/ 
Devel-Monitor-0.9
River stage zero No dependents
/ Devel::Monitor

monitor

DESC Monitoring multiple variables monitor('name for a' => \$a, 'name for b' => \$b, 'name for c' => \$c, 'name for d' => \@d, 'name for e' => \%e, 'name for F' => \&F); DESC Monitoring single constant variable (FOR INTERNAL USE ONLY) monitor('name for F' => \&F, 1); The last flag indicates that it is code reference

printCircularRef

DESC Try to find circular references and print it out into STDERR

_checkCircularRef

DESC Verify if there is a circular reference on the current variable RETV Circular Reference Type One of : CRT_NONE, CRT_CIRC_REF, CRT_WEAK_CIRC_REF, CRT_INTERNAL_CIRC_REF

NAME

Devel::Monitor - Monitor your variables/objects for memory leaks

TABLE OF CONTENT

- SYNOPSIS
- METHOD EXAMPLES : monitor
  - Example 01
    - Example 01 with circular references
    - Example 01 without circular references
- METHOD EXAMPLES : printCircularRef
  - Example 01
- DESCRIPTION
- VERY IMPORTANT THINGS YOU SHOULD BE AWARE
  - Loop vars are passed by references
  - You cannot use references from a tied object because it reuse memory space
  - You cannot weaken a tied object
    - Proof 01 : Devel::Peek
    - Proof 02 : mod_perl
  - Variable using constants are destroyed when the constant is destroyed
- TRACKING MEMORY LEAKS
  - How to remove Circular references in Perl
- CHECKING MODULES SYNTAX
- WHAT THIS MODULE CAN'T DO FOR YOU
- MODULES THAT PRODUCE MEMORY LEAKS
- SCRIPTS TO HELP YOU
- AUTHOR

SYNOPSIS

use Devel::Monitor;

+-----------------------------------------------------------------------------+ | Monitor scalars, arrays, hashes, references, constants | +-----------------------------------------------------------------------------+ my ($a,$b) = (Foo::Bar->new(), Foo::Bar->new()); my ($c, @d, %e); use constant F => [1,2]; monitor('name for a' => \$a, 'name for b' => \$b, 'name for c' => \$c, 'name for d' => \@d, 'name for e' => \%e, 'name for F' => \&F); #NOTE : Dont add parentheses to the end of the constant (\&F())

+-----------------------------------------------------------------------------+ | Unmonitor, not yet tested and not used | +-----------------------------------------------------------------------------+ # unmonitor($a, $b, \$c, \@d, \%e);

+-----------------------------------------------------------------------------+ | Print circular references | +-----------------------------------------------------------------------------+ # NOTE : You cannot use printCircularRef on a monitored/tied variable # (See "We cannot use tied objects references because it reuse memory space" doc) printCircularRef(\$a); printCircularRef(\$b); printCircularRef(\$c); printCircularRef(\@d); printCircularRef(\%e); printCircularRef(\&F); #NOTE : Dont add parentheses to the end of the constant (\&F())

METHOD EXAMPLES : monitor

+-----------------------------------------------------------------------------+ | Example 01 | +-----------------------------------------------------------------------------+ +-------------------------------------------------------------------+ | Example 01 with circular references | +-------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ { my @a; monitor('a' => \@a); $a[0] = \@a; #Add a circular reference print STDERR "Leaving scope\n"; } print STDERR "Scope left\n";

+----------------------+ | Output | +----------------------+ MONITOR ARRAY a Leaving scope Scope left DESTROY ARRAY a

+----------------------+ | Meaning | +----------------------+ The line "DESTROY ARRAY a" should be between scope prints. @a were deleted on program exit.

