Include/object.h

   1 #ifndef Py_OBJECT_H
   2 #define Py_OBJECT_H
   3 #ifdef __cplusplus
   4 extern "C" {
   5 #endif
   6
   7 /***********************************************************
   8 Copyright 1991, 1992, 1993, 1994 by Stichting Mathematisch Centrum,
   9 Amsterdam, The Netherlands.
  10
  11                         All Rights Reserved
  12
  13 Permission to use, copy, modify, and distribute this software and its
  14 documentation for any purpose and without fee is hereby granted,
  15 provided that the above copyright notice appear in all copies and that
  16 both that copyright notice and this permission notice appear in
  17 supporting documentation, and that the names of Stichting Mathematisch
  18 Centrum or CWI not be used in advertising or publicity pertaining to
  19 distribution of the software without specific, written prior permission.
  20
  21 STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
  22 THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
  23 FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
  24 FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  25 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  26 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  27 OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  28
  29 ******************************************************************/
  30
  31 #ifndef DEBUG
  32 #define NDEBUG
  33 #endif
  34
  35 /* Object and type object interface */
  36
  37 /*
  38 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
  39
  40 Objects are structures allocated on the heap.  Special rules apply to
  41 the use of objects to ensure they are properly garbage-collected.
  42 Objects are never allocated statically or on the stack; they must be
  43 accessed through special macros and functions only.  (Type objects are
  44 exceptions to the first rule; the standard types are represented by
  45 statically initialized type objects.)
  46
  47 An object has a 'reference count' that is increased or decreased when a
  48 pointer to the object is copied or deleted; when the reference count
  49 reaches zero there are no references to the object left and it can be
  50 removed from the heap.
  51
  52 An object has a 'type' that determines what it represents and what kind
  53 of data it contains.  An object's type is fixed when it is created.
  54 Types themselves are represented as objects; an object contains a
  55 pointer to the corresponding type object.  The type itself has a type
  56 pointer pointing to the object representing the type 'type', which
  57 contains a pointer to itself!).
  58
  59 Objects do not float around in memory; once allocated an object keeps
  60 the same size and address.  Objects that must hold variable-size data
  61 can contain pointers to variable-size parts of the object.  Not all
  62 objects of the same type have the same size; but the size cannot change
  63 after allocation.  (These restrictions are made so a reference to an
  64 object can be simply a pointer -- moving an object would require
  65 updating all the pointers, and changing an object's size would require
  66 moving it if there was another object right next to it.)
  67
  68 Objects are always accessed through pointers of the type 'object *'.
  69 The type 'object' is a structure that only contains the reference count
  70 and the type pointer.  The actual memory allocated for an object
  71 contains other data that can only be accessed after casting the pointer
  72 to a pointer to a longer structure type.  This longer type must start
  73 with the reference count and type fields; the macro OB_HEAD should be
  74 used for this (to accomodate for future changes).  The implementation
  75 of a particular object type can cast the object pointer to the proper
  76 type and back.
  77
  78 A standard interface exists for objects that contain an array of items
  79 whose size is determined when the object is allocated.
  80
  81 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
  82 */
  83
  84 #ifndef NDEBUG
  85
  86 /* Turn on heavy reference debugging */
  87 #define TRACE_REFS
  88
  89 /* Turn on reference counting */
  90 #define REF_DEBUG
  91
  92 #endif /* NDEBUG */
  93
  94 #ifdef TRACE_REFS
  95 #define OB_HEAD \
  96         struct _object *_ob_next, *_ob_prev; \
  97         int ob_refcnt; \
  98         struct _typeobject *ob_type;
  99 #define OB_HEAD_INIT(type) 0, 0, 1, type,
 100 #else
 101 #define OB_HEAD \
 102         unsigned int ob_refcnt; \
 103         struct _typeobject *ob_type;
 104 #define OB_HEAD_INIT(type) 1, type,
 105 #endif
 106
 107 #define OB_VARHEAD \
 108         OB_HEAD \
 109         unsigned int ob_size; /* Number of items in variable part */
 110
 111 typedef struct _object {
 112         OB_HEAD
 113 } object;
 114
 115 typedef struct {
 116         OB_VARHEAD
 117 } varobject;
 118
 119
 120 /*
 121 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
 122
 123 Type objects contain a string containing the type name (to help somewhat
 124 in debugging), the allocation parameters (see newobj() and newvarobj()),
 125 and methods for accessing objects of the type.  Methods are optional,a
 126 nil pointer meaning that particular kind of access is not available for
 127 this type.  The DECREF() macro uses the tp_dealloc method without
 128 checking for a nil pointer; it should always be implemented except if
 129 the implementation can guarantee that the reference count will never
 130 reach zero (e.g., for type objects).
