add all stash backrefs individually when joining

When joining a thread, a 'mini' interpreter clone is performed to
clone the returned SVs and dependents back into the parent interpreter.
To make things simple in this case, don't clone the xhv_backreferences
array of any stashes, but individually add in any cloned GVs and CVs
whose [CG]vSTASH points that way. This is faster (avoids an expensive test
per CV/GV) and better (doesn't clone unnecessary SVs in the backref array)

diff --git a/sv.c b/sv.c
index 4ca7333..88da54b 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -11222,18 +11222,8 @@ S_sv_dup_common(pTHX_ const SV *const sstr, CLONE_PARAMS *const param)
                    /* Danger Will Robinson - GvGP(dstr) isn't initialised
                       at the point of this comment.  */
                    GvSTASH(dstr) = hv_dup(GvSTASH(dstr), param);
-                   if(param->flags & CLONEf_JOIN_IN) {
-                       const HEK * const hvname
-                        = HvNAME_HEK(GvSTASH(dstr));
-                       if( hvname
-                        && GvSTASH(dstr) == gv_stashpvn(
-                            HEK_KEY(hvname), HEK_LEN(hvname), 0
-                           )
-                         )
-                           Perl_sv_add_backref(
-                            aTHX_ MUTABLE_SV(GvSTASH(dstr)), dstr
-                           );
-                   }
+                   if (param->flags & CLONEf_JOIN_IN)
+                       Perl_sv_add_backref(aTHX_ MUTABLE_SV(GvSTASH(dstr)), dstr);
                    GvGP(dstr)  = gp_dup(GvGP(sstr), param);
                    (void)GpREFCNT_inc(GvGP(dstr));
                } else
@@ -11333,7 +11323,16 @@ S_sv_dup_common(pTHX_ const SV *const sstr, CLONE_PARAMS *const param)
                                        cBOOL(HvSHAREKEYS(sstr)), param) : 0;
                        /* backref array needs refcnt=2; see sv_add_backref */
                        daux->xhv_backreferences =
-                           saux->xhv_backreferences
+                           (param->flags & CLONEf_JOIN_IN)
+                               /* when joining, we let the individual GVs and
+                                * CVs add themselves to backref as
+                                * needed. This avoids pulling in stuff
+                                * that isn't required, and simplifies the
+                                * case where stashes aren't cloned back
+                                * if they already exist in the parent
+                                * thread */
+                           ? NULL
+                           : saux->xhv_backreferences
                            ? MUTABLE_AV(SvREFCNT_inc(
                                                      sv_dup_inc((const SV *)saux->xhv_backreferences, param)))
                                : 0;
@@ -11358,18 +11357,8 @@ S_sv_dup_common(pTHX_ const SV *const sstr, CLONE_PARAMS *const param)
            case SVt_PVFM:
                /* NOTE: not refcounted */
                CvSTASH(dstr)   = hv_dup(CvSTASH(dstr), param);
-               if(param->flags & CLONEf_JOIN_IN && CvSTASH(dstr)) {
-                   const HEK * const hvname
-                    = HvNAME_HEK(CvSTASH(dstr));
-                   if( hvname
-                    && CvSTASH(dstr) == gv_stashpvn(
-                        HEK_KEY(hvname), HEK_LEN(hvname), 0
-                       )
-                     )
-                       Perl_sv_add_backref(
-                        aTHX_ MUTABLE_SV(CvSTASH(dstr)), dstr
-                       );
-               }
+               if ((param->flags & CLONEf_JOIN_IN) && CvSTASH(dstr))
+                   Perl_sv_add_backref(aTHX_ MUTABLE_SV(CvSTASH(dstr)), dstr);
                OP_REFCNT_LOCK;
                if (!CvISXSUB(dstr))
                    CvROOT(dstr) = OpREFCNT_inc(CvROOT(dstr));