按终止顺序打印？(Print in order of termination?)

 我有一个程序产生一个随机数n，然后循环n次。 
 
 在每次迭代中，它随机化sleeptime的值，并调用fork。 子进程睡眠睡眠时间秒，然后用索引变量的值退出。 
 
 然后父级再次循环，等待每个进程终止。 当每个进程终止时，我试图注销进程的pid和childid，但这是我遇到麻烦的地方。 这些pid按顺序打印，并且childid保持为0。 
 
 我究竟做错了什么？ 
 
int main(int argc, char* argv[])
{

    //  Wire up the timer
    long time = elapsedTime(0);

    /*  Generate a random number between MINFORKS and MAXFORKS
     */
    unsigned int seed = generateSeed(0);
    int n = rand_r(&seed) % MAXFORKS + MINFORKS-1;

    /*  Log next step
     */
    time = elapsedTime(1);
    printf("%li: Number of forks = %i\n", time, n);

    /*  Hang on to the PIDs so we can wait for them after forking
     */
    pid_t *PIDs = (pid_t *)(malloc(sizeof(*PIDs)*n));


    /*  Fork n times
     */
    for (int i = 0; i < n ; i++)
    {
        /*  Call fork() and retain the returned identifier
         */
        pid_t processIdentifier = fork();

        /* Randomize the child sleep time
         */
        seed = generateSeed(0);
        int sleeptime = rand_r(&seed)  % MAXPAUSE + MINPAUSE;

        /*  Check for errors
         */
        if (processIdentifier == -1) {
            printf("Error: %i", errno);
        }


        if (!processIdentifier)
        {
            /*  We're in the child process,
             *  sleep and then exit with
             *  i as the error code.
             */

            usleep(sleeptime);
            _exit(i);
        }
        else
        {
            /*  We're in the parent:
             *  Store the PID and
             *  print out the results.
             */

            PIDs[i] = processIdentifier;

            time = elapsedTime(1);
            printf("%li: Child %i, pid = %i, forked, waits %i usec\n", time,  i, processIdentifier, sleeptime);

        }
    }

    /* Log next step
     */
    time = elapsedTime(1);
    printf("%li: Finished forking, going to wait.\n", time);

    /*
     *  Loop through the processes and wait for them
     *  to terminate. Then print the childid, and the
     *  the pid.
     */

    for (int i = 0; i < n; i++)
    {

        /*  Get the PID we want to track
         */
        pid_t pid = PIDs[i];

        /*  Wait for the child process
         *  and grab it's status info
         */
        int status = NULL;


        waitpid(pid, &status, 0);

        int childid = -1;
        if(WIFEXITED(status))
        {
            childid = WTERMSIG(status);
        }

        /*  Log the results
         */
        time = elapsedTime(1);
        printf("%li: Child %i, pid = %i, terminated\n", time, childid, pid);
    }

    /*  All done!
     */
    time = elapsedTime(1);
    printf("All done. It only took %li milliseconds!", time);   
}
 
 免责声明，这是作业（链接在这里，可能随时消失） ，但我已经完成了几乎所有的作业。 我只是无法理解它的这一方面。 

I've got a program which generates a random number, n, then loops n times.
 
On each iteration, it randomizes the value of sleeptime, and calls fork. The child process sleeps for sleeptime seconds, then exits with the value of the index variable.
 
The parent then loops again, waiting for each process to terminate. As each process terminates, I'm trying to log out the pid and childid of the process, but this is where I'm running into trouble. The pids are printing in order, and childid is remaining at 0.
 
What am I doing wrong?
 
int main(int argc, char* argv[])
{

    //  Wire up the timer
    long time = elapsedTime(0);

    /*  Generate a random number between MINFORKS and MAXFORKS
     */
    unsigned int seed = generateSeed(0);
    int n = rand_r(&seed) % MAXFORKS + MINFORKS-1;

    /*  Log next step
     */
    time = elapsedTime(1);
    printf("%li: Number of forks = %i\n", time, n);

    /*  Hang on to the PIDs so we can wait for them after forking
     */
    pid_t *PIDs = (pid_t *)(malloc(sizeof(*PIDs)*n));


    /*  Fork n times
     */
    for (int i = 0; i < n ; i++)
    {
        /*  Call fork() and retain the returned identifier
         */
        pid_t processIdentifier = fork();

        /* Randomize the child sleep time
         */
        seed = generateSeed(0);
        int sleeptime = rand_r(&seed)  % MAXPAUSE + MINPAUSE;

        /*  Check for errors
         */
        if (processIdentifier == -1) {
            printf("Error: %i", errno);
        }


        if (!processIdentifier)
        {
            /*  We're in the child process,
             *  sleep and then exit with
             *  i as the error code.
             */

            usleep(sleeptime);
            _exit(i);
        }
        else
        {
            /*  We're in the parent:
             *  Store the PID and
             *  print out the results.
             */

            PIDs[i] = processIdentifier;

            time = elapsedTime(1);
            printf("%li: Child %i, pid = %i, forked, waits %i usec\n", time,  i, processIdentifier, sleeptime);

        }
    }

    /* Log next step
     */
    time = elapsedTime(1);
    printf("%li: Finished forking, going to wait.\n", time);

    /*
     *  Loop through the processes and wait for them
     *  to terminate. Then print the childid, and the
     *  the pid.
     */

    for (int i = 0; i < n; i++)
    {

        /*  Get the PID we want to track
         */
        pid_t pid = PIDs[i];

        /*  Wait for the child process
         *  and grab it's status info
         */
        int status = NULL;


        waitpid(pid, &status, 0);

        int childid = -1;
        if(WIFEXITED(status))
        {
            childid = WTERMSIG(status);
        }

        /*  Log the results
         */
        time = elapsedTime(1);
        printf("%li: Child %i, pid = %i, terminated\n", time, childid, pid);
    }

    /*  All done!
     */
    time = elapsedTime(1);
    printf("All done. It only took %li milliseconds!", time);   
}
 
Disclaimer, this is homework (link here, may disappear at any time), but I've already done almost all of it. I'm just having trouble grasping this one aspect of it.

原文：https://stackoverflow.com/questions/16742907