package Devel::Monitor; use 5.008006; use strict; use warnings; require Exporter; use AutoLoader qw(AUTOLOAD); our @ISA = qw(Exporter); # Items to export into callers namespace by default. Note: do not export # names by default without a very good reason. Use EXPORT_OK instead. # Do not simply export all your public functions/methods/constants. # This allows declaration use Devel::Monitor ':all'; # If you do not need this, moving things directly into @EXPORT or @EXPORT_OK # will save memory. our @EXPORT = qw(); #Export by default our %EXPORT_TAGS = ( #Export as groups 'all' => [ qw(monitor print_circular_ref ) ] ); Exporter::export_ok_tags( #Export by request (into @EXPORT_OK) 'all'); our $VERSION = '0.9.0.7'; use Error qw(:try); use Scalar::Util qw(isweak); use Devel::Monitor::Common qw(:all); use Devel::Monitor::Trace; use Devel::Monitor::TraceItem; use Devel::Monitor::Array; use Devel::Monitor::Hash; use Devel::Monitor::Scalar; #Circular references type use constant CRT_NONE => undef; use constant CRT_CIRC_REF => 1; use constant CRT_INTERNAL_CIRC_REF => 2; use constant CRT_WEAK_CIRC_REF => 3; # METH 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 sub monitor { my $isCode; $isCode = pop if scalar(@_) % 2 != 0; my %values = @_; foreach my $key (keys %values) { my $varRef = $values{$key}; if ($varRef) { #If the value is undef _dereference(\$varRef); if ($varRef =~ /HASH/ ) { #An hash object or an hash _tieHash($varRef,$key,$isCode); } elsif ($varRef =~ /SCALAR|REF/) { _tieScalar($varRef,$key,$isCode); } elsif ($varRef =~ /ARRAY/) { _tieArray($varRef,$key,$isCode); } elsif ($varRef =~ /CODE/) { ########################################################### # Info on constants ########################################################### # use constant CONST => [1,2]; # print \&CONST."\n"; # print &CONST."\n"; # print \&CONST()."\n"; # print &CONST()."\n"; # # CODE(0x8203000) # ARRAY(0x81d4c04) # REF(0x820303c) # ARRAY(0x81d4c04) # # Code Ref # | | # Array Array # | | # +---+ +---+ # |1,2| |1,2| # +---+ +---+ # ########################################################### # use constant CONST => 'a scalar'; # print \&CONST."\n"; # print &CONST."\n"; # print \&CONST()."\n"; # print &CONST()."\n"; # # CODE(0x820300c) # a scalar # SCALAR(0x81fb2c4) # a scalar # # Code Scalar # | | # 'a scalar' 'a scalar' # # Instead of : # # Code Ref # | | # Scalar Scalar # | | # 'a scalar' 'a scalar' # ########################################################### if (ref(&$varRef) =~ /ARRAY|HASH/) { _monitorRecursively($key => &$varRef); } else { #_tieScalar($varRef); Devel::Monitor::Common::printMsg("Scalar constant $key cannot be monitored\n"); } } else { my $runPatch = 0; try { _tieHash($varRef,$key); } otherwise { ########################################################### # Patch for Error.pm # It seems there is a bug in this module ########################################################### # Example : ########################################################### # #!/usr/bin/perl # use strict; # use warnings; # use Devel::Monitor; # { # my @a = (1,2,3,4); # monitor('a'=>\@a); # print STDERR "Leaving scope\n"; # } # print STDERR "Scope left\n"; ########################################################### # Output without the patch (Very bad for mod_perl) ########################################################### # MONITOR ARRAY : a # Leaving scope # Scope left # DESTROY ARRAY : a ########################################################### # Output with the patch (Ok) ########################################################### # MONITOR ARRAY : a # Leaving scope # DESTROY ARRAY : a # Scope left ########################################################### $runPatch = 1; #try { # _tieArray($varRef,$key); #} otherwise { # Devel::Monitor::Common::printMsg("$varRef($key) cannot be monitored\n"); #}; }; if ($runPatch) { try { _tieArray($varRef,$key); } otherwise { Devel::Monitor::Common::printMsg("$varRef($key) cannot be monitored\n"); }; } } } } } sub _monitorRecursively { my %values = @_; foreach my $key (keys %values) { my $varRef = $values{$key}; if ($varRef) { #If the value is undef _dereference(\$varRef); if ($varRef =~ /HASH/ ) { #An hash object or an hash HASH_ITEM: foreach my $item (keys %$varRef) { #print STDERR "ITEM : ".