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
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
|
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <array>
#include <boost/intrusive_ptr.hpp>
#include <boost/optional.hpp>
#include <cstring>
#include <exception>
#include <iostream>
#include <memory>
#include <string.h>
#include <vector>
#include "mongo/platform/atomic_word.h"
#include "mongo/util/assert_util.h"
namespace mongo {
namespace ephemeral_for_test {
class merge_conflict_exception : std::exception {
virtual const char* what() const noexcept {
return "conflicting changes prevent successful merge";
}
};
struct Metrics {
AtomicWord<int64_t> totalMemory{0};
AtomicWord<int32_t> totalNodes{0};
AtomicWord<int32_t> totalChildren{0};
void addMemory(size_t size) {
totalMemory.fetchAndAdd(size);
}
void subtractMemory(size_t size) {
totalMemory.fetchAndSubtract(size);
}
};
enum class NodeType : uint8_t { LEAF, NODE4, NODE16, NODE48, NODE256 };
/**
* RadixStore is a Trie data structure with the ability to share nodes among copies of trees to
* minimize data duplication. Each node has a notion of ownership and if modifications are made to
* non-uniquely owned nodes, they are copied to prevent dirtying the data for the other owners of
* the node.
*/
template <class Key, class T>
class RadixStore {
class Node;
class Head;
friend class RadixStoreTest;
public:
using mapped_type = T;
using value_type = std::pair<const Key, mapped_type>;
using allocator_type = std::allocator<value_type>;
using pointer = typename std::allocator_traits<allocator_type>::pointer;
using const_pointer = typename std::allocator_traits<allocator_type>::const_pointer;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using uint8_t = std::uint8_t;
using node_ptr = boost::intrusive_ptr<Node>;
using head_ptr = boost::intrusive_ptr<Head>;
static constexpr uint8_t maxByte = 255;
template <class pointer_type, class reference_type>
class radix_iterator {
friend class RadixStore;
public:
using iterator_category = std::forward_iterator_tag;
using value_type = typename RadixStore::value_type;
using difference_type = std::ptrdiff_t;
using pointer = pointer_type;
using reference = reference_type;
radix_iterator() : _root(nullptr), _current(nullptr) {}
~radix_iterator() {
updateTreeView(/*stopIfMultipleCursors=*/true);
}
radix_iterator(const radix_iterator& originalIterator) {
_root = originalIterator._root;
_current = originalIterator._current;
}
radix_iterator& operator=(const radix_iterator& originalIterator) {
if (this != &originalIterator) {
_root = originalIterator._root;
_current = originalIterator._current;
}
return *this;
}
radix_iterator& operator=(radix_iterator&& originalIterator) {
if (this != &originalIterator) {
_root = std::move(originalIterator._root);
_current = std::move(originalIterator._current);
}
return *this;
}
radix_iterator& operator++() {
repositionIfChanged();
_findNext();
return *this;
}
radix_iterator operator++(int) {
repositionIfChanged();
radix_iterator old = *this;
++*this;
return old;
}
bool operator==(const radix_iterator& other) {
repositionIfChanged();
return _current == other._current;
}
bool operator!=(const radix_iterator& other) {
repositionIfChanged();
return _current != other._current;
}
reference operator*() {
repositionIfChanged();
return *(_current->_data);
}
const_pointer operator->() {
repositionIfChanged();
return &*(_current->_data);
}
/**
* Attempts to restore the iterator on its former position in the updated tree if the tree
* has changed.
*
* If the former position has been erased, the iterator finds the next node. It is
* possible that no next node is available, so at that point the cursor is exhausted and
* points to the end.
*/
void repositionIfChanged() {
if (!_current || !_root->_nextVersion)
return;
invariant(_current->_data);
// Copy the key from _current before we move our _root reference.
auto key = _current->_data->first;
updateTreeView();
RadixStore store(*_root);
// Find the same or next node in the updated tree.
_current = store.lower_bound(key)._current;
}
private:
radix_iterator(const head_ptr& root) : _root(root), _current(nullptr) {}
radix_iterator(const head_ptr& root, Node* current) : _root(root), _current(current) {}
/**
* This function traverses the tree to find the next left-most node with data. Modifies
* '_current' to point to this node. It uses a pre-order traversal ('visit' the current
* node itself then 'visit' the child subtrees from left to right).
*/
void _findNext() {
// If 'current' is a nullptr there is no next node to go to.
if (_current == nullptr)
return;
// If 'current' is not a leaf, continue moving down and left in the tree until the next
// node.
if (!_current->isLeaf()) {
_traverseLeftSubtree();
return;
}
// Get path from root to '_current' since it is required to traverse up the tree.
const Key& key = _current->_data->first;
std::vector<Node*> context = RadixStore::_buildContext(key, _root.get());
// 'node' should equal '_current' because that should be the last element in the stack.
// Pop back once more to get access to its parent node. The parent node will enable
// traversal through the neighboring nodes, and if there are none, the iterator will
// move up the tree to continue searching for the next node with data.
Node* node = context.back();
context.pop_back();
// In case there is no next node, set _current to be 'nullptr' which will mark the end
// of the traversal.
_current = nullptr;
while (!context.empty()) {
uint8_t oldKey = node->_trieKey.front();
node = context.back();
context.pop_back();
// Check the children right of the node that the iterator was at already. This way,
// there will be no backtracking in the traversal.
bool res = _forEachChild(node, oldKey + 1, false, [this](node_ptr child) {
// If the current node has data, return it and exit. If not, find the
// left-most node with data in this sub-tree.
if (child->_data) {
_current = child.get();
return false;
}
_current = child.get();
_traverseLeftSubtree();
return false;
});
if (!res) {
return;
}
}
return;
}
void _traverseLeftSubtree() {
// This function finds the next left-most node with data under the sub-tree where
// '_current' is root. However, it cannot return the root, and hence at least 1
// iteration of the while loop is required.
do {
_forEachChild(_current, 0, false, [this](node_ptr child) {
_current = child.get();
return false;
});
} while (!_current->_data);
}
void updateTreeView(bool stopIfMultipleCursors = false) {
while (_root && _root->_nextVersion) {
if (stopIfMultipleCursors && _root->refCount() > 1)
return;
bool clearPreviousFlag = _root->refCount() == 1;
_root = _root->_nextVersion;
if (clearPreviousFlag)
_root->_hasPreviousVersion = false;
}
}
// "_root" is a pointer to the root of the tree over which this is iterating.
head_ptr _root;
// "_current" is the node that the iterator is currently on. _current->_data will never be
// boost::none (unless it is within the process of tree traversal), and _current will be
// become a nullptr once there are no more nodes left to iterate.
Node* _current;
};
using iterator = radix_iterator<pointer, value_type&>;
using const_iterator = radix_iterator<const_pointer, const value_type&>;
template <class pointer_type, class reference_type>
class reverse_radix_iterator {
friend class RadixStore;
friend class radix_iterator<pointer_type, reference_type&>;
public:
using value_type = typename RadixStore::value_type;
using difference_type = std::ptrdiff_t;
using pointer = pointer_type;
using reference = reference_type;
reverse_radix_iterator() : _root(nullptr), _current(nullptr) {}
reverse_radix_iterator(const const_iterator& it) : _root(it._root), _current(it._current) {
// If the iterator passed in is at the end(), then set _current to root which is
// equivalent to rbegin(). Otherwise, move the iterator back one node, due to the fact
// that the relationship &*r == &*(i-1) must be maintained for any reverse iterator 'r'
// and forward iterator 'i'.
if (_current == nullptr) {
// If the tree is empty, then leave '_current' as nullptr.
if (_root->isLeaf())
return;
_current = _root.get();
_traverseRightSubtree();
} else {
_findNextReverse();
}
}
reverse_radix_iterator(const iterator& it) : _root(it._root), _current(it._current) {
if (_current == nullptr) {
_current = _root;
_traverseRightSubtree();
} else {
_findNextReverse();
}
}
~reverse_radix_iterator() {
updateTreeView(/*stopIfMultipleCursors=*/true);
}
reverse_radix_iterator(const reverse_radix_iterator& originalIterator) {
_root = originalIterator._root;
_current = originalIterator._current;
}
reverse_radix_iterator& operator=(const reverse_radix_iterator& originalIterator) {
if (this != &originalIterator) {
_root = originalIterator._root;
_current = originalIterator._current;
}
return *this;
}
reverse_radix_iterator& operator=(reverse_radix_iterator&& originalIterator) {
if (this != &originalIterator) {
_root = std::move(originalIterator._root);
_current = std::move(originalIterator._current);
}
return *this;
}
reverse_radix_iterator& operator++() {
repositionIfChanged();
_findNextReverse();
return *this;
}
reverse_radix_iterator operator++(int) {
repositionIfChanged();
reverse_radix_iterator old = *this;
++*this;
return old;
}
bool operator==(const reverse_radix_iterator& other) {
repositionIfChanged();
return _current == other._current;
}
bool operator!=(const reverse_radix_iterator& other) {
repositionIfChanged();
return _current != other._current;
}
reference operator*() {
repositionIfChanged();
return *(_current->_data);
}
const_pointer operator->() {
repositionIfChanged();
return &*(_current->_data);
}
/**
* Attempts to restore the iterator on its former position in the updated tree if the tree
* has changed.
