Supporting Cyclic Garbage Collection

To create a container type, the tp_flags field of the type object must include the Py_TPFLAGS_HAVE_GC and provide an implementation of the tp_traverse handler. If instances of the type are mutable, a tp_clear implementation must also be provided

Constructors for container types must conform to two rules:

• The memory for the object must be allocated using PyObject_GC_New or PyObject_GC_NewVar.
• Once all the fields which may contain references to other containers are initialized, it must call PyObject_GC_Track().

deallocator for the object must conform to a similar pair of rules

• Before fields which refer to other containers are invalidated, PyObject_GC_UnTrack() must be called.
• The object’s memory must be deallocated using PyObject_GC_Del().

apis

• PyObject_GC_New(TYPE, typeobj)

• PyObject_GC_NewVar(TYPE, typeobj, size)

• TYPE *PyObject_GC_Resize(TYPE, PyVarObject *op, Py_ssize_t newsize)

• void PyObject_GC_Track(PyObject *op)

• int PyObject_IS_GC(PyObject *obj)

• int PyObject_GC_IsTracked(PyObject *op)

• int PyObject_GC_IsFinalized(PyObject *op)

• void PyObject_GC_Del(void *op)

• void PyObject_GC_UnTrack(void *op)

• typedef int (*visitproc)(PyObject *object, void *arg)

• typedef int (*traverseproc)(PyObject *self, visitproc visit, void *arg)

• void Py_VISIT(PyObject *o)

• typedef int (*inquiry)(PyObject *self)

Controlling the Garbage Collector State

• Py_ssize_t PyGC_Collect(void)
• int PyGC_Enable(void)
• int PyGC_Disable(void)
• int PyGC_IsEnabled(void)