Re: Forked pipe deadlock

Your other child processes are keeping the pipe open for the first one. To demonstrate this, just reverse the order in which you close the pipes:

for (my $i = 3; $i >= 0; $i--) {
  close($handles[$i]);
}
[download]

That is, when the parent forks child #2, it will inherit the parent's pipe to child #1, and that is what is keeping child #1 from seeing EOF.

One solution is to explicit close those handles in the new children:

if (!open($handles[$i], "|-") {
  ...close $handles[0..$i-1]...
  child(); exit(0);
}
[download]

Update: Corrected index bounds - thanks psini!

Comment on Re: Forked pipe deadlock Select or Download Code

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Re^2: Forked pipe deadlock by almut (Canon) on May 25, 2008 at 21:33 UTC
`for (my $i = 3; $i >= 0; $i--) { close($handles[$i]); }` [download] In Perl, I'd prefer something like this instead of the C style `for` loop (YMMV of course): `close $handles[$_] for reverse 0..3;` [download] (the explicit `reverse` emphasizes that it's essential here to do something in reverse order of how you'd do it normally)	[reply] [d/l] [select]
Re^2: Forked pipe deadlock by psini (Deacon) on May 25, 2008 at 20:55 UTC
Ehm, you probably meant: `for (my $i = 3; $i >= 0; $i--) { close($handles[$i]); }` [download] Rule One: Do not act incautiously when confronting a little bald wrinkly smiling man.	[reply] [d/l]
Re^2: Forked pipe deadlock by Anonymous Monk on May 25, 2008 at 21:35 UTC
Thanks - that fixed it. Changed the code to: `if(!open($handles[$i], '\|-')) { # child process foreach $handle (@handles) { defined($handle) && close($handle); } child(); exit 0; }` [download] I wouldn't have thought of that, so many thanks - very much appreciated.	[reply] [d/l]