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""" centralserver.py A time-shared computer consists of a single central processing unit (CPU) and a number of terminals. The operator of each terminal `thinks' for a time (exponential, mean 100.0 sec) and then submits a task to the computer with a service time (exponential, mean 1.0 sec). The operator then remains idle until the task completes service and returns to him or her. The arriving tasks form a single FCFS queue in front of the CPU. Upon leaving the CPU a task is either finished (probability 0.20) and returns to its operator to begin another `think' time, or requires data from a disk drive (probability 0.8). If a task requires access to the disk, it joins a FCFS queue before service (service time at the disk, exponential, mean 1.39 sec). When finished with the disk, a task returns to the CPU queue again for another compute time (exp, mean 1.$ sec). the objective is to measure the throughput of the CPU (tasks per second) """ from SimPy.Simulation import * ## from SimPy.SimulationTrace import * import random as ran ## Model components ------------------------ class Task(Process): """ A computer task requires at least one use of the CPU and possibly accesses to a disk drive.""" completed = 0 rate = 0.0 def execute(self,maxCompletions): while Task.completed < maxCompletions: self.debug(" starts thinking") thinktime = ran.expovariate(1.0/MeanThinkTime) yield hold,self,thinktime self.debug(" request cpu") yield request,self,cpu self.debug(" got cpu") CPUtime=ran.expovariate(1.0/MeanCPUTime) yield hold,self,CPUtime yield release,self,cpu self.debug(" finish cpu") while ran.random() < pDisk: self.debug(" request disk") yield request,self,disk self.debug(" got disk") disktime=ran.expovariate(1.0/MeanDiskTime) yield hold,self,disktime self.debug(" finish disk") yield release,self,disk self.debug(" request cpu") yield request,self,cpu self.debug(" got cpu") CPUtime=ran.expovariate(1.0/MeanCPUTime) yield hold,self,CPUtime yield release,self,cpu Task.completed += 1 self.debug(" completed %d tasks"%(Task.completed,)) Task.rate = Task.completed/float(now()) def debug(self,message): FMT="%9.3f %s %s" if DEBUG: print FMT%(now(),self.name,message) ## Model ------------------------------ def main(): initialize() for i in range(Nterminals): t = Task(name="task"+`i`) activate(t,t.execute(MaxCompletions)) simulate(until = MaxrunTime) return (now(),Task.rate) ## Experiment data ------------------------- cpu = Resource(name='cpu') disk = Resource(name='disk') Nterminals = 3 ## Number of terminals = Tasks pDisk = 0.8 ## prob. of going to disk MeanThinkTime = 10.0 ## seconds MeanCPUTime = 1.0 ## seconds MeanDiskTime = 1.39 ## seconds ran.seed(111113333) MaxrunTime = 20000.0 MaxCompletions = 100 DEBUG = False ## Experiment result=main() ## Analysis/output ------------------------- print 'centralserver'

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    centralserver

... print '%7.4f: CPU rate = %7.4f tasks per second'%result |
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    842.7865: CPU rate =  0.1210 tasks per second