如何理解进程调度算法？
我们老师要求写一个操作系统的进程调度算法，自己想了很长时间，没做出来。结果一个同学给了我一个程序（如下）,我呢，也看了很长时间，对这个程序理解不透，所以把这个
程序拿出来和大家讨论一下，到底每个函数到底是实现什么。
也就是说，能不能再多一点注释。这样，我可能会理解的多一些
先谢过各位了喔~~~~
1. 进程调度算法 4学时
/*进程调度-----优先级算法源程序*/
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "conio.h"
typedef struct node /*创建PCB*/
{ char name[10]; /*进程标识*/
int prio; /*进程优先数*/
int cputime; /*进程占用CPU时间*/
int needtime; /*进程完成所需时间*/
int count; /*计数器*/
char state; /*进程的状态*/
struct node *next; /*链指针*/
}PCB;
PCB *finish,*ready,*tail,*run;
int N;
void firstin() /*创建就绪队列对头指针*/
{
run=ready;
run->state='R';
ready=ready->next;
}
void prt() /*演示进程调度*/
{
PCB *p;
printf(" NAME CPUTIME NEEDTIME PRIORITY STATUS\n");
if(run!=NULL)
printf(" %-10s%-10d%-10d%-10d %c\n",run->name,
run->cputime,run->needtime,run->prio,run->state);
p=ready;
while(p!=NULL)
{ printf(" %-10s%-10d%-10d%-10d %c\n",p->name,
p->cputime,p->needtime,p->prio,p->state);
p=p->next;
}
p=finish;
while(p!=NULL)
{ printf(" %-10s%-10d%-10d%-10d %c\n",p->name,
p->cputime,p->needtime,p->prio,p->state);
p=p->next;
}
getch();
}
void insert(PCB *q)
{
PCB *p1,*s,*r;
int b;
s=q;
p1=ready;
r=p1;
b=1;
while((p1!=NULL)&&b)
if(p1->prio>=s->prio)
{
r=p1;
p1=p1->next;
}
else
b=0;
if(r!=p1)
{
r->next=s;
s->next=p1;
}
else
{
s->next=p1;
ready=s;
}
}
void create() /*创建各个进程*/
{
PCB *p;
int i,time;
char na[10];
ready=NULL;
finish=NULL;
run=NULL;
for(i=1;i<=N;i++)
{
p=new PCB();
printf("Enter NAME of process:\n");
scanf("%s",na);
printf("Enter TIME of process(less than 50):\n");
scanf("%d",&time);
strcpy(p->name,na);
p->cputime=0;
p->needtime=time;
p->state='w';
p->prio=50-time; /*假设优先级与耗时之和为50*/
if(ready!=NULL)
insert(p);
else
{
p->next=ready;
ready=p;
}
}
system("cls");
printf(" DISPLAY OF THE PROGRESS:\n");
printf("************************************************\n");
prt();
run=ready;
ready=ready->next;
run->state='R';
}
void priority() /*优先级算法调度*/
{
while(run!=NULL&&run->prio>=0)
{
run->cputime=run->cputime+1;
run->needtime=run->needtime-1;
run->prio=run->prio-3;
if(run->needtime==0)
{
run->next=finish;
finish=run;
run->state='F';
run=NULL;
if(ready!=NULL)
firstin();
}
else
if((ready!=NULL)&&(run->prio<ready->prio))
{
run->state='W';
insert(run);
firstin();
}
prt();
}
}
int main()
{
system("cls");
loop: printf("Enter THE TOTAL NUMBER of PCB(less than 10 is better):\n");
scanf("%d",&N);
if(N>10)
{printf("it's too big,and select a small number.\n");
goto loop;}
create();
priority();
getch();
return 0;
}
