1. Algorithm Programming 1 89-210 Exercise 3 Bar-Ilan University 2007-2008 תשס"ח by Moshe Fresko

2. Exercise 3 – Thread Pool Implementation And Usage  Motivation: Re-use of existing threads  Because thread creation is an expensive task Control the number of threads running concurrently  Not going into starvation 1. Write an interface Job in file Job.java that will define a new job that can be executed in the Thread Pool. Remember the “ Command ” design pattern. interface Job { void execute() ;// Executes the required process void stop() ;// Stops the process in the middle String getDescription(); // A description about the type of the job }

3. Exercise 3 – Thread Pool Implementation And Usage 2. Write a general purpose class ThreadPool in file ThreadPool.java that will have the following functionality. class ThreadPool { // Constructor will get the maximum number of threads // that can run concurrently public ThreadPool(int numOfMaxThreads) { … } // Method for adding a new Job for execution. It returns immediately. public void add(Job j) { … } // Method for getting information on the Thread Pool ’ s State public ThreadPoolState getState() { … } // Method for getting statistics for that Thread Pool public ThreadPoolStatistics getStatistics() { … } // Method for stopping the whole process. void stop() { … } }

4. Exercise 3 – Thread Pool ThreadPoolState and ThreadPoolStatistics  Information on ThreadPool will be get in structures that will be defined by these definitions. interface ThreadPoolState { int getNumberOfThreads() ; String[] getDescriptionsOfRunningJobs() ; String[] getDescriptionsOfWaitingJobs() ; } interface ThreadPoolStatistics { int getNumberOfExecutedJobs() ;// The jobs that their execution is finished int getNumberOfJobsLeftTheQueue() ; // This must be >= the number of executed jobs int getAverageExecutionTime() ; // In milliseconds. For the executed jobs. int getAverageWaitingTime() ; // In milliseconds. For the jobs that left the queue. }  These structures will be filled and returned by the functions getState() and getStatistics() functions. The returned value will be static (will not change). A new value will be returned for each call to those functions.

5. Exercise 3 – Thread Pool Implementation And Usage 3. Write an application Ex3 with a main function, that will do the following. It will prompt for a user input, will run the given command and will return again to prompt. The following are the available commands.  HELP : Will display a general help how to use the program.  COMPRESS FileName CompressedFileName DECOMPRESS CompressedFileName FileName  STATE : Will print the list of running/waiting jobs.  STATISTICS : Will print the information from getStatistics()  EXIT : Stops the ThreadPool and exits from the program.

6. Exercise 3 – Thread Pool Implementation And Usage 4. There will be a single Thread Pool object in the program. 5. Command description:  COMPRESS Algorithm FileName CompressedFileName will create 1 job and put that into the Thread Pool. The job will compress the given file to create the given CompressedFile. For example: COMPRESS A.txt CompressedA.bin will run one job in the thread pool so that the File A.txt will be compressed according to LZW algorithm.  DECOMPRESS CompressedFile OutputFileName This fill open the file and will create the original file  For Example: DECOMPRESS CompressedA.bin B.txt will run one job in the thread pool. After the job was run and finished, B.txt must be created with the same content as previous A.txt.

7. Exercise 3 – Thread Pool Implementation And Usage  Some points: 1. Do not forget to synchronize where necessary. Do not over-synchronize in unnecessary places. 2. ThreadPool class is a general utility class, and it will not have any code connected to Compression, LZW or other special things. You can define specific things in Ex3.java or in other files. 3. The getDescription() for our specific jobs might be the following: 1. “ Job for Compressing ‘ File1 ’ into ‘ File2 ’ with LZW algorithm. ” 2. “ Job for DeCompressing ‘ File1 ’ into ‘ File2 ’ with LZW algorithm. ”

8. Exercise 3 Thread-Pool  Important: You submit via submitex.  Course number: 89-210  Exercise: ex3  Deliver all the necessary files. It must compile/work under Java 1.4/1.5/1.6. You can try it on the Unix environment (on Sunshine). Do not write debugging information to the console or any other place. Write enough comments. Write wherever you think there is a need for the understanding of the code. Write your code according to the OOP principles. Everybody must do it alone.  Deadline: 15 Jan 2008