+-------------------------------------------------------------------+ | Example 01 without circular references | +-------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ { my @a; monitor('a' => \@a); print STDERR "Leaving scope\n"; } print STDERR "Scope left\n";

+----------------------+ | Output | +----------------------+ MONITOR ARRAY a Leaving scope DESTROY ARRAY a Scope left

+----------------------+ | Meaning | +----------------------+ Everything is ok

METHOD EXAMPLES : printCircularRef

+-----------------------------------------------------------------------------+ | Example 01 | +-----------------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ my (@a, @b); $a[0] = 'asdf'; $a[1] = \@b; $b[3] = \@b; printCircularRef(\@a); printCircularRef(\@b);

+----------------------+ | Output | +----------------------+ ------------------------------------------------------------------------------- Checking circular references for ARRAY(0x814e358) ------------------------------------------------------------------------------- Internal circular reference found : ARRAY(0x814e358)[1][3] on ARRAY(0x814e370) 1 - Item : ARRAY(0x814e358) 2 - Source : [1] Item : ARRAY(0x814e370) 3 - Source : [3] Item : ARRAY(0x814e370) ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- Results for ARRAY(0x814e358) Circular reference : 0 Internal circular reference : 1 Weak circular reference : 0 ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- Checking circular references for ARRAY(0x814e370) ------------------------------------------------------------------------------- Circular reference found : ARRAY(0x814e370)[3] 1 - Item : ARRAY(0x814e370) 2 - Source : [3] Item : ARRAY(0x814e370) ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- Results for ARRAY(0x814e370) Circular reference : 1 Internal circular reference : 0 Weak circular reference : 0 -------------------------------------------------------------------------------

DESCRIPTION

See http://www.infocopter.com/perl/monitored-variables.htm (Monitor.pm) for original source code I've made a lot of modifications, debug, tweaks, whatever, using the Tie package

VERY IMPORTANT THINGS YOU SHOULD BE AWARE

+-----------------------------------------------------------------------------+ | Loop vars are passed by references | +-----------------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ { my @list = (1,2,3); print STDERR join(", ",@list)."\n"; for my $item (@list) { monitor("item $item" => \$item); $item+=1000; print "$item\n"; } print STDERR join(", ",@list)."\n"; print "Leaving scope\n"; } print "Scope left\n";

+------------------------+ | What you might want | |(Or something like that)| +------------------------+ 1, 2, 3 MONITOR SCALAR : item 1 1001 DESTROY SCALAR : item 1 MONITOR SCALAR : item 2 1002 DESTROY SCALAR : item 2 MONITOR SCALAR : item 3 1003 DESTROY SCALAR : item 3 1, 2, 3 Leaving scope Scope left

+----------------------+ | Real Output | +----------------------+ 1, 2, 3 MONITOR SCALAR : item 1 1001 MONITOR SCALAR : item 2 1002 MONITOR SCALAR : item 3 1003 1001, 1002, 1003 Leaving scope DESTROY SCALAR : item 3 DESTROY SCALAR : item 2 DESTROY SCALAR : item 1 Scope left

+----------------------+ | Meaning | +----------------------+ Perl passes variables by reference within for/foreach, so the variables you are using are the original ones. (You can print the scalar adresses to be sure) The difference is that normaly, Perl passes variables by value. So, if you monitor those variables, they won't be destroyed until the initial declaration is.

+-----------------------------------------------------------------------------+ | You cannot use references from a tied object because it reuse memory space | +-----------------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ my $self = {'a' => 1, 'b' => 2}; monitor('self' => \$self); print STDERR \($self->{'a'})."\n"; print STDERR \($self->{'b'})."\n"; print STDERR \($self->{'a'}).\($self->{'b'})."\n"; foreach my $key (keys %$self) { my $keyRef = \$key; my $value = $self->{$key}; my $valueRef = \($self->{$key}); print STDERR "KEY:$key, KEY REF:$keyRef, VALUE:$value, VALUE REF:$valueRef\n"; }

+----------------------+ | Output | +----------------------+ MONITOR HASH : self SCALAR(0x8141384) SCALAR(0x8141384) SCALAR(0x8141384)SCALAR(0x81413cc) KEY:a, KEY REF:SCALAR(0x8141420), VALUE:1, VALUE REF:SCALAR(0x824becc) KEY:b, KEY REF:SCALAR(0x81413cc), VALUE:2, VALUE REF:SCALAR(0x824becc) DESTROY HASH : self

