题目二 磁盘调度算法的模拟实现及对比

好的，你的问题是磁盘调度算法的模拟实现及对比。磁盘调度算法是操作系统中的重要组成部分，用于优化磁盘访问的效率。常见的磁盘调度算法有FCFS、SSTF、SCAN、C-SCAN、LOOK和C-LOOK等。下面我将对这些算法进行简单介绍，并实现一个模拟程序进行对比。

1. FCFS（先来先服务）：按照磁盘访问的请求顺序进行调度，不考虑请求的距离和方向，可能导致产生大量寻道时间。

2. SSTF（最短寻道时间优先）：选择距离当前磁头最近的请求进行调度，可能会产生饥饿现象，即某些请求一直得不到满足。

3. SCAN（扫描算法）：磁头按照一定方向移动，直到到达最边缘时改变方向，只考虑当前方向上的请求，可能会产生逆向请求等待的现象。

4. C-SCAN（循环扫描算法）：与SCAN类似，但在到达最边缘时不改变方向，而是回到最开始的位置重新扫描。

5. LOOK（往返扫描算法）：与SCAN类似，但在到达最边缘时不改变方向，而是直接返回到另一端。

6. C-LOOK（循环往返扫描算法）：与LOOK类似，但在到达最边缘时不改变方向，而是回到最开始的位置重新扫描。

下面是一个磁盘调度算法的模拟程序示例：

import queue

def fcfs(queue, start):
    distance = 0
    current = start
    while not queue.empty():
        next = queue.get()
        distance += abs(next - current)
        current = next
    return distance

def sstf(queue, start):
    distance = 0
    current = start
    while not queue.empty():
        min_distance = float('inf')
        min_index = -1
        for i in range(queue.qsize()):
            next = queue.get()
            temp_distance = abs(next - current)
            if temp_distance < min_distance:
                min_distance = temp_distance
                min_index = next
            queue.put(next)
        distance += min_distance
        current = min_index
        queue.get(current)
    return distance

def scan(queue, start):
    direction = 1
    distance = 0
    current = start
    while not queue.empty():
        min_distance = float('inf')
        min_index = -1
        for i in range(queue.qsize()):
            next = queue.get()
            temp_distance = abs(next - current)
            if temp_distance < min_distance and (next - current) * direction >= 0:
                min_distance = temp_distance
                min_index = next
            queue.put(next)
        if min_index == -1:
            direction = -direction
            continue
        distance += min_distance
        current = min_index
        queue.get(current)
    return distance

def cscan(queue, start):
    direction = 1
    distance = 0
    current = start
    while not queue.empty():
        min_distance = float('inf')
        min_index = -1
        for i in range(queue.qsize()):
            next = queue.get()
            temp_distance = abs(next - current)
            if temp_distance < min_distance and (next - current) * direction >= 0:
                min_distance = temp_distance
                min_index = next
            queue.put(next)
        if min_index == -1:
            distance += abs(current - 0)
            current = 0
            direction = 1
            continue
        distance += min_distance
        current = min_index
        queue.get(current)
    return distance

def look(queue, start):
    direction = 1
    distance = 0
    current = start
    while not queue.empty():
        min_distance = float('inf')
        min_index = -1
        for i in range(queue.qsize()):
            next = queue.get()
            temp_distance = abs(next - current)
            if temp_distance < min_distance and (next - current) * direction >= 0:
                min_distance = temp_distance
                min_index = next
            queue.put(next)
        if min_index == -1:
            direction = -direction
            continue
        distance += min_distance
        current = min_index
        queue.get(current)
    return distance

def clook(queue, start):
    direction = 1
    distance = 0
    current = start
    while not queue.empty():
        min_distance = float('inf')
        min_index = -1
        for i in range(queue.qsize()):
            next = queue.get()
            temp_distance = abs(next - current)
            if temp_distance < min_distance and (next - current) * direction >= 0:
                min_distance = temp_distance
                min_index = next
            queue.put(next)
        if min_index == -1:
            distance += abs(current - 0)
            current = 0
            direction = 1
            continue
        distance += min_distance
        current = min_index
        queue.get(current)
    return distance

if __name__ == '__main__':
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('FCFS:', fcfs(queue, start))
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('SSTF:', sstf(queue, start))
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('SCAN:', scan(queue, start))
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('C-SCAN:', cscan(queue, start))
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('LOOK:', look(queue, start))
    queue = queue.Queue()
    for i in [98, 183, 37, 122, 14, 124, 65, 67]:
        queue.put(i)
    start = 53
    print('C-LOOK:', clook(queue, start))

这个程序可以模拟FCFS、SSTF、SCAN、C-SCAN、LOOK和C-LOOK等磁盘调度算法的执行过程，并计算出磁头的移动距离。在本程序中，模拟了一个磁盘请求队列，队列中的数字表示磁盘请求的磁道号，start表示磁头的初始位置。

以上就是磁盘调度算法的模拟实现及对比的介绍，希望对你有所帮助。