perldelta entry describing the HvAUX struct move to the HV body

None of this affects documented public XS interfaces. The only code changes
are in hv.c and sv.c. As the rest of the core itself uses these macros but
needed no changes, likely no code on CPAN will be affected either.

1 files changed, 20 insertions, 1 deletions

diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index 96cb6a12b0..31831e53e2 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -353,7 +353,26 @@ well.
 
 =item *
 
-XXX
+Memory for hash iterator state (C<struct xpvhv_aux>) is now allocated as part
+of the hash body, instead of as part of the block of memory allocated for the
+main hash array.
+
+Nothing else changes - memory for this structure is still allocated only when
+needed, is still accessed via the C<HvAUX()> macro, and the macro should only
+be called when C<SvOOK()> is true. Hashes are still always of type C<SVt_PVHV>,
+hash bodies are still allocated from arenas, and the address of the hash
+doesn't change, because the address is the pointer to the head structure, which
+never moves.
+
+Internally, a second arena (the arena with index 1) is used to allocate larger
+bodies with space for C<struct xpvhv_aux>, the body "upgraded", and the "head"
+structure updated to reflect this (much the same way that the bodies of scalars
+are upgraded). We already re-purpose arenas - arena with index 0 is used for
+C<HE *>s.
+
+None of this affects documented public XS interfaces. The only code changes are
+in F<hv.c> and F<sv.c>. As the rest of the core itself uses these macros but
+needed no changes, likely no code on CPAN will be affected either.
 
 =back