topic Re: Perl untie problem in Operating System - Linux

Perl untie problem

Kalin Evtimov — Thu, 28 Jul 2005 09:07:30 GMT

Hi!
I just got an error from my perl-program, but since I have never used tie/untie, I don't know what to do first.

miniserv.pl: untie attempted while 1 inner references still exist at /opt/perl5/lib/5.8.6/IPC/Open3.pm line 203.

I looked at the line 203 and I found:

my $kid_rdr = gensym;
my $kid_wtr = gensym;
my $kid_err = gensym;

xpipe $kid_rdr, $dad_wtr if !$dup_wtr;
xpipe $dad_rdr, $kid_wtr if !$dup_rdr;
xpipe $dad_err, $kid_err if !$dup_err && $dad_err ne $dad_rdr;

$kidpid = $do_spawn ? -1 : xfork;
if ($kidpid == 0) { # Kid
# A tie in the parent should not be allowed to cause problems.
untie *STDIN;
untie *STDOUT; #this is line 203!!

Could anybody tell me how to find the variable, that is still tied? I couldn't find much bei Google...

Danke!

Re: Perl untie problem

H.Merijn Brand (procura — Thu, 28 Jul 2005 09:42:50 GMT

you probably need some close calls before the untie

close STDIN;
close STDOUT;
untie *STDIN;
untie *STDOUT;

And I don't know if the xpipe calls do other black magic;

Enjoy, Have FUN! H.Merijn

Re: Perl untie problem

Kalin Evtimov — Fri, 29 Jul 2005 03:32:26 GMT

"And I don't know if the xpipe calls do other black magic;"

What do U mean?
This is actually the source of the IPC::Open3 module Open3.pm

close didn't work unfortunately.

Re: Perl untie problem

Ralph Grothe — Fri, 29 Jul 2005 04:01:45 GMT

Hm miniserv.pl sounds like a Webmin problem.
I wouldn't expect the IPC::Open3 module to be broken.
It rather looks that either a prerequisite isn't fulfilled, or it was used improperly.

Can you identify the line where your Perl code aborted?

Re: Perl untie problem

Kalin Evtimov — Fri, 29 Jul 2005 05:49:00 GMT

actually not, I have only the error msg. from above.
As I couldn't make RRDs module from RRDtool working on hp-ux, I rewrote my script for use with RRDp, and since than I get this errormsg. In the miniserv.pl there is a tie to STDIN and STDOUT,

eval {
package main;
tie(*STDOUT, 'miniserv');
tie(*STDIN, 'miniserv');
do $miniserv::full;
die $@ if ($@);
};

but I don't know how to find out what and where fails..

Re: Perl untie problem

H.Merijn Brand (procura — Fri, 29 Jul 2005 06:05:27 GMT

eval {
package main;
tie(*STDOUT, 'miniserv');
tie(*STDIN, 'miniserv');
do $miniserv::full;
untie *STDOUT; # <--
untie *STDIN; # <--
die $@ if ($@);
};

Enjoy, Have FUN! H.Merijn

Re: Perl untie problem

Kalin Evtimov — Fri, 29 Jul 2005 06:41:28 GMT

No, ..:( this didn't work..I quess there must be a very special error that cannot be found out directly. Thank you for your help.

Re: Perl untie problem

Ralph Grothe — Fri, 29 Jul 2005 07:32:52 GMT

I haven't used tied file handles yet,
as you are.
I guess this is more for the advanced Perl hackers like procura.
So far I've only used tied hashes as they are used easiest of all.
As far as my memory serves me correctly one has to implement for each valid operation on the thingy (i.e. scalar, array, hash, filehandle, object reference) a method in order for tying to work.
Maybe you need to override the close method for the filehandle tie?

Have you consulted perldoc perltie yet?

You could also look at the code from your Perl installation to get an idea how implementation of tied variables works.
I'd say a pretty easy one to start with was Config.pm, though it's tying a hash rather than a file handle.
Anyway, have a look at "perldoc -m Config"