操作系统：时间片轮转（RR）调度算法C语言实现

时间片轮转（RR）调度算法是专门为分时系统设计的。它类似于FCFS调度，但是增加了抢占以切换进程。该算法中，将一个较小时间单元定义为时间量或时间片，时间片的大小通常为 10~100ms。就绪队列作为循环队列，CPU 调度程序循环整个就绪队列，为每个进程分配不超过一个时间片的 CPU。为了实现 RR 调度，我们再次将就绪队列视为进程的 FIFO 队列。新进程添加到就绪队列的尾部。CPU调度程序从就绪队列中选择第一个进程，将定时器设置在一个时间片后中断，最后分派这个进程。
  流程图如下所示：
  

#include "string.h"
#include "stdio.h"
#define NULL 0
typedef struct quen
{
    char pname[8];
    int time1;
    int time2;
    char state;
    struct quen *next;
}QUEN;

void main()
{
    QUEN *q, *p, *head, *m;
    char str[8],f;
    int t,d,n;
    printf("Enter the maxnumber of nodes (n):  n");
    scanf ("%d", &n);
    d=n;
    if (d> 0)
    {
        printf ("enter the pname:");
        scanf ("%s", str);
        printf("enter the need time:");
        scanf("%d",&t);
        head=p=(QUEN*)malloc(sizeof(QUEN));
        strcpy(p->pname,str);
        p->time1=t;
        p->time2=0;
        p->state='R';
        p->next=NULL;
        head=p;
        getchar();
        --d;
    }
    while(d>0)
    {
        printf ("enter the pname:");
        scanf ("%s", str);
        printf ("enter need time:");
        scanf ("%d", & t);
        q= (QUEN *) malloc (sizeof (QUEN));
        strcpy (q-> pname, str); q-> time1=t;
        q-> time2=0;
        q->state='R';
        q->next=NULL;
        p->next=q;
        p=q;
        --d;
        p->next=head;
        q=head;
    }
    printf("process name need time runned staticn");
    do
    {
        printf("%s %d %d %cn",q->pname,q->time1,q->time2,q->state);
        q=q->next;
    }while(q!=head);
    printf("n");
    do
    {
        if(head->time2time1)
        {
            head->time2++;
            if(head->time2==head->time1)
            {
                head->state='E';
                q=head;
                printf("The running process is %sn",q->pname);
                printf("process name left time runned static n");
                do
                {
                    printf ("%s %d %d %c n", q-> pname, q-> time1, q-> time2, q-> state);
                    q=q-> next;
                }while (q!=head);
                printf("n");
                head=head->next;
                q=head;
                p->next=head;
            }else
            {
                printf("The running process is %sn",q->pname);
                printf("process name left time runned staticn");
                do
                {
                    printf("%s %d %d %cn",q->pname,q->time1,q->time2,q->state);
                    q=q->next;
                }while(q!=head);
                printf("n");
                head=head->next;
                q=head;
                p=p->next;
            }
            printf("Is it needing new process?(y or n) n ");
            getchar();
            scanf ("%c" ,&f);
            if(f=='Y'||f=='y')
            {
                getchar();
                printf("Enter the new pname:");
                scanf("%s",str);
                printf("Enter the new neededtime:");
                scanf("%d",&t);  m=(QUEN *)malloc(sizeof(QUEN));
                strcpy(m->pname,str);
                m->time1=t;  m->time2=0;
                m->state='R';
                m->next=NULL;
                if(q->next->state=='E')
                {
                    p=m;
                    head=m;
                    p->next=head;
                    q=head;
                }
                else
                {
                    p->next=m;
                    m->next=head;
                    p=m;
                }
            }
        }
    }while(q->next->state!='E');
    printf("The processes are finishedn");
}