CODEWITHSUNDEEP
javamultithreadingconcurrency
Amar
Amar

Reputation: 763

Unable to getting the results from concurrent CompletionService

I am very new to the Java concurrent package. I am using the java.util.concurrent.CompletionService class for getting the results from the pool without any waiting for the other threads to complete the task. But I was unable to get the tasks even after 10 min of code execution. I am just printing the thread name in the task. Here is my code.

public class CompletionService {

    public void execute(ThreadPoolExecutor argThreadPoolExecutor)
            throws InterruptedException, ExecutionException {
        java.util.concurrent.CompletionService<String> completionService = 
                 new ExecutorCompletionService<String>(argThreadPoolExecutor);
        int counter = 0;
        for (int i = 0; i < 4; i++) {
            Task task = new Task();
            completionService.submit(task);
            ++counter;
        }
        print(counter, completionService);
    }

    private void print(int argCounter,
            java.util.concurrent.CompletionService<String> argCompletionService)
            throws InterruptedException, ExecutionException {
        String s = argCompletionService.take().get();
        if (s != null && !s.isEmpty()) {
            System.out.println(s);
        }
    }

    public static void main(String[] args) throws InterruptedException,
            ExecutionException {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(8, 8,
                3000, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
        CompletionService completionService = new CompletionService();
        completionService.execute(threadPoolExecutor);
        threadPoolExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);
    }
}

Task class:

public class Task implements Callable<String> {

@Override

    public String call() throws Exception {
        String name = Thread.currentThread().getName();
        return name;
    }
}

Result: pool-1-thread-1

I am getting only one thread information. I waited 10-15 min still I am not getting the results. Am I wrong anywhere.? Can any one help me on this.?

Thanq.

Upvotes: 0

Views: 239

Answers (2)

Jamie Cockburn
Jamie Cockburn

Reputation: 7555

You're not looping in your print(...) method, so you're only ever taking the first result from the completion service. Try this instead:

private void print(int argCounter, CompletionService<String> argCompletionService) throws InterruptedException, ExecutionException {
    for (int i = 0; i < argCounter; i++) {
        String s = argCompletionService.take().get();
        if (s != null && !s.isEmpty()) 
            System.out.println(s);
    }
}

Also you're not shutting down your ExecutorService. This will mean that your program will never finish. Add a call to shutdown() after your task submission loop.

Upvotes: 1

Brett Okken
Brett Okken

Reputation: 6306

completionService.execute(threadPoolExecutor);
threadPoolExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);

You will block here forever because you have not asked the ThreadPoolExecutor to shutdown.

Upvotes: 3

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