DataAccessPolicyManager.java

public class DataAccessPolicyManager
{
private int readerCount;
private Semaphore mutex;
private Semaphore wrt;
public DataAccessPolicyManager () {
readerCount = 0;
mutex = new Semaphore(1);
wrt = new Semaphore(1);
}
public void acquireReadLock() {
mutex.acquire();
++readerCount;
if (readerCount == 1) // first reader
wrt.acquire();
mutex.release();
}
public void releaseReadLock() {
mutex.acquire();
--readerCount;
if (readerCount == 0) // Last reader
wrt.release();
mutex.release();
}
public void acquireWriteLock() {
wrt.acquire();
}
public void releaseWriteLock() {
wrt.release();
}
}