CountDownLatch实现主线程等待所有子线程运行结束后再继续执行的实现

使用CountDownLatch实现主线程等待所有子线程运行结束后再继续执行的实现。随手写的例子很简单，做个备份吧。

A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.

A CountDownLatch is initialized with a given count. The await methods block until the current count reaches zero due to invocations of the countDown() method, after which all waiting threads are released and any subsequent invocations of await return immediately. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a CyclicBarrier.

A CountDownLatch is a versatile synchronization tool and can be used for a number of purposes. A CountDownLatch initialized with a count of one serves as a simple on/off latch, or gate: all threads invoking await wait at the gate until it is opened by a thread invoking countDown(). A CountDownLatch initialized to N can be used to make one thread wait until N threads have completed some action, or some action has been completed N times.

A useful property of a CountDownLatch is that it doesn't require that threads calling countDown wait for the count to reach zero before proceeding, it simply prevents any thread from proceeding past an await until all threads could pass.

public class TestCountDownLatch {private static CountDownLatch latch;public static void main(String[] args) throws InterruptedException {latch = new CountDownLatch(10);for (int i = 0; i < 10; i++) {new Thread(new MyRunnable(i)).start();}System.out.println("main thread begin to await util all the thread finished");latch.await();System.out.println("main thread is over");}static class MyRunnable implements Runnable {int num;public MyRunnable(int num) {this.num = num;}@Overridepublic void run() {System.out.println("Thread " + num + " run");try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();} finally {latch.countDown();System.out.println("Thread " + num + " latch countDown");}}}}