Simulation with Tracing ¶

Authors:	Klaus Muller <Muller@users.sourceforge.net>
SimPy release:	2.2
Web-site:	http://simpy.sourceforge.net/
Python-Version:	2.3 and later (not 3.0)
Revision:	$Revision: 347 $
Date:	$Date: 2009-07-17 21:26:16 +1200 (Fri, 17 Jul 2009) $

Contents

Simulation with Tracing

Introduction ¶

The tracing utility has been developed to give users insight into the dynamics of the execution of SimPy simulation programs. It can help developers with testing and users with explaining SimPy models to themselves and others (e.g. for documentation or teaching purposes).

Tracing SimPy programs ¶

Tracing any SimPy program is as simple as replacing:

from SimPy.Simulation import *

with:

from SimPy.SimulationTrace import *

This will give a complete trace of all the scheduling statements executed during the program’s execution.

An even nicer way is to replace this import by:

if __debug__:
        from SimPy.SimulationTrace import *
else:
        from SimPy.Simulation import *

This gives a trace during the development and debugging. If one then executes the program with python -O myprog.py, tracing is switched off, and no run-time overhead is incurred. (__debug__ is a global Python constant which is set to False by commandline options -O and -OO.)

For the same reason, any user call to trace methods should be written as:

if __debug__:
        trace.ttext("This will only show during debugging")

Here is an example (bank02.py from the Bank Tutorial):

from SimPy.SimulationTrace import * #   <== changed for tracing
##from SimPy.Simulation import *

""" Simulate a single customer """
class Customer(Process):
        """ Customer arrives, looks around and leaves """
        def __init__(self,name):
                Process.__init__(self)
                self.name = name

def visit(self,timeInBank=0):
        print "%7.4f %s: Here I am"%(now(),self.name)
        yield hold,self,timeInBank
        print "%7.4f %s: I must leave"%(now(),self.name)

def model():
        initialize()
        c1=Customer(name="Klaus")
        activate(c1,c1.visit(timeInBank=10.0),delay=5.0)
        c2=Customer(name="Tony")
        activate(c2,c2.visit(timeInBank=8.0),delay=2.0)
        c3=Customer(name="Evelyn")
        activate(c3,c3.visit(timeInBank=20.0),delay=12.0)
        simulate(until=400.0)

model()

This program produces the following output:

0 activate <Klaus> at time: 5.0 prior: 0
0 activate <Tony> at time: 2.0 prior: 0
0 activate <Evelyn> at time: 12.0 prior: 0
2.0000 Tony: Here I am
2.0 hold <Tony> delay: 8.0
5.0000 Klaus: Here I am
5.0 hold <Klaus> delay: 10.0
10.0000 Tony: I must leave
10.0 <Tony> terminated
12.0000 Evelyn: Here I am
12.0 hold <Evelyn> delay: 20.0
15.0000 Klaus: I must leave
15.0 <Klaus> terminated
32.0000 Evelyn: I must leave
32.0 <Evelyn> terminated

Another example:

""" bank09.py: Simulate customers arriving
    at random, using a Source requesting service
    from several clerks but a single queue
    with a random servicetime
"""
from __future__ import generators
from SimPy.SimulationTrace  import *
from random import Random

class Source(Process):
    """ Source generates customers randomly"""
    def __init__(self,seed=333):
        Process.__init__(self)
        self.SEED = seed

    def generate(self,number,interval):
        rv = Random(self.SEED)
        for i in range(number):
            c = Customer(name = "Customer%02d"%(i,))
            activate(c,c.visit(timeInBank=12.0))
            t = rv.expovariate(1.0/interval)
            yield hold,self,t

class Customer(Process):
    """ Customer arrives, is served and leaves """
    def __init__(self,name):
        Process.__init__(self)
        self.name = name

    def visit(self,timeInBank=0):
        arrive=now()
        print "%7.4f %s: Here I am "%(now(),self.name)
        yield request,self,counter
        wait=now()-arrive
        print "%7.4f %s: Waited %6.3f"%(now(),self.name,wait)
        tib = counterRV.expovariate(1.0/timeInBank)
        yield hold,self,tib
        yield release,self,counter
        print "%7.4f %s: Finished"%(now(),self.name)

def model(counterseed=3939393):
    global counter,counterRV
    counter = Resource(name="Clerk",capacity = 2) #Lcapacity
    counterRV = Random(counterseed)
    initialize()
    sourceseed = 1133
    source = Source(seed = sourceseed)
    activate(source,source.generate(5,10.0),0.0)
    simulate(until=400.0)

model()

This produces:

