| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! The arena, a fast but limited type of allocator. |
| //! |
| //! Arenas are a type of allocator that destroy the objects within, all at |
| //! once, once the arena itself is destroyed. They do not support deallocation |
| //! of individual objects while the arena itself is still alive. The benefit |
| //! of an arena is very fast allocation; just a pointer bump. |
| //! |
| //! This crate has two arenas implemented: `TypedArena`, which is a simpler |
| //! arena but can only hold objects of a single type, and `Arena`, which is a |
| //! more complex, slower arena which can hold objects of any type. |
| |
| #![crate_name = "arena"] |
| #![unstable(feature = "rustc_private", issue = "27812")] |
| #![crate_type = "rlib"] |
| #![crate_type = "dylib"] |
| #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png", |
| html_favicon_url = "https://doc.rust-lang.org/favicon.ico", |
| html_root_url = "https://doc.rust-lang.org/nightly/", |
| test(no_crate_inject, attr(deny(warnings))))] |
| #![cfg_attr(not(stage0), deny(warnings))] |
| |
| #![feature(alloc)] |
| #![feature(core_intrinsics)] |
| #![feature(heap_api)] |
| #![feature(heap_api)] |
| #![feature(staged_api)] |
| #![feature(dropck_parametricity)] |
| #![cfg_attr(test, feature(test))] |
| |
| #![allow(deprecated)] |
| |
| extern crate alloc; |
| |
| use std::cell::{Cell, RefCell}; |
| use std::cmp; |
| use std::intrinsics; |
| use std::marker::{PhantomData, Send}; |
| use std::mem; |
| use std::ptr; |
| |
| use alloc::heap; |
| use alloc::raw_vec::RawVec; |
| |
| /// A faster arena that can hold objects of only one type. |
| pub struct TypedArena<T> { |
| /// 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 arena segments. |
| chunks: RefCell<Vec<TypedArenaChunk<T>>>, |
| |
| /// Marker indicating that dropping the arena causes its owned |
| /// instances of `T` to be dropped. |
| _own: PhantomData<T>, |
| } |
| |
| struct TypedArenaChunk<T> { |
| /// Pointer to the next arena segment. |
| storage: RawVec<T>, |
| } |
| |
| impl<T> TypedArenaChunk<T> { |
| #[inline] |
| unsafe fn new(capacity: usize) -> TypedArenaChunk<T> { |
| TypedArenaChunk { storage: RawVec::with_capacity(capacity) } |
| } |
| |
| /// Destroys this arena chunk. |
| #[inline] |
| unsafe fn destroy(&mut self, len: usize) { |
| // The branch on needs_drop() is an -O1 performance optimization. |
| // Without the branch, dropping TypedArena<u8> takes linear time. |
| if intrinsics::needs_drop::<T>() { |
| let mut start = self.start(); |
| // Destroy all allocated objects. |
| for _ in 0..len { |
| ptr::drop_in_place(start); |
| start = start.offset(1); |
| } |
| } |
| } |
| |
| // Returns a pointer to the first allocated object. |
| #[inline] |
| fn start(&self) -> *mut T { |
| self.storage.ptr() |
| } |
| |
| // Returns a pointer to the end of the allocated space. |
| #[inline] |
| fn end(&self) -> *mut T { |
| unsafe { |
| if mem::size_of::<T>() == 0 { |
| // A pointer as large as possible for zero-sized elements. |
| !0 as *mut T |
| } else { |
| self.start().offset(self.storage.cap() as isize) |
| } |
| } |
| } |
| } |
| |
| const PAGE: usize = 4096; |
| |
| impl<T> TypedArena<T> { |
| /// Creates a new `TypedArena` with preallocated space for many objects. |
| #[inline] |
| pub fn new() -> TypedArena<T> { |
| // Reserve at least one page. |
| let elem_size = cmp::max(1, mem::size_of::<T>()); |
| TypedArena::with_capacity(PAGE / elem_size) |
| } |
| |
| /// Creates a new `TypedArena` with preallocated space for the given number of |
| /// objects. |
| #[inline] |
| pub fn with_capacity(capacity: usize) -> TypedArena<T> { |
| unsafe { |
| let chunk = TypedArenaChunk::<T>::new(cmp::max(1, capacity)); |
| TypedArena { |
| ptr: Cell::new(chunk.start()), |
| end: Cell::new(chunk.end()), |
