Objects/weakrefobject.c

   1 #include "Python.h"
   2 #include "structmember.h"
   3
   4
   5 #define GET_WEAKREFS_LISTPTR(o) \
   6         ((PyWeakReference **) PyObject_GET_WEAKREFS_LISTPTR(o))
   7
   8
   9 Py_ssize_t
  10 _PyWeakref_GetWeakrefCount(PyWeakReference *head)
  11 {
  12     Py_ssize_t count = 0;
  13
  14     while (head != NULL) {
  15         ++count;
  16         head = head->wr_next;
  17     }
  18     return count;
  19 }
  20
  21
  22 static void
  23 init_weakref(PyWeakReference *self, PyObject *ob, PyObject *callback)
  24 {
  25     self->hash = -1;
  26     self->wr_object = ob;
  27     Py_XINCREF(callback);
  28     self->wr_callback = callback;
  29 }
  30
  31 static PyWeakReference *
  32 new_weakref(PyObject *ob, PyObject *callback)
  33 {
  34     PyWeakReference *result;
  35
  36     result = PyObject_GC_New(PyWeakReference, &_PyWeakref_RefType);
  37     if (result) {
  38         init_weakref(result, ob, callback);
  39         PyObject_GC_Track(result);
  40     }
  41     return result;
  42 }
  43
  44
  45 /* This function clears the passed-in reference and removes it from the
  46  * list of weak references for the referent.  This is the only code that
  47  * removes an item from the doubly-linked list of weak references for an
  48  * object; it is also responsible for clearing the callback slot.
  49  */
  50 static void
  51 clear_weakref(PyWeakReference *self)
  52 {
  53     PyObject *callback = self->wr_callback;
  54
  55     if (PyWeakref_GET_OBJECT(self) != Py_None) {
  56         PyWeakReference **list = GET_WEAKREFS_LISTPTR(
  57             PyWeakref_GET_OBJECT(self));
  58
  59         if (*list == self)
  60             *list = self->wr_next;
  61         self->wr_object = Py_None;
  62         if (self->wr_prev != NULL)
  63             self->wr_prev->wr_next = self->wr_next;
  64         if (self->wr_next != NULL)
  65             self->wr_next->wr_prev = self->wr_prev;
  66         self->wr_prev = NULL;
  67         self->wr_next = NULL;
  68     }
  69     if (callback != NULL) {
  70         Py_DECREF(callback);
  71         self->wr_callback = NULL;
  72     }
  73 }
  74
  75 /* Cyclic gc uses this to *just* clear the passed-in reference, leaving
  76  * the callback intact and uncalled.  It must be possible to call self's
  77  * tp_dealloc() after calling this, so self has to be left in a sane enough
  78  * state for that to work.  We expect tp_dealloc to decref the callback
  79  * then.  The reason for not letting clear_weakref() decref the callback
  80  * right now is that if the callback goes away, that may in turn trigger
  81  * another callback (if a weak reference to the callback exists) -- running
  82  * arbitrary Python code in the middle of gc is a disaster.  The convolution
  83  * here allows gc to delay triggering such callbacks until the world is in
  84  * a sane state again.
  85  */
  86 void
  87 _PyWeakref_ClearRef(PyWeakReference *self)
  88 {
  89     PyObject *callback;
  90
  91     assert(self != NULL);
  92     assert(PyWeakref_Check(self));
  93     /* Preserve and restore the callback around clear_weakref. */
  94     callback = self->wr_callback;
  95     self->wr_callback = NULL;
  96     clear_weakref(self);
  97     self->wr_callback = callback;
  98 }
  99
 100 static void
 101 weakref_dealloc(PyObject *self)
 102 {
 103     PyObject_GC_UnTrack(self);
 104     clear_weakref((PyWeakReference *) self);
 105     self->ob_type->tp_free(self);
 106 }
 107
 108
 109 static int
 110 gc_traverse(PyWeakReference *self, visitproc visit, void *arg)
 111 {
 112     Py_VISIT(self->wr_callback);
 113     return 0;
 114 }
 115
 116
 117 static int
 118 gc_clear(PyWeakReference *self)
 119 {
 120     clear_weakref(self);
 121     return 0;
 122 }
 123
 124
 125 static PyObject *
 126 weakref_call(PyWeakReference *self, PyObject *args, PyObject *kw)
 127 {
 128     static char *kwlist[] = {NULL};
 129
 130     if (PyArg_ParseTupleAndKeywords(args, kw, ":__call__", kwlist)) {
