python中基于queue的打印机仿真算法

　　使用打印机的模型是queue中最经典的应用之一，这里就回顾一下queue在这里的使用方法和

起的重要作用。

　　为了仿真打印状态，这里需要把真实环境中的三个物理模型要建模出来，分别是：打印者，打印

任务，和处理队列。

　　首先打印者的实现如下所示：

class Printer:
        def __init__(self,ppm):
                self.page_rate = ppm
                self.current_task = None
                self.time_remaining = 0
        def tick(self):
                if self.current_task != None:
                        self.time_remaining = self.time_remaining - 1
                        if self.time_remaining <= 0:
                                self.current_task = None

        def busy(self):
                if self.current_task != None:
                        return True
                else:
                        return False

        def start_next(self,new_task):
                self.current_task = new_task
                self.time_remaining = new_task.get_pages() * 60 /self.page_rate

　　打印任务的代码实现：

import random

class Task:
        def __init__(self,time):
                self.timestamp = time
                self.pages = random.randrange(1,21)

        def get_stamp(self):
                return self.timestamp

        def get_pages(self):
                return self.pages

        def wait_time(self,current_time):
                return current_time - self.timestamp

　　任务处理：

import random
from queue import *
from Printer import *
from Task import *

print random.randrange(0, 101)

def simulation(num_seconds,pages_per_minute):

        lab_printer = Printer(pages_per_minute)
        print_queue = Queue()
        waiting_times = []

        for current_second in range(num_seconds):
                if new_print_task:
                        task = Task(current_second)
                        print_queue.enqueue(task)

                if(not lab_printer.busy()) and (not print_queue.is_empty()):
                        next_task = print_queue.dequeue()
                        waiting_times.append(next_task.wait_time(current_second))
                        lab_printer.start_next(next_task)

                lab_printer.tick()

        average_wait = sum(waiting_times) / len(waiting_times)
        print("Average Wait %6.2f secs %3d tasks remaining."%(average_wait,print_queue.size()))

def new_print_task():
        num = random.randrange(1,181)
        if num == 180:
                return True
        else:
                return False

for i in range(10):
        simulation(3600,5)

　　测试结果：

Average Wait 1874.00 secs 3572 tasks remaining.
Average Wait 1793.00 secs 3568 tasks remaining.
Average Wait 1700.00 secs 3572 tasks remaining.
Average Wait 1554.00 secs 3573 tasks remaining.
Average Wait 1831.00 secs 3570 tasks remaining.
Average Wait 1723.00 secs 3569 tasks remaining.
Average Wait 1745.00 secs 3568 tasks remaining.
Average Wait 1697.00 secs 3572 tasks remaining.
Average Wait 1596.00 secs 3569 tasks remaining.
Average Wait 1729.00 secs 3572 tasks remaining.