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Guido van Rossuma3309961993-07-28 09:05:47 +00001#ifndef Py_OBJECT_H
2#define Py_OBJECT_H
3#ifdef __cplusplus
4extern "C" {
5#endif
6
Guido van Rossumf70e43a1991-02-19 12:39:46 +00007
Guido van Rossum85a5fbb1990-10-14 12:07:46 +00008/* Object and type object interface */
9
10/*
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000011Objects are structures allocated on the heap. Special rules apply to
12the use of objects to ensure they are properly garbage-collected.
13Objects are never allocated statically or on the stack; they must be
14accessed through special macros and functions only. (Type objects are
15exceptions to the first rule; the standard types are represented by
Tim Peters4be93d02002-07-07 19:59:50 +000016statically initialized type objects, although work on type/class unification
17for Python 2.2 made it possible to have heap-allocated type objects too).
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000018
19An object has a 'reference count' that is increased or decreased when a
20pointer to the object is copied or deleted; when the reference count
21reaches zero there are no references to the object left and it can be
22removed from the heap.
23
24An object has a 'type' that determines what it represents and what kind
25of data it contains. An object's type is fixed when it is created.
26Types themselves are represented as objects; an object contains a
27pointer to the corresponding type object. The type itself has a type
28pointer pointing to the object representing the type 'type', which
29contains a pointer to itself!).
30
31Objects do not float around in memory; once allocated an object keeps
32the same size and address. Objects that must hold variable-size data
33can contain pointers to variable-size parts of the object. Not all
34objects of the same type have the same size; but the size cannot change
35after allocation. (These restrictions are made so a reference to an
36object can be simply a pointer -- moving an object would require
37updating all the pointers, and changing an object's size would require
38moving it if there was another object right next to it.)
39
Guido van Rossumcaa63801995-01-12 11:45:45 +000040Objects are always accessed through pointers of the type 'PyObject *'.
41The type 'PyObject' is a structure that only contains the reference count
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000042and the type pointer. The actual memory allocated for an object
43contains other data that can only be accessed after casting the pointer
44to a pointer to a longer structure type. This longer type must start
Guido van Rossumcaa63801995-01-12 11:45:45 +000045with the reference count and type fields; the macro PyObject_HEAD should be
Thomas Wouters7e474022000-07-16 12:04:32 +000046used for this (to accommodate for future changes). The implementation
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000047of a particular object type can cast the object pointer to the proper
48type and back.
49
50A standard interface exists for objects that contain an array of items
51whose size is determined when the object is allocated.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000052*/
53
Tim Peters34592512002-07-11 06:23:50 +000054/* Py_DEBUG implies Py_TRACE_REFS. */
55#if defined(Py_DEBUG) && !defined(Py_TRACE_REFS)
Tim Peters4be93d02002-07-07 19:59:50 +000056#define Py_TRACE_REFS
Tim Peters34592512002-07-11 06:23:50 +000057#endif
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000058
Tim Peters4be93d02002-07-07 19:59:50 +000059/* Py_TRACE_REFS implies Py_REF_DEBUG. */
60#if defined(Py_TRACE_REFS) && !defined(Py_REF_DEBUG)
61#define Py_REF_DEBUG
62#endif
Guido van Rossum85a5fbb1990-10-14 12:07:46 +000063
Tim Peters4be93d02002-07-07 19:59:50 +000064#ifdef Py_TRACE_REFS
65/* Define pointers to support a doubly-linked list of all live heap objects. */
66#define _PyObject_HEAD_EXTRA \
67 struct _object *_ob_next; \
68 struct _object *_ob_prev;
69
70#define _PyObject_EXTRA_INIT 0, 0,
71
72#else
73#define _PyObject_HEAD_EXTRA
74#define _PyObject_EXTRA_INIT
75#endif
76
77/* PyObject_HEAD defines the initial segment of every PyObject. */
78#define PyObject_HEAD \
79 _PyObject_HEAD_EXTRA \
80 int ob_refcnt; \
81 struct _typeobject *ob_type;
82
83#define PyObject_HEAD_INIT(type) \
84 _PyObject_EXTRA_INIT \
85 1, type,
86
87/* PyObject_VAR_HEAD defines the initial segment of all variable-size
88 * container objects. These end with a declaration of an array with 1
89 * element, but enough space is malloc'ed so that the array actually
90 * has room for ob_size elements. Note that ob_size is an element count,
91 * not necessarily a byte count.
92 */
93#define PyObject_VAR_HEAD \
94 PyObject_HEAD \
Guido van Rossum5799b521995-01-04 19:06:22 +000095 int ob_size; /* Number of items in variable part */
Tim Peters803526b2002-07-07 05:13:56 +000096
Tim Peters4be93d02002-07-07 19:59:50 +000097/* Nothing is actually declared to be a PyObject, but every pointer to
98 * a Python object can be cast to a PyObject*. This is inheritance built
99 * by hand. Similarly every pointer to a variable-size Python object can,
100 * in addition, be cast to PyVarObject*.
101 */
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000102typedef struct _object {
Guido van Rossumcaa63801995-01-12 11:45:45 +0000103 PyObject_HEAD
104} PyObject;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000105
106typedef struct {
Guido van Rossumcaa63801995-01-12 11:45:45 +0000107 PyObject_VAR_HEAD
Guido van Rossumd0c87ee1997-05-15 21:31:03 +0000108} PyVarObject;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000109
110
111/*
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000112Type objects contain a string containing the type name (to help somewhat
Tim Peters4be93d02002-07-07 19:59:50 +0000113in debugging), the allocation parameters (see PyObject_New() and
114PyObject_NewVar()),
115and methods for accessing objects of the type. Methods are optional, a
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000116nil pointer meaning that particular kind of access is not available for
Guido van Rossumcaa63801995-01-12 11:45:45 +0000117this type. The Py_DECREF() macro uses the tp_dealloc method without
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000118checking for a nil pointer; it should always be implemented except if
119the implementation can guarantee that the reference count will never
Tim Peters4be93d02002-07-07 19:59:50 +0000120reach zero (e.g., for statically allocated type objects).
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000121
122NB: the methods for certain type groups are now contained in separate
123method blocks.
