Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 1 | use std::cell::{Cell, RefCell}; |
| 2 | use std::vec; |
| 3 | |
| 4 | /// A trait to unify FnMut for GroupBy with the chunk key in IntoChunks |
| 5 | trait KeyFunction<A> { |
| 6 | type Key; |
| 7 | fn call_mut(&mut self, arg: A) -> Self::Key; |
| 8 | } |
| 9 | |
| 10 | impl<'a, A, K, F: ?Sized> KeyFunction<A> for F |
| 11 | where F: FnMut(A) -> K |
| 12 | { |
| 13 | type Key = K; |
| 14 | #[inline] |
| 15 | fn call_mut(&mut self, arg: A) -> Self::Key { |
| 16 | (*self)(arg) |
| 17 | } |
| 18 | } |
| 19 | |
| 20 | |
| 21 | /// ChunkIndex acts like the grouping key function for IntoChunks |
| 22 | #[derive(Debug)] |
| 23 | struct ChunkIndex { |
| 24 | size: usize, |
| 25 | index: usize, |
| 26 | key: usize, |
| 27 | } |
| 28 | |
| 29 | impl ChunkIndex { |
| 30 | #[inline(always)] |
| 31 | fn new(size: usize) -> Self { |
| 32 | ChunkIndex { |
| 33 | size, |
| 34 | index: 0, |
| 35 | key: 0, |
| 36 | } |
| 37 | } |
| 38 | } |
| 39 | |
| 40 | impl<'a, A> KeyFunction<A> for ChunkIndex { |
| 41 | type Key = usize; |
| 42 | #[inline(always)] |
| 43 | fn call_mut(&mut self, _arg: A) -> Self::Key { |
| 44 | if self.index == self.size { |
| 45 | self.key += 1; |
| 46 | self.index = 0; |
| 47 | } |
| 48 | self.index += 1; |
| 49 | self.key |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | |
| 54 | struct GroupInner<K, I, F> |
| 55 | where I: Iterator |
| 56 | { |
| 57 | key: F, |
| 58 | iter: I, |
| 59 | current_key: Option<K>, |
| 60 | current_elt: Option<I::Item>, |
| 61 | /// flag set if iterator is exhausted |
| 62 | done: bool, |
| 63 | /// Index of group we are currently buffering or visiting |
| 64 | top_group: usize, |
| 65 | /// Least index for which we still have elements buffered |
| 66 | oldest_buffered_group: usize, |
| 67 | /// Group index for `buffer[0]` -- the slots |
| 68 | /// bottom_group..oldest_buffered_group are unused and will be erased when |
| 69 | /// that range is large enough. |
| 70 | bottom_group: usize, |
| 71 | /// Buffered groups, from `bottom_group` (index 0) to `top_group`. |
| 72 | buffer: Vec<vec::IntoIter<I::Item>>, |
| 73 | /// index of last group iter that was dropped, usize::MAX == none |
| 74 | dropped_group: usize, |
| 75 | } |
| 76 | |
| 77 | impl<K, I, F> GroupInner<K, I, F> |
| 78 | where I: Iterator, |
| 79 | F: for<'a> KeyFunction<&'a I::Item, Key=K>, |
| 80 | K: PartialEq, |
| 81 | { |
| 82 | /// `client`: Index of group that requests next element |
| 83 | #[inline(always)] |
| 84 | fn step(&mut self, client: usize) -> Option<I::Item> { |
| 85 | /* |
| 86 | println!("client={}, bottom_group={}, oldest_buffered_group={}, top_group={}, buffers=[{}]", |
| 87 | client, self.bottom_group, self.oldest_buffered_group, |
| 88 | self.top_group, |
| 89 | self.buffer.iter().map(|elt| elt.len()).format(", ")); |
| 90 | */ |
| 91 | if client < self.oldest_buffered_group { |
| 92 | None |
| 93 | } else if client < self.top_group || |
| 94 | (client == self.top_group && |
| 95 | self.buffer.len() > self.top_group - self.bottom_group) |
| 96 | { |
| 97 | self.lookup_buffer(client) |
| 98 | } else if self.done { |
