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# Simulation with Tracing

Authors: | Klaus Muller <Muller@users.sourceforge.net>
SimPy release: | 2.0.1
Web-site: | http://simpy.sourceforge.net/
Python-Version: | 2.3 and later (not 3.0)
Revision: | $Revision: 297 $
Date: | $Date: 2009-03-30 15:24:46 +0200 (Mo, 30 Mrz 2009) $

Contents

- Simulation with Tracing
  - Introduction
  - Tracing SimPy programs
  - trace.change(): 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

## 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 folowing 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.change(): 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).

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