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;
  
  /**
   * Simplest read-write lock implementation. Requires locking and unlocking must be called in pairs.
   *
   * @author Nacos
   */
  public class SimpleReadWriteLock {
      
      /**
       * Zero means no lock; Negative Numbers mean write locks; Positive Numbers mean read locks, and the numeric value
       * represents the number of read locks.
       */
      private int status = 0;
      
      /**
       * Try read lock.
       */
      public synchronized boolean tryReadLock() {
          if (isWriteLocked()) {
              return false;
          } else {
              status++;
              return true;
          }
      }
      
      /**
       * Release the read lock.
       */
      public synchronized void releaseReadLock() {
          // when status equals 0, it should not decrement to negative numbers
          if (status == 0) {
              return;
          }
          status--;
      }
      
      /**
       * Try write lock.
       */
      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;
      }
  
  }
  