《操作系统》的实验代码。
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理解页置换算法

选择四种替换算法(0:LRU置换算法,1:改进的clock 页置换算法,2:工作集页置换算法,3:缺页率置换算法)中的一种来设计一个应用程序(可基于python, ruby, C, C++,LISP等)模拟实现,并给出测试。请参考page-replacement-policy.py 代码或独自实现。

###page-replacement-policy.py 代码

对模拟环境的抽象

虚拟页访问序列:addresses=1,2,3,4,0,5.... 这里面的最大值代表最大页号 页替换算法:policy=FIFO, LRU, OPT, CLOCK CLOCK算法用的bit位数:clockbits=1 物理页帧大小:cachesize 实际保持的也访问序列:addrList [1,2,3,4,0,5,...] 物理页帧内容:memory [] 初始为空 当前占用的页帧数量:count 初始位0

执行过程描述

for nStr in addrList:
       # for clock need to track the ref by reference bits
 
    	try:
			idx = memory.index(n)
			hits = hits + 1
			if policy == 'LRU' :
			    ....
		except:
	        idx = -1   #missing
            miss = miss + 1	
         
        if  idx=-1 and ...:  #missing and need replacement
         	#if phy page frames are full
         	     # for FIFO , LRU
              	 # replace victim item from memory  by " victim = memory.pop(0)" 
               
                 # for CLOCK
                 # find one page for the beginning of scan
                 # check ref[page] and update ref[page] 	 
                 # find a victim which ref[page]=0 by  memory.remove(page)
        else:
            # miss, but no replacement needed (phy page frame not full)
            # now add to memory         
            
        #update ref for clock replacement