磁盘调度算法代码
时间: 2025-05-13 20:48:30 浏览: 16
### 磁盘调度算法实现代码示例
以下是几种常见的磁盘调度算法的 Python 实现代码示例,包括 FCFS(先来先服务)、SSTF(最短寻道时间优先)、SCAN(电梯调度),以及针对 SSD 的简单调度逻辑。
#### 1. FCFS (First-Come First-Served)
FCFS 是一种简单的磁盘调度算法,按照请求到达顺序依次处理 I/O 请求。
```python
def fcfs(requests, head):
total_movement = 0
sequence = [head]
for track in requests:
total_movement += abs(track - head)
head = track
sequence.append(head)
return sequence, total_movement
requests = [98, 183, 37, 122, 14, 124, 65, 67]
current_head = 53
sequence_fcfs, movement_fcfs = fcfs(requests, current_head)
print(f"FCFS Sequence: {sequence_fcfs}")
print(f"Total Head Movement (FCFS): {movement_fcfs} cylinders")
```
上述代码实现了 FCFS 调度算法,并返回磁头的服务序列和总移动距离[^1]。
---
#### 2. SSTF (Shortest Seek Time First)
SSTF 始终选择离当前磁头最近的磁道作为下一个目标,从而减少平均等待时间和磁头移动距离。
```python
import sys
def sstf(requests, head):
total_movement = 0
sequence = []
remaining_requests = list(requests)
while remaining_requests:
closest_track = min(remaining_requests, key=lambda x: abs(x - head))
total_movement += abs(closest_track - head)
head = closest_track
sequence.append(head)
remaining_requests.remove(closest_track)
return sequence, total_movement
sequence_sstf, movement_sstf = sstf(requests, current_head)
print(f"SSTF Sequence: {sequence_sstf}")
print(f"Total Head Movement (SSTF): {movement_sstf} cylinders")
```
此代码通过动态查找最近的目标磁道,减少了不必要的远距离跳转[^2]。
---
#### 3. SCAN (Elevator Algorithm)
SCAN 算法模拟电梯运行方式,在某一方向上逐次访问所有待处理的磁道,直到达到边界后再反向扫描。
```python
def scan(requests, head, max_cylinder=199, direction="right"):
total_movement = 0
sequence = []
sorted_requests = sorted(list(set([head] + requests)))
index = sorted_requests.index(head)
if direction == "right":
# Move to the end of disk first
for i in range(index, len(sorted_requests)):
sequence.append(sorted_requests[i])
total_movement += abs(sorted_requests[i] - head) if not sequence[:-1] else abs(sorted_requests[i] - sequence[-2])
head = sorted_requests[i]
# Reverse and move back from high cylinder number to low
for j in range(len(sorted_requests)-2, -1, -1):
if sorted_requests[j] > head:
continue
sequence.append(sorted_requests[j])
total_movement += abs(sorted_requests[j] - head)
head = sorted_requests[j]
elif direction == "left":
# Move towards lower numbered tracks
for k in range(index, -1, -1):
sequence.append(sorted_requests[k])
total_movement += abs(sorted_requests[k] - head) if not sequence[:-1] else abs(sorted_requests[k] - sequence[-2])
head = sorted_requests[k]
# Then reverse again moving up
for l in range(1, len(sorted_requests)):
if sorted_requests[l] < head:
continue
sequence.append(sorted_requests[l])
total_movement += abs(sorted_requests[l] - head)
head = sorted_requests[l]
return sequence, total_movement
sequence_scan_right, movement_scan_right = scan(requests, current_head, direction="right")
print(f"SCAN Right Sequence: {sequence_scan_right}")
print(f"Total Head Movement (SCAN Right): {movement_scan_right} cylinders")
```
该代码展示了如何基于指定的方向执行 SCAN 算法,适用于 HDD 中的数据读取场景[^3]。
---
#### 4. SSD 调度简化版
由于 SSD 不涉及物理磁头移动,因此其调度更关注于均衡磨损和提高并发性能。下面是一个简化的伪代码:
```python
def ssd_scheduler(requests):
"""
对于 SSD 来说,不存在传统意义上的磁头移动,
所以可以采用队列机制或者多通道并行处理的方式。
这里仅展示一个基本的 FIFO 处理流程。
"""
processed_sequence = []
for request in requests:
processed_sequence.append(request)
return processed_sequence
ssd_sequence = ssd_scheduler(requests)
print(f"SSD Scheduler Sequence: {ssd_sequence}")
```
对于现代固态硬盘而言,内部控制器会自动管理数据分布与垃圾回收等问题,外部应用层无需过多干预具体的低级调度细节[^4]。
---
### 总结
以上分别介绍了四种不同的磁盘/存储设备调度方法及其对应的 Python 实现方案。每种策略都有各自的优缺点,实际部署时需依据具体硬件特性和负载特征做出合理选择。
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