124*/
125
Tim Peters9ace6bc2000-07-08 00:32:04 +0000126typedef PyObject * (*unaryfunc)(PyObject *);
127typedef PyObject * (*binaryfunc)(PyObject *, PyObject *);
128typedef PyObject * (*ternaryfunc)(PyObject *, PyObject *, PyObject *);
129typedef int (*inquiry)(PyObject *);
130typedef int (*coercion)(PyObject **, PyObject **);
131typedef PyObject *(*intargfunc)(PyObject *, int);
132typedef PyObject *(*intintargfunc)(PyObject *, int, int);
133typedef int(*intobjargproc)(PyObject *, int, PyObject *);
134typedef int(*intintobjargproc)(PyObject *, int, int, PyObject *);
135typedef int(*objobjargproc)(PyObject *, PyObject *, PyObject *);
136typedef int (*getreadbufferproc)(PyObject *, int, void **);
137typedef int (*getwritebufferproc)(PyObject *, int, void **);
138typedef int (*getsegcountproc)(PyObject *, int *);
139typedef int (*getcharbufferproc)(PyObject *, int, const char **);
140typedef int (*objobjproc)(PyObject *, PyObject *);
141typedef int (*visitproc)(PyObject *, void *);
142typedef int (*traverseproc)(PyObject *, visitproc, void *);
Guido van Rossumb6775db1994-08-01 11:34:53 +0000143
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000144typedef struct {
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000145 /* For numbers without flag bit Py_TPFLAGS_CHECKTYPES set, all
146 arguments are guaranteed to be of the object's type (modulo
Tim Peters4be93d02002-07-07 19:59:50 +0000147 coercion hacks -- i.e. if the type's coercion function
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000148 returns other types, then these are allowed as well). Numbers that
149 have the Py_TPFLAGS_CHECKTYPES flag bit set should check *both*
150 arguments for proper type and implement the necessary conversions
151 in the slot functions themselves. */
Neil Schemenauera7ed6942001-01-04 01:31:50 +0000152
Guido van Rossumb6775db1994-08-01 11:34:53 +0000153 binaryfunc nb_add;
154 binaryfunc nb_subtract;
155 binaryfunc nb_multiply;
156 binaryfunc nb_divide;
157 binaryfunc nb_remainder;
158 binaryfunc nb_divmod;
Guido van Rossum75abc631994-08-09 13:21:54 +0000159 ternaryfunc nb_power;
Guido van Rossumb6775db1994-08-01 11:34:53 +0000160 unaryfunc nb_negative;
161 unaryfunc nb_positive;
162 unaryfunc nb_absolute;
163 inquiry nb_nonzero;
164 unaryfunc nb_invert;
165 binaryfunc nb_lshift;
166 binaryfunc nb_rshift;
167 binaryfunc nb_and;
168 binaryfunc nb_xor;
169 binaryfunc nb_or;
170 coercion nb_coerce;
171 unaryfunc nb_int;
172 unaryfunc nb_long;
173 unaryfunc nb_float;
174 unaryfunc nb_oct;
175 unaryfunc nb_hex;
Fred Draked55657b2001-08-15 18:32:33 +0000176 /* Added in release 2.0 */
Thomas Woutersdd8dbdb2000-08-24 20:09:45 +0000177 binaryfunc nb_inplace_add;
178 binaryfunc nb_inplace_subtract;
179 binaryfunc nb_inplace_multiply;
180 binaryfunc nb_inplace_divide;
181 binaryfunc nb_inplace_remainder;
182 ternaryfunc nb_inplace_power;
183 binaryfunc nb_inplace_lshift;
184 binaryfunc nb_inplace_rshift;
185 binaryfunc nb_inplace_and;
186 binaryfunc nb_inplace_xor;
187 binaryfunc nb_inplace_or;
Guido van Rossum4668b002001-08-08 05:00:18 +0000188
Fred Draked55657b2001-08-15 18:32:33 +0000189 /* Added in release 2.2 */
Guido van Rossum4668b002001-08-08 05:00:18 +0000190 /* The following require the Py_TPFLAGS_HAVE_CLASS flag */
191 binaryfunc nb_floor_divide;
192 binaryfunc nb_true_divide;
193 binaryfunc nb_inplace_floor_divide;
194 binaryfunc nb_inplace_true_divide;
Guido van Rossumcaa63801995-01-12 11:45:45 +0000195} PyNumberMethods;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000196
197typedef struct {
Guido van Rossumb6775db1994-08-01 11:34:53 +0000198 inquiry sq_length;
199 binaryfunc sq_concat;
200 intargfunc sq_repeat;
201 intargfunc sq_item;
202 intintargfunc sq_slice;
203 intobjargproc sq_ass_item;
204 intintobjargproc sq_ass_slice;
Guido van Rossumcecb27a2000-02-28 15:00:40 +0000205 objobjproc sq_contains;
Fred Draked55657b2001-08-15 18:32:33 +0000206 /* Added in release 2.0 */
Thomas Woutersdd8dbdb2000-08-24 20:09:45 +0000207 binaryfunc sq_inplace_concat;
208 intargfunc sq_inplace_repeat;
Guido van Rossumcaa63801995-01-12 11:45:45 +0000209} PySequenceMethods;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000210
211typedef struct {
Guido van Rossumb6775db1994-08-01 11:34:53 +0000212 inquiry mp_length;
213 binaryfunc mp_subscript;
214 objobjargproc mp_ass_subscript;
Guido van Rossumcaa63801995-01-12 11:45:45 +0000215} PyMappingMethods;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000216
Guido van Rossumfdf95dd1997-05-05 22:15:02 +0000217typedef struct {
218 getreadbufferproc bf_getreadbuffer;
219 getwritebufferproc bf_getwritebuffer;
220 getsegcountproc bf_getsegcount;
Guido van Rossum36eef3c1998-10-08 02:10:56 +0000221 getcharbufferproc bf_getcharbuffer;
Guido van Rossumfdf95dd1997-05-05 22:15:02 +0000222} PyBufferProcs;
Tim Peters803526b2002-07-07 05:13:56 +0000223
Guido van Rossumfdf95dd1997-05-05 22:15:02 +0000224
Neil Schemenauerf6d1ea12002-04-12 01:57:06 +0000225typedef void (*freefunc)(void *);
Tim Peters9ace6bc2000-07-08 00:32:04 +0000226typedef void (*destructor)(PyObject *);
227typedef int (*printfunc)(PyObject *, FILE *, int);
228typedef PyObject *(*getattrfunc)(PyObject *, char *);
229typedef PyObject *(*getattrofunc)(PyObject *, PyObject *);
230typedef int (*setattrfunc)(PyObject *, char *, PyObject *);
231typedef int (*setattrofunc)(PyObject *, PyObject *, PyObject *);
232typedef int (*cmpfunc)(PyObject *, PyObject *);
233typedef PyObject *(*reprfunc)(PyObject *);
234typedef long (*hashfunc)(PyObject *);
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000235typedef PyObject *(*richcmpfunc) (PyObject *, PyObject *, int);
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000236typedef PyObject *(*getiterfunc) (PyObject *);
Guido van Rossum213c7a62001-04-23 14:08:49 +0000237typedef PyObject *(*iternextfunc) (PyObject *);