 131         PyObject *object = PyWeakref_GET_OBJECT(self);
 132         Py_INCREF(object);
 133         return (object);
 134     }
 135     return NULL;
 136 }
 137
 138
 139 static long
 140 weakref_hash(PyWeakReference *self)
 141 {
 142     if (self->hash != -1)
 143         return self->hash;
 144     if (PyWeakref_GET_OBJECT(self) == Py_None) {
 145         PyErr_SetString(PyExc_TypeError, "weak object has gone away");
 146         return -1;
 147     }
 148     self->hash = PyObject_Hash(PyWeakref_GET_OBJECT(self));
 149     return self->hash;
 150 }
 151
 152
 153 static PyObject *
 154 weakref_repr(PyWeakReference *self)
 155 {
 156     char buffer[256];
 157     if (PyWeakref_GET_OBJECT(self) == Py_None) {
 158         PyOS_snprintf(buffer, sizeof(buffer), "<weakref at %p; dead>", self);
 159     }
 160     else {
 161         char *name = NULL;
 162         PyObject *nameobj = PyObject_GetAttrString(PyWeakref_GET_OBJECT(self),
 163                                                    "__name__");
 164         if (nameobj == NULL)
 165                 PyErr_Clear();
 166         else if (PyString_Check(nameobj))
 167                 name = PyString_AS_STRING(nameobj);
 168         PyOS_snprintf(buffer, sizeof(buffer),
 169                       name ? "<weakref at %p; to '%.50s' at %p (%s)>"
 170                            : "<weakref at %p; to '%.50s' at %p>",
 171                       self,
 172                       PyWeakref_GET_OBJECT(self)->ob_type->tp_name,
 173                       PyWeakref_GET_OBJECT(self),
 174                       name);
 175         Py_XDECREF(nameobj);
 176     }
 177     return PyString_FromString(buffer);
 178 }
 179
 180 /* Weak references only support equality, not ordering. Two weak references
 181    are equal if the underlying objects are equal. If the underlying object has
 182    gone away, they are equal if they are identical. */
 183
 184 static PyObject *
 185 weakref_richcompare(PyWeakReference* self, PyWeakReference* other, int op)
 186 {
 187     if (op != Py_EQ || self->ob_type != other->ob_type) {
 188         Py_INCREF(Py_NotImplemented);
 189         return Py_NotImplemented;
 190     }
 191     if (PyWeakref_GET_OBJECT(self) == Py_None
 192         || PyWeakref_GET_OBJECT(other) == Py_None) {
 193         PyObject *res = self==other ? Py_True : Py_False;
 194         Py_INCREF(res);
 195         return res;
 196     }
 197     return PyObject_RichCompare(PyWeakref_GET_OBJECT(self),
 198                                 PyWeakref_GET_OBJECT(other), op);
 199 }
 200
 201 /* Given the head of an object's list of weak references, extract the
 202  * two callback-less refs (ref and proxy).  Used to determine if the
 203  * shared references exist and to determine the back link for newly
 204  * inserted references.
 205  */
 206 static void
 207 get_basic_refs(PyWeakReference *head,
 208                PyWeakReference **refp, PyWeakReference **proxyp)
 209 {
 210     *refp = NULL;
 211     *proxyp = NULL;
 212
 213     if (head != NULL && head->wr_callback == NULL) {
 214         /* We need to be careful that the "basic refs" aren't
 215            subclasses of the main types.  That complicates this a
 216            little. */
 217         if (PyWeakref_CheckRefExact(head)) {
 218             *refp = head;
 219             head = head->wr_next;
 220         }
 221         if (head != NULL
 222             && head->wr_callback == NULL
 223             && PyWeakref_CheckProxy(head)) {
 224             *proxyp = head;
 225             /* head = head->wr_next; */
 226         }
 227     }
 228 }
 229
 230 /* Insert 'newref' in the list after 'prev'.  Both must be non-NULL. */
 231 static void
 232 insert_after(PyWeakReference *newref, PyWeakReference *prev)
 233 {
 234     newref->wr_prev = prev;
 235     newref->wr_next = prev->wr_next;
 236     if (prev->wr_next != NULL)
 237         prev->wr_next->wr_prev = newref;
 238     prev->wr_next = newref;
 239 }
 240
 241 /* Insert 'newref' at the head of the list; 'list' points to the variable
 242  * that stores the head.
