DbUtils写操作加入锁，防止多线程操作写入异常。

Author: wyouflf

library/src/com/lidroid/xutils/DbUtils.java

@@ -31,6 +31,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 public class DbUtils {
 
@@ -801,9 +803,15 @@ private void debugSql(String sql) {
         }
     }
 
+    private Lock writeLock = new ReentrantLock();
+    private volatile boolean writeLocked = false;
+
     private void beginTransaction() {
         if (allowTransaction) {
             database.beginTransaction();
+        } else {
+            writeLock.lock();
+            writeLocked = true;
         }
     }
 
@@ -817,6 +825,10 @@ private void endTransaction() {
         if (allowTransaction) {
             database.endTransaction();
         }
+        if (writeLocked) {
+            writeLock.unlock();
+            writeLocked = false;
+        }
     }