Merge pull request #522 from lulu2panpan/lulu2panpan-patch-1

修复死锁bug

sink/src/main/java/com/alibaba/otter/canal/sink/entry/group/TimelineTransactionBarrier.java

@@ -59,21 +59,22 @@ public class TimelineTransactionBarrier extends TimelineBarrier {
     }
 
     public void clear(Event event) {
-        super.clear(event);
-
-        if (isTransactionEnd(event)) {
+       super.clear(event);
+
+       //应该先判断2，再判断是否是事务尾，因为事务尾也可以导致txState的状态为2
+       //如果先判断事务尾，那么2的状态可能永远没机会被修改了，系统出现死锁
+       //CanalSinkException被注释的代码是不是可以放开？？我们内部使用的时候已经放开了，从代码逻辑的分析上以及实践效果来看，应该抛异常
+        if (txState.intValue() == 2) {// 非事务中
+            boolean result = txState.compareAndSet(2, 0);
+            if (result == false) {
+                throw new CanalSinkException("state is not correct in non-transaction");
+            }
+        } else if (isTransactionEnd(event)) {
             inTransaction.set(false); // 事务结束并且已经成功写入store，清理标记，进入重新排队判断，允许新的事务进入
-            txState.compareAndSet(1, 0);
-            // if (txState.compareAndSet(1, 0) == false) {
-            // throw new
-            // CanalSinkException("state is not correct in transaction");
-            // }
-        } else if (txState.intValue() == 2) {// 非事务中
-            txState.compareAndSet(2, 0);
-            // if (txState.compareAndSet(2, 0) == false) {
-            // throw new
-            // CanalSinkException("state is not correct in non-transaction");
-            // }
+            boolean result = txState.compareAndSet(1, 0);
+            if (result == false) {
+                throw new CanalSinkException("state is not correct in transaction");
+            }
         }
     }
 
@@ -90,7 +91,8 @@ public class TimelineTransactionBarrier extends TimelineBarrier {
                         return true; // 事务允许通过
                     }
                 } else if (txState.compareAndSet(0, 2)) { // 非事务保护中
-                    return true; // DDL/DCL允许通过
+                    //当基于zk-cursor启动的时候，拿到的第一个Event是TransactionEnd
+                    return true; // DDL/DCL/TransactionEnd允许通过
                 }
             }
         }