*
* If the former position has been erased, the iterator finds the next node. It is
* possible that no next node is available, so at that point the cursor is exhausted and
* points to the end.
*/
void repositionIfChanged() {
if (!_current || !_root->_nextVersion)
return;
invariant(_current->_data);
// Copy the key from _current before we move our _root reference.
auto key = _current->_data->first;
updateTreeView();
RadixStore store(*_root);
// Find the same or next node in the updated tree.
const_iterator it = store.lower_bound(key);
// Couldn't find any nodes with key greater than currentKey in lower_bound().
// So make _current point to the beginning, since rbegin() will point to the
// previous node before key.
if (!it._current)
_current = store.rbegin()._current;
else {
_current = it._current;
// lower_bound(), moved us one up in a forwards direction since the currentKey
// didn't exist anymore, move one back.
if (_current->_data->first > key)
_findNextReverse();
}
}
private:
reverse_radix_iterator(const head_ptr& root) : _root(root), _current(nullptr) {}
reverse_radix_iterator(const head_ptr& root, Node* current)
: _root(root), _current(current) {}
void _findNextReverse() {
// Reverse find iterates through the tree to find the "next" node containing data,
// searching from right to left. Normally a pre-order traversal is used, but for
// reverse, the ordering is to visit child nodes from right to left, then 'visit'
// current node.
if (_current == nullptr)
return;
const Key& key = _current->_data->first;
std::vector<Node*> context = RadixStore::_buildContext(key, _root.get());
Node* node = context.back();
context.pop_back();
// Due to the nature of the traversal, it will always be necessary to move up the tree
// first because when the 'current' node was visited, it meant all its children had been
// visited as well.
uint8_t oldKey;
_current = nullptr;
while (!context.empty()) {
oldKey = node->_trieKey.front();
node = context.back();
context.pop_back();
// After moving up in the tree, continue searching for neighboring nodes to see if
// they have data, moving from right to left.
bool res = _forEachChild(node, oldKey - 1, true, [this](node_ptr child) {
// If there is a sub-tree found, it must have data, therefore it's necessary
// to traverse to the right most node.
_current = child.get();
_traverseRightSubtree();
return false;
});
if (!res) {
return;
}
// If there were no sub-trees that contained data, and the 'current' node has data,
// it can now finally be 'visited'.
if (node->_data) {
_current = node;
return;
}
}
}
void _traverseRightSubtree() {
// This function traverses the given tree to the right most leaf of the subtree where
// 'current' is the root.
do {
_forEachChild(_current, maxByte, true, [this](node_ptr child) {
_current = child.get();
return false;
});
} while (!_current->isLeaf());
}
void updateTreeView(bool stopIfMultipleCursors = false) {
while (_root && _root->_nextVersion) {
if (stopIfMultipleCursors && _root->refCount() > 1)
return;
bool clearPreviousFlag = _root->refCount() == 1;
_root = _root->_nextVersion;
if (clearPreviousFlag)
_root->_hasPreviousVersion = false;
}
}
// "_root" is a pointer to the root of the tree over which this is iterating.
head_ptr _root;
// "_current" is a the node that the iterator is currently on. _current->_data will never be
// boost::none, and _current will be become a nullptr once there are no more nodes left to
// iterate.
Node* _current;
};
using reverse_iterator = reverse_radix_iterator<pointer, value_type&>;
using const_reverse_iterator = reverse_radix_iterator<const_pointer, const value_type&>;
// Constructors
RadixStore() : _root(make_intrusive_node<Head>()) {}
RadixStore(const RadixStore& other) : _root(make_intrusive_node<Head>(*(other._root))) {}
RadixStore(const Head& other) : _root(make_intrusive_node<Head>(other)) {}
RadixStore(RadixStore&& other) {
_root = std::move(other._root);
}
RadixStore& operator=(const RadixStore& other) {
if (this != &other) {
_root = make_intrusive_node<Head>(*(other._root));
}
return *this;
}
RadixStore& operator=(RadixStore&& other) {
if (this != &other) {
_root = std::move(other._root);
}
return *this;
}
// Equality
bool operator==(const RadixStore& other) const {
if (_root->_count != other._root->_count || _root->_dataSize != other._root->_dataSize)
return false;
RadixStore::const_iterator iter = this->begin();
RadixStore::const_iterator other_iter = other.begin();
while (iter != this->end()) {
if (other_iter == other.end() || *iter != *other_iter) {
return false;
}
iter++;
other_iter++;
}
return other_iter == other.end();
}
bool operator!=(const RadixStore& other) const {
return !(*this == other);
}
// Capacity
bool empty() const {
// Not relying on size() internally, as it may be updated late.
return _root->isLeaf() && !_root->_data;
}
size_type size() const {
return _root->_count;
}
size_type dataSize() const {
return _root->_dataSize;
}
bool hasBranch() const {
return _root->_nextVersion ? true : false;
}
// Metrics
static int64_t totalMemory() {
return _metrics.totalMemory.load();
}
static int32_t totalNodes() {
return _metrics.totalNodes.load();
}
static float averageChildren() {
auto totalNodes = _metrics.totalNodes.load();
return totalNodes ? _metrics.totalChildren.load() / static_cast<float>(totalNodes) : 0;
}
// Modifiers
void clear() noexcept {
_root = make_intrusive_node<Head>();
}
std::pair<const_iterator, bool> insert(value_type&& value) {
const Key& key = std::move(value).first;
Node* node = _findNode(key);
if (node != nullptr || key.size() == 0)
return std::make_pair(end(), false);
return _upsertWithCopyOnSharedNodes(key, std::move(value));
}
std::pair<const_iterator, bool> update(value_type&& value) {
const Key& key = std::move(value).first;
// Ensure that the item to be updated exists.
auto item = RadixStore::find(key);
if (item == RadixStore::end())
return std::make_pair(item, false);
// Setting the same value is a no-op
if (item->second == value.second)
return std::make_pair(item, false);
return _upsertWithCopyOnSharedNodes(key, std::move(value));
}
/**
* Returns whether the key was removed.
*/
bool erase(const Key& key) {
std::vector<std::pair<Node*, bool>> context;
Node* prev = _root.get();
int rootUseCount = _root->_hasPreviousVersion ? 2 : 1;
bool isUniquelyOwned = _root->refCount() == rootUseCount;
context.push_back(std::make_pair(prev, isUniquelyOwned));
Node* node = nullptr;
const uint8_t* charKey = reinterpret_cast<const uint8_t*>(key.data());
size_t depth = prev->_depth + prev->_trieKey.size();
while (depth < key.size()) {
auto nodePtr = _findChild(prev, charKey[depth]);
node = nodePtr.get();
if (node == nullptr) {
return false;
}
// If the prefixes mismatch, this key cannot exist in the tree.
size_t p = _comparePrefix(node->_trieKey, charKey + depth, key.size() - depth);
if (p != node->_trieKey.size()) {
return false;
}
isUniquelyOwned = isUniquelyOwned && nodePtr->refCount() - 1 == 1;
context.push_back(std::make_pair(node, isUniquelyOwned));
depth = node->_depth + node->_trieKey.size();
prev = node;
}
// Found the node, now remove it.
Node* deleted = context.back().first;
context.pop_back();
// If the to-be deleted node is an internal node without data it is hidden from the user and
// should not be deleted
if (!deleted->_data)
return false;
if (!deleted->isLeaf()) {
// The to-be deleted node is an internal node, and therefore updating its data to be
// boost::none will "delete" it.
_upsertWithCopyOnSharedNodes(key, boost::none);
return true;
}
Node* parent = context.at(0).first;
isUniquelyOwned = context.at(0).second;
if (!isUniquelyOwned) {
invariant(!_root->_nextVersion);
invariant(_root->refCount() > rootUseCount);
_root->_nextVersion = make_intrusive_node<Head>(*_root);
_root = _root->_nextVersion;
_root->_hasPreviousVersion = true;
parent = _root.get();
}
size_t sizeOfRemovedData = node->_data->second.size();
_root->_dataSize -= sizeOfRemovedData;
_root->_count--;
Node* prevParent = nullptr;
for (size_t depth = 1; depth < context.size(); depth++) {
Node* child = context.at(depth).first;
isUniquelyOwned = context.at(depth).second;
uint8_t childFirstChar = child->_trieKey.front();
if (!isUniquelyOwned) {
auto childCopy = _copyNode(child);
_setChildPtr(parent, childFirstChar, childCopy);
child = childCopy.get();
}
prevParent = parent;
parent = child;
}
// Handle the deleted node, as it is a leaf.
