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
use std::cell::{Cell, RefCell};
use std::cmp::max;
use std::fmt::{Debug, Formatter};
use std::marker::PhantomData;
use std::mem::{forget, size_of, transmute};
use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
use std::ptr::{drop_in_place, null_mut, write, NonNull};
use std::slice::{from_raw_parts, from_raw_parts_mut};
use smallvec::SmallVec;
use crate::arena_chunk::ArenaChunk;
use crate::{PtrUnstables, HUGE_PAGE, PAGE};
#[cfg(test)]
mod tests;
/// An arena that can hold objects of only one type, allocations return shared references, and can
/// iterate behind a shared reference
pub type TypedArena<T> = TypedArenaGen<T, Shared>;
/// An arena that can hold objects of only one type, allocations return mutable references, and can
/// only iterate behind a mutable reference
pub type TypedArenaMut<T> = TypedArenaGen<T, Mutable>;
/// An arena that can hold objects of only one type. `RM` determines whether the references
/// returned from allocation are mutable and whether iteration requires a mutable reference; either
/// mutating returned references or iterating via immutable reference are possible, but not both.
pub struct TypedArenaGen<T, RM: RefMutability> {
/// The number of inserted entries
len: Cell<usize>,
/// A pointer to the next object to be allocated.
ptr: Cell<*mut T>,
/// A pointer to the end of the allocated area. When this pointer is
/// reached, a new chunk is allocated.
end: Cell<*mut T>,
/// A vector of arena chunks.
chunks: RefCell<Vec<ArenaChunk<T>>>,
/// The # of chunks actually used by the arena. The rest were allocated but are now empty,
/// and we will try to re-use them before allocating a new chunk.
used_chunks: Cell<usize>,
/// Marker indicating that dropping the arena causes its owned
/// instances of `T` to be dropped.
_own: PhantomData<T>,
/// RM is a phantom type parameter so we need this
_rm: PhantomData<RM>,
}
/// Iterates all elements in an arena, and can handle new elements being allocated during iteration.
pub type Iter<'a, T> = IterGen<'a, T, Shared>;
/// Iterates all elements in an arena.
pub type IterMut<'a, T> = IterGen<'a, T, Mutable>;
/// Iterates all elements in an arena, and if [Shared], can handle new elements being allocated
/// during iteration.
pub struct IterGen<'a, T, RM: RefMutability>(PtrIter<'a, T>, PhantomData<RM>);
/// Iterates pointers to all elements in the arena, and (if shared) can handle new elements being
/// allocated during iteration.
pub struct PtrIter<'a, T> {
/// The arena being iterated. The actual `RM` is irrelevant, we put [Shared] because we only use
/// it like that and there may be other active references, but it may be `transmute`d.
arena: &'a TypedArena<T>,
/// Index of the current chunk being iterated
chunk_index: usize,
/// Pointer to the next entry in the current chunk being iterated
chunk_data: NonNull<T>,
/// Entries remaining in the current chunk being iterated, **except** like [ArenaChunk], if we
/// are iterating the last chunk, this will be 0 (unset) even though we have more entries
chunk_remaining_entries: usize,
/// Index in the arena of the current element being iterated
element_index: usize,
}
/// An iterable which can be allocated faster into the arena than the default [IntoIterator]
/// implementation, using [TypedArenaGen::alloc_raw_slice].
///
/// `rustc_arena` uses default implementations, but those are unstable, so instead you will need to
/// call [TypedArenaGen::alloc_from_iter_fast] manually. Unlike `rustc_arena` you can implement this on
/// your own collections, although they will probably just delegate to one of builtin
/// implementations; and often, simply using [TypedArenaGen::alloc_from_iter_reg] will as fast or fast
/// enough, and you won't need a custom implementation at all.
pub trait IterWithFastAlloc<T> {
fn alloc_into<RM: RefMutability>(self, arena: &TypedArenaGen<T, RM>) -> RM::SliceRef<'_, T>;
}
/// Whether references to allocated objects are mutable, and iteration requires a mutable reference.
