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"Ever since I first saw David Gelernter's Linda programming language almost twenty years ago, I felt that the basic ideas of Linda could be used to make an important advance in the ease of distributed and parallel programming. As part of the fruits of Sun's Jini project, we now have the JavaSpaces technology, a wonderfully simple platform for developing distributed applications that takes advantage of the power of the Java programming language. This important book and its many examples will help you learn about ...
"Ever since I first saw David Gelernter's Linda programming language almost twenty years ago, I felt that the basic ideas of Linda could be used to make an important advance in the ease of distributed and parallel programming. As part of the fruits of Sun's Jini project, we now have the JavaSpaces technology, a wonderfully simple platform for developing distributed applications that takes advantage of the power of the Java programming language. This important book and its many examples will help you learn about distributed and parallel programming. I highly recommend it to students, programmers, and the technically curious." Bill Joy, Chief Scientist and co-founder, Sun Microsystems, Inc.
JavaSpaces technology, a powerful Jini service from Sun Microsystems, facilitates building distributed applications for the Internet and Intranets. The JavaSpaces model involves persistent object exchange "areas" in which remote processes can coordinate their actions and exchange data. It provides a necessary ubiquitous, cross-platform framework for distributed computing, emerging as a key technology in this expanding field.
This book introduces the JavaSpaces architecture, provides a definitive and comprehensive description of the model, and demonstrates how to use it to develop distributed computing applications. The book presents an overview of the JavaSpaces design and walks you through the basics, demonstrating key features through examples. Every aspect of JavaSpaces programming is examined in depth: entries, distributed data structures, synchronization, communication, application patterns, leases, distributed events, and transactions.
You will find information on such vital topics as:
JavaSpaces Principles, Patterns, and Practice also includes two full-scale applications--one collaborative and the other parallel--that demonstrate how to put the JavaSpaces model to work.
Benefits of Distributed Computing.
Challenges of Distributed Computing.
What Is JavaSpaces Technology?
JavaSpaces Technology in Context.
JavaSpaces Technology Overview.
Entries and Operations.
Putting It All Together.
Advantages of JavaSpaces Technologies.
2. JavaSpaces Application Basics.
The Entry Interface.
Instantiating an Entry.
Adding Fields and Methods.
Building an Application.
Writing Entries into a Space.
A Closer Look at write.
Reading and Taking Entries.
The Basics of read and take.
The Rules of Matching.
Dealing with null-valued Fields in Entries.
A Closer Look at read and take.
Going Further with the Example.
Subclassing an Entry.
Adding a Few More Methods.
Trying the Game.
Serialization and Its Effects.
Matching and Equality.
The No-arg Constructor.
The Entry Interface Revisited.
Improving Entry Serialization Using snapshot.
3. Building Blocks.
Introduction to Distributed Data Structures.
Building Distributed Data Structures with Entries.
Creating a Web Counter.
Task Bags and Result Bags.
Distributed Arrays Revisited.
Implementing a Semaphore.
Implementing a License Manager.
The License Manager Installer.
The License Manager Client Library.
Using Multiple Semaphores.
The Dining Philosophers.
Fairly Sharing a Resource.
Using a Queue to Take Turns.
Advanced Synchronization: The Readers/Writers Problem.
Implementing a Readers/Writers Solution.
Implementing a Counter.
Implementing a Space-based Readers/Writers Application.
Basic Message Passing.
Characteristics of Space-based Communication.
Tightly Coupled Communication.
Loosely Coupled Communication.
Benefits of Loose Coupling.
Beyond Message Passing.
A Basic Channel.
The Channel Message.
The Channel Tail.
Creating a Channel.
Appending a Message to a Channel.
Implementing a Channel Writer.
Implementing a Channel Reader.
Demonstrating the Channel Writer and Reader.
Building a Chat Application with Channels.
The Graphical User Interface.
Combining Channel Writing and Reading.
A Consumer Channel.
Implementing a Pager Service.
The Pager Message Entry.
Tracking the Start and End of a Channel.
The Index Entry.
Creating a Consumer Channel.
Sending Messages to the Channel.
Reading and Removing Messages from the Channel.
Demonstrating the Pager.
The Status Entry.