 131
 132 NB: the methods for certain type groups are now contained in separate
 133 method blocks.
 134 */
 135
 136 typedef object * (*unaryfunc) PROTO((object *));
 137 typedef object * (*binaryfunc) PROTO((object *, object *));
 138 typedef int (*inquiry) PROTO((object *));
 139 typedef int (*coercion) PROTO((object **, object **));
 140 typedef object *(*intargfunc) PROTO((object *, int));
 141 typedef object *(*intintargfunc) PROTO((object *, int, int));
 142 typedef int(*intobjargproc) PROTO((object *, int, object *));
 143 typedef int(*intintobjargproc) PROTO((object *, int, int, object *));
 144 typedef int(*objobjargproc) PROTO((object *, object *, object *));
 145
 146 typedef struct {
 147         binaryfunc nb_add;
 148         binaryfunc nb_subtract;
 149         binaryfunc nb_multiply;
 150         binaryfunc nb_divide;
 151         binaryfunc nb_remainder;
 152         binaryfunc nb_divmod;
 153         binaryfunc nb_power;
 154         unaryfunc nb_negative;
 155         unaryfunc nb_positive;
 156         unaryfunc nb_absolute;
 157         inquiry nb_nonzero;
 158         unaryfunc nb_invert;
 159         binaryfunc nb_lshift;
 160         binaryfunc nb_rshift;
 161         binaryfunc nb_and;
 162         binaryfunc nb_xor;
 163         binaryfunc nb_or;
 164         coercion nb_coerce;
 165         unaryfunc nb_int;
 166         unaryfunc nb_long;
 167         unaryfunc nb_float;
 168         unaryfunc nb_oct;
 169         unaryfunc nb_hex;
 170 } number_methods;
 171
 172 typedef struct {
 173         inquiry sq_length;
 174         binaryfunc sq_concat;
 175         intargfunc sq_repeat;
 176         intargfunc sq_item;
 177         intintargfunc sq_slice;
 178         intobjargproc sq_ass_item;
 179         intintobjargproc sq_ass_slice;
 180 } sequence_methods;
 181
 182 typedef struct {
 183         inquiry mp_length;
 184         binaryfunc mp_subscript;
 185         objobjargproc mp_ass_subscript;
 186 } mapping_methods;
 187
 188 typedef void (*destructor) PROTO((object *));
 189 typedef int (*printfunc) PROTO((object *, FILE *, int));
 190 typedef object *(*getattrfunc) PROTO((object *, char *));
 191 typedef int (*setattrfunc) PROTO((object *, char *, object *));
 192 typedef int (*cmpfunc) PROTO((object *, object *));
 193 typedef object *(*reprfunc) PROTO((object *));
 194 typedef long (*hashfunc) PROTO((object *));
 195
 196 typedef struct _typeobject {
 197         OB_VARHEAD
 198         char *tp_name; /* For printing */
 199         unsigned int tp_basicsize, tp_itemsize; /* For allocation */
 200
 201         /* Methods to implement standard operations */
 202
 203         destructor tp_dealloc;
 204         printfunc tp_print;
 205         getattrfunc tp_getattr;
 206         setattrfunc tp_setattr;
 207         cmpfunc tp_compare;
 208         reprfunc tp_repr;
 209
 210         /* Method suites for standard classes */
 211
 212         number_methods *tp_as_number;
 213         sequence_methods *tp_as_sequence;
 214         mapping_methods *tp_as_mapping;
 215
 216         /* More standard operations (at end for binary compatibility) */
 217
 218         hashfunc tp_hash;
 219 #ifdef COUNT_ALLOCS
 220         /* these must be last */
 221         int tp_alloc;
 222         int tp_free;
 223         int tp_maxalloc;
 224         struct _typeobject *tp_next;
 225 #endif
 226 } typeobject;
 227
 228 extern typeobject Typetype; /* The type of type objects */
 229
 230 #define is_typeobject(op) ((op)->ob_type == &Typetype)
 231
 232 /* Generic operations on objects */
 233 extern int printobject PROTO((object *, FILE *, int));
 234 extern object * reprobject PROTO((object *));
 235 extern object * strobject PROTO((object *));
 236 extern int cmpobject PROTO((object *, object *));