 243  */
 244 static void
 245 insert_head(PyWeakReference *newref, PyWeakReference **list)
 246 {
 247     PyWeakReference *next = *list;
 248
 249     newref->wr_prev = NULL;
 250     newref->wr_next = next;
 251     if (next != NULL)
 252         next->wr_prev = newref;
 253     *list = newref;
 254 }
 255
 256 static int
 257 parse_weakref_init_args(char *funcname, PyObject *args, PyObject *kwargs,
 258                         PyObject **obp, PyObject **callbackp)
 259 {
 260     /* XXX Should check that kwargs == NULL or is empty. */
 261     return PyArg_UnpackTuple(args, funcname, 1, 2, obp, callbackp);
 262 }
 263
 264 static PyObject *
 265 weakref___new__(PyTypeObject *type, PyObject *args, PyObject *kwargs)
 266 {
 267     PyWeakReference *self = NULL;
 268     PyObject *ob, *callback = NULL;
 269
 270     if (parse_weakref_init_args("__new__", args, kwargs, &ob, &callback)) {
 271         PyWeakReference *ref, *proxy;
 272         PyWeakReference **list;
 273
 274         if (!PyType_SUPPORTS_WEAKREFS(ob->ob_type)) {
 275             PyErr_Format(PyExc_TypeError,
 276                          "cannot create weak reference to '%s' object",
 277                          ob->ob_type->tp_name);
 278             return NULL;
 279         }
 280         if (callback == Py_None)
 281             callback = NULL;
 282         list = GET_WEAKREFS_LISTPTR(ob);
 283         get_basic_refs(*list, &ref, &proxy);
 284         if (callback == NULL && type == &_PyWeakref_RefType) {
 285             if (ref != NULL) {
 286                 /* We can re-use an existing reference. */
 287                 Py_INCREF(ref);
 288                 return (PyObject *)ref;
 289             }
 290         }
 291         /* We have to create a new reference. */
 292         /* Note: the tp_alloc() can trigger cyclic GC, so the weakref
 293            list on ob can be mutated.  This means that the ref and
 294            proxy pointers we got back earlier may have been collected,
 295            so we need to compute these values again before we use
 296            them. */
 297         self = (PyWeakReference *) (type->tp_alloc(type, 0));
 298         if (self != NULL) {
 299             init_weakref(self, ob, callback);
 300             if (callback == NULL && type == &_PyWeakref_RefType) {
 301                 insert_head(self, list);
 302             }
 303             else {
 304                 PyWeakReference *prev;
 305
 306                 get_basic_refs(*list, &ref, &proxy);
 307                 prev = (proxy == NULL) ? ref : proxy;
 308                 if (prev == NULL)
 309                     insert_head(self, list);
 310                 else
 311                     insert_after(self, prev);
 312             }
 313         }
 314     }
 315     return (PyObject *)self;
 316 }
 317
 318 static int
 319 weakref___init__(PyObject *self, PyObject *args, PyObject *kwargs)
 320 {
 321     PyObject *tmp;
 322
 323     if (parse_weakref_init_args("__init__", args, kwargs, &tmp, &tmp))
 324         return 0;
 325     else
 326         return 1;
 327 }
 328
 329
 330 PyTypeObject
 331 _PyWeakref_RefType = {
 332     PyObject_HEAD_INIT(&PyType_Type)
 333     0,
 334     "weakref",
 335     sizeof(PyWeakReference),
 336     0,
 337     weakref_dealloc,            /*tp_dealloc*/
 338     0,                          /*tp_print*/
 339     0,                          /*tp_getattr*/
 340     0,                          /*tp_setattr*/
 341     0,                          /*tp_compare*/
 342     (reprfunc)weakref_repr,     /*tp_repr*/
 343     0,                          /*tp_as_number*/
 344     0,                          /*tp_as_sequence*/
 345     0,                          /*tp_as_mapping*/
 346     (hashfunc)weakref_hash,     /*tp_hash*/
 347     (ternaryfunc)weakref_call,  /*tp_call*/
 348     0,                          /*tp_str*/
 349     0,                          /*tp_getattro*/
 350     0,                          /*tp_setattro*/
 351     0,                          /*tp_as_buffer*/
 352     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_RICHCOMPARE
 353         | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
 354     0,                          /*tp_doc*/
 355     (traverseproc)gc_traverse,  /*tp_traverse*/
 356     (inquiry)gc_clear,          /*tp_clear*/
 357     (richcmpfunc)weakref_richcompare,   /*tp_richcompare*/
 358     0,                          /*tp_weaklistoffset*/
 359     0,                          /*tp_iter*/
 360     0,                          /*tp_iternext*/
 361     0,                          /*tp_methods*/
 362     0,                          /*tp_members*/
 363     0,                          /*tp_getset*/
 364     0,                          /*tp_base*/
 365     0,                          /*tp_dict*/
 366     0,                          /*tp_descr_get*/
 367     0,                          /*tp_descr_set*/
 368     0,                          /*tp_dictoffset*/
 369     weakref___init__,           /*tp_init*/
 370     PyType_GenericAlloc,        /*tp_alloc*/
 371     weakref___new__,            /*tp_new*/
 372     PyObject_GC_Del,            /*tp_free*/
 373 };
 374
 375
 376 static int
 377 proxy_checkref(PyWeakReference *proxy)
 378 {
 379     if (PyWeakref_GET_OBJECT(proxy) == Py_None) {
 380         PyErr_SetString(PyExc_ReferenceError,
 381                         "weakly-referenced object no longer exists");
 382         return 0;
 383     }
 384     return 1;
 385 }
 386
 387
 388 /* If a parameter is a proxy, check that it is still "live" and wrap it,
 389  * replacing the original value with the raw object.  Raises ReferenceError
 390  * if the param is a dead proxy.
