LeakSanitizer detects memory leaks in test_import with _testsinglephase module in subinterpreter

[ashm-dev]

Bug report

Bug description:

LeakSanitizer detects memory leaks when running test_import with the _testsinglephase module loaded in a subinterpreter.

How to Reproduce

Build:

CC=clang CXX=clang++ ./configure --disable-optimizations --with-pydebug --with-address-sanitizer && make -j$(nproc)

Run:

./python -X dev -X showrefcount -m test test_import -j0

Leak Summary

==643791==ERROR: LeakSanitizer: detected memory leaks
SUMMARY: AddressSanitizer: 6709 byte(s) leaked in 45 allocation(s).

Code Locations

The leaks originate from:

Subinterpreter execution:

• cpython/Modules/_testcapimodule.c

  Line 1223 in e8e0f41

  r = PyRun_SimpleStringFlags(code, &cflags);

  
  (run_in_subinterp)

Module initialization:

• cpython/Modules/_testsinglephase.c

  Line 516 in e8e0f41

  if (init_state(state) < 0) {

  
  (init__testsinglephase_basic)

• cpython/Modules/_testsinglephase.c

  Line 303 in e8e0f41

  state->error = PyErr_NewException("_testsinglephase.error", NULL, NULL);

  
  (init_state with PyErr_NewException)

Import machinery:

• cpython/Python/importdl.c

  Line 429 in e8e0f41

  PyObject *m = p0();

  
  (_PyImport_RunModInitFunc)

Leaked Objects

• Type objects (1016 bytes × 2): via type_new → PyErr_NewException
• Dictionary keys (424 bytes × 2): via new_keys_object → PyDict_SetItemString
• PyCMethod objects (384 bytes × 2 groups): via PyModule_AddFunctions
• Additional: Unicode strings, tuples, dictionaries

Full Output

See attached .log files for complete LeakSanitizer output for each version.

312.log
313.log
314.log
main.log

CPython versions tested on:

3.12, 3.13, 3.14, 3.15, CPython main branch

Operating systems tested on:

Linux

[ZeroIntensity]

I think this is fundamentally an unsolvable problem with single-phase initialization. Single-phase doesn't provide a way to clean up process-global state, so things leak. We added multi-phase to fix this problem.