+#if VMG_MULTIPLICITY && !defined(tTHX)
+# define tTHX PerlInterpreter*
+#endif
+
+#if VMG_MULTIPLICITY && defined(USE_ITHREADS) && defined(dMY_CXT) && defined(MY_CXT) && defined(START_MY_CXT) && defined(MY_CXT_INIT) && (defined(MY_CXT_CLONE) || defined(dMY_CXT_SV))
+# define VMG_THREADSAFE 1
+# ifndef MY_CXT_CLONE
+# define MY_CXT_CLONE \
+ dMY_CXT_SV; \
+ my_cxt_t *my_cxtp = (my_cxt_t*)SvPVX(newSV(sizeof(my_cxt_t)-1)); \
+ Copy(INT2PTR(my_cxt_t*, SvUV(my_cxt_sv)), my_cxtp, 1, my_cxt_t); \
+ sv_setuv(my_cxt_sv, PTR2UV(my_cxtp))
+# endif
+#else
+# define VMG_THREADSAFE 0
+# undef dMY_CXT
+# define dMY_CXT dNOOP
+# undef MY_CXT
+# define MY_CXT vmg_globaldata
+# undef START_MY_CXT
+# define START_MY_CXT STATIC my_cxt_t MY_CXT;
+# undef MY_CXT_INIT
+# define MY_CXT_INIT NOOP
+# undef MY_CXT_CLONE
+# define MY_CXT_CLONE NOOP
+#endif
+
+#if VMG_THREADSAFE
+
+STATIC SV *vmg_clone(pTHX_ SV *sv, tTHX owner) {
+#define vmg_clone(P, O) vmg_clone(aTHX_ (P), (O))
+ CLONE_PARAMS param;
+ param.stashes = NULL; /* don't need it unless sv is a PVHV */
+ param.flags = 0;
+ param.proto_perl = owner;
+ return sv_dup(sv, ¶m);
+}
+
+#endif /* VMG_THREADSAFE */