Tim Peters6d6c1a32001-08-02 04:15:00 +0000238typedef PyObject *(*descrgetfunc) (PyObject *, PyObject *, PyObject *);
239typedef int (*descrsetfunc) (PyObject *, PyObject *, PyObject *);
240typedef int (*initproc)(PyObject *, PyObject *, PyObject *);
241typedef PyObject *(*newfunc)(struct _typeobject *, PyObject *, PyObject *);
242typedef PyObject *(*allocfunc)(struct _typeobject *, int);
Guido van Rossumb6775db1994-08-01 11:34:53 +0000243
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000244typedef struct _typeobject {
Guido van Rossumcaa63801995-01-12 11:45:45 +0000245 PyObject_VAR_HEAD
Guido van Rossum14648392001-12-08 18:02:58 +0000246 char *tp_name; /* For printing, in format "<module>.<name>" */
Guido van Rossum5799b521995-01-04 19:06:22 +0000247 int tp_basicsize, tp_itemsize; /* For allocation */
Tim Peters803526b2002-07-07 05:13:56 +0000248
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000249 /* Methods to implement standard operations */
Tim Peters803526b2002-07-07 05:13:56 +0000250
Guido van Rossumb6775db1994-08-01 11:34:53 +0000251 destructor tp_dealloc;
252 printfunc tp_print;
253 getattrfunc tp_getattr;
254 setattrfunc tp_setattr;
255 cmpfunc tp_compare;
256 reprfunc tp_repr;
Tim Peters803526b2002-07-07 05:13:56 +0000257
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000258 /* Method suites for standard classes */
Tim Peters803526b2002-07-07 05:13:56 +0000259
Guido van Rossumcaa63801995-01-12 11:45:45 +0000260 PyNumberMethods *tp_as_number;
261 PySequenceMethods *tp_as_sequence;
262 PyMappingMethods *tp_as_mapping;
Guido van Rossum9bfef441993-03-29 10:43:31 +0000263
Fred Drake0e12bcd2000-03-21 16:14:47 +0000264 /* More standard operations (here for binary compatibility) */
Guido van Rossum9bfef441993-03-29 10:43:31 +0000265
Guido van Rossumb6775db1994-08-01 11:34:53 +0000266 hashfunc tp_hash;
Guido van Rossum884afd61995-07-18 14:21:06 +0000267 ternaryfunc tp_call;
Guido van Rossum6fde3901995-01-07 10:32:04 +0000268 reprfunc tp_str;
Guido van Rossum0693dd21996-08-09 20:48:52 +0000269 getattrofunc tp_getattro;
270 setattrofunc tp_setattro;
Guido van Rossum6fde3901995-01-07 10:32:04 +0000271
Guido van Rossumfdf95dd1997-05-05 22:15:02 +0000272 /* Functions to access object as input/output buffer */
273 PyBufferProcs *tp_as_buffer;
Tim Peters803526b2002-07-07 05:13:56 +0000274
Guido van Rossum36eef3c1998-10-08 02:10:56 +0000275 /* Flags to define presence of optional/expanded features */
276 long tp_flags;
Guido van Rossum6fde3901995-01-07 10:32:04 +0000277
278 char *tp_doc; /* Documentation string */
279
Fred Draked55657b2001-08-15 18:32:33 +0000280 /* Assigned meaning in release 2.0 */
Jeremy Hylton8caad492000-06-23 14:18:11 +0000281 /* call function for all accessible objects */
282 traverseproc tp_traverse;
Tim Peters803526b2002-07-07 05:13:56 +0000283
Jeremy Hylton8caad492000-06-23 14:18:11 +0000284 /* delete references to contained objects */
285 inquiry tp_clear;
286
Fred Draked55657b2001-08-15 18:32:33 +0000287 /* Assigned meaning in release 2.1 */
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000288 /* rich comparisons */
289 richcmpfunc tp_richcompare;
290
Fred Drake41deb1e2001-02-01 05:27:45 +0000291 /* weak reference enabler */
292 long tp_weaklistoffset;
Guido van Rossuma9c2d7a1998-04-23 19:16:44 +0000293
Fred Draked55657b2001-08-15 18:32:33 +0000294 /* Added in release 2.2 */
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000295 /* Iterators */
296 getiterfunc tp_iter;
Guido van Rossum213c7a62001-04-23 14:08:49 +0000297 iternextfunc tp_iternext;
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000298
Tim Peters6d6c1a32001-08-02 04:15:00 +0000299 /* Attribute descriptor and subclassing stuff */
300 struct PyMethodDef *tp_methods;
Guido van Rossum6f799372001-09-20 20:46:19 +0000301 struct PyMemberDef *tp_members;
Guido van Rossum32d34c82001-09-20 21:45:26 +0000302 struct PyGetSetDef *tp_getset;
Tim Peters6d6c1a32001-08-02 04:15:00 +0000303 struct _typeobject *tp_base;
304 PyObject *tp_dict;
305 descrgetfunc tp_descr_get;
306 descrsetfunc tp_descr_set;
307 long tp_dictoffset;
308 initproc tp_init;
309 allocfunc tp_alloc;
310 newfunc tp_new;
Neil Schemenauerf6d1ea12002-04-12 01:57:06 +0000311 freefunc tp_free; /* Low-level free-memory routine */
Guido van Rossum048eb752001-10-02 21:24:57 +0000312 inquiry tp_is_gc; /* For PyObject_IS_GC */
Tim Peters6d6c1a32001-08-02 04:15:00 +0000313 PyObject *tp_bases;
314 PyObject *tp_mro; /* method resolution order */
Guido van Rossum687ae002001-10-15 22:03:32 +0000315 PyObject *tp_cache;
Guido van Rossum1c450732001-10-08 15:18:27 +0000316 PyObject *tp_subclasses;
317 PyObject *tp_weaklist;
Guido van Rossumfebd61d2002-08-08 20:55:20 +0000318 destructor tp_del;
Tim Peters6d6c1a32001-08-02 04:15:00 +0000319
Sjoerd Mullendera9c3c221993-10-11 12:54:31 +0000320#ifdef COUNT_ALLOCS
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000321 /* these must be last and never explicitly initialized */
Tim Peters6d6c1a32001-08-02 04:15:00 +0000322 int tp_allocs;
323 int tp_frees;
Sjoerd Mullendera9c3c221993-10-11 12:54:31 +0000324 int tp_maxalloc;
325 struct _typeobject *tp_next;
326#endif
Guido van Rossumcaa63801995-01-12 11:45:45 +0000327} PyTypeObject;
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000328
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000329
Guido van Rossume5c691a2003-03-07 15:13:17 +0000330/* The *real* layout of a type object when allocated on the heap */
331typedef struct _heaptypeobject {
332 /* Note: there's a dependency on the order of these members
333 in slotptr() in typeobject.c . */
334 PyTypeObject type;
335 PyNumberMethods as_number;
336 PyMappingMethods as_mapping;
337 PySequenceMethods as_sequence; /* as_sequence comes after as_mapping,
338 so that the mapping wins when both
339 the mapping and the sequence define
340 a given operator (e.g. __getitem__).