 391  */
 392 #define UNWRAP(o) \
 393         if (PyWeakref_CheckProxy(o)) { \
 394             if (!proxy_checkref((PyWeakReference *)o)) \
 395                 return NULL; \
 396             o = PyWeakref_GET_OBJECT(o); \
 397         }
 398
 399 #define UNWRAP_I(o) \
 400         if (PyWeakref_CheckProxy(o)) { \
 401             if (!proxy_checkref((PyWeakReference *)o)) \
 402                 return -1; \
 403             o = PyWeakref_GET_OBJECT(o); \
 404         }
 405
 406 #define WRAP_UNARY(method, generic) \
 407     static PyObject * \
 408     method(PyObject *proxy) { \
 409         UNWRAP(proxy); \
 410         return generic(proxy); \
 411     }
 412
 413 #define WRAP_BINARY(method, generic) \
 414     static PyObject * \
 415     method(PyObject *x, PyObject *y) { \
 416         UNWRAP(x); \
 417         UNWRAP(y); \
 418         return generic(x, y); \
 419     }
 420
 421 /* Note that the third arg needs to be checked for NULL since the tp_call
 422  * slot can receive NULL for this arg.
 423  */
 424 #define WRAP_TERNARY(method, generic) \
 425     static PyObject * \
 426     method(PyObject *proxy, PyObject *v, PyObject *w) { \
 427         UNWRAP(proxy); \
 428         UNWRAP(v); \
 429         if (w != NULL) \
 430             UNWRAP(w); \
 431         return generic(proxy, v, w); \
 432     }
 433
 434
 435 /* direct slots */
 436
 437 WRAP_BINARY(proxy_getattr, PyObject_GetAttr)
 438 WRAP_UNARY(proxy_str, PyObject_Str)
 439 WRAP_TERNARY(proxy_call, PyEval_CallObjectWithKeywords)
 440
 441 static PyObject *
 442 proxy_repr(PyWeakReference *proxy)
 443 {
 444     char buf[160];
 445     PyOS_snprintf(buf, sizeof(buf),
 446                   "<weakproxy at %p to %.100s at %p>", proxy,
 447                   PyWeakref_GET_OBJECT(proxy)->ob_type->tp_name,
 448                   PyWeakref_GET_OBJECT(proxy));
 449     return PyString_FromString(buf);
 450 }
 451
 452
 453 static int
 454 proxy_setattr(PyWeakReference *proxy, PyObject *name, PyObject *value)
 455 {
 456     if (!proxy_checkref(proxy))
 457         return -1;
 458     return PyObject_SetAttr(PyWeakref_GET_OBJECT(proxy), name, value);
 459 }
 460
 461 static int
 462 proxy_compare(PyObject *proxy, PyObject *v)
 463 {
 464     UNWRAP_I(proxy);
 465     UNWRAP_I(v);
 466     return PyObject_Compare(proxy, v);
 467 }
 468
 469 /* number slots */
 470 WRAP_BINARY(proxy_add, PyNumber_Add)
 471 WRAP_BINARY(proxy_sub, PyNumber_Subtract)
 472 WRAP_BINARY(proxy_mul, PyNumber_Multiply)
 473 WRAP_BINARY(proxy_div, PyNumber_Divide)
 474 WRAP_BINARY(proxy_mod, PyNumber_Remainder)
 475 WRAP_BINARY(proxy_divmod, PyNumber_Divmod)
 476 WRAP_TERNARY(proxy_pow, PyNumber_Power)
 477 WRAP_UNARY(proxy_neg, PyNumber_Negative)
 478 WRAP_UNARY(proxy_pos, PyNumber_Positive)
 479 WRAP_UNARY(proxy_abs, PyNumber_Absolute)
 480 WRAP_UNARY(proxy_invert, PyNumber_Invert)
 481 WRAP_BINARY(proxy_lshift, PyNumber_Lshift)
 482 WRAP_BINARY(proxy_rshift, PyNumber_Rshift)
 483 WRAP_BINARY(proxy_and, PyNumber_And)
 484 WRAP_BINARY(proxy_xor, PyNumber_Xor)
 485 WRAP_BINARY(proxy_or, PyNumber_Or)
 486 WRAP_UNARY(proxy_int, PyNumber_Int)
 487 WRAP_UNARY(proxy_long, PyNumber_Long)
 488 WRAP_UNARY(proxy_float, PyNumber_Float)
 489 WRAP_BINARY(proxy_iadd, PyNumber_InPlaceAdd)
 490 WRAP_BINARY(proxy_isub, PyNumber_InPlaceSubtract)
 491 WRAP_BINARY(proxy_imul, PyNumber_InPlaceMultiply)
 492 WRAP_BINARY(proxy_idiv, PyNumber_InPlaceDivide)
 493 WRAP_BINARY(proxy_imod, PyNumber_InPlaceRemainder)
 494 WRAP_TERNARY(proxy_ipow, PyNumber_InPlacePower)
 495 WRAP_BINARY(proxy_ilshift, PyNumber_InPlaceLshift)
 496 WRAP_BINARY(proxy_irshift, PyNumber_InPlaceRshift)
 497 WRAP_BINARY(proxy_iand, PyNumber_InPlaceAnd)
 498 WRAP_BINARY(proxy_ixor, PyNumber_InPlaceXor)
 499 WRAP_BINARY(proxy_ior, PyNumber_InPlaceOr)
 500
 501 static int
 502 proxy_nonzero(PyWeakReference *proxy)
 503 {
 504     PyObject *o = PyWeakref_GET_OBJECT(proxy);
 505     if (!proxy_checkref(proxy))
 506         return -1;
 507     return PyObject_IsTrue(o);
 508 }
 509
 510 static void
 511 proxy_dealloc(PyWeakReference *self)
 512 {
 513     if (self->wr_callback != NULL)
 514         PyObject_GC_UnTrack((PyObject *)self);
 515     clear_weakref(self);
 516     PyObject_GC_Del(self);
 517 }
 518
