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<Process>{                            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> process = new TreeSet<Process>();    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<Process> getProcess() {        return process;    }    public void CarryOut_RR(int Timeperiod){        LinkedList<Process> Tmp = new LinkedList<>();        LinkedList<Process> ProcessSeries = new LinkedList<Process>();        LinkedList<Process> FinsishProcess = new LinkedList<Process>();        LinkedList<Integer> processtime = new LinkedList<Integer>();        Iterator<Process> 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<Process> FinsishProcess){                      //平均周转时间        double avg = 0;        Iterator<Process> 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<Process> FinsishProcess){                      //平均带权周转时间        double avg = 0;        Iterator<Process> it = this.process.iterator();        while( it.hasNext()){            Process p = it.next();            avg += p.getWeightedPeriodTime();        }        avg /= this.process.size();        return avg;    }    public void Print(Collection<Process> 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<Process> 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();    }}