objimpl.h revision b1094f0b1b1dbc3b2d8f779ba53dc4e2093baca6 
1/* The PyObject_ memory family:  high-level object memory interfaces.
2   See pymem.h for the low-level PyMem_ family.
3*/
4
5#ifndef Py_OBJIMPL_H
6#define Py_OBJIMPL_H
7
8#include "pymem.h"
9
10#ifdef __cplusplus
11extern "C" {
12#endif
13
14/* BEWARE:
15
16   Each interface exports both functions and macros.  Extension modules should
17   use the functions, to ensure binary compatibility across Python versions.
18   Because the Python implementation is free to change internal details, and
19   the macros may (or may not) expose details for speed, if you do use the
20   macros you must recompile your extensions with each Python release.
21
22   Never mix calls to PyObject_ memory functions with calls to the platform
23   malloc/realloc/ calloc/free, or with calls to PyMem_.
24*/
25
26/*
27Functions and macros for modules that implement new object types.
28
29 - PyObject_New(type, typeobj) allocates memory for a new object of the given
30   type, and initializes part of it.  'type' must be the C structure type used
31   to represent the object, and 'typeobj' the address of the corresponding
32   type object.  Reference count and type pointer are filled in; the rest of
33   the bytes of the object are *undefined*!  The resulting expression type is
34   'type *'.  The size of the object is determined by the tp_basicsize field
35   of the type object.
36
37 - PyObject_NewVar(type, typeobj, n) is similar but allocates a variable-size
38   object with room for n items.  In addition to the refcount and type pointer
39   fields, this also fills in the ob_size field.
40
41 - PyObject_Del(op) releases the memory allocated for an object.  It does not
42   run a destructor -- it only frees the memory.  PyObject_Free is identical.
43
44 - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) don't
45   allocate memory.  Instead of a 'type' parameter, they take a pointer to a
46   new object (allocated by an arbitrary allocator), and initialize its object
47   header fields.
48
49Note that objects created with PyObject_{New, NewVar} are allocated using the
50specialized Python allocator (implemented in obmalloc.c), if WITH_PYMALLOC is
51enabled.  In addition, a special debugging allocator is used if PYMALLOC_DEBUG
52is also #defined.
53
54In case a specific form of memory management is needed (for example, if you
55must use the platform malloc heap(s), or shared memory, or C++ local storage or
56operator new), you must first allocate the object with your custom allocator,
57then pass its pointer to PyObject_{Init, InitVar} for filling in its Python-
58specific fields:  reference count, type pointer, possibly others.  You should
59be aware that Python no control over these objects because they don't
60cooperate with the Python memory manager.  Such objects may not be eligible
61for automatic garbage collection and you have to make sure that they are
62released accordingly whenever their destructor gets called (cf. the specific
63form of memory management you're using).
64
65Unless you have specific memory management requirements, use
66PyObject_{New, NewVar, Del}.
67*/
68
69/*
70 * Raw object memory interface
71 * ===========================
72 */
73
74/* Functions to call the same malloc/realloc/free as used by Python's
75   object allocator.  If WITH_PYMALLOC is enabled, these may differ from
76   the platform malloc/realloc/free.  The Python object allocator is
77   designed for fast, cache-conscious allocation of many "small" objects,
78   and with low hidden memory overhead.
79
80   PyObject_Malloc(0) returns a unique non-NULL pointer if possible.
81
82   PyObject_Realloc(NULL, n) acts like PyObject_Malloc(n).
83   PyObject_Realloc(p != NULL, 0) does not return  NULL, or free the memory
84   at p.
85
86   Returned pointers must be checked for NULL explicitly; no action is
87   performed on failure other than to return NULL (no warning it printed, no
88   exception is set, etc).
89
90   For allocating objects, use PyObject_{New, NewVar} instead whenever
91   possible.  The PyObject_{Malloc, Realloc, Free} family is exposed
92   so that you can exploit Python's small-block allocator for non-object
93   uses.  If you must use these routines to allocate object memory, make sure
94   the object gets initialized via PyObject_{Init, InitVar} after obtaining
95   the raw memory.
