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Development of Collaborative Tools Using Distributed Systems Technology

Development of Collaborative Tools Using Distributed Systems Technology. Talk Outline. Welcome Overview of semester Applications built Technologies used Comparisons Conclusion. Background Information/Research of possible technologies. Sockets RMI Jini JavaSpaces. Project Overview.

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Development of Collaborative Tools Using Distributed Systems Technology

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  1. Development of Collaborative Tools Using Distributed Systems Technology

  2. Talk Outline • Welcome • Overview of semester • Applications built • Technologies used • Comparisons • Conclusion

  3. Background Information/Research of possible technologies • Sockets • RMI • Jini • JavaSpaces

  4. Project Overview • Text Editor • Basic application working • Implemented shared/distributed version • Added additional features • Whiteboard • Shared application from beginning • Added additional features

  5. Initial Prototype • Text Editor • First Step of Jini Design model Stand-Alone Jini JavaSpaces

  6. Our Implementation • Abstract Windowing Tool Kit • Part of the core classes of the Java 2 platform • The Java TextArea • Def: A multi-line region that displays text • Supports creating, opening and saving • But... • High level structure • No access to direct strings

  7. Implementation Problems • What happens when more than one user wishes to write in the same location? • Should we put a locking mechanism on individual lines, on paragraphs, on pages, etc... • Cursor control • Where does the cursor come from? • Should we use the systems cursor? • Should we provide an application cursor?

  8. What is a Whiteboard? • An infinite space on which users can post other objects • An application of Distributed Collaborative Productivity • Uses “Objects” • greater flexibility / scalability • New application of a previous concept

  9. Remote Method Invocation (RMI) • Server binds to RMI name registry • Clients look up the server on the registry • Method calls on server like other objects • Constraints - exception handling, parameter passing • Java implementation of RPC concept

  10. Why RMI? • Mature - relatively bug-free • Well-documented • Flexible - inherently supports multiple clients • Easy to use - more abstract than sockets • Parameter passing constraints can be overcome using “wrapper” objects

  11. The RMI Whiteboard • “Whiteboard” - Java class maintains collection of displayable “WbObjects” • Clients hold local subsets of the collection • Clients Add(), Remove() objects • Client handles interface and display of objects • Objects have unique IDs to avoid duplicates

  12. WbClient Local Collection Add/Remove Global Object collection Display WbClient Local Collection Whiteboard Add/Remove Display

  13. Synchronization • “Database triggers” approach • Whiteboard has information about whether each client needs updating • Info changes when objects added/removed • Client loops constantly, checking for update • If so, gets the new objects from Whiteboard for display purposes

  14. Why this Design Approach? • Local collections • Bandwidth is not wasted sending duplicate objects • Allows independent views of global objects • Efficient Synchronization - Doughnut Shop Theory • High-level abstraction - easy to understand • Straightforward to implement

  15. The Second Prototype • Whiteboard: Needed a new design • The first step to the Jini approach (again) • Another Stand-Alone model • designed with some knowledge of Jini Stand-Alone Jini JavaSpaces

  16. Design Decisions • Working from past experiences • AWT • MouseListeners and KeyListeners • Functionality: • Lines, Rectangles, Ovals, Text and Printing • Keep everything on the Whiteboard

  17. The Object Class • One class to hold all objects • Contains information regarding the type, the string, x-coordinates and y-coordinates • One array contains all of the whiteboard data

  18. The “Jini Vision” • Network-centric Vs Disk-centric model • Embedded systems, plug n play networking • Dynamic Network required for future vision (connection-based technology) • Federation of Services concept • Raise level of abstraction for distributed systems programming

  19. How Jini Works • Devices talk to each other via Java Interfaces (not traditional net protocols) • Jini clients request services via Java Interfaces and Jini Services return code • Services: make themselves available when they join the network • Clients: locate and contact Jini services

  20. Jini Concepts • Normal Programming • Device Drivers and Files • Function and Method Calls • Jini Programming • User Interface (Frame) • Registering A Service (Server) • Finding and Using A Service (Client) • Programming Difficulties

  21. The Jini Server • Security Manager • Attributes Array • JoinManager • Reggie • How many services are available?

  22. The Jini Client • Security Manager • Lookup Locator • Searching for the Service • Call the program method • Note: Each client gets a separate instance of the service

  23. Difficulties • How does Jini work? • Coding the server and client • Setting Up the Environment • Distributed System? • Javaspaces or RMI • Running the Server and Clients • Steep programming curve = “Users and little things”

  24. The Jini Vision of the Future • Bill Joy on Cell Phones and Microphones • “Once you have lots of different kinds of devices combining in different ways, you can’t do monolithic software anymore. Each of these devices has a certain set of functions, and if we have to assume when we build them what they’re going to be used for, it’s not very [flexible].”

  25. JavaSpaces Introduction • New Jini service based on Linda • Very simple implementation: API consists of only a handful of methods • Handles details of concurrent access • Goal: Reduce time/effort to design and implement sophisticated network apps

  26. JavaSpaces Model • No message passing between processes; JavaSpaces use shared memory (space)!

  27. Operations on JavaSpaces • Write, take, read (copy) objects to space • Template object used for associative matching during take, read operations • TakeIfExists and ReadIfExists • Notify - notifies when new entries are added (using Jini’s distributed event model) • Persistence and lease times

  28. Using JavaSpaces • A space holds entries (objects must implement Java’s Entry interface) • Write entry and JavaSpaces app classes • Start a JavaSpaces server (Jini environment) • Compile and Run the code as a client

  29. Implementations • Difficulties: technology still maturing, few examples and little documentation • Problems “listening” for new entries and synchronizing multiple clients • Examples: Chat system and Whiteboard systems developed

  30. Chat and Whiteboard Examples • Exchanges user messages or whiteboard objects as entries in the space • distributed counter for synchronization Clients Reading 1. Read current msg number from status entry 2. Constantly monitor space waiting for next msg to appear 3. When it does, read a copy and update chat display JavaSpace a status/counter b messages Writing 1. Take status entry and increment msg counter 2. Create a new msg with msg number and write it to the space 3. Replace the updated status entry c

  31. Jini/JavaSpaces approach • Future vision should provide easier use • Possible plug n play networking in the future • Young, evolving technology • Not much documentation • Few examples

  32. RMI approach • Mature technology • Well documented • Easy to use • Re-inventing the wheel

  33. Conclusions • Research and use of new technologies • Successful implementations • Basis for future work

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