341 see add_operators() in typeobject.c . */
342 PyBufferProcs as_buffer;
343 PyObject *name, *slots;
344 /* here are optional user slots, followed by the members. */
345} PyHeapTypeObject;
346
347/* access macro to the members which are floating "behind" the object */
348#define PyHeapType_GET_MEMBERS(etype) \
349 ((PyMemberDef *)(((char *)etype) + (etype)->type.ob_type->tp_basicsize))
350
351
Tim Peters6d6c1a32001-08-02 04:15:00 +0000352/* Generic type check */
Mark Hammonda2905272002-07-29 13:42:14 +0000353PyAPI_FUNC(int) PyType_IsSubtype(PyTypeObject *, PyTypeObject *);
Tim Peters6d6c1a32001-08-02 04:15:00 +0000354#define PyObject_TypeCheck(ob, tp) \
355 ((ob)->ob_type == (tp) || PyType_IsSubtype((ob)->ob_type, (tp)))
356
Mark Hammonda2905272002-07-29 13:42:14 +0000357PyAPI_DATA(PyTypeObject) PyType_Type; /* built-in 'type' */
358PyAPI_DATA(PyTypeObject) PyBaseObject_Type; /* built-in 'object' */
359PyAPI_DATA(PyTypeObject) PySuper_Type; /* built-in 'super' */
Tim Peters6d6c1a32001-08-02 04:15:00 +0000360
361#define PyType_Check(op) PyObject_TypeCheck(op, &PyType_Type)
Tim Peters3abca122001-10-27 19:37:48 +0000362#define PyType_CheckExact(op) ((op)->ob_type == &PyType_Type)
Tim Peters6d6c1a32001-08-02 04:15:00 +0000363
Mark Hammonda2905272002-07-29 13:42:14 +0000364PyAPI_FUNC(int) PyType_Ready(PyTypeObject *);
365PyAPI_FUNC(PyObject *) PyType_GenericAlloc(PyTypeObject *, int);
366PyAPI_FUNC(PyObject *) PyType_GenericNew(PyTypeObject *,
Tim Peters6d6c1a32001-08-02 04:15:00 +0000367 PyObject *, PyObject *);
Mark Hammonda2905272002-07-29 13:42:14 +0000368PyAPI_FUNC(PyObject *) _PyType_Lookup(PyTypeObject *, PyObject *);
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000369
Guido van Rossum3f5da241990-12-20 15:06:42 +0000370/* Generic operations on objects */
Mark Hammonda2905272002-07-29 13:42:14 +0000371PyAPI_FUNC(int) PyObject_Print(PyObject *, FILE *, int);
372PyAPI_FUNC(void) _PyObject_Dump(PyObject *);
373PyAPI_FUNC(PyObject *) PyObject_Repr(PyObject *);
374PyAPI_FUNC(PyObject *) PyObject_Str(PyObject *);
Martin v. Löwis339d0f72001-08-17 18:39:25 +0000375#ifdef Py_USING_UNICODE
Mark Hammonda2905272002-07-29 13:42:14 +0000376PyAPI_FUNC(PyObject *) PyObject_Unicode(PyObject *);
Martin v. Löwis339d0f72001-08-17 18:39:25 +0000377#endif
Mark Hammonda2905272002-07-29 13:42:14 +0000378PyAPI_FUNC(int) PyObject_Compare(PyObject *, PyObject *);
379PyAPI_FUNC(PyObject *) PyObject_RichCompare(PyObject *, PyObject *, int);
380PyAPI_FUNC(int) PyObject_RichCompareBool(PyObject *, PyObject *, int);
381PyAPI_FUNC(PyObject *) PyObject_GetAttrString(PyObject *, char *);
382PyAPI_FUNC(int) PyObject_SetAttrString(PyObject *, char *, PyObject *);
383PyAPI_FUNC(int) PyObject_HasAttrString(PyObject *, char *);
384PyAPI_FUNC(PyObject *) PyObject_GetAttr(PyObject *, PyObject *);
385PyAPI_FUNC(int) PyObject_SetAttr(PyObject *, PyObject *, PyObject *);
386PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
387PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
Raymond Hettinger1da1dbf2003-03-17 19:46:11 +0000388PyAPI_FUNC(PyObject *) PyObject_SelfIter(PyObject *);
Mark Hammonda2905272002-07-29 13:42:14 +0000389PyAPI_FUNC(PyObject *) PyObject_GenericGetAttr(PyObject *, PyObject *);
390PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject *,
Tim Peters6d6c1a32001-08-02 04:15:00 +0000391 PyObject *, PyObject *);
Mark Hammonda2905272002-07-29 13:42:14 +0000392PyAPI_FUNC(long) PyObject_Hash(PyObject *);
393PyAPI_FUNC(int) PyObject_IsTrue(PyObject *);
394PyAPI_FUNC(int) PyObject_Not(PyObject *);
395PyAPI_FUNC(int) PyCallable_Check(PyObject *);
396PyAPI_FUNC(int) PyNumber_Coerce(PyObject **, PyObject **);
397PyAPI_FUNC(int) PyNumber_CoerceEx(PyObject **, PyObject **);
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000398
Mark Hammonda2905272002-07-29 13:42:14 +0000399PyAPI_FUNC(void) PyObject_ClearWeakRefs(PyObject *);
Fred Drake41deb1e2001-02-01 05:27:45 +0000400
Guido van Rossumab3b0342001-09-18 20:38:53 +0000401/* A slot function whose address we need to compare */
402extern int _PyObject_SlotCompare(PyObject *, PyObject *);
403
404
Tim Peters7eea37e2001-09-04 22:08:56 +0000405/* PyObject_Dir(obj) acts like Python __builtin__.dir(obj), returning a
406 list of strings. PyObject_Dir(NULL) is like __builtin__.dir(),
407 returning the names of the current locals. In this case, if there are
408 no current locals, NULL is returned, and PyErr_Occurred() is false.
