TP-systemes-concurrents/TP4/LectRed_PrioLecteur.java

// Time-stamp: <08 Apr 2008 11:35 queinnec@enseeiht.fr>

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Lecteurs/rédacteurs stratégie d'ordonnancement: priorité aux lecteurs,
 * implantation: avec un moniteur.
 */
public class LectRed_PrioLecteur implements LectRed {

    Lock lock;
    Condition requestRead;
    Condition requestWrite;
    boolean activeWriter;
    int activeReaders;

    public LectRed_PrioLecteur() {
        lock = new ReentrantLock();
        requestRead = lock.newCondition();
        requestWrite = lock.newCondition();
        activeWriter = false;
        activeReaders = 0;
    }

    public void demanderLecture() throws InterruptedException {
        lock.lock();
        if (activeWriter) {
            requestRead.await();
        }
        activeReaders++;
        lock.unlock();
    }

    public void terminerLecture() throws InterruptedException {
        lock.lock();
        activeReaders--;
        if (activeReaders == 0) {
            requestWrite.signal();
        }
        lock.unlock();
    }

    public void demanderEcriture() throws InterruptedException {
        lock.lock();
        while (activeWriter || activeReaders > 0) {
            requestWrite.await();
        }
        activeWriter = true;
        lock.unlock();
    }

    public void terminerEcriture() throws InterruptedException {
        lock.lock();
        activeWriter = false;
        requestRead.signalAll();
        requestWrite.signalAll();
        lock.unlock();
    }

    public String nomStrategie() {
        return "Stratégie: Moniteur, prio lecteur.";
    }
}