+----------------------+ | Code 2 | +----------------------+ my %self; #monitor('self' => \$self); tie %self, 'Devel::Monitor::TestHash'; $self{a} = 1; $self{b} = 2; print STDERR \($self{a})."\n"; print STDERR \($self{b})."\n"; print STDERR \($self{a}).\($self{b})."\n"; foreach my $key (keys %self) { my $keyRef = \$key; my $value = $self{$key}; my $valueRef = \($self{$key}); print STDERR "KEY:$key, KEY REF:$keyRef, VALUE:$value, VALUE REF:$valueRef\n"; }

+----------------------+ | Output 2 | +----------------------+ SCALAR(0x8141378) SCALAR(0x8141378) SCALAR(0x8141378)SCALAR(0x8248fe8) KEY:a, KEY REF:SCALAR(0x81413cc), VALUE:1, VALUE REF:SCALAR(0x825567c) KEY:b, KEY REF:SCALAR(0x825564c), VALUE:2, VALUE REF:SCALAR(0x825567c) Devel::Monitor::TestHash::DESTROY : Devel::Monitor::TestHash=HASH(0x81412e8)

+----------------------+ | Meaning | +----------------------+ Hash keys refering 1 and 2 can't be the same reference. But we see the opposite on these small examples. It seems like tied objects reuse memory space instead of refering to the original value from the untied object.

+-----------------------------------------------------------------------------+ | You cannot weaken a tied object | +-----------------------------------------------------------------------------+ +-------------------------------------------------------------------+ | Proof 01 : Devel::Peek | +-------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ #!/usr/bin/perl

use Scalar::Util qw(weaken isweak); my (@a, @b); tie @a, 'Monitor::TestArray'; tie @b, 'Monitor::TestArray'; $a[0] = \@b; $b[0] = \@a; weaken($b[0]); if (isweak($a[0])) { print "\$a[0] is weak\n"; } else { print "\$a[0] is not weak\n"; } if (isweak($b[0])) { print "\$b[0] is weak\n"; } else { print "\$b[0] is not weak\n"; } package Monitor::TestArray; use Tie::Array; use base 'Tie::StdArray';

sub DESTROY { "Monitor::TestArray::DESTROY : $_[0]\n"; }

1;

+----------------------+ | Wanted output | +----------------------+ $a[0] is not weak $b[0] is weak

+----------------------+ | Real output | +----------------------+ $a[0] is not weak $b[0] is not weak

+----------------------+ | Meaning | +----------------------+ We still have this output if we remove one of the "tie" call. But, if we remove those two "tie", it works and we get the wanted output. So there is a problem.

+----------------------+ | Note | +----------------------+ I'm pretty sure this is a perl bug (Tested with 5.8.6 and 5.8.3). The code for Scalar::Util::weaken and Scalar::Util::isweak is written in XS

void weaken(sv) SV *sv PROTOTYPE: $ CODE: #ifdef SvWEAKREF sv_rvweaken(sv); #else croak("weak references are not implemented in this release of perl"); #endif

void isweak(sv) SV *sv PROTOTYPE: $ CODE: #ifdef SvWEAKREF ST(0) = boolSV(SvROK(sv) && SvWEAKREF(sv)); XSRETURN(1); #else croak("weak references are not implemented in this release of perl"); #endif

I don't see any problems in this code. Normally when you weaken a variable, it set the SvWEAKREF flag. You can visualize this behavior with this code :

+----------------------+ | Visualize weak var | | with Devel::Peek | +----------------------+ use Devel::Peek; Dump($yourVariable);

However, when using tied variables, nothing is modified. So i believe that the code behind sv_rvweaken (XS) called by weaken (Perl) does not handle variables with SvTYPE at SVt_PVLV. I believe this is a perl bug (C++ code behind sv_rvweaken).

