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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
11 extern "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 /*
27 Functions 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 
49 Note that objects created with PyObject_{New, NewVar} are allocated using the
50 specialized Python allocator (implemented in obmalloc.c), if WITH_PYMALLOC is
51 enabled.  In addition, a special debugging allocator is used if PYMALLOC_DEBUG
52 is also #defined.
53 
54 In case a specific form of memory management is needed (for example, if you
55 must use the platform malloc heap(s), or shared memory, or C++ local storage or
56 operator new), you must first allocate the object with your custom allocator,
57 then pass its pointer to PyObject_{Init, InitVar} for filling in its Python-
58 specific fields:  reference count, type pointer, possibly others.  You should
59 be aware that Python has no control over these objects because they don't
60 cooperate with the Python memory manager.  Such objects may not be eligible
61 for automatic garbage collection and you have to make sure that they are
62 released accordingly whenever their destructor gets called (cf. the specific
63 form of memory management you're using).
64 
65 Unless you have specific memory management requirements, use
66 PyObject_{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 */
97 PyAPI_FUNC(void *) PyObject_Malloc(size_t size);
98 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03050000
99 PyAPI_FUNC(void *) PyObject_Calloc(size_t nelem, size_t elsize);
100 #endif
101 PyAPI_FUNC(void *) PyObject_Realloc(void *ptr, size_t new_size);
102 PyAPI_FUNC(void) PyObject_Free(void *ptr);
103 
104 #ifndef Py_LIMITED_API
105 /* This function returns the number of allocated memory blocks, regardless of size */
106 PyAPI_FUNC(Py_ssize_t) _Py_GetAllocatedBlocks(void);
107 #endif /* !Py_LIMITED_API */
108 
109 /* Macros */
110 #ifdef WITH_PYMALLOC
111 #ifndef Py_LIMITED_API
112 PyAPI_FUNC(int) _PyObject_DebugMallocStats(FILE *out);
113 #endif /* #ifndef Py_LIMITED_API */
114 #endif
115 
116 /* Macros */
117 #define PyObject_MALLOC         PyObject_Malloc
118 #define PyObject_REALLOC        PyObject_Realloc
119 #define PyObject_FREE           PyObject_Free
120 #define PyObject_Del            PyObject_Free
121 #define PyObject_DEL            PyObject_Free
122 
123 
124 /*
125  * Generic object allocator interface
126  * ==================================
127  */
128 
129 /* Functions */
130 PyAPI_FUNC(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
131 PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *,
132                                                  PyTypeObject *, Py_ssize_t);
133 PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *);
134 PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
135 
136 #define PyObject_New(type, typeobj) \
137                 ( (type *) _PyObject_New(typeobj) )
138 #define PyObject_NewVar(type, typeobj, n) \
139                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
140 
141 /* Macros trading binary compatibility for speed. See also pymem.h.
142    Note that these macros expect non-NULL object pointers.*/
143 #define PyObject_INIT(op, typeobj) \
144     ( Py_TYPE(op) = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
145 #define PyObject_INIT_VAR(op, typeobj, size) \
146     ( Py_SIZE(op) = (size), PyObject_INIT((op), (typeobj)) )
147 
148 #define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
149 
150 /* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
151    vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
152    value is rounded up to the closest multiple of sizeof(void *), in order to
153    ensure that pointer fields at the end of the object are correctly aligned
154    for the platform (this is of special importance for subclasses of, e.g.,
155    str or int, so that pointers can be stored after the embedded data).
156 
157    Note that there's no memory wastage in doing this, as malloc has to
158    return (at worst) pointer-aligned memory anyway.
159 */
160 #if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
161 #   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
162 #endif
163 
164 #define _PyObject_VAR_SIZE(typeobj, nitems)     \
165     _Py_SIZE_ROUND_UP((typeobj)->tp_basicsize + \
166         (nitems)*(typeobj)->tp_itemsize,        \
167         SIZEOF_VOID_P)
168 
169 #define PyObject_NEW(type, typeobj) \
170 ( (type *) PyObject_Init( \
171     (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
172 
173 #define PyObject_NEW_VAR(type, typeobj, n) \
174 ( (type *) PyObject_InitVar( \
175       (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
176       (typeobj), (n)) )
177 
178 /* This example code implements an object constructor with a custom
179    allocator, where PyObject_New is inlined, and shows the important
180    distinction between two steps (at least):
181        1) the actual allocation of the object storage;
182        2) the initialization of the Python specific fields
183       in this storage with PyObject_{Init, InitVar}.
