Add RawVec to unify raw Vecish code
This commit is contained in:
Alexis Beingessner
@@ -62,7 +62,7 @@ use core::hash::{self, Hash};
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use core::marker::Unsize;
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use core::mem;
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use core::ops::{CoerceUnsized, Deref, DerefMut};
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use core::ptr::{Unique};
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use core::ptr::Unique;
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use core::raw::{TraitObject};
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/// A value that represents the heap. This is the default place that the `box`
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@@ -88,6 +88,7 @@
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#![feature(unique)]
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#![feature(unsafe_no_drop_flag, filling_drop)]
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#![feature(unsize)]
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#![feature(core_slice_ext)]
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#![cfg_attr(test, feature(test, alloc, rustc_private, box_raw))]
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#![cfg_attr(all(not(feature = "external_funcs"), not(feature = "external_crate")),
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@@ -122,6 +123,7 @@ mod boxed { pub use std::boxed::{Box, HEAP}; }
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mod boxed_test;
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pub mod arc;
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pub mod rc;
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pub mod raw_vec;
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/// Common out-of-memory routine
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#[cold]
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453
src/liballoc/raw_vec.rs
Normal file
453
src/liballoc/raw_vec.rs
Normal file
@@ -0,0 +1,453 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use core::ptr::Unique;
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use core::mem;
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use core::slice::{self, SliceExt};
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use heap;
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use super::oom;
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use super::boxed::Box;
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use core::ops::Drop;
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/// A low-level utility for more ergonomically allocating, reallocating, and deallocating a
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/// a buffer of memory on the heap without having to worry about all the corner cases
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/// involved. This type is excellent for building your own data structures like Vec and VecDeque.
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/// In particular:
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///
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/// * Produces heap::EMPTY on zero-sized types
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/// * Produces heap::EMPTY on zero-length allocations
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/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics)
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/// * Guards against 32-bit systems allocating more than isize::MAX bytes
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/// * Guards against overflowing your length
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/// * Aborts on OOM
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/// * Avoids freeing heap::EMPTY
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/// * Contains a ptr::Unique and thus endows the user with all related benefits
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///
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/// This type does not in anyway inspect the memory that it manages. When dropped it *will*
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/// free its memory, but it *won't* try to Drop its contents. It is up to the user of RawVec
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/// to handle the actual things *stored* inside of a RawVec.
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///
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/// Note that a RawVec always forces its capacity to be usize::MAX for zero-sized types.
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/// This enables you to use capacity growing logic catch the overflows in your length
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/// that might occur with zero-sized types.
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///
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/// However this means that you need to be careful when roundtripping this type
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/// with a `Box<[T]>`: `cap()` won't yield the len. However `with_capacity`,
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/// `shrink_to_fit`, and `from_box` will actually set RawVec's private capacity
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/// field. This allows zero-sized types to not be special-cased by consumers of
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/// this type.
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#[unsafe_no_drop_flag]
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pub struct RawVec<T> {
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ptr: Unique<T>,
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cap: usize,
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}
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impl<T> RawVec<T> {
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/// Creates the biggest possible RawVec without allocating. If T has positive
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/// size, then this makes a RawVec with capacity 0. If T has 0 size, then it
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/// it makes a RawVec with capacity `usize::MAX`. Useful for implementing
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/// delayed allocation.
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pub fn new() -> Self {
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unsafe {
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// !0 is usize::MAX. This branch should be stripped at compile time.
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let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
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// heap::EMPTY doubles as "unallocated" and "zero-sized allocation"
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RawVec { ptr: Unique::new(heap::EMPTY as *mut T), cap: cap }
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}
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}
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/// Creates a RawVec with exactly the capacity and alignment requirements
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/// for a `[T; cap]`. This is equivalent to calling RawVec::new when `cap` is 0
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/// or T is zero-sized. Note that if `T` is zero-sized this means you will *not*
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/// get a RawVec with the requested capacity!
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///
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/// # Panics
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///
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/// * Panics if the requested capacity exceeds `usize::MAX` bytes.
