在最后一个孩子中显示过程树

Question

我想创建一棵进程树，就像图片上的树一样。 Z进程应在作为程序参数给出的秒数后显示整个树，我需要处理对树的适当破坏。另外，我不能使用sleep()命令。程序输出应如下所示：

I’m the process arb: my pid is 751
I’m the process A: my pid is 752. My father is 751
I’m the process B: my pid is 753. My father is 752, grandfather 751
I’m the process X: my pid is 754. My father is 753, grandfather 752, great-grandfather is 751
I’m the process Y: my pid is 755. My father is 753, grandfather 752, great-grandfather is 751
I’m the process Z: my pid is 756. My father is 753, grandfather 752, great-grandfather is 751
//wait some seconds and display process tree 
I am Z (755) and I die
I am Y (755) and I die
I am X (754) and I die
I am B (753) and I die
I am A (752) and I die
I am arb (751) and I die

找到最后一个孩子并发出警报后，它不会显示进程树，而是开始创建一些新进程而不是杀死它们。这是我的代码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>

int arb;
void z_function() {
printf("pstree\n");
    execl("/bin/pstree", "pstree", "-p", arb, (char*)0);
    printf("I am Z (%d) and I die\n", getpid());
    kill(getpid(), SIGKILL);
}

int main(int argc, char **argv) {
signal(SIGALRM, z_function);
int arg = atoi(argv[1]);
printf("arg: %d\n", arg);
arb = getpid();
printf("I'm the process arb: my pid is %d\n", getpid());
//A 
if (fork() == 0) {      
    int a = getpid();
    printf("I'm the process A: my pid is %d. My father is %d\n", getpid(), getppid());
    //B     
    if (fork() == 0) {
        int b = getpid();
        printf("I'm the process B: my pid is %d. My father is %d, grandfather %d\n", getpid(), getppid(), arb);
        int children[3];
        for (int i = 0; i < 3; i++) {
            if (fork() == 0) {
                children[i] = getpid();
                switch(i) {
                    case 0:
                        printf("I'm the process X: my pid is %d. My father is %d, grandfather %d, great-grandfather is %d\n", getpid(), getppid(), a, arb);
                        wait(NULL);
                        break;                          
                    case 1:     
                        printf("I'm the process Y: my pid is %d. My father is %d, grandfather %d, great-grandfather is %d\n", getpid(), getppid(), a, arb);
                        wait(NULL);
                        break;
                    case 2:
                        printf("I'm the process Z: my pid is %d. My father is %d, grandfather %d, great-grandfather is %d\n", getpid(), getppid(), a, arb);
                        alarm(arg);
                        pause();
                        //exit(0); 
                        break;  
                }   
            }
            else {

                wait(NULL);
            }               
        }
        wait(NULL);
        kill(children[1], SIGKILL);
        printf("I am Y (%d) and I die\n", children[1]);
        kill(children[0], SIGKILL);
        printf("I am X (%d) and I die\n", children[0]);
        printf("I am B (%d) and I die\n", getpid());
        exit(0);        
    }
    wait(NULL);
    printf("I am A (%d) and I die\n", getpid());        
    exit(0);        
}
else {
    wait(NULL);
    printf("I am arb (%d) and I die\n", getpid());
    exit(0);
}
while (wait(NULL) > 0) 
    exit(0);
return 0;
}