〔OS〕磁盘调度算法

C++ 实现的 FCFS、SSTF、SCAN 和 CSCAN 四种磁盘调度算法。

/**磁盘调度算法**/
/**by Darius**/
#include <iostream>
#include <algorithm>
#include <cstdio>

#define MAX 1000
using namespace std;

//求平均寻道长度
double average(int *length, int n){
	double sum=0;
	int i;
	for(i=0;i<n;i++)
		sum+=length[i];
	return sum/n;
}

//先来先服务寻道算法
void First_come_first_server(int *a, int n, int now) {
    int i, k=0;
    int t = n;
    int next[MAX], length[MAX];
    int visit[MAX] = {0};
    while(t--)
    {
        for(i = 0;i < n;i++) {
            if(visit[i])
                continue;
            else {
                length[k] = abs(a[i] - now);
                next[k++] = a[i];
                visit[i] = 1;
                now = a[i];
            }
        }
    }
    cout << endl << "下一个磁道  " << "移动距离" << endl;
    for (i = 0; i < n; i++)
        cout << next[i] << "           " << length[i] << endl;
    cout << "平均寻道长度:";
    printf("%.2f

", average(length, n));
}
//最短寻道时间优先算法
void Shortest_seek_time_first(int *a, int n, int now) {
    int i, min, k = 0;
    int flag;//最短路径的下标
    int t = n;
    int next[MAX], length[MAX];
    int visit[MAX] = {0};//访问数组，已经访问过的为1
    //寻道n次
    while (t--) {
        min = 999999;
        //找没有访问过的中最近的
        for (i = 0; i < n; i++) {
            if (visit[i])
                continue;
            if (abs(a[i] - now) < min) {
                flag = i;
                min = abs(a[i] - now);
            }
        }
        length[k] = min;//移动的距离
        next[k++] = a[flag];//下一个被访问的磁道号
        visit[flag] = 1;//访问过的置1
        now = a[flag];//磁道移动到当前位置
    }
    cout << endl << "下一个磁道  " << "移动距离" << endl;
    for (i = 0; i < n; i++)
        cout << next[i] << "           " << length[i] << endl;
    cout << "平均寻道长度:";
    printf("%.2f

", average(length, n));
}

//扫描算法
void Scan(int *a, int n, int now){
	int i,flag=0,k=0;
	int next[MAX],length[MAX];
	sort(a,a+n);//从小到大排序
	//寻找开始磁道
	for(i=0;i<n;i++){
		if(a[i]>=now){
			flag=i;
			break;
		}
	}

	//往递增方向访问
	for(i=flag;i<n;i++){
		next[k]=a[i];
		length[k++]=abs(a[i]-now);
		now=a[i];
	}

	//回来往递减方向访问
	for(i=flag-1;i>=0;i--){
		next[k]=a[i];
		length[k++]=abs(a[i]-now);
		now=a[i];
	}

	cout<<endl<<"下一个磁道  "<<"移动距离"<<endl;
	for(i=0;i<n;i++)
		cout<<next[i]<<"           "<<length[i]<<endl;
	cout<<"平均寻道长度:";
	printf("%.2f

", average(length, n));
}

void Circle_scan(int *a, int n, int now){
	int i,flag=0,k=0;
	int next[MAX],length[MAX];
	sort(a,a+n);//从小到大排序
	for(i=0;i<n;i++){
		if(a[i]>=now){
			flag=i;
			break;
		}
	}

	//往递增方向访问
	for(i=flag;i<n;i++){
		next[k]=a[i];
		length[k++]=abs(a[i]-now);
		now=a[i];
	}

	//循环往递增方向访问
	for(i=0;i<flag;i++){
		next[k]=a[i];
		length[k++]=abs(a[i]-now);
		now=a[i];
	}

	cout<<endl<<"下一个磁道  "<<"移动距离"<<endl;
	for(i=0;i<n;i++)
		cout<<next[i]<<"           "<<length[i]<<endl;
	cout<<"平均寻道长度:";
	printf("%.2f

", average(length, n));
}

int main(){
	int a[MAX];//存放要用到的磁道号
	int start;//开始的磁道
	int n,i,flag=1;
	cout<<"一共要用到的磁道数："<<endl;
	cin>>n;
	cout<<"随机的磁道："<<endl;
        srand((int)time(0));
	for(i=0;i<n;i++) {
        a[i] = rand()%100;
        cout<<a[i]<<"    ";
	}
	cout<<endl<<"开始的磁道："<<endl;
	cin>>start;

	//磁盘调度目录
	while(flag){
		cout<<"请选一种磁盘调度算法："<<endl;;
		cout<<"1.先来先服务寻道算法"<<endl;
		cout<<"2.最短寻道时间优先"<<endl;
		cout<<"3.扫描算法"<<endl;
		cout<<"4.循环扫描算法"<<endl;
		cout<<"0.退出"<<endl;
		cin>>flag;
		switch(flag){
		    case 1:
		        First_come_first_server(a,n,start);
		        break;
		    case 2:
		        Shortest_seek_time_first(a, n, start);break;
                    case 3:
                        Scan(a, n, start);break;
                    case 4:
                        Circle_scan(a, n, start);break;
                    case 0:
			break;
		}
	}
	return 0;
}