$varRef->{$item}."\n"; _monitorRecursively("$key {$item}" => \($varRef->{$item})); } } elsif ($varRef =~ /SCALAR/) { # nothing } elsif ($varRef =~ /ARRAY/) { ARRAY_ITEM: my $i = 0; foreach my $item (@$varRef) { #print STDERR "ITEM : ".$item."\n"; _monitorRecursively("$key [$i]" => \$item); $i++; } } elsif ($varRef =~ /CODE/) { # nothing } else { my $runPatch = 0; try { goto HASH_ITEM; } otherwise { $runPatch = 1; }; if ($runPatch) { try { goto ARRAY_ITEM; } otherwise { #Devel::Monitor::Common::printMsg("$varRef($key) cannot be monitored recursively\n"); #we call monitor, this one will print the error }; } } # Finally, monitor current variable monitor($key => $varRef, 1); } } } sub _tieHash { my $varRef = shift; my $name = shift; my $isCode = shift; if (not tied %$varRef) { tie %$varRef, 'Devel::Monitor::Hash', $varRef, $name, $isCode; } else { my $self = tied %$varRef; #if tied by our Devel::Monitor if (ref($self) =~ /Devel::Monitor/) { Devel::Monitor::Common::printMsg("Hash from $name is already tied by ".$self->{Devel::Monitor::Common::F_ID()}."\n"); } else { Devel::Monitor::Common::printMsg("Array from $name is already tied by the ".ref($self)." package\n"); } } } sub _tieArray { my $varRef = shift; my $name = shift; my $isCode = shift; if (not tied @$varRef) { tie @$varRef, 'Devel::Monitor::Array', $varRef, $name, $isCode; } else { my $self = tied @$varRef; #if tied by our Devel::Monitor if (ref($self) =~ /Devel::Monitor/) { Devel::Monitor::Common::printMsg("Array from $name is already tied by ".$self->{Devel::Monitor::Common::F_ID()}."\n"); } else { Devel::Monitor::Common::printMsg("Array from $name is already tied by the ".ref($self)." package\n"); } } } sub _tieScalar { my $varRef = shift; my $name = shift; my $isCode = shift; if (not tied $$varRef) { try { tie $$varRef, 'Devel::Monitor::Scalar', $varRef, $name, $isCode; } otherwise { Devel::Monitor::Common::printMsg("Scalar from $name is read-only, monitor skipped\n"); }; } else { my $self = tied $$varRef; #if tied by our Devel::Monitor if (ref($self) =~ /Devel::Monitor/) { Devel::Monitor::Common::printMsg("Scalar from $name is already tied by ".$self->{Devel::Monitor::Common::F_ID()}."\n"); } else { Devel::Monitor::Common::printMsg("Array from $name is already tied by the ".ref($self)." package\n"); } } } #Not used # sub unmonitor { # my @varsRef = @_; # foreach my $varRef (@varsRef) { # if ($varRef) { # _dereference(\$varRef); # if ($varRef =~ /HASH/ ) { #An object or an hash # Devel::Monitor::Hash::unmonitor($varRef); # } # elsif ($varRef =~ /SCALAR/) { # Devel::Monitor::Scalar::unmonitor($varRef); # } # elsif ($varRef =~ /ARRAY/) { # Devel::Monitor::Array::unmonitor($varRef); # } # elsif ($varRef =~ /CODE/) { # unmonitor(&$varRef); #TODO : Unmonitor recursively, do not touch scalars # } # else { # my $runPatch = 0; # try { # Devel::Monitor::Hash::unmonitor($varRef); # } otherwise { # $runPatch = 1; # }; # if ($runPatch) { # try { # Devel::Monitor::Array::unmonitor($varRef); # } otherwise { # Devel::Monitor::Common::printMsg("$varRef cannot be unmonitored\n"); # }; # } # } # } # } # } sub _dereference { my $varRefRef = shift; my $type = ref($$varRefRef); #print STDERR "VARIABLE : $$varRefRef\n"; #print STDERR "TYPE : $type\n"; ############################################################## # You need to dereference, otherwise, you may # get this error : Modification of a read-only value attempted # is you monitor a variable that use a constant by example ############################################################## while ($type =~ /REF/) { $$varRefRef = $$$varRefRef; $type = ref($$varRefRef); #print STDERR "V : $$varRefRef\n"; #print STDERR "T : $type\n"; } } # METH printCircularRef # # DESC Try to find circular references and print it out into STDERR #Little redirect to be "Perl compliant" #TODO : use the underscore syntax sub print_circular_ref { return printCircularRef(@_); } sub printCircularRef { my $varRef = shift; my $hideWeakenedCircRef = shift; #Boolean my $source = shift; my $trace = shift; #A array container containing the current trace my $weakenedRef = shift; #A array containing the trace to the weakened ref it any my $origRef = shift; #Contains original reference to verify circular references my $seenRef = shift; my $circRefTypesRef = shift; #print STDERR "###############################################################\n"; #print STDERR "VARIABLE : ".$varRef."\n"; #print STDERR "TYPE : ".ref($varRef)."\n"; my $isFirst = (!$origRef); $trace = Devel::Monitor::Trace->new() if not $trace; $weakenedRef = [] if not $weakenedRef; $seenRef = {} if not $seenRef; $circRefTypesRef = [] if not $circRefTypesRef; return undef if not $varRef; my $isWeak = 0; my $simpleSeenRef = {}; #Since we dereference scalars, they are not displayed on the final prints while ($varRef =~ /REF/) { #print STDERR "DEREFERING $varRef ($$varRef)\n"; #print STDERR "Current variable : $varRef from ".\$varRef."\n"; if (isweak($$varRef)) { $isWeak = 1; #print STDERR "WEAK for $$varRef\n"; push(@$weakenedRef, $$varRef); } _addSeenRef($varRef,$simpleSeenRef); #Exceptional case : $a = \$a or $a = \$b = \$c #TODO : This "if" should not be handled as an exception (At least, we should try) if (exists($simpleSeenRef->{$varRef}) && ($simpleSeenRef->{$varRef} > 1)) { if ($isFirst) { _printCircularRefHeader($varRef); push(@$circRefTypesRef, CRT_CIRC_REF()); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); Devel::Monitor::Common::printMsg("Circular reference on scalar(s) starting at $varRef\n"); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); _printCircularRefResults($varRef,$circRefTypesRef); } else { push(@$circRefTypesRef, CRT_INTERNAL_CIRC_REF()); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); Devel::Monitor::Common::printMsg('Internal circular reference on scalar(s) starting at : '.$trace->getCircularPath()."\n"); $trace->dump(); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); } return undef; } $varRef = $$varRef; } $trace->push($varRef,$source); _addSeenRef($varRef,$seenRef) if $origRef; #We skip the first item which is $origRef #print STDERR "--------------------------------------------\n"; #print STDERR "Current variable : $varRef from ".\$varRef."\n"; my $circRefType = _checkCircularRef($varRef,$hideWeakenedCircRef,$trace,$weakenedRef,$origRef,$seenRef); #print STDERR "\$circRefType : $circRefType\n"; if ($circRefType) { $trace->pop(); push(@$circRefTypesRef, $circRefType); return undef; #Don't go any further because we loop } if ($isFirst) { $origRef = $varRef; _printCircularRefHeader($origRef); } #print STDERR 'Current trace : '.$trace->getCircularPath()."\n"; _printCircularRef($varRef,$hideWeakenedCircRef,$source,$trace,$weakenedRef,$origRef,$seenRef,$circRefTypesRef); #We go into another branch $trace->pop(); pop(@$weakenedRef) if $isWeak; # Remove weakened item delete($seenRef->{$varRef}); # Remove varRef from "seen" hash _printCircularRefResults($origRef,$circRefTypesRef) if $isFirst; return undef; } sub _printCircularRef { my $varRef = shift; my $hideWeakenedCircRef = shift; my $source = shift; my $trace = shift; my $weakenedRef = shift; my $origRef = shift; my $seenRef = shift; my $circRefTypesRef = shift; if ($varRef =~ /HASH/ ) { #An object or an hash HASH_ITEM: Devel::Monitor::Common::printMsg('Object '.$trace->getCircularPath().' = '.