Authors: |
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SimPy version: | 1.8 |
Web-site: | |
Python-Version: | 2.3, 2.4, 2.5 |
Revision: | $Revision: 1.1.1.12 $ |
Date: | $Date: 2007/01/30 18:18:25 $ |
This manual describes SimulationRT, a SimPy module which supports synchronizing the execution of simulation models with real (wallclock) time.
A capability has been added to SimulationRT to change the model execution speed during the run of a simulation model. This is useful for e.g. a simulation GUI which shows the progress of the simulation run and allows the user to interactively slow down or accelerate the model execution.
SimulationRT is based on an idea by Geoff Jarrad of CSIRO (Australia). He contributed a lot to its development and testing on Windows and Unix.
The code for the adjustment of the execution speed during the simulation run was contributed by Robert C. Ramsdell.
SimulationRT allows synchronizing simulation time and real (wallclock) time. This capability can be used to implement e.g. interactive game applications or to demonstrate a model's execution in real time.
It is identical to Simulation, except for the simulate function which takes an additional parameter controlling real-time execution speed.
Here is an example:
## RealTimeFireworks.py from __future__ import generators from SimPy.SimulationRT import * from random import * import time class Launcher(Process): def launch(self): while True: print "Launch at %.1f; wallclock: %s"%(now(),time.clock()-startTime) yield hold,self,uniform(1,maxFlightTime) print "Boom!!! Aaaah!! at %.1f; wallclock: %s"%(now(),time.clock()-startTime) def model(): initialize() for i in range(nrLaunchers): lau=Launcher() activate(lau,lau.launch()) simulate(real_time=True,rel_speed=1,until=20) ##unit sim time = 1 sec clock nrLaunchers=2 maxFlightTime=5.0 startTime=time.clock() model()
rels_speed=1 sets the synchronization so that 1 simulation time unit is executed in approximately 1 second of wallclock time. Run under Python 2.2.2 on a Windows XP-box (1.7 GHz), this output resulted over about 18 seconds of wallclock time:
Launch at 0.0; wallclock: 0.000195555580376 Launch at 0.0; wallclock: 0.00190107960634 Boom!!! Aaaah!! at 1.8; wallclock: 1.78082661344 Launch at 1.8; wallclock: 1.78274501368 Boom!!! Aaaah!! at 2.8; wallclock: 2.84245930698 Launch at 2.8; wallclock: 2.84435982785 Boom!!! Aaaah!! at 4.1; wallclock: 4.08443978215 Launch at 4.1; wallclock: 4.09004328762 Boom!!! Aaaah!! at 5.2; wallclock: 5.14561822801 Launch at 5.2; wallclock: 5.14878203794 Boom!!! Aaaah!! at 7.0; wallclock: 6.99845622838 Launch at 7.0; wallclock: 7.00175357483 Boom!!! Aaaah!! at 7.4; wallclock: 7.39919794276 Launch at 7.4; wallclock: 7.40245282571 Boom!!! Aaaah!! at 9.7; wallclock: 9.69250728794 Launch at 9.7; wallclock: 9.69912935862 Boom!!! Aaaah!! at 10.6; wallclock: 10.5938587167 Launch at 10.6; wallclock: 10.6006140445 Boom!!! Aaaah!! at 13.8; wallclock: 13.8082362423 Launch at 13.8; wallclock: 13.8134877477 Boom!!! Aaaah!! at 14.1; wallclock: 14.1385670525 Launch at 14.1; wallclock: 14.1438146468 Boom!!! Aaaah!! at 16.4; wallclock: 16.411963811 Launch at 16.4; wallclock: 16.4172373863 Boom!!! Aaaah!! at 17.1; wallclock: 17.1429980626 Launch at 17.1; wallclock: 17.1482308506 Boom!!! Aaaah!! at 18.1; wallclock: 18.0742063586 Launch at 18.1; wallclock: 18.0794469688
Clearly, the wallclock time does not deviate significantly from the simulation time.
By calling method rtset with a parameter, the ratio simulated time to wallclock time can be changed during a run.
