JUC-java.util.concurrent学习（四）---线程池

JUC-java.util.concurrent学习（四）

线程池

三大方法

//ExecutorService executorService = Executors.newSingleThreadExecutor();//单个线程执行任务
//ExecutorService executorService = Executors.newFixedThreadPool(3);//创建固定线程执行任务
ExecutorService executorService = Executors.newCachedThreadPool();//可缓存线程

public static ExecutorService newSingleThreadExecutor() {
    return new FinalizableDelegatedExecutorService
        (new ThreadPoolExecutor(1, 1,
                                0L, TimeUnit.MILLISECONDS,
                                new LinkedBlockingQueue<Runnable>()));
}
public static ExecutorService newFixedThreadPool(int nThreads) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue<Runnable>());
}
public static ExecutorService newCachedThreadPool() {
    return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                  60L, TimeUnit.SECONDS,
                                  new SynchronousQueue<Runnable>());
}

发现通过Executors工具类new出来的线程池都是通过new ThreadPoolExecutor创建出来的

七大参数

public class MyPool {
    public static void main(String[] args) {
        ExecutorService executorService = new ThreadPoolExecutor(
                2,//核心线程数
                5,//最大线程数
                3,//超时等待时间
                TimeUnit.SECONDS,//超时等待时间单位
                new LinkedBlockingDeque<Runnable>(3),//放任务的队列
                Executors.defaultThreadFactory(),//默认工厂
                new ThreadPoolExecutor.AbortPolicy()//拒绝策略
                );

        try {
            for (int i = 0; i < 8; i++) {
                executorService.execute(()->{
                    System.out.println(Thread.currentThread().getName());
                });
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            executorService.shutdown();
        }
    }
}

当最大线程数加上队列容量数小于任务数量时，就会触发拒绝策略

最大线程数可以设置为电脑cpu的核数Runtime.getRuntime().availableProcessors()

四大拒绝策略

/**
 * new ThreadPoolExecutor.AbortPolicy()抛出异常
 * new ThreadPoolExecutor.CallerRunsPolicy()哪来的回哪去，一般main线程
 * new ThreadPoolExecutor.DiscardPolicy()队列满了会丢掉新来的任务
 * new ThreadPoolExecutor.DiscardOldestPolicy()队列满了会尝试获取第一个线程
 */