96*/
97extern DL_IMPORT(void *) PyObject_Malloc(size_t);
98extern DL_IMPORT(void *) PyObject_Realloc(void *, size_t);
99extern DL_IMPORT(void) PyObject_Free(void *);
100
101
102/* Macros */
103#ifdef WITH_PYMALLOC
104#ifdef PYMALLOC_DEBUG
105DL_IMPORT(void *) _PyObject_DebugMalloc(size_t nbytes);
106DL_IMPORT(void *) _PyObject_DebugRealloc(void *p, size_t nbytes);
107DL_IMPORT(void) _PyObject_DebugFree(void *p);
108DL_IMPORT(void) _PyObject_DebugDumpAddress(const void *p);
109DL_IMPORT(void) _PyObject_DebugCheckAddress(const void *p);
110DL_IMPORT(void) _PyObject_DebugMallocStats(void);
111#define PyObject_MALLOC		_PyObject_DebugMalloc
112#define PyObject_Malloc		_PyObject_DebugMalloc
113#define PyObject_REALLOC	_PyObject_DebugRealloc
114#define PyObject_Realloc	_PyObject_DebugRealloc
115#define PyObject_FREE		_PyObject_DebugFree
116#define PyObject_Free		_PyObject_DebugFree
117
118#else	/* WITH_PYMALLOC && ! PYMALLOC_DEBUG */
119#define PyObject_MALLOC		PyObject_Malloc
120#define PyObject_REALLOC	PyObject_Realloc
121#define PyObject_FREE		PyObject_Free
122#endif
123
124#else	/* ! WITH_PYMALLOC */
125#define PyObject_MALLOC		PyMem_MALLOC
126#define PyObject_REALLOC	PyMem_REALLOC
127/* This is an odd one!  For backward compatability with old extensions, the
128   PyMem "release memory" functions have to invoke the object allocator's
129   free() function.  When pymalloc isn't enabled, that leaves us using
130   the platform free(). */
131#define PyObject_FREE		free
132
133#endif	/* WITH_PYMALLOC */
134
135#define PyObject_Del		PyObject_Free
136#define PyObject_DEL		PyObject_FREE
137
138/* for source compatibility with 2.2 */
139#define _PyObject_Del		PyObject_Free
140
141/*
142 * Generic object allocator interface
143 * ==================================
144 */
145
146/* Functions */
147extern DL_IMPORT(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
148extern DL_IMPORT(PyVarObject *) PyObject_InitVar(PyVarObject *,
149                                                 PyTypeObject *, int);
150extern DL_IMPORT(PyObject *) _PyObject_New(PyTypeObject *);
151extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
152
153#define PyObject_New(type, typeobj) \
154		( (type *) _PyObject_New(typeobj) )
155#define PyObject_NewVar(type, typeobj, n) \
156		( (type *) _PyObject_NewVar((typeobj), (n)) )
157
158/* Macros trading binary compatibility for speed. See also pymem.h.
159   Note that these macros expect non-NULL object pointers.*/
160#define PyObject_INIT(op, typeobj) \
161	( (op)->ob_type = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
162#define PyObject_INIT_VAR(op, typeobj, size) \
163	( (op)->ob_size = (size), PyObject_INIT((op), (typeobj)) )
164
165#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
166
167/* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
168   vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
169   value is rounded up to the closest multiple of sizeof(void *), in order to
170   ensure that pointer fields at the end of the object are correctly aligned
171   for the platform (this is of special importance for subclasses of, e.g.,
172   str or long, so that pointers can be stored after the embedded data).
173
174   Note that there's no memory wastage in doing this, as malloc has to
175   return (at worst) pointer-aligned memory anyway.
176*/
177#if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
178#   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
179#endif
180
181#define _PyObject_VAR_SIZE(typeobj, nitems)	\
182	(size_t)				\
183	( ( (typeobj)->tp_basicsize +		\
184	    (nitems)*(typeobj)->tp_itemsize +	\
185	    (SIZEOF_VOID_P - 1)			\
186	  ) & ~(SIZEOF_VOID_P - 1)		\
187	)
188
189#define PyObject_NEW(type, typeobj) \
190( (type *) PyObject_Init( \
191	(PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
192
193#define PyObject_NEW_VAR(type, typeobj, n) \
194( (type *) PyObject_InitVar( \
195      (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
196      (typeobj), (n)) )
197
198/* This example code implements an object constructor with a custom
199   allocator, where PyObject_New is inlined, and shows the important
200   distinction between two steps (at least):
201       1) the actual allocation of the object storage;
202       2) the initialization of the Python specific fields
203          in this storage with PyObject_{Init, InitVar}.
204
205   PyObject *
206   YourObject_New(...)
207   {
208       PyObject *op;
209
210       op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
211       if (op == NULL)
212           return PyErr_NoMemory();
213
214       PyObject_Init(op, &YourTypeStruct);
215
216       op->ob_field = value;
217       ...
