cpython-withatomic / Objects / obmalloc.c

   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
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
#include "Python.h"

#ifdef WITH_PYMALLOC

/* An object allocator for Python.

   Here is an introduction to the layers of the Python memory architecture,
   showing where the object allocator is actually used (layer +2), It is
   called for every object allocation and deallocation (PyObject_New/Del),
   unless the object-specific allocators implement a proprietary allocation
   scheme (ex.: ints use a simple free list). This is also the place where
   the cyclic garbage collector operates selectively on container objects.


        Object-specific allocators
    _____   ______   ______       ________
   [ int ] [ dict ] [ list ] ... [ string ]       Python core         |
+3 | <----- Object-specific memory -----> | <-- Non-object memory --> |
    _______________________________       |                           |
   [   Python's object allocator   ]      |                           |
+2 | ####### Object memory ####### | <------ Internal buffers ------> |
    ______________________________________________________________    |
   [          Python's raw memory allocator (PyMem_ API)          ]   |
+1 | <----- Python memory (under PyMem manager's control) ------> |   |
    __________________________________________________________________
   [    Underlying general-purpose allocator (ex: C library malloc)   ]
 0 | <------ Virtual memory allocated for the python process -------> |

   =========================================================================
    _______________________________________________________________________
   [                OS-specific Virtual Memory Manager (VMM)               ]
-1 | <--- Kernel dynamic storage allocation & management (page-based) ---> |
    __________________________________   __________________________________
   [                                  ] [                                  ]
-2 | <-- Physical memory: ROM/RAM --> | | <-- Secondary storage (swap) --> |

*/
/*==========================================================================*/

/* A fast, special-purpose memory allocator for small blocks, to be used
   on top of a general-purpose malloc -- heavily based on previous art. */

/* Vladimir Marangozov -- August 2000 */

/*
 * "Memory management is where the rubber meets the road -- if we do the wrong
 * thing at any level, the results will not be good. And if we don't make the
 * levels work well together, we are in serious trouble." (1)
 *
 * (1) Paul R. Wilson, Mark S. Johnstone, Michael Neely, and David Boles,
 *    "Dynamic Storage Allocation: A Survey and Critical Review",
 *    in Proc. 1995 Int'l. Workshop on Memory Management, September 1995.
 */

/* #undef WITH_MEMORY_LIMITS */		/* disable mem limit checks  */

/*==========================================================================*/

/*
 * Allocation strategy abstract:
 *
 * For small requests, the allocator sub-allocates <Big> blocks of memory.
 * Requests greater than 256 bytes are routed to the system's allocator.
 *
 * Small requests are grouped in size classes spaced 8 bytes apart, due
 * to the required valid alignment of the returned address. Requests of
 * a particular size are serviced from memory pools of 4K (one VMM page).
 * Pools are fragmented on demand and contain free lists of blocks of one
 * particular size class. In other words, there is a fixed-size allocator
 * for each size class. Free pools are shared by the different allocators
 * thus minimizing the space reserved for a particular size class.
 *
 * This allocation strategy is a variant of what is known as "simple
 * segregated storage based on array of free lists". The main drawback of
 * simple segregated storage is that we might end up with lot of reserved
 * memory for the different free lists, which degenerate in time. To avoid
 * this, we partition each free list in pools and we share dynamically the
 * reserved space between all free lists. This technique is quite efficient
 * for memory intensive programs which allocate mainly small-sized blocks.
 *
 * For small requests we have the following table:
 *
 * Request in bytes	Size of allocated block      Size class idx
 * ----------------------------------------------------------------
 *        1-8                     8                       0
 *	  9-16                   16                       1
 *	 17-24                   24                       2
 *	 25-32                   32                       3
 *	 33-40                   40                       4
 *	 41-48                   48                       5
 *	 49-56                   56                       6
 *	 57-64                   64                       7
 *	 65-72                   72                       8
 *	  ...                   ...                     ...
 *	241-248                 248                      30
 *	249-256                 256                      31
 *
 *	0, 257 and up: routed to the underlying allocator.
 */

/*==========================================================================*/

/*
 * -- Main tunable settings section --
 */

/*
 * Alignment of addresses returned to the user. 8-bytes alignment works
 * on most current architectures (with 32-bit or 64-bit address busses).
 * The alignment value is also used for grouping small requests in size
 * classes spaced ALIGNMENT bytes apart.
 *
 * You shouldn't change this unless you know what you are doing.
 */
#define ALIGNMENT		8		/* must be 2^N */
#define ALIGNMENT_SHIFT		3
#define ALIGNMENT_MASK		(ALIGNMENT - 1)

/* Return the number of bytes in size class I, as a uint. */
#define INDEX2SIZE(I) (((uint)(I) + 1) << ALIGNMENT_SHIFT)

/*
 * Max size threshold below which malloc requests are considered to be
 * small enough in order to use preallocated memory pools. You can tune
 * this value according to your application behaviour and memory needs.
 *
 * The following invariants must hold:
 *	1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
 *	2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
 *
 * Although not required, for better performance and space efficiency,
 * it is recommended that SMALL_REQUEST_THRESHOLD is set to a power of 2.
 */
#define SMALL_REQUEST_THRESHOLD	256
#define NB_SMALL_SIZE_CLASSES	(SMALL_REQUEST_THRESHOLD / ALIGNMENT)

/*
 * The system's VMM page size can be obtained on most unices with a
 * getpagesize() call or deduced from various header files. To make
 * things simpler, we assume that it is 4K, which is OK for most systems.
 * It is probably better if this is the native page size, but it doesn't
 * have to be.  In theory, if SYSTEM_PAGE_SIZE is larger than the native page 
 * size, then `POOL_ADDR(p)->arenaindex' could rarely cause a segmentation 
 * violation fault.  4K is apparently OK for all the platforms that python 
 * currently targets.
 */
#define SYSTEM_PAGE_SIZE	(4 * 1024)
#define SYSTEM_PAGE_SIZE_MASK	(SYSTEM_PAGE_SIZE - 1)

