This is a follow-up on djantzen's post Depth First Search through Digraph Results in Memory Leak.
I played around and simplified the program as far as possible, ending up at the following:
use strict;
use warnings;
sub UNIVERSAL::DESTROY
{
warn "DESTROYING @_\n";
}
sub dfs
{
my ($node, $sub) = @_;
my %visited;
my $dfs;
$dfs = sub {
my ($n) = @_;
$visited{$n}++;
$sub->($n);
for (@$n) {
next unless ref;
$dfs->($_->[0]) unless $visited{$_->[0]};
}
};
$dfs->($node);
}
sub do_dfs
{
my ($node) = @_;
my $nodes = [];
my $search = sub { push @$nodes, $_[0] };
dfs($node,$search);
# UNCOMMENT NEXT LINE to see bug
# return $nodes;
my @nodes = @$nodes;
undef $nodes;
return [@nodes];
}
warn "STARTING\n";
{
my $node1 = bless [1], "Node";
my $node2 = bless [2], "Node";
push @$node1, bless [$node2], "Link";
{
my $nodes = do_dfs($node1);
warn "Neighbors\n";
warn " $_\n" for (@$nodes);
}
}
warn "SHOULD BE THE LAST THING PRINTED.\n";
This gives the following expected output:
STARTING
Neighbors
Node=ARRAY(0x8148a8c)
Node=ARRAY(0x8148b94)
DESTROYING Node=ARRAY(0x8148a8c) at segfault.pl line 6.
DESTROYING Link=ARRAY(0x818fc00) at segfault.pl line 6.
DESTROYING Node=ARRAY(0x8148b94) at segfault.pl line 6.
SHOULD BE THE LAST THING PRINTED.
However, uncommenting the indicated line, leads to the follwing output and a segfault.
STARTING
Neighbors
Node=ARRAY(0x8148a8c)
Node=ARRAY(0x8148b94)
SHOULD BE THE LAST THING PRINTED.
DESTROYING Node=ARRAY(0x8148a8c) at segfault.pl line 6 during global d
+estruction.
DESTROYING Link=ARRAY(0x818fc48) at segfault.pl line 6 during global d
+estruction.
DESTROYING Node=ARRAY(0x8148b94) at segfault.pl line 6 during global d
+estruction.
DESTROYING IO::Handle=IO(0x818fc6c) at segfault.pl line 6 during globa
+l destruction.
DESTROYING IO::Handle=IO(0x815c018) at segfault.pl line 6 during globa
+l destruction.
- Why is the order of destruction changed?
- Where do the two IO::Handles come from?
- Why the segfault?
I'm on Linux running perl 5.8.0. Can someone confirm with other versions of perl?
Update
OK, summing up the results other people got, the follwoing perls segfault
and these perls do
not segfault:
- 5.005_03
- 5.6.0
- 5.6.1d
- 5.6.2
- 5.8.1
- 5.8.2
- 5.8.3-RC1
What is still consistenly wrong is destruction order. The objects referenced in $node1 and $node2 should be destroyed on block exit not during global destruction, shouldn't they?
