Readers Writers

Here is an implementation of Readers Writers solution although it has a major bug . . . .Can you find it??? 

ReaderWriter.java

public class ReaderWriter

{

public static void main(String[] args)

{

DB database = new DB(1);

Mutex mut = new Mutex(1);

Reader reader[] = new Reader[5];

Writer writer[] = new Writer[5];

for(int i=0;i<5;i++)

{

writer[i] = new Writer(i,mut,database);

new Thread(writer[i]).start();

}

for(int i=0;i<5;i++)

{

reader[i] = new Reader(i,mut,database);

new Thread(reader[i]).start();

}

}

}

class Reader implements Runnable

{

int rno;

DB database;

Mutex mut;

Reader(int rno, Mutex mut, DB database)

{

this.rno = rno;

this.mut = mut;

this.database = database;

}

public void run()

{

try

{

mut.downMutex(); // Enter Critical Section

database.incRC();

if(database.rc == 1) // i.e if its the First Reader

{

database.downDB(); // Put a lock on DB

}

mut.upMutex();     // Leave Critical Section

//Thread.sleep(2000);

System.out.println("Value read by Reader "+this.rno+" is :"+database.db); // Access the DB value

mut.downMutex(); // Again Enter Critical Section

database.decRC();

if(database.rc == 0) //If the Reader is done 

{

database.upDB(); // release the Lock on DB

}

mut.upMutex(); // Leave Critical Section

}

catch(Exception e){e.printStackTrace();}

}

}

class Writer implements Runnable

{

int wno;

int value;

DB database;

Mutex mut;

Writer(int wno, Mutex mut, DB database)

{

this.wno = wno;

this.mut = mut;

this.database = database;

}

public void run()

{

try

{

this.value = this.wno + 10 ;  // Creating some data

database.downDB();    // Trying to put lock in Database

database.db = this.value;     // Writing to the Database

System.out.println("Writer "+this.wno+" is writing "+this.value+" to Database");

database.upDB();  // Releasing the lock

}

catch(Exception e){e.printStackTrace();}

}

}

class Mutex

{

int mutex;

Mutex(int mutex)

{

this.mutex = mutex;

}

void upMutex()

{

this.mutex = 1;

}

void downMutex()

{

while(this.mutex==0);

this.mutex = 0;

}

}

class DB

{

int dbLock;

int db;

int rc = 0; // Reader Count

DB(int dbLock)

{

this.dbLock = dbLock;

}

void upDB()

{

this.dbLock = 1;

}

void downDB()

{

while(this.dbLock == 0);

this.dbLock = 0;

}

void incRC()

{

this.rc = this.rc + 1;

}

void decRC()

{

this.rc = this.rc - 1;

}

}