[Operating system] Experiment 3: Document Management (disk scheduling)

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Note : This article documents WHUT- Computer College - courses on operating system　Experiment 3: Document Management (disk scheduling)

Paper come Zhongjue, practice is essential to be aware of the matter!

 

1. Experiment: 

• Experimental preparation: master disk scheduling relevant content, in-depth understanding of the structure and disk scheduling algorithm.

• Experiment: analog implementation, disk scheduling function

• Specific requirements:

• - Choose one high-level computer programming language
• - Select 2-3 Zhong disk scheduling algorithm (first come, first served, shortest seek time priority, elevator algorithm) analog implementation Disk Scheduling
• - be able to enter the current position of the magnetic head, the head moving direction, the track access request sequences and the like
• - be able to display the disk scheduling result (the head track number of sequential access order), and calculates the total number of tracks the head is moved, and the like 

 

2, run shot:

 

3, the source code:

 The experiment is not difficult, the code recommends that reference, is not recommended to fully Ctrl + C and Ctrl + V! ! !

#include <iostream>
#include <cmath>
#include <stack>
using namespace std;

int trackNum = 8;//访问磁道数：8
struct List {
	int track;//访问磁道
	bool isVisited = false;//磁道状态
};
List list[8];

int path[8];//访问顺序
int totalTrack = 0; //磁头走过的总道数

void initList();//初始化

/*先来先服务*/
void FCFS(int start) {
	/*添加：初始化list  */
	initList();

	totalTrack = 0;//清空
	for (int i = 0; i < trackNum; i++) {
		if (i == 0) {
			totalTrack += abs(list[i].track - start);
		}
		else {
			totalTrack += abs(list[i].track - list[i-1].track);
		}
		list[i].isVisited = true;//修改状态为已被访问
		path[i] = i;//访问节点顺序
	}

	//输出顺序
	cout << "走道顺序：" << start << " → ";
	for (int i = 0; i < trackNum-1; i++) {
		cout<<list[path[i]].track<< " → ";
	}
	cout << list[path[trackNum-1]].track << endl;

	//输出移动总磁道数
	cout << "磁头移动总磁道数：" << totalTrack << endl;
	cout << endl;
}

/*最短寻道优先*/
int closest(int now);
void SSTF(int start) {
	/*添加：初始化list 的节点访问状态 */
	initList();

	totalTrack = 0;//清空
	for (int i = 0; i < trackNum; i++) {
		if (i == 0) {
			totalTrack += abs(list[closest(start)].track - start);
			path[i] = closest(start);
		}
		else {
			totalTrack += abs(list[closest(list[path[i - 1]].track)].track - list[path[i - 1]].track);
			path[i] = closest(list[path[i - 1]].track);
		}
		list[path[i]].isVisited = true;//修改状态为已被访问
	}
	
	//输出顺序
	cout << "走道顺序：" << start << " → ";
	for (int i = 0; i < trackNum - 1; i++) {
		cout << list[path[i]].track << " → ";
	}
	cout << list[path[trackNum-1]].track << endl;

	//输出移动总磁道数
	cout << "磁头移动总磁道数：" << totalTrack << endl << endl;

}
//寻找距离当前磁道最近的磁道，返回当前磁道的编号
int closest(int now) {
	int min = 0x7FFFFFFF;
	int flag = -1;
	for (int i = 0; i < trackNum; i++) {
		if (list[i].isVisited == false && abs(list[i].track - now) < min) {
			min = abs(list[i].track - now);
			flag = i;
		}
	}
	return flag;
}

/*扫描算法（电梯算法）*///direct：方向，左为0，右为其他；
void SCAN(int start,int direct) {
	/*添加：初始化list 的节点访问状态 */
	initList();

	//排序，从小到大
	for (int i = 0; i < trackNum; i++) {
		int flag = -1;
		int  min = 0x7FFFFFFF;

		for (int j = 0; j < trackNum; j++) {
			if (list[j].track < min &&list[j].isVisited == false) {
				min = list[j].track;
				flag = j;
			}
		}
		path[i] = flag;
		list[flag].isVisited = true;
	}

	totalTrack = 0;//清空

	//如果读写头起始位置比最小磁道还小
	if (start<=list[path[0]].track) {
		totalTrack = list[path[trackNum]].track - start;

		cout << "走道顺序：" << start << " → ";
		for (int i = 0; i < trackNum - 1; i++) {
			cout << list[path[i]].track << " → ";
		}
		cout << list[path[trackNum-1]].track << endl;
	}

	//如果读写头起始位置比最大磁道还大
	else if (start >= list[path[trackNum-1]].track) {
		totalTrack = start - list[path[0]].track;

		cout << "走道顺序：" << start << " → ";
		for (int i = trackNum - 1; i > 0; i--) {
			cout << list[path[i]].track << " → ";
		}
		cout << list[path[0]].track << endl;

	}
	//如果读写头起始位置 介于最小最大之间
	else{		

		stack<int> tempstack;
		cout << "走道顺序：" << start << " → ";
		int flag = 0;
		for (int i = 0; i < trackNum; i++) {
			if (list[path[i]].track <= start) {
				tempstack.push(list[path[i]].track);
				flag = i;
			}
		}
		//先向左
		if (direct == 0) {
			totalTrack = start - list[path[0]].track + list[path[trackNum - 1]].track - list[path[0]].track;

			while (!tempstack.empty()){
				cout << tempstack.top() << " → ";
				tempstack.pop();
			}
			for (int i = flag + 1; i < trackNum-1; i++) {
				cout << list[path[i]].track << " → ";
			}
			cout << list[path[trackNum-1]].track << endl;
		}
		//向右走
		else {
			totalTrack = list[path[trackNum - 1]].track - list[path[0]].track + list[path[trackNum - 1]].track - start;

			for (int i = flag + 1; i < trackNum; i++) {
				cout << list[path[i]].track << " → ";
			}
			while (!tempstack.empty()) {
				cout << tempstack.top();
				tempstack.pop();
				if (!tempstack.empty())
					cout<< " → ";
			}
			cout << endl;
		}
	}

	//输出移动总磁道数
	cout << "磁头移动总磁道数：" << totalTrack << endl << endl;
}

void initList() {
	for (int i = 0; i < trackNum; i++) {
		list[i].isVisited = false;
	}
}

int main() {

	cout << "请输入磁道访问请求序列：";
	for (int i = 0; i < trackNum; i++) {
		cin >> list[i].track;
	}
	cout << endl;
	while (1)	{
		cout << "　１：先来先服务算法\n　２：最短寻道时间优先算法\n　３：电梯算法\n其他：退出" << endl;
		cout << "请输入您选择的算法：";
		int choose, start, direct;
		cin >> choose;
		if (choose != 1 && choose != 2 && choose != 3)
			break;

		cout << "请输入初始磁头位置：";
		cin >> start;
		switch (choose)
		{
		case 1:
			FCFS(start);
			break;

		case 2:
			SSTF(start);
			break;

		case 3:
			cout << "０　：向左移动\n其他：向右移动\n请输入磁头移动方向：";
			cin >> direct;
			SCAN(start, direct);
			break;

		default:
			break;
		}
	}
}