| 99 | None |
| 100 | } else if self.top_group == client { |
| 101 | self.step_current() |
| 102 | } else { |
| 103 | self.step_buffering(client) |
| 104 | } |
| 105 | } |
| 106 | |
| 107 | #[inline(never)] |
| 108 | fn lookup_buffer(&mut self, client: usize) -> Option<I::Item> { |
| 109 | // if `bufidx` doesn't exist in self.buffer, it might be empty |
| 110 | let bufidx = client - self.bottom_group; |
| 111 | if client < self.oldest_buffered_group { |
| 112 | return None; |
| 113 | } |
| 114 | let elt = self.buffer.get_mut(bufidx).and_then(|queue| queue.next()); |
| 115 | if elt.is_none() && client == self.oldest_buffered_group { |
| 116 | // FIXME: VecDeque is unfortunately not zero allocation when empty, |
| 117 | // so we do this job manually. |
| 118 | // `bottom_group..oldest_buffered_group` is unused, and if it's large enough, erase it. |
| 119 | self.oldest_buffered_group += 1; |
| 120 | // skip forward further empty queues too |
| 121 | while self.buffer.get(self.oldest_buffered_group - self.bottom_group) |
| 122 | .map_or(false, |buf| buf.len() == 0) |
| 123 | { |
| 124 | self.oldest_buffered_group += 1; |
| 125 | } |
| 126 | |
| 127 | let nclear = self.oldest_buffered_group - self.bottom_group; |
| 128 | if nclear > 0 && nclear >= self.buffer.len() / 2 { |
| 129 | let mut i = 0; |
| 130 | self.buffer.retain(|buf| { |
| 131 | i += 1; |
| 132 | debug_assert!(buf.len() == 0 || i > nclear); |
| 133 | i > nclear |
| 134 | }); |
| 135 | self.bottom_group = self.oldest_buffered_group; |
| 136 | } |
| 137 | } |
| 138 | elt |
| 139 | } |
| 140 | |
| 141 | /// Take the next element from the iterator, and set the done |
| 142 | /// flag if exhausted. Must not be called after done. |
| 143 | #[inline(always)] |
| 144 | fn next_element(&mut self) -> Option<I::Item> { |
| 145 | debug_assert!(!self.done); |
| 146 | match self.iter.next() { |
| 147 | None => { self.done = true; None } |
| 148 | otherwise => otherwise, |
| 149 | } |
| 150 | } |
| 151 | |
| 152 | |
| 153 | #[inline(never)] |
| 154 | fn step_buffering(&mut self, client: usize) -> Option<I::Item> { |
| 155 | // requested a later group -- walk through the current group up to |
| 156 | // the requested group index, and buffer the elements (unless |
| 157 | // the group is marked as dropped). |
| 158 | // Because the `Groups` iterator is always the first to request |
| 159 | // each group index, client is the next index efter top_group. |
| 160 | debug_assert!(self.top_group + 1 == client); |
| 161 | let mut group = Vec::new(); |
| 162 | |
| 163 | if let Some(elt) = self.current_elt.take() { |
| 164 | if self.top_group != self.dropped_group { |
| 165 | group.push(elt); |
| 166 | } |
| 167 | } |
| 168 | let mut first_elt = None; // first element of the next group |
| 169 | |
| 170 | while let Some(elt) = self.next_element() { |
| 171 | let key = self.key.call_mut(&elt); |
| 172 | match self.current_key.take() { |
| 173 | None => {} |
| 174 | Some(old_key) => if old_key != key { |
| 175 | self.current_key = Some(key); |
| 176 | first_elt = Some(elt); |
| 177 | break; |
| 178 | }, |
| 179 | } |
| 180 | self.current_key = Some(key); |