 519 /* sequence slots */
 520
 521 static PyObject *
 522 proxy_slice(PyWeakReference *proxy, Py_ssize_t i, Py_ssize_t j)
 523 {
 524     if (!proxy_checkref(proxy))
 525         return NULL;
 526     return PySequence_GetSlice(PyWeakref_GET_OBJECT(proxy), i, j);
 527 }
 528
 529 static int
 530 proxy_ass_slice(PyWeakReference *proxy, Py_ssize_t i, Py_ssize_t j, PyObject *value)
 531 {
 532     if (!proxy_checkref(proxy))
 533         return -1;
 534     return PySequence_SetSlice(PyWeakref_GET_OBJECT(proxy), i, j, value);
 535 }
 536
 537 static int
 538 proxy_contains(PyWeakReference *proxy, PyObject *value)
 539 {
 540     if (!proxy_checkref(proxy))
 541         return -1;
 542     return PySequence_Contains(PyWeakref_GET_OBJECT(proxy), value);
 543 }
 544
 545
 546 /* mapping slots */
 547
 548 static Py_ssize_t
 549 proxy_length(PyWeakReference *proxy)
 550 {
 551     if (!proxy_checkref(proxy))
 552         return -1;
 553     return PyObject_Length(PyWeakref_GET_OBJECT(proxy));
 554 }
 555
 556 WRAP_BINARY(proxy_getitem, PyObject_GetItem)
 557
 558 static int
 559 proxy_setitem(PyWeakReference *proxy, PyObject *key, PyObject *value)
 560 {
 561     if (!proxy_checkref(proxy))
 562         return -1;
 563
 564     if (value == NULL)
 565         return PyObject_DelItem(PyWeakref_GET_OBJECT(proxy), key);
 566     else
 567         return PyObject_SetItem(PyWeakref_GET_OBJECT(proxy), key, value);
 568 }
 569
 570 /* iterator slots */
 571
 572 static PyObject *
 573 proxy_iter(PyWeakReference *proxy)
 574 {
 575     if (!proxy_checkref(proxy))
 576         return NULL;
 577     return PyObject_GetIter(PyWeakref_GET_OBJECT(proxy));
 578 }
 579
 580 static PyObject *
 581 proxy_iternext(PyWeakReference *proxy)
 582 {
 583     if (!proxy_checkref(proxy))
 584         return NULL;
 585     return PyIter_Next(PyWeakref_GET_OBJECT(proxy));
 586 }
 587
 588
 589 static PyNumberMethods proxy_as_number = {
 590     proxy_add,              /*nb_add*/
 591     proxy_sub,              /*nb_subtract*/
 592     proxy_mul,              /*nb_multiply*/
 593     proxy_div,              /*nb_divide*/
 594     proxy_mod,              /*nb_remainder*/
 595     proxy_divmod,           /*nb_divmod*/
 596     proxy_pow,              /*nb_power*/
 597     proxy_neg,              /*nb_negative*/
 598     proxy_pos,              /*nb_positive*/
 599     proxy_abs,              /*nb_absolute*/
 600     (inquiry)proxy_nonzero, /*nb_nonzero*/
 601     proxy_invert,           /*nb_invert*/
 602     proxy_lshift,           /*nb_lshift*/
 603     proxy_rshift,           /*nb_rshift*/
 604     proxy_and,              /*nb_and*/
 605     proxy_xor,              /*nb_xor*/
 606     proxy_or,               /*nb_or*/
 607     0,                      /*nb_coerce*/
 608     proxy_int,              /*nb_int*/
 609     proxy_long,             /*nb_long*/
 610     proxy_float,            /*nb_float*/
 611     0,                      /*nb_oct*/
 612     0,                      /*nb_hex*/
 613     proxy_iadd,             /*nb_inplace_add*/
 614     proxy_isub,             /*nb_inplace_subtract*/
 615     proxy_imul,             /*nb_inplace_multiply*/
 616     proxy_idiv,             /*nb_inplace_divide*/
 617     proxy_imod,             /*nb_inplace_remainder*/
 618     proxy_ipow,             /*nb_inplace_power*/
 619     proxy_ilshift,          /*nb_inplace_lshift*/
 620     proxy_irshift,          /*nb_inplace_rshift*/
 621     proxy_iand,             /*nb_inplace_and*/
 622     proxy_ixor,             /*nb_inplace_xor*/
 623     proxy_ior,              /*nb_inplace_or*/
 624 };
 625
 626 static PySequenceMethods proxy_as_sequence = {
 627     (lenfunc)proxy_length,      /*sq_length*/
 628     0,                          /*sq_concat*/
 629     0,                          /*sq_repeat*/
 630     0,                          /*sq_item*/
 631     (ssizessizeargfunc)proxy_slice, /*sq_slice*/
 632     0,                          /*sq_ass_item*/
 633     (ssizessizeobjargproc)proxy_ass_slice, /*sq_ass_slice*/
 634     (objobjproc)proxy_contains, /* sq_contains */
 635 };
 636
 637 static PyMappingMethods proxy_as_mapping = {
 638     (lenfunc)proxy_length,        /*mp_length*/
 639     proxy_getitem,                /*mp_subscript*/