409*/
Mark Hammonda2905272002-07-29 13:42:14 +0000410PyAPI_FUNC(PyObject *) PyObject_Dir(PyObject *);
Tim Peters7eea37e2001-09-04 22:08:56 +0000411
412
Guido van Rossum26d4ac31998-04-10 22:32:24 +0000413/* Helpers for printing recursive container types */
Mark Hammonda2905272002-07-29 13:42:14 +0000414PyAPI_FUNC(int) Py_ReprEnter(PyObject *);
415PyAPI_FUNC(void) Py_ReprLeave(PyObject *);
Guido van Rossum26d4ac31998-04-10 22:32:24 +0000416
Fred Drake13634cf2000-06-29 19:17:04 +0000417/* Helpers for hash functions */
Mark Hammonda2905272002-07-29 13:42:14 +0000418PyAPI_FUNC(long) _Py_HashDouble(double);
419PyAPI_FUNC(long) _Py_HashPointer(void*);
Fred Drake13634cf2000-06-29 19:17:04 +0000420
Jeremy Hylton483638c2001-02-01 20:20:45 +0000421/* Helper for passing objects to printf and the like */
422#define PyObject_REPR(obj) PyString_AS_STRING(PyObject_Repr(obj))
423
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000424/* Flag bits for printing: */
Guido van Rossumcaa63801995-01-12 11:45:45 +0000425#define Py_PRINT_RAW 1 /* No string quotes etc. */
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000426
427/*
Tim Peters4be93d02002-07-07 19:59:50 +0000428`Type flags (tp_flags)
Guido van Rossum36eef3c1998-10-08 02:10:56 +0000429
430These flags are used to extend the type structure in a backwards-compatible
431fashion. Extensions can use the flags to indicate (and test) when a given
432type structure contains a new feature. The Python core will use these when
433introducing new functionality between major revisions (to avoid mid-version
434changes in the PYTHON_API_VERSION).
435
436Arbitration of the flag bit positions will need to be coordinated among
437all extension writers who publically release their extensions (this will
438be fewer than you might expect!)..
439
440Python 1.5.2 introduced the bf_getcharbuffer slot into PyBufferProcs.
441
442Type definitions should use Py_TPFLAGS_DEFAULT for their tp_flags value.
443
444Code can use PyType_HasFeature(type_ob, flag_value) to test whether the
445given type object has a specified feature.
Guido van Rossum36eef3c1998-10-08 02:10:56 +0000446*/
447
448/* PyBufferProcs contains bf_getcharbuffer */
449#define Py_TPFLAGS_HAVE_GETCHARBUFFER (1L<<0)
450
Guido van Rossumcecb27a2000-02-28 15:00:40 +0000451/* PySequenceMethods contains sq_contains */
452#define Py_TPFLAGS_HAVE_SEQUENCE_IN (1L<<1)
453
Neil Schemenauer31ec1422001-08-29 23:46:35 +0000454/* This is here for backwards compatibility. Extensions that use the old GC
455 * API will still compile but the objects will not be tracked by the GC. */
456#define Py_TPFLAGS_GC 0 /* used to be (1L<<2) */
Jeremy Hyltond08b4c42000-06-23 19:37:02 +0000457
Thomas Woutersdd8dbdb2000-08-24 20:09:45 +0000458/* PySequenceMethods and PyNumberMethods contain in-place operators */
459#define Py_TPFLAGS_HAVE_INPLACEOPS (1L<<3)
460
Neil Schemenauera7ed6942001-01-04 01:31:50 +0000461/* PyNumberMethods do their own coercion */
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000462#define Py_TPFLAGS_CHECKTYPES (1L<<4)
Neil Schemenauera7ed6942001-01-04 01:31:50 +0000463
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000464/* tp_richcompare is defined */
Guido van Rossumbacca542001-01-24 22:13:48 +0000465#define Py_TPFLAGS_HAVE_RICHCOMPARE (1L<<5)
466
Fred Drake033f3122001-02-02 18:17:30 +0000467/* Objects which are weakly referencable if their tp_weaklistoffset is >0 */
Fred Drake033f3122001-02-02 18:17:30 +0000468#define Py_TPFLAGS_HAVE_WEAKREFS (1L<<6)
469
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000470/* tp_iter is defined */
471#define Py_TPFLAGS_HAVE_ITER (1L<<7)
472
Guido van Rossum4668b002001-08-08 05:00:18 +0000473/* New members introduced by Python 2.2 exist */
Tim Peters6d6c1a32001-08-02 04:15:00 +0000474#define Py_TPFLAGS_HAVE_CLASS (1L<<8)
475
476/* Set if the type object is dynamically allocated */
477#define Py_TPFLAGS_HEAPTYPE (1L<<9)
478
479/* Set if the type allows subclassing */
480#define Py_TPFLAGS_BASETYPE (1L<<10)
481
Guido van Rossum9b9c9722001-08-10 17:37:02 +0000482/* Set if the type is 'ready' -- fully initialized */
483#define Py_TPFLAGS_READY (1L<<12)
484
485/* Set while the type is being 'readied', to prevent recursive ready calls */
486#define Py_TPFLAGS_READYING (1L<<13)
487
Neil Schemenauer31ec1422001-08-29 23:46:35 +0000488/* Objects support garbage collection (see objimp.h) */
Neil Schemenauer31ec1422001-08-29 23:46:35 +0000489#define Py_TPFLAGS_HAVE_GC (1L<<14)
Neil Schemenauer31ec1422001-08-29 23:46:35 +0000490
Guido van Rossumbacca542001-01-24 22:13:48 +0000491#define Py_TPFLAGS_DEFAULT ( \
492 Py_TPFLAGS_HAVE_GETCHARBUFFER | \
Thomas Woutersdd8dbdb2000-08-24 20:09:45 +0000493 Py_TPFLAGS_HAVE_SEQUENCE_IN | \
Guido van Rossumbacca542001-01-24 22:13:48 +0000494 Py_TPFLAGS_HAVE_INPLACEOPS | \
495 Py_TPFLAGS_HAVE_RICHCOMPARE | \
Fred Drake033f3122001-02-02 18:17:30 +0000496 Py_TPFLAGS_HAVE_WEAKREFS | \
Guido van Rossum59d1d2b2001-04-20 19:13:02 +0000497 Py_TPFLAGS_HAVE_ITER | \
Tim Peters6d6c1a32001-08-02 04:15:00 +0000498 Py_TPFLAGS_HAVE_CLASS | \
Guido van Rossumbacca542001-01-24 22:13:48 +0000499 0)
Guido van Rossum36eef3c1998-10-08 02:10:56 +0000500
501#define PyType_HasFeature(t,f) (((t)->tp_flags & (f)) != 0)
502
503
504/*
Guido van Rossumcaa63801995-01-12 11:45:45 +0000505The macros Py_INCREF(op) and Py_DECREF(op) are used to increment or decrement
