按时间片轮转调度算法（C++实现）

算法思想：

按时间片轮转调度算法：

（1）假设系统中有5个进程，每个进程有一个进程控制块（PCB）来标识。进程控制块内容包括：进程名，链接指针，到达时间，估计运行时间，进程状态。

进程名即进程标识。

链接指针：按照进程到达系统的时间将处于就绪状态的进程连接成一个就绪队列。指针指出下一个到达进程的进程控制块地址。最后一个进程的链接指针为NULL。

（2）为每个进程任意确定一个到达时间和要求运行时间。

（3）设置一个队首指针head，用来指出最先进入系统的进程。各就绪进程通过链接指针连在一起构成一个循环队列。

（4）处理机调度时开始选择队首指针指向的进程投入运行。由于本实验是模拟试验，所以对被选中进程并不实际启动运行，而只是执行：估计运行时间减1。用这个操作来模拟进程的一次运行，而且省去进程的现场保护和现场恢复工作。

（5）进程运行一次后，以后的调度则将当前指针依次下移一个位置，指向下一个进程。同时还应判断该进程的剩余的运行时间是否为0，若不为0，则等待下一轮的运行；若该进程的剩余时间为0，则把它的状态改为完成态（C)，并撤出就绪队列。

（6）若就绪队列非空，则重复上述的（4）和（5），直到所有进程为完成态。

（7）在所设计的程序中应有显示或打印语句，能显示或打印正运行进程的进程名、已运行时间、还剩时间、就绪队列中的进程等。

代码：

#include 
  
    #include 
   
     using namespace std; typedef struct pcb { string pName;//进程名 struct pcb *next;//指向下一个进程 float arriveTime;//到达时间 float serviceTime;//服务时间 float estimatedRunningtime;//估计运行时间 float startTime;//开始时间 float finishTime;//完成时间 float turnaroundTime;//周转时间 float weightedTuraroundTime;//带权周转时间 char state;//进程的状态 }PCB; void createProcess(PCB *p, int n) {//创建n个进程，带头结点 cout << endl << endl << "创建进程" << endl; PCB *q = p;//工作指针的前一个结点指针 PCB *r = new PCB;//工作指针 for (int i = 0; i 
    
      > r->pName; cin >> r->arriveTime; cin >> r->serviceTime; r->startTime = 0; r->finishTime = 0; r->estimatedRunningtime = r->serviceTime; r->turnaroundTime = 0; r->weightedTuraroundTime = 0; r->state = 'R'; q->next = r; q = r; r->next = new PCB; r = r->next; } r->next = NULL; q->next = NULL; q = NULL; delete q; delete r; cout << endl << endl; } void sortOfArriveTime(PCB *p, int n) {//按到达时间对进程排序 PCB *t = new PCB; PCB *q = new PCB; PCB *m = new PCB; for (int i = 0; i 
     
       next;//q指向链表中的第一个进程 for (int j = 0; j 
      
        next; if (q->arriveTime>m->arriveTime) {//结点信息进行交换 t->pName = q->pName; t->arriveTime = q->arriveTime; t->serviceTime = q->serviceTime; t->estimatedRunningtime = q->estimatedRunningtime; q->pName = m->pName; q->arriveTime = m->arriveTime; q->serviceTime = m->serviceTime; q->estimatedRunningtime = m->estimatedRunningtime; m->pName = t->pName; m->arriveTime = t->arriveTime; m->serviceTime = t->serviceTime; m->estimatedRunningtime = t->estimatedRunningtime; } q = q->next; } } t = NULL; m = NULL; q = NULL; delete t; delete m; delete q; } void runProcess(PCB *p, int n) {//运行进程 PCB *q = new PCB; PCB *m = new PCB; PCB *s = new PCB; int a = n; sortOfArriveTime(p, n); q = p; m = p->next; int currentTime = 0;//当前时间 int i = 0; int number = 0; while (true) { currentTime++; if (i == 0 && m->arriveTime>currentTime)//首次运行进程 continue; number = 0; while (m&&m->state == 'C' || m&&m->arriveTime>currentTime) {//寻找应该访问的进程 number++; q = m; m = m->next; if (m == NULL) { q = p; m = p->next; } if (number>n) break; } if (number>n)//所有进程都不能进行访问 continue; cout << "正在运行的进程" << endl; cout << "当前时间:" << currentTime << endl; cout << "进程名\t到达时间 服务时间 已运行时间 还剩运行时间" << endl;//输出当前正在运行的进程 cout << m->pName << "\t" << m->arriveTime << "\t " << m->serviceTime << "\t "; cout << m->serviceTime - m->estimatedRunningtime << "\t " << m->estimatedRunningtime << endl; m->estimatedRunningtime--; m->finishTime = currentTime + 1; if (m->estimatedRunningtime == 0) m->state = 'C'; cout << "进程" << m->pName << "执行一次之后就绪队列中的进程" << endl; cout << "进程名\t到达时间 服务时间 已运行时间 还剩运行时间" << endl; s = p->next; while (s) {//输出就绪队列 if (s->estimatedRunningtime != 0) { cout << s->pName << "\t" << s->arriveTime << "\t " << s->serviceTime << "\t "; cout << s->serviceTime - s->estimatedRunningtime << "\t " << s->estimatedRunningtime << endl; } s = s->next; } cout << endl << endl << endl; q = m; m = m->next;//q、m指针后移 if (m == NULL) {//回到链表头部 q = p; m = p->next; } s = p->next; while (s&&s->state == 'C') s = s->next; if (s == NULL)//若所有进程已完成，则退出循环 break; i++; } q = p; m = p->next; for (int i = 0; i 
       
         startTime = m->arriveTime; m->turnaroundTime = m->finishTime - m->arriveTime; m->weightedTuraroundTime = m->turnaroundTime*1.0 / m->serviceTime; } else { m->startTime = q->startTime + 1>m->arriveTime ? q->startTime + 1 : m->arriveTime; m->turnaroundTime = m->finishTime - m->arriveTime; m->weightedTuraroundTime = m->turnaroundTime*1.0 / m->serviceTime; } m = m->next; } q = NULL; m = NULL; s = NULL; delete q; delete m; delete s; cout << endl; } void printProcess(PCB *p) {//输出所有进程的信息 PCB *q = p->next; cout << endl << "所有进程运行完成后进程的相关信息" << endl; cout << "进程名\t到达时间 服务时间 开始时间 完成时间 周转时间 带权周转时间" << endl; while (q) { cout << q->pName << "\t" << q->arriveTime << "\t " << q->serviceTime << "\t "; cout << q->startTime << "\t " << q->finishTime << "\t " << q->turnaroundTime << "\t " << q->weightedTuraroundTime << endl; q = q->next; } cout << endl << endl; } int main() { PCB *p = new PCB; int n; cout << "请输入进程的个数:"; cin >> n; createProcess(p, n); runProcess(p, n); printProcess(p); getchar(); getchar(); return 0; } 
        
       
      
     
    
  

实验结果：