Question

How to pass the polling thread to another thread for processing.
The program execution beings in a controller class which has a main method and a thread pool:

The main class Controller

   public static void main(String[] args) throws InterruptedException {
    RunnableController controller = new RunnableController();

    System.out.println(incomingQueue.size());

    controller.initializeDb();
    controller.initialiseThreads();
    System.out.println("Polling");
    controller.initialUpdate(); 

}

The method which has the thread for Polling class

 private void initialiseThreads()
{       
    try {

        threadExecutorRead = Executors.newFixedThreadPool(10);
PollingSynchronizer reader = new PollingSynchronizer(incomingQueue,dbConnection);   
        threadExecutorRead.submit(reader);

    }catch (Exception e){
        e.printStackTrace();
    }

}

The method which has the thread for the proccesor class

    private void initialUpdate()
{
    RunnableController.outgoingQueue = incomingQueue;
    if((RunnableController.outgoingQueue)!= null){
        try {
            threadExecutorFetch = Executors.newFixedThreadPool(10);
        MessageProcessor updater = new MessageProcessor(outgoingQueue, dbConnection);
            threadExecutorFetch.submit(updater);
            DBhandler dbhandler = new DBhandler();
            dbhandler.updateDb(getOutgoingQueue());

        } catch (Exception e) {

        }
    }

}

The Poller Class and the controller class

    public void run() {// Thread in the Poller class 
    int seqId = 0;
    while(true) {
        List<KpiMessage> list = null;
        try {
            list = fullPoll(seqId);
            if (!list.isEmpty()) {
                seqId = list.get(0).getSequence();
                incomingQueue.addAll(list);
                this.outgoingQueue = incomingQueue;             
                System.out.println("waiting");
                System.out.println("new incoming message");
                while(true){
                        wait(3000);
                        notify();
                }
            }
        } catch (Exception e1) {
            e1.printStackTrace();
        }
    }
}


          public void run() {// Second thread in the Processor Class
    synchronized (this){
        RunnableController.setOutgoingQueue(generate(outgoingQueue));
    }
    notify();
}   
 } 

My task and Question is :

1.The controller should handle both the threads Poller & processor and it should only call the poller & processor thread

2.Now My question is how to make the poller thread wait for 3 seconds and paralelly notify the processor.

I get the error as follows:

java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at PollingSynchronizer.run(PollingSynchronizer.java:76)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

How to achieve asynchronous processing here?

Answer 1

You need to read something like this first. You cannot use wait() without holding the object’s monitor. Also, from a short glance, it looks like you use a non-final static member in a multithreading context. Try to make that thread-safe.