CPU Scheduling algorithm with source code

This is the tested code for CPU scheduling algorithm. This code will cover First Come First Serve(FCFS),Shortest Job First(SJF),Shortest Job First with preemption,Shortest Job First with Nonpreemption,Priority schduling and RoundRobin schduling.

This code consist of 3 files.
copy and save the contents in to 3 separate files specified below

1.Header file-save the content below from "//Header file for Cpu scheduling" to
"// Implementation file for Cpu scheduling" as cpuh.h

2.Implementation file-save the content from "// Implementation file for Cpu scheduling" to
" //Application file for cpu Scheduling" as cpua.cpp

3.The content below the line " //Application file for cpu Scheduling" save as cpub.cpp

now compile both cpua.cpp,cpub.cpp and run cpub.cpp

Code :

// Header file for Cpu scheduling

//------>cpuh.h
#include"iostream.h"
#include"stdio.h"
#include"conio.h"

class cpuschedule
{
int n,Bu[20];
float Twt,Awt,A[10],Wt[10],w;
public:
//Getting the No of processes & burst time
void Getdata();
//First come First served Algorithm
void Fcfs();
//Shortest job First Algorithm
void Sjf();
//Shortest job First Algorithm with Preemption
void SjfP();
//Shortest job First Algorithm with NonPreemption
void SjfNp();
//Round Robin Algorithm
void RoundRobin();
//Priority Algorithm
void Priority();
};
// Implementation file for Cpu scheduling

#include "cpuh.h"
//Getting no of processes and Burst time
void cpuschedule::Getdata()
{
int i;
cout<<"Enter the no of processes:"; cin>>n;
for(i=1;i<=n;i++) { cout<<"Enter The BurstTime for Process p"<<<"= "; cin>>Bu[i];
}
}

//First come First served Algorithm
void cpuschedule::Fcfs()
{
int i,B[10];
Twt=0.0;
for(i=1;i<=n;i++) { B[i]=Bu[i]; cout<<"Burst time for process p"<<<"= "; cout<<<"Total Weighting Time="<<<"Average Weighting Time="<<<" "; } //Shortest job First Algorithm void cpuschedule::Sjf() { int i,j,temp,B[10]; Twt=0.0; for(i=1;i<=n;i++) { B[i]=Bu[i]; cout<<"Burst time for process p"<<<"= "; cout<=1;i--)
{
for(j=1;j<=n;j++) { if(B[j-1]>B[j])
{
temp=B[j-1];
B[j-1]=B[j];
B[j]=temp;
}
}
}

Wt[1]=0;
for(i=2;i<=n;i++) { Wt[i]=B[i-1]+Wt[i-1]; } //calculating Average Weighting Time for(i=1;i<=n;i++) Twt=Twt+Wt[i]; Awt=Twt/n; cout<<"Total Weighting Time="<<<"Average Weighting Time="<<<" "; } //Shortest job First Algorithm with NonPreemption void cpuschedule::SjfNp() { int i,B[10],Tt=0,temp,j; char S[10]; float A[10],temp1,t; Twt=0.0; w=0.0; for(i=1;i<=n;i++) { B[i]=Bu[i]; cout<<"Burst time for process p"<<<"= "; cout<<<"Enter the Arrival Time for"<<<"th process= "; cin>>A[i];
}

for(i=n;i>=1;i--)
{
for(j=3;j<=n;j++) { if(B[j-1]>B[j])
{
temp=B[j-1];
temp1=A[j-1];
B[j-1]=B[j];
A[j-1]=A[j];
B[j]=temp;
A[j]=temp1;
}
}
}

for(i=1;i<=n;i++) { cout<<"p"<<<" "<<<" "<<=n) { if(S[i]=='T'&&A[i]<=t) { Wt[i]=w; cout<<"WT"<<<"="<<<"Wt"<<<"=="<<<"Total Weighting Time="<<<" "; cout<<"Average Weighting Time="<<<" "; } //Priority Algorithm void cpuschedule::Priority() { int i,B[10],P[10],j; w=0.0; int max; Twt=0.0; max=1; for(i=1;i<=n;i++) { B[i]=Bu[i]; cout<<"Burst time for process p"<<<"= "; cout<<<"Enter the priority for process P"<<<"= "; cin>>P[i];
if(max<=max) { i=1; while(i<=n) { if(P[i]==j) { Wt[i]=w; w=w+B[i]; } i++; } j++; } //calculating average weighting Time for(i=1;i<=n;i++) Twt=Twt+Wt[i]; Awt=Twt/n; cout<<"Total Weighting Time="<<<" "; cout<<"Average Weighting Time="<<<" "; } //Shortest job First Algorithm with Preemption void cpuschedule::SjfP() { int i,j,m,Wt[10],k,B[10],A[10],Tt=0,Wtm[10],temp; char S[20],start[20]; int max=0,Time=0,min; float Twt=0.0,Awt; for(i=1;i<=n;i++) { B[i]=Bu[i]; cout<<"Burst time for process P"<<<"= "<max)
max=B[i];
Wt[i]=0;
S[i]='T';
start[i]='F';
Tt=Tt+B[i];
cout<<"Enter the Arrival Time for"<<<"th process= "; cin>>A[i];
if(A[i]>Time)
Time=A[i];
}
//cout<<"Max="<<=t && B[i]!=0) { if(flag==0) { Wt[i]=Wt[i]+w; cout<<"Wt["<<<"]="<<=n && flag!=0) { if(S[j]!='F' && B[i]>B[j] && A[j]<=t && i!=j ) { flag=0; Wt[i]=Wt[i]-w; i=j; } else { flag=1; } j++; } } else { i++; j=1; while(A[j]<=t &&j<=n) { if(B[i]>B[j] && S[j]!='F')
{
flag=0;
i=j;
}
j++;
}
}
}
else
if(flag==0)
i++;
}


