Chapter 6 - Multithreading

Reading Materials

·         Head First - Java (Read all the listed chapters)

o    15 - Networking And Threads (pages 489 – 528)

·         Effective.Java.2nd.Edition

o    Chapter 4 - Methods Common to All Objects (Item 15)

o    Chapter 10 - Concurrency

·         Oracle Java Tutorial

o    Java.util.concurrent.locks

§  Interfaces: Condition, Lock, ReadWriteLock.

§  Classes: ReentrantLock, ReentrantReadWriteLock.

o    Java Concurrency Tutorial (All of the subjects)

Exercise:

·         Add an option to encrypt an entire directory.
The directory may contain several files, and the system should encrypt them all with the same key (and the same algorithm).
The encrypted files shall sit under a sub-directory named “encrypted”. File names shall not be changed.
Only files with .txt extension should be encrypted. Do not encrypt any sub directories. The key will be saved inside the directory, as key.txt.

·         After a single file encryption has completed – inform the user of the event and its duration. After all files have been encrypted – inform the user about the event and its whole duration.

·         Because we are dealing with a large number of files, and some may be heavy, you have decided that you want to use multithreading to try and improve the speed of directory encryption.

o    Write an interface named DirectoryProcessor and implement the following classes:

§  SyncDirectoryProcessor – responsible of encrypting a directory “normally”, with a single thread.

§  AsyncDirectoryProcessor – responsible of encrypting a directory concurrently.

o    Think: what changes have to be made in EncryptionLogger? (pay attention to locking and the way it has to be done – synchronized? on what?)

·         Implement the reverse functionality – decryption of a whole directory, similarly.

·         Compare the running time of each method. Apply each encryption method on a directory with some big files (each file should be ~5MB). Selection of the method should be done in the main method.

o    Which method is faster? Why?

Emphasis:

·         In the final implementation you should perform encryption and decryption of a directory asynchronously (AsyncDirectoryProcessor).

·         Pay attention to how are the threads being run? Thread? Executor?

·         For the sake of testing you probably should write something that generates large files. You can write a little Java program for this task.