Let's look at the differences we get when a reference is weakened. If we have this code :

+----------------------+ | Code | +----------------------+ #!/usr/bin/perl use strict; use warnings; use Devel::Peek; use Scalar::Util qw(weaken isweak);

my (@a, @b); $a[0] = \@b; print STDERR "Dump before weaken\n"; Dump(\$a[0]); weaken($a[0]); print STDERR "Dump after weaken\n"; Dump(\$a[0]);

+----------------------+ | Output | +----------------------+ Dump before weaken SV = RV(0x818274c) at 0x81411c8 REFCNT = 1 FLAGS = (TEMP,ROK) RV = 0x814127c SV = RV(0x8182760) at 0x814127c REFCNT = 2 FLAGS = (ROK) RV = 0x814e894 SV = PVAV(0x81426f8) at 0x814e894 REFCNT = 2 FLAGS = (PADBUSY,PADMY) IV = 0 NV = 0 ARRAY = 0x0 FILL = -1 MAX = -1 ARYLEN = 0x0 FLAGS = (REAL) Dump after weaken SV = RV(0x818274c) at 0x81412e8 REFCNT = 1 FLAGS = (TEMP,ROK) RV = 0x814127c SV = RV(0x8182760) at 0x814127c REFCNT = 2 FLAGS = (ROK,WEAKREF,IsUV) RV = 0x814e894 SV = PVAV(0x81426f8) at 0x814e894 REFCNT = 1 FLAGS = (PADBUSY,PADMY,RMG) IV = 0 NV = 0 MAGIC = 0x8208e80 MG_VIRTUAL = &PL_vtbl_backref MG_TYPE = PERL_MAGIC_backref(<) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x81411c8 SV = PVAV(0x8142724) at 0x81411c8 REFCNT = 2 FLAGS = () IV = 0 NV = 0 ARRAY = 0x825ec28 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) Elt No. 0 SV = RV(0x8182760) at 0x814127c REFCNT = 2 FLAGS = (ROK,WEAKREF,IsUV) RV = 0x814e894 ARRAY = 0x0 FILL = -1 MAX = -1 ARYLEN = 0x0 FLAGS = (REAL)

+----------------------+ | Meaning | +----------------------+ The important part is the WEAKREF flag which say that the reference is weaken. Refer to perlapi, perlguts, and any other perl core documentation further informations.

+-------------------------------------------------------------------+ | Proof 02 : mod_perl | +-------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ +------------+ | test.pl | +------------+ #!/usr/bin/perl use strict; use warnings; use Scalar::Util qw(weaken); use Devel::Monitor; use Util::Junk;

my (@a, $b); #tie @a, 'Devel::Monitor::TestArray'; $a[0] = \$b; $b = \@a; $a[1] = Util::Junk::_20M(); weaken($a[0]);

+------------+ | Util::Junk | +------------+ package Util::Junk; use strict; use warnings;

sub _20M() { 'A 20 megs string here filled with zeros' }

1;

+----------------------+ | wget-test.pl | +----------------------+ #!/usr/bin/perl

use strict; use warnings;

my $baseUrl = 'http://localhost/perl/test.pl';

my $i = 0; while (1) { print "Loop ".++$i."\n";

system('wget "'.$baseUrl.'" -O /dev/null') == 0
    or die "\nwget failed or has been interrupted : $?\n";
}

+----------------------+ | Test 01 | +----------------------+ Now that we got a program and a caller (and mod_perl on our apache server), we can start the program.

perl wget-test.pl

When @a is not tied (See the commented tie in test.pl), after loading the page like ten times, the page will be in cache in every apache processes and other loading will be VERY fast. You'll also notice that memory is stable.

However, if you uncomment the tie call in test.pl, you'll see your memory being filled to death and every page loaded will be as long as at the beginning

+----------------------+ | Conclusion | +----------------------+ It is actually impossible to weaken a tied variable

+-----------------------------------------------------------------------------+ | Variable using constants are destroyed when the constant is destroyed | +-----------------------------------------------------------------------------+ +----------------------+ | Code | +----------------------+ #!/usr/bin/perl use strict; use warnings; use Devel::Monitor;

use constant CONST => [1,2,3]; #monitor('CONST', \&CONST); print &CONST."\n"; { my $item = CONST(); monitor('item', \$item); print $item."\n"; print "Leaving scope\n"; } print "Scope left\n";

+------------------------+ | What you might want | |(Or something like that)| +------------------------+ ARRAY(0x81c503c) MONITOR ARRAY : item ARRAY(0x1234567) Leaving scope DESTROY ARRAY : item Scope left

+----------------------+ | Real Output | +----------------------+ ARRAY(0x81c503c) MONITOR ARRAY : item ARRAY(0x81c503c) Leaving scope Scope left DESTROY ARRAY : item

+----------------------+ | Meaning | +----------------------+ It looks like your variable is not destroyed ! But in fact, $item is the same reference that CONST is. So, you are monitoring CONST directly ! If you absolutely want to monitor this code, you must uncomment the "#monitor('CONST', \&CONST);" line in code.

