Hi Marc, Yes, check out this from the 3.9 what's new document:
https://docs.python.org/3/whatsnew/3.9.html#changes-in-the-c-api Instances of heap-allocated types (such as those created with PyType_FromSpec() and similar APIs) hold a reference to their type object since Python 3.8. As indicated in the “Changes in the C API” of Python 3.8, for the vast majority of cases, there should be no side effect but for types that have a custom tp_traverse function, ensure that all custom tp_traverse functions of heap-allocated types visit the object’s type. Example: int foo_traverse(foo_struct *self, visitproc visit, void *arg) { // Rest of the traverse function #if PY_VERSION_HEX >= 0x03090000 // This was not needed before Python 3.9 (Python issue 35810 and 40217) Py_VISIT(Py_TYPE(self)); #endif } If your traverse function delegates to tp_traverse of its base class (or another type), ensure that Py_TYPE(self) is visited only once. Note that only heap types are expected to visit the type in tp_traverse. For example, if your tp_traverse function includes: base->tp_traverse(self, visit, arg) then add: #if PY_VERSION_HEX >= 0x03090000 // This was not needed before Python 3.9 (Python issue 35810 and 40217) if (base->tp_flags & Py_TPFLAGS_HEAPTYPE) { // a heap type's tp_traverse already visited Py_TYPE(self) } else { Py_VISIT(Py_TYPE(self)); } #else (See bpo-35810 and bpo-40217 for more information.) Regards from sunny London, Pablo On Thu, 27 May 2021, 16:36 Marc-Andre Lemburg, <m...@egenix.com> wrote: > Hi Pablo, > > could you or Erlend please explain why types which don't reference > any other objects need to participate in GC for deallocation ? > > Many PRs or checked in patches only do this: > > +static int > +ucd_traverse(PreviousDBVersion *self, visitproc visit, void *arg) > +{ > + Py_VISIT(Py_TYPE(self)); > + return 0; > +} > + > > AFAIK (but could be wrong, of course), the type object itself > does not reference any other objects related to the object > that is being GCed. > > By having (nearly) all stdlib types participate in GC, even ones > which don't reference other objects and cannot be parts of reference > circles, instead of immediately deleting them, we will keep those > objects alive for much longer than necessary, potentially causing a > resource overhead regression. > > -- > Marc-Andre Lemburg > eGenix.com > > Professional Python Services directly from the Experts (#1, May 27 2021) > >>> Python Projects, Coaching and Support ... https://www.egenix.com/ > >>> Python Product Development ... https://consulting.egenix.com/ > ________________________________________________________________________ > > ::: We implement business ideas - efficiently in both time and costs ::: > > eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 > D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg > Registered at Amtsgericht Duesseldorf: HRB 46611 > https://www.egenix.com/company/contact/ > https://www.malemburg.com/ > >
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