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
pub mod array; pub mod cell; pub mod link; use array::Array; use cell::{CellLocker, CellReader, ARRAY_SIZE, MAX_RESIZING_FACTOR}; use crossbeam_epoch::{Atomic, Guard, Owned, Shared}; use std::collections::hash_map::RandomState; use std::convert::TryInto; use std::fmt; use std::hash::{BuildHasher, Hash, Hasher}; use std::iter::FusedIterator; use std::sync::atomic::Ordering::{Acquire, Relaxed, Release}; use std::sync::atomic::{AtomicBool, AtomicUsize}; const DEFAULT_CAPACITY: usize = 64; /// A scalable concurrent hash map implementation. /// /// scc::HashMap is a concurrent hash map data structure that is targeted at a highly concurrent workload. /// The use of epoch-based reclamation technique enables the data structure to implement non-blocking resizing and bucket-level locking. /// It has a single array of metadata cells, and each metadata cell manages a fixed size entry array and a linked list for collision resolution. /// Each metadata cell owns a customized 8-byte read-write mutex to protect the data structure. /// /// ## The key features of scc::HashMap /// * Non-sharded: the data is managed by a single metadata cell array. /// * Automatic resizing: it automatically grows or shrinks. /// * Non-blocking resizing: resizing does not block other threads. /// * Incremental resizing: each access to the data structure is mandated to rehash a certain number of key-value pairs. /// * Optimized resizing: key-value pairs in a single metadata cell are guaranteed to be relocated to adjacent cells. /// * No busy waiting: the customized mutex never spins. /// /// ## The key statistics for scc::HashMap /// * The expected size of metadata for a single key-value pair: 2-byte. /// * The expected number of atomic operations required for an operation on a single key: 2. /// * The expected number of atomic variables accessed during a single key operation: 1. /// * The number of entries managed by a single metadata cell without a linked list: 32. /// * The number of entries a single linked list entry manages: 8. /// * The expected maximum linked list length when resize is triggered: log(capacity) / 8. pub struct HashMap<K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { array: Atomic<Array<K, V>>, minimum_capacity: usize, additional_capacity: AtomicUsize, resize_mutex: AtomicBool, build_hasher: H, } impl<K, V> Default for HashMap<K, V, RandomState> where K: Eq + Hash + Sync, V: Sync, { /// Creates a HashMap instance with the default parameters. /// /// The default hash builder is RandomState, and the default capacity is 256. /// /// # Panics /// /// Panics if memory allocation fails. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.capacity(); /// assert_eq!(result, 64); /// ``` fn default() -> Self { HashMap { array: Atomic::new(Array::<K, V>::new(DEFAULT_CAPACITY, Atomic::null())), minimum_capacity: DEFAULT_CAPACITY, additional_capacity: AtomicUsize::new(0), resize_mutex: AtomicBool::new(false), build_hasher: RandomState::new(), } } } impl<K, V, H> HashMap<K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { /// Creates an empty HashMap instance with the given capacity and build hasher. /// /// The actual capacity is equal to or greater than the given capacity. /// /// # Panics /// /// Panics if memory allocation fails. /// /// # Examples /// ``` /// use scc::HashMap; /// use std::collections::hash_map::RandomState; /// /// let hashmap: HashMap<u64, u32, RandomState> = HashMap::new(1000, RandomState::new()); /// /// let result = hashmap.capacity(); /// assert_eq!(result, 1024); /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// let result = hashmap.capacity(); /// assert_eq!(result, 64); /// ``` pub fn new(capacity: usize, build_hasher: H) -> HashMap<K, V, H> { let initial_capacity = capacity.max(DEFAULT_CAPACITY); let array = Owned::new(Array::<K, V>::new(initial_capacity, Atomic::null())); let current_capacity = array.capacity(); HashMap { array: Atomic::from(array), minimum_capacity: current_capacity, additional_capacity: AtomicUsize::new(0), resize_mutex: AtomicBool::new(false), build_hasher, } } /// Temporarily increases the minimum capacity of the HashMap. /// /// Unused space can be immediately reclaimed when the returned Ticket is dropped. /// /// # Errors /// /// Returns None if the given value is too large. /// /// # Examples /// ``` /// use scc::HashMap; /// use std::collections::hash_map::RandomState; /// /// let hashmap: HashMap<u64, u32, RandomState> = HashMap::new(1000, RandomState::new()); /// assert_eq!