+----------------------+ | Output with monitor | | on \&CONST | +----------------------+ MONITOR CODE SCALAR : CONST [0] MONITOR CODE SCALAR : CONST [1] MONITOR CODE SCALAR : CONST [2] MONITOR CODE ARRAY : CONST ARRAY(0x81c4e30) Array from item is already tied by CONST ARRAY(0x81c4e30) Leaving scope Scope left DESTROY CODE SCALAR : CONST [0] DESTROY CODE SCALAR : CONST [1] DESTROY CODE SCALAR : CONST [2] DESTROY CODE ARRAY : CONST

+----------------------+ | Meaning | +----------------------+ You monitored a constant and you cannot monitor twice a variable, so $item won't be monitored. This way, you can see that there is no memory leak.

TRACKING MEMORY LEAKS

#------------------------------------------------------------------------------+ # # How to remove Circular references in Perl # #------------------------------------------------------------------------------+

#------------------------------------------------------------------------------+ # # Let's say we have this basic code : # #------------------------------------------------------------------------------+

#!/usr/bin/perl

#-------------------------------------------------------------------- # Little program #--------------------------------------------------------------------

use strict; use warnings; use Devel::Monitor;

{ my $a = ClassA->new(); my $b = $a->getClassB(); monitor('$b' => \$b); $b->getClassA()->printSomething(); print "Leaving scope\n"; } print "Scope left\n";

#-------------------------------------------------------------------- # ClassA (Just a class with the "printSomething" method) #--------------------------------------------------------------------

package ClassA; use strict; use warnings; use Scalar::Util qw(weaken isweak);

sub new { my ($class) = @_; my $self = {}; bless($self => $class); return $self; }

sub getClassB { my $self = shift; $self->{_classB} = ClassB->new($self); return $self->{_classB}; }

sub printSomething { print "Something\n"; }

#-------------------------------------------------------------------- # ClassB (A class that got a "parent" which is a ClassA instance) #--------------------------------------------------------------------

package ClassB; use strict; use warnings; use Scalar::Util qw(weaken isweak);

sub new { my ($class, $classA) = @_; my $self = {}; bless($self => $class); $self->setClassA($classA); return $self; }

sub setClassA { my ($self, $classA) = @_; $self->{_classA} = $classA; }

sub getClassA { return shift->{_classA}; }

1;

#------------------------------------------------------------------------------+ # # The output will be # #------------------------------------------------------------------------------+

