Time limited

Question

An attempt to build a Runnable , which should be completed within the specified period.

I am currently using java.util.Timer to interrupt a Runnable thread.

Timer starts immediately after running Runnable .

 import java.util.Timer; import java.util.TimerTask; public class test { Thread task; Timer timer; public void start(){ task = new Thread(new worker()); timer = new Timer("timer",true); task.start(); timer.schedule(new Terminator(),1000*2); } class worker implements Runnable{ @Override public void run() { for (int i = 0 ; i < 2; i++){ try { Thread.sleep(1000); } catch (InterruptedException e) { System.out.println("Test Interrupted !!"); return; } } System.out.println("Test Finished !!"); timer.cancel(); } } class Terminator extends TimerTask{ @Override public void run() { task.interrupt(); System.out.println("Test Terminated !!"); } } } 

But I suspect this leads to a race condition between Timer and Runnable themes: Runnable is about to end, and Timer also firing.

Could this lead to completion? and discontinued !! is printed? If so, how to avoid this?

Update:

It happens:

 11-09 21:14:40.741: INFO/System.out(31442): Test Finished !! 18 11-09 21:14:40.751: INFO/System.out(31442): Test Terminated !! 18 11-09 21:14:40.751: INFO/System.out(31442): Test Finished !! 19 11-09 21:14:40.751: INFO/System.out(31442): Test Terminated !! 19 

Answer 1

Could this lead to completion? and discontinued !! is printed?

Yes. When the message “finished” is printed, it is possible that the timer will light up before it is canceled.

 System.out.println("Finished !!"); // The timer can fire here. timer.cancel(); 

If this happens, both messages will be printed.

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To avoid the problem, you can use synchronization.

 synchronized (someObject) { if (!finished) { finished = true; System.out.println("Finished !!"); timer.cancel(); } } 

And in the terminator:

 synchronized (someObject) { if (!finished) { finished = true; task.interrupt(); System.out.println("Test Terminated !!"); } } 

This prevents the printing of both forms of messages.

Answer 2

Yes. If you want to avoid this, you need to use synchronize and common locking objects:

 public class test { private Object lock = new Object(); ... synchronized(lock) { System.out.println("Test Finished !!"); timer.cancel(); } ... synchronized(lock) { if( ! task.isRunning() ) return; task.interrupt(); System.out.println("Test Terminated !!"); } ...