Tim Peters4be93d02002-07-07 19:59:50 +0000506reference counts. Py_DECREF calls the object's deallocator function when
507the refcount falls to 0; for
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000508objects that don't contain references to other objects or heap memory
509this can be the standard function free(). Both macros can be used
Tim Peters4be93d02002-07-07 19:59:50 +0000510wherever a void expression is allowed. The argument must not be a
511NIL pointer. If it may be NIL, use Py_XINCREF/Py_XDECREF instead.
512The macro _Py_NewReference(op) initialize reference counts to 1, and
513in special builds (Py_REF_DEBUG, Py_TRACE_REFS) performs additional
514bookkeeping appropriate to the special build.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000515
516We assume that the reference count field can never overflow; this can
Tim Peters4be93d02002-07-07 19:59:50 +0000517be proven when the size of the field is the same as the pointer size, so
518we ignore the possibility. Provided a C int is at least 32 bits (which
519is implicitly assumed in many parts of this code), that's enough for
520about 2**31 references to an object.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000521
Tim Peters4be93d02002-07-07 19:59:50 +0000522XXX The following became out of date in Python 2.2, but I'm not sure
523XXX what the full truth is now. Certainly, heap-allocated type objects
524XXX can and should be deallocated.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000525Type objects should never be deallocated; the type pointer in an object
526is not considered to be a reference to the type object, to save
527complications in the deallocation function. (This is actually a
528decision that's up to the implementer of each new type so if you want,
529you can count such references to the type object.)
530
Guido van Rossumcaa63801995-01-12 11:45:45 +0000531*** WARNING*** The Py_DECREF macro must have a side-effect-free argument
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000532since it may evaluate its argument multiple times. (The alternative
533would be to mace it a proper function or assign it to a global temporary
534variable first, both of which are slower; and in a multi-threaded
535environment the global variable trick is not safe.)
536*/
537
Tim Peters34592512002-07-11 06:23:50 +0000538/* First define a pile of simple helper macros, one set per special
539 * build symbol. These either expand to the obvious things, or to
540 * nothing at all when the special mode isn't in effect. The main
541 * macros can later be defined just once then, yet expand to different
542 * things depending on which special build options are and aren't in effect.
543 * Trust me <wink>: while painful, this is 20x easier to understand than,
544 * e.g, defining _Py_NewReference five different times in a maze of nested
545 * #ifdefs (we used to do that -- it was impenetrable).
546 */
Tim Peters4be93d02002-07-07 19:59:50 +0000547#ifdef Py_REF_DEBUG
Mark Hammonda2905272002-07-29 13:42:14 +0000548PyAPI_DATA(long) _Py_RefTotal;
549PyAPI_FUNC(void) _Py_NegativeRefcount(const char *fname,
Tim Peters7c321a82002-07-09 02:57:01 +0000550 int lineno, PyObject *op);
Tim Peters34592512002-07-11 06:23:50 +0000551#define _Py_INC_REFTOTAL _Py_RefTotal++
552#define _Py_DEC_REFTOTAL _Py_RefTotal--
553#define _Py_REF_DEBUG_COMMA ,
554#define _Py_CHECK_REFCNT(OP) \
Tim Peters7c321a82002-07-09 02:57:01 +0000555{ if ((OP)->ob_refcnt < 0) \
556 _Py_NegativeRefcount(__FILE__, __LINE__, \
557 (PyObject *)(OP)); \
558}
Tim Peters4be93d02002-07-07 19:59:50 +0000559#else
Tim Peters34592512002-07-11 06:23:50 +0000560#define _Py_INC_REFTOTAL
561#define _Py_DEC_REFTOTAL
562#define _Py_REF_DEBUG_COMMA
563#define _Py_CHECK_REFCNT(OP) /* a semicolon */;
Tim Peters57f4ddd2002-07-10 06:34:15 +0000564#endif /* Py_REF_DEBUG */
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000565
Sjoerd Mullendera9c3c221993-10-11 12:54:31 +0000566#ifdef COUNT_ALLOCS
Mark Hammonda2905272002-07-29 13:42:14 +0000567PyAPI_FUNC(void) inc_count(PyTypeObject *);
Tim Peters34592512002-07-11 06:23:50 +0000568#define _Py_INC_TPALLOCS(OP) inc_count((OP)->ob_type)
569#define _Py_INC_TPFREES(OP) (OP)->ob_type->tp_frees++
570#define _Py_DEC_TPFREES(OP) (OP)->ob_type->tp_frees--
571#define _Py_COUNT_ALLOCS_COMMA ,
Sjoerd Mullendera9c3c221993-10-11 12:54:31 +0000572#else
Tim Peters34592512002-07-11 06:23:50 +0000573#define _Py_INC_TPALLOCS(OP)
574#define _Py_INC_TPFREES(OP)
575#define _Py_DEC_TPFREES(OP)
576#define _Py_COUNT_ALLOCS_COMMA
Tim Peters57f4ddd2002-07-10 06:34:15 +0000577#endif /* COUNT_ALLOCS */
Tim Peters4be93d02002-07-07 19:59:50 +0000578
579#ifdef Py_TRACE_REFS
580/* Py_TRACE_REFS is such major surgery that we call external routines. */
Mark Hammonda2905272002-07-29 13:42:14 +0000581PyAPI_FUNC(void) _Py_NewReference(PyObject *);
582PyAPI_FUNC(void) _Py_ForgetReference(PyObject *);
583PyAPI_FUNC(void) _Py_Dealloc(PyObject *);
584PyAPI_FUNC(void) _Py_PrintReferences(FILE *);
Tim Peters269b2a62003-04-17 19:52:29 +0000585PyAPI_FUNC(void) _Py_PrintReferenceAddresses(FILE *);
Tim Peters7571a0f2003-03-23 17:52:28 +0000586PyAPI_FUNC(void) _Py_AddToAllObjects(PyObject *, int force);
Tim Peters4be93d02002-07-07 19:59:50 +0000587
588#else
589/* Without Py_TRACE_REFS, there's little enough to do that we expand code
590 * inline.