| 181 | if self.top_group != self.dropped_group { |
| 182 | group.push(elt); |
| 183 | } |
| 184 | } |
| 185 | |
| 186 | if self.top_group != self.dropped_group { |
| 187 | self.push_next_group(group); |
| 188 | } |
| 189 | if first_elt.is_some() { |
| 190 | self.top_group += 1; |
| 191 | debug_assert!(self.top_group == client); |
| 192 | } |
| 193 | first_elt |
| 194 | } |
| 195 | |
| 196 | fn push_next_group(&mut self, group: Vec<I::Item>) { |
| 197 | // When we add a new buffered group, fill up slots between oldest_buffered_group and top_group |
| 198 | while self.top_group - self.bottom_group > self.buffer.len() { |
| 199 | if self.buffer.is_empty() { |
| 200 | self.bottom_group += 1; |
| 201 | self.oldest_buffered_group += 1; |
| 202 | } else { |
| 203 | self.buffer.push(Vec::new().into_iter()); |
| 204 | } |
| 205 | } |
| 206 | self.buffer.push(group.into_iter()); |
| 207 | debug_assert!(self.top_group + 1 - self.bottom_group == self.buffer.len()); |
| 208 | } |
| 209 | |
| 210 | /// This is the immediate case, where we use no buffering |
| 211 | #[inline] |
| 212 | fn step_current(&mut self) -> Option<I::Item> { |
| 213 | debug_assert!(!self.done); |
| 214 | if let elt @ Some(..) = self.current_elt.take() { |
| 215 | return elt; |
| 216 | } |
| 217 | match self.next_element() { |
| 218 | None => None, |
| 219 | Some(elt) => { |
| 220 | let key = self.key.call_mut(&elt); |
| 221 | match self.current_key.take() { |
| 222 | None => {} |
| 223 | Some(old_key) => if old_key != key { |
| 224 | self.current_key = Some(key); |
| 225 | self.current_elt = Some(elt); |
| 226 | self.top_group += 1; |
| 227 | return None; |
| 228 | }, |
| 229 | } |
| 230 | self.current_key = Some(key); |
| 231 | Some(elt) |
| 232 | } |
| 233 | } |
| 234 | } |
| 235 | |
| 236 | /// Request the just started groups' key. |
| 237 | /// |
| 238 | /// `client`: Index of group |
| 239 | /// |
| 240 | /// **Panics** if no group key is available. |
| 241 | fn group_key(&mut self, client: usize) -> K { |
| 242 | // This can only be called after we have just returned the first |
| 243 | // element of a group. |
| 244 | // Perform this by simply buffering one more element, grabbing the |
| 245 | // next key. |
| 246 | debug_assert!(!self.done); |
| 247 | debug_assert!(client == self.top_group); |
| 248 | debug_assert!(self.current_key.is_some()); |
| 249 | debug_assert!(self.current_elt.is_none()); |
| 250 | let old_key = self.current_key.take().unwrap(); |
| 251 | if let Some(elt) = self.next_element() { |
| 252 | let key = self.key.call_mut(&elt); |
| 253 | if old_key != key { |
| 254 | self.top_group += 1; |
| 255 | } |
| 256 | self.current_key = Some(key); |
| 257 | self.current_elt = Some(elt); |
| 258 | } |
| 259 | old_key |
| 260 | } |
| 261 | } |
| 262 | |
| 263 | impl<K, I, F> GroupInner<K, I, F> |
| 264 | where I: Iterator, |
| 265 | { |
| 266 | /// Called when a group is dropped |
| 267 | fn drop_group(&mut self, client: usize) { |
| 268 | // It's only useful to track the maximal index |
| 269 | if self.dropped_group == !0 || client > self.dropped_group { |
| 270 | self.dropped_group = client; |
| 271 | } |
| 272 | } |
| 273 | } |
| 274 | |
