ReaderWriterServer

public class ReaderWriterServer{
    public static void main(String args[]){
        Database server = new Database();
        Reader[] readerArray = new Reader[NUM_OF_READERS];
        Writer[] writerArray = new Writer[NUM_OF_WRITERS];

        for(int i = 0;i < NUM_OF_READERS;i++){
            readerArray[i] = new Reader(i, server);
            readerArray[i].start();
        }

        for(int i = 0;i < NUM_OF_WRITERS;i++){
            writerArray[i] = new Writer(i, server);
            writerArray[i].start();
        }
    }

    private static final int NUM_OF_READERS = 3;
    private static final int NUM_OF_WRITERS = 2;
}

class Reader extends Thread{
    public Reader(int r, Database db){
        readerNum = r;
        server = db;
    }

    public void run(){
        int c;
        while(true){
            Database.tunggu();
            System.out.println("reader "+readerNum+" wants to read");
            c = server.mulaiBaca();
            System.out.println("reader "+readerNum + " is reading. Reader Count = "+c);
            Database.tunggu();
            System.out.println("reader "+readerNum+" is done reading.");
            c = server.selesaiBaca();
        }
    }

    private Database server;
    private int readerNum;
}

class Writer extends Thread{
    public Writer(int w, Database db){
        writerNum = w;
        server = db;
    }

    public void run(){
        while(true){
            // System.out.println("writer "+writerNum+" is sleeping.");
            // Database.tunggu();
            System.out.println("writer "+writerNum+" wants to write.");
            server.mulaiTulis();
            System.out.println("writer "+writerNum+" is writing.");
            Database.tunggu();
            System.out.println("writer "+writerNum+" is done writing.");
            server.selesaiTulis();
        }
    }
    private Database server;
    private int writerNum;
}

final class Semaphore{
    public Semaphore(){
        value = 0;
    }

    public Semaphore(int v){
        value = v;
    }

    public synchronized void tutup(){
        while(value <= 0){
            try{
                wait();
            } catch (InterruptedException e){

            }
        }
        value--;
    }

    public synchronized void buka(){
        ++value;
        notify();
    }

    private int value;
}

class Database{
    public Database(){
        banyakReader = 0;
        mutex = new Semaphore(1);
        db = new Semaphore(1);
    }

    public static void tunggu(){
        int sleepTime = (int) (NAP_TIME * Math.random());
        try {
            Thread.sleep(sleepTime*1000);
        } catch (InterruptedException e) {

        }
    }

    public int mulaiBaca(){
        mutex.tutup();
        ++banyakReader;
        if(banyakReader == 1){
            db.tutup();
        }
        mutex.buka();
        return banyakReader;
    }

    public int selesaiBaca(){
        mutex.tutup();
        --banyakReader;
        if(banyakReader == 0){
            db.buka();
        }
        mutex.buka();
        System.out.println("Reader count = "+banyakReader);
        return banyakReader;
    }

    public void mulaiTulis(){
        db.tutup();
    }

    public void selesaiTulis(){
        db.buka();
    }

    public int jumlahReader(){
        return banyakReader;
    }

    private int banyakReader;
    Semaphore mutex;
    Semaphore db;
    private static final int NAP_TIME = 15;
}