Thread: Non-Preemptive Priority Scheduling Problem!

input file text :

Code:

6
1 0 yellow
2 1 red
3 1 green
4 2 urgent
5 3 green
6 4 red

my program until now:

Code:

#include <iostream>
#include <fstream> 
#include <string>
#include <sstream> 
#include <vector>
#include <time.h>       /* time */
#include <stdlib.h>     /* srand, rand */      
#include <algorithm>
#include <queue>
using namespace std;


struct  process
{
   public:
      int pid;  
      int arrival;  
      int burst;  
      int priority; 
      int status; 
};

bool sortbyarrivel(const process & s1, const process & s2)
{
   if (s1.arrival != s2.arrival) 
   return s1.arrival < s2.arrival;
}
bool sortbypriority(const process & s1, const process & s2)
{
   if (s1.priority == s2.priority) {
    if (s1.arrival > s2.arrival ){
        return s1.priority < s2.priority;
    }
   }
   else if (s1.priority != s2.priority) {
    return s1.priority < s2.priority;
   }

}

int main() {

    process prs;
    vector <process> pr;
    vector <process> r1;

    ifstream infile("inputfile.txt");  // ifstream is used to read the input file
    string line,btime,numofprocesses,prid,arraiveltime;
    int n;



    int current_line = 0;  
    int randNum;

    while (getline(infile, line)) //get the lines inside the file, one by one until the end of the file
    {
        istringstream iss(line); //create string stream and read current line
        if ( current_line ==0){ // first line always contains the number of processes
            if (iss >> numofprocesses){ // store the contents of the stream into numofprocesses
            n =atoi(numofprocesses.c_str());
                    cout<< "number of processes = "<<numofprocesses<<endl<<endl;    
            }
        }
        else {
            if (iss >> prid >>arraiveltime >>btime) { // store the contents of the stream into pid,arraiveltime 

            prs.pid = atoi(prid.c_str());
            prs.arrival = atoi(arraiveltime.c_str());

            if (btime == "green"){ // if btime , which is the priority type is == regular 
                //srand (time(NULL)); 
                //prs.burst = (rand()%(15-10))+ 10; // give this process a random burst time from 10 to 15
                prs.burst = 1;
                prs.priority = 2; // give this process priority = 2 if its regular

            }
            else if(btime == "yellow"){ 
            //  srand (time(NULL));
                //prs.burst = (rand()%(30-20))+ 20;
                prs.burst = 2;
                prs.priority = 1;


            }
            else if(btime == "red"){ 
            //  srand (time(NULL));
                //prs.burst = (rand()%(60-40))+ 40;
                    prs.burst = 3;
                prs.priority = 0;

            }
            prs.status =0;
            pr.push_back(prs);

            }
        }
          current_line++;              // next line ++1
    }


    //sorting by arrivel time
    sort(pr.begin(), pr.end(), sortbyarrivel);


    cout<<endl; cout<<endl; cout<<endl;
    cout<<"The patients are scheduled as follow."<<endl;
    cout<<"In physician room:"<<endl;
    cout<<"Time "<< pr[0].arrival<<" : patient "<<pr[0].pid<<" is coming"<<endl;
    cout<<"Time "<< pr[0].burst<<" : patient "<<pr[0].pid<<" is leaving"<<endl;
    static int currentbursttime=pr[0].burst;
    pr[0].status =1;


int count = 0 ;
    int complated_process = 0 ;

    while (complated_process <pr.size()){

        for(int i=0;i<pr.size();i++){
            if( pr[i].arrival <= currentbursttime &&  pr[i].status ==0 ){
                r1.push_back(pr[i]);
                count++;
            }
        }
        //sorting by priority 
        sort(r1.begin(), r1.end(), sortbypriority);


        for(int i=0;i<count;i++){
            if (i == 0){
                currentbursttime = currentbursttime+1;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[i].pid<<" is entring"<<endl;
                currentbursttime =r1[i].burst+currentbursttime;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[i].pid<<" is going"<<endl;
                pr[r1[i].pid].status =1;
                complated_process = complated_process +1;
            }           
        }

        r1.clear(); 


    }
return 0 ;
}

this program until now is giving me this results:

Code:

number of processes = 6

The patients are scheduled as follow.
In physician room:
Time 0 : patient 1 is coming
Time 2 : patient 1 is leaving
At Time 3 : process 2 is entring
At Time 6 : process 2 is going
At Time 7 : process 6 is entring
At Time 10 : process 6 is going
At Time 11 : process 6 is entring
At Time 14 : process 6 is going
At Time 15 : process 6 is entring
At Time 18 : process 6 is going
At Time 19 : process 6 is entring
At Time 22 : process 6 is going
At Time 23 : process 6 is entring
At Time 26 : process 6 is going

and the result is wrong , its repeating process #6 over and over again .. the result I want is something like this:

Code:

At Time 0 : process 1 is entring
At Time 2 : process 1 is going
At Time 3 : process 2 is entring
At Time 6 : process 2 is going
At Time 7 : process 6 is entring
At Time 10 : process 6 is going
At Time 11 : process 4 is entring
At Time 13: process 4 is going
At Time 14: process 3 is entring
At Time 15: process 3 is going
At Time 16: process 5 is entring
At Time 17 : process 5 is going

The problem has to do with the loops inside while loop. Tried to find a solution but I couldn't.
Hope someone can look at this and show me what I did wrong.

Originally Posted by rakk92

Code:

pr[r1[i].pid].status =1;

Above will eventually try to access an index that's not present. Remember indices start from 0 and your processes start with pid = 1

My understanding is that the only reason you're sorting the processes by arrival time is to get the first process to execute in which case you need to make a copy of the processes instead and keep the original vector instance to be able to do things like:

Code:

pr[r1[i].pid].status =1;

If you sort the processes by arrival time the above will not address the process with the desired pid. Initially the processes sorted by the process id _but_ they are not currently sorted by the process id which mean you cannot use the process id as an index.

You don't need this loop

Code:

   for(int i=0;i<count;i++){
            if (i == 0){
                currentbursttime = currentbursttime+1;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[i].pid<<" is entring"<<endl;
                currentbursttime =r1[i].burst+currentbursttime;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[i].pid<<" is going"<<endl;
                pr[r1[i].pid].status =1;
                complated_process = complated_process +1;
            }           
        }

I assume you want to execute the first process in the queue which should be just

Code:

               currentbursttime = currentbursttime+1;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[i].pid<<" is entring"<<endl;
                currentbursttime =r1[0].burst+currentbursttime;
                cout<<"At Time "<< currentbursttime<<" : process "<<r1[0].pid<<" is going"<<endl;
                pr[r1[0].pid].status =1;
                complated_process = complated_process +1;