 237 extern object *getattr PROTO((object *, char *));
 238 extern int hasattr PROTO((object *, char *));
 239 extern object *getattro PROTO((object *, object *));
 240 extern int setattro PROTO((object *, object *, object *));
 241 extern long hashobject PROTO((object *));
 242
 243 /* Flag bits for printing: */
 244 #define PRINT_RAW       1       /* No string quotes etc. */
 245
 246 /*
 247 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
 248
 249 The macros INCREF(op) and DECREF(op) are used to increment or decrement
 250 reference counts.  DECREF calls the object's deallocator function; for
 251 objects that don't contain references to other objects or heap memory
 252 this can be the standard function free().  Both macros can be used
 253 whereever a void expression is allowed.  The argument shouldn't be a
 254 NIL pointer.  The macro NEWREF(op) is used only to initialize reference
 255 counts to 1; it is defined here for convenience.
 256
 257 We assume that the reference count field can never overflow; this can
 258 be proven when the size of the field is the same as the pointer size
 259 but even with a 16-bit reference count field it is pretty unlikely so
 260 we ignore the possibility.  (If you are paranoid, make it a long.)
 261
 262 Type objects should never be deallocated; the type pointer in an object
 263 is not considered to be a reference to the type object, to save
 264 complications in the deallocation function.  (This is actually a
 265 decision that's up to the implementer of each new type so if you want,
 266 you can count such references to the type object.)
 267
 268 *** WARNING*** The DECREF macro must have a side-effect-free argument
 269 since it may evaluate its argument multiple times.  (The alternative
 270 would be to mace it a proper function or assign it to a global temporary
 271 variable first, both of which are slower; and in a multi-threaded
 272 environment the global variable trick is not safe.)
 273 */
 274
 275 #ifdef TRACE_REFS
 276 #ifndef REF_DEBUG
 277 #define REF_DEBUG
 278 #endif
 279 #endif
 280
 281 #ifndef TRACE_REFS
 282 #ifdef COUNT_ALLOCS
 283 #define DELREF(op) ((op)->ob_type->tp_free++, (*(op)->ob_type->tp_dealloc)((object *)(op)))
 284 #else
 285 #define DELREF(op) (*(op)->ob_type->tp_dealloc)((object *)(op))
 286 #endif
 287 #define UNREF(op) /*empty*/
 288 #endif
 289
 290 #ifdef COUNT_ALLOCS
 291 extern void inc_count PROTO((typeobject *));
 292 #endif
 293
 294 #ifdef REF_DEBUG
 295 extern long ref_total;
 296 #ifndef TRACE_REFS
 297 #ifdef COUNT_ALLOCS
 298 #define NEWREF(op) (inc_count((op)->ob_type), ref_total++, (op)->ob_refcnt = 1)
 299 #else
 300 #define NEWREF(op) (ref_total++, (op)->ob_refcnt = 1)
 301 #endif
 302 #endif
 303 #define INCREF(op) (ref_total++, (op)->ob_refcnt++)
 304 #define DECREF(op) \
 305         if (--ref_total, --(op)->ob_refcnt > 0) \
 306                 ; \
 307         else \
 308                 DELREF(op)
 309 #else
 310 #ifdef COUNT_ALLOCS
 311 #define NEWREF(op) (inc_count((op)->ob_type), (op)->ob_refcnt = 1)
 312 #else
 313 #define NEWREF(op) ((op)->ob_refcnt = 1)
 314 #endif
 315 #define INCREF(op) ((op)->ob_refcnt++)
 316 #define DECREF(op) \
 317         if (--(op)->ob_refcnt > 0) \
 318                 ; \
 319         else \
 320                 DELREF(op)
 321 #endif
 322
 323 /* Macros to use in case the object pointer may be NULL: */
 324
 325 #define XINCREF(op) if ((op) == NULL) ; else INCREF(op)
 326 #define XDECREF(op) if ((op) == NULL) ; else DECREF(op)
 327
 328 /* Definition of NULL, so you don't have to include <stdio.h> */
 329
 330 #ifndef NULL
 331 #define NULL 0
 332 #endif
 333
 334
 335 /*
 336 NoObject is an object of undefined type which can be used in contexts
 337 where NULL (nil) is not suitable (since NULL often means 'error').