/*
 * Maximum amount of memory managed by the allocator for small requests.
 */
#ifdef WITH_MEMORY_LIMITS
#ifndef SMALL_MEMORY_LIMIT
#define SMALL_MEMORY_LIMIT	(64 * 1024 * 1024)	/* 64 MB -- more? */
#endif
#endif

/*
 * The allocator sub-allocates <Big> blocks of memory (called arenas) aligned
 * on a page boundary. This is a reserved virtual address space for the
 * current process (obtained through a malloc call). In no way this means
 * that the memory arenas will be used entirely. A malloc(<Big>) is usually
 * an address range reservation for <Big> bytes, unless all pages within this
 * space are referenced subsequently. So malloc'ing big blocks and not using
 * them does not mean "wasting memory". It's an addressable range wastage...
 *
 * Therefore, allocating arenas with malloc is not optimal, because there is
 * some address space wastage, but this is the most portable way to request
 * memory from the system across various platforms.
 */
#define ARENA_SIZE		(256 << 10)	/* 256KB */

#ifdef WITH_MEMORY_LIMITS
#define MAX_ARENAS		(SMALL_MEMORY_LIMIT / ARENA_SIZE)
#endif

/*
 * Size of the pools used for small blocks. Should be a power of 2,
 * between 1K and SYSTEM_PAGE_SIZE, that is: 1k, 2k, 4k.
 */
#define POOL_SIZE		SYSTEM_PAGE_SIZE	/* must be 2^N */
#define POOL_SIZE_MASK		SYSTEM_PAGE_SIZE_MASK

/*
 * -- End of tunable settings section --
 */

/*==========================================================================*/

/*
 * Locking
 *
 * To reduce lock contention, it would probably be better to refine the
 * crude function locking with per size class locking. I'm not positive
 * however, whether it's worth switching to such locking policy because
 * of the performance penalty it might introduce.
 *
 * The following macros describe the simplest (should also be the fastest)
 * lock object on a particular platform and the init/fini/lock/unlock
 * operations on it. The locks defined here are not expected to be recursive
 * because it is assumed that they will always be called in the order:
 * INIT, [LOCK, UNLOCK]*, FINI.
 */

/*
 * Python's threads are serialized, so object malloc locking is disabled.
 */
#define SIMPLELOCK_DECL(lock)	/* simple lock declaration		*/
#define SIMPLELOCK_INIT(lock)	/* allocate (if needed) and initialize	*/
#define SIMPLELOCK_FINI(lock)	/* free/destroy an existing lock 	*/
#define SIMPLELOCK_LOCK(lock)	/* acquire released lock */
#define SIMPLELOCK_UNLOCK(lock)	/* release acquired lock */

/*
 * Basic types
 * I don't care if these are defined in <sys/types.h> or elsewhere. Axiom.
 */
#undef  uchar
#define uchar			unsigned char	/* assuming == 8 bits  */

#undef  uint
#define uint			unsigned int	/* assuming >= 16 bits */

#undef  ulong
#define ulong			unsigned long	/* assuming >= 32 bits */

#undef uptr
#define uptr			Py_uintptr_t

/* When you say memory, my mind reasons in terms of (pointers to) blocks */
typedef uchar block;

/* Pool for small blocks. */
struct pool_header {
	union { block *_padding;
		uint count; } ref;	/* number of allocated blocks    */
	block *freeblock;		/* pool's free list head         */
	struct pool_header *nextpool;	/* next pool of this size class  */
	struct pool_header *prevpool;	/* previous pool       ""        */
	uint arenaindex;		/* index into arenas of base adr */
	uint szidx;			/* block size class index	 */
	uint nextoffset;		/* bytes to virgin block	 */
	uint maxnextoffset;		/* largest valid nextoffset	 */
};

typedef struct pool_header *poolp;

#undef  ROUNDUP
#define ROUNDUP(x)		(((x) + ALIGNMENT_MASK) & ~ALIGNMENT_MASK)
#define POOL_OVERHEAD		ROUNDUP(sizeof(struct pool_header))

#define DUMMY_SIZE_IDX		0xffff	/* size class of newly cached pools */

/* Round pointer P down to the closest pool-aligned address <= P, as a poolp */
#define POOL_ADDR(P) ((poolp)((uptr)(P) & ~(uptr)POOL_SIZE_MASK))

/* Return total number of blocks in pool of size index I, as a uint. */
#define NUMBLOCKS(I) ((uint)(POOL_SIZE - POOL_OVERHEAD) / INDEX2SIZE(I))

/*==========================================================================*/

/*
 * This malloc lock
 */
SIMPLELOCK_DECL(_malloc_lock)
#define LOCK()		SIMPLELOCK_LOCK(_malloc_lock)
#define UNLOCK()	SIMPLELOCK_UNLOCK(_malloc_lock)
#define LOCK_INIT()	SIMPLELOCK_INIT(_malloc_lock)
#define LOCK_FINI()	SIMPLELOCK_FINI(_malloc_lock)

/*
 * Pool table -- headed, circular, doubly-linked lists of partially used pools.

This is involved.  For an index i, usedpools[i+i] is the header for a list of
all partially used pools holding small blocks with "size class idx" i. So
usedpools[0] corresponds to blocks of size 8, usedpools[2] to blocks of size
16, and so on:  index 2*i <-> blocks of size (i+1)<<ALIGNMENT_SHIFT.

Pools are carved off the current arena highwater mark (file static arenabase)
as needed.  Once carved off, a pool is in one of three states forever after:

used == partially used, neither empty nor full
    At least one block in the pool is currently allocated, and at least one
    block in the pool is not currently allocated (note this implies a pool
    has room for at least two blocks).
    This is a pool's initial state, as a pool is created only when malloc
    needs space.
    The pool holds blocks of a fixed size, and is in the circular list headed
    at usedpools[i] (see above).  It's linked to the other used pools of the
    same size class via the pool_header's nextpool and prevpool members.
    If all but one block is currently allocated, a malloc can cause a
    transition to the full state.  If all but one block is not currently
    allocated, a free can cause a transition to the empty state.

full == all the pool's blocks are currently allocated
    On transition to full, a pool is unlinked from its usedpools[] list.
    It's not linked to from anything then anymore, and its nextpool and
    prevpool members are meaningless until it transitions back to used.
    A free of a block in a full pool puts the pool back in the used state.
    Then it's linked in at the front of the appropriate usedpools[] list, so
    that the next allocation for its size class will reuse the freed block.

empty == all the pool's blocks are currently available for allocation
    On transition to empty, a pool is unlinked from its usedpools[] list,
    and linked to the front of the (file static) singly-linked freepools list,
    via its nextpool member.  The prevpool member has no meaning in this case.
    Empty pools have no inherent size class:  the next time a malloc finds
    an empty list in usedpools[], it takes the first pool off of freepools.
    If the size class needed happens to be the same as the size class the pool
    last had, some pool initialization can be skipped.


