class ZonePartage extends Thread {
    int nLecteurs=0;
    int nEcrivainsEnAttente=0;
    Object accesslock;

    ZonePartage() {
        accesslock = new Object();
    }

    public void accesPartage() {
        synchronized(accesslock) {
            while(nEcrivainsEnAttente>0) attente();
            nLecteurs++;
        }
    }

    public void retourPartage() {
        synchronized(accesslock) {
            nLecteurs--;
            if(nLecteurs==0) notifyAll();
        }
    }

    public void accesExclusif() {
        synchronized(accesslock) {
            nEcrivainsEnAttente++;
            while(nLecteurs!=0) attente();
        }
    }

    public void retourExclusif() {
        synchronized(accesslock) {
            nEcrivainsEnAttente--;
            notifyAll();
        }
    }

    public void attente() {
        try {
            wait(); // bloque jusqu'a un notify()
        } catch(InterruptedException e) {};
    }
}

class Reader extends Thread {
    ZonePartage z;
    String name;
    Reader (ZonePartage z, String name) {
        super(name);
        this.z = z;
        this.name=name;
    }
    public void run() {
        while (true) {
            lecture();
        }
    }
    public void lecture() {
        z.accesPartage();
        System.out.println("" +name +" Lecture (lecteur=" +z.nLecteurs +" / ecrivain=" +z.nEcrivainsEnAttente +")");
        z.retourPartage();
    }

}

class Writer extends Thread {
    ZonePartage z;
    String name;
    Writer (ZonePartage z, String name) {
        super(name);
        this.z = z;
        this.name=name;
    }
    public void run() {
        while (true) {
            ecriture();
        }
    }
    public void ecriture() {
        z.accesExclusif();
        System.out.println("" +name +" Ecriture (lecteur=" +z.nLecteurs +" / ecrivain=" +z.nEcrivainsEnAttente +")");
        z.retourExclusif();
    }
}

public class LectEcrivain {
    public static void main(String args[]) {
    ZonePartage z = new ZonePartage();
        Thread r1 = new Reader(z,"r1");
        Thread r2 = new Reader(z,"r2");
        Thread r3 = new Reader(z,"r3");
        Thread r4 = new Reader(z,"r4");
        Thread w1 = new Writer(z,"w1");
        Thread w2 = new Writer(z,"w2");
        r1.start();
        r2.start();
        r3.start();
        r4.start();
        w1.start();
        w2.start();
    }
}