ExpiryQueue.java

package org.freecode.irc.votebot;

import java.util.LinkedList;
import java.util.Map;
import java.util.concurrent.*;

public class ExpiryQueue<T> implements Runnable {
    private final long expiry;
    private final ConcurrentHashMap<T, Long> entryTimes;
    private final LinkedList<T> queue;
    private Future<?> future;
    private static ScheduledExecutorService service;

    public ExpiryQueue(final long defaultExpiry) {
        this.expiry = defaultExpiry;
        entryTimes = new ConcurrentHashMap<>();
        queue = new LinkedList<>();
        future = service.scheduleAtFixedRate(this, 10, 200, TimeUnit.MILLISECONDS);
    }

    static {
        service = Executors.newScheduledThreadPool(5);
    }

    public boolean insert(T t) {
        if (queue.contains(t)) {
            throw new IllegalArgumentException("Queue already contains this element");
        }
        if (entryTimes.containsKey(t)) {
            entryTimes.replace(t, System.currentTimeMillis());
        } else
            entryTimes.put(t, System.currentTimeMillis());
        return queue.add(t);
    }

    public void run() {
        for (Map.Entry<T, Long> entry : entryTimes.entrySet()) {
            long start = entry.getValue();
            if (System.currentTimeMillis() - start >= expiry) {
                entryTimes.remove(entry.getKey(), entry.getValue());
                queue.remove(entry.getKey());
                onRemoval(entry.getKey());
            }
        }
    }

    public void onRemoval(T t) {

    }

    public boolean remove(T t) {
        if (entryTimes.containsKey(t)) {
            entryTimes.remove(t);
        }
        return queue.remove(t);
    }

    public boolean contains(T t) {
        return queue.contains(t);
    }


}