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package jadeutils.encryption;

import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.atomic.AtomicLong;

public abstract class Pool implements AutoCloseable {
	protected abstract T makeObject() throws E;
	/* 
	 * @param obj
	 * @throws E
	 */
	protected void activateObject(T obj) throws E {/* */}
	/* 
	 * @param obj
	 * @throws E
	 */
	protected void passivateObject(T obj) throws E {/* */}
	/* @param obj */
	protected abstract void destroyObject(T obj);

	class Entry {
		T obj;
		long expire;

		Entry(T obj, long expire) {
			this.obj = obj;
			this.expire = expire;
		}
	}

	private int timeout, interval;
	private ConcurrentLinkedDeque deque = new ConcurrentLinkedDeque<>();
	private AtomicLong accessed = new AtomicLong(System.currentTimeMillis());
	private volatile boolean closed = false;

	public Pool() {
		this(0, 0);
	}

	public Pool(int timeout, int interval) {
		this.timeout = timeout;
		this.interval = interval;
	}

	public T borrowObject() throws E {
		Entry entry;
		if (timeout > 0) {
			long now = System.currentTimeMillis();
			long accessed_ = accessed.get();
			if (now > accessed_ + interval &&
					accessed.compareAndSet(accessed_, now)) {
				while ((entry = deque.pollLast()) != null) {
					if (now < entry.expire) {
						deque.offerLast(entry);
						break;
					}
					destroyObject(entry.obj);
				}
			}
		}

		while ((entry = deque.pollFirst()) != null) {
			try {
				activateObject(entry.obj);
				return entry.obj;
			} catch (RuntimeException e) {
				throw e;
			} catch (Exception e) {
				destroyObject(entry.obj);
			}
		}
		T obj = makeObject();
		try {
			activateObject(obj);
			return obj;
		} catch (RuntimeException e) {
			throw e;
		} catch (Exception e) {
			destroyObject(obj);
			throw e;
		}
	}

	public void returnObject(T obj) {
		try {
			passivateObject(obj);
			if (closed) {
				destroyObject(obj);
			} else {
				deque.offerFirst(new Entry(obj, System.currentTimeMillis() + timeout));
			}
		} catch (RuntimeException e) {
			throw e;
		} catch (Exception e) {
			destroyObject(obj);
		}
	}

	public void reopen() {
		closed = false;
	}

	@Override
	public void close() {
		closed = true;
		Entry entry;
		while ((entry = deque.pollFirst()) != null) {
			destroyObject(entry.obj);
		}
	}
}