pub trait RefMutability: private::Sealed + 'static {
/// `&T` or `&mut T`
type Ref<'a, T>
where
T: 'a;
/// `&[T]` or `&mut T`
type SliceRef<'a, T>
where
T: 'a;
/// Reference to the empty slice
fn empty<'a, T>() -> Self::SliceRef<'a, T>;
/// Dereference a pointer
///
/// # Safety
/// The pointer must be valid: see [pointer::as_ref] and [pointer::as_mut]'s requirements (the
/// latter's are required if `Self` is [Mutable])
///
/// [pointer::as_ref]: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref
/// [pointer::as_mut]: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_mut
unsafe fn from_ptr<'a, T>(t: *mut T) -> Self::Ref<'a, T>;
/// Dereference a pointer and add length metadata to make it a slice reference
///
/// # Safety
/// The pointer must be valid: see [pointer::as_ref] and [pointer::as_mut]'s requirements (the
/// latter's are required if `Self` is [Mutable]). Additionally, you must follow the
/// requirements of [from_raw_parts] or [from_raw_parts_mut]
///
/// [pointer::as_ref]: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref
/// [pointer::as_mut]: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_mut
unsafe fn from_raw_parts<'a, T>(t: *mut T, len: usize) -> Self::SliceRef<'a, T>;
/// Convert a reference of this type into a shared reference
#[allow(clippy::wrong_self_convention)]
fn as_ref<T>(t: Self::Ref<'_, T>) -> &T;
/// Convert a reference of this slice type into a shared reference
#[allow(clippy::wrong_self_convention)]
fn as_slice_ref<T>(t: Self::SliceRef<'_, T>) -> &[T];
/// Dereference a non-null pointer
///
/// # Safety
/// The pointer must be valid: see [NonNull::as_ref] and [NonNull::as_mut]'s requirements (the
/// latter's are required if `Self` is [Mutable])
#[inline]
unsafe fn from_non_null<'a, T>(t: NonNull<T>) -> Self::Ref<'a, T> {
Self::from_ptr(t.as_ptr())
}
}
pub enum Shared {}
pub enum Mutable {}
impl<T, RM: RefMutability> Default for TypedArenaGen<T, RM> {
/// Creates a new, empty arena
#[inline]
fn default() -> Self {
Self::new()
}
}
impl<T, RM: RefMutability> TypedArenaGen<T, RM> {
/// Creates a new, empty arena
#[inline]
pub fn new() -> Self {
Self {
len: Cell::new(0),
// We set both `ptr` and `end` to 0 so that the first call to
// alloc() will trigger a grow().
ptr: Cell::new(null_mut()),
end: Cell::new(null_mut()),
chunks: Default::default(),
used_chunks: Cell::new(0),
_own: PhantomData,
_rm: PhantomData,
}
}
/// Allocates an object in the `TypedArena`, returning a reference to it.
///
/// If the type parameter `RM` is [Shared] we return a shared reference. If `RM` is [Mutable] we
/// return a mutable reference.
#[inline]
pub fn alloc(&self, object: T) -> RM::Ref<'_, T> {
self.len.set(self.len.get() + 1);
if size_of::<T>() == 0 {
// We don't actually allocate ZSTs, just prevent them from being dropped and return a
// reference to random data (this is a valid ZST reference).
unsafe {
let ptr = NonNull::<T>::dangling().as_ptr();
// This `write` is equivalent to `forget`
write(ptr, object);
return RM::from_ptr(ptr);
}
}
if self.ptr == self.end {
self.grow(1)
}
unsafe {
let ptr = self.ptr.get();
// Advance the pointer.
self.ptr.set(self.ptr.get().add(1));
// Write into uninitialized memory.
write(ptr, object);
RM::from_ptr(ptr)
}
}
/// Allocates multiple objects in a contiguous slice, returning a reference to the slice.
///
/// If the type parameter `RM` is [Shared] we return a shared reference. If `RM` is [Mutable] we
/// return a mutable reference.
///
/// This collects into a `SmallVec` and then allocates by copying from it. Use `alloc_from_iter`
/// if possible because it's more efficient, copying directly without the intermediate
/// collecting step. This default could be made more efficient, like
/// [crate::DroplessArena::alloc_from_iter], but it's not hot enough to bother.