$varRef." is tied. Untie it to check circular references for this object.\n") if tied(%$varRef); foreach my $item (keys %$varRef) { my $ref = _getVarRef(\($varRef->{$item})); printCircularRef($ref,$hideWeakenedCircRef,'{'.$item.'}',$trace,$weakenedRef,$origRef,$seenRef,$circRefTypesRef); } } elsif ($varRef =~ /SCALAR|CODE/) { #No circular references are possible here, so we don't do anything } elsif ($varRef =~ /ARRAY/) { ARRAY_ITEM: Devel::Monitor::Common::printMsg('Object '.$trace->getCircularPath().' = '.$varRef." is tied. Untie it to check circular references for this object.\n") if tied(@$varRef); for (my $i=0; $i[$i])." ::: ".$varRef->[$i]."\n"; my $ref = _getVarRef(\($varRef->[$i])); #Devel::Monitor::Common::printMsg('Object at '.$trace->getCircularPath().'['.$i.']'. #" is ARRAY ARRAY ARRAY tied. We cannot check circular references for this object.\n") if $ref =~ /SCALAR/; printCircularRef($ref,$hideWeakenedCircRef,'['.$i.']',$trace,$weakenedRef,$origRef,$seenRef,$circRefTypesRef); } } else { #Other objects my $runPatch = 0; try { goto HASH_ITEM; } otherwise { $runPatch = 1; }; if ($runPatch) { try { goto ARRAY_ITEM; } otherwise { die("Cannot verify circular references for $varRef of type ".ref($varRef)."\n"); }; } } } sub _printCircularRefHeader { my $origRef = shift; Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); Devel::Monitor::Common::printMsg("Checking circular references for $origRef\n"); } sub _printCircularRefResults { my ($origRef, $circRefTypesRef) = @_; my $circRefsCount = 0; my $internalCircRefsCount = 0; my $weakCircRefsCount = 0; foreach my $crt (@$circRefTypesRef) { $weakCircRefsCount++ if $crt == CRT_WEAK_CIRC_REF(); $circRefsCount++ if $crt == CRT_CIRC_REF(); $internalCircRefsCount++ if $crt == CRT_INTERNAL_CIRC_REF(); } Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); Devel::Monitor::Common::printMsg("Results for $origRef\n"); Devel::Monitor::Common::printMsg("Circular reference : $circRefsCount\n"); Devel::Monitor::Common::printMsg("Internal circular reference : $internalCircRefsCount\n"); Devel::Monitor::Common::printMsg("Weak circular reference : $weakCircRefsCount\n"); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); } # METH _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 sub _checkCircularRef { my $varRef = shift; my $hideWeakenedCircRef = shift; my $trace = shift; my $weakenedRef = shift; my $origRef = shift; my $seenRef = shift; if ($varRef) { #print STDERR "\$varRef : $varRef\n"; #print STDERR "\$origRef : $origRef\n"; if ($origRef) { #If we found the original reference my $isCircRef = ($varRef eq $origRef); #If we found a reference more than one time, it means we loop infinitely my $isInternalCircRef = (exists($seenRef->{$varRef}) && ($seenRef->{$varRef} > 1)); if ($isCircRef || $isInternalCircRef) { my $weakenedInCircRefRef = _getWeakenedInCircRef($trace,$weakenedRef); my $isWeakenedItems = (scalar(@$weakenedInCircRefRef) > 0); if (!$hideWeakenedCircRef || #If we show everything ($hideWeakenedCircRef && !$isWeakenedItems)) { #Otherwise, if there is no weak reference Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); if ($isCircRef) { Devel::Monitor::Common::printMsg('Circular reference found : '.$trace->getCircularPath()."\n"); } elsif ($isInternalCircRef) { Devel::Monitor::Common::printMsg('Internal circular reference found : '.$trace->getCircularPath()." on $varRef\n"); } if ($isWeakenedItems) { Devel::Monitor::Common::printMsg('with weakened reference on : '.join(', ', @$weakenedInCircRefRef)."