BasicFuture.java

/*
 * ==================================================================== Licensed to the Apache Software Foundation (ASF)
 * under one or more contributor license agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the
 * License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many individuals on behalf of the Apache Software
 * Foundation. For more information on the Apache Software Foundation, please see <http://www.apache.org/>.
 *
 */
package org.springside.modules.utils.concurrent;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import org.apache.commons.lang3.Validate;

/**
 * 从Apache HttpClient 4.2 移植，一个Future实现类的基本框架.
 */
public abstract class BasicFuture<T> implements Future<T> {

	private volatile boolean completed;
	private volatile boolean cancelled;
	private volatile T result;
	private volatile Exception ex;

	@Override
	public boolean isCancelled() {
		return this.cancelled;
	}

	@Override
	public boolean isDone() {
		return this.completed;
	}

	@Override
	public synchronized T get() throws InterruptedException, ExecutionException {
		while (!this.completed) {
			wait();
		}
		return getResult();
	}

	@Override
	public synchronized T get(final long timeout, final TimeUnit unit)
			throws InterruptedException, ExecutionException, TimeoutException {
		Validate.notNull(unit, "Time unit");
		final long msecs = unit.toMillis(timeout);
		final long startTime = (msecs <= 0) ? 0 : System.currentTimeMillis();
		long waitTime = msecs;
		if (this.completed) {
			return getResult();
		} else if (waitTime <= 0) {
			throw new TimeoutException();
		} else {
			for (;;) {
				wait(waitTime);
				if (this.completed) {
					return getResult();
				} else {
					waitTime = msecs - (System.currentTimeMillis() - startTime);
					if (waitTime <= 0) {
						throw new TimeoutException();
					}
				}
			}
		}
	}

	private T getResult() throws ExecutionException {
		if (this.ex != null) {
			throw new ExecutionException(this.ex);
		}
		return this.result;
	}

	public boolean completed(final T result) {
		synchronized (this) {
			if (this.completed) {
				return false;
			}
			this.completed = true;
			this.result = result;
			notifyAll();
		}
		onCompleted(result);

		return true;
	}

	public boolean failed(final Exception exception) {
		synchronized (this) {
			if (this.completed) {
				return false;
			}
			this.completed = true;
			this.ex = exception;
			notifyAll();
		}

		onFailed(exception);

		return true;
	}

	@Override
	public boolean cancel(final boolean mayInterruptIfRunning) {
		synchronized (this) {
			if (this.completed) {
				return false;
			}
			this.completed = true;
			this.cancelled = true;
			notifyAll();
		}

		onCancelled();

		return true;
	}

	protected abstract void onCompleted(T result);

	protected abstract void onFailed(Exception ex);

	protected abstract void onCancelled();
}