# Proposal for Daemon Package

### (0) Rationale

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 `public static void main(String[])` method.

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 `System.exit(int)` 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.

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.

One common solution to this problem is to create (for example) a `ServerSocket` 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 `System.exit` 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.

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 daemons and are controlled by the operating system with a set of specified signals. Under Windows such programs are called services 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.

### (1) Scope of the Package

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 `public static void main(String[])` method. This specification cover the behavior and life cycle of what we define as "Java ™ daemons", or, in other words, non-interactive Java™ applications.

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 `Daemon` interface, but defines the relation between the operating system process and the `Daemon` implementation life cycle. It should be trivial for implementors to build a native liaison and container for Java™ daemons.

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.

### (1.5) Interaction With Other Packages

Daemon 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.

No external configuration files are utilized.

### (2) Initial Source of the Package

The original Java classes come from the Jakarta Tomcat 4.0 project.

The proposed package name for the new component is `org.apache.commons.daemon`.

### (3) Required Jakarta-Commons Resources

- CVS Repository - New directory `daemon` in the `jakarta-commons` CVS repository.
- Mailing List - Discussions will take place on the general dev@commons.apache.org 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].
- Bugzilla - New component "Daemon" under the "Commons" product category, with appropriate version identifiers as needed.
- Jyve FAQ - New category "commons-daemon" (when available).

### (4) Initial Committers

The initial committers on the Daemon component shall be:

- Jean-Frederic Clere
- Pier Fumagalli
- Remy Maucherat