轮询算法 这是一个印度人写的，学习下。 来自 codeproject

#pragma once
#include<list>
using namespace std;


class roundrobin//class representing round robin scheduling
{
        int *rq;//request times
        int     n;//number of processes
        int     q;//time quantum
        int     *w;//wait times
        int     *t;//turn-around times
        int *a;//arrival times
        list<int> order;
public:
        roundrobin(void);
        ~roundrobin(void);
        int read();//read input from the user
        void calc();//to calculate turn-around and wait times of all processes and the ordering
        void display();
};


#include "roundrobin.h"
#include<iomanip>
#include<iostream>
using namespace std;
roundrobin::roundrobin(void)
{
        rq=w=t=NULL;
}

roundrobin::~roundrobin(void)
{
        if(rq!=NULL)
        {
                delete[] rq;
                delete[] w;
                delete[] t;
                delete[] a;
        }
}
int roundrobin::read()//read input from the user
{
        int i;
        cout<<"Enter number of processes:";
        cin>>n;
        if(rq!=NULL)
        {
                delete[] rq;
                delete[] w;
                delete[] t;
        }
        try
        {
                rq=new int[n];
                w=new int[n];
                t=new int[n];
                a=new int[n];
        }
        catch(bad_alloc &ba)
        {
                cerr<<ba.what()<<endl;
                exit(1);
        }
       cout<<"Enter arrival times:\n";
        for(i=0;i<n;i++)
        {
                cin>>a[i];
        }
        cout<<"Enter request times:\n";
        for(i=0;i<n;i++)
        {
                cin>>rq[i];
                w[i]=t[i]=0;
        }
        cout<<"Enter time quantum:";
        cin>>q;
        return 1;
}
void roundrobin::calc()//to calculate turn-around and wait times of all processes and the ordering
{
        int j=0;
        int     time;
        int k;
        int i;
        int *r;//remaining times
        try
        {
                r=new int[n];
        }
        catch(bad_alloc &ba)
        {
                cerr<<ba.what()<<endl;
                exit(1);
        }
        for(i=0;i<n;i++)        r[i]=rq[i];
        bool f=false;//flag to indicate whether any process was scheduled as i changed from 0 to n-1 in the next for loop
        int sp=0;//time spent
        for(i=0;j<n;i=(i+1)%n)//while there are uncompleted processes
        {
                if(r[i]>0&&sp>=a[i])//find the next uncompleted process which has already or just arrived
                {
                     f=true;
                        if(r[i]<=q)//if the process requests for time less than the quantum
                                time=r[i];//time to be alloted in this turn is the complete requested time
                        else    time=q;//else, it is the quantum time
                        //schedule the process
                        t[i]+=time,r[i]-=time,order.push_back(i+1);
                        if(r[i]==0)     j++;//if the process has got completed, increment j
                        for(k=0;k<n;k++)
                                if(r[k]!=0&&k!=i&&a[k]<sp+time)//for all other arrived processes incompleted after scheduling this process
                                        if(!(a[k]<=sp))//if they arrived while scheduling this process
                                                w[k]+=sp+time-a[k],t[i]+=sp+time-a[k];//account for the time they spent waiting while the process was being scheduled
                                        else
                                                w[k]+=time,t[k]+=time;//add time to their wait times and turn-around times
                        sp+=time;
                        continue;
                }
                if(i==n-1)
                {
                        if(!f)
                        //now there are no more arrived processes to be scheduled
                        //so change sp to the arrival time of next arriving process
                        {
                                int it;
                                int diff=0;//diff between present time spent and arrivaltime of next arriving process
                                for(it=0;it<n;it++)
                                        if(sp<a[it])//if process has'nt yet arrived
                                        {
                                             if(diff==0)     diff=a[it]-sp;
                                                else if(diff>a[it]-sp)  diff=a[it]-sp;
                                        }
                                sp+=diff;
                        }
                        f=false;
                }
        }
        delete[] r;
}
void roundrobin::display()
{
        int i;
        float tav=0;//average turn-around time
        float wav=0;//average wait time                 
        for(i=0;i<n;i++)
                tav+=t[i],wav+=w[i];
        tav/=n,wav/=n;
        cout<<"Scheduling order:\n";
        list<int>::iterator oi;
        for(oi=order.begin();oi!=order.end();oi++)
                cout<<*oi<<"\t";
        cout<<"\nAverage turn-around time = "<<tav<<endl<<"Average wait time = "<<wav<<endl;
}





#include"roundrobin.h"
#include<iostream>
using namespace std;
#include<conio.h>
int main()
{
        roundrobin r;
        r.read();
        r.calc();
        r.display();
        cout<<"Press any key to exit...";
        _getch();
}