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My goal is to listen to changes in 2 or more tables in a database. So I implemented one thread per table. In this case to handle the threads I have used Executor Service.

I need to stop these running threads as per the request of the client side. Here is the current implementation.

public class TableListener extends Thread {

    private String prevName;
    private final String query;

    public TableListener(String query) {
        this.query = query;
    }

    public void run() {

        while (true) {
            try {
                Thread.sleep(Integer.parseInt(Settings.REFRESH.trim()));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            CommonDao commonDao = new CommonDao();
            String name = commonDao.loadTable(this.query);
            if(prevName != null && !prevName.equalsIgnoreCase(name)) {
                System.out.println("prevName: " + prevName + "name: " + name);
            } else {
                System.out.println("no changes");
            }
            prevName = name;
        }
    }
}

public class TableListenerService{

    public static ExecutorService pool;

    public void initializeThreads() {
        pool = Executors.newFixedThreadPool(2);
        pool.execute(new TableListner("select * from person"));
        pool.execute(new TableListner("select * from demo"));
    }

    public void stop() {
        pool.submit(new Runnable() {
            public void run() {
                try {
                    Thread.sleep(20 * 1000);
                } catch (InterruptedException e) {
                    System.out.println("Interrupted, so exiting.");
                }
            }
        });

        try {
            if (pool.awaitTermination(10, TimeUnit.SECONDS)) {
                System.out.println("task completed");
            } else {
                System.out.println("Forcing shutdown...");
                pool.shutdownNow();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

But when executing the stop method, it gets below error

java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at com.example.demo.service.TableListner.run(TableListner.java:19)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at com.example.demo.service.TableListner.run(TableListner.java:19)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

could anyone support me in overcoming this and any optimized solution for this problem?

Charindu Kavishan
  • 11
  • 4
  • You haven't shown the `TableListener` class, which appears to be the one you're having trouble with. What's the relevance of the Runnable with the sleep? – tgdavies May 22 '22 at 09:37
  • thanks for the feedback. here I added the TableListener class. and I followed this https://stackoverflow.com/questions/15900387/how-to-stop-all-runnable-thread-in-java-executor-class – Charindu Kavishan May 22 '22 at 09:40
  • What do you expect calling `shutdownNow()` to do to each Thread? Why do you expect that to stop the Thread, given the implementation you've shown above? – tgdavies May 22 '22 at 09:43
  • See https://stackoverflow.com/questions/812233/getting-events-from-a-database – tgdavies May 22 '22 at 10:06
  • (And you didn't answer either of my questions) – tgdavies May 22 '22 at 10:07
  • @tgdavies I am not much familiar with java Executor Service. now the TableListener class has been added to the question description I tried to stop currently executing tasks from calling shutdownNow() so was expecting to stop the threads for stopping infinite loop inside the thread. (which is in the TableListener class) – Charindu Kavishan May 22 '22 at 10:33
  • See https://stackoverflow.com/questions/10961714/how-to-properly-stop-the-thread-in-java When you call `shutdownNow()`, `interrupt()` will be called on each Thread. – tgdavies May 22 '22 at 11:08

0 Answers0