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Review the design

The LocalLoggingProxy may work well if you are simply testing one client on a single machine; for example, if you use the space as a simplified persistence mechanism for a Java application. However, a local logging proxy for a distributed system doesn't really make too much sense, so we need to consider a couple of potential problems with this implementation thus far.

First, if we run clients on various machines, we must have some way to collect the information to get an overall view of the system's behavior. This means that we need access to all the local files in order to merge them to get a coherent picture, which is an arduous task.

Second, the way in which Jini distributes proxies means that we can't predict where the spaces proxies will run. Also, if we intend to send our logging information to a disk, for example, there is no guarantee that a disk will be present on the device running the client and proxy, or that the device will be able to store more than trivial amounts of debugging information.

However, we do know that the system must have some kind of network connection or the proxy could not have arrived in the first place, unless of course the local machine runs a lookup service and the space runs locally. Therefore, we could build the proxy to move the information back over the network onto a machine that we know has adequate resources.

In Part 2 of this article, coming next week, we will present a second model that retains the LoggingProxy interface but reimplements the proxy to provide its information to a Jini logging service.

Talk Back!

Discuss this article in the News & Ideas Forum topic, Observing JavaSpace-Based Systems.

About the Authors

Philip Bishop is an independent distributed systems consultant, specializing in the design and implementation of large-scale systems for organizations ranging from utility companies to investment banks.

Nigel Warren is cofounder and director of technology at IntaMission Ltd., where he researches and designs agile and evolvable software infrastructures for next-generation distributed systems.

Philip and Nigel are also the joint authors of JavaSpaces in Practice and Java in Practice, both published by Addison-Wesley.

Resources

JavaSpaces in Practice, a new book by by Philip Bishop and Nigel Warren, is at Amazon.com at:
http://www.amazon.com/exec/obidos/ASIN/0321112318/

The website for JavaSpaces in Practice is here:
http://www.jsip.info/

JavaSpaces: Principles, Patterns, and Practice by Eric Freeman, Susanne Hupfer, and Ken Arnold, an introduction to JavaSpaces, is at Amazon.com at:
http://www.amazon.com/exec/obidos/ASIN/0201309556/

The source code for the examples appearing in this article can be downloaded here:
http://www.djip.co.uk/downloads.html#artima

The Jini Community, the central site for signers of the Jini Sun Community Source License to interact:
http://www.jini.org

Download JavaSpaces from:
http://java.sun.com/products/javaspaces/

Make Room for JavaSpaces, Part I - An introduction to JavaSpaces, a simple and powerful distributed programming tool:
http://www.artima.com/jini/jiniology/js1.html

Make Room for JavaSpaces, Part II - Build a compute server with JavaSpaces, Jini's coordination service:
http://www.artima.com/jini/jiniology/js2.html

Make Room for JavaSpaces, Part III - Coordinate your Jini applications with JavaSpaces:
http://www.artima.com/jini/jiniology/js3.html

Make Room for JavaSpaces, Part IV - Explore Jini transactions with JavaSpaces:
http://www.artima.com/jini/jiniology/js4.html

Make Room for JavaSpaces, Part V - Make your compute server robust and scalable with Jini and JavaSpaces:
http://www.artima.com/jini/jiniology/js5.html

Make Room for JavaSpaces, Part VI - Build and use distributed data structures in your JavaSpaces programs:
http://www.artima.com/jini/jiniology/js6.html

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