Source

cpython-withatomic / Modules / gcmodule.c

The branch '2.4' does not exist.
   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
/*

  Reference Cycle Garbage Collection
  ==================================

  Neil Schemenauer <nas@arctrix.com>

  Based on a post on the python-dev list.  Ideas from Guido van Rossum,
  Eric Tiedemann, and various others.

  http://www.arctrix.com/nas/python/gc/
  http://www.python.org/pipermail/python-dev/2000-March/003869.html
  http://www.python.org/pipermail/python-dev/2000-March/004010.html
  http://www.python.org/pipermail/python-dev/2000-March/004022.html

  For a highlevel view of the collection process, read the collect
  function.

*/

#include "Python.h"

/* Get an object's GC head */
#define AS_GC(o) ((PyGC_Head *)(o)-1)

/* Get the object given the GC head */
#define FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1))

/*** Global GC state ***/

struct gc_generation {
	PyGC_Head head;
	int threshold; /* collection threshold */
	int count; /* count of allocations or collections of younger
		      generations */
};

#define NUM_GENERATIONS 3
#define GEN_HEAD(n) (&generations[n].head)

/* linked lists of container objects */
static struct gc_generation generations[NUM_GENERATIONS] = {
	/* PyGC_Head,				threshold,	count */
	{{{GEN_HEAD(0), GEN_HEAD(0), 0}},	700,		0},
	{{{GEN_HEAD(1), GEN_HEAD(1), 0}},	10,		0},
	{{{GEN_HEAD(2), GEN_HEAD(2), 0}},	10,		0},
};

PyGC_Head *_PyGC_generation0 = GEN_HEAD(0);

static int enabled = 1; /* automatic collection enabled? */

/* true if we are currently running the collector */
static int collecting = 0;

/* list of uncollectable objects */
static PyObject *garbage = NULL;

/* Python string to use if unhandled exception occurs */
static PyObject *gc_str = NULL;

/* Python string used to look for __del__ attribute. */
static PyObject *delstr = NULL;

/* set for debugging information */
#define DEBUG_STATS		(1<<0) /* print collection statistics */
#define DEBUG_COLLECTABLE	(1<<1) /* print collectable objects */
#define DEBUG_UNCOLLECTABLE	(1<<2) /* print uncollectable objects */
#define DEBUG_INSTANCES		(1<<3) /* print instances */
#define DEBUG_OBJECTS		(1<<4) /* print other objects */
#define DEBUG_SAVEALL		(1<<5) /* save all garbage in gc.garbage */
#define DEBUG_LEAK		DEBUG_COLLECTABLE | \
				DEBUG_UNCOLLECTABLE | \
				DEBUG_INSTANCES | \
				DEBUG_OBJECTS | \
				DEBUG_SAVEALL
static int debug;

/*--------------------------------------------------------------------------
gc_refs values.

Between collections, every gc'ed object has one of two gc_refs values:

GC_UNTRACKED
    The initial state; objects returned by PyObject_GC_Malloc are in this
    state.  The object doesn't live in any generation list, and its
    tp_traverse slot must not be called.

GC_REACHABLE
    The object lives in some generation list, and its tp_traverse is safe to
    call.  An object transitions to GC_REACHABLE when PyObject_GC_Track
    is called.

During a collection, gc_refs can temporarily take on other states:

>= 0
    At the start of a collection, update_refs() copies the true refcount
    to gc_refs, for each object in the generation being collected.
    subtract_refs() then adjusts gc_refs so that it equals the number of
    times an object is referenced directly from outside the generation
    being collected.
    gc_refs remains >= 0 throughout these steps.

GC_TENTATIVELY_UNREACHABLE
    move_unreachable() then moves objects not reachable (whether directly or
    indirectly) from outside the generation into an "unreachable" set.
    Objects that are found to be reachable have gc_refs set to GC_REACHABLE
    again.  Objects that are found to be unreachable have gc_refs set to
    GC_TENTATIVELY_UNREACHABLE.  It's "tentatively" because the pass doing
    this can't be sure until it ends, and GC_TENTATIVELY_UNREACHABLE may
    transition back to GC_REACHABLE.

    Only objects with GC_TENTATIVELY_UNREACHABLE still set are candidates
    for collection.  If it's decided not to collect such an object (e.g.,
    it has a __del__ method), its gc_refs is restored to GC_REACHABLE again.
----------------------------------------------------------------------------
*/
#define GC_UNTRACKED			_PyGC_REFS_UNTRACKED
#define GC_REACHABLE			_PyGC_REFS_REACHABLE
#define GC_TENTATIVELY_UNREACHABLE	_PyGC_REFS_TENTATIVELY_UNREACHABLE

#define IS_TRACKED(o) ((AS_GC(o))->gc.gc_refs != GC_UNTRACKED)
#define IS_REACHABLE(o) ((AS_GC(o))->gc.gc_refs == GC_REACHABLE)
#define IS_TENTATIVELY_UNREACHABLE(o) ( \
	(AS_GC(o))->gc.gc_refs == GC_TENTATIVELY_UNREACHABLE)

/*** list functions ***/

static void
gc_list_init(PyGC_Head *list)
{
	list->gc.gc_prev = list;
	list->gc.gc_next = list;
}

static int
gc_list_is_empty(PyGC_Head *list)
{
	return (list->gc.gc_next == list);
}

#if 0
/* This became unused after gc_list_move() was introduced. */
/* Append `node` to `list`. */
static void
gc_list_append(PyGC_Head *node, PyGC_Head *list)
{
	node->gc.gc_next = list;
	node->gc.gc_prev = list->gc.gc_prev;
	node->gc.gc_prev->gc.gc_next = node;
	list->gc.gc_prev = node;
}
#endif