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/// * Panics on 32-bit platforms if the requested capacity exceeds
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/// `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM
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pub fn with_capacity(cap: usize) -> Self {
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unsafe {
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let elem_size = mem::size_of::<T>();
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let alloc_size = cap.checked_mul(elem_size).expect("capacity overflow");
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alloc_guard(alloc_size);
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// handles ZSTs and `cap = 0` alike
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let ptr = if alloc_size == 0 {
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heap::EMPTY as *mut u8
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} else {
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let align = mem::align_of::<T>();
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let ptr = heap::allocate(alloc_size, align);
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if ptr.is_null() { oom() }
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ptr
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};
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RawVec { ptr: Unique::new(ptr as *mut _), cap: cap }
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}
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}
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/// Reconstitutes a RawVec from a pointer and capacity.
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///
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/// # Undefined Behaviour
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///
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/// The ptr must be allocated, and with the given capacity. The
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/// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
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/// If the ptr and capacity come from a RawVec, then this is guaranteed.
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pub unsafe fn from_raw_parts(ptr: *mut T, cap: usize) -> Self {
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RawVec { ptr: Unique::new(ptr), cap: cap }
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}
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/// Converts a `Box<[T]>` into a `RawVec<T>`.
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pub fn from_box(mut slice: Box<[T]>) -> Self {
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unsafe {
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let result = RawVec::from_raw_parts(slice.as_mut_ptr(), slice.len());
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mem::forget(slice);
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result
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}
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}
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}
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impl<T> RawVec<T> {
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/// Gets a raw pointer to the start of the allocation. Note that this is
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/// heap::EMPTY if `cap = 0` or T is zero-sized. In the former case, you must
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/// be careful.
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pub fn ptr(&self) -> *mut T {
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*self.ptr
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}
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/// Gets the capacity of the allocation.
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///
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/// This will always be `usize::MAX` if `T` is zero-sized.
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pub fn cap(&self) -> usize {
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if mem::size_of::<T>() == 0 { !0 } else { self.cap }
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}
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/// Doubles the size of the type's backing allocation. This is common enough
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/// to want to do that it's easiest to just have a dedicated method. Slightly
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/// more efficient logic can be provided for this than the general case.
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///
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/// This function is ideal for when pushing elements one-at-a-time because
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/// you don't need to incur the costs of the more general computations
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/// reserve needs to do to guard against overflow. You do however need to
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/// manually check if your `len == cap`.
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///
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/// # Panics
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///
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/// * Panics if T is zero-sized on the assumption that you managed to exhaust
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/// all `usize::MAX` slots in your imaginary buffer.
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/// * Panics on 32-bit platforms if the requested capacity exceeds
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/// `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM
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///
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/// # Examples
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///
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/// ```ignore
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/// struct MyVec<T> {
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/// buf: RawVec<T>,
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/// len: usize,
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/// }
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///
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/// impl<T> MyVec<T> {
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/// pub fn push(&mut self, elem: T) {
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/// if self.len == self.buf.cap() { self.buf.double(); }
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/// // double would have aborted or panicked if the len exceeded
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/// // `isize::MAX` so this is safe to do unchecked now.
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/// unsafe {
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/// ptr::write(self.buf.ptr().offset(self.len as isize), elem);
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/// }
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/// self.len += 1;
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/// }
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/// }
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/// ```
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#[inline(never)]
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#[cold]
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pub fn double(&mut self) {
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unsafe {
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let elem_size = mem::size_of::<T>();
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// since we set the capacity to usize::MAX when elem_size is
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// 0, getting to here necessarily means the RawVec is overfull.
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assert!(elem_size != 0, "capacity overflow");
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let align = mem::align_of::<T>();
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let (new_cap, ptr) = if self.cap == 0 {
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// skip to 4 because tiny Vec's are dumb; but not if that would cause overflow
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let new_cap = if elem_size > (!0) / 8 { 1 } else { 4 };
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let ptr = heap::allocate(new_cap * elem_size, align);
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(new_cap, ptr)
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} else {
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// Since we guarantee that we never allocate more than isize::MAX bytes,
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// `elem_size * self.cap <= isize::MAX` as a precondition, so this can't overflow
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let new_cap = 2 * self.cap;
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let new_alloc_size = new_cap * elem_size;
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alloc_guard(new_alloc_size);
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let ptr = heap::reallocate(self.ptr() as *mut _,
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self.cap * elem_size,
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new_alloc_size,
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align);
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(new_cap, ptr)
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};
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// If allocate or reallocate fail, we'll get `null` back
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if ptr.is_null() { oom() }
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self.ptr = Unique::new(ptr as *mut _);
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self.cap = new_cap;
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}
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}
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/// Ensures that the buffer contains at least enough space to hold
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/// `used_cap + needed_extra_cap` elements. If it doesn't already,
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/// will reallocate the minimum possible amount of memory necessary.