_setChildPtr(parent, deleted->_trieKey.front(), nullptr);
// 'parent' may only have one child, in which case we need to evaluate whether or not
// this node is redundant.
if (auto newParent = _compressOnlyChild(prevParent, parent)) {
parent = newParent;
}
// Don't shrink the root node.
if (prevParent && parent->needShrink()) {
parent = _shrink(prevParent, parent).get();
}
return true;
}
void merge3(const RadixStore& base, const RadixStore& other) {
std::vector<Node*> context;
std::vector<uint8_t> trieKeyIndex;
difference_type deltaCount = _root->_count - base._root->_count;
difference_type deltaDataSize = _root->_dataSize - base._root->_dataSize;
invariant(this->_root->_trieKey.size() == 0 && base._root->_trieKey.size() == 0 &&
other._root->_trieKey.size() == 0);
_merge3Helper(
this->_root.get(), base._root.get(), other._root.get(), context, trieKeyIndex);
_root->_count = other._root->_count + deltaCount;
_root->_dataSize = other._root->_dataSize + deltaDataSize;
}
// Iterators
const_iterator begin() const noexcept {
if (_root->isLeaf() && !_root->_data)
return end();
Node* node = _begin(_root.get());
return RadixStore::const_iterator(_root, node);
}
const_reverse_iterator rbegin() const noexcept {
return const_reverse_iterator(end());
}
const_iterator end() const noexcept {
return const_iterator(_root);
}
const_reverse_iterator rend() const noexcept {
return const_reverse_iterator(_root);
}
const_iterator find(const Key& key) const {
const_iterator it = RadixStore::end();
Node* node = _findNode(key);
if (node == nullptr)
return it;
else
return const_iterator(_root, node);
}
const_iterator lower_bound(const Key& key) const {
Node* node = _root.get();
const uint8_t* charKey = reinterpret_cast<const uint8_t*>(key.data());
std::vector<std::pair<Node*, uint8_t>> context;
size_t depth = 0;
// Traverse the path given the key to see if the node exists.
while (depth < key.size()) {
uint8_t idx = charKey[depth];
// When we go back up the tree to search for the lower bound of key, always search to
// the right of 'idx' so that we never search anything less than what the lower bound
// would be.
if (idx != UINT8_MAX)
context.push_back(std::make_pair(node, idx + 1));
auto nodePtr = _findChild(node, idx);
if (!nodePtr)
break;
node = nodePtr.get();
size_t mismatchIdx =
_comparePrefix(node->_trieKey, charKey + depth, key.size() - depth);
// There is a prefix mismatch, so we don't need to traverse anymore.
if (mismatchIdx < node->_trieKey.size()) {
// Check if the current key in the tree is greater than the one we are looking
// for since it can't be equal at this point. It can be greater in two ways:
// It can be longer or it can have a larger character at the mismatch index.
uint8_t mismatchChar = charKey[mismatchIdx + depth];
if (mismatchIdx == key.size() - depth ||
node->_trieKey[mismatchIdx] > mismatchChar) {
// If the current key is greater and has a value it is the lower bound.
if (node->_data)
return const_iterator(_root, node);
// If the current key has no value, place it in the context
// so that we can search its children.
context.push_back(std::make_pair(node, 0));
}
break;
}
depth = node->_depth + node->_trieKey.size();
}
if (depth == key.size()) {
// If the node exists, then we can just return an iterator to that node.
if (node->_data)
return const_iterator(_root, node);
// The search key is an exact prefix, so we need to search all of this node's
// children.
context.back() = std::make_pair(node, 0);
}
// The node with the provided key did not exist. Now we must find the next largest node, if
// it exists.
while (!context.empty()) {
uint8_t idx = 0;
std::tie(node, idx) = context.back();
context.pop_back();
bool exhausted = _forEachChild(node, idx, false, [&node, &context](node_ptr child) {
node = child.get();
if (!node->_data) {
// Need to search this node's children for the next largest node.
context.push_back(std::make_pair(node, 0));
}
return false;
});
if (!exhausted && node->_data) {
// There exists a node with a key larger than the one given.
return const_iterator(_root, node);
}
if (node->_trieKey.empty() && context.empty()) {
// We have searched the root. There's nothing left to search.
return end();
}
}
// There was no node key at least as large as the one given.
return end();
}
const_iterator upper_bound(const Key& key) const {
const_iterator it = lower_bound(key);
if (it == end())
return it;
if (it->first == key)
return ++it;
return it;
}
typename RadixStore::iterator::difference_type distance(iterator iter1, iterator iter2) {
return std::distance(iter1, iter2);
}
typename RadixStore::iterator::difference_type distance(const_iterator iter1,
const_iterator iter2) {
return std::distance(iter1, iter2);
}
std::string to_string_for_test() {
return _walkTree(_root.get(), 0);
}
private:
/*
* The base class of all other node types.
*/
class Node {
friend class RadixStore;
friend class RadixStoreTest;
public:
Node() {
addNodeMemory();
}
Node(NodeType type, std::vector<uint8_t> key) {
_nodeType = type;
_trieKey = key;
addNodeMemory();
}
Node(const Node& other) {
_nodeType = other._nodeType;
_numChildren = other._numChildren;
_depth = other._depth;
_trieKey = other._trieKey;
if (other._data) {
addData(other._data.value());
}
// _refCount is initialized to 0 and not copied from other.
addNodeMemory();
}
Node(Node&& other)
: _nodeType(other._nodeType),
_numChildren(other._numChildren),
_depth(other._depth),
_trieKey(std::move(other._trieKey)),
_data(std::move(other._data)) {
// _refCount is initialized to 0 and not copied from other.
// The move constructor transfers the dynamic memory so only the static memory of Node
// should be added.
addNodeMemory(-static_cast<int64_t>(_trieKey.capacity()) *
static_cast<int64_t>(sizeof(uint8_t)));
}
Node& operator=(const Node& rhs) = delete;
Node& operator=(Node&& rhs) = delete;
virtual ~Node() {
subtractNodeMemory();
}
bool isLeaf() const {
return !_numChildren;
}
uint16_t numChildren() const {
return _numChildren;
}
int refCount() const {
return _refCount.load();
}
friend void intrusive_ptr_add_ref(Node* ptr) {
ptr->_refCount.fetchAndAdd(1);
}
friend void intrusive_ptr_release(Node* ptr) {
if (ptr->_refCount.fetchAndSubtract(1) == 1) {
delete ptr;
}
}
protected:
NodeType _nodeType = NodeType::LEAF;
uint16_t _numChildren = 0;
unsigned int _depth = 0;
std::vector<uint8_t> _trieKey;
boost::optional<value_type> _data;
AtomicWord<uint32_t> _refCount{0};
private:
bool needGrow() const {
switch (_nodeType) {
case NodeType::LEAF:
return true;
case NodeType::NODE4:
return numChildren() == 4;
case NodeType::NODE16:
return numChildren() == 16;
case NodeType::NODE48:
return numChildren() == 48;
case NodeType::NODE256:
return false;
}
MONGO_UNREACHABLE;
}
bool needShrink() const {
switch (_nodeType) {
case NodeType::LEAF:
return false;
case NodeType::NODE4:
return numChildren() < 1;
case NodeType::NODE16:
return numChildren() < 5;
case NodeType::NODE48:
return numChildren() < 17;
case NodeType::NODE256:
return numChildren() < 49;
}
MONGO_UNREACHABLE;
}
/*
* Only adds non-empty value and handle the increment on memory metrics.
*/
void addData(value_type value) {
_data.emplace(value.first, value.second);
_metrics.addMemory(value.first.capacity() + value.second.capacity());
}
void addNodeMemory(difference_type offset = 0) {
_metrics.totalMemory.fetchAndAdd(sizeof(Node) + _trieKey.capacity() * sizeof(uint8_t) +
offset);
_metrics.totalNodes.fetchAndAdd(1);
}
void subtractNodeMemory() {
size_t memUsage = sizeof(Node) + _trieKey.capacity() * sizeof(uint8_t);
if (_data) {
memUsage += _data->first.capacity() + _data->second.capacity();
}
_metrics.totalMemory.fetchAndSubtract(memUsage);
_metrics.totalNodes.fetchAndSubtract(1);
}
};
class Node4;
class Node16;
class Node48;
class Node256;
class NodeLeaf : public Node {
friend class RadixStore;
public:
NodeLeaf(std::vector<uint8_t> key) : Node(NodeType::LEAF, key) {}
NodeLeaf(const NodeLeaf& other) : Node(other) {}
NodeLeaf(Node4&& other) : Node(std::move(other)) {
this->_nodeType = NodeType::LEAF;
}
};
/*
* Node4 is used when the number of children is in the range of [1, 4].