MONITOR HASH : $b Something Leaving scope Scope left DESTROY HASH : $b

#------------------------------------------------------------------------------+ # # We see that the object reference by $b isn't destroyed when leaving the scope # because $a->{_classB} still use it. So, we got a circular reference here. We must # weaken one side of the circular reference to help Perl disallocate memory. # #------------------------------------------------------------------------------+ #------------------------------------------------------------------------------+ # Wrong way to break circular references #------------------------------------------------------------------------------+ sub getClassB { my $self = shift; $self->{_classB} = ClassB->new($self); #$self->{_classB} is the only #reference to the objects weaken($self->{_classB}); #we weaken the only reference, #so, $self->{_classB} is DESTROYED HERE, #which is very bad print "\$self->{_classB} is now weaken\n" if isweak($self->{_classB}); return $self->{_classB}; } #------------------------------------------------------------------------------+ # Good way #------------------------------------------------------------------------------+ sub getClassB { my $self = shift; my $b = ClassB->new($self); $self->{_classB} = $b; #we create a second reference to the object weaken($self->{_classB}); #we weaken this reference, which is not deleted #because thre is another reference print "\$self->{_classB} is now weaken\n" if isweak($self->{_classB}); return $self->{_classB}; } #------------------------------------------------------------------------------+ # Be careful ! With this code, it won't work #------------------------------------------------------------------------------+ sub getClassB { my $self = shift; { my $b = ClassB->new($self); $self->{_classB} = $b; #we create a second reference to the object weaken($self->{_classB}); #we weaken this reference, which is not deleted #because thre is another reference print "\$self->{_classB} is now weaken\n" if isweak($self->{_classB}); } #$b is destroyed here, and the other reference $self->{_classB} is a weak reference, #so the ClassB instance is destroyed, $self->{_classB} now equal undef return $self->{_classB}; } #------------------------------------------------------------------------------+ # Good way #------------------------------------------------------------------------------+ sub getClassB { my $self = shift; my $b; { $b = ClassB->new($self); $self->{_classB} = $b; #we create a second reference to the object weaken($self->{_classB}); #we weaken this reference, which is not deleted #because thre is another reference print "\$self->{_classB} is now weaken\n" if isweak($self->{_classB}); } #$b is still not destroyed, so we didn't lose our not weak reference return $self->{_classB}; #We return the object, someone on the other side will now keep #the reference, so we don't care if $b lose the reference. #Our job is done ! } #------------------------------------------------------------------------------+ # # Conclusion : You must be sure that you keep a non weak reference to the object # #------------------------------------------------------------------------------+

#------------------------------------------------------------------------------+ # # The output (Using the good way) will be # #------------------------------------------------------------------------------+

$self->{_classB} is now weaken MONITOR HASH : $b Something Leaving scope DESTROY HASH : $b Scope left

#------------------------------------------------------------------------------+ # # There is no circular references now... # #------------------------------------------------------------------------------+

#------------------------------------------------------------------------------+ # # IMPORTANT : Always weaken the caller's reference because someone may use the # child objects (ClassB) this way. Let's see what can happen if you don't. # # If we get the following code # #------------------------------------------------------------------------------+ my $b; { my $a = ClassA->new(); monitor('$a' => \$a); $b = ClassB->new($a); $b->getClassA()->printSomething(); print "Leaving scope\n"; } print "Scope left\n"; $b->getClassA()->printSomething();

#------------------------------------------------------------------------------+ # # And the sub setClassA # #------------------------------------------------------------------------------+ sub setClassA { my ($self, $classA) = @_; $self->{_classA} = $classA; weaken($self->{_classA}); print "\$self->{_classA} is now weaken\n" if isweak($self->{_classA}); }

#------------------------------------------------------------------------------+ # # You'll get this error # #------------------------------------------------------------------------------+ MONITOR HASH : $a $self->{_classA} is now weaken Something Leaving scope DESTROY HASH : $a Scope left Can't call method "printSomething" on an undefined value at test3.pl line 29.

#------------------------------------------------------------------------------+ # # $a is destroyed when leaving the scope, and the other reference to this variable # is weaken, so this one is destroyed too. This clearly demonstrate that you must # weaken the caller's reference. # #------------------------------------------------------------------------------+

CHECKING MODULES SYNTAX

Redirect stderr to stdout and grep it

perl -c MyModule.pm 2>&1 | grep -iv '^(DESTROY|MONITOR|Scalar constant)'

WHAT THIS MODULE CAN'T DO FOR YOU

Even if your modules are memory leak free, it doesn't mean that external modules that you are using don't have it. So, before running your application on mod_perl, you should be sure that EVERY modules are ok. (In particular those perl extensions calling C++ code)

MODULES THAT PRODUCE MEMORY LEAKS

You must destroy them when you don't need anymore those object instances

+----------------------+ | Bio::Graphics::Panel | +----------------------+ my $panel = Bio::Graphics::Panel->new(%options); ... $panel->finished();

+----------------------+ | XML::DOM | +----------------------+ my $parser = new XML::DOM::Parser; my $doc = $parser->parsefile ("file.xml"); ... $doc->dispose();

NOTE : I suggest that you use XML::LibXML instead

CAVEATS

TODO

BUGS

TODO

AUTHOR

Philippe Cote <philippe.cote@usherbrooke.ca>

COPYRIGHT AND LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.