Channel Creation Revisited.
Writing to a Bounded Channel.
Taking from a Bounded Channel.
Demonstrating the Bounded Channel.
6. Application Patterns.
The Replicated-Worker Pattern.
Computing the Mandelbrot Set.
Task and Result Entries.
The Command Pattern.
Implementing a Compute Server.
The Generic Worker.
The Generic Master.
Creating Specialized Tasks and Results.
Creating a Specialized Master.
Running the Compute Server.
The Marketplace Pattern.
An Automobile Marketplace.
Interaction in the Marketplace.
The Bid Entry.
The Application Framework.
Running the Marketplace.
Leases on Entries.
The Lease Object.
Renewing a Lease.
Cancelling a Lease.
Creating a Lease Map.
Adding and Removing Leases.
Automated Lease Renewal.
The LeaseManager Interface.
Implementing the Constructors.
Cancelling a Lease.
Processing Renewal Failures.
Putting It All Together.
8. Distributed Events.
Events in the Distributed Environment.
Hello World Using notify.
The Notification API.
The JavaSpace notify Method.
The EventRegistration Class.
The RemoteEventListener Interface.
The RemoteEvent Object.
Putting the Pieces Together.
The Channel Relay Application.
The Channel Reader Thread.
The Relayer Listener.
The Notify Handler Thread.
The Distributed Transaction Model.
Creating a Transaction.
Web Counter Revisited.
The Spaceis Transactional Properties.
Operational Semantics Under Transactions.
Writing Entries Under a Transaction.
Reading Entries Under a Transaction.
read versus readIfExists.
Taking Entries Under a Transaction.
Notifications Under Transactions.
10. A Collaborative Application.
Implementing a Messenger User.
The Account Object.
The Session Object.
The FriendsList Object.
The FriendsListMonitor Object.
Message Entries and Indices.
The Channel Object.
Retrieving Messages from the Channel.
The Messenger Applet.
Logging in via the Login Object.
The loginCallback Method.
Adding to the Friends List.
Chatting with Friends.
Listening for Messages.
11. A Parallel Application.
The Compute Server.
The Command Interface Revisited.
The Task Entry.
The Generic Worker.
A Generic Master.
The Crypt Application.
The Generic Worker and Crypt Task.
The Crypt Master.
Improving Space Usage with Watermarking.
A Little Poison.
12. Further Exploration.
Related Java and Jini Technologies.
Appendix A: The Jini(TM) Entry Specification.
Entries and Templates.
Serializing Entry Objects.
Unusable Entry Exception.
Templates and Matching.
Appendix B: The Jini(TM) Entry Utilities Specification.
Appendix C: The JavaSpaces(TM) Specification.
The JavaSpaces Application Model and Terms.
JavaSpaces Technology and Databases.
JavaSpaces System Design and Linda Systems.
Goals and Requirements.
readIfExists and read.
takeIfExists and take.
Operations Under Transactions.
Transactions and ACID Properties.
The Java Platform.
Over the next decade the computing landscape will change dramatically as devices become ubiquitous, network-connected, and ready to communicate. As the landscape changes, the way in which we design and build software will change as well: The distributed application (one that involves multiple processes and devices) will become the natural way we build systems, while the standalone desktop application will become nearly extinct.
Designing distributed software is remarkably hard, however. The fundamental characteristics of a networked environment (such as heterogeneity, partial failure, and latency) and the difficulty of "gluing together" multiple, independent processes into a robust, scalable application present the programmer with many challenges that don't arise when designing and building desktop applications.
JavaSpaces(TM) technology is a simple, expressive, and powerful tool that eases the burden of creating distributed applications. Processes are loosely coupled--communicating and synchronizing their activities using a persistent object store called a space, rather than through direct communication. This method of coordinating distributed processes leads to systems that are flexible, scalable, and reliable. While simple, the space-based model is powerful enough to implement advanced distributed applications--from e-commerce systems to groupware to heavy-duty parallel computations. Space-based programming also leverages the Jini(TM) technology's leasing, distributed event, and transaction features, making it suitable for building robust, commercial-quality distributed systems.
