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Implementing a Distributed File System Using Java RMI

This assignment involves creating a small client/server application that implements a distributed file system using Java RMI. The provided interface, RemoteFS, includes methods for reading and writing files. Students are expected to operate the client with commands to read from and write to files. The assignment also discusses important concepts related to garbage collection, such as finalizers, barriers, and weak pointers, ensuring a thorough understanding of memory management in distributed applications.

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Implementing a Distributed File System Using Java RMI

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  1. Overview • Assignment 7: hints • Distributed objects • Assignment 6: solution • Living with a garbage collector

  2. A7 - Distributed Objects public interface RemoteFS { public byte[] readFile(String filename); public void writeFile(String filename, byte[] content); } Imagine a distributed FileSystem as a distributed object of type: Write a small client/server Application using Java/RMI http://java.sun.com/docs/books/tutorial/rmi/

  3. A7 - RMI • Client operates on Interface, Implementation on a remote Server • It should be possible to use the client program in the following way: • java RemoteFSClient <filename> to read a File • echo <anything> | java RemoteFSClient <filename> to write a file • cat <fromFile> | java RemoteFSClient <toFile> copy

  4. Overview • Assignment 7: hints • Distributed objects • Assignment 6: solution • Living with a garbage collector

  5. A6 Ex1 – Finalizers • Finalizers are not executed by the GC: • takes time • could block • Resuscitation: • Finalizers are executed only once • The finalizer of a resuscitated object is not run again (since there is no entry in the finalizer queue) • Finalizers can be re-enabled using ReRegisterForFinalize

  6. A6 Ex1 – Finalizers • Pointers in finalizers: • Objects referenced in finalizers could be invalid since objects are disposed in no particular order. • Dependencies should be handled by the user (e.g. in a close method).

  7. A6 Ex2 – Write barriers • To check if we have a pointer from an older generation to a younger one for each assignment is expensive. • we divide the heap in small regions (cards) • we mark the enclosing region every time we update a pointer • at GC time we check for all the marked cards if such an old-young reference was created.

  8. A6 Ex3 – Weak pointers • .NET • big structures that can be easily reconstructed • ex: file hierarchy, file buffers, I/O buffers • Java • object monitoring (AB) • we can link them without blocking collection • an object (A) receives a notification when the pointed-to object (B) is removed

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