content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.alibaba.nacos.config.server.utils;
  
  /**
   * 最简单的读写锁实现。要求加锁和解锁必须成对调用。
   *
   * @author Nacos
   */
  public class SimpleReadWriteLock {
  
      public synchronized boolean tryReadLock() {
          if (isWriteLocked()) {
              return false;
          } else {
              status++;
              return true;
          }
      }
  
      public synchronized void releaseReadLock() {
          status--;
      }
  
      public synchronized boolean tryWriteLock() {
          if (!isFree()) {
              return false;
          } else {
              status = -1;
              return true;
          }
      }
  
      public synchronized void releaseWriteLock() {
          status = 0;
      }
  
      private boolean isWriteLocked() {
          return status < 0;
      }
  
      private boolean isFree() {
          return status == 0;
      }
  
      /**
       * 零表示没有锁；负数表示加写锁；正数表示加读锁，数值表示读锁的个数。
       */
      private int status = 0;
  }
  