Inventory simulation using SimPy - simulation

Question

I wondered what have I done wrong on the SimPy code? When I changed interarrivalTime_DR > 1.5, the code was hanged. If I changed interarrivalTime_DR < 1.5, it worked fine. Please help yourself to use the code. I was not able to find where is the problem caused the issue.
Can anyone assist?
import simpy
import numpy as np
import random
import math
class P:
externalToDRMean = 1/2
DRorderLotSize = 10
externalToBUMean = 5/60
BUorderLotSize = 20
BU_Q = 100
DR_Q = 20
ROP_BU = 20+(200/30)*7
ROP_DR = 10+(150/30)*`
BU_LT = 7
DR_LT = 2
simulationTimeMax = 1 * 30
class S:
Inv = None
DRwaits = []
BUwaits = []
nBUCustomers = 0
nDRCustomers = 0
BU_Dem_day = list(np.repeat(0, P.simulationTimeMax))
DR_Dem_day = list(np.repeat(0, P.simulationTimeMax))
class Inventory:
def __init__(self, env):
self.env = env
self.SP_inv = simpy.Container(env, init = 10000)
self.BU_inv = simpy.Container(env, init = P.ROP_BU)
self.DR_inv = simpy.Container(env, init = P.ROP_DR)
self.mon_procBU = env.process(self.monitor_BU_inv(env))
self.mon_procDR = env.process(self.monitor_DR_inv(env))
def monitor_BU_inv(self, env):
while True:
#print(f"BU_Inv level:{self.BU_inv.level}")
if self.BU_inv.level <= P.ROP_BU:
print("Time {0}: BU inventory reached ROP: BU places replenishment order to Supply".format(self.env.now))
yield self.SP_inv.get(P.BU_Q)
print("Time {0}: Supply fills BU replenishment request".format(self.env.now))
yield self.env.timeout(P.BU_LT)
print("Time {0}: BU replenishment inventory arrives".format(self.env.now))
yield self.BU_inv.put(P.BU_Q)
print("Time {0}: BU replenishment order is added to inventory".format(self.env.now))
yield self.env.timeout(1)
def monitor_DR_inv(self, env):
while True:
if self.DR_inv.level <= P.ROP_DR:
print("Time {0}: DR inventory reached ROP: DR places replenishment order to BU".format(self.env.now))
yield self.BU_inv.get(P.DR_Q)
print("Time {0}: BU fills DR replenishment request".format(self.env.now))
yield self.env.timeout(P.DR_LT)
print("Time {0}: DR replenishment inventory arrives from BU".format(self.env.now))
yield self.DR_inv.put(P.DR_Q)
print("Time {0}: DR replenishment order is added to inventory".format(self.env.now))
yield self.env.timeout(1)
class DRCustomer(object):
def __init__(self, env, name = ''):
self.env = env
self.action = self.env.process(self.ordertoDR())
if (name==''):
self.name = 'RandomDRCustomer' + str(random.randint(100))
else:
self.name = name
def DRorderToBU(self):
print("Time {1}: DR places order to BU to fill order for {0}".format(self.name, self.env.now))
yield S.Inv.BU_inv.get(P.DRorderLotSize)
yield self.env.timeout(P.DR_LT)
yield S.Inv.DR_inv.put(P.DRorderLotSize)
def ordertoDR(self):
startTime_DR = self.env.now
j = math.floor(self.env.now)
S.DR_Dem_day[j] += 1
print("Time {1}: {0} places order to DR".format(self.name, self.env.now))
if S.Inv.DR_inv.level < P.DRorderLotSize:
self.env.process( self.DRorderToBU() )
yield S.Inv.DR_inv.get(P.DRorderLotSize)
print("Time {1}: {0} receives order from DR".format(self.name, self.env.now ))
waitTime_DR = self.env.now - startTime_DR
print("{0} had to wait {1} days".format(self.name, waitTime_DR))
S.DRwaits.append( waitTime_DR )
class BUCustomer(object):
def __init__(self, env, name = ''):
self.env = env
self.action = self.env.process( self.ordertoBU() )
if (name == ''):
self.name = 'RandomBUCustomer' + str(random.randint(100))
else:
self.name = name
def BUorderToSupply(self):
print("Time {1}: BU places order to Supplier to fill order for {0}".format(self.name, self.env.now))
yield S.Inv.SP_inv.get(P.BUorderLotSize)
yield self.env.timeout(P.BU_LT)
yield S.Inv.BU_inv.put(P.BUorderLotSize)
def ordertoBU(self):
startTime_BU = self.env.now
i = math.floor(self.env.now)
S.BU_Dem_day[i] += 1
print("Time {1}: {0} places order to BU".format(self.name, self.env.now))
print(f"****** {S.Inv.BU_inv.level} ---- {P.BUorderLotSize}")
if S.Inv.BU_inv.level < P.BUorderLotSize:
self.env.process( self.BUorderToSupply() )
yield S.Inv.BU_inv.get(P.BUorderLotSize)
print("Time {1}: {0} receives order".format(self.name, self.env.now))
waitTime_BU = self.env.now - startTime_BU
print("{0} had to wait {1} days".format(self.name, waitTime_BU ))
S.BUwaits.append( waitTime_BU )
class DROrderProcessor(object):
def __init__(self, env, DRlambda):
self.env = env
self.action = env.process(self.DREntrance())
self.lam = DRlambda
def DREntrance(self):
while True:
interarrivalTime_DR = 1.6#np.random.exponential(1/P.externalToDRMean)
print(f"interarrivalTime_DR: {interarrivalTime_DR}")
print()
yield self.env.timeout( interarrivalTime_DR )
c = DRCustomer(self.env, name = "DRCustomer {0}".format(S.nDRCustomers))
S.nDRCustomers += 1
class BUOrderProcessor(object):
def __init__(self, env, BUlambda):
self.env = env
self.action = env.process(self.BUEntrance())
self.lam = BUlambda
def BUEntrance(self):
while True:
interarrivalTime_BU = 1#np.random.exponential(1/P.externalToBUMean)
yield self.env.timeout( interarrivalTime_BU )
c = BUCustomer(self.env, name = "BUCustomer {0}".format(S.nBUCustomers))
S.nBUCustomers += 1
randomSeed=123
random.seed(randomSeed)
S.DRwaits = []
S.BUwaits = []
envr = simpy.Environment()
BU = BUOrderProcessor(envr, BUlambda = P.externalToBUMean)
DR = DROrderProcessor(envr, DRlambda = P.externalToDRMean)
S.Inv = Inventory(envr)
envr.run(until = P.simulationTimeMax)

Answer 1

The indentation of the last line in the functions def monitor_BU_inv(self, env) and def monitor_DR_inv(self, env) is not correct. The line yield self.env.timeout(1) should not be inside the if-statement to avoid the endless loop when the if-statement evaluates to false.
def monitor_BU_inv(self, env):
while True:
if self.BU_inv.level <= P.ROP_BU:
print("Time {0}: BU inv...".format(self.env.now))
yield self.SP_inv.get(P.BU_Q)
print("Time {0}: Supply fills BU ...".format(self.env.now))
yield self.env.timeout(P.BU_LT)
print("Time {0}: BU replenishment...".format(self.env.now))
yield self.BU_inv.put(P.BU_Q)
print("Time {0}: BU replenishment ...".format(self.env.now))
yield self.env.timeout(1)