NAME¶
"Devel::Refcount" - obtain the REFCNT value of a referent
SYNOPSIS¶
use Devel::Refcount qw( refcount );
my $anon = [];
print "Anon ARRAY $anon has " . refcount( $anon ) . " reference\n";
my $otherref = $anon;
print "Anon ARRAY $anon now has " . refcount( $anon ) . " references\n";
assert_oneref $otherref; # This will throw an exception at runtime
DESCRIPTION¶
This module provides a single function which obtains the reference count of the
object being pointed to by the passed reference value. It also provides a
debugging assertion that asserts a given reference has a count of only 1.
FUNCTIONS¶
$count = refcount( $ref )¶
Returns the reference count of the object being pointed to by $ref.
assert_oneref( $ref )¶
Asserts that the given object reference has a reference count of only 1. If this
is true the function does nothing. If it has more than 1 reference then an
exception is thrown. Additionally, if Devel::FindRef is available, it will be
used to print a more detailed trace of where the references are found.
Typically this would be useful in debugging to track down cases where objects
are still being referenced beyond the point at which they are supposed to be
dropped. For example, if an element is delete from a hash that ought to be the
last remaining reference, the return value of the "delete" operator
can be asserted on
assert_oneref delete $self->{some_item};
If at the time of deleting there are any other references to this object then
the assertion will fail; and if "Devel::FindRef" is available the
other locations will be printed.
COMPARISON WITH SvREFCNT¶
This function differs from "Devel::Peek::SvREFCNT" in that
SvREFCNT() gives the reference count of the SV object itself that it is
passed, whereas
refcount() gives the count of the object being pointed
to. This allows it to give the count of any referent (i.e. ARRAY, HASH, CODE,
GLOB and Regexp types) as well.
Consider the following example program:
use Devel::Peek qw( SvREFCNT );
use Devel::Refcount qw( refcount );
sub printcount
{
my $name = shift;
printf "%30s has SvREFCNT=%d, refcount=%d\n",
$name, SvREFCNT( $_[0] ), refcount( $_[0] );
}
my $var = [];
printcount 'Initially, $var', $var;
my $othervar = $var;
printcount 'Before CODE ref, $var', $var;
printcount '$othervar', $othervar;
my $code = sub { undef $var };
printcount 'After CODE ref, $var', $var;
printcount '$othervar', $othervar;
This produces the output
Initially, $var has SvREFCNT=1, refcount=1
Before CODE ref, $var has SvREFCNT=1, refcount=2
$othervar has SvREFCNT=1, refcount=2
After CODE ref, $var has SvREFCNT=2, refcount=2
$othervar has SvREFCNT=1, refcount=2
Here, we see that
SvREFCNT() counts the number of references to the SV
object passed in as the scalar value - the $var or $othervar respectively,
whereas
refcount() counts the number of reference values that point to
the referent object - the anonymous ARRAY in this case.
Before the CODE reference is constructed, both $var and $othervar have
SvREFCNT() of 1, as they exist only in the current lexical pad. The
anonymous ARRAY has a
refcount() of 2, because both $var and $othervar
store a reference to it.
After the CODE reference is constructed, the $var variable now has an
SvREFCNT() of 2, because it also appears in the lexical pad for the new
anonymous CODE block.
PURE-PERL FALLBACK¶
An XS implementation of this function is provided, and is used by default. If
the XS library cannot be loaded, a fallback implementation in pure perl using
the "B" module is used instead. This will behave identically, but is
much slower.
Rate pp xs
pp 225985/s -- -66%
xs 669570/s 196% --
SEE ALSO¶
- •
- Test::Refcount - assert reference counts on objects
AUTHOR¶
Paul Evans <leonerd@leonerd.org.uk>