/*
 * RWLock.java
 *
 * Created on 4 Март 2005 г., 11:27
 */

 package  cache;

 import  java.util.*;

 public   class  RWLock {
     private   int  givenLocks;
     private   int  waitingWriters;
     public   static   boolean  TRACE = false;
    
     private  Object mutex;
    
    
     public  RWLock() {
        mutex =  new  Object();
        givenLocks =  0 ;
        waitingWriters =  0 ;
         new  Date();
    }
    
     public   void  getReadLock(){
         synchronized (mutex){
             try {
                 while ((givenLocks == - 1 ) || (waitingWriters !=  0 )){
                    mutex.wait();
                }
            }  catch (java.lang.InterruptedException e){
                System.out.println(e);
            }
            givenLocks++;
        }
    }
    
     public   void  getWriteLock(){
         synchronized (mutex){
            waitingWriters++;
             try {
                 while (givenLocks !=  0 ){
                    mutex.wait();
                }
            }  catch (java.lang.InterruptedException e){
                System.out.println(e);
            }
            waitingWriters--;
            givenLocks = - 1 ;
        }
    }
    
    
     public   void  releaseLock(){
         synchronized (mutex){
            
             if (givenLocks ==  0 )
                 return ;
            
             if (givenLocks == - 1 )
                givenLocks =  0 ;
             else 
                givenLocks--;

            mutex.notifyAll();
        }
    }
}