How to simulate a starting queue before opening times in a Simulation process with Simpy?

Question

I am studying SimPy and I came across this interesting tutorial that allows to simulate a queue in a bank.

I wanted to know if it is possible and how to create an initial queue.

Let's assume that the bank opens at 09:00 but we have already 20 customers waiting to be served + the other that will come with the defined probabilistic arrival rate.

How to do that? Thank you for you support.

"""
Bank with multiple queues example
Covers:
- Resources: Resource
- Iterating processes
Scenario:
  A multi-counter bank with a random service time and customers arrival process. Based on the
  program bank10.py from TheBank tutorial of SimPy 2. (KGM)
By Aaron Janeiro Stone
"""
from simpy import *
import random

maxNumber = 30      # Max number of customers
maxTime = 400.0     # Rumtime limit
timeInBank = 20.0   # Mean time in bank
arrivalMean = 10.0  # Mean of arrival process
seed = 12345        # Seed for simulation


def Customer(env, name, counters):
    arrive = env.now
    Qlength = [NoInSystem(counters[i]) for i in range(len(counters))]
    print("%7.4f %s: Here I am. %s" % (env.now, name, Qlength))
    for i in range(len(Qlength)):
        if Qlength[i] == 0 or Qlength[i] == min(Qlength):
            choice = i  # the chosen queue number
            break
    with counters[choice].request() as req:
        # Wait for the counter
        yield req
        wait = env.now - arrive
        # We got to the counter
        print('%7.4f %s: Waited %6.3f' % (env.now, name, wait))
        tib = random.expovariate(1.0 / timeInBank)
        yield env.timeout(tib)
        print('%7.4f %s: Finished' % (env.now, name))


def NoInSystem(R):
    """Total number of customers in the resource R"""
    return max([0, len(R.put_queue) + len(R.users)])


def Source(env, number, interval, counters):
    for i in range(number):
        c = Customer(env, 'Customer%02d' % i, counters)
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)


# Setup and start the simulation
print('Bank with multiple queues')
random.seed(seed)
env = Environment()

counters = [Resource(env), Resource(env)]
env.process(Source(env, maxNumber, arrivalMean, counters))
env.run(until=maxTime)

you need another process that will look almost exactly line the source function, except it will not have a yield env.timeout(t) at the end, and change the loop range from number to 20. Without the yield at the end of the loop, all 20 customers will be started at time 0. — Michael, May 27 '23 at 19:29

score 1 · Accepted Answer · answered May 28 '23 at 01:45

added a function to load the queues with customers before the bank opens which is time 0.

"""
Bank with multiple queues example
Covers:
- Resources: Resource
- Iterating processes
Scenario:
  A multi-counter bank with a random service time and customers arrival process. Based on the
  program bank10.py from TheBank tutorial of SimPy 2. (KGM)
By Aaron Janeiro Stone
"""
from simpy import *
import random

qStartNum = 20      # number of people in queue at start
maxNumber = 30      # Max number of customers after start
maxTime = 400.0     # Rumtime limit
timeInBank = 20.0   # Mean time in bank
arrivalMean = 10.0  # Mean of arrival process
seed = 12345        # Seed for simulation


def Customer(env, name, counters):
    arrive = env.now
    Qlength = [NoInSystem(counters[i]) for i in range(len(counters))]
    print("%7.4f %s: Here I am. %s" % (env.now, name, Qlength))
    for i in range(len(Qlength)):
        if Qlength[i] == 0 or Qlength[i] == min(Qlength):
            choice = i  # the chosen queue number
            break
    with counters[choice].request() as req:
        # Wait for the counter
        yield req
        wait = env.now - arrive
        # We got to the counter
        print('%7.4f %s: Waited %6.3f' % (env.now, name, wait))
        tib = random.expovariate(1.0 / timeInBank)
        yield env.timeout(tib)
        print('%7.4f %s: Finished' % (env.now, name))


def NoInSystem(R):
    """Total number of customers in the resource R"""
    return max([0, len(R.put_queue) + len(R.users)])


def Source(env, minNumber, maxNumber, interval, counters):
    for i in range(minNumber, maxNumber):
        c = Customer(env, 'Customer%02d' % i, counters)
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)

def preSource(env, number, counters):
    """
    Queues customers before bank opens
    """
    for i in range(number):
        c = Customer(env, 'Customer%02d' % i, counters)
        env.process(c)


# Setup and start the simulation
print('Bank with multiple queues')
random.seed(seed)
env = Environment()

counters = [Resource(env), Resource(env)]
preSource(env, qStartNum, counters)
env.process(Source(env, qStartNum, qStartNum + maxNumber, arrivalMean, counters))
env.run(until=maxTime)

How to simulate a starting queue before opening times in a Simulation process with Simpy?

1 Answers1