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Priority CPU Scheduling with different arrival time – Set 2

  • Difficulty Level : Medium
  • Last Updated : 27 Jul, 2021

Prerequisite – Program for Priority Scheduling – Set 1
Priority scheduling is a non-preemptive algorithm and one of the most common scheduling algorithms in batch systems. Each process is assigned first arrival time (less arrival time process first) if two processes have same arrival time, then compare to priorities (highest process first). Also, if two processes have same priority then compare to process number (less process number first). This process is repeated while all process get executed.
Implementation – 

  1. First input the processes with their arrival time, burst time and priority.
  2. First process will schedule, which have the lowest arrival time, if two or more processes will have lowest arrival time, then whoever has higher priority will schedule first.
  3. Now further processes will be schedule according to the arrival time and priority of the process. (Here we are assuming that lower the priority number having higher priority). If two process priority are same then sort according to process number.
    Note: In the question, They will clearly mention, which number will have higher priority and which number will have lower priority.
  4. Once all the processes have been arrived, we can schedule them based on their priority.

 

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Gantt Chart – 
 

Examples – 
 

Input :
process no-> 1 2 3 4 5 
arrival time-> 0 1 3 2 4
burst time-> 3 6 1 2 4
priority-> 3 4 9 7 8
Output :
Process_no   arrival_time   Burst_time   Complete_time    Turn_Around_Time       Wating_Time
1             0               3                3                   3               0
2             1               6                9                   8               2 
3             3               1                16                  13              12
4             2               2                11                  9               7
5             4               4                15                  11              7
Average Wating Time is : 5.6
Average Turn Around time is : 8.8 

 

 

C++




// C++ implementation for Priority Scheduling with
//Different Arrival Time priority scheduling
/*1. sort the processes according to arrival time
2. if arrival time is same the acc to priority
3. apply fcfs
*/
 
#include <bits/stdc++.h>
 
using namespace std;
 
#define totalprocess 5
 
// Making a struct to hold the given input
 
struct process
{
int at,bt,pr,pno;
};
 
process proc[50];
 
/*
Writing comparator function to sort according to priority if
arrival time is same
*/
 
bool comp(process a,process b)
{
if(a.at == b.at)
{
return a.pr<b.pr;
}
else
{
    return a.at<b.at;
}
}
 
// Using FCFS Algorithm to find Waiting time
void get_wt_time(int wt[])
{
// declaring service array that stores cumulative burst time
int service[50];
 
// Initialising initial elements of the arrays
service[0] = proc[0].at;
wt[0]=0;
 
 
for(int i=1;i<totalprocess;i++)
{
service[i]=proc[i-1].bt+service[i-1];
 
wt[i]=service[i]-proc[i].at;
 
// If waiting time is negative, change it into zero
     
    if(wt[i]<0)
    {
    wt[i]=0;
    }
}
 
}
 
void get_tat_time(int tat[],int wt[])
{
// Filling turnaroundtime array
 
for(int i=0;i<totalprocess;i++)
{
    tat[i]=proc[i].bt+wt[i];
}
     
}
 
void findgc()
{
//Declare waiting time and turnaround time array
int wt[50],tat[50];
 
double wavg=0,tavg=0;
 
// Function call to find waiting time array
get_wt_time(wt);
//Function call to find turnaround time
get_tat_time(tat,wt);
     
int stime[50],ctime[50];
 
stime[0] = proc[0].at;
ctime[0]=stime[0]+tat[0];
 
// calculating starting and ending time
for(int i=1;i<totalprocess;i++)
    {
        stime[i]=ctime[i-1];
        ctime[i]=stime[i]+tat[i]-wt[i];
    }
     
cout<<"Process_no\tStart_time\tComplete_time\tTurn_Around_Time\tWaiting_Time"<<endl;
     
    // display the process details
     
for(int i=0;i<totalprocess;i++)
    {
        wavg += wt[i];
        tavg += tat[i];
         
        cout<<proc[i].pno<<"\t\t"<<
            stime[i]<<"\t\t"<<ctime[i]<<"\t\t"<<
            tat[i]<<"\t\t\t"<<wt[i]<<endl;
    }
     
        // display the average waiting time
        //and average turn around time
     
    cout<<"Average waiting time is : ";
    cout<<wavg/(float)totalprocess<<endl;
    cout<<"average turnaround time : ";
    cout<<tavg/(float)totalprocess<<endl;
 
}
 
int main()
{
int arrivaltime[] = { 1, 2, 3, 4, 5 };
int bursttime[] = { 3, 5, 1, 7, 4 };
int priority[] = { 3, 4, 1, 7, 8 };
     
for(int i=0;i<totalprocess;i++)
{
    proc[i].at=arrivaltime[i];
    proc[i].bt=bursttime[i];
    proc[i].pr=priority[i];
    proc[i].pno=i+1;
    }
     
    //Using inbuilt sort function
     
    sort(proc,proc+totalprocess,comp);
     
    //Calling function findgc for finding Gantt Chart
     
    findgc();
 
    return 0;
}
 
// This code is contributed by Anukul Chand.

