操作系统实验报告

实验题目：实验八：磁盘移臂调度算法实验

软件环境：Linux操作系统

实验目的：加深对于操作系统设备管理技术的了解，体验磁盘移臂调度算法的重要性；掌握几种重要的磁盘移臂调度算法，练习模拟算法的编程技巧，锻炼研究分析试验数据的能力。

实验内容：请在示例实验程序中补充SCAN，C-SCAN，LOOK磁盘移臂调度算法的模拟程序。输入不同的磁盘柱面请求序列，观察和分析其调度效果和性能，并将其与FCFS和SSTF算法进行比较。改进以上示例实验程序，使之能够随机的产生磁盘柱面请求序列，以便能动态的观测各种调度算法的性能。

实验思路：首先明确了SCAN，C-SCAN，LOOK磁盘移臂调度算法的思想，明确需要完成的任务即给出寻道序列，并根据方向转换次数和寻到数分析算法的优劣并比较。其次，结合私立程序给出的SSTF算法和SCAN算法，写出SCAN，C-SCAN，LOOK算法，并添加到示例程序中。编译后执行，多次磁盘请求序列的测试，查看实验结果是否正确。

实验代码：//dask.h

#include

#include

#include

#include

#include

using namespace std;

class DiskArm{

public:

DiskArm();

~DiskArm();

void InitSpace(char * MethodName); //初始化寻道记录

void Report(void); // 报告算法执行情况

void Fcfs(void); //先来先服务算法

void Sstf(void); //最短寻道时间优先算法

void Scan(void); //电梯调度算法

void CScan(void); //均匀电梯调度算法

void Look(void); //LOOK 调度算法

private:

int *Request ;

//磁盘请求道号

int *Cylinder;

//工作柱面道号号

int RequestNumber;

//磁盘请求数

int CurrentCylinder;

//当前道号

int SeekDirection;

//磁头方向

int SeekNumber;

//移臂总数

int SeekChang;

//磁头调头数

};

//dask.c

#include "dask.h"

DiskArm::DiskArm(){

int

i;

//输入当前道号

cout

<< "Please input Current cylinder :"

;

cin

>> CurrentCylinder;

//磁头方向,输入 0 表示向小道号移动,1 表示向大道号移动

cout

<< "Please input Current Direction

(0/1) :" ;

cin

>> SeekDirection;

//输入磁盘请求数,请求道号

cout

<< "Please input Request Numbers :"

;

cin

>> RequestNumber;

cout

<< "Please input Request cylinder

string :";

Request =

new int[sizeof(int) * RequestNumber];

Cylinder

= new int[sizeof(int) * RequestNumber];

for (i =

0; i < RequestNumber; i++)

cin

>> Request[i];

}

DiskArm::~DiskArm(){

}

//初始化道号,寻道记录

void DiskArm::InitSpace(char * MethodName)

{

int

i;

cout

<< endl

<< MethodName

<< endl;

SeekNumber = 0;

SeekChang

= 0;

for (i =

0; i < RequestNumber; i++)

Cylinder[i] = Request[i];

}

// 统计报告算法执行情况

void DiskArm::Report(void){

cout

<< endl;

cout

<< "Seek Number: "

<< SeekNumber

<< endl;

cout

<< "Chang Direction: "

<< SeekChang

<< endl

<< endl;

}

//先来先服务算法

void DiskArm::Fcfs(void)

{

int

Current = CurrentCylinder;

int

Direction = SeekDirection;

InitSpace("FCFS");

cout

<< Current;

for(int

i=0; i

if(((Cylinder[i] >= Current)

&& !Direction)||((Cylinder[i]

< Current) &&

Direction)){

//需要调头

SeekChang++; //调头数加 1

Direction = !Direction ; //改变方向标志

//报告当前响应的道号

cout << endl

<< Current

<< " -> "

<< Cylinder[i];

}

else //不需调头,报告当前响应的道号

cout << " -> "

<< Cylinder[i] ;

//累计寻道数,响应过的道号变为当前道号

SeekNumber += abs(Current -Cylinder[i]);

Current = Cylinder[i];

}

//报告磁盘移臂调度的情况

Report();

}

void DiskArm::Sstf(void)

{

int

Shortest;

int

Distance = 999999 ;

int

Direction = SeekDirection;

int

Current = CurrentCylinder;

InitSpace("SSTF");

cout

<< Current;

for(int

i=0; i

//查找当前最近道号

for(int j=0; j

if(Cylinder[j] == -1) continue; //-1 表示已经响应过了

if(Distance > abs(Current-Cylinder[j])){

//到下一道号比当前距离近,下一道号为当前距离

Distance = abs(Current-Cylinder[j]);

