Question

我正在尝试与子进程进行通信，并使它们成为列表的一部分。我的问题是儿童过程阅读了所有内容，但在此之后什么都不做。

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）循环中进行等待，但是当我从父进程关闭管道的写入结束时，它们应该离开循环。

Answer 1

您可能认为某个特定pipe[2]由父母及其各自的子流程共享。这是真的......然而，它也会在您创建的所有其他子进程中共享 - 并且因为它已经打开，其他子进程也会将其继承为已打开。

在孩子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]);
        }
    }
    ...
}

Answer 2

我怀疑从管道读取：

while（读取（fd [i] [0]，＆amp; received，sizeof（int））＆gt; 0）

在管道上有数据可用之前，

被阻止/阻止。如果是这样，这可以解释在此之后您的代码缺乏响应。

多个管道和流程

2 个答案: