use strict;
use warnings;
use DBI;
use File::Copy qw(copy);

my $dsn = 'DBI:ODBC:somedb';
my $db_user = '';
my $db_pass = '';

my $dbh = DBI->connect($dsn,$db_user,$db_pass ) or die $DBI::errstr;

if (1) {
  # This causes the warning
  my $loh = $dbh->selectall_hashref('select 1 as a, 2 as b','a');
}
if (0) {
  # This causes the warning
  my $sth = $dbh->prepare('select 1 as a, 2 as b');
  $sth->execute();
  my $loh = $sth->fetchall_hashref('a');
  $sth->finish;
}
if (0) {
  # This does not cause the warning
  my $aoa = $dbh->selectall_arrayref('select 1 as a, 2 as b');
}
if (0) {
  # This does not cause the warning
  my $sth = $dbh->prepare('select 1 as a, 2 as b');
  $sth->execute();
  my $hash = $sth->fetchrow_hashref();
  $sth->finish;
}
copy('a','b') or die "Failed to copy a to b. $!\n";
$dbh->disconnect;
[download]

Run with the following versions:

* activestate perl 5.8.8
* Win32 0.2601
* DBI 1.50
* File::Copy 2.09

++imp, it is DBI! more specifically, its the combination of DBI and File::Copy. And it doesnt reproduce on my debian or gentoo servers either, so, I'd assume its activestate specific.

__________
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.
- Terry Pratchett

Are you using DBD::ODBC or a different driver?

I'm still investigating the issue but it's slow going as I learn more about perl internals.

After reading your post, I tried directly calling Win32::CopyFile(), and it worked with no warning:

use Win32;
Win32::CopyFile(
  "$src_path/$upc/$realtracknum.mp3",
  "$dst_path/$upc/$realtracknum.mp3",
  1
) or
  warn "couldnt File::Copy $src_path/$upc/$realtracknum.mp3: $!";
[download]

And the actual call to Win32::CopyFile() in File/Copy.pm (nested within a large, unwieldy if..else chain) uses the same syntax:

return 0 unless @_ == 2;
return Win32::CopyFile(@_, 1);
[download]

So the problem seems to be with File/Copy.pm calling Win32::CopyFile(). Whatever that seems to indicate, though, I'm not quite sure.


Addendum: I also tried passing an actual array, to see if that somehow pooched the XS code, but this still works without any warnings:

my @copy_args = (
  "$src_path/$upc/$realtracknum.mp3",
  "$dst_path/$upc/$realtracknum.mp3"
);
Win32::CopyFile(@copy_args, 1) or
  warn "couldnt File::Copy $src_path/$upc/$realtracknum.mp3: $!";
[download]

__________
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.
- Terry Pratchett

Are you using threads?

I'm not using threads in my program, and I don't think ActiveState even compiles in threading support...Not 100% certain about that, though.

__________
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.
- Terry Pratchett

I don't think ActiveState even compiles in threading support

They do, and have since 5.6.1. Maybe before.

Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY USE_ITHREADS USE_LARGE_FILES PERL
+_IMPLICIT_CONTEXT PERL_IMPLICIT_SYS
  Locally applied patches:
        ActivePerl Build 811
        21540 Fix backward-compatibility issues in if.pm
        23565 Wrong MANIFEST.SKIP
  Built under MSWin32
  Compiled at Dec 13 2004 09:52:01
[download]

Are you using fork?

Why these questions. The error message

Attempt to free unreferenced scalar: SV 0x1e77330, Perl interpreter: 0
+x15d45fc ...
[download]

Is telling you that during garbage collection (sorry, Reference Counting Automated Memory Management Cleanup! Hereafter referred to as GC :), the Perl interpreter represented by the handle 0x15d45fc, attempted to free the scalar at location 0x1e77330 and discovered that it didn't own that piece of memory.

To my knowledge, this can only occur when a reference is passed between two separate instances of the Perl Interpreter running within the same process. And that, (to my knowledge), can only occur if you are using threads. Either explicitly through the use of threads, or (whatever that word is that means the opposite of explicitly that simply won't form in my head just now), through the use of ActivePerl's fork emulation, which uses threads.

In general, as the warning occurs during cleanup of a variable, if it happens when the program is exiting, then you can usually safely ignore it as your program is exiting anyway. If you are using a very recent version of perl, 5.8.8 or later from memory, then you can disable the warning using no warnings 'threads';. But if it occurs at some other time in the code, and particulary if you get the same message (with different scalars), repeatedly, it probably represents and memory leak.

It's also possible that the cross-interpreter-passed scalar has (silently), caused other problems that have not been detected, so it usually worth tracking the problem down to the source. To do that, you would need to post more code, preferably a minimal testcase.

Most of the above is based upon my own investigations of the problem--I've seen it a lot in my threaded code, though much less recently. I've never seen the title error occur outside of either threaded, or pseudo-forked code. By implication, there would need to be multiple interpreters involved for one of them to discover a scalar it did not own. The only way I know of to have multiple interpreters is via threads, though theoretically, if you were embedding Perl into a C program, you could create multiple interpreters without using threads. There may be other situations in which the message could occur that I am unaware of.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

use strict;
use warnings;
use Config;
use DBI;

my $dsn = 'DBI:ODBC:somedb';
my $db_user = '';
my $db_pass = '';

my $dbh = DBI->connect($dsn,$db_user,$db_pass ) or die $DBI::errstr;

my $loh = $dbh->selectall_hashref('select 1 as a, 2 as b','a');

print "checking d_symlink\n";
print "found\n" if ($Config{d_symlink});

print "checking d_readlink\n";
print "found\n" if ($Config{d_readlink});

print "checking d_link\n";
print "found\n" if ($Config{d_link});

print "checking d_symlink && d_readlink\n";
print "found\n" if (($Config{d_symlink} && $Config{d_readlink}));

print "checking (d_symlink && d_readlink) || d_link)\n";
print "found\n" if (($Config{d_symlink} && $Config{d_readlink}) || $Co
+nfig{d_link});

print "All done.\n";

$dbh->disconnect;
[download]

checking d_symlink
checking d_readlink
checking d_link
found
checking d_symlink && d_readlink
checking (d_symlink && d_readlink) || d_link)
found
Attempt to free unreferenced scalar: SV 0x1a61cdc, Perl interpreter: 0
+x223ecc at copytest.pl line 26.
All done.
[download]

use warnings;
use File::Copy;

# The files 't1.txt', 't2.txt', 't3.txt',
# 't4.txt', and 't5.txt' all exist in the cwd.

for(1..5) {
   if (copy("t${_}.txt", "u${_}.txt")) {
      print "copied t${_}.txt to u${_}.txt\n";
   }
   else {print "$_: Copy failed\n"}
}

__END__
Outputs:

copied t1.txt to u1.txt
copied t2.txt to u2.txt
copied t3.txt to u3.txt
copied t4.txt to u4.txt
copied t5.txt to u5.txt
[download]