Linux编程：模拟进程调度算法稍稍有点操作系统基础的朋友应该知道进程的调度算法，在这⾥Koala还是给⼤家略微介绍⼀下接下来将要⽤到的⼏种算法：1. 先来先服务（FCFS）采⽤FCFS调度，先请求CPU的进程会先分配到CPU。
使⽤FCFS调度的等待时间通常较长，CPU利⽤率也会较低2. 最短作业优先调度（SJF）采⽤SJF调度会选择具有最短CPU运⾏时间的进程分配CPU使⽤权。
如果两个进程的CPU区间相同，则按照FCFS来进⾏选择。
SJF调度可以证明是最佳的，它降低了平均等待时间。
3. 轮转法调度（RR）RR调度将CPU时间分为较⼩的时间⽚，调度程序循环就绪队列。
为每⼀个进程分配不超过⼀个时间⽚的CPU。
RR调度专门⽤于分时系统。
4. 优先级调度每⼀个进程都有⼀个优先级与其关联，具有最⾼优先级的进程会分配到CPU。
优先级调度的⼀个主要问题是优先级较低的进程会产⽣饥饿现象。
整个编程思路按照如下进⾏：创建主线程，主线程创建⼦线程，⼦线程有⼀个虚拟PCB主线程创建20个⼦线程，分别实现FCFS调度、SJF调度、RR调度、优先级调度，并且计算每个调度的平均等待时间。
对于每个⼦线程，在其运⾏期间，输出其占⽤的时间标号（例如，第3个线程占⽤了第10秒的CPU时间，输出为：“Thread3：10”）。
下⾯是整个的代码（仅供参考）：#include<stdio.h>#include<stdlib.h>#include<sys/types.h>#include<unistd.h>#include<pthread.h>#include<time.h>#include<iostream>#define Thread_Num 20using namespace std;pthread_mutex_t Device_mutex ;//Virtual PCB of threadsstruct VirtualPCB{int tid;int priority;int waittime;int runtime;int arrivetime;int visited;int tempruntime;public:int gettid(){return tid;}int getwaittime(){return waittime;}int getpriority(){return priority;}int getruntime(){return runtime;}int getarrivetime(){return arrivetime;}void setvisit(int a){visited=a;}int getvisit(){return visited;}int gettempruntime(){return tempruntime;}void setwaittime(int n){waittime = n;}void settempruntime(int n){tempruntime = tempruntime - n;}}TCB[Thread_Num];//Function to initial virtual PCBvoid t_init(){int n;srand(time(NULL));for(n =0;n<Thread_Num;n++){TCB[n].tid = n + 1;//⽤线程创建序号作为虚拟进程id//⽤随机数随机产⽣虚拟PCB的值TCB[n].priority = 1 + rand()%19;TCB[n].runtime = 1 + rand()%19;TCB[n].arrivetime = 0;//模拟时，默认进程按创建顺序依次在0时刻到达TCB[n].waittime = 0;TCB[n].visited =0;TCB[n].tempruntime = TCB[n].runtime;}}//Threads run functionvoid *t_print(void *arg){int n = *(int *)arg;//get argumentwhile(1){pthread_mutex_lock(&Device_mutex);printf("Thread_%-2d: ",n);printf("tid:%-2d priority:%-2d runtime:%-2d \n",TCB[n-1].gettid(),TCB[n-1].priority,TCB[n-1].runtime); pthread_mutex_unlock(&Device_mutex);sleep(1);break;}//printf("Error %d\n",n);pthread_exit(0);}//First come first service schedule functionvoid FCFS(){cout<<"-----------FCFS:"<<endl;int i,j;int start = 0;float waittime = 0;float avwait = 0;for(i=0;i<Thread_Num/2;i++){for(j=0;j<Thread_Num;j++){if(TCB[j].getarrivetime()==i && TCB[j].getvisit()==0){printf("Thread: %-2d Start: %-3d Runtime: %-2d\n",TCB[j].gettid(),start,TCB[j].getruntime()); waittime = waittime + (float)start;start = start + TCB[j].getruntime();TCB[j].setvisit(1);}}}avwait = waittime / (float)Thread_Num;printf("Total waitting time : %f\n",waittime);printf("Average waitting time : %f\n",avwait);}//Shortest job first schedule functionvoid SJF(){for(int k=0 ;k<Thread_Num;k++){TCB[k].setvisit(0);}cout<<"-------------SJF:"<<endl;int i,j;int start = 0;float waittime = 0;float avwait = 0;for(i=1;i<Thread_Num;i++){for(j=0;j<Thread_Num;j++){if(TCB[j].getruntime()==i && TCB[j].getvisit()==0){printf("Thread: %-2d Start: %-3d Runtime: %-2d\n",TCB[j].gettid(),start,TCB[j].getruntime()); waittime = waittime + (float)start;start = start + TCB[j].getruntime();TCB[j].setvisit(1);}}}avwait = waittime / (float)Thread_Num;printf("Total waitting time : %f\n",waittime);printf("Average waitting time : %f\n",avwait);}//Round R schedule functionvoid RR(int r){cout<<"--------------RR:"<<endl;int start = 0;float waittime = 0;float avwait = 0;for(int i=0;i<Thread_Num;i++){int totaltime = totaltime + TCB[i].getruntime();TCB[i].setvisit(0);}for(int j=0;j<20*Thread_Num;j=j+r){int k = (j%(20*r))/r;if(TCB[k].gettempruntime() > 0){int tepruntime = r;if(TCB[k].gettempruntime()-r<=0){tepruntime = TCB[k].gettempruntime();TCB[k].setwaittime(start + tepruntime - TCB[k].getruntime());}printf("Thread: %-2d Start: %-3d Runtime:%-2d \n",TCB[k].gettid(), start,tepruntime);start = start + tepruntime;TCB[k].settempruntime(r) ;}}for(int m=0;m<Thread_Num;m++){waittime += TCB[m].getwaittime();//printf("TCB[%d].getwaittime():%d\n",m+1,TCB[m].getwaittime());}avwait = waittime / (float)Thread_Num;printf("Total waitting time : %f\n",waittime);printf("Average waitting time : %f\n",avwait);}//Priority schedule functionvoid Priority(){for(int k=0 ;k<Thread_Num;k++){TCB[k].setvisit(0);}cout<<"-----------Priority:"<<endl;int i,j;int start = 0;float waittime = 0;float avwait = 0;for(i=1;i<Thread_Num;i++){for(j=0;j<Thread_Num;j++){if(TCB[j].getpriority()==i && TCB[j].getvisit()==0){printf("Thread: %-2d Start: %-3d Runtime: %-2d\n",TCB[j].gettid(),start,TCB[j].getruntime()); waittime = waittime + (float)start;start = start + TCB[j].getruntime();TCB[j].setvisit(1);}}}avwait = waittime / (float)Thread_Num;printf("Total waitting time : %f\n",waittime);printf("Average waitting time : %f\n",avwait);}//Main thread execute function to create 20 children threadsvoid *Children(void*){int ret[Thread_Num];t_init();pthread_t tid[Thread_Num];pthread_mutex_init(&Device_mutex,NULL);int i,j;for(i=0;i<Thread_Num;i++){int k =i+1;ret[i] = pthread_create(&tid[i],NULL,&t_print, &k);if(ret[i] == 0) {sleep(1);}else{printf("Thread_%-2d failed!\n",i+1);}}for(j=0;j<Thread_Num;j++)pthread_join (tid[i], NULL);pthread_mutex_destroy(&Device_mutex);pthread_exit(0);}int main(){int ret1;pthread_t tid1;//Declare main threadret1 = pthread_create(&tid1,NULL,&Children,NULL);//Create main threadif(ret1 == 0){printf("Main Thread ok!\n");sleep(20);}else{printf("Thread failed!\n");}FCFS();SJF();cout<<"Please enter RR time:\n";//Request RR timeint rr;scanf("%d",&rr);RR(rr);Priority();return 0;}OK！此代码的运⾏结果如下（部分）：第⼀张图打印了⼀下虚拟PCB的部分内容：第⼆张图⽚打印了FCFS调度算法运⾏结果：第三张图⽚打印了SJF调度算法运⾏结果：第四张图⽚打印了RR调度算法运⾏结果（部分）：第五张图⽚打印了Priority调度算法运⾏结果：注意看每张图下⾯的两⾏数据，分别是不同算法对应的总的进程的等待时间以及平均等待时间的⼤⼩，印证了SJF算法通常是最少平均等待时间的调度算法最后希望⼤家能够积极提建议，指出纰漏！。
