Executors.newFixedThreadPool How to stop all active threads on synchronized method

Question

I have an executor service that submits x amount of threads concurrently to do a long task. I need to be able to stop all the current threads that are running and prevent queued tasks from starting. I am trying to implement a way to handle stopping threads that are waiting for a synchronized method in which the runnable passes a list of strings back to the interface that called it.

    @Override
        public synchronized void FilterResults(List<String> Results)  {
            //System.out.println("Result found: " + Results.size());
            try {
            Set<String> hs = new HashSet<>();
            hs.addAll(Results);
            Results.clear();
            Results.addAll(hs);
            for (String tempURL : Results) {
                //System.out.println("Found url: " + tempURL);
                if (!isCompleted(tempURL) && !isQueued(tempURL) && !isRunning(tempURL)) {
                    System.out.println("Added: " + tempURL + " to queue.");
                    queueLink(tempURL);
                    startNewThread(tempURL);
                }
            }
            }catch(Exception e) {

            }
            return;
        }
        private synchronized void startNewThread(String seedURL) {
                if (!isCompleted(seedURL) && !isRunning(seedURL)  ) {
                    if (completedSize("") + runningSize() > 99) {
                        Stop();
                    }

                    String tempProxy = "";
                    String tempPort = "";
                    if (UseProxies) {
                    String Proxy = grabFreeProxy();
                    String[] splitProxy = Proxy.split(":");
                    tempProxy = splitProxy[0]; // 004
                    tempPort = splitProxy[1]; // 034556
                    }
                    //System.out.println("Proxy: " + tempProxy);
                    //System.out.println("Port: " + tempPort);
                    execService.submit(new Crawl(seedURL, this, tempProxy, tempPort, UseProxies));
                    removeFromQueue(url);
                }

            }

@Override
    public Collection<String> Stop() {
        try {
            execService.shutdown();
            if (execService.awaitTermination(45, TimeUnit.SECONDS)) {
                  System.out.println("task completed");
                } else {

                  execService.shutdownNow();

                }
        } catch (InterruptedException e) {

        }
        return PROFILES;
    }

    The Runnable

    public class Crawl implements Runnable{
    public void run() {
            while(!Thread.currentThread().isInterrupted() && shutdown == false) {
             try {
                     //System.out.println(crawler.queueSize());
                     Thread.sleep(100);
                         Crawl(url);
             }catch (InterruptedException e) {
                    Thread.currentThread().interrupt();  // set interrupt flag
                }
       }

      public void crawl(){
         try {
                submitResults(urls); //Calls FilterResults()
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                //e.printStackTrace();
                Thread.currentThread().interrupt();
            }
             crawler.removeUsedProxy(Proxy + ":" + Port);
             this.shutdown();
     }
    }

When I call my shutdown method it takes 45 seconds+ is there anyway to reliably cancel the task without the long wait? This number grows as I have more threads, and since all the threads are blocking waiting to submit the results, it can take some time. If I cancel the task manually I do not care if the results are stored, I just need to be able to cancel. Any ideas?

Update I've tried ExecutorService#shutdownNow. It has not been reliable when it comes to killing the tasks that are still blocked on the synchronized method.

Answer 1

Looks like you need to use ExecutorService#shutdownNow in case you don't want to wait and finish all the work and you'll receive a list with the tasks that weren't executed. You may use ExecutionService#awaitTermination (with different parameters than 45 seconds) if you want/need to provide a time to wait for the tasks to finish.