Block Management

Blocks within pools are again carved out as needed.  pool->freeblock points to
the start of a singly-linked list of free blocks within the pool.  When a
block is freed, it's inserted at the front of its pool's freeblock list.  Note
that the available blocks in a pool are *not* linked all together when a pool
is initialized.  Instead only "the first two" (lowest addresses) blocks are
set up, returning the first such block, and setting pool->freeblock to a
one-block list holding the second such block.  This is consistent with that
pymalloc strives at all levels (arena, pool, and block) never to touch a piece
of memory until it's actually needed.

So long as a pool is in the used state, we're certain there *is* a block
available for allocating, and pool->freeblock is not NULL.  If pool->freeblock
points to the end of the free list before we've carved the entire pool into
blocks, that means we simply haven't yet gotten to one of the higher-address
blocks.  The offset from the pool_header to the start of "the next" virgin
block is stored in the pool_header nextoffset member, and the largest value
of nextoffset that makes sense is stored in the maxnextoffset member when a
pool is initialized.  All the blocks in a pool have been passed out at least
once when and only when nextoffset > maxnextoffset.


Major obscurity:  While the usedpools vector is declared to have poolp
entries, it doesn't really.  It really contains two pointers per (conceptual)
poolp entry, the nextpool and prevpool members of a pool_header.  The
excruciating initialization code below fools C so that

    usedpool[i+i]

"acts like" a genuine poolp, but only so long as you only reference its
nextpool and prevpool members.  The "- 2*sizeof(block *)" gibberish is
compensating for that a pool_header's nextpool and prevpool members
immediately follow a pool_header's first two members:

	union { block *_padding;
		uint count; } ref;
	block *freeblock;

each of which consume sizeof(block *) bytes.  So what usedpools[i+i] really
contains is a fudged-up pointer p such that *if* C believes it's a poolp
pointer, then p->nextpool and p->prevpool are both p (meaning that the headed
circular list is empty).

It's unclear why the usedpools setup is so convoluted.  It could be to
minimize the amount of cache required to hold this heavily-referenced table
(which only *needs* the two interpool pointer members of a pool_header). OTOH,
referencing code has to remember to "double the index" and doing so isn't
free, usedpools[0] isn't a strictly legal pointer, and we're crucially relying
on that C doesn't insert any padding anywhere in a pool_header at or before
the prevpool member.
**************************************************************************** */

#define PTA(x)	((poolp )((uchar *)&(usedpools[2*(x)]) - 2*sizeof(block *)))
#define PT(x)	PTA(x), PTA(x)

static poolp usedpools[2 * ((NB_SMALL_SIZE_CLASSES + 7) / 8) * 8] = {
	PT(0), PT(1), PT(2), PT(3), PT(4), PT(5), PT(6), PT(7)
#if NB_SMALL_SIZE_CLASSES > 8
	, PT(8), PT(9), PT(10), PT(11), PT(12), PT(13), PT(14), PT(15)
#if NB_SMALL_SIZE_CLASSES > 16
	, PT(16), PT(17), PT(18), PT(19), PT(20), PT(21), PT(22), PT(23)
#if NB_SMALL_SIZE_CLASSES > 24
	, PT(24), PT(25), PT(26), PT(27), PT(28), PT(29), PT(30), PT(31)
#if NB_SMALL_SIZE_CLASSES > 32
	, PT(32), PT(33), PT(34), PT(35), PT(36), PT(37), PT(38), PT(39)
#if NB_SMALL_SIZE_CLASSES > 40
	, PT(40), PT(41), PT(42), PT(43), PT(44), PT(45), PT(46), PT(47)
#if NB_SMALL_SIZE_CLASSES > 48
	, PT(48), PT(49), PT(50), PT(51), PT(52), PT(53), PT(54), PT(55)
#if NB_SMALL_SIZE_CLASSES > 56
	, PT(56), PT(57), PT(58), PT(59), PT(60), PT(61), PT(62), PT(63)
#endif /* NB_SMALL_SIZE_CLASSES > 56 */
#endif /* NB_SMALL_SIZE_CLASSES > 48 */
#endif /* NB_SMALL_SIZE_CLASSES > 40 */
#endif /* NB_SMALL_SIZE_CLASSES > 32 */
#endif /* NB_SMALL_SIZE_CLASSES > 24 */
#endif /* NB_SMALL_SIZE_CLASSES > 16 */
#endif /* NB_SMALL_SIZE_CLASSES >  8 */
};

/*
 * Free (cached) pools
 */
static poolp freepools = NULL;		/* free list for cached pools */

/*==========================================================================*/
/* Arena management. */

/* arenas is a vector of arena base addresses, in order of allocation time.
 * arenas currently contains narenas entries, and has space allocated
 * for at most maxarenas entries.
 *
 * CAUTION:  See the long comment block about thread safety in new_arena():
 * the code currently relies in deep ways on that this vector only grows,
 * and only grows by appending at the end.  For now we never return an arena
 * to the OS.
 */
static uptr *volatile arenas = NULL;	/* the pointer itself is volatile */
static volatile uint narenas = 0;
static uint maxarenas = 0;

/* Number of pools still available to be allocated in the current arena. */
static uint nfreepools = 0;

/* Free space start address in current arena.  This is pool-aligned. */
static block *arenabase = NULL;

/* Allocate a new arena and return its base address.  If we run out of
 * memory, return NULL.
 */
static block *
new_arena(void)
{
	uint excess;	/* number of bytes above pool alignment */
	block *bp = (block *)malloc(ARENA_SIZE);
	if (bp == NULL)
		return NULL;

#ifdef PYMALLOC_DEBUG
	if (Py_GETENV("PYTHONMALLOCSTATS"))
		_PyObject_DebugMallocStats();
#endif

	/* arenabase <- first pool-aligned address in the arena
	   nfreepools <- number of whole pools that fit after alignment */
	arenabase = bp;
	nfreepools = ARENA_SIZE / POOL_SIZE;
	assert(POOL_SIZE * nfreepools == ARENA_SIZE);
	excess = (uint) ((Py_uintptr_t)bp & POOL_SIZE_MASK);
	if (excess != 0) {
		--nfreepools;
		arenabase += POOL_SIZE - excess;
	}

	/* Make room for a new entry in the arenas vector. */
	if (arenas == NULL) {
		assert(narenas == 0 && maxarenas == 0);
		arenas = (uptr *)malloc(16 * sizeof(*arenas));
		if (arenas == NULL)
			goto error;
		maxarenas = 16;
	}
	else if (narenas == maxarenas) {
		/* Grow arenas.
		 *
		 * Exceedingly subtle:  Someone may be calling the pymalloc
		 * free via PyMem_{DEL, Del, FREE, Free} without holding the
		 *.GIL.  Someone else may simultaneously be calling the
		 * pymalloc malloc while holding the GIL via, e.g.,
		 * PyObject_New.  Now the pymalloc free may index into arenas
		 * for an address check, while the pymalloc malloc calls
		 * new_arena and we end up here to grow a new arena *and*
		 * grow the arenas vector.  If the value for arenas pymalloc
		 * free picks up "vanishes" during this resize, anything may
		 * happen, and it would be an incredibly rare bug.  Therefore
		 * the code here takes great pains to make sure that, at every
		 * moment, arenas always points to an intact vector of
		 * addresses.  It doesn't matter whether arenas points to a
		 * wholly up-to-date vector when pymalloc free checks it in
		 * this case, because the only legal (and that even this is
		 * legal is debatable) way to call PyMem_{Del, etc} while not
		 * holding the GIL is if the memory being released is not
		 * object memory, i.e. if the address check in pymalloc free
		 * is supposed to fail.  Having an incomplete vector can't
		 * make a supposed-to-fail case succeed by mistake (it could
		 * only make a supposed-to-succeed case fail by mistake).
		 *
		 * In addition, without a lock we can't know for sure when
		 * an old vector is no longer referenced, so we simply let
		 * old vectors leak.
		 *
		 * And on top of that, since narenas and arenas can't be
		 * changed as-a-pair atomically without a lock, we're also
		 * careful to declare them volatile and ensure that we change
		 * arenas first.  This prevents another thread from picking
		 * up an narenas value too large for the arenas value it
		 * reads up (arenas never shrinks).
		 *
		 * Read the above 50 times before changing anything in this
		 * block.
		 */
		uptr *p;
		uint newmax = maxarenas << 1;
		if (newmax <= maxarenas)	/* overflow */
			goto error;
		p = (uptr *)malloc(newmax * sizeof(*arenas));
		if (p == NULL)
			goto error;
		memcpy(p, arenas, narenas * sizeof(*arenas));
		arenas = p;	/* old arenas deliberately leaked */
		maxarenas = newmax;
	}

	/* Append the new arena address to arenas. */
	assert(narenas < maxarenas);
	arenas[narenas] = (uptr)bp;
	++narenas;	/* can't overflow, since narenas < maxarenas before */
	return bp;

error:
	free(bp);
	nfreepools = 0;
	return NULL;
}

/* Return true if and only if P is an address that was allocated by
 * pymalloc.  I must be the index into arenas that the address claims
 * to come from.
 *
 * Tricky:  Letting B be the arena base address in arenas[I], P belongs to the
 * arena if and only if
 *	B <= P < B + ARENA_SIZE
 * Subtracting B throughout, this is true iff
 *	0 <= P-B < ARENA_SIZE
 * By using unsigned arithmetic, the "0 <=" half of the test can be skipped.
 *
 * Obscure:  A PyMem "free memory" function can call the pymalloc free or
 * realloc before the first arena has been allocated.  arenas is still
 * NULL in that case.  We're relying on that narenas is also 0 in that case,
 * so the (I) < narenas must be false, saving us from trying to index into
 * a NULL arenas.
 */
#define ADDRESS_IN_RANGE(P, I) \
	((I) < narenas && (uptr)(P) - arenas[I] < (uptr)ARENA_SIZE)

/*==========================================================================*/

/* malloc.  Note that nbytes==0 tries to return a non-NULL pointer, distinct
 * from all other currently live pointers.  This may not be possible.
 */

/*
 * The basic blocks are ordered by decreasing execution frequency,
 * which minimizes the number of jumps in the most common cases,
 * improves branching prediction and instruction scheduling (small
 * block allocations typically result in a couple of instructions).
 * Unless the optimizer reorders everything, being too smart...
 */

#undef PyObject_Malloc
void *
PyObject_Malloc(size_t nbytes)
{
	block *bp;
	poolp pool;
	poolp next;
	uint size;

