In light of our current community-challenge I decided to build an Elevator Management System.
Initially I intended to program the EMS like a real-time operating system and the elevators as finite-state machine threads with each their own handler. It didn't go according to plan, but it works. For some values of works, since my current infrastructure makes writing tests quite hard.
Thread safety is quite an issue here. I'm grasping this opportunity to learn a thing or two about multi-threading and best practices surrounding that topic.
There's also a generalization problem. As in, there's way too much copy-paste going on. I would fix that, but since I think the architectural flaws are a much bigger problem than copied code.
This project is not finished. However, I think the current state is perfectly reviewable since it's doing what it's supposed to do.
Smaller issues:
broadcast_eventis global while it should be a member ofBank. Putting it in there bricked the function, probably due to another design flaw.- I'm using
sys.stdout.writeinstead ofprintbecauseprintis not thread-safe. However, this feels like an ugly hack. - I should probably split up the code to split the module from the invocations. This is planned after the
broadcast_eventissue mentioned earlier is fixed. - The
elevator.targetattribute is unused. This should be the final destination of the elevator before it turnsIDLEagain, while still stopping at all floors in between. - The elevators are unfamiliar with the concept of doors. Same goes for time and size.
- The message handling of the elevators should probably be split from the actual movement.
- No documentation yet. This is a known problem and will be addressed in the next version.
import sys import threading import Queue import time banks_mail = [] elevators_mail = [] elevators = [] floors_mail = [] class Bank(threading.Thread): def __init__(self): threading.Thread.__init__(self) self.mailbox = Queue.Queue() banks_mail.append(self.mailbox) def run(self): while True: data = self.mailbox.get() sys.stdout.write(str(self) + ' received: ' + str(data) + '\n') if data == 'shutdown': sys.stdout.write(str(self) + ' shutting down' + '\n') return elif data[1] == 'UP': for idx, elevator in enumerate(elevators): if elevator.floor <= data[0] and (elevator.direction == 'UP' or elevator.direction == 'IDLE'): sys.stdout.write('Elevator ' + str(idx) + ' available for floor ' + str(data[0]) + '\n') elevators_mail[idx].put(data) break elif data[1] == 'DOWN': for idx, elevator in enumerate(elevators): if elevator.floor >= data[0] and (elevator.direction == 'DOWN' or elevator.direction == 'IDLE'): sys.stdout.write('Elevator ' + str(idx) + ' available for floor ' + str(data[0]) + '\n') elevators_mail[idx].put(data) break else: sys.stdout.write('Invalid direction received') def stop(self): banks_mail.remove(self.mailbox) self.mailbox.put('shutdown') self.join() class Elevator(threading.Thread): def __init__(self, floor=0, direction='IDLE'): threading.Thread.__init__(self) self.mailbox = Queue.Queue() elevators_mail.append(self.mailbox) elevators.append(self) self.floor = floor self.direction = direction self.target = self.floor def run(self): while True: data = self.mailbox.get() sys.stdout.write(str(self) + ' received: ' + str(data) + '\n') sys.stdout.write(str(data)) if data == 'shutdown': sys.stdout.write(str(self) + ' shutting down' + '\n') return elif data[0] == self.floor: sys.stdout.write(str(self) + ' already at ' + str(data[0]) + '\n') break elif data[0] >= self.floor: self.direction = 'UP' for i in xrange(self.floor, data[0]): sys.stdout.write(str(self.floor) + ' from/to ' + str(data[0]) + '\n') self.floor += 1 sys.stdout.write(str(self) + ' at ' + str(self.floor) + ' going up\n') self.direction = 'IDLE' elif data[0] <= self.floor: self.direction = 'DOWN' for i in xrange(data[0], self.floor): sys.stdout.write(str(self.floor) + ' from/to ' + str(data[0]) + '\n') self.floor -= 1 sys.stdout.write(str(self) + ' at ' + str(self.floor) + ' going down' + '\n') self.direction = 'IDLE' def stop(self): elevators_mail.remove(self.mailbox) self.mailbox.put('shutdown') self.join() class Floor(threading.Thread): def __init__(self, number=0): threading.Thread.__init__(self) self.mailbox = Queue.Queue() floors_mail.append(self.mailbox) self.number = number def run(self): while True: data = self.mailbox.get() if data == 'shutdown': sys.stdout.write(str(self) + ' shutting down' + '\n') return sys.stdout.write(str(self) + ' received: ' + str(data) + '\n') def stop(self): floors_mail.remove(self.mailbox) self.mailbox.put('shutdown') self.join() def call(self, data): banks_mail[0].put((self.number, data)) def broadcast_event(data): for q in elevators_mail: q.put(data) b0 = Bank() b0.start() t1 = Elevator() t2 = Elevator() t3 = Elevator(8, 'DOWN') t1.start() t2.start() t3.start() f0 = Floor(0) f1 = Floor(1) f2 = Floor(2) f3 = Floor(3) f4 = Floor(4) f5 = Floor(5) f6 = Floor(6) f7 = Floor(7) f8 = Floor(8) f0.start() f1.start() f2.start() f3.start() f4.start() f5.start() f6.start() f7.start() f8.start() f1.call('UP') f4.call('UP') f6.call('DOWN') time.sleep(0.5) # Make sure all other calls are finished before shutdown sys.stdout.write('\nRecall all elevators back to Floor 0\n\n') broadcast_event((0, 'IDLE')) f0.stop() f1.stop() f2.stop() f3.stop() f4.stop() f5.stop() f6.stop() f7.stop() f8.stop() t1.stop() t2.stop() t3.stop() b0.stop() 