Java




// Java implementation for Priority Scheduling with
//Different Arrival Time priority scheduling
import java.util.*;
 
/// Data Structure
class Process {
    int at, bt, pri, pno;
    Process(int pno, int at, int bt, int pri)
    {
        this.pno = pno;
        this.pri = pri;
        this.at = at;
        this.bt = bt;
    }
}
 
/// Gantt chart structure
class GChart {
    // process number, start time, complete time,
    // turn around time, waiting time
    int pno, stime, ctime, wtime, ttime;
}
 
// user define comparative method (first arrival first serve,
// if arrival time same then heigh priority first)
class MyComparator implements Comparator {
 
    public int compare(Object o1, Object o2)
    {
 
        Process p1 = (Process)o1;
        Process p2 = (Process)o2;
        if (p1.at < p2.at)
            return (-1);
 
        else if (p1.at == p2.at && p1.pri > p2.pri)
            return (-1);
 
        else
            return (1);
    }
}
 
 
// class to find Gantt chart
class FindGantChart {
    void findGc(LinkedList queue)
    {
 
        // initial time = 0
        int time = 0;
 
        // priority Queue sort data according
        // to arrival time or priority (ready queue)
        TreeSet prique = new TreeSet(new MyComparator());
 
        // link list for store processes data
        LinkedList result = new LinkedList();
 
        // process in ready queue from new state queue
        while (queue.size() > 0)
            prique.add((Process)queue.removeFirst());
 
        Iterator it = prique.iterator();
 
        // time set to according to first process
        time = ((Process)prique.first()).at;
 
        // scheduling process
        while (it.hasNext()) {
 
            // dispatcher dispatch the
            // process ready to running state
            Process obj = (Process)it.next();
 
            GChart gc1 = new GChart();
            gc1.pno = obj.pno;
            gc1.stime = time;
            time += obj.bt;
            gc1.ctime = time;
            gc1.ttime = gc1.ctime - obj.at;
            gc1.wtime = gc1.ttime - obj.bt;
 
            /// store the exxtreted process
            result.add(gc1);
        }
 
        // create object of output class and call method
        new ResultOutput(result);
    }
}

Python3




# Python3 implementation for Priority Scheduling with
# Different Arrival Time priority scheduling
"""1. sort the processes according to arrival time
   2. if arrival time is same the acc to priority
   3. apply fcfs """
  
totalprocess = 5
proc = []
for i in range(5):
    l = []
    for j in range(4):
        l.append(0)
    proc.append(l)
 
# Using FCFS Algorithm to find Waiting time
def get_wt_time( wt):
 
    # declaring service array that stores
    # cumulative burst time
    service = [0] * 5
 
    # Initialising initial elements
    # of the arrays
    service[0] = 0
    wt[0] = 0
 
    for i in range(1, totalprocess):
        service[i] = proc[i - 1][1] + service[i - 1]
        wt[i] = service[i] - proc[i][0] + 1
 
        # If waiting time is negative,
        # change it o zero
        if(wt[i] < 0) :    
            wt[i] = 0
         
def get_tat_time(tat, wt):
 
    # Filling turnaroundtime array
    for i in range(totalprocess):
        tat[i] = proc[i][1] + wt[i]
 
def findgc():
     
    # Declare waiting time and
    # turnaround time array
    wt = [0] * 5
    tat = [0] * 5
 
    wavg = 0
    tavg = 0
 
    # Function call to find waiting time array
    get_wt_time(wt)
     
    # Function call to find turnaround time
    get_tat_time(tat, wt)
 
    stime = [0] * 5
    ctime = [0] * 5
    stime[0] = 1
    ctime[0] = stime[0] + tat[0]
     
    # calculating starting and ending time
    for i in range(1, totalprocess):
        stime[i] = ctime[i - 1]
        ctime[i] = stime[i] + tat[i] - wt[i]
 
    print("Process_no\tStart_time\tComplete_time",
               "\tTurn_Around_Time\tWaiting_Time")
 
    # display the process details
    for i in range(totalprocess):
        wavg += wt[i]
        tavg += tat[i]
         
        print(proc[i][3], "\t\t", stime[i],
                         "\t\t", end = " ")
        print(ctime[i], "\t\t", tat[i], "\t\t\t", wt[i])
 
 
    # display the average waiting time
    # and average turn around time
    print("Average waiting time is : ", end = " ")
    print(wavg / totalprocess)
    print("average turnaround time : " , end = " ")
    print(tavg / totalprocess)
 
# Driver code
if __name__ =="__main__":
    arrivaltime = [1, 2, 3, 4, 5]
    bursttime = [3, 5, 1, 7, 4]
    priority = [3, 4, 1, 7, 8]
     
    for i in range(totalprocess):
 
        proc[i][0] = arrivaltime[i]
        proc[i][1] = bursttime[i]
        proc[i][2] = priority[i]
        proc[i][3] = i + 1
     
    # Using inbuilt sort function
    proc = sorted (proc, key = lambda x:x[2])
    proc = sorted (proc)
     
    # Calling function findgc for
    # finding Gantt Chart
    findgc()
 
# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

Output: 
 

Process_no Start_time Complete_time Turn_Around_Time Waiting_Time
1           1           4              3              0 
2           5           10             8              3
3           4           5              2              1
4          10           17             13             6
5          17           21             16             12
Average Waiting Time is : 4.4 
Average Turn Around time is : 8.4

Time Complexity: O(N * logN), where N is the total number of processes. 
Auxiliary Space: O(N) 

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