\n"); } $trace->dump(); Devel::Monitor::Common::printMsg("-------------------------------------------------------------------------------\n"); return CRT_WEAK_CIRC_REF() if $isWeakenedItems; return CRT_CIRC_REF() if $isCircRef; return CRT_INTERNAL_CIRC_REF() if $isInternalCircRef; die("_checkCircularRef : Should not be here (1)\n"); } elsif ($hideWeakenedCircRef && $isWeakenedItems) { return CRT_WEAK_CIRC_REF(); } } } return CRT_NONE(); } die("_checkCircularRef : \$varRef is undefined\n"); } sub _addSeenRef { my $varRef = shift; my $seenRef = shift; #print STDERR "_addSeenRef: $varRef\n"; if (exists($seenRef->{$varRef})) { $seenRef->{$varRef}++; } else { $seenRef->{$varRef} = 1; } } sub _getVarRef { my $varRef = shift; ########################################################### # We cannot use tied objects because it reuse memory space ########################################################### # use Tie::Hash; # # my $self = {'a' => 1, # 'b' => 2}; # #monitor('self' => \$self); # tie %$self, 'Tie::StdHash'; # 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 ########################################################### # We see clearly that it reuse memory space instead of # refering to the original values from the untied object ########################################################### my $ref; #if ($$varRef && # ($varRef =~ /SCALAR/) && # ($$varRef =~ /(ARRAY|HASH)/)) { # $ref = $$varRef; #} else { $ref = $varRef; #} return $ref; } sub _getWeakenedInCircRef { my $trace = shift; my $weakenedRef = shift; my @weakenedInCircRef; my $traceItemsRef = $trace->getTraceItems; #The last item represent the circular reference my $traceItemCircRef = $traceItemsRef->[$#$traceItemsRef]; #for my $i (($#$traceItemsRef-1)..0) { for (my $i=($#$traceItemsRef-1); $i>=0; $i--) { #Get the current item my $traceItem = $traceItemsRef->[$i]; #print STDERR "traceItem ".$traceItem->getVarRef()."\n"; #We verify that the item is a weaken reference or not foreach my $weakened (@$weakenedRef) { #print STDERR "weakened ".$weakened."\n"; if ($traceItem->getVarRef() eq $weakened) { #print STDERR "push\n"; push(@weakenedInCircRef, $weakened); } } #We finish when we end the circular reference last if ($traceItem->getVarRef() eq $traceItemCircRef->getVarRef()); } #print STDERR "RETURN ".join(', ', @weakenedInCircRef)."\n"; return \@weakenedInCircRef; } 1; __END__ =head1 NAME Devel::Monitor - Monitor your variables/objects for memory leaks =head1 DESCRIPTION You have memory leaks, and you want to remove it... You can use this tool to help you find which variables/objects that are not destroyed when they should be, and thereafter, you can visualise exactly where is the circular reference for some specific variables/objects. =head1 WHAT IT CAN'T DO Even if your modules are memory leak free, it doesn't mean that external modules that you are using don't have it. So, before running your application on mod_perl, you should be sure that EVERY modules are ok. (In particular those perl extensions calling C++ code) =head1 SYNOPSIS use Devel::Monitor qw(:all); #----------------------------------------------------------------------------- # Monitor scalars, arrays, hashes, references, constants #----------------------------------------------------------------------------- my ($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()) #----------------------------------------------------------------------------- # Print circular references #----------------------------------------------------------------------------- # NOTE : You cannot use print_circular_ref on a monitored/tied variable # (See "We cannot use tied objects references because it reuse memory space" doc) print_circular_ref(\$a); print_circular_ref(\$b); print_circular_ref(\$c); print_circular_ref(\@d); print_circular_ref(\%e); print_circular_ref(\&F); #NOTE : Dont add parentheses to the end of the constant (\&F()) =head1 USAGE : monitor =head2 Example with a circular reference +----------------------+ | 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. =head2 Example without a circular reference +----------------------+ | 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 Now that you know there is a circular reference, you can track it