#[inline]
pub fn alloc_from_iter_reg(&self, iter: impl IntoIterator<Item = T>) -> RM::SliceRef<'_, T> {
self.alloc_from_iter_fast(iter.into_iter().collect::<SmallVec<[_; 8]>>())
}
/// Allocates multiple objects in a contiguous slice, returning a reference to the slice.
///
/// If the type parameter `RM` is [Shared] we return a shared reference. If `RM` is [Mutable] we
/// return a mutable reference.
///
/// This is equivalent semantics to [Self::alloc_from_iter_reg] except it's faster, whereas
/// [Self::alloc_from_iter_reg] permits more types.
#[inline]
pub fn alloc_from_iter_fast(&self, iter: impl IterWithFastAlloc<T>) -> RM::SliceRef<'_, T> {
iter.alloc_into(self)
}
/// Number of allocated elements in the arena.
#[inline]
pub fn len(&self) -> usize {
self.len.get()
}
/// Does the arena have any allocated elements?
#[inline]
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Iterates all allocated elements in the arena behind a mutable reference.
#[inline]
pub fn iter_mut(&mut self) -> IterMut<'_, T> {
// SAFETY: Same repr, this transmuted version won't be publicly exposed or used incorrectly
// (we can't use while [IterMut] is alive), and we're not actually violating any borrow
// rules with a mutable phantom type like we would if this was a mutable reference.
IterMut::new(unsafe { transmute(self) })
}
/// Iterates pointers to all allocated elements in the arena behind a shared reference. This is
/// allows since we can have pointers even to mutably borrowed elements.
#[inline]
pub fn ptr_iter(&self) -> PtrIter<'_, T> {
PtrIter::new(self)
}
/// Clears the arena, dropping all elements, but doesn't free up its memory.
///
/// This means we can insert new elements without having to reallocate, until we reach the old
/// capacity or allocate a slice too large to fit in an existing region.
#[inline]
pub fn clear(&mut self) {
// Ensure that, even on panic, we resize len (we leak elements we didn't drop yet instead of
// double-freeing elements we did)
let panic_result = catch_unwind(AssertUnwindSafe(|| {
for elem in self.ptr_iter() {
// SAFETY: we're shrinking the arena, so we A) won't drop later if we drop the arena
// before growing it again, and B) if we do grow it again, we'll overwrite this data
// before setting it to "initialized" (we might also grow past this data but it will
// still be uninitialized and therefore not dropped).
//
// Also, elem.as_ptr() is alive, and we have the only reference since we have a mutable
// reference to the entire arena.
unsafe {
drop_in_place(elem.as_ptr());
}
}
}));
// This code will run even if we panic
// Update len, num used chunks, used chunk entries, ptr, and end
self.len.set(0);
if size_of::<T>() != 0 {
for chunk in self
.chunks
.borrow_mut()
.iter_mut()
.take(self.used_chunks.get())
{
chunk.entries = 0;
}
self.used_chunks.set(0);
// ptr and end can be null and we'll still reuse instead of allocating new chunks
self.ptr.set(null_mut());
self.end.set(null_mut());
}
// Still unwind if we panicked
if let Err(caught_panic) = panic_result {
resume_unwind(caught_panic)
}
}
/// Removes some elements from this arena, and coalesces the rest so that we don't have gaps.
///
/// Pointers to regions in the memory may be invalidated as elements get rearranged. This
/// function is behind a mutable reference, which ensures that there are no references to
/// rearranged elements, but if there are any raw pointers they can no longer be dereferenced
/// without UB.
#[inline]
pub fn retain(&mut self, mut predicate: impl FnMut(&mut T) -> bool) {
// Ensure that, even on panic, we resize len (we leak elements we didn't drop yet instead of
// double-freeing elements we did). Furthermore, kept elements are still in the arena,
// although this doesn't really matter and is subject to change between versions.
let mut num_kept = 0;
let panic_result = catch_unwind(AssertUnwindSafe(|| {
let mut write_iter = self.ptr_iter();
let mut is_write_iter_at_read_iter = true;
for mut elem in self.ptr_iter() {
let elem_ptr = elem.as_ptr();
// SAFETY: elem is alive (Self::iter and Self::ptr_iter only iterate initialized data)
// and we have a mutable reference to the arena, so there are no other references to
// elem. Therefore, we can dereference and drop elem_ptr.
