Dear Monks,

According to perlfork:

Lifetime of the parent process and pseudo-processes

During the normal course of events, the parent process and every pseudo-process started by it will wait for their respective pseudo-children to complete before they exit.

However, when I call fork, and the parent does nothing and terminates, the child does not finish executing. For example, in the following program a child writes to a file every 2 seconds:

use strict;
use warnings;
use 5.010;

my $child_pid = fork;
$| = 1;

if (!defined $child_pid) {
    say "**My error**: couldn't fork: $!";
}

if ($child_pid) { #then in parent
    say "in parent...";
    sleep 1;
}
else { #then in child
    open my $OUTFILE, '>', 'data1.txt'
        or die "**My error: couldn't open data1.txt: $!";

    for (1 .. 10) {
        say $OUTFILE $_;
        sleep 2;
    }

    close $OUTFILE;
}

[download]

...and the output is:

$ perl 1perl.pl 
in parent...
$ cat data1.txt
$

[download]

In other words, nothing gets written to the file--usually. About one in ten tries, this is the output:

$ perl 1perl.pl 
in parent...
$ cat data1.txt
1
2
3
4
5
6
7
8
9
10
$

[download]

Can someone explain what is supposed to happen when the parent terminates before the child finishes executing?

In reply to fork(): when parent exits, what happens to child? by 7stud

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