	/*
	 * This implicitly redirects malloc(0).
	 */
	if ((nbytes - 1) < SMALL_REQUEST_THRESHOLD) {
		LOCK();
		/*
		 * Most frequent paths first
		 */
		size = (uint )(nbytes - 1) >> ALIGNMENT_SHIFT;
		pool = usedpools[size + size];
		if (pool != pool->nextpool) {
			/*
			 * There is a used pool for this size class.
			 * Pick up the head block of its free list.
			 */
			++pool->ref.count;
			bp = pool->freeblock;
			assert(bp != NULL);
			if ((pool->freeblock = *(block **)bp) != NULL) {
				UNLOCK();
				return (void *)bp;
			}
			/*
			 * Reached the end of the free list, try to extend it
			 */
			if (pool->nextoffset <= pool->maxnextoffset) {
				/*
				 * There is room for another block
				 */
				pool->freeblock = (block *)pool +
						  pool->nextoffset;
				pool->nextoffset += INDEX2SIZE(size);
				*(block **)(pool->freeblock) = NULL;
				UNLOCK();
				return (void *)bp;
			}
			/*
			 * Pool is full, unlink from used pools
			 */
			next = pool->nextpool;
			pool = pool->prevpool;
			next->prevpool = pool;
			pool->nextpool = next;
			UNLOCK();
			return (void *)bp;
		}
		/*
		 * Try to get a cached free pool
		 */
		pool = freepools;
		if (pool != NULL) {
			/*
			 * Unlink from cached pools
			 */
			freepools = pool->nextpool;
		init_pool:
			/*
			 * Frontlink to used pools
			 */
			next = usedpools[size + size]; /* == prev */
			pool->nextpool = next;
			pool->prevpool = next;
			next->nextpool = pool;
			next->prevpool = pool;
			pool->ref.count = 1;
			if (pool->szidx == size) {
				/*
				 * Luckily, this pool last contained blocks
				 * of the same size class, so its header
				 * and free list are already initialized.
				 */
				bp = pool->freeblock;
				pool->freeblock = *(block **)bp;
				UNLOCK();
				return (void *)bp;
			}
			/*
			 * Initialize the pool header, set up the free list to
			 * contain just the second block, and return the first
			 * block.
			 */
			pool->szidx = size;
			size = INDEX2SIZE(size);
			bp = (block *)pool + POOL_OVERHEAD;
			pool->nextoffset = POOL_OVERHEAD + (size << 1);
			pool->maxnextoffset = POOL_SIZE - size;
			pool->freeblock = bp + size;
			*(block **)(pool->freeblock) = NULL;
			UNLOCK();
			return (void *)bp;
		}
		/*
		 * Allocate new pool
		 */
		if (nfreepools) {
		commit_pool:
			--nfreepools;
			pool = (poolp)arenabase;
			arenabase += POOL_SIZE;
			pool->arenaindex = narenas - 1;
			pool->szidx = DUMMY_SIZE_IDX;
			goto init_pool;
		}
		/*
		 * Allocate new arena
		 */
#ifdef WITH_MEMORY_LIMITS
		if (!(narenas < MAX_ARENAS)) {
			UNLOCK();
			goto redirect;
		}
#endif
		bp = new_arena();
		if (bp != NULL)
			goto commit_pool;
		UNLOCK();
		goto redirect;
	}

        /* The small block allocator ends here. */

redirect:
	/*
	 * Redirect the original request to the underlying (libc) allocator.
	 * We jump here on bigger requests, on error in the code above (as a
	 * last chance to serve the request) or when the max memory limit
	 * has been reached.
	 */
	if (nbytes == 0)
		nbytes = 1;
	return (void *)malloc(nbytes);
}

/* free */

#undef PyObject_Free
void
PyObject_Free(void *p)
{
	poolp pool;
	block *lastfree;
	poolp next, prev;
	uint size;

	if (p == NULL)	/* free(NULL) has no effect */
		return;

	pool = POOL_ADDR(p);
	if (ADDRESS_IN_RANGE(p, pool->arenaindex)) {
		/* We allocated this address. */
		LOCK();
		/*
		 * Link p to the start of the pool's freeblock list.  Since
		 * the pool had at least the p block outstanding, the pool
		 * wasn't empty (so it's already in a usedpools[] list, or
		 * was full and is in no list -- it's not in the freeblocks
		 * list in any case).
		 */
		assert(pool->ref.count > 0);	/* else it was empty */
		*(block **)p = lastfree = pool->freeblock;
		pool->freeblock = (block *)p;
		if (lastfree) {
			/*
			 * freeblock wasn't NULL, so the pool wasn't full,
			 * and the pool is in a usedpools[] list.
			 */
			if (--pool->ref.count != 0) {
				/* pool isn't empty:  leave it in usedpools */
				UNLOCK();
				return;
			}
			/*
			 * Pool is now empty:  unlink from usedpools, and
			 * link to the front of freepools.  This ensures that
			 * previously freed pools will be allocated later
			 * (being not referenced, they are perhaps paged out).
			 */
			next = pool->nextpool;
			prev = pool->prevpool;
			next->prevpool = prev;
			prev->nextpool = next;
			/* Link to freepools.  This is a singly-linked list,
			 * and pool->prevpool isn't used there.
			 */
			pool->nextpool = freepools;
			freepools = pool;
			UNLOCK();
			return;
		}
		/*
		 * Pool was full, so doesn't currently live in any list:
		 * link it to the front of the appropriate usedpools[] list.
		 * This mimics LRU pool usage for new allocations and
		 * targets optimal filling when several pools contain
		 * blocks of the same size class.
		 */
		--pool->ref.count;
		assert(pool->ref.count > 0);	/* else the pool is empty */
		size = pool->szidx;
		next = usedpools[size + size];
		prev = next->prevpool;
		/* insert pool before next:   prev <-> pool <-> next */
		pool->nextpool = next;
		pool->prevpool = prev;
		next->prevpool = pool;
		prev->nextpool = pool;
		UNLOCK();
		return;
	}

	/* We didn't allocate this address. */
	free(p);
}

/* realloc.  If p is NULL, this acts like malloc(nbytes).  Else if nbytes==0,
 * then as the Python docs promise, we do not treat this like free(p), and
 * return a non-NULL result.
 */

