操作系统：C++实现SJF（短作业优先调度算法）

算法描述：

短作业(进程)优先调度算法(SJF)，是指对短作业或短进程优先调度的算法。它们可以分 别用于作业调度和进程调度。短作业优先(SJF)的调度算法是从后备队列中选择一个或若干个 估计运行时间最短的作业，将它们调入内存运行。而短进程优先(SPF)调度算法则是从就绪队 列中选出一个估计运行时间最短的进程，将处理机分配给它，使它立即执行并一直执行到完 成，或发生某事件而被阻塞放弃处理机时再重新调度

代码：

#include <iostream>
#include<iomanip>
#include<queue>
#include<list>
#include<algorithm>

using namespace std;

class PCB
{
public:
    int pid;
    int arrivalTime;
    int needTime;
    int leaveTime;

    PCB()
    {
    }
    PCB(int pid,int arriveTime,int needTime)
    {
        this->pid=pid;
        this->arrivalTime=arriveTime;
        this->needTime=needTime;
        leaveTime=0;
    }

    bool operator < (const PCB &a)const
    {
        return needTime>a.needTime;
    }
    bool operator == (const PCB &a)const
    {
////        if(pid==a.pid){
////            return true;
////        }
////        else
////            return false;
        return pid==a.pid?true:false;
    }
};

class SJF
{
public:
    priority_queue<PCB> pq;
    list<PCB> allNeedList;
    list<PCB> allFinishList;

    void prepareProcess(int pid,int arriveTime,int needTime);
    void schedule();
    void printFinishList();
};
void SJF::schedule()
{
    int currentTime=0,finishTime=-1;
    bool isBusy=false;
    PCB currentProcess;
    while (true)
    {

        if(currentTime==finishTime)  //这里是每秒都做。currentTime++，故==
        {
            isBusy=false;
            currentProcess.leaveTime=currentTime;
            allFinishList.push_back(currentProcess);
            cout<<"已结束 ";
            cout<<"周转时间："<<finishTime-currentProcess.arrivalTime;
            cout<<"带权周转时间："<<(finishTime-currentProcess.arrivalTime)/(double)currentProcess.needTime<<endl;
        }
      //从链表中把到达的进程假如有先队列
        for(list<PCB>::iterator i=allNeedList.begin(); i!=allNeedList.end();)
        {
            if((*i).arrivalTime<=currentTime)
            {
                pq.push(*i);
                allNeedList.erase(i++);
            }
            else
            {
                i++;
            }
        }
        if(!isBusy&&!pq.empty())
        {
            currentProcess=pq.top();
            pq.pop();
            finishTime=currentProcess.needTime+currentTime;
            isBusy=true;
            cout<<"进程"<<currentProcess.pid<<"开始占用处理机,到达时间："<<currentProcess.arrivalTime<<",需要时间:"<<currentProcess.needTime<<",开始时间："<<currentTime<<"\n";
        }

        currentTime++;
        //最后所有进程结束，退出
        if(allNeedList.empty()&&pq.empty()&&!isBusy)
            break;
    }

}

void SJF::prepareProcess(int pid,int arriveTime,int needTime)
{
    PCB newProcess(pid,arriveTime,needTime);
    allNeedList.push_back(newProcess);
}


void SJF::printFinishList()
{
    allFinishList.sort();
    setiosflags(ios::left);
    cout<<setw(15)<<"进程"<<setw(15)<<"到达时间"<<setw(15)<<"服务时间"<<setw(15)<<"周转时间"<<setw(15)<<"带权周转时间\n";
    for (list<PCB>::iterator i=allFinishList.begin(); i!=allFinishList.end(); i++)
    {
        cout<<setw(15)<<(*i).pid<<setw(15)<<(*i).arrivalTime<<setw(15)<<(*i).needTime<<setw(15)<<(*i).leaveTime-(*i).arrivalTime<<setw(15)<<((*i).leaveTime-(*i).arrivalTime)/(double)(*i).needTime<<"\n";
    }
}


int main()
{
    SJF one;
//    one.prepareProcess(1,1,4);
//    one.prepareProcess(2,2,3);
//    one.prepareProcess(3,3,7);
//    one.prepareProcess(4,4,2);
//    one.prepareProcess(5,5,1);
//    one.prepareProcess(6,6,4);
//    one.prepareProcess(7,7,2);
//    one.prepareProcess(8,8,2);

    one.prepareProcess(1,2,4);
    one.prepareProcess(2,2,3);
    one.prepareProcess(3,1,7);
    one.prepareProcess(4,4,2);
    one.prepareProcess(5,6,1);
    one.prepareProcess(6,8,4);
    one.prepareProcess(7,11,2);
    one.prepareProcess(8,13,2);

    one.schedule();
    one.printFinishList();
    return 0;
}

注意事项

1.将程序信息使用PCB的类存储，接近操作系统工作原理
2.程序写的比较顺，但是对基本的语法有些不熟，比如stl中的priority_queue，list。优先队列是从大到小排列，要从小到大排列故重载<运算符，用erase函数，故重载==运算符
3.#include<iomanip> setw \n不一样