java并发编程--Executor框架

对Executor框架简介

Executor框架实现了线程的提交和执行的解耦开发,易于扩展,采用线程中的生产者和消费者模式进行解耦开发,比如线程的提交相当于生产者,线程的执行相当于消费者.

1.Executor框架继承实现介绍:

Executor的UML图:

 Executor:一个接口,只有一个接收runnable的构造方法:

ExecutorService:比Executor使用更广泛的接口,继承了Executor接口:

AbstractExecutorService:实现了ExecutorService的接口:

 ScheduledExecutorService：继承了ExecutorService,作用是可定时调度任务的接口 :

ThreadPoolExecutor：继承了AbstractExecutorService，对线程进行管理

 :

ScheduledThreadPoolExecutor:实现了ScheduledExecutorService,继承了ThreadPoolExecutor,可定时调度任务的线程池

2.ThreadPoolExecutor构造函数的各个参数说明:

源码:英文版说明:

 /**
     * Creates a new {@code ThreadPoolExecutor} with the given initial
     * parameters and default rejected execution handler.
     *
     * @param corePoolSize the number of threads to keep in the pool, even
     *        if they are idle, unless {@code allowCoreThreadTimeOut} is set
     * @param maximumPoolSize the maximum number of threads to allow in the
     *        pool
     * @param keepAliveTime when the number of threads is greater than
     *        the core, this is the maximum time that excess idle threads
     *        will wait for new tasks before terminating.
     * @param unit the time unit for the {@code keepAliveTime} argument
     * @param workQueue the queue to use for holding tasks before they are
     *        executed.  This queue will hold only the {@code Runnable}
     *        tasks submitted by the {@code execute} method.
     * @param threadFactory the factory to use when the executor
     *        creates a new thread
     * @throws IllegalArgumentException if one of the following holds:

     *         {@code corePoolSize < 0}

     *         {@code keepAliveTime < 0}

     *         {@code maximumPoolSize <= 0}

     *         {@code maximumPoolSize < corePoolSize}
     * @throws NullPointerException if {@code workQueue}
     *         or {@code threadFactory} is null
     */
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue workQueue,
                              ThreadFactory threadFactory) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             threadFactory, defaultHandler);
    }

中文翻译:

corePoolSize:保留在池中的线程数，即使它们是空闲的，也就是说,你设置了4,但是你只放了3个线程,那它还是会创建一个线程,即使它是空的.如果你没有设置最大线程maximumPoolSize,那它就是最大线程数量;

maximumPoolSize:最大线程数,maximumPoolSize>=corePoolSize;

keepAliveTime:当执行的线程数量大于corePoolSize的数量时,它空闲等待的时间,如果超过的话,就终止;

unit:keepAliveTime参数的时间单位;

workQueue:

保存任务的阻塞队列，与线程池的大小有关：

  当运行的线程数少于corePoolSize时，在有新任务时直接创建新线程来执行任务而无需再进队列

  当运行的线程数等于或多于corePoolSize，在有新任务添加时则选加入队列，不直接创建线程

  当队列满时，在有新任务时就创建新线程;

threadFactory :执行器(executor)使用的工厂;

3.Executors工具类的使用:

newFixedThreadPool:创建一个固定数量的线程池,如果出现额外的线程,要等池中的线程执行完之后才能进入,而这个额外的线程将放入到队列中等待.

public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue());
    }

 

newScheduledThreadPool:创建一个可延迟执行或定期执行的线程池

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

举例子:

(newFixedThreadPool这个构造方法就不讲了)

newScheduledThreadPool:

public static void main(String[] args) {
		ScheduledExecutorService pool = Executors.newScheduledThreadPool(5);
		Runnable task1=new Runnable() {
			public void run() {
				System.out.println("我是任务1,检测了!");
			}
		};
		Runnable task2=new Runnable() {
			public void run() {
				System.out.println("我是任务2,检测了!");
			}
		};
		pool.scheduleWithFixedDelay(task1, 1, 3, TimeUnit.SECONDS);
		pool.scheduleWithFixedDelay(task2, 2, 3, TimeUnit.SECONDS);
	}

结果:

4.Executor的生命周期

包括:运行/关闭和终止三个状态

public static void main(String[] args) {
		ExecutorService pool = Executors.newScheduledThreadPool(5);
		Thread task1=new Thread(()-> {
			System.out.println("i am task1");
		});
		Thread task2=new Thread(()-> {
			System.out.println("i am task2");
		});
//		pool.execute(task1);
//		pool.execute(task2);
		pool.submit(task1);
		pool.submit(task2);
	}

通过Executor来设计应用程序可以简化开发过程，提高开发效率，并有助于实现并发，在开发中如果需要创建线程可优先考虑使用Executor