c - 检测多个子进程的终止

Question

我必须编写代码来使用父进程创建多个子进程。父进程应该处于休眠状态，直到它创建了一定数量的进程。子进程向父进程发送 SIGCHLD 信号以中断 sleep ，并强制父进程调用 wait 来收集已终止子进程的状态集合。

我在UBUNTU上编写了以下代码:

#include <stdlib.h> /* needed to define exit() */
#include <unistd.h> /* needed for fork() and getpid() */
#include <signal.h> /* needed for signal */
#include <stdio.h>  /* needed for printf() */

int main(int argc, char **argv)
{
void catch(int);    /* signal handler */
void child(int);    /* the child calls this */
void parent(int pid);   /* the parent calls this */
int pid;        /* process ID */
int i;          /* Number of processes*/

signal(SIGCHLD, catch); /* detect child termination */

for(i=0;i<5;i++)
{
    pid = fork();   /* create child process*/
    switch (pid) 
    {
    case -1:    /* something went wrong */
        perror("fork");
        exit(1);
    case 0:     /* a fork returns 0 to the child */
        child(i+1);
        break;
    default:    /* a fork returns a pid to the parent */
        //parent(pid);
        break;
    }
}
exit(0);
}

void child(int id)
{
    printf("\tchild%d: I'm the child\n",id);
    sleep(10);      /* do nothing for 3 seconds */
    printf("\tchild: I'm exiting\n");
    exit(id);       /* exit with a return code of 123 */
}

void parent(int pid)
{
    printf("parent: I'm the parent\n");
    sleep(15);      /* do nothing for five seconds */
    printf("parent: exiting\n");
}

void catch(int snum)
{
    int pid;
    int status;

    pid = wait(&status);
    printf("parent: child process exited with value %d\n",WEXITSTATUS(status));
    /* WEXITSTATUS(status):
     * Since only the last 8 bits are available 
     * it will be logical to mask the upper bit by   
     * doing a bitwise and operation with 255. 
     * A system defined macro does this for us. 
     */
}

我得到这样的输出:

parent: I'm the parent
    child1: I'm the child
    child: I'm exiting
parent: child process exited with value 1
parent: exiting
parent: I'm the parent
    child2: I'm the child
    child: I'm exiting
parent: child process exited with value 2
parent: exiting
parent: I'm the parent
    child3: I'm the child
    child: I'm exiting
parent: child process exited with value 3
parent: exiting
parent: I'm the parent
    child4: I'm the child
    child: I'm exiting
parent: child process exited with value 4
parent: exiting
parent: I'm the parent
    child5: I'm the child
    child: I'm exiting
parent: child process exited with value 5
parent: exiting

而我想要这样的输出:

parent: I'm the parent
    child1: I'm the child
    child: I'm exiting
parent: child process exited with value 1
    child2: I'm the child
    child: I'm exiting
parent: child process exited with value 2
    child3: I'm the child
    child: I'm exiting
parent: child process exited with value 3
    child4: I'm the child
    child: I'm exiting
parent: child process exited with value 4
    child5: I'm the child
    child: I'm exiting
parent: child process exited with value 5
parent: exiting

我应该在代码中进行哪些更改...？请帮忙..!!!

Answer 1

您正在循环内打印 parent: I'm the Parent 和 parent: exiting 。如果您希望它们只打印一次，请将它们移出循环。

您可能还想考虑使用 wait 或 waitpid 函数来等待子进程终止，而不是使用信号处理程序和 sleep.