Add lock for repository operation.

src/main/scala/util/LockUtil.scala

@@ -0,0 +1,36 @@
+package util
+
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.locks.{ReentrantLock, Lock}
+
+object LockUtil {
+
+  /**
+   * lock objects
+   */
+  private val locks = new ConcurrentHashMap[String, Lock]()
+
+  /**
+   * Returns the lock object for the specified repository.
+   */
+  private def getLockObject(key: String): Lock = synchronized {
+    if(!locks.containsKey(key)){
+      locks.put(key, new ReentrantLock())
+    }
+    locks.get(key)
+  }
+
+  /**
+   * Synchronizes a given function which modifies the working copy of the wiki repository.
+   */
+  def lock[T](key: String)(f: => T): T = {
+    val lock = getLockObject(key)
+    try {
+      lock.lock()
+      f
+    } finally {
+      lock.unlock()
+    }
+  }
+
+}