Java Executor框架

java.util.concurrent 包中包含灵活的线程池实现，但是更重要的是，它包含用于管理实现 Runnable 的任务的执行的整个框架，该框架称为 Executor 框架。该框架基于生产者-消费者模式，提交任务的操作相当于生产者，执行任务的线程则是相当于消费者。其类图结构：

ThreadPoolExecutor是可以扩展的，它提供了几个可以在子类中可扩展的方法：beforeExecute 、afterExecute、terminated。无论任务是从run中正常返回还是抛出一个异常，afterExecute都会被调用[如果任务在完成后带有一个Error，那么就不会调用afterExecute]。如果抛出一个RuntimeException，那么任务将不被执行，并且afterExecute也不会被调用。在线程池完成关闭时调用terminated，也就是在所有的任务都已经完成并且所有工作者线程也已经关闭后。

public class JHThreadPoolExecutor extends ThreadPoolExecutor {

    // 记录每个线程执行任务开始时间
    private ThreadLocal<Long> start = new ThreadLocal<Long>();

    // 记录所有任务完成使用的时间
    private AtomicLong totals = new AtomicLong();

    // 记录线程池完成的任务数
    private AtomicInteger tasks = new AtomicInteger();

    public JHThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
            BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    public JHThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
            BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);
    }

    public JHThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
            BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
    }

    public JHThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
            BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory);
    }

    /**
     * 每个线程在调用run方法之前调用该方法
     * */
    protected void beforeExecute(Thread t, Runnable r) {
        super.beforeExecute(t, r);
        start.set(System.currentTimeMillis());
    }

    /**
     * 每个线程在执行完run方法后调用该方法
     * */
    protected void afterExecute(Runnable r, Throwable t) {
        super.afterExecute(r, t);
        tasks.incrementAndGet();
        totals.addAndGet(System.currentTimeMillis() - start.get());
    }

    @Override
    protected void terminated() {
        super.terminated();
        System.out.println("[THREADPOOL]完成"+ tasks.get() +"个任务,平均耗时:" + totals.get() / tasks.get() + ".ms");
    }

}

public class Task implements Runnable {

    @Override
    public void run() {
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }
    }

}

public class Main {

    public static void main(String []args) {
        BlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>();
        JHThreadPoolExecutor  executor = new JHThreadPoolExecutor(3, 5, 5, TimeUnit.MINUTES, queue);
        for(int i = 0 ; i < 5 ; ++i) {
            executor.submit(new Task());
        }
        executor.shutdown();
    }

}

上述结果输出：

[THREADPOOL]完成5个任务,平均耗时:5001.ms