down using the print_circular_ref method =head1 USAGE : print_circular_ref =head2 Example +----------------------+ | Code | | a | | / \ | | [0] [1] | | / \ | | 'asdf' b <--| | | \ | | | [3]-| | | | +----------------------+ my (@a, @b); $a[0] = 'asdf'; $a[1] = \@b; $b[3] = \@b; print_circular_ref(\@a); print_circular_ref(\@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 ------------------------------------------------------------------------------- =head1 TRACKING MEMORY LEAKS =head2 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 qw(:all); { 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. # #------------------------------------------------------------------------------+ =head1 THINGS YOU SHOULD BE AWARE OF =head2 Loop variables are passed by references Let's see in details what output you get when monitoring variables inside a loop. +----------------------+ | 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. =head2 Variable using constants are destroyed when the constant is destroyed Let's look at this small example : +----------------------+ | Code | +----------------------+ #!/usr/bin/perl use strict; use warnings; use Devel::Monitor qw(:all); 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. =head2 Perl problems =head3 You cannot use references from a tied object because it reuse memory space Let's see in details what happen when you try to print circular references with a tied object (An object with a monitor by example !!!) +----------------------+ | 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. =head3 You cannot weaken a tied object This is actually an unhandled reference by Perl (Verified with 5.9.2-). It means that if you monitor (or tie explicitly) an object, any weaken references into this one will simply be ignored. =head4 Proof 01 : Basic test +----------------------+ | 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. =head4 Proof 02 : mod_perl +----------------------+ | Code | +----------------------+ +------------+ | test.pl | +------------+ #!/usr/bin/perl use strict; use warnings; use Scalar::Util qw(weaken); use Devel::Monitor qw(:all); 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 =head4 Proof 03 : Final assault Firstly, we must be sure that the methods Scalar::Util::weaken and Scalar::Util::isweak doesn't contain bugs. The code for these method follows : 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 We easily see that there is absolutely no problems here. Now let's see what happen if we dump a tied variable by using Devel::Peek. It should activate the WEAKREF flag if the reference is weak. Let's see what result we should get : +----------------------+ | Code | +----------------------+ #!/usr/bin/perl use strict; use warnings; use Devel::Monitor qw(:all); use Scalar::Util qw(weaken); use Devel::Peek; { my (@a); $a[0] = \@a; #tie @a, 'TestArray'; Dump($a[0],1); weaken($a[0]); Dump($a[0],1); print "Leaving scope\n"; } print "Scope left\n"; package TestArray; use Tie::Array; use base 'Tie::StdArray'; sub DESTROY { print "Monitor::TestArray::DESTROY : $_[0]\n"; } 1; +-------------------------------+ | Output without the "tie" call | +-------------------------------+ SV = RV(0x81829c0) at 0x814127c REFCNT = 1 FLAGS = (ROK) RV = 0x814e740 SV = PVAV(0x81426cc) at 0x814e740 REFCNT = 2 FLAGS = (PADBUSY,PADMY) IV = 0 NV = 0 ARRAY = 0x8148888 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) SV = RV(0x81829c0) at 0x814127c REFCNT = 1 FLAGS = (ROK,WEAKREF,IsUV) RV = 0x814e740 SV = PVAV(0x81426cc) at 0x814e740 REFCNT = 1 FLAGS = (PADBUSY,PADMY,RMG) IV = 0 NV = 0 MAGIC = 0x8266f08 MG_VIRTUAL = &PL_vtbl_backref MG_TYPE = PERL_MAGIC_backref(<) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x81411c8 SV = PVAV(0x8263704) at 0x81411c8 REFCNT = 2 FLAGS = () IV = 0 NV = 0 ARRAY = 0x82677e8 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) ARRAY = 0x8148888 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) Leaving scope Scope left +----------------------+ | Explanations | +----------------------+ We actually see the WEAKREF flag that confirms us that the reference is weak. However, let's see what happen when we uncomment the 11th line (the tie call on @a) +----------------------------+ | Output with the "tie" call | +----------------------------+ SV = PVLV(0x817c568) at 0x81413f0 REFCNT = 1 FLAGS = (TEMP,GMG,SMG,RMG) IV = 0 NV = 0 PV = 0 MAGIC = 0x81505b8 MG_VIRTUAL = &PL_vtbl_packelem MG_TYPE = PERL_MAGIC_tiedelem(p) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x814139c SV = RV(0x81829ac) at 0x814139c REFCNT = 2 FLAGS = (ROK) RV = 0x8141354 TYPE = t TARGOFF = 0 TARGLEN = 0 TARG = 0x81413f0 SV = PVLV(0x817c568) at 0x81413f0 REFCNT = 1 FLAGS = (TEMP,GMG,SMG,RMG) IV = 0 NV = 0 PV = 0 MAGIC = 0x81505b8 MG_VIRTUAL = &PL_vtbl_packelem MG_TYPE = PERL_MAGIC_tiedelem(p) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x814139c SV = RV(0x81829ac) at 0x814139c REFCNT = 2 FLAGS = (ROK) RV = 0x8141354 TYPE = t TARGOFF = 0 TARGLEN = 0 TARG = 0x81413f0 Leaving scope Scope left Monitor::TestArray::DESTROY : TestArray=ARRAY(0x8141354) +----------------------+ | Explanations | +----------------------+ Absolutely nothing has changed before and after. IT IS A PROBLEM ! So, I debugged the perl source code to verify what happen with a tied variable. The method goes like this : /* =for apidoc sv_rvweaken Weaken a reference: set the C flag on this RV; give the referred-to SV C magic if it hasn't already; and push a back-reference to this RV onto the array of backreferences associated with that magic. =cut */ SV * Perl_sv_rvweaken(pTHX_ SV *sv) { SV *tsv; if (!SvOK(sv)) /* let undefs pass */ return sv; if (!SvROK(sv)) Perl_croak(aTHX_ "Can't weaken a nonreference"); else if (SvWEAKREF(sv)) { if (ckWARN(WARN_MISC)) Perl_warner(aTHX_ packWARN(WARN_MISC), "Reference is already weak"); return sv; } tsv = SvRV(sv); sv_add_backref(tsv, sv); SvWEAKREF_on(sv); SvREFCNT_dec(tsv); return sv; } The problem is at the line "if (!SvOK(sv))". A tied variable enter this condition and returns itself without any modifications... The reason is that our variables has those flags FLAGS = (TEMP,GMG,SMG,RMG). The code should be something like this : if (!SvOK(sv)) if (SvMAGIC(sv)) { //*************************************** //Do something here !!! //*************************************** } else { return sv; } This bug has been submitted and is unanswered for now. (See http://rt.perl.org/rt3/Ticket/Display.html?id=34524) =head4 Conclusion It is actually impossible to weaken a tied variable =head1 TRICKS =head2 Checking modules syntax Since monitored are executed when you check syntax of a module, it will print out to stderr some messages with constants and some global variables. So to remove those prints, simple grep it by redirecting stderr to stdout and grep it perl -c MyModule.pm 2>&1 | grep -iv '^(DESTROY|MONITOR|Scalar constant)' =head1 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(); #Don't forget to call this destructor +----------------------+ | XML::DOM | +----------------------+ my $parser = new XML::DOM::Parser; my $doc = $parser->parsefile ("file.xml"); ... $doc->dispose(); #Don't forget to call this destructor NOTE : I suggest that you use XML::LibXML instead =head1 NOTE This module has been tested with scalars, hashes, arrays, blessed hashes, blessed arrays, tied hashes, tied arrays, tied scalars. =head1 BUGS None known =head1 AUTHOR Philippe Cote E philippe.cote@usherbrooke.ca E Génome Québec E http://www.genomequebec.com E =head1 CREDITS I got the main idea from a module that is not on CPAN. See http://www.infocopter.com/perl/monitored-variables.htm (Monitor.pm) =head1 COPYRIGHT AND LICENSE This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. =cut