184 
185    PyObject *
186    YourObject_New(...)
187    {
188        PyObject *op;
189 
190        op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
191        if (op == NULL)
192        return PyErr_NoMemory();
193 
194        PyObject_Init(op, &YourTypeStruct);
195 
196        op->ob_field = value;
197        ...
198        return op;
199    }
200 
201    Note that in C++, the use of the new operator usually implies that
202    the 1st step is performed automatically for you, so in a C++ class
203    constructor you would start directly with PyObject_Init/InitVar
204 */
205 
206 #ifndef Py_LIMITED_API
207 typedef struct {
208     /* user context passed as the first argument to the 2 functions */
209     void *ctx;
210 
211     /* allocate an arena of size bytes */
212     void* (*alloc) (void *ctx, size_t size);
213 
214     /* free an arena */
215     void (*free) (void *ctx, void *ptr, size_t size);
216 } PyObjectArenaAllocator;
217 
218 /* Get the arena allocator. */
219 PyAPI_FUNC(void) PyObject_GetArenaAllocator(PyObjectArenaAllocator *allocator);
220 
221 /* Set the arena allocator. */
222 PyAPI_FUNC(void) PyObject_SetArenaAllocator(PyObjectArenaAllocator *allocator);
223 #endif
224 
225 
226 /*
227  * Garbage Collection Support
228  * ==========================
229  */
230 
231 /* C equivalent of gc.collect() which ignores the state of gc.enabled. */
232 PyAPI_FUNC(Py_ssize_t) PyGC_Collect(void);
233 
234 #ifndef Py_LIMITED_API
235 PyAPI_FUNC(Py_ssize_t) _PyGC_CollectNoFail(void);
236 PyAPI_FUNC(Py_ssize_t) _PyGC_CollectIfEnabled(void);
237 #endif
238 
239 /* Test if a type has a GC head */
240 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
241 
242 /* Test if an object has a GC head */
243 #define PyObject_IS_GC(o) (PyType_IS_GC(Py_TYPE(o)) && \
244     (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
245 
246 PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
247 #define PyObject_GC_Resize(type, op, n) \
248                 ( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) )
249 
250 /* GC information is stored BEFORE the object structure. */
251 #ifndef Py_LIMITED_API
252 typedef union _gc_head {
253     struct {
254         union _gc_head *gc_next;
255         union _gc_head *gc_prev;
256         Py_ssize_t gc_refs;
257     } gc;
258     double dummy;  /* force worst-case alignment */
259 } PyGC_Head;
260 
261 extern PyGC_Head *_PyGC_generation0;
262 
263 #define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
264 
265 /* Bit 0 is set when tp_finalize is called */
266 #define _PyGC_REFS_MASK_FINALIZED  (1 << 0)
267 /* The (N-1) most significant bits contain the gc state / refcount */
268 #define _PyGC_REFS_SHIFT           (1)
269 #define _PyGC_REFS_MASK            (((size_t) -1) << _PyGC_REFS_SHIFT)
270 
271 #define _PyGCHead_REFS(g) ((g)->gc.gc_refs >> _PyGC_REFS_SHIFT)
272 #define _PyGCHead_SET_REFS(g, v) do { \
273     (g)->gc.gc_refs = ((g)->gc.gc_refs & ~_PyGC_REFS_MASK) \
274         | (((size_t)(v)) << _PyGC_REFS_SHIFT);             \
275     } while (0)
276 #define _PyGCHead_DECREF(g) ((g)->gc.gc_refs -= 1 << _PyGC_REFS_SHIFT)
277 
278 #define _PyGCHead_FINALIZED(g) (((g)->gc.gc_refs & _PyGC_REFS_MASK_FINALIZED) != 0)
279 #define _PyGCHead_SET_FINALIZED(g, v) do {  \
280     (g)->gc.gc_refs = ((g)->gc.gc_refs & ~_PyGC_REFS_MASK_FINALIZED) \
281         | (v != 0); \
282     } while (0)
283 
284 #define _PyGC_FINALIZED(o) _PyGCHead_FINALIZED(_Py_AS_GC(o))
285 #define _PyGC_SET_FINALIZED(o, v) _PyGCHead_SET_FINALIZED(_Py_AS_GC(o), v)
286 
287 #define _PyGC_REFS(o) _PyGCHead_REFS(_Py_AS_GC(o))
288 
289 #define _PyGC_REFS_UNTRACKED                    (-2)