  0 activate <a_process> at time: 0 prior: 0
0 activate <Customer00> at time: 0 prior: 0
0 hold <a_process> delay: 8.73140489458
 0.0000 Customer00: Here I am
0 request <Customer00> <Clerk>  priority: default
. . .waitQ: []
. . .activeQ: ['Customer00']
 0.0000 Customer00: Waited  0.000
0 hold <Customer00> delay: 8.90355092634
8.73140489458 activate <Customer01> at time: 8.73140489458 prior: 0
8.73140489458 hold <a_process> delay: 8.76709801376
 8.7314 Customer01: Here I am
8.73140489458 request <Customer01> <Clerk>  priority: default
. . .waitQ: []
. . .activeQ: ['Customer00', 'Customer01']
 8.7314 Customer01: Waited  0.000
8.73140489458 hold <Customer01> delay: 21.6676883425
8.90355092634 release <Customer00> <Clerk>
. . .waitQ: []
. . .activeQ: ['Customer01']
 8.9036 Customer00: Finished
8.90355092634 <Customer00> terminated
17.4985029083 activate <Customer02> at time: 17.4985029083 prior: 0

. . . . .

And here is an example showing the trace output for compound yield statements:

from SimPy.SimulationTrace import *
class Client(Process):
    def __init__(self,name):
        Process.__init__(self,name)
    def getServed(self,tank):
        yield (get,self,tank,10),(hold,self,1.5)
        if self.acquired(tank):
            print "%s got 10 %s"%(self.name,tank.unitName)
        else:
            print "%s reneged"%self.name
class Filler(Process):
    def __init__(self,name):
        Process.__init__(self,name)
    def fill(self,tank):
        for i in range(3):
            yield hold,self,1
            yield put,self,tank,10
initialize()
tank=Level(name="Tank",unitName="gallons")
for i in range(2):
    c=Client("Client %s"%i)
    activate(c,c.getServed(tank))
f=Filler("Tanker")
activate(f,f.fill(tank))
simulate(until=10)

It produces this output:

0 get <Client 0>to get: 10 gallons from <Tank>  priority: default
. . .getQ: ['Client 0']
. . .putQ: []
. . .in buffer: 0
|| RENEGE COMMAND:
||  hold <Client 0> delay: 1.5
0 get <Client 1>to get: 10 gallons from <Tank>  priority: default
. . .getQ: ['Client 0', 'Client 1']
. . .putQ: []
. . .in buffer: 0
|| RENEGE COMMAND:
||  hold <Client 1> delay: 1.5
0 hold <Tanker> delay: 1
0 hold <RENEGE-hold for Client 0> delay: 1.5
0 hold <RENEGE-hold for Client 1> delay: 1.5
1 put <Tanker> to put: 10 gallons into <Tank>  priority: default
. . .getQ: ['Client 1']
. . .putQ: []
. . .in buffer: 0
1 hold <Tanker> delay: 1
Client 0 got 10 gallons
1 <Client 0> terminated
1.5 <RENEGE-hold for Client 1> terminated
Client 1 reneged
1.5 <Client 1> terminated
2 put <Tanker> to put: 10 gallons into <Tank>  priority: default
. . .getQ: []
. . .putQ: []
. . .in buffer: 10
2 hold <Tanker> delay: 1
3 put <Tanker> to put: 10 gallons into <Tank>  priority: default
. . .getQ: []
. . .putQ: []
. . .in buffer: 20
3 <Tanker> terminated

In this example, the Client entities are requesting 10 gallons from the tank (a Level object). If they can’t get them within 1.5 time units, they renege (give up waiting). The renege command parts of the compound statements (hold,self,1.5)are shown in the trace output with a prefix of || to indicate that they are being executed in parallel with the primary command part (get,self,tank,10). They are being executed by behind-the-scenes processes (e.g. RENEGE-hold for Client 0).

The trace contains all calls of scheduling statements (yield . . ., activate(), reactivate(), cancel() and also the termination of processes (at completion of all their scheduling statements). For yield request and yield release calls, it provides also the queue status (waiting customers in waitQ and customers being served in activeQ.

trace.tchange(): Changing the tracing ¶

trace is an instance of the Trace class defined in SimulationTrace.py. This gets automatically initialized upon importing SimulationTrace..

The tracing can be changed at runtime by calling trace.tchange() with one or more of the following named parameters:

start:

changes the tracing start time. Default is 0. Example: trace.tchange(start=222.2) to start tracing at simulation time 222.2.

end :

changes the tracing end time. Default is a very large number (hopefully past any simulation endtime you will ever use). Example: trace.tchange(end=33) to stop tracing at time 33.

toTrace:

changes the commands to be traced. Default is [“hold”,”activate”,”cancel”,”reactivate”,”passivate”,”request”, “release”,”interrupt”,”waitevent”,”queueevent”, “signal”,”waituntil”,”put”,”get”,”terminated”]. Value must be a list containing one or more of those values in the default. Note: “terminated” causes tracing of all process terminations. Example: trace.tchange(toTrace=[“hold”,”activate”]) traces only the yield hold and activate() statements.

outfile:

redirects the trace out put to a file (default is sys.stdout). Value must be a file object open for writing. Example: trace.tchange(outfile=open(r”c:\python25\bank02trace.txt”,”w”))

All these parameters can be combined. Example: trace.tchange(start=45.0,toTrace=[“terminated”]) will trace all process terminations from time 45.0 till the end of the simulation.