 640     (objobjargproc)proxy_setitem, /*mp_ass_subscript*/
 641 };
 642
 643
 644 PyTypeObject
 645 _PyWeakref_ProxyType = {
 646     PyObject_HEAD_INIT(&PyType_Type)
 647     0,
 648     "weakproxy",
 649     sizeof(PyWeakReference),
 650     0,
 651     /* methods */
 652     (destructor)proxy_dealloc,          /* tp_dealloc */
 653     0,                                  /* tp_print */
 654     0,                                  /* tp_getattr */
 655     0,                                  /* tp_setattr */
 656     proxy_compare,                      /* tp_compare */
 657     (reprfunc)proxy_repr,               /* tp_repr */
 658     &proxy_as_number,                   /* tp_as_number */
 659     &proxy_as_sequence,                 /* tp_as_sequence */
 660     &proxy_as_mapping,                  /* tp_as_mapping */
 661     0,                                  /* tp_hash */
 662     0,                                  /* tp_call */
 663     proxy_str,                          /* tp_str */
 664     proxy_getattr,                      /* tp_getattro */
 665     (setattrofunc)proxy_setattr,        /* tp_setattro */
 666     0,                                  /* tp_as_buffer */
 667     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC
 668     | Py_TPFLAGS_CHECKTYPES,            /* tp_flags */
 669     0,                                  /* tp_doc */
 670     (traverseproc)gc_traverse,          /* tp_traverse */
 671     (inquiry)gc_clear,                  /* tp_clear */
 672     0,                                  /* tp_richcompare */
 673     0,                                  /* tp_weaklistoffset */
 674     (getiterfunc)proxy_iter,            /* tp_iter */
 675     (iternextfunc)proxy_iternext,       /* tp_iternext */
 676 };
 677
 678
 679 PyTypeObject
 680 _PyWeakref_CallableProxyType = {
 681     PyObject_HEAD_INIT(&PyType_Type)
 682     0,
 683     "weakcallableproxy",
 684     sizeof(PyWeakReference),
 685     0,
 686     /* methods */
 687     (destructor)proxy_dealloc,          /* tp_dealloc */
 688     0,                                  /* tp_print */
 689     0,                                  /* tp_getattr */
 690     0,                                  /* tp_setattr */
 691     proxy_compare,                      /* tp_compare */
 692     (unaryfunc)proxy_repr,              /* tp_repr */
 693     &proxy_as_number,                   /* tp_as_number */
 694     &proxy_as_sequence,                 /* tp_as_sequence */
 695     &proxy_as_mapping,                  /* tp_as_mapping */
 696     0,                                  /* tp_hash */
 697     proxy_call,                         /* tp_call */
 698     proxy_str,                          /* tp_str */
 699     proxy_getattr,                      /* tp_getattro */
 700     (setattrofunc)proxy_setattr,        /* tp_setattro */
 701     0,                                  /* tp_as_buffer */
 702     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC
 703     | Py_TPFLAGS_CHECKTYPES,            /* tp_flags */
 704     0,                                  /* tp_doc */
 705     (traverseproc)gc_traverse,          /* tp_traverse */
 706     (inquiry)gc_clear,                  /* tp_clear */
 707     0,                                  /* tp_richcompare */
 708     0,                                  /* tp_weaklistoffset */
 709     (getiterfunc)proxy_iter,            /* tp_iter */
 710     (iternextfunc)proxy_iternext,       /* tp_iternext */
 711 };
 712
 713
 714
 715 PyObject *
 716 PyWeakref_NewRef(PyObject *ob, PyObject *callback)
 717 {
 718     PyWeakReference *result = NULL;
 719     PyWeakReference **list;
 720     PyWeakReference *ref, *proxy;
 721
 722     if (!PyType_SUPPORTS_WEAKREFS(ob->ob_type)) {
 723         PyErr_Format(PyExc_TypeError,
 724                      "cannot create weak reference to '%s' object",
 725                      ob->ob_type->tp_name);
 726         return NULL;
 727     }
 728     list = GET_WEAKREFS_LISTPTR(ob);
 729     get_basic_refs(*list, &ref, &proxy);
 730     if (callback == Py_None)
 731         callback = NULL;
 732     if (callback == NULL)
 733         /* return existing weak reference if it exists */
 734         result = ref;
 735     if (result != NULL)
 736         Py_INCREF(result);
 737     else {