//
// write_ptr is allocated (inside this struct) and aligned (came from Self::ptr_iter).
// It has previously pointed to a live object since it has been elem_ptr, but we may
// have dropped that elem_ptr so it's no longer alive. However, we can still write to
// it.
//
// Lastly, we can read from elem_ptr when we write to write_ptr (effectively copying the
// value) because we will either overwrite the value when write_ptr advances to it, or
// (if elem_ptr advances to the end first) we will shrink the arena to be before it, so
// that it is effectively forgotten; and then it will either be re-allocated if we grow
// the arena again, or released without drop if we drop the arena.
unsafe {
if !predicate(elem.as_mut()) {
// Drop the element, keep write_iter at the same position
is_write_iter_at_read_iter = false;
drop_in_place(elem_ptr);
} else {
// Keep the element, but move it to write_iter if unaligned. Advance write_iter
num_kept += 1;
// If write_chunk can hold more elements (length < capacity), we should
// desync write_iter from read_iter and do so (length = capacity)
let mut next_is_write_iter_at_read_iter = is_write_iter_at_read_iter;
if write_iter.chunk_remaining_entries == 1 {
let mut chunks = self.chunks.borrow_mut();
let write_chunk = chunks
.get_mut(write_iter.chunk_index)
.expect("write_iter chunk index out of bounds");
let difference = write_chunk.capacity - write_chunk.entries;
if difference > 0 {
// If write_iter and read_iter are still synced, they'll be synced
// for this element and then desynced after.
//
// Also, we can't just put write_iter.next() before this block
// because we need to catch chunk_remaining_entries == 1 first
next_is_write_iter_at_read_iter = false;
// This may not be the last chunk, so we need to update the count.
// We also need to update write_iter's count so that it won't reach
// the chunk end until it reaches write_chunk's capacity.
write_chunk.entries += difference;
write_iter.chunk_remaining_entries += difference;
// Even if elem_iter (the implicit iterator returning elem) is
// synced, we still want it to move on, not read the chunk's
// remaining memory because it;s uninitialized
}
}
let write_ptr = write_iter.next()
.expect("read_iter not done but write_iter is, write_iter should always be behind")
.as_ptr();
if size_of::<T>() != 0 && !is_write_iter_at_read_iter {
write_ptr.write(elem_ptr.read());
}
is_write_iter_at_read_iter = next_is_write_iter_at_read_iter;
}
}
}
}));
// This code will run even if we panic
// Update len, num used chunks, used chunk entries, ptr, and end
let old_len = self.len.get();
self.len.set(num_kept);
if size_of::<T>() != 0 {
let mut chunks = self.chunks.borrow_mut();
let mut num_entries = 0;
let used_chunks = chunks
.iter()
.take_while(|chunk| {
if num_entries < num_kept {
num_entries += chunk.entries;
true
} else {
false
}
})
.count();
if num_entries < num_kept {
debug_assert_eq!(used_chunks, self.used_chunks.get());
num_entries = old_len;
} else {
self.used_chunks.set(used_chunks);
}
if used_chunks == 0 {
// These assertions are pretty obvious
debug_assert_eq!((num_entries, num_kept), (0, 0));
self.ptr.set(null_mut());
self.end.set(null_mut());
} else {
let num_in_last = num_entries - num_kept;
let last_chunk = &mut chunks[used_chunks - 1];
// This is the last chunk, so unset (0) its entries, even though there actually are some
last_chunk.entries = 0;
// Set ptr and end to this chunk, and make sure ptr is offset past the existing entries
self.ptr.set(unsafe { last_chunk.storage.add(num_in_last) });
self.end.set(last_chunk.end());
}
}
// Still unwind if we panicked
if let Err(caught_panic) = panic_result {
resume_unwind(caught_panic)
}
}
/// Return `self` but with a different [RefMutability].
///
/// With a mutable reference, we can convert between mutable and immutable variants, since there
/// are no live allocated references.
#[inline]
pub fn convert<RM2: RefMutability>(self) -> TypedArenaGen<T, RM2> {
// SAFETY: Same repr
unsafe { transmute(self) }
}
/// Destroys this arena and collects all elements into a vector.