| 275 | /// `GroupBy` is the storage for the lazy grouping operation. |
| 276 | /// |
| 277 | /// If the groups are consumed in their original order, or if each |
| 278 | /// group is dropped without keeping it around, then `GroupBy` uses |
| 279 | /// no allocations. It needs allocations only if several group iterators |
| 280 | /// are alive at the same time. |
| 281 | /// |
| 282 | /// This type implements `IntoIterator` (it is **not** an iterator |
| 283 | /// itself), because the group iterators need to borrow from this |
| 284 | /// value. It should be stored in a local variable or temporary and |
| 285 | /// iterated. |
| 286 | /// |
| 287 | /// See [`.group_by()`](../trait.Itertools.html#method.group_by) for more information. |
| 288 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 289 | pub struct GroupBy<K, I, F> |
| 290 | where I: Iterator, |
| 291 | { |
| 292 | inner: RefCell<GroupInner<K, I, F>>, |
| 293 | // the group iterator's current index. Keep this in the main value |
| 294 | // so that simultaneous iterators all use the same state. |
| 295 | index: Cell<usize>, |
| 296 | } |
| 297 | |
| 298 | /// Create a new |
| 299 | pub fn new<K, J, F>(iter: J, f: F) -> GroupBy<K, J::IntoIter, F> |
| 300 | where J: IntoIterator, |
| 301 | F: FnMut(&J::Item) -> K, |
| 302 | { |
| 303 | GroupBy { |
| 304 | inner: RefCell::new(GroupInner { |
| 305 | key: f, |
| 306 | iter: iter.into_iter(), |
| 307 | current_key: None, |
| 308 | current_elt: None, |
| 309 | done: false, |
| 310 | top_group: 0, |
| 311 | oldest_buffered_group: 0, |
| 312 | bottom_group: 0, |
| 313 | buffer: Vec::new(), |
| 314 | dropped_group: !0, |
| 315 | }), |
| 316 | index: Cell::new(0), |
| 317 | } |
| 318 | } |
| 319 | |
| 320 | impl<K, I, F> GroupBy<K, I, F> |
| 321 | where I: Iterator, |
| 322 | { |
| 323 | /// `client`: Index of group that requests next element |
| 324 | fn step(&self, client: usize) -> Option<I::Item> |
| 325 | where F: FnMut(&I::Item) -> K, |
| 326 | K: PartialEq, |
| 327 | { |
| 328 | self.inner.borrow_mut().step(client) |
| 329 | } |
| 330 | |
| 331 | /// `client`: Index of group |
| 332 | fn drop_group(&self, client: usize) { |
| 333 | self.inner.borrow_mut().drop_group(client) |
| 334 | } |
| 335 | } |
| 336 | |
| 337 | impl<'a, K, I, F> IntoIterator for &'a GroupBy<K, I, F> |
| 338 | where I: Iterator, |
| 339 | I::Item: 'a, |
| 340 | F: FnMut(&I::Item) -> K, |
| 341 | K: PartialEq |
| 342 | { |
| 343 | type Item = (K, Group<'a, K, I, F>); |
| 344 | type IntoIter = Groups<'a, K, I, F>; |
| 345 | |
| 346 | fn into_iter(self) -> Self::IntoIter { |
| 347 | Groups { parent: self } |
| 348 | } |
| 349 | } |
| 350 | |
| 351 | |
| 352 | /// An iterator that yields the Group iterators. |
| 353 | /// |
| 354 | /// Iterator element type is `(K, Group)`: |
| 355 | /// the group's key `K` and the group's iterator. |
| 356 | /// |
| 357 | /// See [`.group_by()`](../trait.Itertools.html#method.group_by) for more information. |
| 358 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 359 | pub struct Groups<'a, K: 'a, I: 'a, F: 'a> |
| 360 | where I: Iterator, |
| 361 | I::Item: 'a |
| 362 | { |