/* Remove `node` from the gc list it's currently in. */
static void
gc_list_remove(PyGC_Head *node)
{
	node->gc.gc_prev->gc.gc_next = node->gc.gc_next;
	node->gc.gc_next->gc.gc_prev = node->gc.gc_prev;
	node->gc.gc_next = NULL; /* object is not currently tracked */
}

/* Move `node` from the gc list it's currently in (which is not explicitly
 * named here) to the end of `list`.  This is semantically the same as
 * gc_list_remove(node) followed by gc_list_append(node, list).
 */
static void
gc_list_move(PyGC_Head *node, PyGC_Head *list)
{
	PyGC_Head *new_prev;
	PyGC_Head *current_prev = node->gc.gc_prev;
	PyGC_Head *current_next = node->gc.gc_next;
	/* Unlink from current list. */
	current_prev->gc.gc_next = current_next;
	current_next->gc.gc_prev = current_prev;
	/* Relink at end of new list. */
	new_prev = node->gc.gc_prev = list->gc.gc_prev;
	new_prev->gc.gc_next = list->gc.gc_prev = node;
	node->gc.gc_next = list;
}

/* append list `from` onto list `to`; `from` becomes an empty list */
static void
gc_list_merge(PyGC_Head *from, PyGC_Head *to)
{
	PyGC_Head *tail;
	assert(from != to);
	if (!gc_list_is_empty(from)) {
		tail = to->gc.gc_prev;
		tail->gc.gc_next = from->gc.gc_next;
		tail->gc.gc_next->gc.gc_prev = tail;
		to->gc.gc_prev = from->gc.gc_prev;
		to->gc.gc_prev->gc.gc_next = to;
	}
	gc_list_init(from);
}

static long
gc_list_size(PyGC_Head *list)
{
	PyGC_Head *gc;
	long n = 0;
	for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) {
		n++;
	}
	return n;
}

/* Append objects in a GC list to a Python list.
 * Return 0 if all OK, < 0 if error (out of memory for list).
 */
static int
append_objects(PyObject *py_list, PyGC_Head *gc_list)
{
	PyGC_Head *gc;
	for (gc = gc_list->gc.gc_next; gc != gc_list; gc = gc->gc.gc_next) {
		PyObject *op = FROM_GC(gc);
		if (op != py_list) {
			if (PyList_Append(py_list, op)) {
				return -1; /* exception */
			}
		}
	}
	return 0;
}

/*** end of list stuff ***/


/* Set all gc_refs = ob_refcnt.  After this, gc_refs is > 0 for all objects
 * in containers, and is GC_REACHABLE for all tracked gc objects not in
 * containers.
 */
static void
update_refs(PyGC_Head *containers)
{
	PyGC_Head *gc = containers->gc.gc_next;
	for (; gc != containers; gc = gc->gc.gc_next) {
		assert(gc->gc.gc_refs == GC_REACHABLE);
		gc->gc.gc_refs = FROM_GC(gc)->ob_refcnt;
		/* Python's cyclic gc should never see an incoming refcount
		 * of 0:  if something decref'ed to 0, it should have been
		 * deallocated immediately at that time.
		 * Possible cause (if the assert triggers):  a tp_dealloc
		 * routine left a gc-aware object tracked during its teardown
		 * phase, and did something-- or allowed something to happen --
		 * that called back into Python.  gc can trigger then, and may
		 * see the still-tracked dying object.  Before this assert
		 * was added, such mistakes went on to allow gc to try to
		 * delete the object again.  In a debug build, that caused
		 * a mysterious segfault, when _Py_ForgetReference tried
		 * to remove the object from the doubly-linked list of all
		 * objects a second time.  In a release build, an actual
		 * double deallocation occurred, which leads to corruption
		 * of the allocator's internal bookkeeping pointers.  That's
		 * so serious that maybe this should be a release-build
		 * check instead of an assert?
		 */
		assert(gc->gc.gc_refs != 0);
	}
}

/* A traversal callback for subtract_refs. */
static int
visit_decref(PyObject *op, void *data)
{
        assert(op != NULL);
	if (PyObject_IS_GC(op)) {
		PyGC_Head *gc = AS_GC(op);
		/* We're only interested in gc_refs for objects in the
		 * generation being collected, which can be recognized
		 * because only they have positive gc_refs.
		 */
		assert(gc->gc.gc_refs != 0); /* else refcount was too small */
		if (gc->gc.gc_refs > 0)
			gc->gc.gc_refs--;
	}
	return 0;
}

/* Subtract internal references from gc_refs.  After this, gc_refs is >= 0
 * for all objects in containers, and is GC_REACHABLE for all tracked gc
 * objects not in containers.  The ones with gc_refs > 0 are directly
 * reachable from outside containers, and so can't be collected.
 */
static void
subtract_refs(PyGC_Head *containers)
{
	traverseproc traverse;
	PyGC_Head *gc = containers->gc.gc_next;
	for (; gc != containers; gc=gc->gc.gc_next) {
		traverse = FROM_GC(gc)->ob_type->tp_traverse;
		(void) traverse(FROM_GC(gc),
			       (visitproc)visit_decref,
			       NULL);
	}
}

