Bank Renege


  • Resources: Resource

  • Condition events

A counter with a random service time and customers who renege. Based on the program from TheBank tutorial of SimPy 2. (KGM)

This example models a bank counter and customers arriving at random times. Each customer has a certain patience. She waits to get to the counter until she’s at the end of her tether. If she gets to the counter, she uses it for a while before releasing it.

New customers are created by the source process every few time steps.

Bank renege example


- Resources: Resource
- Condition events

  A counter with a random service time and customers who renege. Based on the
  program from TheBank tutorial of SimPy 2. (KGM)

import random

import simpy

NEW_CUSTOMERS = 5  # Total number of customers
INTERVAL_CUSTOMERS = 10.0  # Generate new customers roughly every x seconds
MIN_PATIENCE = 1  # Min. customer patience
MAX_PATIENCE = 3  # Max. customer patience

def source(env, number, interval, counter):
    """Source generates customers randomly"""
    for i in range(number):
        c = customer(env, f'Customer{i:02d}', counter, time_in_bank=12.0)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)

def customer(env, name, counter, time_in_bank):
    """Customer arrives, is served and leaves."""
    arrive =
    print(f'{arrive:7.4f} {name}: Here I am')

    with counter.request() as req:
        patience = random.uniform(MIN_PATIENCE, MAX_PATIENCE)
        # Wait for the counter or abort at the end of our tether
        results = yield req | env.timeout(patience)

        wait = - arrive

        if req in results:
            # We got to the counter
            print(f'{} {name}: Waited {wait:6.3f}')

            tib = random.expovariate(1.0 / time_in_bank)
            yield env.timeout(tib)
            print(f'{} {name}: Finished')

            # We reneged
            print(f'{} {name}: RENEGED after {wait:6.3f}')

# Setup and start the simulation
print('Bank renege')
env = simpy.Environment()

# Start processes and run
counter = simpy.Resource(env, capacity=1)
env.process(source(env, NEW_CUSTOMERS, INTERVAL_CUSTOMERS, counter))

The simulation’s output:

Bank renege
 0.0000 Customer00: Here I am
 0.0000 Customer00: Waited  0.000
 3.8595 Customer00: Finished
10.2006 Customer01: Here I am
10.2006 Customer01: Waited  0.000
12.7265 Customer02: Here I am
13.9003 Customer02: RENEGED after  1.174
23.7507 Customer01: Finished
34.9993 Customer03: Here I am
34.9993 Customer03: Waited  0.000
37.9599 Customer03: Finished
40.4798 Customer04: Here I am
40.4798 Customer04: Waited  0.000
43.1401 Customer04: Finished