_{Lecture 10}

Lecture Topic:
Threads, Synchronization and Atomic Operations

Threads

Enable parallelism within the program

Threads simply extend that concept from switching between several different programs, to switching between several different functions executing simultaneously within a single program.

Core Java

public class <class_name> extends Applet implements runnable {

Thread t_name;

public void start ( ){---------------}
public void stop ( ){---------------}
public void run ( ){-----------------}

}

Example

public class Digital Threads extends Applet implements runnable

{

Thread runner;
Graphic g;
Frame f;
public void start( ) {

if ( runner == null ) {

runner = new Thread(this);
runner.start( );
}

}

public void stop ( ){

if ( runner != null ) {

runner == null;
runner.stop( );
}

}

 

Synchronization

 
Synchronized methods CANNOT
 
be Interrupt by other Threads

 

Synchronized methods prevent other Threads

 

Example

synchronized private void draw ( ) { 

Dimension dim = f.size ( );
int height = dim.height - 60;
int width = dim.width;


Date theDate = new Date( );


g.clearRect( 10, height, 150, 15 );


g.drawString( theDate, toString( ), 
10, height + 10 );

}
public void run ( ){

while ( true ) {

draw ( );
try { Thread, sleep(1000); }
catch ( Interrupted exception e) { }

}

 

Atomic Operations

• Synchronized methods are atomic!
• appear to happen all at once
• Synchronized methods cannot be interrupted by other threads.
• Synchronized methods prevent other threads from running.
• A pulldown menu can run on a synchronized method which stops your method from running.
• If your task takes longer than your sleep time, it may not be updated frequenctly enough
• Synchronized methods allow only one thread to access data at a time. This can prevent data corruption. It prevents rave conditions. Just like logic hazards.
• No two synchronized methods may run at the same time!

 
 
Implement a java application that has 3 random
 
threads, each of which sleep between 50~1000ms. Use System.out.println(
 
runner1,++++); print out the numbers of + sign, i.e., 
 
 
runner1 ++
 
 
runner2 +++
 
 
runner4 +++++
 
 
runner3 ++++. Runs until winner reaches 10. 
 


Last Update: 2/6/97
 
 
Copyright © 1996,1997 - Douglas Lyon
 
 
Lyon@cse.bridgeport.edu