时间片轮转算法

代码：

#include<iostream>
#include<string>
#include<fstream>
#include<vector>
#include<algorithm>
#include<cstdlib>
#include<ctime>
using namespace std;

//初始化进程池
//初始化就绪队列
//RR算法

 struct PCB {
	string name;
	int atime;  //到达时间
	int rtime;  //估计运行时间
	char status;  //进程状态 R是就绪，W是等待，C是结束
	PCB* next;  //指针

	PCB(){
		this->name = "";
		this->atime = -1;
		this->rtime = -1;
		this->status = NULL;
		this->next = NULL;
	}

	PCB(string name, int atime, int rtime, char status, PCB* next=NULL) {
		this->name = name;
		this->atime = atime;
		this->rtime = rtime;
		this->status = status;
		this->next = next;
	}

	//复制构造
	PCB(const PCB& pcb) {
		this->name = pcb.name;
		this->atime = pcb.atime;
		this->rtime = pcb.rtime;
		this->status = pcb.status;
	}

	void show() {
		cout << name << " " << atime << " " << rtime << " " << status << endl;
	}
};

 bool cmp(PCB& a, PCB& b) {
	 return a.atime < b.atime;
 }

 //打印队列所有进程的情况
 void show_status(PCB* Q_head) {
	 if (!Q_head)return;
	 PCB* node = Q_head;
	 node->show();
	 while (node->next != Q_head) {
		 node = node->next;
		 node->show();
	 }
 }

 //初始化进程池
 void initPool(vector<PCB>& PCBPool, string fileName) {
	 ifstream inFile(fileName);
	 if (!inFile.is_open()) {
		 cout << "文件打开失败！
";
		 return;
	 }
	 string name;
	 int atime;  //到达时间
	 int rtime;  //估计运行时间
	 char status;  //进程状态 
	 //读入文件数据
	 while (inFile >> name >> atime >> rtime >> status) {
		 PCB pcb(name, atime, rtime, status);
		 PCBPool.push_back(pcb);
	 }
	 //按照到达时间进行升序排序
	 sort(PCBPool.begin(), PCBPool.end(),cmp);
	 cout << "初始化成功！
";
	 inFile.close();
	 return;
}
 //头结点移到尾部
 void headToTail(PCB*& Q_head, PCB*& Q_tail) {
	 if (Q_head) {
		 Q_tail = Q_head;
		 Q_head = Q_tail->next = Q_head->next;
	 }
 }
 //删除头结点
 void delHead(PCB*& Q_head, PCB*& Q_tail) {
	 if (Q_head) {
		 PCB* node = Q_head;
		 if (Q_head == Q_tail) {
			 Q_head = Q_tail = NULL;
		 }
		 else {
			 Q_head = Q_tail->next = Q_head->next;
		 }
		 delete node;
	 }
 }
 //扫描并添加新进程
 void scanAndAdd(PCB*& Q_head,PCB*& Q_tail, vector<PCB>& PCBPool,int time) {
	 while (PCBPool.size()&&PCBPool[0].atime == time) {
		 PCB * node = new PCB(PCBPool[0]);
		
		 //从进程池中删除该进程
		 PCBPool.erase(PCBPool.begin());
		 //如果队列为空
		 if (Q_head == NULL) {
			 node->status = 'R';
			 Q_head = Q_tail = node;
			 Q_tail->next = Q_head;
		 }
		 else{
		 node->status = 'W';
		 //插入队尾
		 Q_tail->next = node;
		 //尾指针后移
		 Q_tail = Q_tail->next;
		 //最后一个结点指向头结点
		 Q_tail->next = Q_head;
		 }
	 }
 }

 //时间片轮转算法
 void RR(PCB*& Q_head, PCB*& Q_tail, vector<PCB>& PCBPool) {
	 //时间一直流动，在每一个时间步里，如果就绪队列不为空，则先处理就绪队列的进程再扫描添加新进程，再把没完成的放到队尾；如果为空，则直接扫描添加

	 int time = 0;

	 while (!Q_head == NULL || !PCBPool.empty()) {
		 cout << "===========================
";
		 cout << "时间：" << time << endl;
		 //添加进程
		 scanAndAdd(Q_head, Q_tail, PCBPool, time);

		 bool notRun = true;
		 while (notRun&&Q_head) {
			 if (Q_head->status == 'R') {
				 cout << "当前正在运行的进程是：" << Q_head->name << endl;
				 Q_head->rtime--;
				 notRun = false;  //运行过了
				 //运行完
				 if (Q_head->rtime == 0) {
					 Q_head->status = 'C';
				 }
				 //还没运行完
				 else {
					 Q_head->status = 'W';
				 }
				 show_status(Q_head);
			 }
			 else if (Q_head->status == 'W') {
				 headToTail(Q_head, Q_tail);
				 Q_head->status = 'R';
			 }
			 else if (Q_head->status == 'C') {
				 delHead(Q_head, Q_tail);
				 if (Q_head) {
					 Q_head->status = 'R';
				 }
			 }
		 }
		 time++;
	 }
	
 }
 //生成随机数据
 void createData(string fileName, int n) {
	 ofstream outFile(fileName);
	 if (!outFile.is_open()) {
		 cout << "文件打开失败！" << endl;
		 return;
	 }
	 srand((int)time(0));
	 string name;
	 int atime;  //到达时间
	 int rtime;  //估计运行时间
	 char status='W';  //进程状态 
	 for (int i = 0; i < n; i++) {
		 name = "P" + to_string(i);
		 atime = rand() % n;
		 rtime = rand() % 10 + 1;
		 outFile << name << " " << atime << " " << rtime << " "<<status << endl;
	 }
	 outFile.close();
 }

int main() {
	
	createData("test.txt", 4);
	
	vector<PCB> pool;
	
	initPool(pool,"test.txt");
	
	PCB* Q_head = NULL;
	PCB* Q_tail = NULL;

	RR(Q_head, Q_tail, pool);
	
	system("pause");
}