进程调度（二）——时间片轮转算法

一 定义

时间片轮转算法是将所有的就绪进程按先来先服务的原则，排成一个队列，按时间片轮转。时间片的大小从几ms到几百ms。当执行的时间片用完时，由一个计时器发出时钟中断请求，调度程序便据此信号来停止该进程的执行，并将它送往就绪队列的末尾；然后，再把处理机分配给就绪队列中新的队首进程，同时也让它执行一个时间片。这样就可以保证就绪队列中的所有进程，在一给定的时间内，均能获得一时间片的处理机执行时间。

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二 代码

进程类如下：

import java.util.Iterator;
import java.util.Scanner;
import java.util.TreeSet;

public class Process implements Comparable{                        
    private String ProcessName;             //进程名
    private int ReachTime;                  //到达时间
    private int ProcessTime;                //处理时间
    private int FinishTime;                 //完成时间
    private int PeriodTime;                 //周转时间
    private int StartTime;                  //开始时间
    private double WeightedPeriodTime;      //带权周转时间
    private int Priority;                   //优先级

    public Process(String processname,int reachTime, int processTime) {
        super();
        ProcessName = processname;
        ReachTime = reachTime;
        ProcessTime = processTime;
    }

    public Process(String processName, int reachTime, int processTime, int priority) {
        super();
        ProcessName = processName;
        ReachTime = reachTime;
        ProcessTime = processTime;
        Priority = priority;
    }

    public int getPriority() {
        return Priority;
    }

    public String getProcessName() {
        return ProcessName;
    }

    public int getReachTime() {
        return ReachTime;
    }

    public int getProcessTime() {
        return ProcessTime;
    }

    public int getFinishTime() {
        return FinishTime;
    }

    public int getPeriodTime() {
        return PeriodTime;
    }

    public void setProcessTime(int processTime) {
        ProcessTime = processTime;
    }

    public void setFinishTime(int finishTime) {
        FinishTime = finishTime;
    }

    public void setPeriodTime(int periodTime) {
        PeriodTime = periodTime;
    }

    public int getStartTime() {
        return StartTime;
    }

    public void setStartTime(int startTime) {
        StartTime = startTime;
    }

    public double getWeightedPeriodTime() {
        return WeightedPeriodTime;
    }

    public void setWeightedPeriodTime(double weightedPeriodTime) {
        WeightedPeriodTime = weightedPeriodTime;
    }

    @Override
    public int compareTo(Process o) {
        // TODO Auto-generated method stub
        if ( this.ReachTime > o.ReachTime)
            return 1;
        else if ( this.ReachTime < o.ReachTime)
            return -1;
        return 0;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ReachTime;
        return result;
    }

    public void Print(){
        System.out.print(this.ProcessName+" "+this.ReachTime+"  "+this.ProcessTime+"    "+" "+this.StartTime+"  "+this.FinishTime+" "+this.PeriodTime+" ");
        System.out.printf("%.4f",this.WeightedPeriodTime);
        System.out.println();
    }
}

时间片轮转算法实现如下:

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.TreeSet;

public class RR {
    private TreeSet process = new TreeSet();

    public RR() {
        System.out.println("请输入要添加的进程数:");
        Scanner in = new Scanner(System.in);
        int Num = in.nextInt();
        System.out.println("开始初始化进程信息(进程名 到达时间 耗时):");
        for ( int i = 0 ; i < Num ; i++){
            String processname = in.next();
            int reachtime = in.nextInt();
            int processtime = in.nextInt();
            Process p = new Process(processname,reachtime, processtime); 
            process.add(p);
        }
    }