/* A traversal callback for move_unreachable. */
static int
visit_reachable(PyObject *op, PyGC_Head *reachable)
{
	if (PyObject_IS_GC(op)) {
		PyGC_Head *gc = AS_GC(op);
		const int gc_refs = gc->gc.gc_refs;

		if (gc_refs == 0) {
			/* This is in move_unreachable's 'young' list, but
			 * the traversal hasn't yet gotten to it.  All
			 * we need to do is tell move_unreachable that it's
			 * reachable.
			 */
			gc->gc.gc_refs = 1;
		}
		else if (gc_refs == GC_TENTATIVELY_UNREACHABLE) {
			/* This had gc_refs = 0 when move_unreachable got
			 * to it, but turns out it's reachable after all.
			 * Move it back to move_unreachable's 'young' list,
			 * and move_unreachable will eventually get to it
			 * again.
			 */
			gc_list_move(gc, reachable);
			gc->gc.gc_refs = 1;
		}
		/* Else there's nothing to do.
		 * If gc_refs > 0, it must be in move_unreachable's 'young'
		 * list, and move_unreachable will eventually get to it.
		 * If gc_refs == GC_REACHABLE, it's either in some other
		 * generation so we don't care about it, or move_unreachable
		 * already dealt with it.
		 * If gc_refs == GC_UNTRACKED, it must be ignored.
		 */
		 else {
		 	assert(gc_refs > 0
		 	       || gc_refs == GC_REACHABLE
		 	       || gc_refs == GC_UNTRACKED);
		 }
	}
	return 0;
}

/* Move the unreachable objects from young to unreachable.  After this,
 * all objects in young have gc_refs = GC_REACHABLE, and all objects in
 * unreachable have gc_refs = GC_TENTATIVELY_UNREACHABLE.  All tracked
 * gc objects not in young or unreachable still have gc_refs = GC_REACHABLE.
 * All objects in young after this are directly or indirectly reachable
 * from outside the original young; and all objects in unreachable are
 * not.
 */
static void
move_unreachable(PyGC_Head *young, PyGC_Head *unreachable)
{
	PyGC_Head *gc = young->gc.gc_next;

	/* Invariants:  all objects "to the left" of us in young have gc_refs
	 * = GC_REACHABLE, and are indeed reachable (directly or indirectly)
	 * from outside the young list as it was at entry.  All other objects
	 * from the original young "to the left" of us are in unreachable now,
	 * and have gc_refs = GC_TENTATIVELY_UNREACHABLE.  All objects to the
	 * left of us in 'young' now have been scanned, and no objects here
	 * or to the right have been scanned yet.
	 */

	while (gc != young) {
		PyGC_Head *next;

		if (gc->gc.gc_refs) {
                        /* gc is definitely reachable from outside the
                         * original 'young'.  Mark it as such, and traverse
                         * its pointers to find any other objects that may
                         * be directly reachable from it.  Note that the
                         * call to tp_traverse may append objects to young,
                         * so we have to wait until it returns to determine
                         * the next object to visit.
                         */
                        PyObject *op = FROM_GC(gc);
                        traverseproc traverse = op->ob_type->tp_traverse;
                        assert(gc->gc.gc_refs > 0);
                        gc->gc.gc_refs = GC_REACHABLE;
                        (void) traverse(op,
                                        (visitproc)visit_reachable,
                                        (void *)young);
                        next = gc->gc.gc_next;
		}
		else {
			/* This *may* be unreachable.  To make progress,
			 * assume it is.  gc isn't directly reachable from
			 * any object we've already traversed, but may be
			 * reachable from an object we haven't gotten to yet.
			 * visit_reachable will eventually move gc back into
			 * young if that's so, and we'll see it again.
			 */
			next = gc->gc.gc_next;
			gc_list_move(gc, unreachable);
			gc->gc.gc_refs = GC_TENTATIVELY_UNREACHABLE;
		}
		gc = next;
	}
}

/* Return true if object has a finalization method.
 * CAUTION:  An instance of an old-style class has to be checked for a
 *__del__ method, and earlier versions of this used to call PyObject_HasAttr,
 * which in turn could call the class's __getattr__ hook (if any).  That
 * could invoke arbitrary Python code, mutating the object graph in arbitrary
 * ways, and that was the source of some excruciatingly subtle bugs.
 */
static int
has_finalizer(PyObject *op)
{
	if (PyInstance_Check(op)) {
		assert(delstr != NULL);
		return _PyInstance_Lookup(op, delstr) != NULL;
	}
	else if (PyType_HasFeature(op->ob_type, Py_TPFLAGS_HEAPTYPE))
		return op->ob_type->tp_del != NULL;
	else
		return 0;
}

/* Move the objects in unreachable with __del__ methods into `finalizers`.
 * Objects moved into `finalizers` have gc_refs set to GC_REACHABLE; the
 * objects remaining in unreachable are left at GC_TENTATIVELY_UNREACHABLE.
 */
static void
move_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers)
{
	PyGC_Head *gc;
	PyGC_Head *next;

	/* March over unreachable.  Move objects with finalizers into
	 * `finalizers`.
	 */
	for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) {
		PyObject *op = FROM_GC(gc);

		assert(IS_TENTATIVELY_UNREACHABLE(op));
		next = gc->gc.gc_next;

		if (has_finalizer(op)) {
			gc_list_move(gc, finalizers);
			gc->gc.gc_refs = GC_REACHABLE;
		}
	}
}

/* A traversal callback for move_finalizer_reachable. */
static int
visit_move(PyObject *op, PyGC_Head *tolist)
{
	if (PyObject_IS_GC(op)) {
		if (IS_TENTATIVELY_UNREACHABLE(op)) {
			PyGC_Head *gc = AS_GC(op);
			gc_list_move(gc, tolist);
			gc->gc.gc_refs = GC_REACHABLE;
		}
	}
	return 0;
}

/* Move objects that are reachable from finalizers, from the unreachable set
 * into finalizers set.
 */
static void
move_finalizer_reachable(PyGC_Head *finalizers)
{
	traverseproc traverse;
	PyGC_Head *gc = finalizers->gc.gc_next;
	for (; gc != finalizers; gc = gc->gc.gc_next) {
		/* Note that the finalizers list may grow during this. */
		traverse = FROM_GC(gc)->ob_type->tp_traverse;
		(void) traverse(FROM_GC(gc),
				(visitproc)visit_move,
				(void *)finalizers);
	}
}

