clarify when HV backref is in magic

Fix up the comments in and above some functions to clarify that backref
bagic for hVs may sometimes be moved back to HvAUX.

diff --git a/hv.c b/hv.c
index 9b5a3ba..e221499 100644 (file)
--- a/hv.c
+++ b/hv.c
@@ -1678,8 +1678,10 @@ S_hfreeentries(pTHX_ HV *hv)
             * If, during the entry freeing, a destructor happens to add
             * a new weak backref, then sv_add_backref will look in both
             * places (magic in HvAUX) for the AV, but will create a new
-            * AV in HvAUX if it can't find one. So at the end of the
-            * iteration we have to allow for this. */
+            * AV in HvAUX if it can't find one (if it finds it in magic,
+            * it moves it back into HvAUX. So at the end of the iteration
+            * we have to allow for this. */
+
 
            if (iter->xhv_backreferences) {
                if (SvTYPE(iter->xhv_backreferences) == SVt_PVAV) {

diff --git a/sv.c b/sv.c
index 5d744c5..a2f9867 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -5310,6 +5310,8 @@ Perl_sv_rvweaken(pTHX_ SV *const sv)
  * store it directly in the HvAUX or mg_obj slot, avoiding the need to
  * allocate an AV. (Whether the slot holds an AV tells us whether this is
  * active.)
+ *
+ * If an HV's backref is stored in magic, it is moved back to HvAUX.
  */
 
 /* A discussion about the backreferences array and its refcount:
@@ -5420,10 +5422,6 @@ Perl_sv_del_backref(pTHX_ SV *const tsv, SV *const sv)
 
     if (SvTYPE(tsv) == SVt_PVHV && SvOOK(tsv)) {
        svp = (SV**)Perl_hv_backreferences_p(aTHX_ MUTABLE_HV(tsv));
-       /* We mustn't attempt to "fix up" the hash here by moving the
-          backreference array back to the hv_aux structure, as that is stored
-          in the main HvARRAY(), and hfreentries assumes that no-one
-          reallocates HvARRAY() while it is running.  */
     }
     if (!svp || !*svp) {
        MAGIC *const mg