Skip to main content

Consider the classic queuing problem, where one thread is producing some data and another is consuming it. To make the problem more interesting, suppose that the producer has to wait until the consumer is finished before it generates more data.
In a polling system, the consumer would waste many CPU cycles while it waited for the producer to produce. Once the producer was finished, it would start polling, wasting more CPU cycles waiting for the consumer to finish, and so on. Clearly, this situation is undesirable.
To avoid polling, Java includes an elegant interprocess communication mechanism via the following methods:
  • wait( ): This method tells the calling thread to give up the monitor and go to sleep until some other thread enters the same monitor and calls notify( ).
  • notify( ): This method wakes up the first thread that called wait( ) on the same object.
  • notifyAll( ): This method wakes up all the threads that called wait( ) on the same object.c The highest priority thread will run first.
These methods are implemented as final methods in Object, so all classes have them. All three methods can be called only from within a synchronized context.
These methods are declared within Object. Various forms of wait( ) exist that allow you to specify a period of time to wait.


The following sample program consists of four classes: Q, the queue that you're trying to synchronize; Producer, the threaded object that is producing queue entries; Consumer, the threaded object that is consuming queue entries; and PC, the tiny class that creates the single Q, Producer, and Consumer.
The proper way to write this program in Java is to use wait( ) and notify( ) to signal in both directions, as shown here:
class Q {
   int n;
   boolean valueSet = false;
   synchronized int get() {
      try {
      } catch(InterruptedException e) {
         System.out.println("InterruptedException caught");
      System.out.println("Got: " + n);
      valueSet = false;
      return n;

   synchronized void put(int n) {
      try {
      } catch(InterruptedException e) {
         System.out.println("InterruptedException caught");
      this.n = n;
      valueSet = true;
      System.out.println("Put: " + n);

class Producer implements Runnable {
   Q q;
   Producer(Q q) {
      this.q = q;
      new Thread(this, "Producer").start();

   public void run() {
      int i = 0;
      while(true) {

class Consumer implements Runnable {
    Q q;
    Consumer(Q q) {
       this.q = q;
       new Thread(this, "Consumer").start();
    public void run() {
       while(true) {
class PCFixed {
   public static void main(String args[]) {
      Q q = new Q();
      new Producer(q);
      new Consumer(q);
      System.out.println("Press Control-C to stop.");
Inside get( ), wait( ) is called. This causes its execution to suspend until the Producer notifies you that some data is ready.
When this happens, execution inside get( ) resumes. After the data has been obtained, get( ) calls notify( ). This tells Producer that it is okay to put more data in the queue.
Inside put( ), wait( ) suspends execution until the Consumer has removed the item from the queue. When execution resumes, the next item of data is put in the queue, and notify( ) is called. This tells the Consumer that it should now remove it.
Here is some output from this program, which shows the clean synchronous behavior:
Put: 1
Got: 1
Put: 2
Got: 2
Put: 3
Got: 3
Put: 4
Got: 4
Put: 5
Got: 5


Popular posts from this blog

C# Interviews Questions

Amatya  Feel free to share information Email WhatsUp 09731764134
1. What is C#? C# is an object oriented, type safe and managed language that is compiled by .Net framework to generate Microsoft Intermediate Language. 2. What are the types of comment in C# with examples? i)Single line
 // Single Line
ii. Multiple line (/* */)
/* Amatya
iii. XML Comments (///).Eg:/// XMLComments 3. Can multiple catch blocks be executed? No, Multiple catch blocks can’t be executed. Once the proper catch code executed, the control is transferred to the finally block and then the code that follows the finally block gets executed. 4. What is the difference between public, static and void? Public declared variables or methods are accessible anywhere in the application. Static declared variables or methods are globally accessible without creating an instance of the class. The compiler stores the address of the method as the entry point and uses this information to begin execu…

ASP .Net Basic Concept

Feel Free to share the Information Email: WhatsUp: 09731764134
Any one who want to develop a web application must have the following systems:

1. A web server.
2. An editor to develop the web pages.
3. A browser to view the web page you develop.
4. A database program like MS Access, SQL Server etc, if your web site need to save data into a database.

In the real world situation, a web server will be hosted on a secure server, located in a safe place and will be always connected to high speed internet. However, to develop a web application, you don't need to worry about security and internet connectivity. You can use your own development computer as the 'Web Server'. Web Server:-
There are several types of web servers. But if you like to develop ASP.NET web applications, you need a specific web server called 'Internet Information Server' (IIS).

IIS comes as part of Windows. But it is not installed by default, when you install Windows. Editor to d…
Importing Classes and Packages The first two lines of the following listing import two classes used in the applet: Applet and Graphics. import java.applet.Applet; import java.awt.Graphics; public class HelloWorld extends Applet { public void paint(Graphics g) { g.drawString("Hello world!", 50, 25); } } If you removed the first two lines, the applet could still compile and run, but only if you changed the rest of the code like this:
public class HelloWorld extends java.applet.Applet { public void paint(java.awt.Graphics g) { g.drawString("Hello world!", 50, 25); } } As you can see, importing the Applet and Graphics classes lets the program refer to them later without any prefixes. The java.applet. and java.awt. prefixes tell the compiler which packages it should search for the Applet and Graphics classes. Both the java.applet and java.awt packages are part of the core Java API -- API that every Java program can count on being …