591 */
Tim Peters34592512002-07-11 06:23:50 +0000592#define _Py_NewReference(op) ( \
593 _Py_INC_TPALLOCS(op) _Py_COUNT_ALLOCS_COMMA \
594 _Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
Tim Peters4be93d02002-07-07 19:59:50 +0000595 (op)->ob_refcnt = 1)
596
Tim Peters34592512002-07-11 06:23:50 +0000597#define _Py_ForgetReference(op) _Py_INC_TPFREES(op)
Tim Peters4be93d02002-07-07 19:59:50 +0000598
Tim Peters57f4ddd2002-07-10 06:34:15 +0000599#define _Py_Dealloc(op) ( \
Tim Peters34592512002-07-11 06:23:50 +0000600 _Py_INC_TPFREES(op) _Py_COUNT_ALLOCS_COMMA \
Tim Peters4be93d02002-07-07 19:59:50 +0000601 (*(op)->ob_type->tp_dealloc)((PyObject *)(op)))
Guido van Rossum60be1db1996-05-22 16:33:22 +0000602#endif /* !Py_TRACE_REFS */
603
Tim Peters34592512002-07-11 06:23:50 +0000604#define Py_INCREF(op) ( \
605 _Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
Tim Peters4be93d02002-07-07 19:59:50 +0000606 (op)->ob_refcnt++)
607
Tim Peters34592512002-07-11 06:23:50 +0000608#define Py_DECREF(op) \
609 if (_Py_DEC_REFTOTAL _Py_REF_DEBUG_COMMA \
610 --(op)->ob_refcnt != 0) \
611 _Py_CHECK_REFCNT(op) \
612 else \
Guido van Rossum1d529d11997-08-05 02:30:44 +0000613 _Py_Dealloc((PyObject *)(op))
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000614
Guido van Rossum3f5da241990-12-20 15:06:42 +0000615/* Macros to use in case the object pointer may be NULL: */
Guido van Rossumcaa63801995-01-12 11:45:45 +0000616#define Py_XINCREF(op) if ((op) == NULL) ; else Py_INCREF(op)
617#define Py_XDECREF(op) if ((op) == NULL) ; else Py_DECREF(op)
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000618
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000619/*
Guido van Rossumcaa63801995-01-12 11:45:45 +0000620_Py_NoneStruct is an object of undefined type which can be used in contexts
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000621where NULL (nil) is not suitable (since NULL often means 'error').
622
Guido van Rossumcaa63801995-01-12 11:45:45 +0000623Don't forget to apply Py_INCREF() when returning this value!!!
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000624*/
Mark Hammonda2905272002-07-29 13:42:14 +0000625PyAPI_DATA(PyObject) _Py_NoneStruct; /* Don't use this directly */
Guido van Rossumcaa63801995-01-12 11:45:45 +0000626#define Py_None (&_Py_NoneStruct)
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000627
Neil Schemenauera7ed6942001-01-04 01:31:50 +0000628/*
629Py_NotImplemented is a singleton used to signal that an operation is
630not implemented for a given type combination.
631*/
Mark Hammonda2905272002-07-29 13:42:14 +0000632PyAPI_DATA(PyObject) _Py_NotImplementedStruct; /* Don't use this directly */
Neil Schemenauera7ed6942001-01-04 01:31:50 +0000633#define Py_NotImplemented (&_Py_NotImplementedStruct)
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000634
Guido van Rossum5f284ce2001-01-17 15:20:39 +0000635/* Rich comparison opcodes */
636#define Py_LT 0
637#define Py_LE 1
638#define Py_EQ 2
639#define Py_NE 3
640#define Py_GT 4
641#define Py_GE 5
642
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000643/*
Jeremy Hylton938ace62002-07-17 16:30:39 +0000644Define staticforward and statichere for source compatibility with old
645C extensions.
646
647The staticforward define was needed to support certain broken C
648compilers (notably SCO ODT 3.0, perhaps early AIX as well) botched the
649static keyword when it was used with a forward declaration of a static
650initialized structure. Standard C allows the forward declaration with
651static, and we've decided to stop catering to broken C compilers.
652(In fact, we expect that the compilers are all fixed eight years later.)
Guido van Rossumb6775db1994-08-01 11:34:53 +0000653*/
654
Guido van Rossumb6775db1994-08-01 11:34:53 +0000655#define staticforward static
Guido van Rossum57836fe1995-02-21 21:06:10 +0000656#define statichere static
Guido van Rossumb6775db1994-08-01 11:34:53 +0000657
658
659/*
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000660More conventions
661================
662
663Argument Checking
664-----------------
665
666Functions that take objects as arguments normally don't check for nil
667arguments, but they do check the type of the argument, and return an
668error if the function doesn't apply to the type.
669
670Failure Modes
671-------------
672
673Functions may fail for a variety of reasons, including running out of
Guido van Rossum3f5da241990-12-20 15:06:42 +0000674memory. This is communicated to the caller in two ways: an error string
675is set (see errors.h), and the function result differs: functions that
676normally return a pointer return NULL for failure, functions returning
677an integer return -1 (which could be a legal return value too!), and
678other functions return 0 for success and -1 for failure.
