线程池秒懂

前言

    工作中很多地方都用到了线程池，不仅可以减少线程不停创建，销毁对资源的消耗，还能极大地提高资源利用率 ，
 今天就线程池做一个详尽介绍

干货

/**
  * seven big param
  * 核心线程数
  * 最大线程数
  * 存活时间（非核心线程空闲）
  * 存活时间单位
  * 存放线程的队列（等待执行任务的一个阻塞对列）
  * 创建线程的工厂类
  * 当请求达到一定值时的一个执行策略
  *   AbortPolicy (默认策略,抛弃新增任务，并给调用线程抛出异常)
  *   DiscardPolicy（抛弃新增任务,不抛异常）
  *   DiscardOldestPolicy(喜新厌旧【把新任务添加到线程池执行，抛弃线程池里面待的最久的任务】)
  *   CallerRunsPolicy(自己处理不了，直接返还调用者)
  */
 public static void main(String[] args) throws InterruptedException {
        int corePoolThread = Runtime.getRuntime().availableProcessors();
        System.out.println("corePoolThread = " + corePoolThread);
        final ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolThread, corePoolThread * 2, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>(200), Executors.defaultThreadFactory(), new ThreadPoolExecutor.CallerRunsPolicy());
  
// final ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolThread, corePoolThread * 2, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>(200),  new CustomizableThreadFactory("functionName-Thread-Pool-"), new ThreadPoolExecutor.CallerRunsPolicy());

// final ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolThread, corePoolThread * 2, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>(200), myThread->{
                Thread thread = new Thread(myThread);
        thread.setName("业务pool-");
        thread.setUncaughtExceptionHandler((t,e)->{
            System.out.println(t.getName() + t.getId()+ " 在 " + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) +" 发生异常,堆栈信息:" + e);
        });
        return thread;
        }, new ThreadPoolExecutor.CallerRunsPolicy());
        CountDownLatch countDownLatch = new CountDownLatch(210);
        for (int i = 0; i < 210; i++) {

            int finalI = i;
            threadPoolExecutor.execute(() -> {
                System.out.println("测试数据-execute = " + finalI + "---"+Thread.currentThread().getName());
                countDownLatch.countDown();
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    threadPoolExecutor.shutdown();
                }
            });
            if(i==209){
                System.out.println("运行中====================>"+threadPoolExecutor.getActiveCount());

            }
        }
        countDownLatch.await();
        System.out.println(threadPoolExecutor.getActiveCount());
        TimeUnit.SECONDS.sleep(4);
        System.out.println(threadPoolExecutor.getActiveCount());
    }

验证一下执行顺序

1. i < corePoolThread +200 ,没有创建新线程
   2.

2. i< num num>corePoolThread +200 有线程创建

3. 

i< num num>maxpool(corePoolThread * 2) 执行策略开始执行