 738         /* Note: new_weakref() can trigger cyclic GC, so the weakref
 739            list on ob can be mutated.  This means that the ref and
 740            proxy pointers we got back earlier may have been collected,
 741            so we need to compute these values again before we use
 742            them. */
 743         result = new_weakref(ob, callback);
 744         if (result != NULL) {
 745             get_basic_refs(*list, &ref, &proxy);
 746             if (callback == NULL) {
 747                 if (ref == NULL)
 748                     insert_head(result, list);
 749                 else {
 750                     /* Someone else added a ref without a callback
 751                        during GC.  Return that one instead of this one
 752                        to avoid violating the invariants of the list
 753                        of weakrefs for ob. */
 754                     Py_DECREF(result);
 755                     Py_INCREF(ref);
 756                     result = ref;
 757                 }
 758             }
 759             else {
 760                 PyWeakReference *prev;
 761
 762                 prev = (proxy == NULL) ? ref : proxy;
 763                 if (prev == NULL)
 764                     insert_head(result, list);
 765                 else
 766                     insert_after(result, prev);
 767             }
 768         }
 769     }
 770     return (PyObject *) result;
 771 }
 772
 773
 774 PyObject *
 775 PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
 776 {
 777     PyWeakReference *result = NULL;
 778     PyWeakReference **list;
 779     PyWeakReference *ref, *proxy;
 780
 781     if (!PyType_SUPPORTS_WEAKREFS(ob->ob_type)) {
 782         PyErr_Format(PyExc_TypeError,
 783                      "cannot create weak reference to '%s' object",
 784                      ob->ob_type->tp_name);
 785         return NULL;
 786     }
 787     list = GET_WEAKREFS_LISTPTR(ob);
 788     get_basic_refs(*list, &ref, &proxy);
 789     if (callback == Py_None)
 790         callback = NULL;
 791     if (callback == NULL)
 792         /* attempt to return an existing weak reference if it exists */
 793         result = proxy;
 794     if (result != NULL)
 795         Py_INCREF(result);
 796     else {
 797         /* Note: new_weakref() can trigger cyclic GC, so the weakref
 798            list on ob can be mutated.  This means that the ref and
 799            proxy pointers we got back earlier may have been collected,
 800            so we need to compute these values again before we use
 801            them. */
 802         result = new_weakref(ob, callback);
 803         if (result != NULL) {
 804             PyWeakReference *prev;
 805
 806             if (PyCallable_Check(ob))
 807                 result->ob_type = &_PyWeakref_CallableProxyType;
 808             else
 809                 result->ob_type = &_PyWeakref_ProxyType;
 810             get_basic_refs(*list, &ref, &proxy);
 811             if (callback == NULL) {
 812                 if (proxy != NULL) {
 813                     /* Someone else added a proxy without a callback
 814                        during GC.  Return that one instead of this one
 815                        to avoid violating the invariants of the list
 816                        of weakrefs for ob. */
 817                     Py_DECREF(result);
 818                     Py_INCREF(result = proxy);
 819                     goto skip_insert;
 820                 }
 821                 prev = ref;
 822             }
 823             else
 824                 prev = (proxy == NULL) ? ref : proxy;
 825
 826             if (prev == NULL)
 827                 insert_head(result, list);
 828             else
 829                 insert_after(result, prev);
 830         skip_insert:
 831             ;
 832         }
 833     }
 834     return (PyObject *) result;
 835 }
 836
 837
 838 PyObject *
 839 PyWeakref_GetObject(PyObject *ref)
 840 {
 841     if (ref == NULL || !PyWeakref_Check(ref)) {
 842         PyErr_BadInternalCall();
 843         return NULL;
 844     }
 845     return PyWeakref_GET_OBJECT(ref);
 846 }
 847
 848 /* Note that there's an inlined copy-paste of handle_callback() in gcmodule.c's
 849  * handle_weakrefs().
