Merge pull request crossoverJie#17 from crossoverJie/dev

crossoverJie · web-flow · commit e518cb03d853 · 2018-03-19T00:04:00.000+08:00
CyclicBarrier
diff --git a/MD/concurrent/thread-communication.md b/MD/concurrent/thread-communication.md
@@ -334,6 +334,83 @@ CountDownLatch 也是基于 AQS(AbstractQueuedSynchronizer) 实现的，更多
 - 该方法会将 AQS 内置的一个 state 状态 -1 。
 - 最终在主线程调用 await() 方法，它会阻塞直到 `state == 0` 的时候返回。
 
+## CyclicBarrier 并发工具
+
+```java
+    private static void cyclicBarrier() throws Exception {
+        CyclicBarrier cyclicBarrier = new CyclicBarrier(3) ;
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    Thread.sleep(5000);
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        LOGGER.info("main thread");
+    }
+```
+
+CyclicBarrier 中文名叫做屏障或者是栅栏，也可以用于线程间通信。
+
+它可以等待 N 个线程都达到某个状态后继续运行的效果。
+
+1. 首先初始化线程参与者。
+2. 调用 `await()` 将会在所有参与者线程都调用之前等待。
+3. 直到所有参与者都调用了 `await()` 后，所有线程从 `await()` 返回继续后续逻辑。
+
+运行结果:
+
+```
+2018-03-18 22:40:00.731 [Thread-0] INFO  c.c.actual.ThreadCommunication - thread run
+2018-03-18 22:40:00.731 [Thread-1] INFO  c.c.actual.ThreadCommunication - thread run
+2018-03-18 22:40:00.731 [Thread-2] INFO  c.c.actual.ThreadCommunication - thread run
+2018-03-18 22:40:00.731 [main] INFO  c.c.actual.ThreadCommunication - main thread
+2018-03-18 22:40:05.741 [Thread-0] INFO  c.c.actual.ThreadCommunication - thread end do something
+2018-03-18 22:40:05.741 [Thread-1] INFO  c.c.actual.ThreadCommunication - thread end do something
+2018-03-18 22:40:05.741 [Thread-2] INFO  c.c.actual.ThreadCommunication - thread end do something
+```
+
+可以看出由于其中一个线程休眠了五秒，所有其余所有的线程都得等待这个线程调用 `await()` 。
+
+该工具可以实现 CountDownLatch 同样的功能，但是要更加灵活。甚至可以调用 `reset()` 方法重置 CyclicBarrier (需要自行捕获 BrokenBarrierException 处理) 然后重新执行。
+
 ## 线程响应中断
 
 ```java
diff --git a/src/main/java/com/crossoverjie/actual/ThreadCommunication.java b/src/main/java/com/crossoverjie/actual/ThreadCommunication.java
@@ -20,18 +20,67 @@ public class ThreadCommunication {
     private final static Logger LOGGER = LoggerFactory.getLogger(ThreadCommunication.class);
 
     public static void main(String[] args) throws Exception {
-        join();
+        //join();
         //executorService();
         //countDownLatch();
         //piped();
-
+        cyclicBarrier();
     }
 
     /**
-     * 使用countDownLatch 每执行完一个就减一，最后等待全部完成
+     * CyclicBarrier
      *
      * @throws Exception
      */
+    private static void cyclicBarrier() throws Exception {
+        CyclicBarrier cyclicBarrier = new CyclicBarrier(3) ;
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                LOGGER.info("thread run");
+                try {
+                    Thread.sleep(5000);
+                    cyclicBarrier.await() ;
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+
+                LOGGER.info("thread end do something");
+            }
+        }).start();
+
+        LOGGER.info("main thread");
+    }
+
     private static void countDownLatch() throws Exception {
         int thread = 3;
         long start = System.currentTimeMillis();
