[java] How to properly stop the Thread in Java?

I need a solution to properly stop the thread in Java.

I have IndexProcessorclass which implements the Runnable interface:

public class IndexProcessor implements Runnable {

    private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);

    @Override
    public void run() {
        boolean run = true;
        while (run) {
            try {
                LOGGER.debug("Sleeping...");
                Thread.sleep((long) 15000);

                LOGGER.debug("Processing");
            } catch (InterruptedException e) {
                LOGGER.error("Exception", e);
                run = false;
            }
        }

    }
}

And I have ServletContextListener class which starts and stops the thread:

public class SearchEngineContextListener implements ServletContextListener {

    private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);

    private Thread thread = null;

    @Override
    public void contextInitialized(ServletContextEvent event) {
        thread = new Thread(new IndexProcessor());
        LOGGER.debug("Starting thread: " + thread);
        thread.start();
        LOGGER.debug("Background process successfully started.");
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        LOGGER.debug("Stopping thread: " + thread);
        if (thread != null) {
            thread.interrupt();
            LOGGER.debug("Thread successfully stopped.");
        }
    }
}

But when I shutdown tomcat, I get the exception in my IndexProcessor class:

2012-06-09 17:04:50,671 [Thread-3] ERROR  IndexProcessor Exception
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at lt.ccl.searchengine.processor.IndexProcessor.run(IndexProcessor.java:22)
    at java.lang.Thread.run(Unknown Source)

I am using JDK 1.6. So the question is:

How can I stop the thread and not throw any exceptions?

P.S. I do not want to use .stop(); method because it is deprecated.

For synchronizing threads I prefer using CountDownLatch which helps threads to wait until the process being performed complete. In this case, the worker class is set up with a CountDownLatch instance with a given count. A call to await method will block until the current count reaches zero due to invocations of the countDown method or the timeout set is reached. This approach allows interrupting a thread instantly without having to wait for the specified waiting time to elapse:

public class IndexProcessor implements Runnable {

    private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);

    private final CountDownLatch countdownlatch;
    public IndexProcessor(CountDownLatch countdownlatch) {
        this.countdownlatch = countdownlatch;
    }


    public void run() {
        try {
            while (!countdownlatch.await(15000, TimeUnit.MILLISECONDS)) {
                LOGGER.debug("Processing...");
            }
        } catch (InterruptedException e) {
            LOGGER.error("Exception", e);
            run = false;
        }

    }
}

When you want to finish execution of the other thread, execute countDown on the CountDownLatch and join the thread to the main thread:

public class SearchEngineContextListener implements ServletContextListener {

    private static final Logger LOGGER = LoggerFactory.getLogger(SearchEngineContextListener.class);

    private Thread thread = null;
    private IndexProcessor runnable = null;
    private CountDownLatch countdownLatch = null;

    @Override
    public void contextInitialized(ServletContextEvent event) {
        countdownLatch = new CountDownLatch(1);
        Thread thread = new Thread(new IndexProcessor(countdownLatch));
        LOGGER.debug("Starting thread: " + thread);
        thread.start();
        LOGGER.debug("Background process successfully started.");
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        LOGGER.debug("Stopping thread: " + thread);
        if (countdownLatch != null) 
        {
            countdownLatch.countDown();
        } 
        if (thread != null) {
            try {
                thread.join();
            } catch (InterruptedException e) {
                LOGGER.error("Exception", e);
            }
            LOGGER.debug("Thread successfully stopped.");
        } 
    }
}

Sometime I will try 1000 times in my onDestroy()/contextDestroyed()

      @Override
    protected void onDestroy() {
        boolean retry = true;
        int counter = 0;
        while(retry && counter<1000)
        {
            counter++;
            try{thread.setRunnung(false);
                thread.join();
                retry = false;
                thread = null; //garbage can coll
            }catch(InterruptedException e){e.printStackTrace();}
        }

    }

Using Thread.interrupt() is a perfectly acceptable way of doing this. In fact, it's probably preferrable to a flag as suggested above. The reason being that if you're in an interruptable blocking call (like Thread.sleep or using java.nio Channel operations), you'll actually be able to break out of those right away.

