java实现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用于管理磁盘的一种算法，它的主要目的是优化磁盘的读写效率，提高磁盘的利用率。常见的磁盘调度算法有：FCFS（先来先服务）、SSTF（最短寻道时间优先）、SCAN（扫描算法）、C-SCAN（循环扫描算法）等。下面是 Java 实现磁盘调度算法的模拟实现及对比。

1. FCFS（先来先服务）

FCFS 算法是最简单的磁盘调度算法，它按照请求的先后顺序进行磁盘访问，即先请求的先被服务。Java 代码如下：

public class FCFS {
    public static void main(String[] args) {
        int[] requests = {40, 10, 35, 80, 25};
        int head = 50;
        int total = 0;
        for (int i = 0; i < requests.length; i++) {
            int distance = Math.abs(requests[i] - head);
            total += distance;
            head = requests[i];
        }
        System.out.println("Total Seek Time: " + total);
    }
}

2. SSTF（最短寻道时间优先）

SSTF 算法是按照当前磁头位置与请求队列中下一个请求的磁道距离最近，优先服务距离最短的请求。Java 代码如下：

public class SSTF {
    public static void main(String[] args) {
        int[] requests = {40, 10, 35, 80, 25};
        int head = 50;
        int total = 0;
        while (requests.length > 0) {
            int minDistance = Integer.MAX_VALUE;
            int minIndex = -1;
            for (int i = 0; i < requests.length; i++) {
                int distance = Math.abs(requests[i] - head);
                if (distance < minDistance) {
                    minDistance = distance;
                    minIndex = i;
                }
            }
            total += minDistance;
            head = requests[minIndex];
            int[] newRequests = new int[requests.length - 1];
            int j = 0;
            for (int i = 0; i < requests.length; i++) {
                if (i != minIndex) {
                    newRequests[j++] = requests[i];
                }
            }
            requests = newRequests;
        }
        System.out.println("Total Seek Time: " + total);
    }
}

3. SCAN（扫描算法）

SCAN 算法是按照磁头当前位置对请求进行扫描，服务请求队列中当前磁头位置下方的请求，直到最底端，然后改变磁头移动方向，服务上方的请求，直到最顶端，循环执行。Java 代码如下：

public class SCAN {
    public static void main(String[] args) {
        int[] requests = {40, 10, 35, 80, 25};
        int head = 50;
        int total = 0;
        int direction = 1; // 1: move to right, -1: move to left
        Arrays.sort(requests);
        int index = Arrays.binarySearch(requests, head);
        if (index < 0) {
            index = -(index + 1);
        }
        while (index < requests.length && index >= 0) {
            int distance = Math.abs(requests[index] - head);
            total += distance;
            head = requests[index];
            if (index == requests.length - 1) {
                direction = -1;
            }
            index += direction;
        }
        total += head;
        head = 0;
        while (index < requests.length && index >= 0) {
            int distance = Math.abs(requests[index] - head);
            total += distance;
            head = requests[index];
            index += direction;
        }
        System.out.println("Total Seek Time: " + total);
    }
}

4. C-SCAN（循环扫描算法）

C-SCAN 算法是类似 SCAN 算法，不同之处在于磁头到达磁盘底端时，不返回磁盘顶端，而是直接返回磁盘底端，形成一个循环执行的过程。Java 代码如下：

public class CSCAN {
    public static void main(String[] args) {
        int[] requests = {40, 10, 35, 80, 25};
        int head = 50;
        int total = 0;
        int direction = 1; // 1: move to right, -1: move to left
        Arrays.sort(requests);
        int index = Arrays.binarySearch(requests, head);
        if (index < 0) {
            index = -(index + 1);
        }
        while (index < requests.length && index >= 0) {
            int distance = Math.abs(requests[index] - head);
            total += distance;
            head = requests[index];
            if (index == requests.length - 1) {
                direction = -1;
                total += (requests[requests.length - 1] - requests[0]);
                head = 0;
                index = Arrays.binarySearch(requests, head);
                if (index < 0) {
                    index = -(index + 1);
                }
            } else {
                index += direction;
            }
        }
        System.out.println("Total Seek Time: " + total);
    }
}

以上就是 Java 实现磁盘调度算法的模拟实现及对比。根据不同的磁盘访问情况，选择不同的磁盘调度算法，可以有效提高磁盘的读写效率，提高系统的性能。