多个管道和进程

Question

我正在尝试与子进程通信并让它们对列表的一部分进行排序。我的问题是子进程读取所有内容但之后什么也不做。

int main(int argc, char *argv[]){
    int i;
    int num_children;
    pid_t pid;

    num_children= 3;

    int fd[num_children][2];      //PIPES

    for (i=0; i<num_children; i++)
    {
        if (pipe(fd[i]) == -1)
        {
            printf("couldnt create the pipe\n");
            exit(EXIT_FAILURE);
        }
    }


    for (i=0; i<num_children; i++)
    {
        pid = fork();
        if (pid == -1)
        {
            printf("couldnt create child process %i\n",i);
            exit(EXIT_FAILURE);
        }

        if (pid == 0)
        {                         //this is child process
            close(fd[i][1]);         //closing fd[1] the write end of the pipe
            int received;
            node *list = NULL;
            while ( read(fd[i][0], &received, sizeof(int)) > 0)
            {
                list = insert(list, received);
                printf("Process %i got the number: %i\n",i,received);  //this part is working perfect
            }

            printf("Im process %i here is my list: \n",i);   //i couldnt get any output from here
            printList(list);

            close(fd[i][0]);
            exit(EXIT_SUCCESS);
         }       
    }


    for (i=0; i<num_children; i++)  //closing the read end of pipe for parent
    {
        close(fd[i][0]);
    }

    int number;
    int mod;
    FILE *fileIn = fopen ("<file directory>","r");
    while(fscanf(fileIn, "%i", &number)>=0)
    {
        mod = number % num_children;
        write(fd[mod][1], &number, sizeof(int));
    }  

    for (int i=0; i<num_children; i++)
    {
        if(close(fd[i][1])==0)
        {
            printf("cant close the pipe");  
            //tried to catch errors, but pipes are closing with no problem i think
        }
    }

    return 0;

我试图查看子进程是否在 while(read) 循环中等待，但是当我关闭父进程的管道写入端时，它们应该离开循环。

Answer 1

我怀疑管道读数来自：

while (读取(fd[i][0], &received, sizeof(int)) > 0)

正在 blocked/haulted 直到数据在管道上可用。如果是这样，这将解释您的代码在此之后没有响应。

Answer 2

您可能认为某些特定的 pipe[2] 由 parent 共享，并且是各自的 child 进程。没错……但是它也被您在此过程中创建的所有其他 children 进程共享 - 因为它已打开，所以其他 children 进程也会在打开时继承它。

在 child pid 检查开始时这样做对我有用：

if (pid == 0) {
    int j;
    for (j = 0; j < num_children; j++) {
        if (j != i) {
            close(fd[j][0]);
            close(fd[j][1]);
        }
    }
    ...
}

多个管道和进程

Multiple pipes and processes

c

operating-system

fork

pipe

child-process