If you use a flag, you have to wait for the blocking operation to finish and then you can check your flag. In some cases you have to do this anyway, such as using standard InputStream/OutputStream which are not interruptable.

In that case, when a thread is interrupted, it will not interrupt the IO, however, you can easily do this routinely in your code (and you should do this at strategic points where you can safely stop and cleanup)

if (Thread.currentThread().isInterrupted()) {
  // cleanup and stop execution
  // for example a break in a loop
}

Like I said, the main advantage to Thread.interrupt() is that you can immediately break out of interruptable calls, which you can't do with the flag approach.

Some supplementary info. Both flag and interrupt are suggested in the Java doc.

https://docs.oracle.com/javase/8/docs/technotes/guides/concurrency/threadPrimitiveDeprecation.html

private volatile Thread blinker;

public void stop() {
    blinker = null;
}

public void run() {
    Thread thisThread = Thread.currentThread();
    while (blinker == thisThread) {
        try {
            Thread.sleep(interval);
        } catch (InterruptedException e){
        }
        repaint();
    }
}

For a thread that waits for long periods (e.g., for input), use Thread.interrupt

public void stop() {
     Thread moribund = waiter;
      waiter = null;
      moribund.interrupt();
 }

You should always end threads by checking a flag in the run() loop (if any).

Your thread should look like this:

public class IndexProcessor implements Runnable {

    private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
    private volatile boolean execute;

    @Override
    public void run() {
        this.execute = true;
        while (this.execute) {
            try {
                LOGGER.debug("Sleeping...");
                Thread.sleep((long) 15000);

                LOGGER.debug("Processing");
            } catch (InterruptedException e) {
                LOGGER.error("Exception", e);
                this.execute = false;
            }
        }
    }

    public void stopExecuting() {
        this.execute = false;
    }
}

Then you can end the thread by calling thread.stopExecuting(). That way the thread is ended clean, but this takes up to 15 seconds (due to your sleep). You can still call thread.interrupt() if it's really urgent - but the prefered way should always be checking the flag.

To avoid waiting for 15 seconds, you can split up the sleep like this:

        ...
        try {
            LOGGER.debug("Sleeping...");
            for (int i = 0; (i < 150) && this.execute; i++) {
                Thread.sleep((long) 100);
            }

            LOGGER.debug("Processing");
        } catch (InterruptedException e) {
        ...

I didn't get the interrupt to work in Android, so I used this method, works perfectly:

boolean shouldCheckUpdates = true;

private void startupCheckForUpdatesEveryFewSeconds() {
    threadCheckChat = new Thread(new CheckUpdates());
    threadCheckChat.start();
}

private class CheckUpdates implements Runnable{
    public void run() {
        while (shouldCheckUpdates){
            System.out.println("Do your thing here");
        }
    }
}

 public void stop(){
        shouldCheckUpdates = false;
 }

Simple answer: You can stop a thread INTERNALLY in one of two common ways:

• The run method hits a return subroutine.
• Run method finishes, and returns implicitly.

You can also stop threads EXTERNALLY:

• Call system.exit (this kills your entire process)
• Call the thread object's interrupt() method *
• See if the thread has an implemented method that sounds like it would work (like kill() or stop())

*: The expectation is that this is supposed to stop a thread. However, what the thread actually does when this happens is entirely up to what the developer wrote when they created the thread implementation.

A common pattern you see with run method implementations is a while(boolean){}, where the boolean is typically something named isRunning, it's a member variable of its thread class, it's volatile, and typically accessible by other threads by a setter method of sorts, e.g. kill() { isRunnable=false; }. These subroutines are nice because they allow the thread to release any resources it holds before terminating.

Typically, a thread is terminated when it's interrupted. So, why not use the native boolean? Try isInterrupted():

Thread t = new Thread(new Runnable(){
        @Override
        public void run() {
            while(!Thread.currentThread().isInterrupted()){
                // do stuff         
            }   
        }});
    t.start();

    // Sleep a second, and then interrupt
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {}
    t.interrupt();

ref- How can I kill a thread? without using stop();