Incomplete execution with join

Question

there is some problem in this code, its not getting executing. but when i am uncommenting the finally block, its just printing the "complete" without printing "holas" , Any idea?

import java.util.ArrayList;
import java.util.List;


public class MyThread {

    /**
     * @param args
     */
    public static boolean interruptTask=false;

    public static class D extends Thread{
        public void run(){
            while(!interruptTask){
                System.out.print("Hello");
            }
        }
    }


    public static void main(String[] args) {
        // TODO Auto-generated method stub
    Thread task = new D();
    task.start();
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    interruptTask=true;
    try {
        task.join();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }/*finally{
        System.out.println("holas");
    }*/
    System.out.println("complete");
    }

}

yes, you may also try on eclipse, hopefully you will get same result — user3363969, Sep 05 '14 at 19:40
I very much doubt your results. Please turn your `sleep` amount to like `1000`. And put a `sleep` in the `run()` as well so as not to fill up your console buffer. — Sotirios Delimanolis, Sep 05 '14 at 19:41
No, `sleep` doesn't affect anything, just the amount of text you'll have in console. — Sotirios Delimanolis, Sep 05 '14 at 19:43
Even if i am increasing sleep time, i should atleast get "Hello" printed on console by other thread, even i am not getting thats — user3363969, Sep 05 '14 at 19:52
That's absolutely not normal. Make sure you are running the code you've pasted. — Sotirios Delimanolis, Sep 05 '14 at 19:55
Well, this looks like it might be a genuine issue. I get the same results, even with `volatile` and even adding a `flush()` call in the loop. However, with `println()` I get the correct output. More research is needed. — Jim Garrison, Sep 05 '14 at 20:16
What java version(and what OS) are you using? I can't reproduce your results(your code works properly for me). — kraskevich, Sep 05 '14 at 20:17

Jim Garrison · Accepted Answer · 2014-09-05T20:54:20.387

There is nothing wrong with your code, this is a bug in Eclipse.

When I run the code within Eclipse I get the behavior described by the OP. When I run the generated class file from the command line it works as expected. I suspect Eclipse is buffering the output and "forgetting" to write it out to the console window. The fact that println() works while print() doesn't supports this, but then I would have expected the final println() to cause Eclipse to see the buffer.

I also ran a test where I decreased the timeout from 5000 to 10 (milliseconds), in which case the output is correct in Eclipse.

I suspect an internal buffer in Eclipse, where it stores console output, fills up. My guess is that Eclipse is looking for \n to flush to the console window. It never sees this with the OP's original code, and when the buffer fills up Eclipse just discards additional output. Since no \n is ever written to the console buffer, it never gets displayed.

I will submit a bug on the Eclipse Bugzilla. This is a very nice testcase.

EDIT: Here's an even better testcase:

public class EclipseBug
{
    private static int count = 781;
    public static void main(String[] args)
    {
        for (int i=0; i<count; i++)
            System.out.print("hello ");
        System.out.println();
    }
}

With count = 780 it works. With count = 781 no output is produced.

Eclipse Bug Filed: https://bugs.eclipse.org/bugs/show_bug.cgi?id=443433

Incomplete execution with join

1 Answers1