 338
 339 Don't forget to apply INCREF() when returning this value!!!
 340 */
 341
 342 extern object NoObject; /* Don't use this directly */
 343
 344 #define None (&NoObject)
 345
 346
 347 /*
 348 A common programming style in Python requires the forward declaration
 349 of static, initialized structures, e.g. for a typeobject that is used
 350 by the functions whose address must be used in the initializer.
 351 Some compilers (notably SCO ODT 3.0, I seem to remember early AIX as
 352 well) botch this if you use the static keyword for both declarations
 353 (they allocate two objects, and use the first, uninitialized one until
 354 the second declaration is encountered).  Therefore, the forward
 355 declaration should use the 'forwardstatic' keyword.  This expands to
 356 static on most systems, but to extern on a few.  The actual storage
 357 and name will still be static because the second declaration is
 358 static, so no linker visible symbols will be generated.  (Standard C
 359 compilers take offense to the extern forward declaration of a static
 360 object, so I can't just put extern in all cases. :-( )
 361 */
 362
 363 #ifdef BAD_STATIC_FORWARD
 364 #define staticforward extern
 365 #else
 366 #define staticforward static
 367 #endif /* BAD_STATIC_FORWARD */
 368
 369
 370 /*
 371 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
 372
 373 More conventions
 374 ================
 375
 376 Argument Checking
 377 -----------------
 378
 379 Functions that take objects as arguments normally don't check for nil
 380 arguments, but they do check the type of the argument, and return an
 381 error if the function doesn't apply to the type.
 382
 383 Failure Modes
 384 -------------
 385
 386 Functions may fail for a variety of reasons, including running out of
 387 memory.  This is communicated to the caller in two ways: an error string
 388 is set (see errors.h), and the function result differs: functions that
 389 normally return a pointer return NULL for failure, functions returning
 390 an integer return -1 (which could be a legal return value too!), and
 391 other functions return 0 for success and -1 for failure.
 392 Callers should always check for errors before using the result.
 393
 394 Reference Counts
 395 ----------------
 396
 397 It takes a while to get used to the proper usage of reference counts.
 398
 399 Functions that create an object set the reference count to 1; such new
 400 objects must be stored somewhere or destroyed again with DECREF().
 401 Functions that 'store' objects such as settupleitem() and dictinsert()
 402 don't increment the reference count of the object, since the most
 403 frequent use is to store a fresh object.  Functions that 'retrieve'
 404 objects such as gettupleitem() and dictlookup() also don't increment
 405 the reference count, since most frequently the object is only looked at
 406 quickly.  Thus, to retrieve an object and store it again, the caller
 407 must call INCREF() explicitly.
 408
 409 NOTE: functions that 'consume' a reference count like dictinsert() even
 410 consume the reference if the object wasn't stored, to simplify error
 411 handling.
 412
 413 It seems attractive to make other functions that take an object as
 414 argument consume a reference count; however this may quickly get
 415 confusing (even the current practice is already confusing).  Consider
 416 it carefully, it may safe lots of calls to INCREF() and DECREF() at
 417 times.
 418
 419 123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
 420 */
 421
 422 #ifdef __cplusplus
 423 }
 424 #endif
 425 #endif /* !Py_OBJECT_H */