✨ Introducing new features. join

crossoverJie · crossoverJie · commit d8655b026607 · 2018-03-16T01:02:05.000+08:00
diff --git a/MD/concurrent/thread-communication.md b/MD/concurrent/thread-communication.md
@@ -158,6 +158,58 @@ synchronized(Object){
 
 ## join() 方法
 
+```java
+    private static void join() throws InterruptedException {
+        Thread t1 = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("running");
+                try {
+                    Thread.sleep(3000);
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+            }
+        }) ;
+        Thread t2 = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("running2");
+                try {
+                    Thread.sleep(4000);
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+            }
+        }) ;
+
+        t1.start();
+        t2.start();
+
+        //等待线程1终止
+        t1.join();
+
+        //等待线程2终止
+        t2.join();
+
+        LOGGER.info("main over");
+    }
+```
+
+在  `t1.join()` 时会一直阻塞到 t1 执行完毕，所以最终主线程会等待 t1 和 t2 线程执行完毕。
+
+其实从源码可以看出，join() 也是利用的等待通知机制：
+
+核心逻辑:
+
+```java
+    while (isAlive()) {
+        wait(0);
+    }
+```
+
+在 join 线程完成后会调用 notifyAll() 方法，是在 JVM 实现中调用，所以这里看不出来。
+
 ## volatile 共享内存
 
 ## CountDownLatch 并发工具
diff --git a/src/main/java/com/crossoverjie/actual/ThreadCommunication.java b/src/main/java/com/crossoverjie/actual/ThreadCommunication.java
@@ -15,9 +15,9 @@
 public class ThreadCommunication {
     private final static Logger LOGGER = LoggerFactory.getLogger(ThreadCommunication.class);
     public static void main(String[] args) throws Exception {
-        //join();
+        join();
         //executorService();
-        countDownLatch();
+        //countDownLatch();
 
     }
 
@@ -118,10 +118,11 @@ public void run() {
         }) ;
 
         t1.start();
+        t2.start();
+
         //等待线程1终止
         t1.join();
 
-        t2.start();
         //等待线程2终止
         t2.join();
 
