add README.md

train-server/README.md

@@ -0,0 +1,8 @@
+## 共享数据+锁
+
+```java
+private static Map<String, CacheState> stateCache=new ConcurrentHashMap<>();
+private final ReentrantReadWriteLock cacheLock=new ReentrantReadWriteLock(true);
+private final Lock writeLock=cacheLock.writeLock();
+private final Lock readLock=cacheLock.readLock();
+```