Illustration about locking (Threads)

[pedro abs]

Please, would you give me an opinion if this image illustrates correctly the concept about thread locking :

I'm studying Java Threads and drafted this image.

Thank you very much !

[Divyeshh Patel]

It is impossible to say whether this is correct or not without looking at the full code, but assuming the code is as usual for threads(e.g. o is a Runnable and object1 is same as o, etc), you are right, the picture correctly depicts the concept.
Also, instead of writing synchronized(object1), it would even be okay if you declare the method as synchronized in this case. When run method of one thread finishes, notifyAll() method is automatically called and another random thread waiting for this monitor will be picked up for running.

[Deepak Bala]

Do post the entire code. It is not possible to visualize the threads until you do so.

PS: I like the thread running man

[pedro abs]

Hi guys:

I thing the better code to illustrate that image is:

   
public class TestThread16 {
	public static void main(String[] args) {
		BigCalc bc = new BigCalc();
		Thread t0 = new Thread(bc, "Thread-0");
		Thread t1 = new Thread(bc, "Thread-1");
		Thread t2 = new Thread(bc, "Thread-2");
		t0.start();
		t1.start();
		t2.start();
	}
}

class BigCalc implements Runnable {

	private Object object1 = new Object();

	@Override
	public void run() {
		synchronized (object1) {

			for (int i = 0; i < 5; i++) {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException ex) {
				}
				System.out
						.println(Thread.currentThread().getName() + " = " + i);
			}

		}
	}
}
 

The possible output is:
Thread-0 = 0
Thread-0 = 1
Thread-0 = 2
Thread-0 = 3
Thread-0 = 4
Thread-2 = 0
Thread-2 = 1
Thread-2 = 2
Thread-2 = 3
Thread-2 = 4
Thread-1 = 0
Thread-1 = 1
Thread-1 = 2
Thread-1 = 3
Thread-1 = 4


or I could replace the use of 'object1' for the keyword 'this'. I think the idea would be the same.

The output is the same.

    
@Override
	public void run() {
		synchronized (this) {

			for (int i = 0; i < 5; i++) {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException ex) {
				}
				System.out
						.println(Thread.currentThread().getName() + " = " + i);
			}

		}
	}

What I wanted to illustrate with this picture is the idea of the threads 'fighting' for the lock of the object at which they will execute a method that contains an excerpt synchronized.


Thanks a lot !!!

[pedro abs]

Another example using wait and notifyAll:

 

public class TestThread17 {
	public static void main(String[] args) {
		MyObjectX bc = new MyObjectX();
		Thread t0 = new Thread(bc, "Thread-0");
		Thread t1 = new Thread(bc, "Thread-1");
		Thread t2 = new Thread(bc, "Thread-2");
		t0.start();
		t1.start();
		t2.start();
		
		try {
			Thread.sleep(10000);
		} catch (InterruptedException ex){}
		
		synchronized(bc){
			System.out.println("after 10 seconds: wake up all threads !!!");
			bc.notifyAll();	
		}
	}
}

class MyObjectX implements Runnable {
	@Override
	public void run() {
		synchronized (this) {
			for (int i = 0; i < 5; i++) {
				try {
					// Thread.sleep: just to slow execution
					Thread.sleep(500);
					
					if (i == 2 ){
						System.out.println(Thread.currentThread().getName() + " waiting....");
						this.wait();
					}
				} catch (InterruptedException ex) {}

				System.out.println(Thread.currentThread().getName() + " = " + i);
			}

		}
	}
}   

Possible output:

Thread-0 = 0
Thread-0 = 1
Thread-0 waiting....
Thread-2 = 0
Thread-2 = 1
Thread-2 waiting....
Thread-1 = 0
Thread-1 = 1
Thread-1 waiting....
after 10 seconds: wake up all threads !!!
Thread-1 = 2
Thread-1 = 3
Thread-1 = 4
Thread-2 = 2
Thread-2 = 3
Thread-2 = 4
Thread-0 = 2
Thread-0 = 3
Thread-0 = 4

[Abimaran Kugathasan]

pedro abs wrote:

or I could replace the use of 'object1' for the keyword 'this'. I think the idea would be the same.

Output only will be the same!