Java并发编程---Executors多任务线程框架

悠悠 2022-06-02 07:06 200阅读 0赞

**一.概念**

**为了更好地控制多线程,JDK提供了一套线程框架Executor,帮助开发人员有效地进行线程控制.他们都在java.util.concurrent包中,是JDK并发包的核心.其中有一个比较重要的类Executors,他扮演这线程工厂的角色,我们通过Executors可以创建特定功能的线程池.**

**Executors创建线程池的方法:**

newFixedThreadPool()方法,该方法返回一个固定数量的线程池,该方法的线程数始终不变,当有一个任务提交时,若线程池中空闲,则立即执行;若没有,则会被暂缓在一个任务队列中等待有空闲的线程去执行.

newSingleThreadExecutor()方法,创建一个线程的线程池,若空闲则执行,若没有空闲线程则暂缓在任务队列中

newCachedThreadPool()方法,返回一个可根据实际情况调整线程数量的线程池,不限制最大线程数量,若有任务,则创建线程;若无任务,则不创建线程.若果没有任务,则线程在60s后自动回收(空闲时间60s)

newScheduledThreadPool()方法,该方法返回一个ScheduledExecutorService对象,但该线程池可以指定线程的数量

**二.使用示例**

package com.thread.executors;
    
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    /**
     * 多任务线程框架
     * @author lhy
     * @time 2017.01.05
     *
     */
    public class UseExecutors {
    
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    
    		ExecutorService pool = Executors.newFixedThreadPool(10);         //定义固定的线程池数量
    		
    		ExecutorService pool2 = Executors.newSingleThreadExecutor();
    		
    		ExecutorService pool3 = Executors.newCachedThreadPool();
    		
    		ExecutorService pool4 = Executors.newScheduledThreadPool(10);
    	}
    
    }

**2.1 newFixedThreadPool()方法JDK底层实现**

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

**2.2 newSingleThreadExecutor()方法JDK底层实现**

public static ExecutorService newSingleThreadExecutor() {
            return new FinalizableDelegatedExecutorService
                (new ThreadPoolExecutor(1, 1,
                                        0L, TimeUnit.MILLISECONDS,
                                        new LinkedBlockingQueue<Runnable>()));
        }

**2.3 newCachedThreadPool() 方法JDK底层实现**

public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                          60L, TimeUnit.SECONDS,
                                          new SynchronousQueue<Runnable>());
        }

**2.4 newScheduledThreadPool() 方法JDK底层实现**

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