clock页面置换算法python实现
时间: 2023-11-26 22:05:49 浏览: 62
下面是一个简单的时钟页面置换算法的 Python 实现:
```python
class Page:
def __init__(self, page_id):
self.page_id = page_id
self.referenced = False
self.dirty = False
class Clock:
def __init__(self, frame_count):
self.frame_count = frame_count
self.frames = [None] * frame_count
self.hand = 0
def page_fault(self, page_id):
page = Page(page_id)
while True:
frame = self.frames[self.hand]
if frame is None:
self.frames[self.hand] = page
self.hand = (self.hand + 1) % self.frame_count
return True
elif frame.referenced:
frame.referenced = False
self.hand = (self.hand + 1) % self.frame_count
else:
if frame.dirty:
# write page back to disk
frame.dirty = False
self.frames[self.hand] = page
self.hand = (self.hand + 1) % self.frame_count
return True
def access_page(self, page_id, write=False):
for frame in self.frames:
if frame is not None and frame.page_id == page_id:
frame.referenced = True
if write:
frame.dirty = True
return True
return self.page_fault(page_id)
```
使用示例:
```python
clock = Clock(3)
clock.access_page(1) # page fault
clock.access_page(2) # page fault
clock.access_page(3) # page fault
clock.access_page(1) # hit
clock.access_page(4) # page fault
clock.access_page(2, write=True) # hit, mark as dirty
clock.access_page(3) # hit
```
该实现中,`Page` 类表示页面,有页面 ID、是否被引用(`referenced`)和是否被修改(`dirty`)三个属性。`Clock` 类表示时钟页面置换算法,有帧数(`frame_count`)、帧数组(`frames`)和手指位置(`hand`)三个属性。`page_fault` 方法模拟缺页中断,返回值表示是否发生了缺页中断;`access_page` 方法模拟访问页面,返回值表示是否命中。在访问页面时,如果页面已经在某个帧中,将其标记为被引用(如果是写操作,还要标记为被修改);否则,执行页面置换操作,将新页面放到手指位置,如果原帧被修改过,需要将其写回磁盘。
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