/* Clear all weakrefs to unreachable objects, and if such a weakref has a
 * callback, invoke it if necessary.  Note that it's possible for such
 * weakrefs to be outside the unreachable set -- indeed, those are precisely
 * the weakrefs whose callbacks must be invoked.  See gc_weakref.txt for
 * overview & some details.  Some weakrefs with callbacks may be reclaimed
 * directly by this routine; the number reclaimed is the return value.  Other
 * weakrefs with callbacks may be moved into the `old` generation.  Objects
 * moved into `old` have gc_refs set to GC_REACHABLE; the objects remaining in
 * unreachable are left at GC_TENTATIVELY_UNREACHABLE.  When this returns,
 * no object in `unreachable` is weakly referenced anymore.
 */
static int
handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
{
	PyGC_Head *gc;
	PyObject *op;		/* generally FROM_GC(gc) */
	PyWeakReference *wr;	/* generally a cast of op */
	PyGC_Head wrcb_to_call;	/* weakrefs with callbacks to call */
	PyGC_Head *next;
	int num_freed = 0;

	gc_list_init(&wrcb_to_call);

	/* Clear all weakrefs to the objects in unreachable.  If such a weakref
	 * also has a callback, move it into `wrcb_to_call` if the callback
	 * needs to be invoked.  Note that we cannot invoke any callbacks until
	 * all weakrefs to unreachable objects are cleared, lest the callback
	 * resurrect an unreachable object via a still-active weakref.  We
	 * make another pass over wrcb_to_call, invoking callbacks, after this
	 * pass completes.
	 */
	for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) {
		PyWeakReference **wrlist;

		op = FROM_GC(gc);
		assert(IS_TENTATIVELY_UNREACHABLE(op));
		next = gc->gc.gc_next;

		if (! PyType_SUPPORTS_WEAKREFS(op->ob_type))
			continue;

		/* It supports weakrefs.  Does it have any? */
		wrlist = (PyWeakReference **)
			     		PyObject_GET_WEAKREFS_LISTPTR(op);

		/* `op` may have some weakrefs.  March over the list, clear
		 * all the weakrefs, and move the weakrefs with callbacks
		 * that must be called into wrcb_to_call.
		 */
		for (wr = *wrlist; wr != NULL; wr = *wrlist) {
			PyGC_Head *wrasgc;	/* AS_GC(wr) */

			/* _PyWeakref_ClearRef clears the weakref but leaves
			 * the callback pointer intact.  Obscure:  it also
			 * changes *wrlist.
			 */
			assert(wr->wr_object == op);
			_PyWeakref_ClearRef(wr);
			assert(wr->wr_object == Py_None);
			if (wr->wr_callback == NULL)
				continue;	/* no callback */

	/* Headache time.  `op` is going away, and is weakly referenced by
	 * `wr`, which has a callback.  Should the callback be invoked?  If wr
	 * is also trash, no:
	 *
	 * 1. There's no need to call it.  The object and the weakref are
	 *    both going away, so it's legitimate to pretend the weakref is
	 *    going away first.  The user has to ensure a weakref outlives its
	 *    referent if they want a guarantee that the wr callback will get
	 *    invoked.
	 *
	 * 2. It may be catastrophic to call it.  If the callback is also in
	 *    cyclic trash (CT), then although the CT is unreachable from
	 *    outside the current generation, CT may be reachable from the
	 *    callback.  Then the callback could resurrect insane objects.
	 *
	 * Since the callback is never needed and may be unsafe in this case,
	 * wr is simply left in the unreachable set.  Note that because we
	 * already called _PyWeakref_ClearRef(wr), its callback will never
	 * trigger.
	 *
	 * OTOH, if wr isn't part of CT, we should invoke the callback:  the
	 * weakref outlived the trash.  Note that since wr isn't CT in this
	 * case, its callback can't be CT either -- wr acted as an external
	 * root to this generation, and therefore its callback did too.  So
	 * nothing in CT is reachable from the callback either, so it's hard
	 * to imagine how calling it later could create a problem for us.  wr
	 * is moved to wrcb_to_call in this case.
	 */
	 		if (IS_TENTATIVELY_UNREACHABLE(wr))
	 			continue;
			assert(IS_REACHABLE(wr));

			/* Create a new reference so that wr can't go away
			 * before we can process it again.
			 */
			Py_INCREF(wr);

			/* Move wr to wrcb_to_call, for the next pass. */
			wrasgc = AS_GC(wr);
			assert(wrasgc != next); /* wrasgc is reachable, but
			                           next isn't, so they can't
			                           be the same */
			gc_list_move(wrasgc, &wrcb_to_call);
		}
	}

	/* Invoke the callbacks we decided to honor.  It's safe to invoke them
	 * because they can't reference unreachable objects.
	 */
	while (! gc_list_is_empty(&wrcb_to_call)) {
		PyObject *temp;
		PyObject *callback;

		gc = wrcb_to_call.gc.gc_next;
		op = FROM_GC(gc);
		assert(IS_REACHABLE(op));
		assert(PyWeakref_Check(op));
		wr = (PyWeakReference *)op;
		callback = wr->wr_callback;
		assert(callback != NULL);

		/* copy-paste of weakrefobject.c's handle_callback() */
		temp = PyObject_CallFunction(callback, "O", wr);
		if (temp == NULL)
			PyErr_WriteUnraisable(callback);
		else
			Py_DECREF(temp);

