> Which API should be used in C extensions to be "subinterpreter-safe"? ?> Currently, Py_None is a singleton shared by multiple interpreters. > > > Should suddenly all C extensions use a new Py_GetNone() function which > returns the per-interpreter singleton? If yes, that's basically what my > PR 18301 does:

>   #define Py_None Py_GetNone()

after read you [WIP] bpo-39511: Add Py_GetNone() and Py_GetNoneRef() functions #18301.

Actually, interp->none shared _Py_NoneStruct variable.

when two interperter modify interp->none refcount,will modify _Py_NoneStruct variable.

> the CPU cacheline of common singletons like None, True and False can quickly become a performance bottleneck.

even if add Py_INCREF(none);. 
In the scenario of parallel interpreter, will also have thread safety issues.
> PyStatus
> _Py_InitSingletons(PyThreadState *tstate)
> {
>     PyObject *none = &_Py_NoneStruct;
>     Py_INCREF(none);
>     tstate->interp->none = none;
>     return _PyStatus_OK();
> }