(hashmap.capacity(), 1024); /// /// let ticket = hashmap.book(10000); /// assert!(ticket.is_some()); /// assert_eq!(hashmap.capacity(), 16384); /// drop(ticket); /// /// assert_eq!(hashmap.capacity(), 1024); /// ``` pub fn book(&self, capacity: usize) -> Option<Ticket<K, V, H>> { let mut current_additional_capacity = self.additional_capacity.load(Relaxed); loop { if usize::MAX - self.minimum_capacity - current_additional_capacity <= capacity { // The given value is too large. return None; } match self.additional_capacity.compare_exchange( current_additional_capacity, current_additional_capacity + capacity, Relaxed, Relaxed, ) { Ok(_) => { self.resize(); return Some(Ticket { hash_map: self, increment: capacity, }); } Err(current) => current_additional_capacity = current, } } } /// Inserts a key-value pair into the HashMap. /// /// # Errors /// /// Returns an error with a mutable reference to the existing key-value pair. /// /// # Panics /// /// Panics if memory allocation fails, or the number of entries in the target cell reaches u32::MAX. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } else { /// assert!(false); /// } /// /// let result = hashmap.insert(1, 1); /// if let Err((accessor, key, value)) = result { /// assert_eq!(accessor.get(), (&1, &mut 0)); /// assert_eq!(key, 1); /// assert_eq!(value, 1); /// } else { /// assert!(false); /// } /// ``` pub fn insert(&self, key: K, value: V) -> Result<Accessor<K, V, H>, (Accessor<K, V, H>, K, V)> { match self.reserve(key) { Ok((mut accessor, key, partial_hash)) => { let (sub_index, entry_array_link_ptr, entry_ptr) = accessor.cell_locker.insert(key, partial_hash, value); accessor.sub_index = sub_index; accessor.entry_array_link_ptr = entry_array_link_ptr; accessor.entry_ptr = entry_ptr; Ok(accessor) } Err((accessor, key)) => Err((accessor, key, value)), } } /// Constructs the value in-place. /// /// The given closure is never invoked if the key exists. /// /// # Panics /// /// Panics if memory allocation fails, or the number of entries in the target cell reaches u32::MAX. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let mut current = 0; /// let result = hashmap.emplace(1, || { current += 1; current }); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 1)); /// } else { /// assert!(false); /// } /// /// let result = hashmap.emplace(1, || { current += 1; current }); /// if let Err((result, key)) = result { /// assert_eq!(result.get(), (&1, &mut 1)); /// assert_eq!(key, 1); /// assert_eq!(current, 1); /// } else { /// assert!(false); /// } /// ``` pub fn emplace<F: FnOnce() -> V>( &self, key: K, constructor: F, ) -> Result<Accessor<K, V, H>, (Accessor<K, V, H>, K)> { match self.reserve(key) { Ok((mut accessor, key, partial_hash)) => { let (sub_index, entry_array_link_ptr, entry_ptr) = accessor .cell_locker .insert(key, partial_hash, constructor()); accessor.sub_index = sub_index; accessor.entry_array_link_ptr = entry_array_link_ptr; accessor.entry_ptr = entry_ptr; Ok(accessor) } Err((accessor, key)) => Err((accessor, key)), } } /// Upserts a key-value pair into the HashMap. /// /// # Panics /// /// Panics if memory allocation fails, or the number of entries in the target cell reaches u32::MAX. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } else { /// assert!(false); /// } /// /// let result = hashmap.upsert(1, 1); /// assert_eq!(result.get(), (&1, &mut 1)); /// ``` pub fn upsert(&self, key: K, value: V) -> Accessor<K, V, H> { match self.insert(key, value) { Ok(result) => result, Err((accessor, _, value)) => { *self.entry(accessor.entry_ptr).1 = value; accessor } } } /// Gets a mutable reference to the value associated with the key. /// /// # Errors /// /// Returns None if the key does not exist. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.get(&1); /// assert!(result.is_none()); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.get(&1); /// assert_eq!