Java Concurrency -JUC-CountDownLatch countdown latch device - wait for completion of multi-threaded and then release - single use

If that (summary points)

• CountDownLatch countdown latch device,
• Allow 1-n-1 threads waiting for other multithreading job done.
• (Sheet of resolving multiple Excel, and ultimately wait parsed completely; to achieve the main thread waits for all threads to complete sheet resolve operation, the easiest is to join)
• CountDownLatch latch = new CountDownLatch (2); // use count down latch is forced into the main thread wait; set of N nodes, threads or n-steps
• latch.countDown();
• latch.await (1000, TimeUnit.MILLISECONDS); // blocks the current thread until the counter becomes 0
• Original link:

Learn from the article list

• ALiBaBaJavaCodingGuideLines something to say:
  • Use the thread pool better!

Simple Test 1. Test 1

public class Test03_countdownlatch {
    public static void main(String[] args) {

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println("hello ");
            }
        };
        Thread thread1 = new Thread(runnable);
        Thread thread2 = new Thread(runnable);
        System.out.println("all thread finish");
    }
}

2. Results 1: the thread has not finished in time, the main thread is over, so the first print finish

all thread finish
hello 
hello 

3. Test 2 forcing the main thread waits for the current sub-thread is finished by the join method of sub-thread

 public static void main(String[] args) {

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println("hello ");
            }
        };
        Thread thread1 = new Thread(runnable);
        Thread thread2 = new Thread(runnable);

        thread1.start();
        thread2.start();

        try {
            // 迫使主线程通过join方法等待当前的子线程执行完毕
            thread1.join();
            // 主线程第二次等待
            thread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("all thread finish");
    }

Test Results

hello 
hello 
all thread finish

Test 3 is used to count down latch

public static void main(String[] args) {

        Runnable runnable = () -> System.out.println("hello ");
        Thread thread1 = new Thread(runnable);
        Thread thread2 = new Thread(runnable);

        // 使用倒计数门闩器 ，迫使主线程进入等待 ；设置N个结点 ，n个线程或者步骤都可以
        CountDownLatch latch = new CountDownLatch(2);
        thread1.start();
        latch.countDown();
        thread2.start();
        latch.countDown();

        try {
            // 阻塞当前线程，直到计数器变为0； await（long time）;也可以带时间！
            latch.await(1000, TimeUnit.MILLISECONDS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("all thread finish");


    }

Test Results

hello 
hello 
all thread finish