在c中创建顺序子进程

Question

我希望创建一个顺序进程来创建指定数量的子进程。例如，如果父进程 ID 为 769，则进程将如下所示:

769(parent) -> 770(first child) -> 771(grand child) ... -> xx (n*grand child)

基于我想要的 child 数量。只要子级是连续的并且没有 sibling ，它们的 PID 并不重要。

int main(int argc, char **argv) {
    int i;
    int iterations;

    if (argc != 2) {
        fprintf(stderr, "Usage: forkloop <iterations>\n");
        exit(1);
    }

    iterations = strtol(argv[1], NULL, 10);

    int n = fork();
    for (i = 0; i < iterations; i++) {
        if(n == 0) {
            printf("ppid = %d, pid = %d, i = %d\n", getppid(), getpid(), i);
            n = fork();
        }
        if (n < 0) {
            perror("fork");
            exit(1);
        }
       //printf("ppid = %d, pid = %d, i = %d\n", getppid(), getpid(), i);
    }
    // printf("ppid = %d, pid = %d\n", getppid(), getpid());
    return 0;
}

我已经做到了，但我相信这有点错误。有人可以帮忙吗？

Answer 1

仔细思考逻辑。你们很接近，但需要再靠近一点。这有效:

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

int main(int argc, char **argv)
{
    if (argc != 2)
    {
        fprintf(stderr, "Usage: forkloop <iterations>\n");
        exit(1);
    }

    int iterations = strtol(argv[1], NULL, 10);
    if (iterations < 1 || iterations > 20)
    {
        fprintf(stderr, "invalid iterations %d (1..20 allowed)\n", iterations);
        exit(1);
    }
    printf("Initial process: PID %d (parent %d)\n", (int)getpid(), (int)getppid());
    fflush(stdout);
    int i;
    for (i = 0; i < iterations; i++)
    {
        int pid = fork();
        if (pid < 0)
        {
            perror("fork");
            exit(1);
        }
        else if (pid == 0)
        {
            /* Child - report ID */
            printf("ppid = %d, pid = %d, i = %d\n", getppid(), getpid(), i);
            fflush(stdout);
        }
        if (pid != 0)
        {
            /* Parent - break loop and wait for kid (and grandkid, and ...) to die */
            break;
        }
    }

    int corpse;
    int status;
    while ((corpse = wait(&status)) > 0)
    {
        printf("PID %d: child %d exited with status 0x%.4X\n",
               (int)getpid(), corpse, status);
        fflush(stdout);
    }

    return i;
}

(不能保证 getpid() 等返回的 pid_t 实际上是 int，尽管它通常是等效的。我添加了强制转换以确保没有问题，尽管实际上您可以不用它们。最后一个 fflush() 并不是严格需要的；进程退出，无论如何都会刷新输出。前面的是好主意；如果它们不存在，并且程序的输出通过管道传输到某个进程来捕获它，您可能会得到令人困惑的输出。在 fork() 之前，最好不要有待处理的输出 —所以一般来说，fflush(0)又名fflush(NULL)也许是一个好主意，尽管这里没有必要。)

示例输出(源代码 kids17.c，程序名称 kids17):

$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -Wmissing-prototypes \
>     -Wstrict-prototypes kids17.c -o kids17 
$ kids17
Usage: forkloop <iterations>
$ kids17 4
Initial process: PID 2686 (parent 888)
ppid = 2686, pid = 2687, i = 0
ppid = 2687, pid = 2688, i = 1
ppid = 2688, pid = 2689, i = 2
ppid = 2689, pid = 2690, i = 3
PID 2689: child 2690 exited with status 0x0400
PID 2688: child 2689 exited with status 0x0300
PID 2687: child 2688 exited with status 0x0200
PID 2686: child 2687 exited with status 0x0100
$ …some work done…
$ kids17 10
Initial process: PID 2704 (parent 888)
ppid = 2704, pid = 2705, i = 0
ppid = 2705, pid = 2706, i = 1
ppid = 2706, pid = 2707, i = 2
ppid = 2707, pid = 2708, i = 3
ppid = 2708, pid = 2709, i = 4
ppid = 2709, pid = 2710, i = 5
ppid = 2710, pid = 2711, i = 6
ppid = 2711, pid = 2712, i = 7
ppid = 2712, pid = 2713, i = 8
ppid = 2713, pid = 2714, i = 9
PID 2713: child 2714 exited with status 0x0A00
PID 2712: child 2713 exited with status 0x0900
PID 2711: child 2712 exited with status 0x0800
PID 2710: child 2711 exited with status 0x0700
PID 2709: child 2710 exited with status 0x0600
PID 2708: child 2709 exited with status 0x0500
PID 2707: child 2708 exited with status 0x0400
PID 2706: child 2707 exited with status 0x0300
PID 2705: child 2706 exited with status 0x0200
PID 2704: child 2705 exited with status 0x0100
$

在运行此测试时，我没有任何其他进程主动生成子进程。