NAME¶
Devel::Cycle - Find memory cycles in objects
SYNOPSIS¶
#!/usr/bin/perl
use Devel::Cycle;
my $test = {fred => [qw(a b c d e)],
ethel => [qw(1 2 3 4 5)],
george => {martha => 23,
agnes => 19}
};
$test->{george}{phyllis} = $test;
$test->{fred}[3] = $test->{george};
$test->{george}{mary} = $test->{fred};
find_cycle($test);
exit 0;
# output:
Cycle (1):
$A->{'george'} => \%B
$B->{'phyllis'} => \%A
Cycle (2):
$A->{'george'} => \%B
$B->{'mary'} => \@A
$A->[3] => \%B
Cycle (3):
$A->{'fred'} => \@A
$A->[3] => \%B
$B->{'phyllis'} => \%A
Cycle (4):
$A->{'fred'} => \@A
$A->[3] => \%B
$B->{'mary'} => \@A
# you can also check weakened references
weaken($test->{george}->{phyllis});
find_weakened_cycle($test);
exit 0;
# output:
Cycle (1):
$A->{'george'} => \%B
$B->{'mary'} => \@C
$C->[3] => \%B
Cycle (2):
$A->{'george'} => \%B
w-> $B->{'phyllis'} => \%A
Cycle (3):
$A->{'fred'} => \@C
$C->[3] => \%B
$B->{'mary'} => \@C
Cycle (4):
$A->{'fred'} => \@C
$C->[3] => \%B
w-> $B->{'phyllis'} => \%A
DESCRIPTION¶
This is a simple developer's tool for finding circular references in objects and
other types of references. Because of Perl's reference-count based memory
management, circular references will cause memory leaks.
EXPORT¶
The
find_cycle() and
find_weakened_cycle() subroutine are exported
by default.
- find_cycle($object_reference,[$callback])
- The find_cycle() function will traverse the object
reference and print a report to STDOUT identifying any memory cycles it
finds.
If an optional callback code reference is provided, then this callback will
be invoked on each cycle that is found. The callback will be passed an
array reference pointing to a list of lists with the following format:
$arg = [ ['REFTYPE',$index,$reference,$reference_value],
['REFTYPE',$index,$reference,$reference_value],
['REFTYPE',$index,$reference,$reference_value],
...
]
Each element in the array reference describes one edge in the memory cycle.
'REFTYPE' describes the type of the reference and is one of
'SCALAR','ARRAY' or 'HASH'. $index is the index affected by the reference,
and is undef for a scalar, an integer for an array reference, or a hash
key for a hash. $reference is the memory reference, and $reference_value
is its dereferenced value. For example, if the edge is an ARRAY, then the
following relationship holds:
$reference->[$index] eq $reference_value
The first element of the array reference is the $object_reference that you
passed to find_cycle() and may not be directly involved in the
cycle.
If a reference is a weak ref produced using Scalar::Util's weaken()
function then it won't contribute to cycles.
- find_weakened_cycle($object_reference,[$callback])
- The find_weakened_cycle() function will traverse the
object reference and print a report to STDOUT identifying any memory
cycles it finds, including any weakened cycles produced using
Scalar::Util's weaken().
If an optional callback code reference is provided, then this callback will
be invoked on each cycle that is found. The callback will be passed an
array reference pointing to a list of lists with the following format:
$arg = [ ['REFTYPE',$index,$reference,$reference_value,$is_weakened],
['REFTYPE',$index,$reference,$reference_value,$is_weakened],
['REFTYPE',$index,$reference,$reference_value,$is_weakened],
...
]
Each element in the array reference describes one edge in the memory cycle.
'REFTYPE' describes the type of the reference and is one of
'SCALAR','ARRAY' or 'HASH'. $index is the index affected by the reference,
and is undef for a scalar, an integer for an array reference, or a hash
key for a hash. $reference is the memory reference, and $reference_value
is its dereferenced value. $is_weakened is a boolean specifying if the
reference is weakened or not. For example, if the edge is an ARRAY, then
the following relationship holds:
$reference->[$index] eq $reference_value
The first element of the array reference is the $object_reference that you
passed to find_cycle() and may not be directly involved in the
cycle.
The default callback prints out a trace of each cycle it finds. You can control
the format of the trace by setting the package variable
$Devel::Cycle::FORMATTING to one of "raw," "cooked," or
"roasted".
The "raw" format prints out anonymous memory references using standard
Perl memory location nomenclature. For example, a "Foo::Bar" object
that points to an ordinary hash will appear in the trace like this:
Foo::Bar=HASH(0x8124394)->{'phyllis'} => HASH(0x81b4a90)
The "cooked" format (the default), uses short names for anonymous
memory locations, beginning with "A" and moving upward with the
magic ++ operator. This leads to a much more readable display:
$Foo::Bar=B->{'phyllis'} => \%A
The "roasted" format is similar to the "cooked" format,
except that object references are formatted slightly differently:
$Foo::Bar::B->{'phyllis'} => \%A
If a reference is a weakened ref, then it will have a 'w->' prepended to it,
like this:
w-> $Foo::Bar::B->{'phyllis'} => \%A
For your convenience, $Devel::Cycle::FORMATTING can be imported:
use Devel::Cycle qw(:DEFAULT $FORMATTING);
$FORMATTING = 'raw';
Alternatively, you can control the formatting at compile time by passing one of
the options -raw, -cooked, or -roasted to "use" as illustrated here:
use Devel::Cycle -raw;
Code references (closures)¶
If the PadWalker module is installed, Devel::Cycle will also report cycles in
code closures. If PadWalker is not installed and Devel::Cycle detects a CODE
reference in one of the data structures, it will warn (once per data
structure) that it cannot inspect the CODE unless PadWalker is available. You
can turn this warning off by passing -quiet to Devel::Cycle at compile time:
use Devel::Cycle -quiet;
SEE ALSO¶
Test::Memory::Cycle Devel::Leak Scalar::Util
AUTHOR¶
Lincoln Stein, <lstein@cshl.edu>
COPYRIGHT AND LICENSE¶
Copyright (C) 2003 by Lincoln Stein
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself, either Perl version 5.8.2 or, at your option,
any later version of Perl 5 you may have available.