(result.unwrap().get(), (&1, &mut 0)); /// ``` pub fn get<'h>(&'h self, key: &K) -> Option<Accessor<'h, K, V, H>> { let (hash, partial_hash) = self.hash(key); let accessor = self.acquire(key, hash, partial_hash); if accessor.entry_ptr.is_null() { return None; } Some(accessor) } /// Removes a key-value pair. /// /// # Errors /// /// Returns None if the key does not exist. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.remove(&1); /// assert!(result.is_none()); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.remove(&1); /// assert_eq!(result.unwrap(), 0); /// ``` pub fn remove(&self, key: &K) -> Option<V> { self.get(key) .map_or_else(|| None, |accessor| accessor.erase()) } /// Reads a key-value pair. /// /// # Errors /// /// Returns None if the key does not exist. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.read(&1, |key, value| *value); /// assert_eq!(result.unwrap(), 0); /// ``` pub fn read<R, F: FnOnce(&K, &V) -> R>(&self, key: &K, f: F) -> Option<R> { let (hash, partial_hash) = self.hash(key); let guard = crossbeam_epoch::pin(); // An acquire fence is required to correctly load the contents of the array. let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); let old_array = current_array_ref.old_array(&guard); for array in [&old_array, ¤t_array].iter() { if array.is_null() { continue; } if array.as_raw() == old_array.as_raw() { let old_array_removed = current_array_ref.partial_rehash(|key| self.hash(key), &guard); if old_array_removed { continue; } } let array_ref = Self::array(**array); let cell_index = array_ref.calculate_cell_index(hash); let reader = CellReader::read(array_ref.cell(cell_index), &key, partial_hash, &guard); if let Some((key, value)) = reader.get() { return Some(f(key, value)); } } None } /// Checks if the key exists. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.contains(&1); /// assert!(!result); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.contains(&1); /// assert!(result); /// ``` pub fn contains(&self, key: &K) -> bool { self.read(key, |_, _| ()).is_some() } /// Retains the key-value pairs that satisfy the given predicate. /// /// It returns the number of entries remaining and removed. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.insert(2, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&2, &mut 0)); /// } /// /// let result = hashmap.retain(|key, value| *key == 1 && *value == 0); /// assert_eq!(result, (1, 1)); /// /// let result = hashmap.get(&1); /// assert_eq!(result.unwrap().get(), (&1, &mut 0)); /// /// let result = hashmap.get(&2); /// assert!(result.is_none()); /// ``` pub fn retain<F: Fn(&K, &mut V) -> bool>(&self, f: F) -> (usize, usize) { let mut retained_entries = 0; let mut removed_entries = 0; let mut cursor = self.iter(); while let Some((key, value)) = cursor.next() { if !f(key, value) { cursor.erase_on_next = true; removed_entries += 1; } else { retained_entries += 1; } } let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); if retained_entries <= current_array_ref.capacity() / 8 { self.resize(); } (retained_entries, removed_entries) } /// Clears all the key-value pairs. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.insert(2, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&2, &mut 0)); /// } /// /// let result = hashmap.clear(); /// assert_eq!(result, 2); /// /// let result = hashmap.get(&1); /// assert!(result.is_none()); /// /// let result = hashmap.get(&2); /// assert!(result.is_none()); /// ``` pub fn clear(&self) -> usize { self.retain(|_, _| false).1 } /// Returns the number of entries in the HashMap. /// /// It scans the entire metadata cell array to calculate the number of valid entries, /// making its time complexity O(N). /// Apart from being inefficient, it may return a smaller number when the HashMap is being resized. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } else { /// assert!(false); /// } /// /// let result = hashmap.len(); /// assert_eq!