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"""
Carwash example.
Covers:
- Waiting for other processes
- Resources: Resource
Scenario:
A carwash has a limited number of washing machines and defines
a washing processes that takes some (random) time.
Car processes arrive at the carwash at a random time. If one washing
machine is available, they start the washing process and wait for it
to finish. If not, they wait until they an use one.
"""
import random
import simpy
RANDOM_SEED = 42
NUM_MACHINES = 2 # Number of machines in the carwash
WASHTIME = 5 # Minutes it takes to clean a car
T_INTER = 7 # Create a car every ~7 minutes
SIM_TIME = 20 # Simulation time in minutes
class Carwash(object):
"""A carwash has a limited number of machines (``NUM_MACHINES``) to
clean cars in parallel.
Cars have to request one of the machines. When they got one, they
can start the washing processes and wait for it to finish (which
takes ``washtime`` minutes).
"""
def __init__(self, env, num_machines, washtime):
self.env = env
self.machine = simpy.Resource(env, num_machines)
self.washtime = washtime
def wash(self, car):
"""The washing processes. It takes a ``car`` processes and tries
to clean it."""
yield self.env.timeout(WASHTIME)
print("Carwash removed %d%% of %s's dirt." %
(random.randint(50, 99), car))
def car(env, name, cw):
"""The car process (each car has a ``name``) arrives at the carwash
(``cw``) and requests a cleaning machine.
It then starts the washing process, waits for it to finish and
leaves to never come back ...
"""
print('%s arrives at the carwash at %.2f.' % (name, env.now))
with cw.machine.request() as request:
yield request
print('%s enters the carwash at %.2f.' % (name, env.now))
yield env.process(cw.wash(name))
print('%s leaves the carwash at %.2f.' % (name, env.now))
def setup(env, num_machines, washtime, t_inter):
"""Create a carwash, a number of initial cars and keep creating cars
approx. every ``t_inter`` minutes."""
# Create the carwash
carwash = Carwash(env, num_machines, washtime)
# Create 4 initial cars
for i in range(4):
env.process(car(env, 'Car %d' % i, carwash))
# Create more cars while the simulation is running
while True:
yield env.timeout(random.randint(t_inter - 2, t_inter + 2))
i += 1
env.process(car(env, 'Car %d' % i, carwash))
# Setup and start the simulation
print('Carwash')
print('Check out http://youtu.be/fXXmeP9TvBg while simulating ... ;-)')
random.seed(RANDOM_SEED) # This helps reproducing the results
# Create an environment and start the setup process
env = simpy.Environment()
env.process(setup(env, NUM_MACHINES, WASHTIME, T_INTER))
# Execute!
env.run(until=SIM_TIME)
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