Re: memory leak when using tail recursion?

I ran into a memory leak in a system I'm working on

I see no leekage. Memory usage is more or less constant.

#!/usr/bin/perl
use strict;
use warnings;

sub bar {
    if ( foo() ) {
        goto &bar;
    }
    return;
}

my $i;
sub foo {
    return $i++ < 500_000;
}

$i=0; bar(); print("Press Enter to continue"); <STDIN>;  # 32,824K
$i=0; bar(); print("Press Enter to continue"); <STDIN>;  # 32,872K
$i=0; bar(); print("Press Enter to continue"); <STDIN>;  # 32,860K
$i=0; bar(); print("Press Enter to continue"); <STDIN>;  # 32,856K
[download]

The stack and all lexical variables should be deallocated when goto is called, right?

Should? Dunno. Does? No. ( That's why the memory usage increases for each recursive call to bar. )

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Re^2: memory leak when using tail recursion? by Limbic~Region (Chancellor) on Feb 14, 2007 at 00:07 UTC
ikegami, What version of perl? I ask because I see the memory leak locally with perl -v `This is perl, v5.8.8 built for MSWin32-x86-multi-thread (with 25 registered patches, see perl -V for more detail) Copyright 1987-2006, Larry Wall Binary build 817 [257965] provided by ActiveState http://www.ActiveSta +te.com Built Mar 20 2006 17:54:25` [download] Cheers - L~R	[reply] [d/l]
Re^3: memory leak when using tail recursion? by ikegami (Patriarch) on Feb 14, 2007 at 00:10 UTC
The exact same build. The memory usage does go up for each recursive call to `bar` (which is why I had to lower the max value for `$i`), but it does get reclaimed.	[reply] [d/l] [select]
Re^4: memory leak when using tail recursion? by Limbic~Region (Chancellor) on Feb 14, 2007 at 00:14 UTC
ikegami, Very interesting. I am up over 200MB in 30 seconds if I use the block form of if. If I use the post modifier form of if, it stays fixed at 2MB. Cheers - L~R	[reply]
Re^5: memory leak when using tail recursion? by ikegami (Patriarch) on Feb 14, 2007 at 00:20 UTC
Re^6: memory leak when using tail recursion? by juddhuck (Acolyte) on Feb 14, 2007 at 00:29 UTC
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Re^2: memory leak when using tail recursion? by juddhuck (Acolyte) on Feb 15, 2007 at 19:42 UTC
I should clarify. The memory does eventually get reclaimed, so this isn't a true memory leak. The memory is just tied up until the final recursive call returns. If the value returned by foo() is large, or if there a large number of recursive calls, then this can cause the system to run out of memory. I originally ran into this problem when using Exception::Class to handle errors. I had an exception that caused a tail-recursive call to the current function, and this exception was happening repeatedly because there were a lot of invalid records in a row. Exception::Class objects are pretty large, so the system eventually ran out of memory. The code looked something like this: `sub get { my ($self) = @_; my ($record, $e); eval { $record = $self->create_record(); }; if ( $e = Exception::Record::Corrupt->caught() ) { # We got a recoverable error, so skip this record. goto &get; } elsif ( $e = Exception::Class->caught() ) { # Rethrow any generic exception caught and abort. ref $e ? $e->rethrow : die $e; } return $record; }` [download] Anyway, there are plenty of ways to fix this problem. The easiest is to not use tail-recursion, but it should work with tail recursion. The odd thing to me is that this problem only occurs when the function call is in the if-conditional.	[reply] [d/l]