| chunks: RefCell::new(vec![chunk]), |
| _own: PhantomData, |
| } |
| } |
| } |
| |
| /// Allocates an object in the `TypedArena`, returning a reference to it. |
| #[inline] |
| pub fn alloc(&self, object: T) -> &mut T { |
| if self.ptr == self.end { |
| self.grow() |
| } |
| |
| unsafe { |
| if mem::size_of::<T>() == 0 { |
| self.ptr.set(intrinsics::arith_offset(self.ptr.get() as *mut u8, 1) as *mut T); |
| let ptr = heap::EMPTY as *mut T; |
| // Don't drop the object. This `write` is equivalent to `forget`. |
| ptr::write(ptr, object); |
| &mut *ptr |
| } else { |
| let ptr = self.ptr.get(); |
| // Advance the pointer. |
| self.ptr.set(self.ptr.get().offset(1)); |
| // Write into uninitialized memory. |
| ptr::write(ptr, object); |
| &mut *ptr |
| } |
| } |
| } |
| |
| /// Grows the arena. |
| #[inline(never)] |
| #[cold] |
| fn grow(&self) { |
| unsafe { |
| let mut chunks = self.chunks.borrow_mut(); |
| let prev_capacity = chunks.last().unwrap().storage.cap(); |
| let new_capacity = prev_capacity.checked_mul(2).unwrap(); |
| if chunks.last_mut().unwrap().storage.double_in_place() { |
| self.end.set(chunks.last().unwrap().end()); |
| } else { |
| let chunk = TypedArenaChunk::<T>::new(new_capacity); |
| self.ptr.set(chunk.start()); |
| self.end.set(chunk.end()); |
| chunks.push(chunk); |
| } |
| } |
| } |
| /// Clears the arena. Deallocates all but the longest chunk which may be reused. |
| pub fn clear(&mut self) { |
| unsafe { |
| // Clear the last chunk, which is partially filled. |
| let mut chunks_borrow = self.chunks.borrow_mut(); |
| let last_idx = chunks_borrow.len() - 1; |
| self.clear_last_chunk(&mut chunks_borrow[last_idx]); |
| // If `T` is ZST, code below has no effect. |
| for mut chunk in chunks_borrow.drain(..last_idx) { |
| let cap = chunk.storage.cap(); |
| chunk.destroy(cap); |
| } |
| } |
| } |
| |
| // 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 TypedArenaChunk<T>) { |
| // Determine how much was filled. |
| let start = last_chunk.start() as usize; |
| // We obtain the value of the pointer to the first uninitialized element. |
| let end = self.ptr.get() as usize; |
| // We then calculate the number of elements to be dropped in the last chunk, |
| // which is the filled area's length. |
| let diff = if mem::size_of::<T>() == 0 { |
| // `T` is ZST. It can't have a drop flag, so the value here doesn't matter. We get |
| // the number of zero-sized values in the last and only chunk, just out of caution. |
| // Recall that `end` was incremented for each allocated value. |
| end - start |
| } else { |
| (end - start) / mem::size_of::<T>() |
| }; |
| // Pass that to the `destroy` method. |
| unsafe { |
| last_chunk.destroy(diff); |
| } |
| // Reset the chunk. |
| self.ptr.set(last_chunk.start()); |
| } |
| } |
| |
| impl<T> Drop for TypedArena<T> { |
| #[unsafe_destructor_blind_to_params] |
| fn drop(&mut self) { |
| unsafe { |
| // Determine how much was filled. |
| let mut chunks_borrow = self.chunks.borrow_mut(); |
| let mut last_chunk = chunks_borrow.pop().unwrap(); |
| // 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() { |
| let cap = chunk.storage.cap(); |
| chunk.destroy(cap); |
| } |
| // RawVec handles deallocation of `last_chunk` and `self.chunks`. |
| } |
| } |
| } |
| |
| unsafe impl<T: Send> Send for TypedArena<T> {} |
| |
| #[cfg(test)] |
| mod tests { |
| extern crate test; |
| use self::test::Bencher; |
| use super::TypedArena; |
| use std::cell::Cell; |
| |
| #[allow(dead_code)] |
| #[derive(Debug, Eq, PartialEq)] |
| struct Point { |
| x: i32, |
| y: i32, |
| z: i32, |
| } |
| |
| #[test] |
| fn test_arena_alloc_nested() { |
| struct Inner { |
| value: u8, |
| } |
| struct Outer<'a> { |
| inner: &'a Inner, |
| } |
| enum EI<'e> { |
| I(Inner), |
| O(Outer<'e>), |
| } |
| |
| struct Wrap<'a>(TypedArena<EI<'a>>); |