 850  */
 851 static void
 852 handle_callback(PyWeakReference *ref, PyObject *callback)
 853 {
 854     PyObject *cbresult = PyObject_CallFunctionObjArgs(callback, ref, NULL);
 855
 856     if (cbresult == NULL)
 857         PyErr_WriteUnraisable(callback);
 858     else
 859         Py_DECREF(cbresult);
 860 }
 861
 862 /* This function is called by the tp_dealloc handler to clear weak references.
 863  *
 864  * This iterates through the weak references for 'object' and calls callbacks
 865  * for those references which have one.  It returns when all callbacks have
 866  * been attempted.
 867  */
 868 void
 869 PyObject_ClearWeakRefs(PyObject *object)
 870 {
 871     PyWeakReference **list;
 872
 873     if (object == NULL
 874         || !PyType_SUPPORTS_WEAKREFS(object->ob_type)
 875         || object->ob_refcnt != 0) {
 876         PyErr_BadInternalCall();
 877         return;
 878     }
 879     list = GET_WEAKREFS_LISTPTR(object);
 880     /* Remove the callback-less basic and proxy references */
 881     if (*list != NULL && (*list)->wr_callback == NULL) {
 882         clear_weakref(*list);
 883         if (*list != NULL && (*list)->wr_callback == NULL)
 884             clear_weakref(*list);
 885     }
 886     if (*list != NULL) {
 887         PyWeakReference *current = *list;
 888         Py_ssize_t count = _PyWeakref_GetWeakrefCount(current);
 889         int restore_error = PyErr_Occurred() ? 1 : 0;
 890         PyObject *err_type, *err_value, *err_tb;
 891
 892         if (restore_error)
 893             PyErr_Fetch(&err_type, &err_value, &err_tb);
 894         if (count == 1) {
 895             PyObject *callback = current->wr_callback;
 896
 897             current->wr_callback = NULL;
 898             clear_weakref(current);
 899             if (callback != NULL) {
 900                 handle_callback(current, callback);
 901                 Py_DECREF(callback);
 902             }
 903         }
 904         else {
 905             PyObject *tuple;
 906             Py_ssize_t i = 0;
 907
 908             tuple = PyTuple_New(count * 2);
 909             if (tuple == NULL) {
 910                 if (restore_error)
 911                     PyErr_Fetch(&err_type, &err_value, &err_tb);
 912                 return;
 913             }
 914
 915             for (i = 0; i < count; ++i) {
 916                 PyWeakReference *next = current->wr_next;
 917
 918                 Py_INCREF(current);
 919                 PyTuple_SET_ITEM(tuple, i * 2, (PyObject *) current);
 920                 PyTuple_SET_ITEM(tuple, i * 2 + 1, current->wr_callback);
 921                 current->wr_callback = NULL;
 922                 clear_weakref(current);
 923                 current = next;
 924             }
 925             for (i = 0; i < count; ++i) {
 926                 PyObject *callback = PyTuple_GET_ITEM(tuple, i * 2 + 1);
 927
 928                 if (callback != NULL) {
 929                     PyObject *item = PyTuple_GET_ITEM(tuple, i * 2);
 930                     handle_callback((PyWeakReference *)item, callback);
 931                 }
 932             }
 933             Py_DECREF(tuple);
 934         }
 935         if (restore_error)
 936             PyErr_Restore(err_type, err_value, err_tb);
 937     }
 938 }