    public TreeSet getProcess() {
        return process;
    }

    public void CarryOut_RR(int Timeperiod){
        LinkedList Tmp = new LinkedList<>();
        LinkedList ProcessSeries = new LinkedList();
        LinkedList FinsishProcess = new LinkedList();
        LinkedList processtime = new LinkedList();
        Iterator it = this.process.iterator();
        while(it.hasNext()){
            Process p = it.next();
            Tmp.add(p);
            processtime.add(p.getProcessTime());
        }
        int NowTime = Tmp.peekFirst().getReachTime();                       //当前时间
        int NowProcessTime = processtime.pop();
        //第一个进程特殊情况
        Process p = Tmp.pop();
        p.setStartTime(NowTime);
        p.setFinishTime(p.getFinishTime()+Timeperiod);
        p.setPeriodTime(p.getFinishTime() - p.getReachTime());
        p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
        NowTime += Timeperiod;
        int FinishTime = p.getFinishTime();                                 //完成时间
        NowProcessTime -= Timeperiod;
        if ( NowProcessTime > 0){
            ProcessSeries.add(p);
            processtime.add(NowProcessTime);
        }else{
            if ( NowProcessTime < 0){
                p.setFinishTime(p.getFinishTime() + NowProcessTime);
                p.setPeriodTime(p.getFinishTime() - p.getReachTime());
                p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
                NowTime += NowProcessTime;
                FinishTime = p.getFinishTime();
            }
            FinsishProcess.add(p);
        }
        //时间轮转法
        int len = this.process.size() - 1;
        for ( int i = 0 ; i < len ; i++){
            p = Tmp.pop();
            NowProcessTime = processtime.pop();
            if ( NowTime >= p.getReachTime())
            p.setStartTime(NowTime);
            p.setFinishTime(Timeperiod + FinishTime);
            p.setPeriodTime(p.getFinishTime() - p.getReachTime());
            p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
            FinishTime = p.getFinishTime();
            NowTime += Timeperiod;
            NowProcessTime -= Timeperiod;
            if ( NowProcessTime > 0){
                ProcessSeries.add(p);
                processtime.add(NowProcessTime);
            }else{
                if ( NowProcessTime < 0){
                    p.setFinishTime(p.getFinishTime() + NowProcessTime);
                    p.setPeriodTime(p.getFinishTime() - p.getReachTime());
                    p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
                    NowTime += NowProcessTime;
                    FinishTime = p.getFinishTime();
                }
                FinsishProcess.add(p);
            }
        }
        while ( !processtime.isEmpty()){
            p = ProcessSeries.pop();
            NowProcessTime = processtime.pop();
            p.setFinishTime(Timeperiod + FinishTime);
            p.setPeriodTime(p.getFinishTime() - p.getReachTime());
            p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
            FinishTime = p.getFinishTime();
            NowProcessTime -= Timeperiod;
            if ( NowProcessTime > 0){
                ProcessSeries.add(p);
                processtime.add(NowProcessTime);
            }else{
                if ( NowProcessTime < 0){
                    p.setFinishTime(p.getFinishTime() + NowProcessTime);
                    p.setPeriodTime(p.getFinishTime() - p.getReachTime());
                    p.setWeightedPeriodTime(p.getPeriodTime() * 1.0 / p.getProcessTime());
                    FinishTime = p.getFinishTime();
                }
                FinsishProcess.add(p);
            }
        }

        this.Print(FinsishProcess);
        System.out.printf("平均周转时间:%.4f",this.Avg_ProcessTime(FinsishProcess));
        System.out.println();
        System.out.printf("平均带权周转时间:%.4f",this.Avg_WeightedProcessTime(FinsishProcess));
        System.out.println();
    }

    public double Avg_ProcessTime(Collection FinsishProcess){                      //平均周转时间
        double avg = 0;
        Iterator it = this.process.iterator();
        while( it.hasNext()){
            Process p = it.next();
            avg += p.getPeriodTime();
        }
        avg /= this.process.size();
        return avg;
    }

    public double Avg_WeightedProcessTime(Collection FinsishProcess){                      //平均带权周转时间
        double avg = 0;
        Iterator it = this.process.iterator();
        while( it.hasNext()){
            Process p = it.next();
            avg += p.getWeightedPeriodTime();
        }
        avg /= this.process.size();
        return avg;
    }

    public void Print(Collection FinsishProcess){
        System.out.println("            调度示意图");
        System.out.println("进程  到达时间    耗时  开始时间    完成时间    周转时间    带权周转时间");
        Iterator it = FinsishProcess.iterator();
        while( it.hasNext()){
            Process p = it.next();
            p.Print();
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        RR rr = new RR();
        rr.Print(rr.getProcess());
        System.out.println("请输入时间片：");
        Scanner in = new Scanner(System.in);
        int Timeperiod = in.nextInt();                                      //时间片
        rr.CarryOut_RR(Timeperiod);
        in.close();
    }

}