Internals(3perl) Perl Programmers Reference Guide Internals(3perl)
NAME
Internals - Reserved special namespace for internals related functions
SYNOPSIS
$is_ro= Internals::SvREADONLY($x)
$refcnt= Internals::SvREFCNT($x)
hv_clear_placeholders(%hash);
if (Internals::stack_refcounted & 1) { .... }
DESCRIPTION
The Internals namespace is used by the core Perl development team to
expose certain low level internals routines for testing and other
purposes.
In theory these routines were not and are not intended to be used
outside of the perl core, and are subject to change and removal at any
time.
In practice people have come to depend on these over the years, despite
being historically undocumented, so we will provide some level of
forward compatibility for some time. Nevertheless you can assume that
any routine documented here is experimental or deprecated and you should
find alternatives to their use.
FUNCTIONS
SvREFCNT(THING [, $value])
Historically Perl has been a refcounted language. This means that
each variable tracks how many things reference it, and when the
variable is no longer referenced it will automatically free itself.
In theory Perl code should not have to care about this, and in a
future version Perl might change to some other strategy, although in
practice this is unlikely.
This function allows one to violate the abstraction of variables and
get or set the refcount of a variable, and in generally is really
only useful in code that is testing refcount behavior.
*NOTE* You are strongly discouraged from using this function in non-
test code and especially discouraged from using the set form of this
function. The results of doing so may result in segmentation faults
or other undefined behavior.
SvREADONLY(THING, [, $value])
Set or get whether a variable is readonly or not. Exactly what the
readonly flag means depend on the type of the variable affected and
the version of perl used.
You are strongly discouraged from using this function directly. It
is used by various core modules, like "Hash::Util", and the
"constant" pragma to implement higher-level behavior which should be
used instead.
See the core implementation for the exact meaning of the readonly
flag for each internal variable type.
hv_clear_placeholders(%hash)
Clear any placeholders from a locked hash. Should not be used
directly. You should use the wrapper functions provided by
Hash::Util instead. As of 5.25 also available as
Hash::Util::_clear_placeholders(%hash)
stack_refcounted
Returns an integer indicating whether the perl binary has been
configured and built with an argument stack which reference-counts
any items pushed onto it. The value should be treated as flag bits.
Currently only bit 0 is used, indicating that "PERL_RC_STACK" was
enabled during the build.
AUTHOR
Perl core development team.
SEE ALSO
perlguts Hash::Util constant universal.c
perl v5.40.1 2026-08-30 Internals(3perl)
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