Tim Peters4be93d02002-07-07 19:59:50 +0000679Callers should always check for errors before using the result. If
680an error was set, the caller must either explicitly clear it, or pass
681the error on to its caller.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000682
683Reference Counts
684----------------
685
686It takes a while to get used to the proper usage of reference counts.
687
688Functions that create an object set the reference count to 1; such new
Guido van Rossumcaa63801995-01-12 11:45:45 +0000689objects must be stored somewhere or destroyed again with Py_DECREF().
690Functions that 'store' objects such as PyTuple_SetItem() and
691PyDict_SetItemString()
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000692don't increment the reference count of the object, since the most
693frequent use is to store a fresh object. Functions that 'retrieve'
Guido van Rossumcaa63801995-01-12 11:45:45 +0000694objects such as PyTuple_GetItem() and PyDict_GetItemString() also
695don't increment
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000696the reference count, since most frequently the object is only looked at
697quickly. Thus, to retrieve an object and store it again, the caller
Guido van Rossumcaa63801995-01-12 11:45:45 +0000698must call Py_INCREF() explicitly.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000699
Guido van Rossumcaa63801995-01-12 11:45:45 +0000700NOTE: functions that 'consume' a reference count like
Fred Drake49bb0e31997-09-05 17:53:53 +0000701PyList_SetItemString() even consume the reference if the object wasn't
702stored, to simplify error handling.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000703
704It seems attractive to make other functions that take an object as
705argument consume a reference count; however this may quickly get
706confusing (even the current practice is already confusing). Consider
Guido van Rossumcaa63801995-01-12 11:45:45 +0000707it carefully, it may save lots of calls to Py_INCREF() and Py_DECREF() at
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000708times.
Guido van Rossum85a5fbb1990-10-14 12:07:46 +0000709*/
Guido van Rossuma3309961993-07-28 09:05:47 +0000710
Guido van Rossumd724b232000-03-13 16:01:29 +0000711
Tim Peters803526b2002-07-07 05:13:56 +0000712/* Trashcan mechanism, thanks to Christian Tismer.
Guido van Rossumd724b232000-03-13 16:01:29 +0000713
Tim Peters803526b2002-07-07 05:13:56 +0000714When deallocating a container object, it's possible to trigger an unbounded
715chain of deallocations, as each Py_DECREF in turn drops the refcount on "the
716next" object in the chain to 0. This can easily lead to stack faults, and
717especially in threads (which typically have less stack space to work with).
Guido van Rossumd724b232000-03-13 16:01:29 +0000718
Tim Peters803526b2002-07-07 05:13:56 +0000719A container object that participates in cyclic gc can avoid this by
720bracketing the body of its tp_dealloc function with a pair of macros:
Guido van Rossume92e6102000-04-24 15:40:53 +0000721
Tim Peters803526b2002-07-07 05:13:56 +0000722static void
723mytype_dealloc(mytype *p)
724{
725 ... declarations go here ...
726
727 PyObject_GC_UnTrack(p); // must untrack first
728 Py_TRASHCAN_SAFE_BEGIN(p)
729 ... The body of the deallocator goes here, including all calls ...
730 ... to Py_DECREF on contained objects. ...
731 Py_TRASHCAN_SAFE_END(p)
732}
733
Tim Peters808eb592002-08-07 20:53:05 +0000734CAUTION: Never return from the middle of the body! If the body needs to
735"get out early", put a label immediately before the Py_TRASHCAN_SAFE_END
736call, and goto it. Else the call-depth counter (see below) will stay
737above 0 forever, and the trashcan will never get emptied.
738
Tim Peters803526b2002-07-07 05:13:56 +0000739How it works: The BEGIN macro increments a call-depth counter. So long
740as this counter is small, the body of the deallocator is run directly without
741further ado. But if the counter gets large, it instead adds p to a list of
742objects to be deallocated later, skips the body of the deallocator, and
743resumes execution after the END macro. The tp_dealloc routine then returns
744without deallocating anything (and so unbounded call-stack depth is avoided).
745
746When the call stack finishes unwinding again, code generated by the END macro
747notices this, and calls another routine to deallocate all the objects that
748may have been added to the list of deferred deallocations. In effect, a
749chain of N deallocations is broken into N / PyTrash_UNWIND_LEVEL pieces,
750with the call stack never exceeding a depth of PyTrash_UNWIND_LEVEL.
Guido van Rossumd724b232000-03-13 16:01:29 +0000751*/
752
Mark Hammonda2905272002-07-29 13:42:14 +0000753PyAPI_FUNC(void) _PyTrash_deposit_object(PyObject*);
754PyAPI_FUNC(void) _PyTrash_destroy_chain(void);
755PyAPI_DATA(int) _PyTrash_delete_nesting;
756PyAPI_DATA(PyObject *) _PyTrash_delete_later;
Tim Peters803526b2002-07-07 05:13:56 +0000757
Guido van Rossumd724b232000-03-13 16:01:29 +0000758#define PyTrash_UNWIND_LEVEL 50
759
760#define Py_TRASHCAN_SAFE_BEGIN(op) \
Tim Peters803526b2002-07-07 05:13:56 +0000761 if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL) { \
762 ++_PyTrash_delete_nesting;
763 /* The body of the deallocator is here. */
Guido van Rossumd724b232000-03-13 16:01:29 +0000764#define Py_TRASHCAN_SAFE_END(op) \
Guido van Rossumd724b232000-03-13 16:01:29 +0000765 --_PyTrash_delete_nesting; \
766 if (_PyTrash_delete_later && _PyTrash_delete_nesting <= 0) \
Guido van Rossume92e6102000-04-24 15:40:53 +0000767 _PyTrash_destroy_chain(); \
Guido van Rossumd724b232000-03-13 16:01:29 +0000768 } \
Tim Peters803526b2002-07-07 05:13:56 +0000769 else \
770 _PyTrash_deposit_object((PyObject*)op);
Guido van Rossume92e6102000-04-24 15:40:53 +0000771
Guido van Rossuma3309961993-07-28 09:05:47 +0000772#ifdef __cplusplus
773}
774#endif
775#endif /* !Py_OBJECT_H */