cout<<"Printing remaining burst time"; for(i=1;i<=n;i++) cout<<"B["<<<"]="<<<" "; while(w<=n) { if(min>B[i] && S[i]=='T')
{
min=B[i];
j=i;
}
i++;
}
i=j;
if(w==Time && start[i]=='T')
{
w=w+B[i];
S[i]='F';
}
else
{
Wt[i]=Wt[i]+w;
w=w+B[i];
S[i]='F';
}
}

cout<<"Weight info"; for(i=1;i<=n;i++) cout<<"WT["<<<"]="<<<"after subtracting arrival time"; for(i=1;i<=n;i++) { Wt[i]=Wt[i]-A[i]; cout<<"WT["<<<"]="<<<"Average Weighting Time="<<<"Burst time for process p"<<<"= "; cout<<<"Enter the Time Quantum="; cin>>tq;
//TO find the dimension of the Rrobin array
m=max/tq+1;

//initializing Rrobin array
for(i=1;i<=n;i++) { for(j=1;j<=m;j++) { Rrobin[i][j]=0; } } //placing value in the Rrobin array i=1; while(i<=n) { j=1; while(B[i]>0)
{
if(B[i]>=tq)
{
B[i]=B[i]-tq;
Rrobin[i][j]=tq;
j++;
}
else
{
Rrobin[i][j]=B[i];
B[i]=0;
j++;
}
}
count[i]=j-1;
i++;
}

cout<<"Display"; for(i=1;i<=n;i++) { for(j=1;j<=m;j++) { cout<<"Rr["<<<","<<<"]="<<<" "; } cout<<" "; } //calculating weighting time int x=1; i=1; while(x<=n) { for(int a=1;a<=j-1) { if(i==n+1) { i=1; k++; } else { if(i!=z) { Wt[z]=Wt[z]+Rrobin[i][k]; } i++; } } x++; } for(i=1;i<=n;i++) cout<<"Weighting Time for process P"<<<"="<<<"Total Weighting Time="<<<"Average Weighting Time="<<<" "; } //Application file for cpu Scheduling #include "cpuh.h" void main() { int ch,cho; cpuschedule c; do { cout<<" MENU"; cout<<"1.Getting BurstTime"; cout<<"2.FirstComeFirstServed"; cout<<"3.ShortestJobFirst"; cout<<"4.RoundRobin"; cout<<"5.Priority"; cout<<"6.EXIT"; cout<<"Enter your choice"; cin>>ch;
switch(ch)
{
case 1:
c.Getdata();
break;
case 2:
cout<<"FIRST COME FIRST SERVED SCHEDULING"; c.Fcfs(); break; case 3: cout<<"SHORTEST JOB FIRST SCHEDULING"; do { cout<<"1.SJF-Normel"; cout<<"2.SJF-Preemptive"; cout<<"3.SJF-NonPreemptive"; cout<<"Enter your choice"; cin>>cho;
switch(cho)
{
case 1:
c.Sjf();
break;
case 2:
c.SjfP();
break;
case 3:
c.SjfNp();
break;
}
}while(cho<=3); break; case 4: cout<<"ROUND ROBIN SCHEDULING"; c.RoundRobin(); break; case 5: cout<<"PRIORITY SCHEDULING"; c.Priority(); break; case 6: break; } }while(ch<=5); }

CPU Scheduling

What is CPU scheduling?

• Determining which processes run when there are multiple runnable processes.
• Cpu scheduling is very important for system productivity and performance.
• Necessary in multiprogramming environment.
  

What are possible process states?

• Running - process is running on CPU.
• Ready - ready to run, but not actually running on the CPU.
• Waiting - waiting for some event like IO to happen.

Role of Dispatcher?

Dispatcher is a component of OS that is used to switch between processes.
It will stop the process,save the context of the stopped process,Load context of new process and resume the new process.

what is Dispatch latency?
Time taken for the dispatcher to stop one process and start another running process.

Role of CPU scheduler?
Whenever the CPU becomes idle a ready process must be selected for execution. The scheduler selects one process from the list of processes in memory that are ready to execute and allocates the cpu to one of the ready process.