		/* Give up the reference we created in the first pass.  When
		 * op's refcount hits 0 (which it may or may not do right now),
		 * op's tp_dealloc will decref op->wr_callback too.  Note
		 * that the refcount probably will hit 0 now, and because this
		 * weakref was reachable to begin with, gc didn't already
		 * add it to its count of freed objects.  Example:  a reachable
		 * weak value dict maps some key to this reachable weakref.
		 * The callback removes this key->weakref mapping from the
		 * dict, leaving no other references to the weakref (excepting
		 * ours).
		 */
		Py_DECREF(op);
		if (wrcb_to_call.gc.gc_next == gc) {
			/* object is still alive -- move it */
			gc_list_move(gc, old);
		}
		else
			++num_freed;
	}

	return num_freed;
}

static void
debug_instance(char *msg, PyInstanceObject *inst)
{
	char *cname;
	/* simple version of instance_repr */
	PyObject *classname = inst->in_class->cl_name;
	if (classname != NULL && PyString_Check(classname))
		cname = PyString_AsString(classname);
	else
		cname = "?";
	PySys_WriteStderr("gc: %.100s <%.100s instance at %p>\n",
			  msg, cname, inst);
}

static void
debug_cycle(char *msg, PyObject *op)
{
	if ((debug & DEBUG_INSTANCES) && PyInstance_Check(op)) {
		debug_instance(msg, (PyInstanceObject *)op);
	}
	else if (debug & DEBUG_OBJECTS) {
		PySys_WriteStderr("gc: %.100s <%.100s %p>\n",
				  msg, op->ob_type->tp_name, op);
	}
}

/* Handle uncollectable garbage (cycles with finalizers, and stuff reachable
 * only from such cycles).
 * If DEBUG_SAVEALL, all objects in finalizers are appended to the module
 * garbage list (a Python list), else only the objects in finalizers with
 * __del__ methods are appended to garbage.  All objects in finalizers are
 * merged into the old list regardless.
 * Returns 0 if all OK, <0 on error (out of memory to grow the garbage list).
 * The finalizers list is made empty on a successful return.
 */
static int
handle_finalizers(PyGC_Head *finalizers, PyGC_Head *old)
{
	PyGC_Head *gc = finalizers->gc.gc_next;

	if (garbage == NULL) {
		garbage = PyList_New(0);
		if (garbage == NULL)
			Py_FatalError("gc couldn't create gc.garbage list");
	}
	for (; gc != finalizers; gc = gc->gc.gc_next) {
		PyObject *op = FROM_GC(gc);

		if ((debug & DEBUG_SAVEALL) || has_finalizer(op)) {
			if (PyList_Append(garbage, op) < 0)
				return -1;
		}
	}

	gc_list_merge(finalizers, old);
	return 0;
}

/* Break reference cycles by clearing the containers involved.	This is
 * tricky business as the lists can be changing and we don't know which
 * objects may be freed.  It is possible I screwed something up here.
 */
static void
delete_garbage(PyGC_Head *collectable, PyGC_Head *old)
{
	inquiry clear;

	while (!gc_list_is_empty(collectable)) {
		PyGC_Head *gc = collectable->gc.gc_next;
		PyObject *op = FROM_GC(gc);

		assert(IS_TENTATIVELY_UNREACHABLE(op));
		if (debug & DEBUG_SAVEALL) {
			PyList_Append(garbage, op);
		}
		else {
			if ((clear = op->ob_type->tp_clear) != NULL) {
				Py_INCREF(op);
				clear(op);
				Py_DECREF(op);
			}
		}
		if (collectable->gc.gc_next == gc) {
			/* object is still alive, move it, it may die later */
			gc_list_move(gc, old);
			gc->gc.gc_refs = GC_REACHABLE;
		}
	}
}

/* This is the main function.  Read this to understand how the
 * collection process works. */
static long
collect(int generation)
{
	int i;
	long m = 0;	/* # objects collected */
	long n = 0;	/* # unreachable objects that couldn't be collected */
	PyGC_Head *young; /* the generation we are examining */
	PyGC_Head *old; /* next older generation */
	PyGC_Head unreachable; /* non-problematic unreachable trash */
	PyGC_Head finalizers;  /* objects with, & reachable from, __del__ */
	PyGC_Head *gc;

	if (delstr == NULL) {
		delstr = PyString_InternFromString("__del__");
		if (delstr == NULL)
			Py_FatalError("gc couldn't allocate \"__del__\"");
	}

	if (debug & DEBUG_STATS) {
		PySys_WriteStderr("gc: collecting generation %d...\n",
				  generation);
		PySys_WriteStderr("gc: objects in each generation:");
		for (i = 0; i < NUM_GENERATIONS; i++) {
			PySys_WriteStderr(" %ld", gc_list_size(GEN_HEAD(i)));
		}
		PySys_WriteStderr("\n");
	}

	/* update collection and allocation counters */
	if (generation+1 < NUM_GENERATIONS)
		generations[generation+1].count += 1;
	for (i = 0; i <= generation; i++)
		generations[i].count = 0;

	/* merge younger generations with one we are currently collecting */
	for (i = 0; i < generation; i++) {
		gc_list_merge(GEN_HEAD(i), GEN_HEAD(generation));
	}

	/* handy references */
	young = GEN_HEAD(generation);
	if (generation < NUM_GENERATIONS-1)
		old = GEN_HEAD(generation+1);
	else
		old = young;

	/* Using ob_refcnt and gc_refs, calculate which objects in the
	 * container set are reachable from outside the set (i.e., have a
	 * refcount greater than 0 when all the references within the
	 * set are taken into account).
	 */
	update_refs(young);
	subtract_refs(young);

