Multi-Threading in Java

1. Multi-Threading in Java

2. Thread • Thread: a flow of control in a program • Process: a running instance of a program including all variables and other states • In Java, • Application: the Java interpreter starts a thread for the main method. • Applet: the Web browser starts a thread to run the applet. • Java has built-in support for multi-threading.

3. A typical program Multi-Thread Start Start Task1 Task2 Task1 Task2 Task3 Task3 Stop Stop

4. Multi-Threading • Multi-threading is the capability of running multiple tasks concurrently within a program. • Multi-threading can make your program more responsive and interactive, and run faster than a non-threaded version. • Issues • Prioritization • Synchronization

5. Creating Thread • Thread class • Extend Thread class and override the run method • Example class SimpleThread extends Thread {             public void run() {             // work for thread           }        } SimpleThread t = new SimpleThread () ;// create thread t.start(); // begin running thread

6. Runnable interface • Create object implementing Runnable interface • Pass it to Thread object via Thread constructor • Example class SimpleThread extends Frame implements Runnable{             public void run() {             // work for thread           }        } Thread t = new Thread(new SimpleThread()); // create thread t.start(); // begin running thread

7. Life cycle of Thread start new I/O complete, time-out, notify, resume new ready yield (dispatch) running blocked I/O, sleep, wait, suspend terminate dead

8. Overview of the Thread Methods • run():void • start():void – to make a Thread eligible for use • sleep():void – to make a Thread inactive • interrupt():void – to interrupt a running Thread • isAlive():boolean – to check status of a Thread • Other methods • Stop(), setPriority(p: int), wait(), notify()…

9. Examples • MyThread • Show simple multi-threading • PriThread • Use the method setPriority(p: int)

10. Thread Synchronization • To avoid resource conflicts, may synchronize method invocation so that only one thread can access a method at a time. • Keyword synchronized • Only one thread at a time to execute statements within synchronized blocks. • All other threads block until the method finishes. • If several synchronized statements are trying to execute on an object at the same time, only one of them is active on the object. • Example: ConcurrenyDemo