| |
| impl<'a> Wrap<'a> { |
| fn alloc_inner<F: Fn() -> Inner>(&self, f: F) -> &Inner { |
| let r: &EI = self.0.alloc(EI::I(f())); |
| if let &EI::I(ref i) = r { |
| i |
| } else { |
| panic!("mismatch"); |
| } |
| } |
| fn alloc_outer<F: Fn() -> Outer<'a>>(&self, f: F) -> &Outer { |
| let r: &EI = self.0.alloc(EI::O(f())); |
| if let &EI::O(ref o) = r { |
| o |
| } else { |
| panic!("mismatch"); |
| } |
| } |
| } |
| |
| let arena = Wrap(TypedArena::new()); |
| |
| let result = arena.alloc_outer(|| { |
| Outer { inner: arena.alloc_inner(|| Inner { value: 10 }) } |
| }); |
| |
| assert_eq!(result.inner.value, 10); |
| } |
| |
| #[test] |
| pub fn test_copy() { |
| let arena = TypedArena::new(); |
| for _ in 0..100000 { |
| arena.alloc(Point { x: 1, y: 2, z: 3 }); |
| } |
| } |
| |
| #[bench] |
| pub fn bench_copy(b: &mut Bencher) { |
| let arena = TypedArena::new(); |
| b.iter(|| arena.alloc(Point { x: 1, y: 2, z: 3 })) |
| } |
| |
| #[bench] |
| pub fn bench_copy_nonarena(b: &mut Bencher) { |
| b.iter(|| { |
| let _: Box<_> = Box::new(Point { x: 1, y: 2, z: 3 }); |
| }) |
| } |
| |
| #[allow(dead_code)] |
| struct Noncopy { |
| string: String, |
| array: Vec<i32>, |
| } |
| |
| #[test] |
| pub fn test_noncopy() { |
| let arena = TypedArena::new(); |
| for _ in 0..100000 { |
| arena.alloc(Noncopy { |
| string: "hello world".to_string(), |
| array: vec![1, 2, 3, 4, 5], |
| }); |
| } |
| } |
| |
| #[test] |
| pub fn test_typed_arena_zero_sized() { |
| let arena = TypedArena::new(); |
| for _ in 0..100000 { |
| arena.alloc(()); |
| } |
| } |
| |
| #[test] |
| pub fn test_typed_arena_clear() { |
| let mut arena = TypedArena::new(); |
| for _ in 0..10 { |
| arena.clear(); |
| for _ in 0..10000 { |
| arena.alloc(Point { x: 1, y: 2, z: 3 }); |
| } |
| } |
| } |
| |
| // Drop tests |
| |
| struct DropCounter<'a> { |
| count: &'a Cell<u32>, |
| } |
| |
| impl<'a> Drop for DropCounter<'a> { |
| fn drop(&mut self) { |
| self.count.set(self.count.get() + 1); |
| } |
| } |
| |
| #[test] |
| fn test_typed_arena_drop_count() { |
| let counter = Cell::new(0); |
| { |
| let arena: TypedArena<DropCounter> = TypedArena::new(); |
| for _ in 0..100 { |
| // Allocate something with drop glue to make sure it doesn't leak. |
| arena.alloc(DropCounter { count: &counter }); |
| } |
| }; |
| assert_eq!(counter.get(), 100); |
| } |
| |
| #[test] |
| fn test_typed_arena_drop_on_clear() { |
| let counter = Cell::new(0); |
| let mut arena: TypedArena<DropCounter> = TypedArena::new(); |
| for i in 0..10 { |
| for _ in 0..100 { |
| // Allocate something with drop glue to make sure it doesn't leak. |
| arena.alloc(DropCounter { count: &counter }); |
| } |
| arena.clear(); |
| assert_eq!(counter.get(), i * 100 + 100); |
| } |
| } |
| |
| thread_local! { |
| static DROP_COUNTER: Cell<u32> = Cell::new(0) |
| } |
| |
| struct SmallDroppable; |
| |
| impl Drop for SmallDroppable { |
| fn drop(&mut self) { |
| DROP_COUNTER.with(|c| c.set(c.get() + 1)); |
| } |
| } |
| |
| #[test] |
| fn test_typed_arena_drop_small_count() { |
| DROP_COUNTER.with(|c| c.set(0)); |
| { |
| let arena: TypedArena<SmallDroppable> = TypedArena::new(); |
| for _ in 0..100 { |
| // Allocate something with drop glue to make sure it doesn't leak. |
| arena.alloc(SmallDroppable); |
| } |
| // dropping |
| }; |
| assert_eq!(DROP_COUNTER.with(|c| c.get()), 100); |
| } |
| |
| #[bench] |
| pub fn bench_noncopy(b: &mut Bencher) { |
| let arena = TypedArena::new(); |
| b.iter(|| { |
| arena.alloc(Noncopy { |
| string: "hello world".to_string(), |
| array: vec![1, 2, 3, 4, 5], |
| }) |
| }) |
| } |
| |
| #[bench] |
| pub fn bench_noncopy_nonarena(b: &mut Bencher) { |
| b.iter(|| { |
| let _: Box<_> = Box::new(Noncopy { |
| string: "hello world".to_string(), |
| array: vec![1, 2, 3, 4, 5], |
| }); |
| }) |
| } |
| } |