Read-Write-Lock模式

读写锁

public class Data{
  private String buffer;
  private final ReadWriteLock lock = new ReadWriteLock();

  public String read(){
      lock.readLock();
      try{
            return doRead();
      }finally{
            lock.readUnlock();  
      }
  }

public void write(String buffer){
      lock.writeLock();
      try{
            return doWrite();
      }finally{
            lock.writeUnlock();  
      }
  }

}

ReentrantReadWriteLock 重入读写锁

public class ReentrantData{

  private String buffer;
  
  private final ReadWriteLock lock = new ReentrantReadWriteLock();
  private final readLock = lock.readLock();
  private final writeLock = lock.writeLock();

  public String read(){
      readLock.lock();
      try{
            return doRead();
      }finally{
            readLock.unLock();
      }
  }

public void write(String buffer){
      writeLock.lock();
      try{
            return doWrite();
      }finally{
            writeLock.unLock();  
      }
  }

}

锁降级 降级为读锁

获取写入锁 获取读取锁 释放写入锁