| 363 | parent: &'a GroupBy<K, I, F>, |
| 364 | } |
| 365 | |
| 366 | impl<'a, K, I, F> Iterator for Groups<'a, K, I, F> |
| 367 | where I: Iterator, |
| 368 | I::Item: 'a, |
| 369 | F: FnMut(&I::Item) -> K, |
| 370 | K: PartialEq |
| 371 | { |
| 372 | type Item = (K, Group<'a, K, I, F>); |
| 373 | |
| 374 | #[inline] |
| 375 | fn next(&mut self) -> Option<Self::Item> { |
| 376 | let index = self.parent.index.get(); |
| 377 | self.parent.index.set(index + 1); |
| 378 | let inner = &mut *self.parent.inner.borrow_mut(); |
| 379 | inner.step(index).map(|elt| { |
| 380 | let key = inner.group_key(index); |
| 381 | (key, Group { |
| 382 | parent: self.parent, |
| 383 | index, |
| 384 | first: Some(elt), |
| 385 | }) |
| 386 | }) |
| 387 | } |
| 388 | } |
| 389 | |
| 390 | /// An iterator for the elements in a single group. |
| 391 | /// |
| 392 | /// Iterator element type is `I::Item`. |
| 393 | pub struct Group<'a, K: 'a, I: 'a, F: 'a> |
| 394 | where I: Iterator, |
| 395 | I::Item: 'a, |
| 396 | { |
| 397 | parent: &'a GroupBy<K, I, F>, |
| 398 | index: usize, |
| 399 | first: Option<I::Item>, |
| 400 | } |
| 401 | |
| 402 | impl<'a, K, I, F> Drop for Group<'a, K, I, F> |
| 403 | where I: Iterator, |
| 404 | I::Item: 'a, |
| 405 | { |
| 406 | fn drop(&mut self) { |
| 407 | self.parent.drop_group(self.index); |
| 408 | } |
| 409 | } |
| 410 | |
| 411 | impl<'a, K, I, F> Iterator for Group<'a, K, I, F> |
| 412 | where I: Iterator, |
| 413 | I::Item: 'a, |
| 414 | F: FnMut(&I::Item) -> K, |
| 415 | K: PartialEq, |
| 416 | { |
| 417 | type Item = I::Item; |
| 418 | #[inline] |
| 419 | fn next(&mut self) -> Option<Self::Item> { |
| 420 | if let elt @ Some(..) = self.first.take() { |
| 421 | return elt; |
| 422 | } |
| 423 | self.parent.step(self.index) |
| 424 | } |
| 425 | } |
| 426 | |
| 427 | ///// IntoChunks ///// |
| 428 | |
| 429 | /// Create a new |
| 430 | pub fn new_chunks<J>(iter: J, size: usize) -> IntoChunks<J::IntoIter> |
| 431 | where J: IntoIterator, |
| 432 | { |
| 433 | IntoChunks { |
| 434 | inner: RefCell::new(GroupInner { |
| 435 | key: ChunkIndex::new(size), |
| 436 | iter: iter.into_iter(), |
| 437 | current_key: None, |
| 438 | current_elt: None, |
| 439 | done: false, |
| 440 | top_group: 0, |
| 441 | oldest_buffered_group: 0, |
| 442 | bottom_group: 0, |
| 443 | buffer: Vec::new(), |
| 444 | dropped_group: !0, |
| 445 | }), |
| 446 | index: Cell::new(0), |
| 447 | } |
| 448 | } |
| 449 | |
| 450 | |
| 451 | /// `ChunkLazy` is the storage for a lazy chunking operation. |
| 452 | /// |
| 453 | /// `IntoChunks` behaves just like `GroupBy`: it is iterable, and |
| 454 | /// it only buffers if several chunk iterators are alive at the same time. |
| 455 | /// |
| 456 | /// This type implements `IntoIterator` (it is **not** an iterator |
| 457 | /// itself), because the chunk iterators need to borrow from this |
| 458 | /// value. It should be stored in a local variable or temporary and |
| 459 | /// iterated. |
| 460 | /// |
| 461 | /// Iterator element type is `Chunk`, each chunk's iterator. |
| 462 | /// |
| 463 | /// See [`.chunks()`](../trait.Itertools.html#method.chunks) for more information. |
