如何计算一个方法调用超时？

在日常的编程中我们经常会为一些特别消耗资源的动作添加一些限制，比如：timeout，超时。当超过这个时间的时候，我们应该采取某些措施。

该如何验证这个方法已经超时了呢？我们可以参考一下apache的做法。

代码如下：

/*
 * ====================================================================
 * 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.apache.http.concurrent;

import org.apache.http.util.Args;

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

/**
 * Basic implementation of the {@link Future} interface. <tt>BasicFuture<tt>
 * can be put into a completed state by invoking any of the following methods:
 * {@link #cancel()}, {@link #failed(Exception)}, or {@link #completed(Object)}.
 *
 * @param <T> the future result type of an asynchronous operation.
 * @since 4.2
 */
public class BasicFuture<T> implements Future<T>, Cancellable {

    private final FutureCallback<T> callback;

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

    public BasicFuture(final FutureCallback<T> callback) {
        super();
        this.callback = callback;
    }

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

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

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

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

    public synchronized T get(final long timeout, final TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
        Args.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();
                    }
                }
            }
        }
    }

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

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

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

    public boolean cancel() {
        return cancel(true);
    }

}

 

 我们要关注的是这个类的接口 java.util.concurrent.Future的方法：

    /**
     * Waits if necessary for at most the given time for the computation
     * to complete, and then retrieves its result, if available.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return the computed result
     * @throws CancellationException if the computation was cancelled
     * @throws ExecutionException if the computation threw an
     * exception
     * @throws InterruptedException if the current thread was interrupted
     * while waiting
     * @throws TimeoutException if the wait timed out
     */
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;

 这个get就有一个timeout的参数。