进程调度，关于状态机的问题
我想用fork产生3个子进程执行不同的任务，各个子进程分别按照他们自己的优先级做事情，这个咋弄啊。我原本是通过setpriority函数来设定他们的优先级，可以步行。进程1，child1的优先级是14.child2的优先级是10.child3的优先级是-3.按道理应该是子进程child3先执行。可事实上并不是如此。代码如下
据说可以用状态机可以实现，不知道怎么做。

#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>
#include<sys/time.h>
#include<sys/resource.h>
#include<sys/types.h>


void main()
{
pid_t father,child1,child2,child3;
int prio;
father=getpid();
setpriority(PRIO_PROCESS,0,20);
//nice(10);
printf("the father ID is : %d\n",father);
prio=getpriority(PRIO_PROCESS,0);
printf("the father priority is %d\n",prio);
child1=fork();
if(child1==0) {
setpriority(PRIO_PROCESS,0,14);
prio=getpriority(PRIO_PROCESS,0);
printf("the child one ID is : %d\n",getpid());
printf("the child one priority is %d\n",prio);
}
else if(child1>0){
child2=fork();
if(child2==0) {
setpriority(PRIO_PROCESS,0,10);
prio=getpriority(PRIO_PROCESS,0);
printf("the child two ID is : %d\n",getpid());
printf("the child two priority is %d\n",prio);
}
else if(child2>0){
child3=fork();
if(child3==0) {
setpriority(PRIO_PROCESS,0,-3);
prio=getpriority(PRIO_PROCESS,0);
printf("the child three ID is : %d\n",getpid());
printf("the child three priority is %d\n",prio);
}
else if(child3>0) {
printf("my ID is %d\n",getpid());
printf("my prio is %d\n",getpriority(PRIO_PROCESS,0));
}

}
}

}
执行结果是：
先执行1，再 2，再3

[解决办法]

C/C++ code

#include<unistd.h>#include<stdio.h>#include<stdlib.h>#include<sys/time.h>#include<sys/resource.h>#include<sys/types.h>#include<sys/mman.h>int main(){  pid_t father,child1,child2,child3;  int prio;  int *flag;    flag = (int *)mmap(NULL,sizeof(int),PROT_READ|PROT_WRITE,MAP_SHARED|MAP_ANONYMOUS,-1,0);  (*flag)=3;  father=getpid();  setpriority(PRIO_PROCESS,0,20);  //nice(10);  printf("the father ID is : %d\n",father);  prio=getpriority(PRIO_PROCESS,0);  printf("the father priority is %d\n",prio);  child1=fork();  if(child1==0) {  while(1 != (*flag)){      //printf("child1 wait\n");      sleep(1);  }  setpriority(PRIO_PROCESS,0,14);  prio=getpriority(PRIO_PROCESS,0);  printf("the child one ID is : %d\n",getpid());  printf("the child one priority is %d\n",prio);  }  else if(child1>0){  child2=fork();  if(child2==0) {  while(2 != (*flag)){      //printf("child2 wait\n");      sleep(1);  }  setpriority(PRIO_PROCESS,0,10);  prio=getpriority(PRIO_PROCESS,0);  printf("the child two ID is : %d\n",getpid());  printf("the child two priority is %d\n",prio);  (*flag) = 1;  }  else if(child2>0){  child3=fork();  if(child3==0) {  setpriority(PRIO_PROCESS,0,-3);  prio=getpriority(PRIO_PROCESS,0);  printf("the child three ID is : %d\n",getpid());  printf("the child three priority is %d\n",prio);  (*flag) = 2;  }  else if(child3>0) {  printf("my ID is %d\n",getpid());  printf("my prio is %d\n",getpriority(PRIO_PROCESS,0));  }      }  }    return 0;}