A task simulation tool to illustrate load factor vs wait time in Simpy

task_simulation.py

"""
Adapted from https://simpy.readthedocs.io/en/latest/examples/bank_renege.html
Bank renege example

Covers:

- Resources: Resource
- Condition events

Scenario:
  A counter with a random service time and customers who renege. Based on the
  program bank08.py from TheBank tutorial of SimPy 2. (KGM)

"""
import random

import simpy
import simpy.rt
    
def start_simulation(RANDOM_SEED = 1098,
                     NEW_CUSTOMERS = 250,  # Total number of customers
                     INTERVAL_CUSTOMERS = 1.0,  # Generate new customers roughly every x seconds
                     PATIENCE = 100000000,  # customer patience
                     TIME_IN_JOB = 1.0,
                     RANDOM_TYPE = True,
                     REALTIME = 0.5,
                     VERBOSE = True):
    # Setup and start the simulation
    def source(env, number, interval, counter, verbose):
        """Source generates customers randomly"""
        env.work_time = []
        env.wait_time = []
        for i in range(number):
            c = customer(env, 'Task%02d' % i, counter, time_in_bank=TIME_IN_JOB, verbose=verbose)
            env.process(c)
            if(RANDOM_TYPE):
                t = random.expovariate(1.0 / interval)
            else:
                t = interval

            yield env.timeout(t)
            

    def customer(env, name, counter, time_in_bank, verbose=True):
        """Customer arrives, is served and leaves."""
        arrive = env.now
        if(verbose):

            print('%7.4f %s: Here I am' % (arrive, name))

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

            wait = env.now - arrive
            env.wait_time.append(wait)
        

            if req in results:
                # We got to the counter
                if(verbose):
                    print('%7.4f %s: Waited %6.3f' % (env.now, name, wait))
                if(RANDOM_TYPE):
                    tib = random.expovariate(1.0 / time_in_bank)
                else:
                    tib = time_in_bank
                env.work_time.append(tib)
                yield env.timeout(tib)
                if(verbose):
                    print('%7.4f %s: Finished' % (env.now, name))

            else:
                # We reneged
                if(verbose):
                    print('%7.4f %s: RENEGED after %6.3f' % (env.now, name, wait))

    print('Task Simulation')
    random.seed(RANDOM_SEED)

    if(REALTIME is not None):
        env = simpy.rt.RealtimeEnvironment(factor=REALTIME)
    else:
        env = simpy.Environment()

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

    
    print("Simulated number of tasks: %d" %NEW_CUSTOMERS)
    print("Average task length: %7.2f" % (sum(env.work_time)/NEW_CUSTOMERS))
    print("Average wait time: %7.2f" % (sum(env.wait_time)/NEW_CUSTOMERS))
    print("Total time taken %7.2f" % float(env.now))
    print("Period Busy %2.2f %%" % (float(sum(env.work_time))/float(env.now)*100))



##
# CASE 1
start_simulation(NEW_CUSTOMERS = 100,  # Total number of customers
                 INTERVAL_CUSTOMERS = 1.0,  # Generate new customers roughly every x seconds
                 TIME_IN_JOB = 1.0,
                 RANDOM_TYPE = False,
                 VERBOSE = True
                 )

# CASE 2
start_simulation(NEW_CUSTOMERS = 100,
                 RANDOM_TYPE=True)



# CASE 2b
# Wait time actually grows over time
start_simulation(NEW_CUSTOMERS = 250, RANDOM_TYPE=True, REALTIME=None)
start_simulation(NEW_CUSTOMERS=750, RANDOM_TYPE=True, VERBOSE=False, REALTIME=None)
start_simulation(NEW_CUSTOMERS=5000, RANDOM_TYPE=True, VERBOSE=False, REALTIME=None)


# Solution
# Tasks coming in slightly faster
start_simulation(RANDOM_TYPE=True, INTERVAL_CUSTOMERS=1.0, TIME_IN_JOB=0.8)
start_simulation(NEW_CUSTOMERS=100000, RANDOM_TYPE=True, INTERVAL_CUSTOMERS=1.0, TIME_IN_JOB=0.8, VERBOSE=False, REALTIME=None)

start_simulation(NEW_CUSTOMERS=100000, RANDOM_TYPE=True, INTERVAL_CUSTOMERS=1.0, TIME_IN_JOB=0.9, VERBOSE=False, REALTIME=None)