#[inline]
pub fn into_vec(self) -> Vec<T> {
let mut elements = Vec::with_capacity(self.len());
if size_of::<T>() == 0 {
// Create `len` ZSTs which will be dropped when the vector is.
// Remember: a random non-null pointer is a valid reference to a ZST, and dereferencing
// is probably a no-op
elements.extend(
(0..self.len()).map(|_| unsafe { NonNull::<T>::dangling().as_ptr().read() }),
);
return elements;
}
let mut remaining = self.len();
let mut chunks_borrow = self.chunks.borrow_mut();
let mut prev_chunk = None;
for chunk in chunks_borrow.iter_mut().take(self.used_chunks.get()) {
if let Some(prev_chunk) = prev_chunk.replace(chunk) {
// SAFETY: This chunk has all entries filled because we've moved on to the next one
// (and we resize the chunk's entries when we move on, even though it has more capacity).
let mut prev_entries = unsafe { prev_chunk.destroy_and_return(prev_chunk.entries) };
elements.append(&mut prev_entries);
remaining -= prev_chunk.entries;
}
}
if let Some(last_chunk) = prev_chunk {
// SAFETY: This chunk only has `remaining` entries filled
let mut last_entries = unsafe { last_chunk.destroy_and_return(remaining) };
elements.append(&mut last_entries);
}
// Ensure we don't destroy these chunks' contents in `Drop`, only free their memory
self.used_chunks.set(0);
elements
}
/// Checks if `additional` elements can be inserted into the arena without creating a new chunk
#[inline]
fn can_allocate(&self, additional: usize) -> bool {
debug_assert_ne!(size_of::<T>(), 0);
// FIXME: this should *likely* use `offset_from`, but more
// investigation is needed (including running tests in miri).
let available_bytes = self.end.get().addr_() - self.ptr.get().addr_();
let additional_bytes = additional.checked_mul(size_of::<T>()).unwrap();
available_bytes >= additional_bytes
}
/// Ensures there's enough space in the current chunk to fit `len` objects. If not, it will
/// create a new chunk.
#[inline]
fn ensure_capacity(&self, additional: usize) {
if !self.can_allocate(additional) {
self.grow(additional);
debug_assert!(self.can_allocate(additional));
}
}
/// Allocate a contiguous slice of data and return a pointer to the start of the slice. The
/// slice is uninitialized (why we return a pointer), and you must initialize it before calling
/// other arena methods or dropping the arena, or you will cause UB.
///
/// # Safety
///
/// You must initialize the slice before calling other arena methods or dropping the arena. If
/// iterating, you must initialize the slice before advancing the iterator.
#[inline]
pub unsafe fn alloc_raw_slice(&self, len: usize) -> *mut T {
assert_ne!(len, 0);
self.len.set(self.len.get() + len);
if size_of::<T>() == 0 {
// ZSTs have no memory, so we won't allocate.
// Remember: a random non-null pointer is a valid reference to a ZST
return NonNull::<T>::dangling().as_ptr();
}
self.ensure_capacity(len);
let start_ptr = self.ptr.get();
self.ptr.set(start_ptr.add(len));
start_ptr
}
/// Grows the arena = creates a new chunk which will hold at least `additional` elements,
/// or reuses a chunk if we have extras.
#[inline(never)]
#[cold]
fn grow(&self, additional: usize) {
debug_assert_ne!(size_of::<T>(), 0);
let used_chunks = self.used_chunks.get();
let mut chunks = self.chunks.borrow_mut();
let mut reused_a_chunk = false;
for potential_reuse_idx in used_chunks..chunks.len() {
let potential_reuse_chunk = &mut chunks[potential_reuse_idx];
if potential_reuse_chunk.capacity >= additional {
// We found a chunk that can hold the additional elements, so we'll use it.