| 464 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 465 | pub struct IntoChunks<I> |
| 466 | where I: Iterator, |
| 467 | { |
| 468 | inner: RefCell<GroupInner<usize, I, ChunkIndex>>, |
| 469 | // the chunk iterator's current index. Keep this in the main value |
| 470 | // so that simultaneous iterators all use the same state. |
| 471 | index: Cell<usize>, |
| 472 | } |
| 473 | |
| 474 | |
| 475 | impl<I> IntoChunks<I> |
| 476 | where I: Iterator, |
| 477 | { |
| 478 | /// `client`: Index of chunk that requests next element |
| 479 | fn step(&self, client: usize) -> Option<I::Item> { |
| 480 | self.inner.borrow_mut().step(client) |
| 481 | } |
| 482 | |
| 483 | /// `client`: Index of chunk |
| 484 | fn drop_group(&self, client: usize) { |
| 485 | self.inner.borrow_mut().drop_group(client) |
| 486 | } |
| 487 | } |
| 488 | |
| 489 | impl<'a, I> IntoIterator for &'a IntoChunks<I> |
| 490 | where I: Iterator, |
| 491 | I::Item: 'a, |
| 492 | { |
| 493 | type Item = Chunk<'a, I>; |
| 494 | type IntoIter = Chunks<'a, I>; |
| 495 | |
| 496 | fn into_iter(self) -> Self::IntoIter { |
| 497 | Chunks { |
| 498 | parent: self, |
| 499 | } |
| 500 | } |
| 501 | } |
| 502 | |
| 503 | |
| 504 | /// An iterator that yields the Chunk iterators. |
| 505 | /// |
| 506 | /// Iterator element type is `Chunk`. |
| 507 | /// |
| 508 | /// See [`.chunks()`](../trait.Itertools.html#method.chunks) for more information. |
| 509 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 510 | pub struct Chunks<'a, I: 'a> |
| 511 | where I: Iterator, |
| 512 | I::Item: 'a, |
| 513 | { |
| 514 | parent: &'a IntoChunks<I>, |
| 515 | } |
| 516 | |
| 517 | impl<'a, I> Iterator for Chunks<'a, I> |
| 518 | where I: Iterator, |
| 519 | I::Item: 'a, |
| 520 | { |
| 521 | type Item = Chunk<'a, I>; |
| 522 | |
| 523 | #[inline] |
| 524 | fn next(&mut self) -> Option<Self::Item> { |
| 525 | let index = self.parent.index.get(); |
| 526 | self.parent.index.set(index + 1); |
| 527 | let inner = &mut *self.parent.inner.borrow_mut(); |
| 528 | inner.step(index).map(|elt| { |
| 529 | Chunk { |
| 530 | parent: self.parent, |
| 531 | index, |
| 532 | first: Some(elt), |
| 533 | } |
| 534 | }) |
| 535 | } |
| 536 | } |
| 537 | |
| 538 | /// An iterator for the elements in a single chunk. |
| 539 | /// |
| 540 | /// Iterator element type is `I::Item`. |
| 541 | pub struct Chunk<'a, I: 'a> |
| 542 | where I: Iterator, |
| 543 | I::Item: 'a, |
| 544 | { |
| 545 | parent: &'a IntoChunks<I>, |
| 546 | index: usize, |
| 547 | first: Option<I::Item>, |
| 548 | } |
| 549 | |
| 550 | impl<'a, I> Drop for Chunk<'a, I> |
| 551 | where I: Iterator, |
| 552 | I::Item: 'a, |
| 553 | { |
| 554 | fn drop(&mut self) { |
| 555 | self.parent.drop_group(self.index); |
| 556 | } |
| 557 | } |
| 558 | |
| 559 | impl<'a, I> Iterator for Chunk<'a, I> |
| 560 | where I: Iterator, |
| 561 | I::Item: 'a, |
| 562 | { |
| 563 | type Item = I::Item; |
| 564 | #[inline] |
| 565 | fn next(&mut self) -> Option<Self::Item> { |
| 566 | if let elt @ Some(..) = self.first.take() { |
| 567 | return elt; |
| 568 | } |
| 569 | self.parent.step(self.index) |
| 570 | } |
| 571 | } |