#include "semaphore.h"

/*
 * This class provides the reader and writer lock controls using semaphores
 * as described in the text.
 */
class readerwriter {
public:
	readerwriter(): m_readcount(0), m_writesem(1), m_mutex(1) { }

	/*
	 * Operations to synchronize readers and writers.
	 */
	void enter_read()
	{
		// This locks the mutex until it is destroyed at method exit.
		m_mutex.down();
		if(++m_readcount == 1) m_writesem.down();
		m_mutex.up();
	}

	void leave_read()
	{
		m_mutex.down();
		if(--m_readcount == 0) m_writesem.up();
		m_mutex.up();
	}

	void enter_write()
	{
		m_writesem.down();
	}

	void leave_write()
	{
		m_writesem.up();
	}

private:
	int m_readcount;
	semaphore m_mutex;
	semaphore m_writesem;
};