// Make sure to update the # entries; since this is the last chunk, we unset (0) it
// even though there are actually additional (see `ArenaChunk.entries` doc)
potential_reuse_chunk.entries = 0;
// Set ptr and end to the reused chunk
self.ptr.set(potential_reuse_chunk.storage);
self.end.set(potential_reuse_chunk.end());
if used_chunks != potential_reuse_idx {
// We have to ensure the reused chunk is the next one
chunks.swap(used_chunks, potential_reuse_idx);
}
reused_a_chunk = true;
break;
}
}
if !reused_a_chunk {
// Actually grow = insert a chunk at used_chunks with the required capacity
unsafe {
// We need the element size to convert chunk sizes (ranging from
// PAGE to HUGE_PAGE bytes) to element counts.
let elem_size = max(1, size_of::<T>());
let mut new_cap;
if let Some(last_chunk) = used_chunks.checked_sub(1).map(|i| &mut chunks[i]) {
// If a type is `!needs_drop`, we don't need to keep track of how many elements
// the chunk stores - the field will be ignored anyway.
// FIXME: this should *likely* use `offset_from`, but more
// investigation is needed (including running tests in miri).
let used_bytes = self.ptr.get().addr_() - last_chunk.storage.addr_();
// Set # entries since this is no longer the last chunk
last_chunk.entries = used_bytes / size_of::<T>();
// If the previous chunk's capacity is less than HUGE_PAGE
// bytes, then this chunk will be least double the previous
// chunk's size.
new_cap = last_chunk.capacity.min(HUGE_PAGE / elem_size / 2);
new_cap *= 2;
} else {
new_cap = PAGE / elem_size;
}
// Also ensure that this chunk can fit `additional`.
new_cap = max(additional, new_cap);
let mut chunk = ArenaChunk::<T>::new(new_cap);
// Set ptr and end to the new chunk
self.ptr.set(chunk.storage);
self.end.set(chunk.end());
// Add chunk to index used_chunks (used_chunks will be incremented in grow())
let last_index = chunks.len();
chunks.push(chunk);
if used_chunks < last_index {
chunks.swap(used_chunks, last_index);
}
}
}
self.used_chunks.set(used_chunks + 1);
}
/// Drops the contents of the last chunk. The last chunk is partially empty, unlike all other
/// chunks.
fn clear_last_chunk(&self, last_chunk: &mut ArenaChunk<T>) {
debug_assert_ne!(size_of::<T>(), 0);
// Determine how much was filled.
let start = last_chunk.storage.addr_();
// We obtain the value of the pointer to the first uninitialized element.
let end = self.ptr.get().addr_();
// We then calculate the number of elements to be dropped in the last chunk,
// which is the filled area's length.
// FIXME: this should *likely* use `offset_from`, but more
// investigation is needed (including running tests in miri).
let diff = (end - start) / size_of::<T>();
// Pass that to the `destroy` method.
unsafe {
last_chunk.destroy(diff);
}
// Reset the chunk.
self.ptr.set(last_chunk.storage);
}
}
impl<T> TypedArenaGen<T, Shared> {
/// Iterates all allocated elements in the arena behind a shared reference.
///
/// The iterator can handle new objects being allocated. If you allocate new objects they will
/// be added to the end. If the iterator has already ended and you allocate new objects, it will
/// suddenly have more elements; if you don't want that behavior use `fuse`.
#[inline]
pub fn iter(&self) -> Iter<'_, T> {
Iter::new(self)
}
}
impl<T: Debug> Debug for TypedArena<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
write!(f, "TypedArena")?;
f.debug_list().entries(self.iter()).finish()
}
}
impl<T, RM: RefMutability> Drop for TypedArenaGen<T, RM> {
fn drop(&mut self) {
if size_of::<T>() == 0 {
// These invariants always hold, we only assert them here
debug_assert!(self.ptr.get().is_null());
debug_assert!(self.end.get().is_null());
debug_assert_eq!(self.chunks.borrow().len(), 0);
debug_assert_eq!(self.used_chunks.get(), 0);
// Drop `len` ZSTs.
