Home » Algorithms

Implementation of Priority scheduling (Non Pre-emptive) algorithm using C++

In this article, we are going to learn about priority scheduling algorithm (non pre-emptive) and implementing this algorithm using C++ program.
Submitted by Aleesha Ali, on January 29, 2018

Non pre-emptive: We cannot remove a process until it completes it execution.

Scheduling criteria tells us that any algorithm is how much efficient, the main criteria of scheduling are given below:

• CPU Utilization
• Throughput
• Arrival time
• Turnaround time
• Waiting time
• Completion time
• Burst time

*Ready Queue is a queue where all the processes wait to get CPU for its execution.

CPU Utilization: The amount of time CPU is busy.

Throughput: The number of process computed per unit time.

Arrival time: The time at which the process enters into ready queue.

Turn around time: The interval between the time of submission of a process to the time of completion.

Waiting time: The total amount of the time a process spends in ready queue.

Completion time: The time at which process completes its execution.

Burst time: The time needed by CPU to completes its execution.

Priority Scheduling Algorithm (Non Pre-emptive)

In this algorithm priority is defined by manufacture of operating system, sometimes we assume minimum number has higher priority or vice a versa.

In my algorithm I use higher number has higher priority means process having higher priority will be schedule first.

C++ Program for Priority Algorithm (Non-preemptive)

//Implementation of Priority(Non-Preeemptive) Using C++
#include <iostream>
#include <algorithm>
using namespace std;

typedef struct proccess
{
	int at,bt,pr,ct,ta,wt;
	string pro_id;

			  /*
	artime = Arrival time,
	bt = Burst time,
	ct = Completion time,
	ta = Turn around time,
	wt = Waiting time
	*/

}process;

bool compare(process a,process b)
{
	return a.at<b.at;
		 /* This schedule will always return TRUE
if above condition comes*/

}

bool compare2(process a,process b)
{
	return a.pr>b.pr;
	 /* This schedule will always return TRUE
if above condition comes*/

}

int main()
{
	process pro[10];
	int n,i,j;
	cout<<"Enter the number of process::";
	cin>>n;
	cout<<"Enter the process id arrival time burst time and priority :::";

	for(i=0;i<n;i++)
	{
		cin>>pro[i].pro_id;
		cin>>pro[i].at;
		cin>>pro[i].bt;
		cin>>pro[i].pr;
	}

	sort(pro,pro+n,compare);

	 /*sort is a predefined funcion  defined in algorithm.h header file,
it will sort the schedulees according to their arrival time*/

	pro[0].ct=pro[0].bt+pro[0].at;
	pro[0].ta=pro[0].ct-pro[0].at;
	pro[0].wt=pro[0].ta-pro[0].bt;
	i=1;

	while(i<n-1)
	{

		for(j=i;j<n;j++)
		{
			if(pro[j].at>pro[i-1].ct)
			break;
		}
		sort(pro+i,pro+i+(j-i),compare2);
		pro[i].ct=pro[i-1].ct+pro[i].bt;
		pro[i].ta=pro[i].ct-pro[i].at;
		pro[i].wt=pro[i].ta-pro[i].bt;
		i++;
		}
		pro[i].ct=pro[i-1].ct+pro[i].bt;
		pro[i].ta=pro[i].ct-pro[i].at;
		pro[i].wt=pro[i].ta-pro[i].bt;

	for(i=0;i<n;i++)
	{
		//desplaying all the values
		cout<<pro[i].pro_id<<"\t"<<pro[i].at<<"\t"<<pro[i].bt<<"\t"<<pro[i].ct<<"\t"<<pro[i].ta<<"\t"<<pro[i].wt<<"\t"<<pro[i].pr;
		cout<<endl;
	}
	return 0;
}

Output