cpython/Include/internal/pycore_object.h

#ifndef Py_INTERNAL_OBJECT_H
#define Py_INTERNAL_OBJECT_H
#ifdef __cplusplus
extern "C" {
#endif

#ifndef Py_BUILD_CORE
#  error "this header requires Py_BUILD_CORE define"
#endif

#include "pycore_pystate.h"   /* _PyRuntime */

PyAPI_FUNC(int) _PyType_CheckConsistency(PyTypeObject *type);
PyAPI_FUNC(int) _PyUnicode_CheckConsistency(PyObject *op, int check_content);
PyAPI_FUNC(int) _PyDict_CheckConsistency(PyObject *mp, int check_content);

/* Tell the GC to track this object.
 *
 * NB: While the object is tracked by the collector, it must be safe to call the
 * ob_traverse method.
 *
 * Internal note: _PyRuntime.gc.generation0->_gc_prev doesn't have any bit flags
 * because it's not object header.  So we don't use _PyGCHead_PREV() and
 * _PyGCHead_SET_PREV() for it to avoid unnecessary bitwise operations.
 *
 * The PyObject_GC_Track() function is the public version of this macro.
 */
static inline void _PyObject_GC_TRACK_impl(const char *filename, int lineno,
                                           PyObject *op)
{
    _PyObject_ASSERT_FROM(op, !_PyObject_GC_IS_TRACKED(op),
                          "object already tracked by the garbage collector",
                          filename, lineno, "_PyObject_GC_TRACK");

    PyGC_Head *gc = _Py_AS_GC(op);
    _PyObject_ASSERT_FROM(op,
                          (gc->_gc_prev & _PyGC_PREV_MASK_COLLECTING) == 0,
                          "object is in generation which is garbage collected",
                          filename, lineno, "_PyObject_GC_TRACK");

    PyGC_Head *last = (PyGC_Head*)(_PyRuntime.gc.generation0->_gc_prev);
    _PyGCHead_SET_NEXT(last, gc);
    _PyGCHead_SET_PREV(gc, last);
    _PyGCHead_SET_NEXT(gc, _PyRuntime.gc.generation0);
    _PyRuntime.gc.generation0->_gc_prev = (uintptr_t)gc;
}

#define _PyObject_GC_TRACK(op) \
    _PyObject_GC_TRACK_impl(__FILE__, __LINE__, _PyObject_CAST(op))

/* Tell the GC to stop tracking this object.
 *
 * Internal note: This may be called while GC. So _PyGC_PREV_MASK_COLLECTING
 * must be cleared. But _PyGC_PREV_MASK_FINALIZED bit is kept.
 *
 * The object must be tracked by the GC.
 *
 * The PyObject_GC_UnTrack() function is the public version of this macro.
 */
static inline void _PyObject_GC_UNTRACK_impl(const char *filename, int lineno,
                                             PyObject *op)
{
    _PyObject_ASSERT_FROM(op, _PyObject_GC_IS_TRACKED(op),
                          "object not tracked by the garbage collector",
                          filename, lineno, "_PyObject_GC_UNTRACK");

    PyGC_Head *gc = _Py_AS_GC(op);
    PyGC_Head *prev = _PyGCHead_PREV(gc);
    PyGC_Head *next = _PyGCHead_NEXT(gc);
    _PyGCHead_SET_NEXT(prev, next);
    _PyGCHead_SET_PREV(next, prev);
    gc->_gc_next = 0;
    gc->_gc_prev &= _PyGC_PREV_MASK_FINALIZED;
}

#define _PyObject_GC_UNTRACK(op) \
    _PyObject_GC_UNTRACK_impl(__FILE__, __LINE__, _PyObject_CAST(op))

#ifdef __cplusplus
}
#endif
#endif /* !Py_INTERNAL_OBJECT_H */