shell">twistd</code> runs, it records its process id in a

<code>twistd.pid</code> file (this can be configured via a command line

switch). In order to shutdown the <code class="shell">twistd</code> process, kill that

pid (usually you would do <code class="shell">kill `cat twistd.pid`</code>).

</p>

<p>As always, the gory details are in the manual page.</p>

<p>

For Twisted-based server application developers who want to deploy on

Debian, Twisted supplies the <code class="shell">tap2deb</code> program. This program

wraps a Twisted Application file (of any of the supported formats -- Python,

source, xml or pickle)

in a Debian package, including correct installation and removal scripts

and <code>init.d</code> scripts. This frees the installer from manually

stopping or starting the service, and will make sure it goes properly up

on startup and down on shutdown and that it obeys the init levels.

</p>

<p>

For the more savvy Debian users, the

<code class="shell">tap2deb</code> also generates the source package, allowing her

to modify and polish things which automated software cannot detect

(such as dependencies or relationships to virtual packages). In addition,

the Twisted team itself intends to produce Debian packages for some common

services, such as web servers and an inetd replacement. Those packages

will enjoy the best of all worlds -- both the consistency which comes

from being based on the <code class="shell">tap2deb</code> and the delicate manual

tweaking of a Debian maintainer, insuring perfect integration with

Debian.

</p>

<p><code class="shell">tap2rpm</code> is similar to <code class="shell">tap2deb</code>, except that

it generates RPMs for Redhat and other related platforms.</p>

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<p><a href="index.html">Index</a></p>

<span class="version">Version: 10.0.0</span>

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