c - 在链中 fork N 个进程

Question

我想解决某个问题，但我不知道如何正确解决。我必须在链中创建 N 个进程，在我完成所有这些之后，初始进程将随机一个数字并将其写入管道，其他进程从管道中读取该数字，它们随机化一个数字并从中减去结果读取的数字，将其写回管道等。这是我试过的

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

#define P_READ 0
#define P_WRITE 1


void forker(int nprocesses, int** pipes, int fd[2])
{
    pid_t pid;
    int buf;

    if(nprocesses > 0)
    {
        if ((pid = fork()) < 0)
        {
            perror("fork");
        }
        else if (pid == 0)
        {
            //Child
            printf("Child %d created PID : %d , PPID : %d\n", nprocesses-1, getpid(), getppid());
            int i = nprocesses - 1;

            time_t t;
            srand((int)time(&t) % getpid()); // get unique seed for every child
            int r = (rand() % 11) + 10;

            if (i==0) {
                read(fd[P_READ], &buf, sizeof(int));
                close(fd[P_READ]);
            }else{
                read(pipes[i-1][P_READ], &buf, sizeof(int));
                close(pipes[i-1][P_READ]);
            }
            close(pipes[i][P_READ]);
            buf -= r;
            printf("%d|%d|%d|%d\n", buf, r, getpid(), getppid());
            write(pipes[i][P_WRITE], &buf, sizeof(int)); // write
            close(pipes[i][P_WRITE]);
            printf("Child %d end\n", nprocesses-1);
        }
        else if(pid > 0)
        {
         forker(nprocesses - 1, pipes, fd);
        }

    }
}


int main (void)
{

    int status = 0;
    srand(time(NULL));
    pid_t pid = getpid();
    pid_t parent = getpid();
    pid_t wpid;
    int n, fd[2], buf;


    printf("Please enter how many processes you want(between 6 and 15): ");
    scanf("%d", &n);
    while ( n < 6 || n > 15)
        scanf("%d", &n);

    int **pipes = (int **)malloc(n * sizeof(int*));
    for(int i = 0; i < n; i++) pipes[i] = (int *)malloc(2 * sizeof(int));

    printf("I'm parent - my pid is %d\n",pid);

    pipe(fd);


    for(int i=0; i<n; i++) {
        if(pipe(pipes[i])) {
            printf("pipe error");
            return -1;
        }
    }

    forker(n, pipes, fd);

    if(parent == getpid()) {
        close(fd[P_READ]);
        buf = (rand() % 9001) + 1000;
        printf("The initial number is %d created by process with pid : %d\n", buf, getpid());
        write(fd[P_WRITE], &buf, sizeof(int));
        close(fd[P_WRITE]);
    }

    while ((wpid = wait(&status)) > 0); // WAIT
    if (pid == getpid()) printf("End of parent and my pid was %d\n", pid);
    return 0;
}

输出看起来像这样:

Please enter how many processes you want(between 6 and 15): 10
I'm parent - my pid is 3827
Child 9 created PID : 3828 , PPID : 3827
Child 8 created PID : 3829 , PPID : 3827
Child 7 created PID : 3830 , PPID : 3827
Child 6 created PID : 3831 , PPID : 3827
Child 5 created PID : 3832 , PPID : 3827
Child 2 created PID : 3835 , PPID : 3827
Child 3 created PID : 3834 , PPID : 3827
The initial number is 1625 created by process with pid : 3827
Child 1 created PID : 3836 , PPID : 3827
Child 4 created PID : 3833 , PPID : 3827
Child 0 created PID : 3837 , PPID : 3827
1609|16|3837|3827
Child 0 end
1589|20|3836|3827
1573|16|3835|3827
Child 2 end
1559|14|3834|3827
Child 3 end
1543|16|3833|3827
Child 4 end
1530|13|3832|3827
Child 5 end
Child 1 end
1511|19|3831|3827
Child 6 end
1498|13|3830|3827
Child 7 end
1488|10|3829|3827
Child 8 end
1470|18|3828|3827
Child 9 end
End of parent and my pid was 3827

问题是，我不确定第一个数字是否在进程创建之前是随机的(但这不是这里的大问题)。最大的问题是初始进程创建了所有子进程并且它不是“链式”的。

Answer 1

首先fork你处理N次，然后生成随机数并传递给其他进程。所以将随机数的创建放在循环之外以 fork 主进程