#undef PyObject_Realloc
void *
PyObject_Realloc(void *p, size_t nbytes)
{
	void *bp;
	poolp pool;
	uint size;

	if (p == NULL)
		return PyObject_Malloc(nbytes);

	pool = POOL_ADDR(p);
	if (ADDRESS_IN_RANGE(p, pool->arenaindex)) {
		/* We're in charge of this block */
		size = INDEX2SIZE(pool->szidx);
		if (nbytes <= size) {
			/* The block is staying the same or shrinking.  If
			 * it's shrinking, there's a tradeoff:  it costs
			 * cycles to copy the block to a smaller size class,
			 * but it wastes memory not to copy it.  The
			 * compromise here is to copy on shrink only if at
			 * least 25% of size can be shaved off.
			 */
			if (4 * nbytes > 3 * size) {
				/* It's the same,
				 * or shrinking and new/old > 3/4.
				 */
				return p;
			}
			size = nbytes;
		}
		bp = PyObject_Malloc(nbytes);
		if (bp != NULL) {
			memcpy(bp, p, size);
			PyObject_Free(p);
		}
		return bp;
	}
	/* We're not managing this block. */
	if (nbytes <= SMALL_REQUEST_THRESHOLD) {
		/* Take over this block -- ask for at least one byte so
		 * we really do take it over (PyObject_Malloc(0) goes to
		 * the system malloc).
		 */
		bp = PyObject_Malloc(nbytes ? nbytes : 1);
		if (bp != NULL) {
			memcpy(bp, p, nbytes);
			free(p);
		}
		else if (nbytes == 0) {
			/* Meet the doc's promise that nbytes==0 will
			 * never return a NULL pointer when p isn't NULL.
			 */
			bp = p;
		}

	}
	else {
		assert(nbytes != 0);
		bp = realloc(p, nbytes);
	}
	return bp;
}

#else	/* ! WITH_PYMALLOC */

/*==========================================================================*/
/* pymalloc not enabled:  Redirect the entry points to malloc.  These will
 * only be used by extensions that are compiled with pymalloc enabled. */

void *
PyObject_Malloc(size_t n)
{
	return PyMem_MALLOC(n);
}

void *
PyObject_Realloc(void *p, size_t n)
{
	return PyMem_REALLOC(p, n);
}

void
PyObject_Free(void *p)
{
	PyMem_FREE(p);
}
#endif /* WITH_PYMALLOC */

#ifdef PYMALLOC_DEBUG
/*==========================================================================*/
/* A x-platform debugging allocator.  This doesn't manage memory directly,
 * it wraps a real allocator, adding extra debugging info to the memory blocks.
 */

/* Special bytes broadcast into debug memory blocks at appropriate times.
 * Strings of these are unlikely to be valid addresses, floats, ints or
 * 7-bit ASCII.
 */
#undef CLEANBYTE
#undef DEADBYTE
#undef FORBIDDENBYTE
#define CLEANBYTE      0xCB    /* clean (newly allocated) memory */
#define DEADBYTE       0xDB    /* dead (newly freed) memory */
#define FORBIDDENBYTE  0xFB    /* untouchable bytes at each end of a block */

static ulong serialno = 0;	/* incremented on each debug {m,re}alloc */

/* serialno is always incremented via calling this routine.  The point is
   to supply a single place to set a breakpoint.
*/
static void
bumpserialno(void)
{
	++serialno;
}


/* Read 4 bytes at p as a big-endian ulong. */
static ulong
read4(const void *p)
{
	const uchar *q = (const uchar *)p;
	return ((ulong)q[0] << 24) |
	       ((ulong)q[1] << 16) |
	       ((ulong)q[2] <<  8) |
	        (ulong)q[3];
}

/* Write the 4 least-significant bytes of n as a big-endian unsigned int,
   MSB at address p, LSB at p+3. */
static void
write4(void *p, ulong n)
{
	uchar *q = (uchar *)p;
	q[0] = (uchar)((n >> 24) & 0xff);
	q[1] = (uchar)((n >> 16) & 0xff);
	q[2] = (uchar)((n >>  8) & 0xff);
	q[3] = (uchar)( n        & 0xff);
}

#ifdef Py_DEBUG
/* Is target in the list?  The list is traversed via the nextpool pointers.
 * The list may be NULL-terminated, or circular.  Return 1 if target is in
 * list, else 0.
 */
static int
pool_is_in_list(const poolp target, poolp list)
{
	poolp origlist = list;
	assert(target != NULL);
	if (list == NULL)
		return 0;
	do {
		if (target == list)
			return 1;
		list = list->nextpool;
	} while (list != NULL && list != origlist);
	return 0;
}

#else
#define pool_is_in_list(X, Y) 1

#endif	/* Py_DEBUG */

/* The debug malloc asks for 16 extra bytes and fills them with useful stuff,
   here calling the underlying malloc's result p:

p[0:4]
    Number of bytes originally asked for.  4-byte unsigned integer,
    big-endian (easier to read in a memory dump).
p[4:8]
    Copies of FORBIDDENBYTE.  Used to catch under- writes and reads.
p[8:8+n]
    The requested memory, filled with copies of CLEANBYTE.
    Used to catch reference to uninitialized memory.
    &p[8] is returned.  Note that this is 8-byte aligned if pymalloc
    handled the request itself.
p[8+n:8+n+4]
    Copies of FORBIDDENBYTE.  Used to catch over- writes and reads.
p[8+n+4:8+n+8]
    A serial number, incremented by 1 on each call to _PyObject_DebugMalloc
    and _PyObject_DebugRealloc.
    4-byte unsigned integer, big-endian.
    If "bad memory" is detected later, the serial number gives an
    excellent way to set a breakpoint on the next run, to capture the
    instant at which this block was passed out.
*/

void *
_PyObject_DebugMalloc(size_t nbytes)
{
	uchar *p;	/* base address of malloc'ed block */
	uchar *tail;	/* p + 8 + nbytes == pointer to tail pad bytes */
	size_t total;	/* nbytes + 16 */

	bumpserialno();
	total = nbytes + 16;
	if (total < nbytes || (total >> 31) > 1) {
		/* overflow, or we can't represent it in 4 bytes */
		/* Obscure:  can't do (total >> 32) != 0 instead, because
		   C doesn't define what happens for a right-shift of 32
		   when size_t is a 32-bit type.  At least C guarantees
		   size_t is an unsigned type. */
		return NULL;
	}

	p = (uchar *)PyObject_Malloc(total);
	if (p == NULL)
		return NULL;

	write4(p, nbytes);
	p[4] = p[5] = p[6] = p[7] = FORBIDDENBYTE;