*/
class Node4 : public Node {
friend class RadixStore;
public:
Node4(std::vector<uint8_t> key) : Node(NodeType::NODE4, key) {
std::fill(_childKey.begin(), _childKey.end(), 0);
addNodeMemory();
}
Node4(const Node4& other)
: Node(other), _childKey(other._childKey), _children(other._children) {
addNodeMemory();
}
/*
* This move constructor should only be used when growing NodeLeaf to Node4.
*/
Node4(NodeLeaf&& other) : Node(std::move(other)) {
this->_nodeType = NodeType::NODE4;
std::fill(_childKey.begin(), _childKey.end(), 0);
addNodeMemory();
}
/*
* This move constructor should only be used when shrinking Node16 to Node4.
*/
Node4(Node16&& other) : Node(std::move(other)) {
invariant(other.needShrink());
this->_nodeType = NodeType::NODE4;
std::fill(_childKey.begin(), _childKey.end(), 0);
for (size_t i = 0; i < other.numChildren(); ++i) {
_childKey[i] = other._childKey[i];
_children[i] = std::move(other._children[i]);
}
addNodeMemory();
}
~Node4() {
_metrics.subtractMemory(sizeof(Node4) - sizeof(Node));
_metrics.totalChildren.fetchAndSubtract(_children.size());
}
private:
void addNodeMemory() {
_metrics.totalMemory.fetchAndAdd(sizeof(Node4) - sizeof(Node));
_metrics.totalChildren.fetchAndAdd(_children.size());
}
// The first bytes of each child's key is stored in a sorted order.
std::array<uint8_t, 4> _childKey;
std::array<node_ptr, 4> _children;
};
/*
* Node16 is used when the number of children is in the range of [5, 16].
*/
class Node16 : public Node {
friend class RadixStore;
public:
Node16(std::vector<uint8_t> key) : Node(NodeType::NODE16, key) {
std::fill(_childKey.begin(), _childKey.end(), 0);
addNodeMemory();
}
Node16(const Node16& other)
: Node(other), _childKey(other._childKey), _children(other._children) {
addNodeMemory();
}
/*
* This move constructor should only be used when growing Node4 to Node16.
*/
Node16(Node4&& other) : Node(std::move(other)) {
invariant(other.needGrow());
this->_nodeType = NodeType::NODE16;
auto n = other._childKey.size();
for (size_t i = 0; i < n; ++i) {
_childKey[i] = other._childKey[i];
_children[i] = std::move(other._children[i]);
}
std::fill(_childKey.begin() + n, _childKey.end(), 0);
addNodeMemory();
}
/*
* This move constructor should only be used when shrinking Node48 to Node16.
*/
Node16(Node48&& other) : Node(std::move(other)) {
invariant(other.needShrink());
this->_nodeType = NodeType::NODE16;
std::fill(_childKey.begin(), _childKey.end(), 0);
size_t cur = 0;
for (size_t i = 0; i < other._childIndex.size(); ++i) {
auto index = other._childIndex[i];
if (index != maxByte) {
_childKey[cur] = i;
_children[cur++] = std::move(other._children[index]);
}
}
addNodeMemory();
}
~Node16() {
_metrics.subtractMemory(sizeof(Node16) - sizeof(Node));
_metrics.totalChildren.fetchAndSubtract(_children.size());
}
private:
void addNodeMemory() {
_metrics.totalMemory.fetchAndAdd(sizeof(Node16) - sizeof(Node));
_metrics.totalChildren.fetchAndAdd(_children.size());
}
// _childKey is sorted ascendingly.
std::array<uint8_t, 16> _childKey;
std::array<node_ptr, 16> _children;
};
/*
* Node48 is used when the number of children is in the range of [17, 48].
*/
class Node48 : public Node {
friend class RadixStore;
public:
Node48(std::vector<uint8_t> key) : Node(NodeType::NODE48, key) {
std::fill(_childIndex.begin(), _childIndex.end(), maxByte);
addNodeMemory();
}
Node48(const Node48& other)
: Node(other), _childIndex(other._childIndex), _children(other._children) {
addNodeMemory();
}
/*
* This move constructor should only be used when growing Node16 to Node48.
*/
Node48(Node16&& other) : Node(std::move(other)) {
invariant(other.needGrow());
this->_nodeType = NodeType::NODE48;
std::fill(_childIndex.begin(), _childIndex.end(), maxByte);
for (uint8_t i = 0; i < other._children.size(); ++i) {
_childIndex[other._childKey[i]] = i;
_children[i] = std::move(other._children[i]);
}
addNodeMemory();
}
/*
* This move constructor should only be used when shrinking Node256 to Node48.
*/
Node48(Node256&& other) : Node(std::move(other)) {
invariant(other.needShrink());
this->_nodeType = NodeType::NODE48;
std::fill(_childIndex.begin(), _childIndex.end(), maxByte);
size_t cur = 0;
for (size_t i = 0; i < other._children.size(); ++i) {
auto child = other._children[i];
if (child) {
_childIndex[i] = cur;
_children[cur++] = child;
}
}
addNodeMemory();
}
~Node48() {
_metrics.subtractMemory(sizeof(Node48) - sizeof(Node));
_metrics.totalChildren.fetchAndSubtract(_children.size());
}
private:
void addNodeMemory() {
_metrics.totalMemory.fetchAndAdd(sizeof(Node48) - sizeof(Node));
_metrics.totalChildren.fetchAndAdd(_children.size());
}
// A lookup table for child pointers. It has values from 0 to 48, where 0
// represents empty, and all other index i maps to index i - 1 in _children.
std::array<uint8_t, 256> _childIndex;
std::array<node_ptr, 48> _children;
};
/*
* Node256 is used when the number of children is in the range of [49, 256].
*/
class Node256 : public Node {
friend class RadixStore;
public:
Node256() {
this->_nodeType = NodeType::NODE256;
addNodeMemory();
}
Node256(std::vector<uint8_t> key) : Node(NodeType::NODE256, key) {
addNodeMemory();
}
Node256(const NodeLeaf& other) : Node(other) {
addNodeMemory();
}
Node256(const Node4& other) : Node(other) {
this->_nodeType = NodeType::NODE256;
for (size_t i = 0; i < other.numChildren(); ++i) {
this->_children[other._childKey[i]] = other._children[i];
}
addNodeMemory();
}
Node256(const Node16& other) : Node(other) {
this->_nodeType = NodeType::NODE256;
for (size_t i = 0; i < other.numChildren(); ++i) {
this->_children[other._childKey[i]] = other._children[i];
}
addNodeMemory();
}
Node256(const Node48& other) : Node(other) {
this->_nodeType = NodeType::NODE256;
for (size_t i = 0; i < other._childIndex.size(); ++i) {
auto index = other._childIndex[i];
if (index != maxByte) {
this->_children[i] = other._children[index];
}
}
addNodeMemory();
}
Node256(const Node256& other) : Node(other), _children(other._children) {
addNodeMemory();
}
/*
* This move constructor should only be used when growing Node48 to Node256.
*/
Node256(Node48&& other) : Node(std::move(other)) {
invariant(other.needGrow());
this->_nodeType = NodeType::NODE256;
for (size_t i = 0; i < other._childIndex.size(); ++i) {
auto index = other._childIndex[i];
if (index != maxByte) {
_children[i] = std::move(other._children[index]);
}
}
addNodeMemory();
}
~Node256() {
_metrics.subtractMemory(sizeof(Node256) - sizeof(Node));
_metrics.totalChildren.fetchAndSubtract(_children.size());
}
private:
void addNodeMemory() {
_metrics.totalMemory.fetchAndAdd(sizeof(Node256) - sizeof(Node));
_metrics.totalChildren.fetchAndAdd(_children.size());
}
std::array<node_ptr, 256> _children;
};
template <typename Node, typename... Args>
boost::intrusive_ptr<Node> make_intrusive_node(Args&&... args) {
auto ptr = new Node(std::forward<Args>(args)...);
return boost::intrusive_ptr<Node>(ptr, true);
}
/**
* Head is the root node of every RadixStore, it contains extra information used by cursors to
* be able to see when the tree is modified and to respond to these changes by ensuring they are
* not iterating over stale trees.