// Remember: a dangling pointer is a valid ZST reference, `drop_in_place` will only run
// the ZSTs drop code (which probably shouldn't rely on the address, since it was
// allocated into an arena and therefore already in an effectively undefined location,
// without any adjacent structures)
for _ in 0..self.len() {
unsafe {
drop_in_place(NonNull::<T>::dangling().as_ptr());
}
}
} else {
// `ArenaChunk` drop ensures that the memory is dropped, but we have to drop the contents
// here because chunks can't because they don't always know their size
unsafe {
// Determine how much was filled.
let mut chunks_borrow = self.chunks.borrow_mut();
// Remove unused chunks (we don't need to destroy because we've already dropped or moved
// their contents)
for _ in 0..(chunks_borrow.len() - self.used_chunks.get()) {
chunks_borrow.pop();
}
// Drop elements in the used chunks
if let Some(mut last_chunk) = chunks_borrow.pop() {
// Drop the contents of the last chunk.
self.clear_last_chunk(&mut last_chunk);
// The last chunk will be dropped. Destroy all other chunks.
for chunk in chunks_borrow.iter_mut() {
chunk.destroy(chunk.entries);
}
}
}
}
}
}
impl<'a, T> IntoIterator for &'a TypedArenaGen<T, Shared> {
type Item = &'a T;
type IntoIter = Iter<'a, T>;
#[inline]
fn into_iter(self) -> Self::IntoIter {
self.iter()
}
}
impl<'a, T, RM: RefMutability> IntoIterator for &'a mut TypedArenaGen<T, RM> {
type Item = &'a mut T;
type IntoIter = IterMut<'a, T>;
#[inline]
fn into_iter(self) -> Self::IntoIter {
self.iter_mut()
}
}
unsafe impl<T: Send, RM: RefMutability> Send for TypedArenaGen<T, RM> {}
impl<'a, T> PtrIter<'a, T> {
/// Create a new iterator for the arena
#[inline]
fn new<RM: RefMutability>(arena: &'a TypedArenaGen<T, RM>) -> Self {
// SAFETY: Same repr, this transmuted version won't be publicly exposed or used incorrectly
// (see [PtrIter] type doc), and we're not actually violating any borrow rules.
let arena = unsafe { transmute::<&'a TypedArenaGen<T, RM>, &'a TypedArena<T>>(arena) };
let chunks = arena.chunks.borrow();
let chunk = chunks.first();
Self {
arena,
chunk_index: 0,
chunk_data: chunk.map_or(NonNull::dangling(), |c| NonNull::new(c.storage).unwrap()),
chunk_remaining_entries: chunk.map_or(0, |c| c.entries),
element_index: 0,
}
}
/// Get the number of remaining elements, assuming there are no new ones
#[inline]
pub fn remaining(&self) -> usize {
self.arena.len() - self.element_index
}
/// Whether we have a next element
#[inline]
pub fn has_next(&self) -> bool {
self.remaining() > 0
}
}
impl<'a, T> Iterator for PtrIter<'a, T> {
type Item = NonNull<T>;
/// Gets a the next element as a pointer
fn next(&mut self) -> Option<Self::Item> {
if !self.has_next() {
return None;
}
let element = self.chunk_data;
self.element_index += 1;
// If this is a ZST we only need to count the # of items to iterate, and `chunk_data` is
// already a dangling pointer fron `Self::new` since there are no chunks.
if size_of::<T>() != 0 {
// If chunk_remaining_entries is 0, we actually still have entries but are on the last
// chunk. We'll run out when `has_next` returns false.
if self.chunk_remaining_entries == 1 {
// We've exhausted the current chunk, so move to the next one
self.chunk_index += 1;
let chunks = self.arena.chunks.borrow();
let chunk = chunks.get(self.chunk_index).expect(
"ArenaIter::next invariant error: arena has more elements but no more chunks",
);
self.chunk_data = NonNull::new(chunk.storage).unwrap();
self.chunk_remaining_entries = chunk.entries;
} else {
// SAFETY: We're still in the chunk, so we have a valid pointer and add is valid
self.chunk_data =
unsafe { NonNull::new_unchecked(self.chunk_data.as_ptr().add(1)) };
self.chunk_remaining_entries = self.chunk_remaining_entries.saturating_sub(1);
}
}
Some(element)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
// We will return at least len more elements, but we can't return an upper bound in case
// some get added
(self.remaining(), None)
}
}
impl<'a, T, RM: RefMutability> IterGen<'a, T, RM> {
/// Create a new iterator for the arena
#[inline]
fn new(arena: &'a TypedArenaGen<T, RM>) -> Self {
Self(PtrIter::new(arena), PhantomData)
}
/// Gets a the next element as a pointer
pub fn next_ptr(&mut self) -> Option<NonNull<T>> {
self.0.next()
}
/// Get the number of remaining elements, assuming there are no new ones
#[inline]
pub fn remaining(&self) -> usize {
self.0.remaining()
}
/// Whether we have a next element
#[inline]
pub fn has_next(&self) -> bool {
self.0.has_next()
}
}
impl<'a, T> PartialEq for PtrIter<'a, T> {
#[inline]
fn eq(&self, other: &Self) -> bool {
std::ptr::eq(self.arena, other.arena) && self.element_index == other.element_index
}
}
impl<'a, T, RM: RefMutability> PartialEq for IterGen<'a, T, RM> {
#[inline]
fn eq(&self, other: &Self) -> bool {
self.0 == other.0
}
}
impl<'a, T, RM: RefMutability> Iterator for IterGen<'a, T, RM> {
type Item = RM::Ref<'a, T>;
/// Gets the next element as a reference. Mutable or shared depends on the `RM` type parameter.