The changes become effective at the time trace.tchange() is called. This implies for example that, if the call trace.tchange(start=50) is made at time 100, it has no effect before now()==100.

treset(): Resetting the trace to default values ¶

The trace parameters can be reset to their default values by calling trace.treset().

trace.tstart(), trace.tstop(): Enabling/disabling the trace ¶

Calling trace.tstart() enables the tracing, and trace.tstop() disables it. Neither call changes any tracing parameters.

trace.ttext(): Annotating the trace ¶

The event-by-event trace output is already very useful in showing the sequence in which SimPy’s quasi-parallel processes are executed.

For documentation, publishing or teaching purposes, it is even more useful if the trace output can be intermingled with output which not only shows the command executed, but also contextual information such as the values of state variables. If one outputs the reason why a specific scheduling command is executed, the trace can give a natural language description of the simulation scenario.

For such in-line annotation, the trace.ttext(<string>) method is available. It provides a string which is output together with the trace of the next scheduling statement. This string is valid only for the scheduling statement following it.

Example:

class Bus(Process):
    def __init__(self,name):
        Process.__init__(self,name)

    def operate(self,repairduration=0):
        tripleft = 1000
        while tripleft > 0:
            trace.ttext("Try to go for %s"%tripleft)
            yield hold,self,tripleft
            if self.interrupted():
                tripleft=self.interruptLeft
                self.interruptReset()
                trace.ttext("Start repair taking %s time units"%repairduration)
                yield hold,self,repairduration
            else:
                break # no breakdown, ergo bus arrived
        trace.ttext("<%s> has arrived"%self.name)

class Breakdown(Process):
    def __init__(self,myBus):
        Process.__init__(self,name="Breakdown "+myBus.name)
        self.bus=myBus

    def breakBus(self,interval):

        while True:
            trace.ttext("Breakdown process waiting for %s"%interval)
            yield hold,self,interval
            if self.bus.terminated(): break
            trace.ttext("Breakdown of %s"%self.bus.name)
            self.interrupt(self.bus)

print"\n\n+++test_interrupt"
initialize()
b=Bus("Bus 1")
trace.ttext("Start %s"%b.name)
activate(b,b.operate(repairduration=20))
br=Breakdown(b)
trace.ttext("Start the Breakdown process for %s"%b.name)
activate(br,br.breakBus(200))
trace.start=100
print simulate(until=4000)

This produces:

0 activate <Bus 1> at time: 0 prior: 0
---- Start Bus 1
0 activate <Breakdown Bus 1> at time: 0 prior: 0
---- Start the Breakdown process for Bus 1
200 reactivate <Bus 1> time: 200 prior: 0
200 interrupt by: <Breakdown Bus 1> of: <Bus 1>
---- Breakdown of Bus 1
200 hold <Breakdown Bus 1> delay: 200
---- Breakdown process waiting for 200
200 hold <Bus 1> delay: 20
---- Start repair taking 20 time units
220 hold <Bus 1> delay: 800
---- Try to go for 800
400 reactivate <Bus 1> time: 400 prior: 0
400 interrupt by: <Breakdown Bus 1> of: <Bus 1>
---- Breakdown of Bus 1
400 hold <Breakdown Bus 1> delay: 200
---- Breakdown process waiting for 200
400 hold <Bus 1> delay: 20
---- Start repair taking 20 time units
420 hold <Bus 1> delay: 620

 . . . . .

The line starting with “—-” is the comment related to the command traced in the preceding output line.

Nice output of class instances ¶

After the import of SimPy.SimulationTrace, all instances of classes Process and Resource (and all their subclasses) have a nice string representation like so:

   >>> class Bus(Process):
...         def __init__(self,id):
...                 Process.__init__(self,name=id)
...                 self.typ="Bus"
...
>>> b=Bus("Line 15")
>>> b
<Instance of Bus, id 21860960:
     .name=Line 15
     .typ=Bus
>
>>>

This can be handy in statements like trace.ttext(“Status of %s”%b).

Simulation with Tracing ¶

Introduction ¶

Tracing SimPy programs ¶

trace.tchange(): Changing the tracing ¶

treset(): Resetting the trace to default values ¶

trace.tstart(), trace.tstop(): Enabling/disabling the trace ¶

trace.ttext(): Annotating the trace ¶

Nice output of class instances ¶

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