218       return op;
219   }
220
221   Note that in C++, the use of the new operator usually implies that
222   the 1st step is performed automatically for you, so in a C++ class
223   constructor you would start directly with PyObject_Init/InitVar
224*/
225
226/*
227 * Garbage Collection Support
228 * ==========================
229 *
230 * Some of the functions and macros below are always defined; when
231 * WITH_CYCLE_GC is undefined, they simply don't do anything different
232 * than their non-GC counterparts.
233 */
234
235/* Test if a type has a GC head */
236#define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
237
238/* Test if an object has a GC head */
239#define PyObject_IS_GC(o) (PyType_IS_GC((o)->ob_type) && \
240	((o)->ob_type->tp_is_gc == NULL || (o)->ob_type->tp_is_gc(o)))
241
242extern DL_IMPORT(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, int);
243#define PyObject_GC_Resize(type, op, n) \
244		( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) )
245
246/* for source compatibility with 2.2 */
247#define _PyObject_GC_Del PyObject_GC_Del
248
249#ifdef WITH_CYCLE_GC
250
251/* GC information is stored BEFORE the object structure. */
252typedef union _gc_head {
253	struct {
254		union _gc_head *gc_next; /* not NULL if object is tracked */
255		union _gc_head *gc_prev;
256		int gc_refs;
257	} gc;
258	long double dummy;  /* force worst-case alignment */
259} PyGC_Head;
260
261extern PyGC_Head *_PyGC_generation0;
262
263#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
264
265/* Tell the GC to track this object.  NB: While the object is tracked the
266 * collector it must be safe to call the ob_traverse method. */
267#define _PyObject_GC_TRACK(o) do { \
268	PyGC_Head *g = _Py_AS_GC(o); \
269	if (g->gc.gc_next != NULL) \
270		Py_FatalError("GC object already in linked list"); \
271	g->gc.gc_next = _PyGC_generation0; \
272	g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \
273	g->gc.gc_prev->gc.gc_next = g; \
274	_PyGC_generation0->gc.gc_prev = g; \
275    } while (0);
276
277/* Tell the GC to stop tracking this object. */
278#define _PyObject_GC_UNTRACK(o) do { \
279	PyGC_Head *g = _Py_AS_GC(o); \
280	g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
281	g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
282	g->gc.gc_next = NULL; \
283    } while (0);
284
285extern DL_IMPORT(PyObject *) _PyObject_GC_Malloc(size_t);
286extern DL_IMPORT(PyObject *) _PyObject_GC_New(PyTypeObject *);
287extern DL_IMPORT(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, int);
288extern DL_IMPORT(void) PyObject_GC_Track(void *);
289extern DL_IMPORT(void) PyObject_GC_UnTrack(void *);
290extern DL_IMPORT(void) PyObject_GC_Del(void *);
291
292#define PyObject_GC_New(type, typeobj) \
293		( (type *) _PyObject_GC_New(typeobj) )
294#define PyObject_GC_NewVar(type, typeobj, n) \
295		( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
296
297
298#else /* !WITH_CYCLE_GC */
299
300#define _PyObject_GC_Malloc	PyObject_Malloc
301#define PyObject_GC_New		PyObject_New
302#define PyObject_GC_NewVar	PyObject_NewVar
303#define PyObject_GC_Del		PyObject_Del
304#define _PyObject_GC_TRACK(op)
305#define _PyObject_GC_UNTRACK(op)
306#define PyObject_GC_Track(op)
307#define PyObject_GC_UnTrack(op)
308
309#endif
310
311/* This is here for the sake of backwards compatibility.  Extensions that
312 * use the old GC API will still compile but the objects will not be
313 * tracked by the GC. */
314#define PyGC_HEAD_SIZE 0
315#define PyObject_GC_Init(op)
316#define PyObject_GC_Fini(op)
317#define PyObject_AS_GC(op) (op)
318#define PyObject_FROM_GC(op) (op)
319
320
321/* Test if a type supports weak references */
322#define PyType_SUPPORTS_WEAKREFS(t) \
323        (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \
324         && ((t)->tp_weaklistoffset > 0))
325
326#define PyObject_GET_WEAKREFS_LISTPTR(o) \
327	((PyObject **) (((char *) (o)) + (o)->ob_type->tp_weaklistoffset))
328
329#ifdef __cplusplus
330}
331#endif
332#endif /* !Py_OBJIMPL_H */
333