package threadsafe;

/**
 * Created by pyq on 4/19/15.
 */
class Chopstick {

    // TODO - change if need be

    private final int numberAroundTable;
    private boolean isUsing;

    public Chopstick(int numberAroundTable) {
        this.numberAroundTable = numberAroundTable;
        this.isUsing = false;
    }

    public int getNumberAroundTable() {
        return numberAroundTable;
    }
    public synchronized void pickUp() {
        isUsing = true;
    }
    public synchronized void putDown() {
        isUsing = false;
    }
    public synchronized boolean isAvailable() {
        return isUsing == false;
    }
}

//for DijkstraPhilosopher

    @Override
    public boolean attemptEat(Chopstick left, Chopstick right, Callback callback) {
        //pick up the smaller number of chopsitck
        if(left.getNumberAroundTable() < right.getNumberAroundTable()) {
            if(left.isAvailable()) {
                    callback.pickedUpChopstick(left);
                    left.pickUp(false);
                    if (right.isAvailable()) {
                        callback.pickedUpChopstick(right);
                        right.pickUp();
                        return true;
                    }
                    callback.putDownChopstick(left);
                    right.putDown();
            }

// In my opinion, Chopstick is thread safe, it ensures only one thread use a chopstick instance,
//but is not threadthread in attemptEat
// for example if 2 philosophers are trying to use a chopstick '3',
//when they use check method isAvailable(), both return true, they might
// use try to pickup this chopstick twice. It is a little like you've told me the Vector.
//every method is thread safe, but it is possible
// add an element twice.