	if (nbytes > 0)
		memset(p+8, CLEANBYTE, nbytes);

	tail = p + 8 + nbytes;
	tail[0] = tail[1] = tail[2] = tail[3] = FORBIDDENBYTE;
	write4(tail + 4, serialno);

	return p+8;
}

/* The debug free first checks the 8 bytes on each end for sanity (in
   particular, that the FORBIDDENBYTEs are still intact).
   Then fills the original bytes with DEADBYTE.
   Then calls the underlying free.
*/
void
_PyObject_DebugFree(void *p)
{
	uchar *q = (uchar *)p;
	size_t nbytes;

	if (p == NULL)
		return;
	_PyObject_DebugCheckAddress(p);
	nbytes = read4(q-8);
	if (nbytes > 0)
		memset(q, DEADBYTE, nbytes);
	PyObject_Free(q-8);
}

void *
_PyObject_DebugRealloc(void *p, size_t nbytes)
{
	uchar *q = (uchar *)p;
	uchar *tail;
	size_t total;	/* nbytes + 16 */
	size_t original_nbytes;

	if (p == NULL)
		return _PyObject_DebugMalloc(nbytes);

	_PyObject_DebugCheckAddress(p);
	bumpserialno();
	original_nbytes = read4(q-8);
	total = nbytes + 16;
	if (total < nbytes || (total >> 31) > 1) {
		/* overflow, or we can't represent it in 4 bytes */
		return NULL;
	}

	if (nbytes < original_nbytes) {
		/* shrinking:  mark old extra memory dead */
		memset(q + nbytes, DEADBYTE, original_nbytes - nbytes);
	}

	/* Resize and add decorations. */
	q = (uchar *)PyObject_Realloc(q-8, total);
	if (q == NULL)
		return NULL;

	write4(q, nbytes);
	assert(q[4] == FORBIDDENBYTE &&
	       q[5] == FORBIDDENBYTE &&
	       q[6] == FORBIDDENBYTE &&
	       q[7] == FORBIDDENBYTE);
	q += 8;
	tail = q + nbytes;
	tail[0] = tail[1] = tail[2] = tail[3] = FORBIDDENBYTE;
	write4(tail + 4, serialno);

	if (nbytes > original_nbytes) {
		/* growing:  mark new extra memory clean */
		memset(q + original_nbytes, CLEANBYTE,
			nbytes - original_nbytes);
	}

	return q;
}

/* Check the forbidden bytes on both ends of the memory allocated for p.
 * If anything is wrong, print info to stderr via _PyObject_DebugDumpAddress,
 * and call Py_FatalError to kill the program.
 */
 void
_PyObject_DebugCheckAddress(const void *p)
{
	const uchar *q = (const uchar *)p;
	char *msg;
	ulong nbytes;
	const uchar *tail;
	int i;

	if (p == NULL) {
		msg = "didn't expect a NULL pointer";
		goto error;
	}

	/* Check the stuff at the start of p first:  if there's underwrite
	 * corruption, the number-of-bytes field may be nuts, and checking
	 * the tail could lead to a segfault then.
	 */
	for (i = 4; i >= 1; --i) {
		if (*(q-i) != FORBIDDENBYTE) {
			msg = "bad leading pad byte";
			goto error;
		}
	}

	nbytes = read4(q-8);
	tail = q + nbytes;
	for (i = 0; i < 4; ++i) {
		if (tail[i] != FORBIDDENBYTE) {
			msg = "bad trailing pad byte";
			goto error;
		}
	}

	return;

error:
	_PyObject_DebugDumpAddress(p);
	Py_FatalError(msg);
}

/* Display info to stderr about the memory block at p. */
void
_PyObject_DebugDumpAddress(const void *p)
{
	const uchar *q = (const uchar *)p;
	const uchar *tail;
	ulong nbytes, serial;
	int i;

	fprintf(stderr, "Debug memory block at address p=%p:\n", p);
	if (p == NULL)
		return;

	nbytes = read4(q-8);
	fprintf(stderr, "    %lu bytes originally requested\n", nbytes);

	/* In case this is nuts, check the leading pad bytes first. */
	fputs("    The 4 pad bytes at p-4 are ", stderr);
	if (*(q-4) == FORBIDDENBYTE &&
	    *(q-3) == FORBIDDENBYTE &&
	    *(q-2) == FORBIDDENBYTE &&
	    *(q-1) == FORBIDDENBYTE) {
		fputs("FORBIDDENBYTE, as expected.\n", stderr);
	}
	else {
		fprintf(stderr, "not all FORBIDDENBYTE (0x%02x):\n",
			FORBIDDENBYTE);
		for (i = 4; i >= 1; --i) {
			const uchar byte = *(q-i);
			fprintf(stderr, "        at p-%d: 0x%02x", i, byte);
			if (byte != FORBIDDENBYTE)
				fputs(" *** OUCH", stderr);
			fputc('\n', stderr);
		}

		fputs("    Because memory is corrupted at the start, the "
		      "count of bytes requested\n"
		      "       may be bogus, and checking the trailing pad "
		      "bytes may segfault.\n", stderr);
	}

	tail = q + nbytes;
	fprintf(stderr, "    The 4 pad bytes at tail=%p are ", tail);
	if (tail[0] == FORBIDDENBYTE &&
	    tail[1] == FORBIDDENBYTE &&
	    tail[2] == FORBIDDENBYTE &&
	    tail[3] == FORBIDDENBYTE) {
		fputs("FORBIDDENBYTE, as expected.\n", stderr);
	}
	else {
		fprintf(stderr, "not all FORBIDDENBYTE (0x%02x):\n",
			FORBIDDENBYTE);
		for (i = 0; i < 4; ++i) {
			const uchar byte = tail[i];
			fprintf(stderr, "        at tail+%d: 0x%02x",
				i, byte);
			if (byte != FORBIDDENBYTE)
				fputs(" *** OUCH", stderr);
			fputc('\n', stderr);
		}
	}

	serial = read4(tail+4);
	fprintf(stderr, "    The block was made by call #%lu to "
	                "debug malloc/realloc.\n", serial);

	if (nbytes > 0) {
		int i = 0;
		fputs("    Data at p:", stderr);
		/* print up to 8 bytes at the start */
		while (q < tail && i < 8) {
			fprintf(stderr, " %02x", *q);
			++i;
			++q;
		}
		/* and up to 8 at the end */
		if (q < tail) {
			if (tail - q > 8) {
				fputs(" ...", stderr);
				q = tail - 8;
			}
			while (q < tail) {
				fprintf(stderr, " %02x", *q);
				++q;
			}
		}
		fputc('\n', stderr);
	}
}

static ulong
printone(const char* msg, ulong value)
{
	int i, k;
	char buf[100];
	ulong origvalue = value;

	fputs(msg, stderr);
	for (i = (int)strlen(msg); i < 35; ++i)
		fputc(' ', stderr);
	fputc('=', stderr);

