cpython/Include/objimpl.h

#ifndef Py_OBJIMPL_H
#define Py_OBJIMPL_H

#include "pymem.h"

#ifdef __cplusplus
extern "C" {
#endif

/*
Functions and macros for modules that implement new object types.
You must first include "object.h".

 - PyObject_New(type, typeobj) allocates memory for a new object of
   the given type; here 'type' must be the C structure type used to
   represent the object and 'typeobj' the address of the corresponding
   type object.  Reference count and type pointer are filled in; the
   rest of the bytes of the object are *undefined*!  The resulting
   expression type is 'type *'.  The size of the object is actually
   determined by the tp_basicsize field of the type object.

 - PyObject_NewVar(type, typeobj, n) is similar but allocates a
   variable-size object with n extra items.  The size is computed as
   tp_basicsize plus n * tp_itemsize.  This fills in the ob_size field
   as well.

 - PyObject_Del(op) releases the memory allocated for an object.

 - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) are
   similar to PyObject_{New, NewVar} except that they don't allocate
   the memory needed for an object. Instead of the 'type' parameter,
   they accept the pointer of a new object (allocated by an arbitrary
   allocator) and initialize its object header fields.

Note that objects created with PyObject_{New, NewVar} are allocated
within the Python heap by the raw memory allocator (usually the system
malloc).  If you want to use the specialized Python allocator use
PyMalloc_New and PyMalloc_NewVar to allocate the objects and
PyMalloc_Del to free them.

In case a specific form of memory management is needed, implying that
the objects would not reside in the Python heap (for example standard
malloc heap(s) are mandatory, use of shared memory, C++ local storage
or operator new), you must first allocate the object with your custom
allocator, then pass its pointer to PyObject_{Init, InitVar} for
filling in its Python-specific fields: reference count, type pointer,
possibly others. You should be aware that Python has very limited
control over these objects because they don't cooperate with the
Python memory manager. Such objects may not be eligible for automatic
garbage collection and you have to make sure that they are released
accordingly whenever their destructor gets called (cf. the specific
form of memory management you're using).

Unless you have specific memory management requirements, it is
recommended to use PyObject_{New, NewVar, Del}. */

/*
 * Raw object memory interface
 * ===========================
 */

/* The use of this API should be avoided, unless a builtin object
   constructor inlines PyObject_{New, NewVar}, either because the
   latter functions cannot allocate the exact amount of needed memory,
   either for speed. This situation is exceptional, but occurs for
   some object constructors (PyBuffer_New, PyList_New...).  Inlining
   PyObject_{New, NewVar} for objects that are supposed to belong to
   the Python heap is discouraged. If you really have to, make sure
   the object is initialized with PyObject_{Init, InitVar}. Do *not*
   inline PyObject_{Init, InitVar} for user-extension types or you
   might seriously interfere with Python's memory management. */

/* Functions */

/* Wrappers that useful if you need to be sure that you are using the
   same object memory allocator as Python. These wrappers *do not* make
   sure that allocating 0 bytes returns a non-NULL pointer. Returned
   pointers must be checked for NULL explicitly; no action is performed
   on failure. */
extern DL_IMPORT(void *) PyObject_Malloc(size_t);
extern DL_IMPORT(void *) PyObject_Realloc(void *, size_t);
extern DL_IMPORT(void) PyObject_Free(void *);

/* Macros */
#define PyObject_MALLOC(n)           PyMem_MALLOC(n)
#define PyObject_REALLOC(op, n)      PyMem_REALLOC((void *)(op), (n))
#define PyObject_FREE(op)            PyMem_FREE((void *)(op))

/*
 * Generic object allocator interface
 * ==================================
 */

/* Functions */
extern DL_IMPORT(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
extern DL_IMPORT(PyVarObject *) PyObject_InitVar(PyVarObject *,
                                                 PyTypeObject *, int);
extern DL_IMPORT(PyObject *) _PyObject_New(PyTypeObject *);
extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
extern DL_IMPORT(void) _PyObject_Del(PyObject *);

#define PyObject_New(type, typeobj) \
		( (type *) _PyObject_New(typeobj) )
#define PyObject_NewVar(type, typeobj, n) \
		( (type *) _PyObject_NewVar((typeobj), (n)) )
#define PyObject_Del(op) _PyObject_Del((PyObject *)(op))

/* Macros trading binary compatibility for speed. See also pymem.h.
   Note that these macros expect non-NULL object pointers.*/
#define PyObject_INIT(op, typeobj) \
	( (op)->ob_type = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
#define PyObject_INIT_VAR(op, typeobj, size) \
	( (op)->ob_size = (size), PyObject_INIT((op), (typeobj)) )

#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )

/* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
   vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
   value is rounded up to the closest multiple of sizeof(void *), in order to
   ensure that pointer fields at the end of the object are correctly aligned
   for the platform (this is of special importance for subclasses of, e.g.,
   str or long, so that pointers can be stored after the embedded data).

   Note that there's no memory wastage in doing this, as malloc has to
   return (at worst) pointer-aligned memory anyway.
*/
#if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
#   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
#endif

#define _PyObject_VAR_SIZE(typeobj, nitems)	\
	(size_t)				\
	( ( (typeobj)->tp_basicsize +		\
	    (nitems)*(typeobj)->tp_itemsize +	\
	    (SIZEOF_VOID_P - 1)			\
	  ) & ~(SIZEOF_VOID_P - 1)		\
	)

#define PyObject_NEW(type, typeobj) \
( (type *) PyObject_Init( \
	(PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )

#define PyObject_NEW_VAR(type, typeobj, n) \
( (type *) PyObject_InitVar( \
      (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
      (typeobj), (n)) )

#define PyObject_DEL(op) PyObject_FREE(op)

/* This example code implements an object constructor with a custom
   allocator, where PyObject_New is inlined, and shows the important
   distinction between two steps (at least):
       1) the actual allocation of the object storage;
       2) the initialization of the Python specific fields
          in this storage with PyObject_{Init, InitVar}.