This book teaches you how to use JavaSpaces technology to design and build distributed applications. It is intended for computer professionals, students, and Java enthusiasts--anyone who wants experience building networked applications. Through experimentation with the code examples, you'll develop a repertoire of useful techniques and patterns for creating space-based systems. We assume that you already have some programming experience and basic working knowledge of Java programming language fundamentals, but this book doesn't require any specific knowledge of network programming.
JavaSpaces technology is new, and writing a book before the technology is in widespread use presents a unique challenge. We've approached the project from complementary perspectives. Two of the authors, Eric Freeman and Susanne Hupfer, spent much of the past decade designing and building space-based systems as part of the Linda research group at Yale University and used the JavaSpaces technology during the two years of its development. The third, Ken Arnold, was in charge of the JavaSpaces project at Sun Microsystems, working with a team of engineers to design and build the technology this book is all about.
In this book, we present the foundations of programming with JavaSpaces technology, and a set of common patterns and frameworks for approaching space-based programs. As the technology becomes more widely used, the JavaSpace programming community will discover new ways of using it. We would like future editions of this book to incorporate these new patterns, and we invite you to send comments, suggestions, and ideas to firstname.lastname@example.org and to make use of the book's web site at http://java.sun.com/docs/books/jini/javaspaces.
The code examples in this book have been compiled and run against the following packages from Sun Microsystems:
which is available for download at http://www.java.sun.com/products/, and
both of which are available for download at http://developer.java.sun.com/developer/products/jini/product.offerings.html.
You can obtain the complete source code of the examples in the book at http://java.sun.com/docs/books/jini/javaspaces. This site is the official web site for the book and contains links to resources and information relating to the JavaSpaces technology, errata, and supplementary material generated after this book went to press.
We are indebted to many people for their contributions to the development of the JavaSpaces technology. Bill Joy pushed the Linda-style distributed computing idea hard enough to make Sun take it seriously. Jim Waldo, Ann Wollrath, Roger Riggs, and Bob Scheiffler worked on the design, with input from Peter Jones. Gary Holness and John McClain joined the JavaSpaces implementation team and made a difference both in the detailed semantics and the implementation design. Bob Resendes joined near the end but was important in getting the product finished, and Jimmy Torres and Frank Barnaby built and ran the release processes that got the it out the door. And, of course, nothing could have been done without Helen Leary, but then, nothing ever is.
We are equally grateful to the many people who helped us turn the idea for this book into a reality. We especially want to thank our editor Mike Hendrickson at Addison-Wesley and Series editor Lisa Friendly at Sun Microsystems, who both recognized the value of the project early on. Mike provided enthusiastic support, ideas, push and encouragement along the way. Lisa held the book to the highest standards.
The team at Addison-Wesley was an enormous help at every stage of the project. In particular, Marina Lang and Julie DeBaggis were supportive, made the publishing process run smoothly, and steered us clear of many potholes. Without the dedicated efforts of Sarah Weaver, Marty Rabinowitz, Diane Freed, Bob Russell, Tracy Russ, Katherine Kwack, Sara Connell, Simone Payment, and others working behind the production and marketing scenes, this book would not have been possible.
A number of reviewers greatly improved the bookis content through their careful reading and helpful suggestions. Jen McGinn supplied a thorough technical and editorial review, and was instrumental in refining our usage of Sun Microsystems trademarks. Bob Resendes, Gary Holness, and John McClain provided in-depth technical review of the manuscript based on their intimate knowledge of the technology. Andreas Doerr, Laird Dornin, Howard Lee Harkness, Bruce Hopkins, Pascal Ledru, and Nigel Warren contributed useful technical and editorial commentary. Our appreciation also goes to Elisabeth Freeman for her careful reading of many drafts, and to Peter Sparago for his comments.
The wonderful illustrations throughout the book are due to the creative energy and talent of Jim Dustin. Tony Welch of Sun Microsystems gave helpful advice on the use of trademarks in the illustrations.
We also wish to thank the Jini team at Sun Microsystems, in particular Mark Hodapp and Theresa Lanowitz, who were generous with their time and assistance.
Finally, we'd especially like to thank David Gelernter, who planted the seed for the JavaSpaces technology nearly two decades ago, and who was supportive of this book throughout its development.