跟着ZooKeeper学Java——CountDownLatch和Join的使用

public void runFromConfig(ServerConfig config) throws IOException {
    //1 创建ZooKeeper服务器
    final ZooKeeperServer zkServer = new ZooKeeperServer();
    final CountDownLatch shutdownLatch = new CountDownLatch(1);
    zkServer.registerServerShutdownHandler(
                    new ZooKeeperServerShutdownHandler(shutdownLatch));
    ...
    //2 创建ZooKeeper的NIO线程
    cnxnFactory = ServerCnxnFactory.createFactory();
    cnxnFactory.configure(config.getClientPortAddress(),
            config.getMaxClientCnxns());
    cnxnFactory.startup(zkServer);
    
    // 3 调用shutdownLatch阻塞，服务器在新线程正常处理请求
    shutdownLatch.await();
    // 4 如果有错误，直接调用shutdown
    shutdown();
    // 5 执行cnx.join()等待NIO线程关闭
    cnxnFactory.join();
    if (zkServer.canShutdown()) {
        zkServer.shutdown(true);
    }
}
...
protected void shutdown() {
    if (cnxnFactory != null) {
        cnxnFactory.shutdown();
    }
}

public class JoinTest {
    public static void main(String[] args) throws InterruptedException {
        Thread A = new Thread(()->{
            System.out.println("进入线程A");
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("A:线程A结束");
        });
        A.start();

        System.out.println("Main:等待线程A结束");
        A.join();
        System.out.println("Main:线程A已经结束，退出");
    }
}

Main:等待线程A结束
进入线程A
A:线程A结束
Main:线程A已经结束，退出