(result, 1); /// ``` pub fn len(&self) -> usize { let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); let mut num_entries = 0; for i in 0..current_array_ref.num_cells() { num_entries += current_array_ref.cell(i).size(); } let old_array = current_array_ref.old_array(&guard); if !old_array.is_null() { let old_array_ref = Self::array(old_array); for i in 0..old_array_ref.num_cells() { num_entries += old_array_ref.cell(i).size(); } } num_entries } /// Returns the capacity of the HashMap. /// /// # Examples /// ``` /// use scc::HashMap; /// use std::collections::hash_map::RandomState; /// /// let hashmap: HashMap<u64, u32, RandomState> = HashMap::new(1000000, RandomState::new()); /// assert_eq!(hashmap.capacity(), 1048576); /// ``` pub fn capacity(&self) -> usize { let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); if !current_array_ref.old_array(&guard).is_null() { current_array_ref.partial_rehash(|key| self.hash(key), &guard); } current_array_ref.capacity() } /// Returns a reference to its build hasher. /// /// # Examples /// ``` /// use scc::HashMap; /// use std::collections::hash_map::RandomState; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// let result: &RandomState = hashmap.hasher(); /// ``` pub fn hasher(&self) -> &H { &self.build_hasher } /// Returns the statistics of the current state of the HashMap. /// /// # Examples /// ``` /// use scc::HashMap; /// use std::collections::hash_map::RandomState; /// /// let hashmap: HashMap<u64, u32, RandomState> = HashMap::new(1000, RandomState::new()); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let result = hashmap.statistics(); /// assert_eq!(result.effective_capacity(), 1024); /// assert_eq!(result.num_entries(), 1); /// ``` pub fn statistics(&self) -> Statistics { let mut statistics = Statistics { effective_capacity: 0, deprecated_capacity: 0, num_entries: 0, num_killed_entries: 0, num_cells: 0, num_empty_cells: 0, num_max_consecutive_empty_cells: 0, }; let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let old_array = Self::array(current_array).old_array(&guard); for array in [old_array, current_array].iter() { if array.is_null() { continue; } let array_ref = Self::array(*array); let num_cells = array_ref.num_cells(); let mut consecutive_empty_cells = 0; if array.as_raw() == current_array.as_raw() { statistics.effective_capacity = array_ref.capacity(); } else { statistics.deprecated_capacity += array_ref.capacity(); } statistics.num_cells += num_cells; for i in 0..num_cells { let size = array_ref.cell(i).size(); statistics.num_entries += size; if size == 0 { statistics.num_empty_cells += 1; consecutive_empty_cells += 1; } else { if statistics.num_max_consecutive_empty_cells < consecutive_empty_cells { statistics.num_max_consecutive_empty_cells = consecutive_empty_cells; } consecutive_empty_cells = 0; } if array_ref.cell(i).killed() { statistics.num_killed_entries += 1; } } } statistics } /// Returns a Cursor. /// /// It is guaranteed to go through all the key-value pairs pertaining in the HashMap at the moment, /// however the same key-value pair can be visited more than once if the HashMap is being resized. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// let mut iter = hashmap.iter(); /// assert_eq!(iter.next(), Some((&1, &mut 0))); /// assert_eq!(iter.next(), None); /// /// for iter in hashmap.iter() { /// assert_eq!(iter, (&1, &mut 0)); /// } /// ``` pub fn iter(&self) -> Cursor<K, V, H> { let (cell_locker, array_ptr, cell_index) = self.first(); if let Some(cell_locker) = cell_locker { if let Some(cursor) = self.pick(cell_locker, array_ptr, cell_index) { return cursor; } } Cursor { accessor: None, array_ptr: std::ptr::null(), activated: false, erase_on_next: false, } } /// Returns the hash value of the given key. fn hash(&self, key: &K) -> (u64, u8) { // Generates a hash value. let mut h = self.build_hasher.build_hasher(); key.hash(&mut h); let mut hash = h.finish(); // Bitmix: https://mostlymangling.blogspot.com/2019/01/better-stronger-mixer-and-test-procedure.html hash = hash ^ (hash.rotate_right(25) ^ hash.rotate_right(50)); hash = hash.overflowing_mul(0xA24BAED4963EE407u64).0; hash = hash ^ (hash.rotate_right(24) ^ hash.rotate_right(49)); hash = hash.overflowing_mul(0x9FB21C651E98DF25u64).0; hash = hash ^ (hash >> 28); (hash, (hash & ((1 << 8) - 1)).try_into().unwrap()) } /// Reserves a Cell for inserting a new key-value pair. fn reserve(&self, key: K) -> Result<(Accessor<K, V, H>, K, u8), (Accessor<K, V, H>, K)> { let (hash, partial_hash) = self.hash(&key); let mut resize_triggered = false; loop { let accessor = self.acquire(&key, hash, partial_hash); if !accessor.entry_ptr.is_null() { return Err((accessor, key)); } if !resize_triggered && accessor.cell_index < ARRAY_SIZE && accessor.cell_locker.size() >= ARRAY_SIZE { drop(accessor); resize_triggered = true; let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); if current_array_ref.old_array(&guard).is_null() { // Triggers resize if the estimated load factor is greater than 7/8. let sample_size = current_array_ref.num_sample_size(); let threshold = sample_size * (ARRAY_SIZE / 8) * 7; let mut num_entries = 0; for i in 0..sample_size { num_entries += current_array_ref.cell(i).size(); if num_entries > threshold { self.resize(); break; } } } continue; } return Ok((accessor, key, partial_hash)); } } /// Acquires a cell. fn acquire<'h>(&'h self, key: &K, hash: u64, partial_hash: u8) -> Accessor<'h, K, V, H> { let guard = crossbeam_epoch::pin(); // It is guaranteed that the thread reads a consistent snapshot of the current and // old array pair by a release fence in the resize function, hence the following // procedure is correct. // - The thread reads self.array, and it kills the target cell in the old array // if there is one attached to it, and inserts the key into array. // There are two cases. // 1. The thread reads an old version of self.array. // If there is another thread having read the latest version of self.array, // trying to insert the same key, it will try to kill the Cell in the old version // of self.array, thus competing with each other. // 2. The thread reads the latest version of self.array. // If the array is deprecated while inserting the key, it falls into case 1. loop { // An acquire fence is required to correctly load the contents of the array. let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); let old_array = current_array_ref.old_array(&guard); if !old_array.is_null() { if current_array_ref.partial_rehash(|key| self.hash(key), &guard) { continue; } let (mut cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr) = self.search(&key, hash, partial_hash, old_array.as_raw(), &guard); if !entry_ptr.is_null() { return Accessor { hash_map: &self, cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr, }; } else if !cell_locker.killed() { // Kills the Cell. current_array_ref.kill_cell( &mut cell_locker, Self::array(old_array), cell_index, &|key| self.hash(key), &guard, ); } } let (cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr) = self.search(&key, hash, partial_hash, current_array.as_raw(), &guard); if !cell_locker.killed() { return Accessor { hash_map: &self, cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr, }; } // Reaching here indicates that self.array is updated. } } /// Erases a key-value pair owned by the Accessor. fn erase<'h>(&'h self, mut accessor: Accessor<'h, K, V, H>) -> V { let value = Array::<K, V>::extract_key_value(accessor.entry_ptr).1; accessor.cell_locker.remove( false, accessor.sub_index, accessor.entry_array_link_ptr, accessor.entry_ptr, ); if accessor.cell_locker.empty() && accessor.cell_index < ARRAY_SIZE { drop(accessor); let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); if current_array_ref.old_array(&guard).is_null() && current_array_ref.capacity() > self.minimum_capacity + self.additional_capacity.load(Relaxed) { // Triggers resize if the estimated load factor is smaller than 1/16. let sample_size = current_array_ref.num_sample_size(); let mut num_entries = 0; for i in 0..sample_size { num_entries += current_array_ref.cell(i).size(); if num_entries >= sample_size * ARRAY_SIZE / 16 { return value; } } self.resize(); } } value } /// Searches a cell for the key. fn search<'c>( &self, key: &K, hash: u64, partial_hash: u8, array_ptr: *const Array<K, V>, guard: &Guard, ) -> ( CellLocker<'c, K, V>, usize, u8, *const link::EntryArrayLink<K, V>, *const (K, V), ) { let array_ref = unsafe { &(*array_ptr) }; let cell_index = array_ref.calculate_cell_index(hash); let cell_locker = CellLocker::lock(array_ref.cell(cell_index), guard); if !cell_locker.killed() && !cell_locker.empty() { if let Some((sub_index, entry_array_link_ptr, entry_ptr)) = cell_locker.search(key, partial_hash) { return ( cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr, ); } } ( cell_locker, cell_index, 0, std::ptr::null(), std::ptr::null(), ) } /// Returns the first valid cell. fn first(&self) -> (Option<CellLocker<K, V>>, *const Array<K, V>, usize) { let guard = crossbeam_epoch::pin(); // An acquire fence is required to correctly load the contents of the array. let mut current_array = self.array.load(Acquire, &guard); loop { let old_array = Self::array(current_array).old_array(&guard); for array_ptr in [old_array.as_raw(), current_array.as_raw()].iter() { if array_ptr.is_null() { continue; } let array_ref = unsafe { &(**array_ptr) }; let num_cells = array_ref.num_cells(); for cell_index in 0..num_cells { let cell_locker = CellLocker::lock(array_ref.cell(cell_index), &guard); if !cell_locker.empty() { // once a valid cell is locked, the array is guaranteed to retain return (Some(cell_locker), *array_ptr, cell_index); } } } // No valid cells found. let current_array_new = self.array.load(Acquire, &guard); if current_array == current_array_new { break; } // Resized in the meantime. current_array = current_array_new; } (None, std::ptr::null(), 0) } /// Returns the next valid cell. fn next(&self, array_ptr: *const Array<K, V>, current_index: usize) -> Option<Cursor<K, V, H>> { let guard = crossbeam_epoch::pin(); // An acquire fence is required to correctly load the contents of the array. let current_array = self.array.load(Acquire, &guard); // Bypasses the lifetime checker by not calling Shared::deref(). let current_array_ref = unsafe { &(*current_array.as_raw()) }; let old_array = current_array_ref.old_array(&guard); // Either one of the two arrays must match with array_ptr. debug_assert!(array_ptr == current_array.as_raw() || array_ptr == old_array.as_raw()); if old_array.as_raw() == array_ptr { // Bypasses the lifetime checker by not calling Shared::deref(). let old_array_ref = unsafe { &(*old_array.as_raw()) }; let num_cells = old_array_ref.num_cells(); for cell_index in (current_index + 1)..num_cells { let cell_locker = CellLocker::lock(old_array_ref.cell(cell_index), &guard); if !cell_locker.killed() && !cell_locker.empty() { if let Some(cursor) = self.pick(cell_locker, old_array.as_raw(), cell_index) { return Some(cursor); } } } } let mut new_array = Shared::<Array<K, V>>::null(); let num_cells = current_array_ref.num_cells(); let start_index = if old_array.as_raw() == array_ptr { 0 } else { current_index + 1 }; for cell_index in (start_index)..num_cells { let cell_locker = CellLocker::lock(current_array_ref.cell(cell_index), &guard); if !cell_locker.killed() && !cell_locker.empty() { if let Some(cursor) = self.pick(cell_locker, current_array.as_raw(), cell_index) { return Some(cursor); } } else if cell_locker.killed() && new_array.is_null() { new_array = self.array.load(Acquire, &guard); } } if !new_array.is_null() { // Bypasses the lifetime checker by not calling Shared::deref(). let new_array_ref = unsafe { &(*new_array.as_raw()) }; let num_cells = new_array_ref.num_cells(); for cell_index in 0..num_cells { let cell_locker = CellLocker::lock(new_array_ref.cell(cell_index), &guard); if !cell_locker.killed() && !cell_locker.empty() { if let Some(cursor) = self.pick(cell_locker, new_array.as_raw(), cell_index) { return Some(cursor); } } } } None } /// Picks a key-value pair entry using the given CellLocker. fn pick<'h>( &'h self, cell_locker: CellLocker<'h, K, V>, array_ptr: *const Array<K, V>, cell_index: usize, ) -> Option<Cursor<'h, K, V, H>> { if let Some((sub_index, entry_array_link_ptr, entry_ptr)) = cell_locker.first() { return Some(Cursor { accessor: Some(Accessor { hash_map: &self, cell_locker, cell_index, sub_index, entry_array_link_ptr, entry_ptr, }), array_ptr, activated: false, erase_on_next: false, }); } None } /// Resizes the array. fn resize(&self) { // Initial rough size estimation using a small number of cells. let guard = crossbeam_epoch::pin(); let current_array = self.array.load(Acquire, &guard); let current_array_ref = Self::array(current_array); let old_array = current_array_ref.old_array(&guard); if !old_array.is_null() { let old_array_removed = current_array_ref.partial_rehash(|key| self.hash(key), &guard); if !old_array_removed { return; } } if !self.resize_mutex.swap(true, Acquire) { let memory_ordering = Relaxed; let mut mutex_guard = scopeguard::guard(memory_ordering, |memory_ordering| { self.resize_mutex.store(false, memory_ordering); }); if current_array != self.array.load(Acquire, &guard) { return; } // The resizing policies are as follows. // - The load factor reaches 7/8, then the array grows up to 64x. // - The load factor reaches 1/16, then the array shrinks to fit. let capacity = current_array_ref.capacity(); let num_cells = current_array_ref.num_cells(); let num_cells_to_sample = (num_cells / 8).max(DEFAULT_CAPACITY / ARRAY_SIZE).min(4096); let estimated_num_entries = self.estimate(current_array_ref, num_cells_to_sample); let new_capacity = if estimated_num_entries >= (capacity / 8) * 7 { let max_capacity = 1usize << (std::mem::size_of::<usize>() * 8 - 1); if capacity == max_capacity { // Do not resize if the capacity cannot be increased. capacity } else if estimated_num_entries <= (capacity / 8) * 9 { // Doubles if the estimated size marginally exceeds the capacity. capacity * 2 } else { // Grows up to 64x let new_capacity_candidate = estimated_num_entries .next_power_of_two() .min(max_capacity / 2) * 2; if new_capacity_candidate / capacity > (1 << MAX_RESIZING_FACTOR) { capacity * (1 << MAX_RESIZING_FACTOR) } else { new_capacity_candidate } } } else if estimated_num_entries <= capacity / 8 { // Shrinks to fit. estimated_num_entries .max(self.minimum_capacity + self.additional_capacity.load(Relaxed)) .next_power_of_two() } else { capacity }; // Array::new may not be able to allocate the requested number of cells. if new_capacity != capacity { self.array.store( Owned::new(Array::<K, V>::new( new_capacity, Atomic::from(current_array), )), Release, ); // The release fence assures that future calls to the function see the latest state. *mutex_guard = Release; } } } /// Estimates the number of entries using the given number of cells. fn estimate(&self, current_array_ref: &Array<K, V>, num_cells_to_sample: usize) -> usize { let mut num_entries = 0; for i in 0..num_cells_to_sample { num_entries += current_array_ref.cell(i).size(); } num_entries * (current_array_ref.num_cells() / num_cells_to_sample) } /// Returns a reference to the Array instance. fn array(array: Shared<Array<K, V>>) -> &Array<K, V> { unsafe { array.deref() } } /// Returns a reference to the entry. fn entry(&self, entry_ptr: *const (K, V)) -> (&K, &mut V) { unsafe { let key_ptr = &(*entry_ptr).0 as *const K; let value_ptr = &(*entry_ptr).1 as *const V; let value_mut_ptr = value_ptr as *mut V; (&(*key_ptr), &mut (*value_mut_ptr)) } } } impl<K, V, H> Drop for HashMap<K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { fn drop(&mut self) { // The HashMap has become unreachable, therefore pinning is unnecessary. self.clear(); let guard = unsafe { crossbeam_epoch::unprotected() }; let current_array = self.array.load(Acquire, guard); let current_array_ref = Self::array(current_array); current_array_ref.drop_old_array(true, guard); let array = self.array.swap(Shared::null(), Relaxed, guard); if !array.is_null() { drop(unsafe { array.into_owned() }); } } } /// Ticket keeps the minimum capacity of the HashMap at a higher level. /// /// The minimum capacity is lowered when the Ticket is dropped, thereby allowing unused space to be reclaimed. pub struct Ticket<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { hash_map: &'h HashMap<K, V, H>, increment: usize, } impl<'h, K, V, H> Drop for Ticket<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { fn drop(&mut self) { let result = self .hash_map .additional_capacity .fetch_sub(self.increment, Relaxed); self.hash_map.resize(); debug_assert!(result >= self.increment); } } /// Accessor owns a key-value pair in the HashMap. /// /// It is !Send, thus disallowing other threads to have references to it. /// It acquires an exclusive lock on the Cell managing the key. /// A thread having multiple Accessor or Cursor instances poses a possibility of deadlock. pub struct Accessor<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { hash_map: &'h HashMap<K, V, H>, cell_locker: CellLocker<'h, K, V>, cell_index: usize, sub_index: u8, entry_array_link_ptr: *const link::EntryArrayLink<K, V>, entry_ptr: *const (K, V), } impl<'h, K, V, H> Accessor<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { /// Returns a reference to the key-value pair. