java实现磁道算法

题目描述

设磁盘的磁道数为M；假设多个进程将随机的进行磁盘访问，每个进程的磁道访问序列可随机产生；如何用java语言来实现先来先服务算法（FCFS）、最短寻道时间优先算法（SSTF）、扫描算法（SCAN）、循环扫描算法（CSCAN）

代码案例

下面是使用 Java 语言实现磁盘调度算法的示例代码。

首先，我们定义一个DiskScheduler类，其中包含先来先服务算法（FCFS）、最短寻道时间优先算法（SSTF）、扫描算法（SCAN）和循环扫描算法（CSCAN）的实现方法。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class DiskScheduler {
    private static final int MAX_TRACK = 200;  // 磁道总数

    // 先来先服务算法（FCFS）
    public void fcfs(List<Integer> requests, int initialPosition) {
        System.out.println("FCFS:");
        int totalMovement = 0;

        for (int i = 0; i < requests.size(); i++) {
            int currentPosition = i == 0 ? initialPosition : requests.get(i - 1);
            int nextPosition = requests.get(i);
            int movement = Math.abs(nextPosition - currentPosition);
            totalMovement += movement;

            System.out.printf("Move from %d to %d, distance = %d\n", currentPosition, nextPosition, movement);
        }

        System.out.println("Total head movement: " + totalMovement);
    }

    // 最短寻道时间优先算法（SSTF）
    public void sstf(List<Integer> requests, int initialPosition) {
        System.out.println("SSTF:");

        List<Integer> sortedRequests = new ArrayList<>(requests);
        Collections.sort(sortedRequests);

        int currentPosition = initialPosition;
        int totalMovement = 0;

        while (!sortedRequests.isEmpty()) {
            int closestIndex = 0;
            int closestDistance = Integer.MAX_VALUE;

            for (int i = 0; i < sortedRequests.size(); i++) {
                int distance = Math.abs(sortedRequests.get(i) - currentPosition);
                if (distance < closestDistance) {
                    closestIndex = i;
                    closestDistance = distance;
                }
            }

            int nextPosition = sortedRequests.remove(closestIndex);
            int movement = Math.abs(nextPosition - currentPosition);
            totalMovement += movement;

            System.out.printf("Move from %d to %d, distance = %d\n", currentPosition, nextPosition, movement);
            currentPosition = nextPosition;
        }

        System.out.println("Total head movement: " + totalMovement);
    }

    // 扫描算法（SCAN）
    public void scan(List<Integer> requests, int initialPosition) {
        System.out.println("SCAN:");
        int totalMovement = 0;

        List<Integer> sortedRequests = new ArrayList<>(requests);
        Collections.sort(sortedRequests);

        int currentPosition = initialPosition;
        int direction = 1;  // 1 for moving towards the higher tracks, -1 for moving towards the lower tracks

        while (!sortedRequests.isEmpty()) {
            int closestIndex = -1;
            int closestDistance = Integer.MAX_VALUE;

            for (int i = 0; i < sortedRequests.size(); i++) {
                int distance = Math.abs(sortedRequests.get(i) - currentPosition);
                if (distance < closestDistance && (sortedRequests.get(i) - currentPosition) * direction >= 0) {
                    closestIndex = i;
                    closestDistance = distance;
                }
            }

            if (closestIndex == -1) {
                // Change direction when there are no more requests in the current direction
                direction *= -1;
                continue;
            }

            int nextPosition = sortedRequests.remove(closestIndex);
            int movement = Math.abs(nextPosition - currentPosition);
            totalMovement += movement;

            System.out.printf("Move from %d to %d, distance = %d\n", currentPosition, nextPosition, movement);
            currentPosition = nextPosition;
        }

        System.out.println("Total head movement: " + totalMovement);
    }

    // 循环扫描算法（CSCAN）
    public void cscan(List<Integer> requests, int initialPosition) {
        System.out.println("CSCAN:");
        int totalMovement = 0;

        List<Integer> sortedRequests = new ArrayList<>(requests);
        Collections.sort(sortedRequests);

        int currentPosition = initialPosition;
        int direction = 1;  // 1 for moving towards the higher tracks, -1 for moving towards the lower tracks

        while (!sortedRequests.isEmpty()) {
            int closestIndex = -1;
            int closestDistance = Integer.MAX_VALUE;

            for (int i = 0; i < sortedRequests.size(); i++) {
                int distance = Math.abs(sortedRequests.get(i) - currentPosition);
                if (distance < closestDistance && (sortedRequests.get(i) - currentPosition) * direction >= 0) {
                    closestIndex = i;
                    closestDistance = distance;
                }
            }

            if (closestIndex == -1) {
                // Move to the edge track and change direction
                if (direction > 0) {
                    totalMovement += MAX_TRACK - currentPosition;
                    currentPosition = 0;
                } else {
                    totalMovement += currentPosition;
                    currentPosition = MAX_TRACK;
                }
                direction *= -1;
                continue;
            }

            int nextPosition = sortedRequests.remove(closestIndex);
            int movement = Math.abs(nextPosition - currentPosition);
            totalMovement += movement;

            System.out.printf("Move from %d to %d, distance = %d\n", currentPosition, nextPosition, movement);
            currentPosition = nextPosition;
        }

        System.out.println("Total head movement: " + totalMovement);
    }

    public static void main(String[] args) {
        DiskScheduler diskScheduler = new DiskScheduler();

        // 生成随机的磁道访问序列
        List<Integer> requests = new ArrayList<>();
        for (int i = 0; i < 50; i++) {
            requests.add((int) (Math.random() * MAX_TRACK));
        }

        int initialPosition = (int) (Math.random() * MAX_TRACK);

        diskScheduler.fcfs(requests, initialPosition);
        System.out.println();
        diskScheduler.sstf(requests, initialPosition);
        System.out.println();
        diskScheduler.scan(requests, initialPosition);
        System.out.println();
        diskScheduler.cscan(requests, initialPosition);
    }
}

在示例代码中，我们使用DiskScheduler类来实现四种磁盘调度算法：先来先服务算法（FCFS）、最短寻道时间优先算法（SSTF）、扫描算法（SCAN）和循环扫描算法（CSCAN）。

我们通过main方法生成了一个随机的磁道访问序列，并随机选择了一个初始位置。然后，我们分别调用各个磁盘调度算法的方法，并输出每次移动的轨道和总的头移动次数。

你可以根据需要修改和扩展这些算法以适应特定的问题和场景。