Specify task order execution in Java

Question

I\'ve searched a lot but couldn\'t find any solution. I use java thread pool in such way:

ExecutorService c = Executors.newFixedThreadPool(3);
for (int i = 0         


        

Answer 1

You can use PriorityBlockingQueue to specify Queue to ThreadPoolExecutor.

public class PriorityExecutor extends ThreadPoolExecutor {

    public PriorityExecutor(int corePoolSize, int maximumPoolSize,
            long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }
    //Utitlity method to create thread pool easily
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new PriorityExecutor(nThreads, nThreads, 0L,
                TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>());
    }
    //Submit with New comparable task 
    public Future<?> submit(Runnable task, int priority) {
        return super.submit(new ComparableFutureTask(task, null, priority));
    }
    //execute with New comparable task 
    public void execute(Runnable command, int priority) {
        super.execute(new ComparableFutureTask(command, null, priority));
    }
}

Define ComparableFutureTask to compare on Priority.

class ComparableFutureTask<T> extends FutureTask<T>
        implements
            Comparable<ComparableFutureTask<T>> {

    volatile int priority = 0;

    public ComparableFutureTask(Runnable runnable, T result, int priority) {
        super(runnable, result);
        this.priority = priority;
    }
    public ComparableFutureTask(Callable<T> callable, int priority) {
        super(callable);
        this.priority = priority;
    }
    @Override
    public int compareTo(ComparableFutureTask<T> o) {
        return Integer.valueOf(priority).compareTo(o.priority);
    }
  }

Answer 2

ThreadPoolExecutor constructor accepts BlockingQueue. You can pass queue as PriorityBlockingQueue. It does not make any grantee on ordering you need to pass custom comparators to maintain order.

static BlockingQueue<Task> queue=new PriorityBlockingQueue<Task>(MAXPOOL,new TaskComparator());

static ThreadPoolExecutor threadpool = new ThreadPoolExecutor(30, MAXPOOL, 
        MAXPOOL, TimeUnit.SECONDS, (PriorityBlockingQueue) queue, new mThreadFactory());



class TaskComparator implements Comparator<Task>{
  public int compare(Task t1, Task t2){
    //write you own logic to compare two task.
  }
}