Here is an example:
"""variableTimeRatio.py Shows the SimulationRT capability to change the ratio simulation time to wallclock time during the run of a simulation. """ from SimulationRT import * class Changer(Process): def change(self,when,rat): global ratio yield hold,self,when rtset(rat) ratio=rat class Series(Process): def tick(self,nrTicks): oldratio=ratio for i in range(nrTicks): tLastSim=now() tLastWallclock=wallclock() yield hold,self,1 diffSim=now()-tLastSim diffWall=wallclock()-tLastWallclock print "now(): %s, sim. time elapsed: %s, wall clock elapsed: "\ "%6.3f, sim/wall time ratio: %6.3f"\ %(now(),diffSim,diffWall,diffSim/diffWall) if not ratio==oldratio: print "At simulation time %s: ratio simulation/wallclock "\ "time now changed to %s"%(now(),ratio) oldratio=ratio initialize() ticks=15 s=Series() activate(s,s.tick(nrTicks=ticks)) c=Changer() activate(c,c.change(5,5)) c=Changer() activate(c,c.change(10,0.1)) ratio=1 print "At simulation time %s: set ratio simulation/wallclock time to %s"\ %(now(),ratio) simulate(until=100,real_time=True,rel_speed=ratio)
The program changes the time ratio twice, at simulation times 5 and 10.
When run on a Windows XP computer under Python 2.3, this results in this output:
At simulation time 0: set ratio simulation/wallclock time to 1 now(): 1, sim. time elapsed: 1, wall clock elapsed: 0.999, sim/wall time ratio: 1.001 now(): 2, sim. time elapsed: 1, wall clock elapsed: 0.999, sim/wall time ratio: 1.001 now(): 3, sim. time elapsed: 1, wall clock elapsed: 0.999, sim/wall time ratio: 1.001 now(): 4, sim. time elapsed: 1, wall clock elapsed: 0.999, sim/wall time ratio: 1.001 now(): 5, sim. time elapsed: 1, wall clock elapsed: 0.999, sim/wall time ratio: 1.001 At simulation time 5: ratio simulation/wallclock time now changed to 5 now(): 6, sim. time elapsed: 1, wall clock elapsed: 0.199, sim/wall time ratio: 5.021 now(): 7, sim. time elapsed: 1, wall clock elapsed: 0.199, sim/wall time ratio: 5.020 now(): 8, sim. time elapsed: 1, wall clock elapsed: 0.199, sim/wall time ratio: 5.020 now(): 9, sim. time elapsed: 1, wall clock elapsed: 0.199, sim/wall time ratio: 5.020 now(): 10, sim. time elapsed: 1, wall clock elapsed: 0.199, sim/wall time ratio: 5.019 At simulation time 10: ratio simulation/wallclock time now changed to 0.1 now(): 11, sim. time elapsed: 1, wall clock elapsed: 10.001, sim/wall time ratio: 0.100 now(): 12, sim. time elapsed: 1, wall clock elapsed: 10.001, sim/wall time ratio: 0.100 now(): 13, sim. time elapsed: 1, wall clock elapsed: 10.001, sim/wall time ratio: 0.100 now(): 14, sim. time elapsed: 1, wall clock elapsed: 10.001, sim/wall time ratio: 0.100 now(): 15, sim. time elapsed: 1, wall clock elapsed: 10.001, sim/wall time ratio: 0.100
This module works much better under Windows than under Unix or Linux, i.e., it gives much closer synchronization. Unfortunately, the handling of time in Python is not platform-independent at all. Here is a quote from the documentation of the time module:
"clock() On Unix, return the current processor time as a floating point number expressed in seconds. The precision, and in fact the very definition of the meaning of ``processor time'' , depends on that of the C function of the same name, but in any case, this is the function to use for benchmarking Python or timing algorithms. On Windows, this function returns wall-clock seconds elapsed since the first call to this function, as a floating point number, based on the Win32 function QueryPerformanceCounter(). The resolution is typically better than one microsecond. "
Basically, SimulationStep has the same API as Simulation, but with:
- a change in the definition of simulate, and
- an additional method to change execution speed during a simulation run.
Executes the simulation model.
Call:
simulate(<optional parameters>)
Changes the ratio simulation time over wall clock time.
Call:
rtset(<new ratio>)
$Revision: 1.1.1.12 $ $Date: 2007/01/30 18:18:25 $ kgm