*/
class Head : public Node256 {
friend class RadixStore;
public:
Head() {
addNodeMemory();
}
Head(std::vector<uint8_t> key) : Node256(key) {
addNodeMemory();
}
Head(const Head& other) : Node256(other), _count(other._count), _dataSize(other._dataSize) {
addNodeMemory();
}
// Copy constructor template for the five node types.
template <typename NodeT>
Head(const NodeT& other) : Node256(other) {
addNodeMemory();
}
~Head() {
if (_nextVersion)
_nextVersion->_hasPreviousVersion = false;
subtractNodeMemory();
}
Head(Head&& other)
: Node256(std::move(other)), _count(other._count), _dataSize(other._dataSize) {
addNodeMemory();
}
Head& operator=(const Head& rhs) = delete;
Head& operator=(Head&& rhs) = delete;
bool hasPreviousVersion() const {
return _hasPreviousVersion;
}
protected:
// Forms a singly linked list of versions that is needed to reposition cursors after
// modifications have been made.
head_ptr _nextVersion;
// While we have cursors that haven't been repositioned to the latest tree, this will be
// true to help us understand when to copy on modifications due to the extra shared pointer
// _nextVersion.
bool _hasPreviousVersion = false;
private:
void addNodeMemory() {
_metrics.addMemory(sizeof(Head) - sizeof(Node256));
}
void subtractNodeMemory() {
_metrics.subtractMemory(sizeof(Head) - sizeof(Node256));
}
size_type _count = 0;
size_type _dataSize = 0;
};
/**
* Return a string representation of all the nodes in this tree.
* The string will look like:
*
* food
* s
* bar
*
* The number of spaces in front of each node indicates the depth
* at which the node lies.
*/
std::string _walkTree(Node* node, int depth) {
std::string ret;
for (int i = 0; i < depth; i++) {
ret.push_back(' ');
}
for (uint8_t ch : node->_trieKey) {
ret.push_back(ch);
}
if (node->_data) {
ret.push_back('*');
}
ret.push_back('\n');
_forEachChild(node, 0, false, [this, &ret, depth](node_ptr child) {
ret.append(_walkTree(child.get(), depth + 1));
return true;
});
return ret;
}
/*
* Helper function to iterate through _children array for different node types and execute the
* given function on each child. The given function returns false when it intends to break the
* iteration.
* Returns false when the given function returns false on an element. Returns true
* when the end of the array is reached.
*/
static bool _forEachChild(Node* node,
uint16_t startKey,
bool reverse,
const std::function<bool(node_ptr)>& func) {
if (startKey > maxByte || !node->_numChildren) {
return true;
}
// Sets the step depending on the direction of iteration.
int16_t step = reverse ? -1 : 1;
switch (node->_nodeType) {
case NodeType::LEAF:
return true;
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
// Locates the actual starting position first.
auto first = node4->_childKey.begin();
auto numChildren = node4->numChildren();
auto pos = std::find_if(first, first + numChildren, [&startKey](uint8_t keyByte) {
return keyByte >= startKey;
});
if (reverse) {
if (pos == first && *pos != startKey) {
return true;
}
if (pos == first + numChildren || *pos != startKey) {
--pos;
}
}
// No qualified elements.
if (pos == first + numChildren) {
return true;
}
auto end = reverse ? -1 : numChildren;
for (auto cur = pos - first; cur != end; cur += step) {
// All children within the range will not be null since they are stored
// consecutively.
if (!func(node4->_children[cur])) {
// Breaks the loop if the given function decides to.
return false;
}
}
return true;
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
// Locates the actual starting position first.
auto first = node16->_childKey.begin();
auto numChildren = node16->numChildren();
auto pos = std::find_if(first, first + numChildren, [&startKey](uint8_t keyByte) {
return keyByte >= startKey;
});
if (reverse) {
if (pos == first && *pos != startKey) {
return true;
}
if (pos == first + numChildren || *pos != startKey) {
--pos;
}
}
// No qualified elements.
if (pos == first + numChildren) {
return true;
}
int16_t end = reverse ? -1 : numChildren;
for (auto cur = pos - first; cur != end; cur += step) {
// All children within the range will not be null since they are stored
// consecutively.
if (!func(node16->_children[cur])) {
return false;
}
}
return true;
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
size_t end = reverse ? -1 : node48->_childIndex.size();
for (size_t cur = startKey; cur != end; cur += step) {
auto index = node48->_childIndex[cur];
if (index != maxByte && !func(node48->_children[index])) {
return false;
}
}
return true;
}
case NodeType::NODE256: {
Node256* node256 = static_cast<Node256*>(node);
size_t end = reverse ? -1 : node256->_children.size();
for (size_t cur = startKey; cur != end; cur += step) {
auto child = node256->_children[cur];
if (child && !func(child)) {
return false;
}
}
return true;
}
}
MONGO_UNREACHABLE;
}
/*
* Gets the child mapped by the key for different node types. Node4 just does a simple linear
* search. Node16 uses binary search. Node48 does one extra lookup with the index table. Node256
* has direct mapping.
*/
static node_ptr _findChild(const Node* node, uint8_t key) {
switch (node->_nodeType) {
case NodeType::LEAF:
return node_ptr(nullptr);
case NodeType::NODE4: {
const Node4* node4 = static_cast<const Node4*>(node);
auto start = node4->_childKey.begin();
auto end = start + node4->numChildren();
auto pos = std::find(start, end, key);
return pos != end ? node4->_children[pos - start] : node_ptr(nullptr);
}
case NodeType::NODE16: {
const Node16* node16 = static_cast<const Node16*>(node);
auto start = node16->_childKey.begin();
auto end = start + node16->numChildren();
auto pos = std::find(start, end, key);
return pos != end ? node16->_children[pos - start] : node_ptr(nullptr);
}
case NodeType::NODE48: {
const Node48* node48 = static_cast<const Node48*>(node);
auto index = node48->_childIndex[key];
if (index != maxByte) {
return node48->_children[index];
}
return node_ptr(nullptr);
}
case NodeType::NODE256: {
const Node256* node256 = static_cast<const Node256*>(node);
return node256->_children[key];
}
}
MONGO_UNREACHABLE;
}
Node* _findNode(const Key& key) const {
const uint8_t* charKey = reinterpret_cast<const uint8_t*>(key.data());
unsigned int depth = _root->_depth;
unsigned int initialDepthOffset = depth;
// If the root node's triekey is not empty then the tree is a subtree, and so we examine it.
for (unsigned int i = 0; i < _root->_trieKey.size(); i++) {
if (charKey[i + initialDepthOffset] != _root->_trieKey[i]) {
return nullptr;
}
depth++;
// Return node if entire trieKey matches.
if (depth == key.size() && _root->_data &&
(key.size() - initialDepthOffset) == _root->_trieKey.size()) {
return _root.get();
}
}
depth = _root->_depth + _root->_trieKey.size();
uint8_t childFirstChar = charKey[depth];
auto node = _findChild(_root.get(), childFirstChar);
while (node != nullptr) {
depth = node->_depth;
size_t mismatchIdx =
_comparePrefix(node->_trieKey, charKey + depth, key.size() - depth);
if (mismatchIdx != node->_trieKey.size()) {
return nullptr;
} else if (mismatchIdx == key.size() - depth && node->_data) {
return node.get();
}
depth = node->_depth + node->_trieKey.size();
childFirstChar = charKey[depth];
node = _findChild(node.get(), childFirstChar);
}
return nullptr;
}
/**
* Makes a copy of the _root node if it isn't uniquely owned during an operation that will
* modify the tree.
*
* The _root node wouldn't be uniquely owned only when there are cursors positioned on the
* latest version of the tree. Cursors that are not yet repositioned onto the latest version of
* the tree are not considered to be sharing the _root for modifying operations.
*/
void _makeRootUnique() {
int rootUseCount = _root->_hasPreviousVersion ? 2 : 1;
if (_root->refCount() == rootUseCount)
return;
invariant(_root->refCount() > rootUseCount);
// Copy the node on a modifying operation when the root isn't unique.
// There should not be any _nextVersion set in the _root otherwise our tree would have
// multiple HEADs.
invariant(!_root->_nextVersion);
_root->_nextVersion = make_intrusive_node<Head>(*_root);
_root = _root->_nextVersion;
_root->_hasPreviousVersion = true;
}
/*
* Moves a smaller node's contents to a larger one. The method should only be called when the
* node is full.
