Download Lecture 1 Object Oriented Programming Using Java

Lecture 9
Object Oriented Programming
Using Java
By Rashid Ahmad
Department of Computer Science
University of Peshawar
Multithreading
• A multithreaded program contains two or more parts that
can run concurrently. Each part of such program is called
thread.
• A thread defines the path of execution. Each thread
defines a separate path of execution.
• Multitasking is a specialized form of multithreading
Kinds of threads
Introduction
• A process is actually a program in execution. In process
based threads the unit is a program.
• In thread based threading the unit is a thread.
Difference is Big picture vs. Details
Process based threads
T1
Thread based threads
T2
P1
P2
P3
T3
P1
P2
Comparison of Thread Types
•
•
•
•
•
Processes are heavy weight tasks than threads.
IPC is expensive in processes.
Context switching is expensive.
Threads shares the same address space.
Why multithreading?
Java Thread Model
Event loop with polling approach (single threaded app)
In multithreaded applications this approach is eliminated
Born
Life Cycle of a
Thread
Start
Ready
Thread dispatch
Quantum expiration
Timeout
Expires
Running
Wait
Waiting
I/O Completes
Issue I/O or
Synchronized
Statement
Sleep
Blocked
Sleeping
Complete
Juggling of a ball
And Multithreading
How Threads can be
Implemented in Java
Using Runnable Interface
Using Thread Class
public class Main {
public Main() {
}
public static void main(String[] args) {
Thread t = Thread.currentThread();
System.out.println("Current Thread: " + t);
t.setName("My Thread");
System.out.println("After name change: " + t);
try{
for(int n=5; n > 0; n--)
{
System.out.println(n);
Thread.sleep(1000);
}}
catch(InterruptedException ex){
} }}
A simple program
on Threads
Thread implementation using Runnable
Interface
public class Main implements Runnable {
Thread t;
public Main() {
t = new Thread(this,"Testing Thread");
System.out.println("Child Thread: " + t);
t.start();
}
public void run(){
try{
for(int x=5; x > 0; x--){
System.out.println("Child Thread: " + x);
Thread.sleep(500);
} }
catch(InterruptedException ex){
} }
public static void main(String[] args) {
new Main();
try{
for(int i=5; i > 0; i--){
System.out.println("Main Thread: " + i);
Thread.sleep(1000);
}
}
catch(InterruptedException ex){
System.out.println("Main Thread Interrupted");
}
System.out.println("Main Thread Exiting");
} }
public class Main extends Thread {
Threads extending
Threads
Thread t;
public Main() {
t = new Thread(this,"Testing Thread");
System.out.println("Child Thread: " + t);
t.start();
}
public void run(){
try{
for(int x=5; x > 0; x--){
System.out.println("Child Thread: " + x);
Thread.sleep(500);
} }
catch(InterruptedException ex){
System.out.println("Child Interrupted"); }
System.out.println("Child Thread Exiting"); }
public class Main extends Thread {
Thread t;
public Main() {
t = new Thread(this,"Testing Thread");
System.out.println("Child Thread: " + t);
t.start();
}
public void run(){
try{
for(int x=5; x > 0; x--){
System.out.println("Child Thread: " + x);
Thread.sleep(500);
} }
catch(InterruptedException ex){
System.out.println("Child Interrupted"); }
System.out.println("Child Thread Exiting"); }
Threads extending
Threads
Creating Multiple Threads
public class Main extends Thread {
String name;
Thread t;
public Main(String threadname) {
name = threadname;
t = new Thread(this,name);
System.out.println("New Thread: " + t);
t.start();
}
Creating Multiple Threads
public void run(){
try{
for(int x=5; x > 0; x--){
System.out.println("name: " + x);
Thread.sleep(500);
}
}
catch(InterruptedException ex){
System.out.println(name + " Interrupted");
}
System.out.println(name + " Thread Exiting");
}
Creating Multiple Threads
public static void main(String[] args) {
new Main("One");
new Main("Two");
new Main("Three");
try{
Thread.sleep(1000);
}
catch(InterruptedException ex){
System.out.println("Main Thread Interrupted");
}
System.out.println("Main Thread Exiting");
}
}