	/* Leave everything reachable from outside young in young, and move
	 * everything else (in young) to unreachable.
	 * NOTE:  This used to move the reachable objects into a reachable
	 * set instead.  But most things usually turn out to be reachable,
	 * so it's more efficient to move the unreachable things.
	 */
	gc_list_init(&unreachable);
	move_unreachable(young, &unreachable);

	/* Move reachable objects to next generation. */
	if (young != old)
		gc_list_merge(young, old);

	/* All objects in unreachable are trash, but objects reachable from
	 * finalizers can't safely be deleted.  Python programmers should take
	 * care not to create such things.  For Python, finalizers means
	 * instance objects with __del__ methods.  Weakrefs with callbacks
	 * can also call arbitrary Python code but they will be dealt with by
	 * handle_weakrefs().
 	 */
	gc_list_init(&finalizers);
	move_finalizers(&unreachable, &finalizers);
	/* finalizers contains the unreachable objects with a finalizer;
	 * unreachable objects reachable *from* those are also uncollectable,
	 * and we move those into the finalizers list too.
	 */
	move_finalizer_reachable(&finalizers);

	/* Collect statistics on collectable objects found and print
	 * debugging information.
	 */
	for (gc = unreachable.gc.gc_next; gc != &unreachable;
			gc = gc->gc.gc_next) {
		m++;
		if (debug & DEBUG_COLLECTABLE) {
			debug_cycle("collectable", FROM_GC(gc));
		}
	}

	/* Clear weakrefs and invoke callbacks as necessary. */
	m += handle_weakrefs(&unreachable, old);

	/* Call tp_clear on objects in the unreachable set.  This will cause
	 * the reference cycles to be broken.  It may also cause some objects
	 * in finalizers to be freed.
	 */
	delete_garbage(&unreachable, old);

	/* Collect statistics on uncollectable objects found and print
	 * debugging information. */
	for (gc = finalizers.gc.gc_next;
	     gc != &finalizers;
	     gc = gc->gc.gc_next) {
		n++;
		if (debug & DEBUG_UNCOLLECTABLE)
			debug_cycle("uncollectable", FROM_GC(gc));
	}
	if (debug & DEBUG_STATS) {
		if (m == 0 && n == 0) {
			PySys_WriteStderr("gc: done.\n");
		}
		else {
			PySys_WriteStderr(
			    "gc: done, %ld unreachable, %ld uncollectable.\n",
			    n+m, n);
		}
	}

	/* Append instances in the uncollectable set to a Python
	 * reachable list of garbage.  The programmer has to deal with
	 * this if they insist on creating this type of structure.
	 */
	(void)handle_finalizers(&finalizers, old);

	if (PyErr_Occurred()) {
		if (gc_str == NULL)
			gc_str = PyString_FromString("garbage collection");
		PyErr_WriteUnraisable(gc_str);
		Py_FatalError("unexpected exception during garbage collection");
	}
	return n+m;
}

static long
collect_generations(void)
{
	int i;
	long n = 0;

	/* Find the oldest generation (higest numbered) where the count
	 * exceeds the threshold.  Objects in the that generation and
	 * generations younger than it will be collected. */
	for (i = NUM_GENERATIONS-1; i >= 0; i--) {
		if (generations[i].count > generations[i].threshold) {
			n = collect(i);
			break;
		}
	}
	return n;
}

PyDoc_STRVAR(gc_enable__doc__,
"enable() -> None\n"
"\n"
"Enable automatic garbage collection.\n");

static PyObject *
gc_enable(PyObject *self, PyObject *noargs)
{
	enabled = 1;
	Py_INCREF(Py_None);
	return Py_None;
}

PyDoc_STRVAR(gc_disable__doc__,
"disable() -> None\n"
"\n"
"Disable automatic garbage collection.\n");

static PyObject *
gc_disable(PyObject *self, PyObject *noargs)
{
	enabled = 0;
	Py_INCREF(Py_None);
	return Py_None;
}

PyDoc_STRVAR(gc_isenabled__doc__,
"isenabled() -> status\n"
"\n"
"Returns true if automatic garbage collection is enabled.\n");

static PyObject *
gc_isenabled(PyObject *self, PyObject *noargs)
{
	return PyBool_FromLong((long)enabled);
}

PyDoc_STRVAR(gc_collect__doc__,
"collect() -> n\n"
"\n"
"Run a full collection.  The number of unreachable objects is returned.\n");

static PyObject *
gc_collect(PyObject *self, PyObject *noargs)
{
	long n;

	if (collecting)
		n = 0; /* already collecting, don't do anything */
	else {
		collecting = 1;
		n = collect(NUM_GENERATIONS - 1);
		collecting = 0;
	}

	return Py_BuildValue("l", n);
}

PyDoc_STRVAR(gc_set_debug__doc__,
"set_debug(flags) -> None\n"
"\n"
"Set the garbage collection debugging flags. Debugging information is\n"
"written to sys.stderr.\n"
"\n"
"flags is an integer and can have the following bits turned on:\n"
"\n"
"  DEBUG_STATS - Print statistics during collection.\n"
"  DEBUG_COLLECTABLE - Print collectable objects found.\n"
"  DEBUG_UNCOLLECTABLE - Print unreachable but uncollectable objects found.\n"
"  DEBUG_INSTANCES - Print instance objects.\n"
"  DEBUG_OBJECTS - Print objects other than instances.\n"
"  DEBUG_SAVEALL - Save objects to gc.garbage rather than freeing them.\n"
"  DEBUG_LEAK - Debug leaking programs (everything but STATS).\n");

static PyObject *
gc_set_debug(PyObject *self, PyObject *args)
{
	if (!PyArg_ParseTuple(args, "i:set_debug", &debug))
		return NULL;