*/
node_ptr _grow(Node* parent, Node* node) {
invariant(node->_nodeType != NodeType::NODE256);
auto key = node->_trieKey.front();
switch (node->_nodeType) {
case NodeType::NODE256:
return nullptr;
case NodeType::LEAF: {
NodeLeaf* leaf = static_cast<NodeLeaf*>(node);
auto newNode = make_intrusive_node<Node4>(std::move(*leaf));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
auto newNode = make_intrusive_node<Node16>(std::move(*node4));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
auto newNode = make_intrusive_node<Node48>(std::move(*node16));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
auto newNode = make_intrusive_node<Node256>(std::move(*node48));
_setChildPtr(parent, key, newNode);
return newNode;
}
}
MONGO_UNREACHABLE;
}
node_ptr _shrink(Node* parent, Node* node) {
invariant(node->_nodeType != NodeType::LEAF);
auto key = node->_trieKey.front();
switch (node->_nodeType) {
case NodeType::LEAF:
return nullptr;
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
auto newNode = make_intrusive_node<NodeLeaf>(std::move(*node4));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
auto newNode = make_intrusive_node<Node4>(std::move(*node16));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
auto newNode = make_intrusive_node<Node16>(std::move(*node48));
_setChildPtr(parent, key, newNode);
return newNode;
}
case NodeType::NODE256: {
Node256* node256 = static_cast<Node256*>(node);
auto newNode = make_intrusive_node<Node48>(std::move(*node256));
_setChildPtr(parent, key, newNode);
return newNode;
}
}
MONGO_UNREACHABLE;
}
/**
* _upsertWithCopyOnSharedNodes is a helper function to help manage copy on modification for the
* tree. This function follows the path for the to-be modified node using the keystring. If at
* any point, the path is no longer uniquely owned, the following nodes are copied to prevent
* modification to other owner's data.
*
* 'key' is the key which can be followed to find the data.
* 'value' is the data to be inserted or updated. It can be an empty value in which case it is
* equivalent to removing that data from the tree.
*/
std::pair<const_iterator, bool> _upsertWithCopyOnSharedNodes(
const Key& key, boost::optional<value_type> value) {
const uint8_t* charKey = reinterpret_cast<const uint8_t*>(key.data());
int depth = _root->_depth + _root->_trieKey.size();
uint8_t childFirstChar = charKey[depth];
_makeRootUnique();
Node* prevParent = nullptr;
Node* prev = _root.get();
node_ptr node = _findChild(prev, childFirstChar);
while (node != nullptr) {
if (node->refCount() - 1 > 1) {
// Copy node on a modifying operation when it isn't owned uniquely.
node = _copyNode(node.get());
_setChildPtr(prev, childFirstChar, node);
}
// 'node' is uniquely owned at this point, so we are free to modify it.
// Get the index at which node->_trieKey and the new key differ.
size_t mismatchIdx =
_comparePrefix(node->_trieKey, charKey + depth, key.size() - depth);
// The keys mismatch, so we need to split this node.
if (mismatchIdx != node->_trieKey.size()) {
// Make a new node with whatever prefix is shared between node->_trieKey
// and the new key. This will replace the current node in the tree.
std::vector<uint8_t> newKey = _makeKey(node->_trieKey, 0, mismatchIdx);
Node* newNode = _addChild(prev, newKey, boost::none, NodeType::NODE4);
depth += mismatchIdx;
const_iterator it(_root, newNode);
if (key.size() - depth != 0) {
// Make a child with whatever is left of the new key.
newKey = _makeKey(charKey + depth, key.size() - depth);
Node* newChild = _addChild(newNode, newKey, value);
it = const_iterator(_root, newChild);
} else {
// The new key is a prefix of an existing key, and has its own node, so we don't
// need to add any new nodes.
newNode->addData(value.value());
}
_root->_count++;
_root->_dataSize += value->second.size();
// Change the current node's trieKey and make a child of the new node.
newKey = _makeKey(node->_trieKey, mismatchIdx, node->_trieKey.size() - mismatchIdx);
_setChildPtr(newNode, newKey.front(), node);
// Handle key size change to the new key.
_metrics.subtractMemory(sizeof(uint8_t) *
(node->_trieKey.capacity() - newKey.capacity()));
node->_trieKey = newKey;
node->_depth = newNode->_depth + newNode->_trieKey.size();
return std::pair<const_iterator, bool>(it, true);
} else if (mismatchIdx == key.size() - depth) {
auto& data = node->_data;
// The key already exists. If there's an element as well, account for its removal.
if (data) {
_root->_count--;
_root->_dataSize -= data->second.size();
_metrics.subtractMemory(data->first.capacity() + data->second.capacity());
}
// Update an internal node.
if (!value) {
data = boost::none;
auto keyByte = node->_trieKey.front();
if (_compressOnlyChild(prev, node.get())) {
node = _findChild(prev, keyByte);
}
} else {
_root->_count++;
_root->_dataSize += value->second.size();
node->addData(value.value());
}
const_iterator it(_root, node.get());
return std::pair<const_iterator, bool>(it, true);
}
depth = node->_depth + node->_trieKey.size();
childFirstChar = charKey[depth];
prevParent = prev;
prev = node.get();
node = _findChild(node.get(), childFirstChar);
}
// Add a completely new child to a node. The new key at this depth does not
// share a prefix with any existing keys.
std::vector<uint8_t> newKey = _makeKey(charKey + depth, key.size() - depth);
if (prev->needGrow()) {
prev = _grow(prevParent, prev).get();
}
Node* newNode = _addChild(prev, newKey, value);
_root->_count++;
_root->_dataSize += value->second.size();
const_iterator it(_root, newNode);
return std::pair<const_iterator, bool>(it, true);
}
/**
* Return a uint8_t vector with the first 'count' characters of
* 'old'.
*/
std::vector<uint8_t> _makeKey(const uint8_t* old, size_t count) {
std::vector<uint8_t> key;
for (size_t i = 0; i < count; ++i) {
uint8_t c = old[i];
key.push_back(c);
}
return key;
}
/**
* Return a uint8_t vector with the [pos, pos+count) characters from old.
*/
std::vector<uint8_t> _makeKey(std::vector<uint8_t> old, size_t pos, size_t count) {
std::vector<uint8_t> key;
for (size_t i = pos; i < pos + count; ++i) {
key.push_back(old[i]);
}
return key;
}
/*
* Wraps around the copy constructor for different node types.
*/
node_ptr _copyNode(Node* node) {
switch (node->_nodeType) {
case NodeType::LEAF: {
NodeLeaf* leaf = static_cast<NodeLeaf*>(node);
return make_intrusive_node<NodeLeaf>(*leaf);
}
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
return make_intrusive_node<Node4>(*node4);
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
return make_intrusive_node<Node16>(*node16);
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
return make_intrusive_node<Node48>(*node48);
}
case NodeType::NODE256: {
Node256* node256 = static_cast<Node256*>(node);
return make_intrusive_node<Node256>(*node256);
}
}
MONGO_UNREACHABLE;
}
head_ptr _makeHead(Node* node) {
switch (node->_nodeType) {
case NodeType::LEAF: {
NodeLeaf* leaf = static_cast<NodeLeaf*>(node);
return make_intrusive_node<Head>(*leaf);
}
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
return make_intrusive_node<Head>(*node4);
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
return make_intrusive_node<Head>(*node16);
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
return make_intrusive_node<Head>(*node48);
}
case NodeType::NODE256: {
Node256* node256 = static_cast<Node256*>(node);
return make_intrusive_node<Head>(*node256);
}
}
MONGO_UNREACHABLE;
}
/**
* Add a child with trieKey 'key' and value 'value' to 'node'. The new child node created should
* only be the type NodeLeaf or Node4.
*/
Node* _addChild(Node* node,
std::vector<uint8_t> key,
boost::optional<value_type> value,
NodeType childType = NodeType::LEAF) {
invariant(childType == NodeType::LEAF || childType == NodeType::NODE4);
node_ptr newNode;
if (childType == NodeType::LEAF) {
newNode = make_intrusive_node<NodeLeaf>(key);
} else {
newNode = make_intrusive_node<Node4>(key);
}
newNode->_depth = node->_depth + node->_trieKey.size();
if (value) {
newNode->addData(value.value());
}
auto newNodeRaw = newNode.get();
_setChildPtr(node, key.front(), std::move(newNode));
return newNodeRaw;
}
/*
* Inserts, updates, or deletes a child node at index and then maintains the key and children
* array for Node4 and Node16 in _setChildPtr().
*/
template <class Node4Or16>
bool _setChildAtIndex(Node4Or16* node, node_ptr child, uint8_t key, size_t index) {
// Adds to the end of the array.
if (!node->_childKey[index] && !node->_children[index]) {
node->_childKey[index] = key;
node->_children[index] = child;
++node->_numChildren;
return true;
}
if (node->_childKey[index] == key) {
if (!child) {
// Deletes a child and shifts
auto n = node->numChildren();
for (int j = index; j < n - 1; ++j) {
node->_childKey[j] = node->_childKey[j + 1];
node->_children[j] = node->_children[j + 1];
}
node->_childKey[n - 1] = 0;
node->_children[n - 1] = nullptr;
--node->_numChildren;
return true;
}
node->_children[index] = child;
return true;
}
if (node->_childKey[index] > key) {
// _children is guaranteed not to be full.
