public class Database 
{
	private int activeReaders;
	private boolean writing;

	public Database() 
	{
		this.activeReaders = 0;
		this.writing = false;
	}

	public void read() 
	{
		synchronized (this)
		{
			while (this.writing)
			{
				try 
				{
					this.wait();
				} 
				catch (InterruptedException e) 
				{
					e.printStackTrace();
				}
			}
			this.activeReaders++;
		}

		// read

		synchronized (this)
		{
			this.activeReaders--;
			if (this.activeReaders == 0)
			{
				this.notify();
			}
		}
	}

	public void write() 
	{
		synchronized (this)
		{
			while (this.activeReaders != 0 || this.writing)
			{ 
				try 
				{
					this.wait();
				} 
				catch (InterruptedException e) 
				{
					e.printStackTrace();
				}
			}
			this.writing = true;
		}

		// write

		synchronized (this)
		{
			this.writing = false;
			this.notifyAll();
		}
	}
}