Python 3.8 moved PyInterpreterState to the internal C API (commit be3b295838547bba267eb08434b418ef0df87ee0 of bpo-35886)... which caused bpo-38500 issue.

In Python 3.9, I provided Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() as regular functions for the limited API: commit f4b1e3d7c64985f5d5b00f6cc9a1c146bbbfd613 of bpo-38644. Previously, there were defined as macros, but these macros didn’t compile with the limited C API which cannot access PyThreadState.recursion_depth field (the structure is opaque in the limited C API).

That's an enhancement for the limited C API, but PyThreadState is still exposed to the "cpython" C API (Include/cpython/).


We should prepare the C API to make the PyThreadState structure opaque. It cannot be done at once, there are different consumers of the PyThreadState structure. In CPython code base, I found:

* Py_TRASHCAN_BEGIN_CONDITION and Py_TRASHCAN_END macros access tstate->trash_delete_nesting field. Maybe we can hide these implementation details into new private function calls.

* faulthandler.c: faulthandler_py_enable() reads tstate->interp. We should maybe provide a getter function.

* _tracemalloc.c: traceback_get_frames() reads tstate->frame. We should maybe provide a getter function.

* Private _Py_EnterRecursiveCall() and _Py_LeaveRecursiveCall() access tstate->recursion_depth. One solution is to move these functions to the internal C API.


faulthandler and _tracemalloc are low-level debugging C extensions. Maybe it's ok for them to use the internal C API. But they are examples of C extensions accessing directly the PyThreadState structure.


See also bpo-39946 "Is it time to remove _PyThreadState_GetFrame() hook?" about PyThreadState.frame.

New changeset 224481a8c988fca12f488544edd2f01c0af2a91d by Victor Stinner in branch 'master':
bpo-39947: Move Py_EnterRecursiveCall() to internal C API (GH-18972)
https://github.com/python/cpython/commit/224481a8c988fca12f488544edd2f01c0af2a91d

As a note, externally I have to use it in pydevd to set the tracing for different threads -- i.e.: https://bugs.python.org/issue35370

Will that still be possible?

> As a note, externally I have to use it in pydevd to set the tracing for different threads -- i.e.: https://bugs.python.org/issue35370 Will that still be possible?

My intent is not to prevent third-party C extension modules to modify PyThreadState, but to make the structure opaque. I mean that we should add getter and setter function for the most commonly used PyThreadState fields.

New changeset 3f2f4fefca388bc62fc2a7d07cb6ef24197c84bd by Victor Stinner in branch 'master':
bpo-39947: Move get_recursion_depth() to _testinternalcapi (GH-18974)
https://github.com/python/cpython/commit/3f2f4fefca388bc62fc2a7d07cb6ef24197c84bd

New changeset 38965ec5411da60d312b59be281f3510d58e0cf1 by Victor Stinner in branch 'master':
bpo-39947: Hide implementation detail of trashcan macros (GH-18971)
https://github.com/python/cpython/commit/38965ec5411da60d312b59be281f3510d58e0cf1

I tested to build numpy with an opaque PyThreadState. First issue, Plex gets the current interpreter using PyThreadState.interp:

    /tmp/pip-install-aq60p8w2/Cython/Cython/Plex/Scanners.c:7447:73: erreur: déréférencement d'un pointeur du type incomplet « PyThreadState » {alias « struct _ts »}
     7447 |     PY_INT64_T current_id = PyInterpreterState_GetID(PyThreadState_Get()->interp);

We should add a PyThreadState_GetInterpreter(tstate) getter. faulthandler_py_enable() would use it for example.

Maybe _PyInterpreterState_Get() can be used, but it's a private function. There are also _PyThreadState_UncheckedGet() and _PyGILState_GetInterpreterStateUnsafe() which are worse: don't check for NULL pointers.

New changeset ff4584caca04cb3da0dbd5b1e9bf67e40adf5312 by Victor Stinner in branch 'master':
bpo-39947: Use _PyInterpreterState_GET_UNSAFE() (GH-18978)
https://github.com/python/cpython/commit/ff4584caca04cb3da0dbd5b1e9bf67e40adf5312

New changeset be79373a78c0d75fc715ab64253c9b757987a848 by Victor Stinner in branch 'master':
bpo-39947: Add PyInterpreterState_Get() function (GH-18979)
https://github.com/python/cpython/commit/be79373a78c0d75fc715ab64253c9b757987a848

New changeset 8fb02b6e1942811c8d81041e7df3f5f1f4b1d410 by Victor Stinner in branch 'master':
bpo-39947: Add PyThreadState_GetInterpreter() (GH-18981)
https://github.com/python/cpython/commit/8fb02b6e1942811c8d81041e7df3f5f1f4b1d410

I added PyInterpreterState_Get() and PyThreadState_GetInterpreter() functions to get the interpreter.

