TP-systemes-concurrents/TP4/LectRed_FIFO.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 FIFO, implantation:
 * avec un moniteur.
 */
public class LectRed_FIFO implements LectRed {

    Lock lock;
    Condition requestAccess;
    Condition SAS;
    boolean activeWriter;
    int activeReaders;
    boolean SASoccupied;
    int FIFOsize;

    public LectRed_FIFO() {
        lock = new ReentrantLock();
        requestAccess = lock.newCondition();
        SAS = lock.newCondition();
        activeWriter = false;
        activeReaders = 0;
        SASoccupied = false;
        FIFOsize = 0;
    }

    public void demanderLecture() throws InterruptedException {
        lock.lock();
        if (activeWriter || FIFOsize > 0) {
            FIFOsize++;
            requestAccess.await();
            FIFOsize--;
        }
        activeReaders++;
        requestAccess.signal();
        lock.unlock();
    }

    public void terminerLecture() throws InterruptedException {
        lock.lock();
        activeReaders--;
        if (activeReaders == 0) {
            if (SASoccupied) {
                SAS.signal();
            } else {
                requestAccess.signal();
            }
        }
        lock.unlock();
    }

    public void demanderEcriture() throws InterruptedException {
        lock.lock();
        if (activeWriter || activeReaders > 0 || FIFOsize > 0 || SASoccupied) {
            FIFOsize++;
            requestAccess.await();
            FIFOsize--;
        }
        if (activeReaders > 0) {
            SASoccupied = true;
            SAS.await();
            SASoccupied = false;
        }
        activeWriter = true;
        lock.unlock();
    }

    public void terminerEcriture() throws InterruptedException {
        lock.lock();
        activeWriter = false;
        requestAccess.signal();
        lock.unlock();
    }

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