// Inserts to 'index' and shift larger keys to the right.
for (size_t j = node->numChildren(); j > index; --j) {
node->_childKey[j] = node->_childKey[j - 1];
node->_children[j] = node->_children[j - 1];
}
node->_childKey[index] = key;
node->_children[index] = child;
++node->_numChildren;
return true;
}
return false;
}
/*
* Sets the child pointer of 'key' to the 'newNode' in 'node'.
*/
void _setChildPtr(Node* node, uint8_t key, node_ptr newNode) {
switch (node->_nodeType) {
case NodeType::LEAF:
return;
case NodeType::NODE4: {
Node4* node4 = static_cast<Node4*>(node);
auto start = node4->_childKey.begin();
// Find the position of the first larger or equal key to insert.
auto pos = std::find_if(start,
start + node4->numChildren(),
[&key](uint8_t keyByte) { return keyByte >= key; });
_setChildAtIndex(node4, newNode, key, pos - start);
return;
}
case NodeType::NODE16: {
Node16* node16 = static_cast<Node16*>(node);
auto start = node16->_childKey.begin();
auto pos = std::find_if(start,
start + node16->numChildren(),
[&key](uint8_t keyByte) { return keyByte >= key; });
_setChildAtIndex(node16, newNode, key, pos - start);
return;
}
case NodeType::NODE48: {
Node48* node48 = static_cast<Node48*>(node);
auto index = node48->_childIndex[key];
if (index != maxByte) {
// Pointer already exists. Delete or update it.
if (!newNode) {
node48->_childIndex[key] = maxByte;
--node48->_numChildren;
}
node48->_children[index] = newNode;
return;
} else {
// Finds the first empty slot to insert the newNode.
for (size_t i = 0; i < node48->_children.size(); ++i) {
auto& child = node48->_children[i];
if (!child) {
child = newNode;
node48->_childIndex[key] = i;
++node48->_numChildren;
return;
}
}
}
return;
}
case NodeType::NODE256: {
Node256* node256 = static_cast<Node256*>(node);
auto& child = node256->_children[key];
if (!child) {
++node256->_numChildren;
} else if (!newNode) {
--node256->_numChildren;
}
child = newNode;
return;
}
}
MONGO_UNREACHABLE;
}
/**
* This function traverses the tree starting at the provided node using the provided the
* key. It returns the stack which is used in tree traversals for both the forward and
* reverse iterators. Since both iterator classes use this function, it is declared
* statically under RadixStore.
*
* This assumes that the key is present in the tree.
*/
static std::vector<Node*> _buildContext(const Key& key, Node* node) {
std::vector<Node*> context;
context.push_back(node);
const uint8_t* charKey = reinterpret_cast<const uint8_t*>(key.data());
size_t depth = node->_depth + node->_trieKey.size();
while (depth < key.size()) {
node = _findChild(node, charKey[depth]).get();
context.push_back(node);
depth = node->_depth + node->_trieKey.size();
}
return context;
}
/**
* Return the index at which 'key1' and 'key2' differ.
* This function will interpret the bytes in 'key2' as unsigned values.
*/
size_t _comparePrefix(std::vector<uint8_t> key1, const uint8_t* key2, size_t len2) const {
size_t smaller = std::min(key1.size(), len2);
size_t i = 0;
for (; i < smaller; ++i) {
uint8_t c = key2[i];
if (key1[i] != c) {
return i;
}
}
return i;
}
/**
* Compresses a child node into its parent if necessary. This is required when an erase results
* in a node with no value and only one child.
* Returns true if compression occurred and false otherwise.
*/
Node* _compressOnlyChild(Node* parent, Node* node) {
// Don't compress if this node is not of type Node4, has an actual value associated with it,
// or doesn't have only one child.
if (node->_nodeType != NodeType::NODE4 || node->_data || node->_trieKey.empty() ||
node->numChildren() != 1) {
return nullptr;
}
Node4* node4 = static_cast<Node4*>(node);
node_ptr onlyChild = std::move(node4->_children[0]);
node4->_childKey[0] = 0;
node4->_numChildren = 0;
auto oldCapacity = node4->_trieKey.capacity();
for (char item : onlyChild->_trieKey) {
node4->_trieKey.push_back(item);
}
_metrics.addMemory(sizeof(uint8_t) * (node4->_trieKey.capacity() - oldCapacity));
if (onlyChild->_data) {
node4->addData(onlyChild->_data.value());
}
_forEachChild(onlyChild.get(), 0, false, [this, &parent, &node](node_ptr child) {
if (node->needGrow()) {
node = _grow(parent, node).get();
}
auto keyByte = child->_trieKey.front();
_setChildPtr(node, keyByte, std::move(child));
return true;
});
if (node->needShrink()) {
node = _shrink(parent, node).get();
}
return node;
}
/**
* Rebuilds the context by replacing stale raw pointers with the new pointers. The pointers
* can become stale when running an operation that copies the node on modification, like
* insert or erase.
*/
void _rebuildContext(std::vector<Node*>& context, std::vector<uint8_t>& trieKeyIndex) {
Node* replaceNode = _root.get();
context[0] = replaceNode;
for (size_t node = 1; node < context.size(); node++) {
replaceNode = _findChild(replaceNode, trieKeyIndex[node - 1]).get();
context[node] = replaceNode;
}
}
Node* _makeBranchUnique(std::vector<Node*>& context) {
if (context.empty())
return nullptr;
// The first node should always be the root node.
_makeRootUnique();
context[0] = _root.get();
// If the context only contains the root, and it was copied, return the new root.
if (context.size() == 1)
return _root.get();
Node* node = nullptr;
Node* prev = _root.get();
// Create copies of the nodes until the leaf node.
for (size_t idx = 1; idx < context.size(); idx++) {
node = context[idx];
auto next = _findChild(prev, node->_trieKey.front());
if (next->refCount() - 1 > 1) {
node_ptr nodeCopy = _copyNode(node);
_setChildPtr(prev, nodeCopy->_trieKey.front(), nodeCopy);
context[idx] = nodeCopy.get();
prev = nodeCopy.get();
} else {
prev = next.get();
}
}
return context.back();
}
/**
* Resolves conflicts within subtrees due to the complicated structure of path-compressed radix
* tries.
*/
void _mergeResolveConflict(Node* current, Node* baseNode, Node* otherNode) {
// Merges all differences between this and other, using base to determine whether operations
// are allowed or should throw a merge conflict.
RadixStore base, other, node;
node._root = _makeHead(current);
base._root = _makeHead(baseNode);
other._root = _makeHead(otherNode);
// Merges insertions and updates from the master tree into the working tree, if possible.
for (const value_type& otherVal : other) {
RadixStore::const_iterator baseIter = base.find(otherVal.first);
RadixStore::const_iterator thisIter = node.find(otherVal.first);
if (thisIter != node.end() && baseIter != base.end()) {
// All three trees have a record of the node with the same key.
if (thisIter->second == baseIter->second && baseIter->second != otherVal.second) {
// No changes occurred in the working tree, so the value in the master tree can
// be merged in cleanly.
this->update(RadixStore::value_type(otherVal));
} else if (thisIter->second != baseIter->second &&
baseIter->second != otherVal.second) {
// Both the working copy and master nodes changed the same value at the same
// key. This results in a merge conflict.
throw merge_conflict_exception();
} else if (thisIter->second != baseIter->second &&
thisIter->second == otherVal.second) {
// Both the working copy and master nodes are inserting the same value at the
// same key. But this is a merge conflict because if that operation was an
// increment, it's no different than a race condition on an unguarded variable.
throw merge_conflict_exception();
}
} else if (baseIter != base.end() && baseIter->second != otherVal.second) {
// The working tree removed this node while the master updated the node, this
// results in a merge conflict.
throw merge_conflict_exception();
} else if (thisIter != node.end()) {
// Both the working copy and master tree are either inserting the same value or
// different values at the same node, resulting in a merge conflict.
throw merge_conflict_exception();
} else if (thisIter == node.end() && baseIter == base.end()) {
// The working tree and merge base do not have any record of this node. The node can
// be merged in cleanly from the master tree.
this->insert(RadixStore::value_type(otherVal));
}
}
// Perform deletions from the master tree in the working tree, if possible.
for (const value_type& baseVal : base) {
RadixStore::const_iterator otherIter = other.find(baseVal.first);
RadixStore::const_iterator thisIter = node.find(baseVal.first);
if (otherIter == other.end()) {
if (thisIter != node.end() && thisIter->second == baseVal.second) {
// Nothing changed between the working tree and merge base, so it is safe to
// perform the deletion that occurred in the master tree.
this->erase(baseVal.first);
} else if (thisIter != node.end() && thisIter->second != baseVal.second) {
// The working tree made a change to the node while the master tree removed the
// node, resulting in a merge conflict.
throw merge_conflict_exception();
}
}
}
}
/**
* Merges elements from the master tree into the working copy if they have no presence in the
* working copy, otherwise we throw a merge conflict.
