Devel-Monitor
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# }
# 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; $i<scalar(@$varRef); $i++) {
#print STDERR "CURRENT VAR : ".\($varRef->[$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 |
+----------------------+
lib/Devel/Monitor.pm view on Meta::CPAN
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
lib/Devel/Monitor.pm view on Meta::CPAN
+----------------------+
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)
lib/Devel/Monitor.pm view on Meta::CPAN
| 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<SvWEAKREF> flag on this RV; give the
referred-to SV C<PERL_MAGIC_backref> 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<lt> philippe.cote@usherbrooke.ca E<gt>
Génome Québec E<lt> http://www.genomequebec.com E<gt>
=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
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