#[inline]
fn next(&mut self) -> Option<Self::Item> {
// SAFETY: The value is initialized, because the chunk has more entries and (important for
// the last chunk) the arena has more elements
self.next_ptr().map(|e| unsafe { RM::from_non_null(e) })
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.0.size_hint()
}
}
impl<T, const N: usize> IterWithFastAlloc<T> for std::array::IntoIter<T, N> {
#[inline]
fn alloc_into<RM: RefMutability>(self, arena: &TypedArenaGen<T, RM>) -> RM::SliceRef<'_, T> {
let len = self.len();
if len == 0 {
return RM::empty();
}
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_slice()
.as_ptr()
.copy_to_nonoverlapping(start_ptr, len);
forget(self);
RM::from_raw_parts(start_ptr, len)
}
}
}
impl<T> IterWithFastAlloc<T> for Vec<T> {
#[inline]
fn alloc_into<RM: RefMutability>(
mut self,
arena: &TypedArenaGen<T, RM>,
) -> RM::SliceRef<'_, T> {
let len = self.len();
if len == 0 {
return RM::empty();
}
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
self.set_len(0);
RM::from_raw_parts(start_ptr, len)
}
}
}
impl<A: smallvec::Array> IterWithFastAlloc<A::Item> for SmallVec<A> {
#[inline]
fn alloc_into<RM: RefMutability>(
mut self,
arena: &TypedArenaGen<A::Item, RM>,
) -> RM::SliceRef<'_, A::Item> {
let len = self.len();
if len == 0 {
return RM::empty();
}
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
self.set_len(0);
RM::from_raw_parts(start_ptr, len)
}
}
}
impl RefMutability for Shared {
type Ref<'a, T> = &'a T where T: 'a;
type SliceRef<'a, T> = &'a [T] where T: 'a;
fn empty<'a, T>() -> Self::SliceRef<'a, T> {
&[]
}
unsafe fn from_ptr<'a, T>(t: *mut T) -> Self::Ref<'a, T> {
&*t
}
unsafe fn from_raw_parts<'a, T>(t: *mut T, len: usize) -> Self::SliceRef<'a, T> {
from_raw_parts(t, len)
}
fn as_ref<T>(t: Self::Ref<'_, T>) -> &T {
t
}
fn as_slice_ref<T>(t: Self::SliceRef<'_, T>) -> &[T] {
t
}
}
impl RefMutability for Mutable {
type Ref<'a, T> = &'a mut T where T: 'a;
type SliceRef<'a, T> = &'a mut [T] where T: 'a;
fn empty<'a, T>() -> Self::SliceRef<'a, T> {
&mut []
}
unsafe fn from_ptr<'a, T>(t: *mut T) -> Self::Ref<'a, T> {
&mut *t
}
unsafe fn from_raw_parts<'a, T>(t: *mut T, len: usize) -> Self::SliceRef<'a, T> {
from_raw_parts_mut(t, len)
}
fn as_ref<T>(t: Self::Ref<'_, T>) -> &T {
t
}
fn as_slice_ref<T>(t: Self::SliceRef<'_, T>) -> &[T] {
t
}
}
mod private {
use super::{Mutable, Shared};
pub trait Sealed {}
impl Sealed for Shared {}
impl Sealed for Mutable {}
}