	Py_INCREF(Py_None);
	return Py_None;
}

PyDoc_STRVAR(gc_get_debug__doc__,
"get_debug() -> flags\n"
"\n"
"Get the garbage collection debugging flags.\n");

static PyObject *
gc_get_debug(PyObject *self, PyObject *noargs)
{
	return Py_BuildValue("i", debug);
}

PyDoc_STRVAR(gc_set_thresh__doc__,
"set_threshold(threshold0, [threshold1, threshold2]) -> None\n"
"\n"
"Sets the collection thresholds.  Setting threshold0 to zero disables\n"
"collection.\n");

static PyObject *
gc_set_thresh(PyObject *self, PyObject *args)
{
	int i;
	if (!PyArg_ParseTuple(args, "i|ii:set_threshold",
			      &generations[0].threshold,
			      &generations[1].threshold,
			      &generations[2].threshold))
		return NULL;
	for (i = 2; i < NUM_GENERATIONS; i++) {
 		/* generations higher than 2 get the same threshold */
		generations[i].threshold = generations[2].threshold;
	}

	Py_INCREF(Py_None);
	return Py_None;
}

PyDoc_STRVAR(gc_get_thresh__doc__,
"get_threshold() -> (threshold0, threshold1, threshold2)\n"
"\n"
"Return the current collection thresholds\n");

static PyObject *
gc_get_thresh(PyObject *self, PyObject *noargs)
{
	return Py_BuildValue("(iii)",
			     generations[0].threshold,
			     generations[1].threshold,
			     generations[2].threshold);
}

static int
referrersvisit(PyObject* obj, PyObject *objs)
{
	int i;
	for (i = 0; i < PyTuple_GET_SIZE(objs); i++)
		if (PyTuple_GET_ITEM(objs, i) == obj)
			return 1;
	return 0;
}

static int
gc_referrers_for(PyObject *objs, PyGC_Head *list, PyObject *resultlist)
{
	PyGC_Head *gc;
	PyObject *obj;
	traverseproc traverse;
	for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) {
		obj = FROM_GC(gc);
		traverse = obj->ob_type->tp_traverse;
		if (obj == objs || obj == resultlist)
			continue;
		if (traverse(obj, (visitproc)referrersvisit, objs)) {
			if (PyList_Append(resultlist, obj) < 0)
				return 0; /* error */
		}
	}
	return 1; /* no error */
}

PyDoc_STRVAR(gc_get_referrers__doc__,
"get_referrers(*objs) -> list\n\
Return the list of objects that directly refer to any of objs.");

static PyObject *
gc_get_referrers(PyObject *self, PyObject *args)
{
	int i;
	PyObject *result = PyList_New(0);
	if (!result) return NULL;
	for (i = 0; i < NUM_GENERATIONS; i++) {
		if (!(gc_referrers_for(args, GEN_HEAD(i), result))) {
			Py_DECREF(result);
			return NULL;
		}
	}
	return result;
}

/* Append obj to list; return true if error (out of memory), false if OK. */
static int
referentsvisit(PyObject *obj, PyObject *list)
{
	return PyList_Append(list, obj) < 0;
}

PyDoc_STRVAR(gc_get_referents__doc__,
"get_referents(*objs) -> list\n\
Return the list of objects that are directly referred to by objs.");

static PyObject *
gc_get_referents(PyObject *self, PyObject *args)
{
	int i;
	PyObject *result = PyList_New(0);

	if (result == NULL)
		return NULL;

	for (i = 0; i < PyTuple_GET_SIZE(args); i++) {
		traverseproc traverse;
		PyObject *obj = PyTuple_GET_ITEM(args, i);

		if (! PyObject_IS_GC(obj))
			continue;
		traverse = obj->ob_type->tp_traverse;
		if (! traverse)
			continue;
		if (traverse(obj, (visitproc)referentsvisit, result)) {
			Py_DECREF(result);
			return NULL;
		}
	}
	return result;
}

PyDoc_STRVAR(gc_get_objects__doc__,
"get_objects() -> [...]\n"
"\n"
"Return a list of objects tracked by the collector (excluding the list\n"
"returned).\n");

static PyObject *
gc_get_objects(PyObject *self, PyObject *noargs)
{
	int i;
	PyObject* result;

	result = PyList_New(0);
	if (result == NULL)
		return NULL;
	for (i = 0; i < NUM_GENERATIONS; i++) {
		if (append_objects(result, GEN_HEAD(i))) {
			Py_DECREF(result);
			return NULL;
		}
	}
	return result;
}


PyDoc_STRVAR(gc__doc__,
"This module provides access to the garbage collector for reference cycles.\n"
"\n"
"enable() -- Enable automatic garbage collection.\n"
"disable() -- Disable automatic garbage collection.\n"
"isenabled() -- Returns true if automatic collection is enabled.\n"
"collect() -- Do a full collection right now.\n"
"set_debug() -- Set debugging flags.\n"
"get_debug() -- Get debugging flags.\n"
"set_threshold() -- Set the collection thresholds.\n"
"get_threshold() -- Return the current the collection thresholds.\n"
"get_objects() -- Return a list of all objects tracked by the collector.\n"
"get_referrers() -- Return the list of objects that refer to an object.\n"
"get_referents() -- Return the list of objects that an object refers to.\n");

static PyMethodDef GcMethods[] = {
	{"enable",	   gc_enable,	  METH_NOARGS,  gc_enable__doc__},
	{"disable",	   gc_disable,	  METH_NOARGS,  gc_disable__doc__},
	{"isenabled",	   gc_isenabled,  METH_NOARGS,  gc_isenabled__doc__},
	{"set_debug",	   gc_set_debug,  METH_VARARGS, gc_set_debug__doc__},
	{"get_debug",	   gc_get_debug,  METH_NOARGS,  gc_get_debug__doc__},
	{"set_threshold",  gc_set_thresh, METH_VARARGS, gc_set_thresh__doc__},
	{"get_threshold",  gc_get_thresh, METH_NOARGS,  gc_get_thresh__doc__},
	{"collect",	   gc_collect,	  METH_NOARGS,  gc_collect__doc__},
	{"get_objects",    gc_get_objects,METH_NOARGS,  gc_get_objects__doc__},
	{"get_referrers",  gc_get_referrers, METH_VARARGS,
		gc_get_referrers__doc__},
	{"get_referents",  gc_get_referents, METH_VARARGS,
		gc_get_referents__doc__},
	{NULL,	NULL}		/* Sentinel */
};

