From owner-freebsd-hackers  Wed Apr  7 17:31:35 1999
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Date: Wed, 07 Apr 1999 20:32:55 -0400 (EDT)
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Reply-To: shimon@simon-shapiro.org
Organization: Simon's Garage
From: Simon Shapiro <shimon@simon-shapiro.org>
To: freebsd-hackers@freebsd.org
Subject: wait4 - Proof I am stupid
Sender: owner-freebsd-hackers@FreeBSD.ORG
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X-Loop: FreeBSD.ORG

Hi Y'll,

Please bear with me:

int x;

pid_t my_pgid;

switch (fork()) {
case 0:
        (void)setpgid(getpid(), getpid());

        my_pgid = getpgrp();

        for (x = 0; x < 10; x++) {
                switch (fork()) {
                case 0:
                        /* Go do something useful */
                        break;
                case -1:
                        /* Ooops! */
                                break;
                default:
                        /* Ignore */
                        break;
                }
        }
        exit(0);
        break;;
case -1:
        /* Ooops! */
        break;
default:
        /* ignore */
        break;
}

/*
 *  So far, this code should (and does) fork a process.
 *  This process (child then changes its process group to something else
 *  than the parent and then forks 10 children.
 *
 *  Now the parent wants to wait for the grandchidren...
 */

x = 10; /* redundant, for demo purposes... */

while (x) {
        pid_t y;
        int   z;

        switch (y = wait4((-1)* my_pgid, &z, NULL)) {
        case 0:
                /* Never happens */
                break;
        case -1:
                /* ALWAYS HAPPENS */
                break;
        default:
                /* Never happens */
                break;
        }
}

Question:  Why?  Obviously I am doing something wrong, but what?

I tried changing just about any argument to the wait4() function.
Eliminating the child and having the grandparent fork and wait for the
chilfren via ``wait(0);'' works.
The chilfren are there and all seems correct;  the children are in a
new process group (different than grandpa's), once the son exits, they
all have ppid of 1, etc.

Any suggestion will be greatly appreciated.

Note:  The ``code'' above is illutration only...

Sincerely Yours,                 Shimon@Simon-Shapiro.ORG
                                             770.265.7340
Simon Shapiro

Unwritten code has no bugs and executes at twice the speed of mouth



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