*/
void _mergeTwoBranches(Node* current, Node* otherNode) {
RadixStore other, node;
node._root = _makeHead(current);
other._root = _makeHead(otherNode);
for (const value_type& otherVal : other) {
RadixStore::const_iterator thisIter = node.find(otherVal.first);
if (thisIter != node.end())
throw merge_conflict_exception();
this->insert(RadixStore::value_type(otherVal));
}
}
/**
* Merges changes from base to other into current. Throws merge_conflict_exception if there are
* merge conflicts.
* It returns the updated current node and a boolean indicating that conflict resolution is
* required after recursion
*/
std::pair<Node*, bool> _merge3Helper(Node* current,
const Node* base,
const Node* other,
std::vector<Node*>& context,
std::vector<uint8_t>& trieKeyIndex) {
context.push_back(current);
// Root doesn't have a trie key.
if (!current->_trieKey.empty())
trieKeyIndex.push_back(current->_trieKey.at(0));
auto hasParent = [](std::vector<Node*>& context) { return context.size() >= 2; };
auto getParent = [&](std::vector<Node*>& context) {
// We should never get here unless we are at sufficient depth already, so the invariant
// should indeed actually hold. If coverity complains, treat as a false alarm.
invariant(hasParent(context));
return context[context.size() - 2];
};
auto currentHasBeenCompressed = [&]() {
// This can only happen when conflict resolution erases nodes that causes compression on
// the current node.
return current->_trieKey.size() != other->_trieKey.size();
};
auto splitCurrentBeforeWriteIfNeeded = [&](Node* child) {
// If current has not been compressed there's nothing to do
if (!currentHasBeenCompressed())
return child;
// This can only happen if we've done previous writes to current so it should already be
// unique and safe to write to.
size_t mismatchIdx =
_comparePrefix(current->_trieKey, other->_trieKey.data(), other->_trieKey.size());
auto parent = getParent(context);
auto key = current->_trieKey.front();
auto newTrieKeyBegin = current->_trieKey.begin();
auto newTrieKeyEnd = current->_trieKey.begin() + mismatchIdx;
auto shared_current = std::move(_findChild(parent, key));
auto newTrieKey = std::vector<uint8_t>(newTrieKeyBegin, newTrieKeyEnd);
// Replace current with a new node with no data
auto newNode = _addChild(parent, newTrieKey, boost::none, NodeType::NODE4);
// Remove the part of the trieKey that is used by the new node.
current->_trieKey.erase(current->_trieKey.begin(),
current->_trieKey.begin() + mismatchIdx);
_metrics.subtractMemory(sizeof(uint8_t) * mismatchIdx);
current->_depth += mismatchIdx;
// Add what was the current node as a child to the new internal node
key = current->_trieKey.front();
_setChildPtr(newNode, key, std::move(shared_current));
// Update current pointer and context
child = current;
current = newNode;
context.back() = current;
return child;
};
bool resolveConflictNeeded = false;
for (size_t key = 0; key < 256; ++key) {
// Since _makeBranchUnique may make changes to the pointer addresses in recursive calls.
current = context.back();
Node* node = _findChild(current, key).get();
Node* baseNode = _findChild(base, key).get();
Node* otherNode = _findChild(other, key).get();
if (!node && !baseNode && !otherNode)
continue;
bool unique = node != otherNode && node != baseNode;
// If the current tree does not have this node, check if the other trees do.
if (!node) {
if (!baseNode && otherNode) {
splitCurrentBeforeWriteIfNeeded(nullptr);
// If base and node do NOT have this branch, but other does, then
// merge in the other's branch.
current = _makeBranchUnique(context);
if (current->needGrow() && hasParent(context)) {
current = _grow(getParent(context), current).get();
}
// Need to rebuild our context to have updated pointers due to the
// modifications that go on in _makeBranchUnique.
_rebuildContext(context, trieKeyIndex);
_setChildPtr(current, key, _findChild(other, key));
} else if (!otherNode || (baseNode && baseNode != otherNode)) {
// Either the master tree and working tree remove the same branch, or the master
// tree updated the branch while the working tree removed the branch, resulting
// in a merge conflict.
throw merge_conflict_exception();
}
} else if (!unique) {
if (baseNode && !otherNode && baseNode == node) {
node = splitCurrentBeforeWriteIfNeeded(node);
// Other has a deleted branch that must also be removed from current tree.
current = _makeBranchUnique(context);
_setChildPtr(current, key, nullptr);
if (current->needShrink() && hasParent(context)) {
current = _shrink(getParent(context), current).get();
}
_rebuildContext(context, trieKeyIndex);
} else if (baseNode && otherNode && baseNode == node) {
node = splitCurrentBeforeWriteIfNeeded(node);
// If base and current point to the same node, then master changed.
current = _makeBranchUnique(context);
if (current->needGrow() && hasParent(context)) {
current = _grow(getParent(context), current).get();
}
_rebuildContext(context, trieKeyIndex);
_setChildPtr(current, key, _findChild(other, key));
}
} else if (baseNode && otherNode && baseNode != otherNode) {
// If all three are unique and leaf nodes with different data, then it is a merge
// conflict.
if (node->isLeaf() && baseNode->isLeaf() && otherNode->isLeaf()) {
bool dataChanged = node->_data != baseNode->_data;
bool otherDataChanged = baseNode->_data != otherNode->_data;
if (dataChanged && otherDataChanged) {
// All three nodes have different data, that is a merge conflict
throw merge_conflict_exception();
}
if (otherDataChanged) {
// Only other changed the data. Take that node
current = _makeBranchUnique(context);
_rebuildContext(context, trieKeyIndex);
_setChildPtr(current, key, _findChild(other, key));
}
continue;
}
if (currentHasBeenCompressed()) {
resolveConflictNeeded = true;
break;
}
// If the keys and data are all the exact same, then we can keep recursing.
// Otherwise, we manually resolve the differences element by element. The
// structure of compressed radix tries makes it difficult to compare the
// trees node by node, hence the reason for resolving these differences
// element by element.
bool resolveConflict =
!(node->_trieKey == baseNode->_trieKey &&
baseNode->_trieKey == otherNode->_trieKey && node->_data == baseNode->_data &&
baseNode->_data == otherNode->_data);
if (!resolveConflict) {
std::tie(node, resolveConflict) =
_merge3Helper(node, baseNode, otherNode, context, trieKeyIndex);
if (node && !node->_data) {
// Drop if leaf node without data, that is not valid. Otherwise we might
// need to compress if we have only one child.
if (node->isLeaf()) {
_setChildPtr(current, key, nullptr);
// Don't shrink the root node.
if (current->needShrink() && hasParent(context)) {
current = _shrink(getParent(context), current).get();
}
_rebuildContext(context, trieKeyIndex);
} else {
if (auto compressedNode = _compressOnlyChild(current, node)) {
node = compressedNode;
}
}
}
}
if (resolveConflict) {
Node* nodeToResolve = node;
if (hasParent(context)) {
if (auto compressed = _compressOnlyChild(getParent(context), current)) {
current = compressed;
nodeToResolve = current;
}
}
_mergeResolveConflict(nodeToResolve, baseNode, otherNode);
_rebuildContext(context, trieKeyIndex);
// If we compressed above, resolving the conflict can result in erasing current.
// Break out of the recursion as there is nothing more to do.
if (!context.back())
break;
}
} else if (baseNode && !otherNode) {
// Throw a write conflict since current has modified a branch but master has
// removed it.
throw merge_conflict_exception();
} else if (!baseNode && otherNode) {
// Both the working tree and master added branches that were nonexistent in base.
// This requires us to resolve these differences element by element since the
// changes may not be conflicting.
if (currentHasBeenCompressed()) {
resolveConflictNeeded = true;
break;
}
_mergeTwoBranches(node, otherNode);
_rebuildContext(context, trieKeyIndex);
}
}
current = context.back();
context.pop_back();
if (!trieKeyIndex.empty())
trieKeyIndex.pop_back();
return std::make_pair(current, resolveConflictNeeded);
}
Node* _begin(Node* root) const noexcept {
Node* node = root;
while (!node->_data) {
_forEachChild(node, 0, false, [&node](node_ptr child) {
node = child.get();
return false;
});
}
return node;
}
head_ptr _root = nullptr;
static Metrics _metrics;
};
template <class Key, class T>
Metrics RadixStore<Key, T>::_metrics;
using StringStore = RadixStore<std::string, std::string>;
} // namespace ephemeral_for_test
} // namespace mongo
|