290 #define _PyGC_REFS_REACHABLE                    (-3)
291 #define _PyGC_REFS_TENTATIVELY_UNREACHABLE      (-4)
292 
293 /* Tell the GC to track this object.  NB: While the object is tracked the
294  * collector it must be safe to call the ob_traverse method. */
295 #define _PyObject_GC_TRACK(o) do { \
296     PyGC_Head *g = _Py_AS_GC(o); \
297     if (_PyGCHead_REFS(g) != _PyGC_REFS_UNTRACKED) \
298         Py_FatalError("GC object already tracked"); \
299     _PyGCHead_SET_REFS(g, _PyGC_REFS_REACHABLE); \
300     g->gc.gc_next = _PyGC_generation0; \
301     g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \
302     g->gc.gc_prev->gc.gc_next = g; \
303     _PyGC_generation0->gc.gc_prev = g; \
304     } while (0);
305 
306 /* Tell the GC to stop tracking this object.
307  * gc_next doesn't need to be set to NULL, but doing so is a good
308  * way to provoke memory errors if calling code is confused.
309  */
310 #define _PyObject_GC_UNTRACK(o) do { \
311     PyGC_Head *g = _Py_AS_GC(o); \
312     assert(_PyGCHead_REFS(g) != _PyGC_REFS_UNTRACKED); \
313     _PyGCHead_SET_REFS(g, _PyGC_REFS_UNTRACKED); \
314     g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
315     g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
316     g->gc.gc_next = NULL; \
317     } while (0);
318 
319 /* True if the object is currently tracked by the GC. */
320 #define _PyObject_GC_IS_TRACKED(o) \
321     (_PyGC_REFS(o) != _PyGC_REFS_UNTRACKED)
322 
323 /* True if the object may be tracked by the GC in the future, or already is.
324    This can be useful to implement some optimizations. */
325 #define _PyObject_GC_MAY_BE_TRACKED(obj) \
326     (PyObject_IS_GC(obj) && \
327         (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
328 #endif /* Py_LIMITED_API */
329 
330 #ifndef Py_LIMITED_API
331 PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t size);
332 PyAPI_FUNC(PyObject *) _PyObject_GC_Calloc(size_t size);
333 #endif /* !Py_LIMITED_API */
334 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
335 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, Py_ssize_t);
336 PyAPI_FUNC(void) PyObject_GC_Track(void *);
337 PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
338 PyAPI_FUNC(void) PyObject_GC_Del(void *);
339 
340 #define PyObject_GC_New(type, typeobj) \
341                 ( (type *) _PyObject_GC_New(typeobj) )
342 #define PyObject_GC_NewVar(type, typeobj, n) \
343                 ( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
344 
345 
346 /* Utility macro to help write tp_traverse functions.
347  * To use this macro, the tp_traverse function must name its arguments
348  * "visit" and "arg".  This is intended to keep tp_traverse functions
349  * looking as much alike as possible.
350  */
351 #define Py_VISIT(op)                                                    \
352     do {                                                                \
353         if (op) {                                                       \
354             int vret = visit((PyObject *)(op), arg);                    \
355             if (vret)                                                   \
356                 return vret;                                            \
357         }                                                               \
358     } while (0)
359 
360 
361 /* Test if a type supports weak references */
362 #define PyType_SUPPORTS_WEAKREFS(t) ((t)->tp_weaklistoffset > 0)
363 
364 #define PyObject_GET_WEAKREFS_LISTPTR(o) \
365     ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
366 
367 #ifdef __cplusplus
368 }
369 #endif
370 #endif /* !Py_OBJIMPL_H */
371