Thread without sleep?

[CongSon Nguyen]

class A implements Runnable{

    private String title;
    
    public A(String title){
        this.title = title;
    }
    
    public void run() {
        while(true){
            System.out.println(title + " is running");
        }
    }
    
}

public class myThread {

    public static void main(String[] args){
        Thread t1 = new Thread(new A("AAA"));
        Thread t2 = new Thread(new A("BBB"));
        t1.start();
        t2.start();

    }
}

When we use Thread, we should call Thread.sleep() so that other thread has a chance to execute. However, in my simple app above, I do not need to use Thread.sleep(...), but both thread still have a chance to execute. So, why is it ? Is it because of multicore in my CPU ? If so, we do not need to use Thread.sleep(...). Can anyone please help me ? Thanks a lot.

[Henry Wong]

CongSon Nguyen wrote:
When we use Thread, we should call Thread.sleep() so that other thread has a chance to execute.

Where did you hear this? ... because this is simply not true.


It may have been somewhat true, back with the early JVMs, when it was implemented on top of a user threading library (green threads). However, even with green threads, this was only true if you were completely compute intensive -- it did scheduling when you made library calls, like the system out IO calls.

Henry

[CongSon Nguyen]

I still don't get it. Can you please explain more clearly ?

Java.sun.com said "Thread.sleep causes the current thread to suspend execution for a specified period. This is an efficient means of making processor time available to the other threads of an application or other applications that might be running on a computer system".
Even when we don't use Thread.sleep(...), processor time is still available to the other threads -> I do not really understand it.

[Stephan van Hulst]

No, what they probably mean is that you should use Thread.sleep() instead of some busy wait (looping in code that does nothing until a certain amount of time has elapsed).