New changeset fd1e1a18fa3befe5b6eeac32e0561e15c7e5164b by Victor Stinner in branch 'master':
bpo-39947: Add PyThreadState_GetFrame() function (GH-19092)
https://github.com/python/cpython/commit/fd1e1a18fa3befe5b6eeac32e0561e15c7e5164b

New changeset 3072338642156a5edfa2deef2557288fff73c22a by Victor Stinner in branch 'master':
bpo-39947: Use PyThreadState_GetFrame() (GH-19159)
https://github.com/python/cpython/commit/3072338642156a5edfa2deef2557288fff73c22a

New changeset 0e427c6d159e86f17270770cd8dc37372e3c4004 by Victor Stinner in branch 'master':
bpo-39947: Add _PyThreadState_GetDict() function (GH-19160)
https://github.com/python/cpython/commit/0e427c6d159e86f17270770cd8dc37372e3c4004

New changeset 5c3cda0d1a850a1a9b43892f48376b8876bd5863 by Victor Stinner in branch 'master':
bpo-39947: Add PyThreadState_GetID() function (GH-19163)
https://github.com/python/cpython/commit/5c3cda0d1a850a1a9b43892f48376b8876bd5863

Cython still access multiple PyThreadState members which have no getter or setter yet.

__Pyx_PyErr_ExceptionMatchesInState():

    PyObject *exc_type = tstate->curexc_type;
    ...

=> internal _PyErr_Occurred(tstate) could solve this issue: move it the public/private API? Or expose internal _PyErr_ExceptionMatches(tstate, exc)?

__Pyx_ErrRestoreInState() is a reimplementation of internal _PyErr_Restore(): get/set curexc_type, curexc_value and curexc_traceback members.

__Pyx_PyFunction_FastCallNoKw:

static PyObject* __Pyx_PyFunction_FastCallNoKw(...) {
    ...
    ++tstate->recursion_depth;
    Py_DECREF(f);
    --tstate->recursion_depth;
    return result;
}

Why not calling Py_EnterRecursiveCall/Py_LeaveRecursiveCall?

There are likely others.

I marked bpo-35949 "Move PyThreadState into Include/internal/pycore_pystate.h" as a duplicate of this issue.

bpo-35949 lists Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION which access PyThreadState.recursion_critical member directly.

> bpo-35949 lists Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION which access PyThreadState.recursion_critical member directly.

Oh, problem solved by:

commit dcc54215ac1eb4b6fab2a9ffe1abcdf3ac4bb77e
Author: Serhiy Storchaka <storchaka@gmail.com>
Date:   Mon Oct 5 12:32:00 2020 +0300

    bpo-41936. Remove macros Py_ALLOW_RECURSION/Py_END_ALLOW_RECURSION (GH-22552)

New changeset fcc6935384b933fbe1a1ef659ed455a3b74c849a by Victor Stinner in branch 'master':
Add symbols of the stable ABI to python3dll.c (GH-23598)
https://github.com/python/cpython/commit/fcc6935384b933fbe1a1ef659ed455a3b74c849a

New changeset 166286849048eccadecf02b242dbc4042b780944 by Victor Stinner in branch '3.9':
Add symbols of the stable ABI to python3dll.c (GH-23598) (GH-23801)
https://github.com/python/cpython/commit/166286849048eccadecf02b242dbc4042b780944

About setting frame local variables, see:

* bpo-42197: Disable automatic update of frame locals during tracing
* bpo-30744: Local variable assignment is broken when combined with threads + tracing + closures
* PEP 558: Defined semantics for locals()
  https://www.python.org/dev/peps/pep-0558/

New changeset db532a09990c837ec1348e6e6bd2719f5d4a8216 by Victor Stinner in branch 'main':
bpo-39947: Remove old private trashcan C API functions (GH-26869)
https://github.com/python/cpython/commit/db532a09990c837ec1348e6e6bd2719f5d4a8216

See bpo-43760 and PR 28498 for a discussion about the PyThreadState.use_tracing member.

See also bpo-45247: [C API] Add explicit support for Cython to the C API.