An example with DelayQueue in Java. #DelayQueue #java

DelayQueueExample.java

import java.time.Duration;
import java.util.concurrent.Callable;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class DelayQueueExample
{
    // A simple adapter for Delayed interface
    static class DelayedItem <T> implements Delayed
    {
        private final T item;
        private final long expiresAt;
        
        DelayedItem(T item, long delayMillis)
        {
            this.item = item;
            this.expiresAt = System.currentTimeMillis() + delayMillis;
        }
        
        public static <U> DelayedItem<U> of(U item, long delayMillis) 
        {
            return new DelayedItem<U> (item, delayMillis);
        }
        
        public T getItem()
        {
            return item;
        }
        
        @SuppressWarnings("unchecked")
        @Override
        public int compareTo(Delayed other)
        {
            return Long.compare(expiresAt, ((DelayedItem<T>) other).expiresAt);
        }

        @Override
        public long getDelay(TimeUnit unit)
        {
            final long delay = expiresAt - System.currentTimeMillis();
            return unit.convert(Duration.ofMillis(delay));
        }
    }
    
    public static void main(String[] args) throws Exception
    {
        final ExecutorService executor = Executors.newFixedThreadPool(2);
        
        final DelayQueue<DelayedItem<String>> q = new DelayQueue<>();
        
        final long delayMillis = 3000L; 
        
        executor.submit(new Callable<Integer>()
        {
            @Override
            public Integer call() throws Exception
            {
                for (int i = 0; i < 10; i++) {
                    Thread.sleep(1000L + Math.round(Math.random() * 2000.0));
                    String msg = "hello" + String.valueOf(i + 1);
                    q.offer(DelayedItem.of(msg, delayMillis));
                    System.err.println("<< Added item: [msg=" + msg + "]");
                }
                return null;
            }
        });
        
        executor.submit(new Callable<Integer>()
        {
            @Override
            public Integer call() throws Exception
            {
                for (int i = 0; i < 10; i++) {
                    DelayedItem<String> d = q.take();
                    System.err.println(">> Received item: [msg=" + d.getItem() + "]");
                }
                return null;
            }
        });
        
        executor.shutdown();
        executor.awaitTermination(1, TimeUnit.MINUTES);
        System.err.println("Done");
    }
}