05-28 Executor 执行器

简介：Executor 执行器，通常用在线程池中

一、Executor 执行器

具体实现如下：

/* @since 1.5
 * @author Doug Lea
 */
public interface Executor {

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}

1.5时，Doug Lea 添加

二、Executor 同步执行

可能由于多用线程池，误以为是异步，但是实际上Executor执行器由于包含的是单一的方法，于是具体如何执行可以自己控制。

   Executor executor = (Runnable command) ->command.run();//同步的，指定调用runnable 的 run方法

        executor.execute(()->{

            System.out.println("thread:"+Thread.currentThread().getName()+" run...");
        });

三、Executor 异步执行

  Executor async = (Runnable command) -> new Thread(command).start();//直接线程来执行任务
        async.execute(()->{

            System.out.println("thread:"+Thread.currentThread().getName()+" run...");});

四、Executor的实现 ThreadPoolExecutor 带有线程池的执行器

public class ThreadPoolExecutor extends AbstractExecutorService {
    
    // 核心线程数
    private volatile int corePoolSize;
    // 最大线程数
    private volatile int maximumPoolSize;
    // 任务队列（当任务太多了，就放在这里排队）
    private final BlockingQueue<Runnable> workQueue;
    // 空闲线程的超时时间，超时就回收它（非core线程）
    private volatile long keepAliveTime;
    // 不解释
    private volatile ThreadFactory threadFactory;
    // 线程池拒绝处理函数（如任务太多了，如何拒绝）
    // 默认策略是：AbortPolicy。要决绝是抛出异常：RejectedExecutionException
    private volatile RejectedExecutionHandler handler;
    
}