gistfile1.java

    private process TicketShop {
        // Wait to receive the array containing the references to all cars
        receive this.cars(this.cars);
        
        // Light sanity check to ensure that we have a valid cars array
        // NOTE: We don't test for null values here and the whole array is
        //       passed by reference (are we sure? How behaves JR when passing
        //       values around using messages between multiple virtual machines?)
        assert this.cars != null && this.cars.length > 0; 
        
        // Wait until the park is open
        receive this.open();
        
        out("The roller coaster is now open!");
        
        int prev = this.cars.length - 1; // The index of the previous car
        
        // Send to each car a message containing his ID and the car which comes
        // before it on the ramp.
        //
        // The previous car is then used to synchronize the cars queue and to
        // avoid overtakings along the ride.
        for (int i = 0; i<this.cars.length; i++) {
            send this.cars[i].prevCar(i, prev, this.cars[prev]);
            prev = (prev + 1) % this.cars.length;
        }
        
        // Notify the first car in the queue that the roller coaster is now open
        send this.cars[this.cars.length-1].ready();
        
        // The name of the last registered passenger (used only for the output)
        String name;
        
        // This loops runs until it blocks because a part of passengers has already
        // finished their iterations and the remaining passengers are not enough to
        // fill up a car. This causes a deadlock which is detected by the JR
        // runtime, causing it to execute the registered quiescence action.
        //
        // This function will do one more iteration and then the JR park will
        // definitively close.
        while (!this.stopped) {
            out("Waiting for the next car");
            
            int id;         // The id of the next free car
            int capacity;   // The capacity of the next free car
            
            // The callback used to send the "ride start" message
            cap void (remote Passenger[]) start;
            
            // The seats of the passengers of this car
            remote Passenger[] passengers = new remote Passenger[capacity];
            
            // Wait for the next free car
            receive nextCar(start, id, capacity);
            out("Car %d is now ready, load %d passengers!", id, capacity);
            
            // Collect tickets
            for (int i = 0; i < capacity; i++) {
                // Wait for a passenger
                receive nextPassenger(name, passengers[i]);
                
                // If the last passenger was null, then shorten the array to hold
                // only non null values and start the car with only the passengers
                // currently in the array.
                // This happens only when the quiescence action sends a nextPassenger
                // message holding null values to start the last ride.
                if (passengers[i] == null) {
                    assert this.stopped; // We start the last tour with an incomplete
                                         // car only if the park is already closed.
                    
                    // Temporary array to shorten the current one
                    remote Passenger[] temp = passengers;
                    passengers = new remote Passenger[i];
                    System.arraycopy(temp, 0, passengers, 0, i);
                    
                    // Stop waiting for others passengers, they will never arrive.
                    break;
                }
                
                // Let the passenger take his place
                out("%s (%d/%d) is sitting down", name, i + 1, capacity);
            }
            
            if (passengers.length > 0) { // Start the ride only if there is at least
                                         // one passenger.
                
                if (passengers.length == capacity) { // The car is full
                    out("Car %d is now full, start it!", id);
                } else {
                    out("Starting car %d with %d out of %d passengers.", id, passengers.length, capacity);
                }
                
                // Start the car
                send start(passengers);
            }
        }
    }