CSC 480 Software Engineering Lab 2 – Multi-Threading Oct 18, 2002

Thread – an analog Program without multithreading is like driving on a one-lane country road  You may stuck behind a large, wide hay-truck With multithreading, different sequences of activities can carry out concurrently  Like on a multi-lane highway, you can pass truck and enjoy the scenery

Thread – the definition A thread--sometimes called an execution context or a lightweight process--is a single sequential flow of control within a program You use threads to isolate tasks

Java Thread Class You extend Java’s Thread class to implement threads The run method gives a thread something to do  This method is the entry point for threads, just like the main method for applications A thread can be started by calling the start method on the Thread object  This method start the thread by calling the run method

Example – the knock-knock app In the knock-knock application, a server that can serve multiple clients needs the following class public class KKMultiServerThread extends Thread { private Socket socket = null; public KKMultiServerThread(Socket socket) { super("KKMultiServerThread"); this.socket = socket; } public void run() { //… }

Example – the KKMultiServer In the KKMultiServer, a new KKMultiServerThread is spawn when a new client is identified public class KKMultiServer { public static void main(String[] args) throws IOException { boolean listening = true; //… while (listening) new KKMultiServerThread( serverSocket.accept()).start(); }

Synchronizing Threads Each KKMultiServerThread threads can be executed independently, since they don’t share any common resources In the bank application, the execution of bank service threads need to be synchronized We’ll learn how to use object locks to synchronize threads

The synchronized Keyword The code segments within a program that access the same object from separate, concurrent threads are called critical sections. In the Java language, a critical section can be a block or a method and are identified with the synchronized keyword. The Java platform then associates a lock with every object that has synchronized code.

Association – The Bank Server App BankMultiServerBankMulti BankAccountBankMultiService doService() processCommand()

Association – The Bank Client App BankClientMultiMainBankClientMultiFrame BankClientConnector request(String cmd):String