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PROPOSAL.html
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<html>
<head>
<title>Proposal for Daemon Package</title>
</head>
<body bgcolor="white">
<div align="center">
<h1>Proposal for <em>Daemon</em> Package</h1>
</div>
<h3>(0) Rationale</h3>
<P>
Since 1994, the Java™ programming language evolved and became a
valid tool to develop, other than applets and client applications,
reliable and performant server applications. The major disadvantage of
the Java™ platform is that still today the only portable way to
start a Java™ application relies on a single point of entry: the
<CODE><EM CLASS="key">public static void</EM> main(<EM CLASS="ref">String</EM>[])</CODE>
method.
</P>
<P>
Having a single-point of entry is a valid solution for client
applications, where interactively a user can command to the application
to quit (which can terminate the Virtual Machine process at calling the
<CODE><EM CLASS="ref">System</EM>.exit(<EM CLASS="key">int</EM>)</CODE>
method), but in those cases where the application is not interactive
(server applications) there is currently no portable way to notify
the Virtual Machine of its imminent shutdown.
</P>
<P>
A server application written in Java might have to perform several tasks
before being able to shut down the Virtual Machine process. For example
in the case of a Servlet container, before the VM process is shut down,
sessions might need to be serialized to disk, and web applications need
to be destroyed.
</P>
<P>
One common solution to this problem is to create (for example) a
<CODE><EM CLASS="ref">ServerSocket</EM></CODE> and wait for a particular
message to be issued. When the message is received, all operations
required to shut down the server applications are performed and at the
end the <CODE><EM CLASS="ref">System</EM>.exit</CODE> method is called
to terminate the Virtual Machine process. This method, however, implies
several disadvantages and risks: for example in case of a system-wide
shutdown, it might happen that the Virtual Machine process will be shut
down directly by the operating system, without notifying the running
server application. Or, for example, if an attacker finds out what is
the required message to send to the server, and discovers a way to send
this message to the running server application, he can easily interrupt
the operation of a server, bypassing all the security restrictions
implemented in the operating system.
</P>
<P>
Most multi-user operating systems already have a way in which server
applications are started and stopped, under Unix based operating systems
non-interactive server applications are called <em>daemons</em> and are
controlled by the operating system with a set of specified
<em>signals</em>. Under Windows such programs are called <em>services</em>
and are controlled by appropriate calls to specific functions defined in
the application binary, but although the ways of dealing with the problem
are different, in both cases the operating system can notify a server
application of its imminent shutdown, and the application has the
ability to perform certain tasks before its process of execution is
destroyed.
</P>
<h3>(1) Scope of the Package</h3>
<P>
The scope of this specification is to define an API in line with the
current Java™ Platform APIs to support an alternative invocation
mechanism which could be used instead of the above mentioned
<CODE><EM CLASS="key">public static void</EM> main(<EM CLASS="ref">String</EM>[])</CODE>
method. This specification cover the behavior and life cycle of what
we define as "Java ™ daemons", or, in other words,
non-interactive Java™ applications.
</P>
<P>
This specification does not cover how the container of a Java™
daemon must be implemented, or how to build a native liaison between
the operating system and the <CODE><EM CLASS="ref">Daemon</EM></CODE>
interface, but defines the relation between the operating system
process and the <CODE><EM CLASS="ref">Daemon</EM></CODE> implementation
life cycle. It should be trivial for implementors to build a native
liaison and container for Java™ daemons.
</P>
<P>
This specification, together with the related API documentation, can be
used by software developers to build portable non-interactive applications
based on the Java™ platform.
</P>
<h3>(1.5) Interaction With Other Packages</h3>
<p><em>Daemon</em> relies only on standard JDK 1.2 (or later) APIs for
production deployment. It utilizes the JUnit unit testing framework for
developing and executing unit tests, but this is of interest only to
developers of the component. Daemon will be a dependency for
several existing components in the open source world.</p>
<p>No external configuration files are utilized.</p>
<h3>(2) Initial Source of the Package</h3>
<p>The original Java classes come from the Jakarta Tomcat 4.0 project.</p>
<p>The proposed package name for the new component is
<code>org.apache.commons.daemon</code>.</p>
<h3>(3) Required Jakarta-Commons Resources</h3>
<ul>
<li>CVS Repository - New directory <code>daemon</code> in the
<code>jakarta-commons</code> CVS repository.</li>
<li>Mailing List - Discussions will take place on the general
<em>dev@commons.apache.org</em> mailing list. To help
list subscribers identify messages of interest, it is suggested that
the message subject of messages about this component be prefixed with
[Daemon].</li>
<li>Bugzilla - New component "Daemon" under the "Commons" product
category, with appropriate version identifiers as needed.</li>
<li>Jyve FAQ - New category "commons-daemon" (when available).</li>
</ul>
<h3>(4) Initial Committers</h3>
<p>The initial committers on the Daemon component shall be:</p>
<ul>
<li>Jean-Frederic Clere</li>
<li>Pier Fumagalli</li>
<li>Remy Maucherat</li>
</body>
</html>