Hi,

we have a script that cron runs to run user scripts for us, log their results, make sure that only one of them is running, etc. Couple of days ago a user's script was hung for no apparent reason. So I tried to reproduce similar behavior and a buddy and I got it down to a pretty small subset of the functionality. I'm hoping maybe someone can shed a little light on what's going on here.

The stripped down version of the script-running script is this: 

#!/usr/bin/perl -w

use strict;

use Proc::Spawn;

my ($pid, $IN, $OUT, $ERROR) = spawn(\@ARGV);

#fix by uncommenting this 
#while( <$ERROR>){};

# either of these hang
my $junk = eof($OUT);
#while (<$OUT>){};

[download]

And the stripped-down version of the user code is this: 

#!/usr/bin/perl -w
use strict;

warn "x" x shift(@ARGV) . "\n";

[download]

so, save them puppies in "runner.pl" and "user.pl", chmod +x them, and issue this command: 

[msouth@jinx GUI-APP bin]$ ./runner.pl ./user.pl 4095

[download]

then issue this command: 

[msouth@jinx GUI-APP bin]$ ./runner.pl ./user.pl 4096

[download]

(then, if your system works like mine, you will want to do a control-c or something because it's just hanging there).

You can also test the commented assertion that unloading user.pl's stderr of its burden eliminates the problem. (Does on my system.)

(BTW, perl -v says:

This is perl, v5.6.1 built for i686-linux )

Just to make sure that I'm not confusing anyone, Proc::Spawn is producing IO::Handle objects there (lest anyone think that my subject implied I was doing this on vanilla filehandles).

I don't know diddly about IO. Anyone? (I would like to hear even if it's just that you can/can't reproduce it.)

In reply to eof(FH) hanging when 4096 chars waiting on stderr (or something like that) by Anonymous Monk

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