磁盘调度算法代码

### 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。