Lift

A rudimentary elevator scheduling simulation.

Overview

This library is designed to support the allocation of elevator requests to a set of available elevators.

Design

The design is supposed to separate into 2 main pieces:

1. Book keeping of available elevators (ElevatorControlSystem)
2. Scheduling of an elevator request to an available elevator (ElevatorScheduler)

Elevator Control System

• Offers idle elevators to the scheduler for allocating requests.
• Manages the simulation moving each elevator towards its destination.
• Accepts and submits ElevatorRequests to the scheduler.

Elevator

• Maintains queue of ElevatorRequests for its own elevator.
• Moves closer to its destination in FIFO order.

Elevator Request

• Requests (startFloor, endFloor) that are submitted to the scheduler for allocation to an elevator.

Elevator Scheduler

• Provides a generic interface for allocating ElevatorRequests to available Elevators.

How to run

1. Install Java 8
2. java -jar lift.jar
3. Lift will listen over stdin for the following args:

<num_elevators> <num_requests> <scheduler_class_name>
<start_floor> <end_floor> (num_requests times)

Only supported scheduler: FirstComeFirstServeScheduler

Sample Input

2 3 FirstComeFirstServeScheduler
0 5
5 0
2 4

Sample Output

// Shows what decision each elevator made at each step
elevator(id: 1878246837, floor: 0, dir: STATIONARY, status: IDLE)
elevator(id: 789451787, floor: 0, dir: STATIONARY, status: IDLE)
elevator(id: 1878246837, floor: 1, dir: UP, status: OCCUPIED)
elevator(id: 789451787, floor: 1, dir: UP, status: PICKUP)
elevator(id: 1878246837, floor: 2, dir: UP, status: OCCUPIED)
elevator(id: 789451787, floor: 2, dir: UP, status: PICKUP)
...

Allocation History =======
// Shows what rides where schedules to what elevators
[elevator: elevator(id: 1878246837, floor: 3, dir: STATIONARY, status: IDLE), req: [1625635731: 0 -> 3]]
[elevator: elevator(id: 789451787, floor: 0, dir: DOWN, status: OCCUPIED), req: [644117698: 2 -> 0]]

Shortcomings

• Spent too much time on design; didn't get to do any of the fun scheduling algorithms :(
• Not as clear separation between elevator movement and scheduling as I would like.
  • Right now schedule must be given carefully to elevator and trusted that it follows the way you'd like.
• Need a better approach to dealing with the simulation. How to test/run a real workload. Right now all requests are frontloaded, scheduler basically gets farthest in the future look at the world.
• Didn't get to add metrics for utilization, avg. wait, avg completion, requests completed per step