   PyObject *
   YourObject_New(...)
   {
       PyObject *op;

       op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
       if (op == NULL)
           return PyErr_NoMemory();

       op = PyObject_Init(op, &YourTypeStruct);
       if (op == NULL)
           return NULL;

       op->ob_field = value;
       ...
       return op;
   }

   Note that in C++, the use of the new operator usually implies that
   the 1st step is performed automatically for you, so in a C++ class
   constructor you would start directly with PyObject_Init/InitVar. */

/*
 * The PyMalloc Object Allocator
 * =============================
 */

extern DL_IMPORT(PyObject *) _PyMalloc_New(PyTypeObject *);
extern DL_IMPORT(PyVarObject *) _PyMalloc_NewVar(PyTypeObject *, int);
extern DL_IMPORT(void) _PyMalloc_Del(PyObject *);

#define PyMalloc_New(type, typeobj) \
		( (type *) _PyMalloc_New(typeobj) )
#define PyMalloc_NewVar(type, typeobj, n) \
		( (type *) _PyMalloc_NewVar((typeobj), (n)) )
#define PyMalloc_Del(op) _PyMalloc_Del((PyObject *)(op))


/*
 * Garbage Collection Support
 * ==========================
 *
 * Some of the functions and macros below are always defined; when
 * WITH_CYCLE_GC is undefined, they simply don't do anything different
 * than their non-GC counterparts.
 */

/* Test if a type has a GC head */
#define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)

/* Test if an object has a GC head */
#define PyObject_IS_GC(o) (PyType_IS_GC((o)->ob_type) && \
	((o)->ob_type->tp_is_gc == NULL || (o)->ob_type->tp_is_gc(o)))

extern DL_IMPORT(PyObject *) _PyObject_GC_Malloc(PyTypeObject *, int);
extern DL_IMPORT(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, int);

#define PyObject_GC_Resize(type, op, n) \
		( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) )

extern DL_IMPORT(PyObject *) _PyObject_GC_New(PyTypeObject *);
extern DL_IMPORT(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, int);
extern DL_IMPORT(void) _PyObject_GC_Del(PyObject *);
extern DL_IMPORT(void) _PyObject_GC_Track(PyObject *);
extern DL_IMPORT(void) _PyObject_GC_UnTrack(PyObject *);

#ifdef WITH_CYCLE_GC

/* GC information is stored BEFORE the object structure */
typedef union _gc_head {
	struct {
		union _gc_head *gc_next; /* not NULL if object is tracked */
		union _gc_head *gc_prev;
		int gc_refs;
	} gc;
	long double dummy;  /* force worst-case alignment */
} PyGC_Head;

extern PyGC_Head _PyGC_generation0;

#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)

/* Tell the GC to track this object.  NB: While the object is tracked the
 * collector it must be safe to call the ob_traverse method. */
#define _PyObject_GC_TRACK(o) do { \
	PyGC_Head *g = _Py_AS_GC(o); \
	if (g->gc.gc_next != NULL) \
		Py_FatalError("GC object already in linked list"); \
	g->gc.gc_next = &_PyGC_generation0; \
	g->gc.gc_prev = _PyGC_generation0.gc.gc_prev; \
	g->gc.gc_prev->gc.gc_next = g; \
	_PyGC_generation0.gc.gc_prev = g; \
    } while (0);

/* Tell the GC to stop tracking this object. */
#define _PyObject_GC_UNTRACK(o) do { \
	PyGC_Head *g = _Py_AS_GC(o); \
	g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
	g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
	g->gc.gc_next = NULL; \
    } while (0);

#define PyObject_GC_Track(op) _PyObject_GC_Track((PyObject *)op)
#define PyObject_GC_UnTrack(op) _PyObject_GC_UnTrack((PyObject *)op)


#define PyObject_GC_New(type, typeobj) \
		( (type *) _PyObject_GC_New(typeobj) )
#define PyObject_GC_NewVar(type, typeobj, n) \
		( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
#define PyObject_GC_Del(op) _PyObject_GC_Del((PyObject *)(op))

#else /* !WITH_CYCLE_GC */

#define PyObject_GC_New PyObject_New
#define PyObject_GC_NewVar PyObject_NewVar
#define PyObject_GC_Del	 PyObject_Del
#define _PyObject_GC_TRACK(op)
#define _PyObject_GC_UNTRACK(op)
#define PyObject_GC_Track(op)
#define PyObject_GC_UnTrack(op)

#endif

/* This is here for the sake of backwards compatibility.  Extensions that
 * use the old GC API will still compile but the objects will not be
 * tracked by the GC. */
#define PyGC_HEAD_SIZE 0
#define PyObject_GC_Init(op)
#define PyObject_GC_Fini(op)
#define PyObject_AS_GC(op) (op)
#define PyObject_FROM_GC(op) (op)


/* Test if a type supports weak references */
#define PyType_SUPPORTS_WEAKREFS(t) \
        (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \
         && ((t)->tp_weaklistoffset > 0))

#define PyObject_GET_WEAKREFS_LISTPTR(o) \
	((PyObject **) (((char *) (o)) + (o)->ob_type->tp_weaklistoffset))

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