Shortest = j;

}

}

if((( Cylinder[Shortest] >= Current)

&& !Direction)||((

Cylinder[Shortest] < CurrentCylinder)

&& Direction)){

//需要调头

SeekChang++; //调头数加 1

Direction = !Direction ; //改变方向标志

//报告当前响应的道号

cout << endl

<< Current

<< " -> "

<< Cylinder[Shortest];

}

else //不需调头,报告当前响应的道号

cout << " -> "

<< Cylinder[Shortest] ;

//累计寻道数,响应过的道号变为当前道号

SeekNumber += abs(Current -Cylinder[Shortest]);

Current = Cylinder[Shortest];

//恢复最近距离,销去响应过的道号

Distance = 999999;

Cylinder[Shortest] = -1;

}

Report();

}

//电梯调度算法

void DiskArm::Scan(void){

int

Current = CurrentCylinder;

int

Direction = SeekDirection;

InitSpace("SCAN");

cout

<< Current;

for(int

i=0; i

int index=-1;

int Distance = 999999;

for(int j=0;j

if(Cylinder[j]==-1)

continue;

else

if((Direction==0&&Cylinder[j]

||(Direction==1&&Cylinder[j]>Current&&(Cylinder[j]-Current)

index=j;

Distance=abs(Current-Cylinder[j]);

}

}

if(Direction==0){

if(index!=-1){

cout<"<

SeekNumber+=Current-Cylinder[index];

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

cout<"<<0<

SeekNumber+=Current;

Direction=!Direction;

//cout<<0;

Current=0;

SeekChang++;

i--;

}

}

else if(Direction==1){

if(index!=-1){

cout<"<

SeekNumber+=Cylinder[index]-Current;

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

cout<"<<199<

SeekNumber+=199-Current;

Direction=!Direction;

//cout<<199;

Current=199;

SeekChang++;

i--;

}

}

}

//报告磁盘移臂调度的情况

Report();

}

//均匀电梯调度算法

void DiskArm::Look(void){

int

Current = CurrentCylinder;

int

Direction = SeekDirection;

InitSpace("Look");

cout

<< Current;

for(int

i=0; i

int index=-1;

int Distance = 999999;

for(int j=0;j

if(Cylinder[j]==-1)

continue;

else

if((Direction==0&&Cylinder[j]

||(Direction==1&&Cylinder[j]>Current&&(Cylinder[j]-Current)

index=j;

Distance=abs(Current-Cylinder[j]);

}

}

if(Direction==0){

if(index!=-1){

cout<"<

SeekNumber+=Current-Cylinder[index];

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

//cout<

Direction=!Direction;

SeekChang++;

i--;

}

}

else if(Direction==1){

if(index!=-1){

cout<"<

SeekNumber+=Cylinder[index]-Current;

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

//cout<

Direction=!Direction;

SeekChang++;

i--;

}

}

}

//报告磁盘移臂调度的情况

Report();

}

//LOOK 调度算法

void DiskArm::CScan(void)

{

int Current = CurrentCylinder;

int

Direction = SeekDirection;

InitSpace("CScan");

cout

<< Current;

for(int

i=0; i

int index=-1;

int Distance = 999999;

for(int j=0;j

if(Cylinder[j]==-1)

continue;

else

if((Direction==0&&Cylinder[j]

||(Direction==1&&Cylinder[j]>Current&&(Cylinder[j]-Current)

index=j;

Distance=abs(Current-Cylinder[j]);

}

}

if(Direction==0){

if(index!=-1){

cout<"<

SeekNumber+=Current-Cylinder[index];

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

cout<"<<0<

SeekNumber+=Current;

Current=199;

cout<199";

SeekChang++;

i--;

}

}

else if(Direction==1){

if(index!=-1){

cout<"<

SeekNumber+=Cylinder[index]-Current;

Current=Cylinder[index];

Cylinder[index]=-1;

}else{

cout<"<<199<

SeekNumber+=199-Current;

Current=0;

SeekChang++;

i--;

}

}

}

Report();

}

//程序启动入口

int main(int argc,char *argv[]){

//建立磁盘移臂调度类

DiskArm *dask = new DiskArm();

//比较和分析 FCFS 和 SSTF 两种调度算法的性能

dask->Fcfs();

dask->Sstf();

dask->Scan();

dask->CScan();

dask->Look();

}