	/* Write the value with commas. */
	i = 22;
	buf[i--] = '\0';
	buf[i--] = '\n';
	k = 3;
	do {
		ulong nextvalue = value / 10UL;
		uint digit = value - nextvalue * 10UL;
		value = nextvalue;
		buf[i--] = (char)(digit + '0');
		--k;
		if (k == 0 && value && i >= 0) {
			k = 3;
			buf[i--] = ',';
		}
	} while (value && i >= 0);

	while (i >= 0)
		buf[i--] = ' ';
	fputs(buf, stderr);

	return origvalue;
}

/* Print summary info to stderr about the state of pymalloc's structures.
 * In Py_DEBUG mode, also perform some expensive internal consistency
 * checks.
 */
void
_PyObject_DebugMallocStats(void)
{
	uint i;
	const uint numclasses = SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT;
	/* # of pools, allocated blocks, and free blocks per class index */
	ulong numpools[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
	ulong numblocks[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
	ulong numfreeblocks[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
	/* total # of allocated bytes in used and full pools */
	ulong allocated_bytes = 0;
	/* total # of available bytes in used pools */
	ulong available_bytes = 0;
	/* # of free pools + pools not yet carved out of current arena */
	uint numfreepools = 0;
	/* # of bytes for arena alignment padding */
	ulong arena_alignment = 0;
	/* # of bytes in used and full pools used for pool_headers */
	ulong pool_header_bytes = 0;
	/* # of bytes in used and full pools wasted due to quantization,
	 * i.e. the necessarily leftover space at the ends of used and
	 * full pools.
	 */
	ulong quantization = 0;
	/* running total -- should equal narenas * ARENA_SIZE */
	ulong total;
	char buf[128];

	fprintf(stderr, "Small block threshold = %d, in %u size classes.\n",
		SMALL_REQUEST_THRESHOLD, numclasses);

	for (i = 0; i < numclasses; ++i)
		numpools[i] = numblocks[i] = numfreeblocks[i] = 0;

	/* Because full pools aren't linked to from anything, it's easiest
	 * to march over all the arenas.  If we're lucky, most of the memory
	 * will be living in full pools -- would be a shame to miss them.
	 */
	for (i = 0; i < narenas; ++i) {
		uint poolsinarena;
		uint j;
		uptr base = arenas[i];

		/* round up to pool alignment */
		poolsinarena = ARENA_SIZE / POOL_SIZE;
		if (base & (uptr)POOL_SIZE_MASK) {
			--poolsinarena;
			arena_alignment += POOL_SIZE;
			base &= ~(uptr)POOL_SIZE_MASK;
			base += POOL_SIZE;
		}

		if (i == narenas - 1) {
			/* current arena may have raw memory at the end */
			numfreepools += nfreepools;
			poolsinarena -= nfreepools;
		}

		/* visit every pool in the arena */
		for (j = 0; j < poolsinarena; ++j, base += POOL_SIZE) {
			poolp p = (poolp)base;
			const uint sz = p->szidx;
			uint freeblocks;

			if (p->ref.count == 0) {
				/* currently unused */
				++numfreepools;
				assert(pool_is_in_list(p, freepools));
				continue;
			}
			++numpools[sz];
			numblocks[sz] += p->ref.count;
			freeblocks = NUMBLOCKS(sz) - p->ref.count;
			numfreeblocks[sz] += freeblocks;
#ifdef Py_DEBUG
			if (freeblocks > 0)
				assert(pool_is_in_list(p, usedpools[sz + sz]));
#endif
		}
	}

	fputc('\n', stderr);
	fputs("class   size   num pools   blocks in use  avail blocks\n"
	      "-----   ----   ---------   -------------  ------------\n",
		stderr);

	for (i = 0; i < numclasses; ++i) {
		ulong p = numpools[i];
		ulong b = numblocks[i];
		ulong f = numfreeblocks[i];
		uint size = INDEX2SIZE(i);
		if (p == 0) {
			assert(b == 0 && f == 0);
			continue;
		}
		fprintf(stderr, "%5u %6u %11lu %15lu %13lu\n",
			i, size, p, b, f);
		allocated_bytes += b * size;
		available_bytes += f * size;
		pool_header_bytes += p * POOL_OVERHEAD;
		quantization += p * ((POOL_SIZE - POOL_OVERHEAD) % size);
	}
	fputc('\n', stderr);
	(void)printone("# times object malloc called", serialno);

	PyOS_snprintf(buf, sizeof(buf),
		"%u arenas * %d bytes/arena", narenas, ARENA_SIZE);
	(void)printone(buf, (ulong)narenas * ARENA_SIZE);

	fputc('\n', stderr);

	total = printone("# bytes in allocated blocks", allocated_bytes);
	total += printone("# bytes in available blocks", available_bytes);

	PyOS_snprintf(buf, sizeof(buf),
		"%u unused pools * %d bytes", numfreepools, POOL_SIZE);
	total += printone(buf, (ulong)numfreepools * POOL_SIZE);

	total += printone("# bytes lost to pool headers", pool_header_bytes);
	total += printone("# bytes lost to quantization", quantization);
	total += printone("# bytes lost to arena alignment", arena_alignment);
	(void)printone("Total", total);
}

#endif	/* PYMALLOC_DEBUG */
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.