PyMODINIT_FUNC
initgc(void)
{
	PyObject *m;

	m = Py_InitModule4("gc",
			      GcMethods,
			      gc__doc__,
			      NULL,
			      PYTHON_API_VERSION);
	if (m == NULL)
		return;

	if (garbage == NULL) {
		garbage = PyList_New(0);
		if (garbage == NULL)
			return;
	}
	Py_INCREF(garbage);
	if (PyModule_AddObject(m, "garbage", garbage) < 0)
		return;
#define ADD_INT(NAME) if (PyModule_AddIntConstant(m, #NAME, NAME) < 0) return
	ADD_INT(DEBUG_STATS);
	ADD_INT(DEBUG_COLLECTABLE);
	ADD_INT(DEBUG_UNCOLLECTABLE);
	ADD_INT(DEBUG_INSTANCES);
	ADD_INT(DEBUG_OBJECTS);
	ADD_INT(DEBUG_SAVEALL);
	ADD_INT(DEBUG_LEAK);
#undef ADD_INT
}

/* API to invoke gc.collect() from C */
long
PyGC_Collect(void)
{
	long n;

	if (collecting)
		n = 0; /* already collecting, don't do anything */
	else {
		collecting = 1;
		n = collect(NUM_GENERATIONS - 1);
		collecting = 0;
	}

	return n;
}

/* for debugging */
void
_PyGC_Dump(PyGC_Head *g)
{
	_PyObject_Dump(FROM_GC(g));
}

/* extension modules might be compiled with GC support so these
   functions must always be available */

#undef PyObject_GC_Track
#undef PyObject_GC_UnTrack
#undef PyObject_GC_Del
#undef _PyObject_GC_Malloc

void
PyObject_GC_Track(void *op)
{
	_PyObject_GC_TRACK(op);
}

/* for binary compatibility with 2.2 */
void
_PyObject_GC_Track(PyObject *op)
{
    PyObject_GC_Track(op);
}

void
PyObject_GC_UnTrack(void *op)
{
	/* Obscure:  the Py_TRASHCAN mechanism requires that we be able to
	 * call PyObject_GC_UnTrack twice on an object.
	 */
	if (IS_TRACKED(op))
		_PyObject_GC_UNTRACK(op);
}

/* for binary compatibility with 2.2 */
void
_PyObject_GC_UnTrack(PyObject *op)
{
    PyObject_GC_UnTrack(op);
}

PyObject *
_PyObject_GC_Malloc(size_t basicsize)
{
	PyObject *op;
	PyGC_Head *g;
 	if (basicsize > INT_MAX - sizeof(PyGC_Head))
 		return PyErr_NoMemory();
	g = PyObject_MALLOC(sizeof(PyGC_Head) + basicsize);
	if (g == NULL)
		return PyErr_NoMemory();
	g->gc.gc_refs = GC_UNTRACKED;
	generations[0].count++; /* number of allocated GC objects */
 	if (generations[0].count > generations[0].threshold &&
 	    enabled &&
 	    generations[0].threshold &&
 	    !collecting &&
 	    !PyErr_Occurred()) {
		collecting = 1;
		collect_generations();
		collecting = 0;
	}
	op = FROM_GC(g);
	return op;
}

PyObject *
_PyObject_GC_New(PyTypeObject *tp)
{
	PyObject *op = _PyObject_GC_Malloc(_PyObject_SIZE(tp));
	if (op != NULL)
		op = PyObject_INIT(op, tp);
	return op;
}

PyVarObject *
_PyObject_GC_NewVar(PyTypeObject *tp, int nitems)
{
	const size_t size = _PyObject_VAR_SIZE(tp, nitems);
	PyVarObject *op = (PyVarObject *) _PyObject_GC_Malloc(size);
	if (op != NULL)
		op = PyObject_INIT_VAR(op, tp, nitems);
	return op;
}

PyVarObject *
_PyObject_GC_Resize(PyVarObject *op, int nitems)
{
	const size_t basicsize = _PyObject_VAR_SIZE(op->ob_type, nitems);
	PyGC_Head *g = AS_GC(op);
 	if (basicsize > INT_MAX - sizeof(PyGC_Head))
 		return (PyVarObject *)PyErr_NoMemory();
	g = PyObject_REALLOC(g,  sizeof(PyGC_Head) + basicsize);
	if (g == NULL)
		return (PyVarObject *)PyErr_NoMemory();
	op = (PyVarObject *) FROM_GC(g);
	op->ob_size = nitems;
	return op;
}

void
PyObject_GC_Del(void *op)
{
	PyGC_Head *g = AS_GC(op);
	if (IS_TRACKED(op))
		gc_list_remove(g);
	if (generations[0].count > 0) {
		generations[0].count--;
	}
	PyObject_FREE(g);
}

/* for binary compatibility with 2.2 */
#undef _PyObject_GC_Del
void
_PyObject_GC_Del(PyObject *op)
{
    PyObject_GC_Del(op);
}
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.