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.get(&1); /// assert!(result.is_none()); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// (*result.get().1) = 2; /// } /// /// let result = hashmap.get(&1); /// assert_eq!(result.unwrap().get(), (&1, &mut 2)); /// ``` pub fn get(&'h self) -> (&'h K, &'h mut V) { self.hash_map.entry(self.entry_ptr) } /// Erases the key-value pair owned by the Accessor. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// let result = result.erase(); /// assert_eq!(result.unwrap(), 0); /// } /// /// let result = hashmap.get(&1); /// assert!(result.is_none()); /// ``` pub fn erase(self) -> Option<V> { if self.entry_ptr.is_null() { return None; } Some(self.hash_map.erase(self)) } } /// Cursor implements Iterator for HashMap. /// /// It is !Send, thus disallowing other threads to have references to it. /// It acquires an exclusive lock on the Cell that is currently being visited. /// A thread having multiple Accessor or Cursor instances poses a possibility of deadlock. pub struct Cursor<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { accessor: Option<Accessor<'h, K, V, H>>, array_ptr: *const Array<K, V>, activated: bool, erase_on_next: bool, } impl<'h, K, V, H> Iterator for Cursor<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { type Item = (&'h K, &'h mut V); fn next(&mut self) -> Option<Self::Item> { if !self.activated { self.activated = true; } else if self.accessor.is_some() { let erase = self.erase_on_next; if erase { self.erase_on_next = false; } if let Some((next_sub_index, next_entry_array_link_ptr, next_entry_ptr)) = self.accessor.as_mut().map_or_else( || None, |accessor| { accessor.cell_locker.next( erase, true, accessor.sub_index, accessor.entry_array_link_ptr, accessor.entry_ptr, ) }, ) { self.accessor.as_mut().map_or_else( || (), |accessor| { accessor.sub_index = next_sub_index; accessor.entry_array_link_ptr = next_entry_array_link_ptr; accessor.entry_ptr = next_entry_ptr; }, ); } else { let current_array_ptr = self.array_ptr; let cursor = self.accessor.as_ref().map_or_else( || None, |accessor| { accessor .hash_map .next(current_array_ptr, accessor.cell_index) }, ); self.accessor.take(); if let Some(mut cursor) = cursor { self.accessor = cursor.accessor.take(); self.array_ptr = cursor.array_ptr; } } } if let Some(accessor) = &self.accessor { return Some(accessor.hash_map.entry(accessor.entry_ptr)); } None } } impl<'h, K, V, H> FusedIterator for Cursor<'h, K, V, H> where K: Eq + Hash + Sync, V: Sync, H: BuildHasher, { } /// Statistics shows aggregated views of the HashMap. /// /// # Examples /// ``` /// use scc::HashMap; /// /// let hashmap: HashMap<u64, u32, _> = Default::default(); /// /// let result = hashmap.insert(1, 0); /// if let Ok(result) = result { /// assert_eq!(result.get(), (&1, &mut 0)); /// } /// /// println!("{}", hashmap.statistics()); /// ``` pub struct Statistics { effective_capacity: usize, deprecated_capacity: usize, num_entries: usize, num_killed_entries: usize, num_cells: usize, num_empty_cells: usize, num_max_consecutive_empty_cells: usize, } impl Statistics { pub fn effective_capacity(&self) -> usize { self.effective_capacity } pub fn deprecated_capacity(&self) -> usize { self.deprecated_capacity } pub fn num_entries(&self) -> usize { self.num_entries } pub fn num_killed_entries(&self) -> usize { self.num_killed_entries } pub fn num_cells(&self) -> usize { self.num_cells } pub fn num_empty_cells(&self) -> usize { self.num_empty_cells } pub fn num_max_consecutive_empty_cells(&self) -> usize { self.num_max_consecutive_empty_cells } } impl fmt::Display for Statistics { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!( f, "effective_capacity: {}, deprecated_capacity: {}, entries: {}, killed_entries: {}, cells: {}, empty_cells: {}, max_consecutive_empty_cells: {}", self.effective_capacity, self.deprecated_capacity, self.num_entries, self.num_killed_entries, self.num_cells, self.num_empty_cells, self.num_max_consecutive_empty_cells, ) } }