C 在具有事件等待的子进程之间共享内存时出错

Question

我正在尝试编写一个在子进程和父进程之间共享内存的程序。该程序还使用 fork 。

练习的目的是:-父亲发送给 child (共享内存)3次主动等待的 vector

- child 收到vec，打印它并改变同步变量

  Struct:
    typedef struct{
    int change[NUM_TOTAL];
    int synchronize;
    }Exchange; 

---

Exchange *vec;

int fd = shm_open("/shmtest8",O_CREAT| O_RDWR,S_IRUSR|S_IWUSR); 
//Check shm_open error
ftruncate(fd, 100);
vec = (Exchange*)  mmap(NULL,100,PROT_READ|PROT_WRITE, MAP_SHARED, fd ,0);      

     x = forkFunc()  //Creates a fork, and return 0 to parente and > 0 to child process
    if(x == 0){  //Parent
    int cont = 0;

    while(cont != 3){
        printf("Father\n");
        vec->synchronize = 1;  //Now go to to the child

        while(vec->synchronize!=0); //the child change the variable to 0                
        cont++;
        printf("cont %d",cont);
    }


    wait(NULL);

    munmap(vec,sizeof(vec));
    close(fd);
    shm_unlink("/shmtest8");


}else if(x > 0){   //Child

    int cont = 0;

        while(vec->synchronize!=1);   //Exit while when father change the variable to 1
        int i;

    for(i = 0; i < 10; i++){
            printf("%d\t",i);
        }

        vec->synchronize =0;    //Return to the father
}   

这是一个输出的例子:

     Father
     Child
      0 1   2   3   4   5   6   7   8   9
     cont 1
     Father

在第一次迭代之后，程序在“while(vec->synchronize!=0);”之后卡住...我想问题存在于子进程中，但我不知道为什么...有什么想法吗？

谢谢

Answer 1

我认为你的子进程部分应该有 1 个 while 循环

while(cont != 3){
     while(vec->synchronize!=1);   //Exit while when father change the variable to 1
     int i;
     for(i = 0; i < 10; i++){
          printf("%d\t",i);
     }

     ec->synchronize =0;    //Return to the father
     cont++
 }