src/site/xdoc/index.xml - commons-daemon - Git at Google

 <?xml version="1.0"?>
 <!--
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 -->

 <document>

  <properties>
   <title>Daemon : Java based daemons or services</title>
   <author email="jfrederic.clere@fujitsu-siemens.con">Jean-Frederic Clere</author>
  </properties>

 <body>
 <section name="Introduction">
 <p>
       Since 1994, the Java programming language evolved and became a
       valid tool to develop reliable and performant server applications as
       opposed to just applets and client 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 shutdown 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, has
       several disadvantages and risks:
       <ul>
       <li>
       In case of a system-wide shutdown, the Virtual Machine process may be
       shut down directly by the operating system without notifying the running
       server application.
       </li>
       <li>
       If an attacker finds out the shutdown message to send to the server
       and discovers a way to send this message, he can easily interrupt
       the server's operation, bypassing all the security restrictions
       implemented in the operating system.
       </li>
       </ul>
 </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>
 </section>

 <section name="Structure">
 <p>
       Daemon is made of 2 parts. One written in C that makes the interface to
       the operating system and the other in Java that provides the
       Daemon API.
 </p>
 </section>

 <section name="Platforms">
 <p>
       Both Win32 and UNIX like platforms are supported.
       For Win32 platforms use <a href="procrun.html">procrun</a>.
       For UNIX like platforms use <a href="jsvc.html">jsvc</a>.
 </p>
 </section>
 <section name="Initial Source of the Package">

 <p>The original Java classes came from the Jakarta Tomcat 4.0 project.</p>

 <p>The package name for the Daemon component is
 <code>org.apache.commons.daemon</code>.
 </p>
 </section>

 </body>
 </document>
	<?xml version="1.0"?>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->

	<document>

	<properties>
	<title>Daemon : Java based daemons or services</title>
	<author email="jfrederic.clere@fujitsu-siemens.con">Jean-Frederic Clere</author>
	</properties>

	<body>
	<section name="Introduction">
	<p>
	Since 1994, the Java programming language evolved and became a
	valid tool to develop reliable and performant server applications as
	opposed to just applets and client 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 shutdown 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, has
	several disadvantages and risks:
	<ul>
	<li>
	In case of a system-wide shutdown, the Virtual Machine process may be
	shut down directly by the operating system without notifying the running
	server application.
	</li>
	<li>
	If an attacker finds out the shutdown message to send to the server
	and discovers a way to send this message, he can easily interrupt
	the server's operation, bypassing all the security restrictions
	implemented in the operating system.
	</li>
	</ul>
	</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>
	</section>

	<section name="Structure">
	<p>
	Daemon is made of 2 parts. One written in C that makes the interface to
	the operating system and the other in Java that provides the
	Daemon API.
	</p>
	</section>

	<section name="Platforms">
	<p>
	Both Win32 and UNIX like platforms are supported.
	For Win32 platforms use <a href="procrun.html">procrun</a>.
	For UNIX like platforms use <a href="jsvc.html">jsvc</a>.
	</p>
	</section>
	<section name="Initial Source of the Package">

	<p>The original Java classes came from the Jakarta Tomcat 4.0 project.</p>

	<p>The package name for the Daemon component is
	<code>org.apache.commons.daemon</code>.
	</p>
	</section>

	</body>
	</document>