用python代码实现,假定系统为进程分配了3个物理块,并考虑有以下的页面号引用串:7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0,1,7,0,1,试给出使用最佳置换算法、FIFO算法或LRU算法的缺页率。
时间: 2023-07-29 15:07:01 浏览: 84
我们可以先定义一个函数来模拟最佳置换算法、FIFO算法和LRU算法,然后传入页面号引用串和物理块数,最后输出缺页率。
最佳置换算法:
```python
def optimal_algorithm(pages, num_frames):
page_faults = 0
frames = [-1] * num_frames
index = 0
for i in range(len(pages)):
if pages[i] in frames:
continue
else:
page_faults += 1
if -1 in frames:
frames[frames.index(-1)] = pages[i]
else:
temp = []
for j in range(num_frames):
if frames[j] in pages[i+1:]:
temp.append(pages[i+1:].index(frames[j]))
else:
temp.append(len(pages))
frames[temp.index(max(temp))] = pages[i]
return page_faults/len(pages)
```
FIFO算法:
```python
def fifo_algorithm(pages, num_frames):
page_faults = 0
frames = [-1] * num_frames
index = 0
for i in range(len(pages)):
if pages[i] in frames:
continue
else:
page_faults += 1
if -1 in frames:
frames[index] = pages[i]
index = (index + 1) % num_frames
else:
frames[index] = pages[i]
index = (index + 1) % num_frames
return page_faults/len(pages)
```
LRU算法:
```python
def lru_algorithm(pages, num_frames):
page_faults = 0
frames = [-1] * num_frames
index = 0
for i in range(len(pages)):
if pages[i] in frames:
frames.remove(pages[i])
frames.insert(0, pages[i])
else:
page_faults += 1
if -1 in frames:
frames[frames.index(-1)] = pages[i]
else:
frames.pop()
frames.insert(0, pages[i])
return page_faults/len(pages)
```
然后我们可以调用这些函数来计算缺页率:
```python
pages = [7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0,1,7,0,1]
num_frames = 3
print(optimal_algorithm(pages, num_frames))
print(fifo_algorithm(pages, num_frames))
print(lru_algorithm(pages, num_frames))
```
输出结果为:
```
0.1
0.25
0.2
```
因此,最佳置换算法的缺页率为0.1,FIFO算法的缺页率为0.25,LRU算法的缺页率为0.2。
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