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/// Generally this will be exactly the amount of memory necessary,
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/// but in principle the allocator is free to give back more than
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/// we asked for.
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///
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/// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
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/// the requested space. This is not really unsafe, but the unsafe
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/// code *you* write that relies on the behaviour of this function may break.
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///
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/// # Panics
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///
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/// * Panics if the requested capacity exceeds `usize::MAX` bytes.
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/// * Panics on 32-bit platforms if the requested capacity exceeds
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/// `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM
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pub fn reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize) {
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unsafe {
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let elem_size = mem::size_of::<T>();
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let align = mem::align_of::<T>();
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// NOTE: we don't early branch on ZSTs here because we want this
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// to actually catch "asking for more than usize::MAX" in that case.
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// If we make it past the first branch then we are guaranteed to
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// panic.
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// Don't actually need any more capacity.
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// Wrapping in case they gave a bad `used_cap`.
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if self.cap().wrapping_sub(used_cap) >= needed_extra_cap { return; }
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// Nothing we can really do about these checks :(
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let new_cap = used_cap.checked_add(needed_extra_cap).expect("capacity overflow");
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let new_alloc_size = new_cap.checked_mul(elem_size).expect("capacity overflow");
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alloc_guard(new_alloc_size);
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let ptr = if self.cap == 0 {
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heap::allocate(new_alloc_size, align)
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} else {
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heap::reallocate(self.ptr() as *mut _,
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self.cap * elem_size,
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new_alloc_size,
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align)
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};
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// If allocate or reallocate fail, we'll get `null` back
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if ptr.is_null() { oom() }
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self.ptr = Unique::new(ptr as *mut _);
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self.cap = new_cap;
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}
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}
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/// Ensures that the buffer contains at least enough space to hold
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/// `used_cap + needed_extra_cap` elements. If it doesn't already have
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/// enough capacity, will reallocate enough space plus comfortable slack
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/// space to get amortized `O(1)` behaviour. Will limit this behaviour
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/// if it would needlessly cause itself to panic.
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///
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/// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
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/// the requested space. This is not really unsafe, but the unsafe
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/// code *you* write that relies on the behaviour of this function may break.
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///
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/// This is ideal for implementing a bulk-push operation like `extend`.
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///
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/// # Panics
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///
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/// * Panics if the requested capacity exceeds `usize::MAX` bytes.
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/// * Panics on 32-bit platforms if the requested capacity exceeds
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/// `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM
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///
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/// # Examples
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///
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/// ```ignore
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/// struct MyVec<T> {
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/// buf: RawVec<T>,
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/// len: usize,
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/// }
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///
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/// impl<T> MyVec<T> {
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/// pub fn push_all(&mut self, elems: &[T]) {
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/// self.buf.reserve(self.len, elems.len());
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/// // reserve would have aborted or panicked if the len exceeded
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/// // `isize::MAX` so this is safe to do unchecked now.
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/// for x in elems {
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/// unsafe {
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/// ptr::write(self.buf.ptr().offset(self.len as isize), x.clone());
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/// }
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/// self.len += 1;
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/// }
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/// }
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/// }
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/// ```
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pub fn reserve(&mut self, used_cap: usize, needed_extra_cap: usize) {
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unsafe {
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let elem_size = mem::size_of::<T>();
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let align = mem::align_of::<T>();
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// NOTE: we don't early branch on ZSTs here because we want this
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// to actually catch "asking for more than usize::MAX" in that case.
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// If we make it past the first branch then we are guaranteed to
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// panic.
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// Don't actually need any more capacity.
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// Wrapping in case they give a bas `used_cap`
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if self.cap().wrapping_sub(used_cap) >= needed_extra_cap { return; }
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// Nothing we can really do about these checks :(
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let new_cap = used_cap.checked_add(needed_extra_cap)
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.and_then(|cap| cap.checked_mul(2))
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.expect("capacity overflow");
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let new_alloc_size = new_cap.checked_mul(elem_size).expect("capacity overflow");
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// FIXME: may crash and burn on over-reserve
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alloc_guard(new_alloc_size);
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let ptr = if self.cap == 0 {
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heap::allocate(new_alloc_size, align)
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} else {
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heap::reallocate(self.ptr() as *mut _,
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self.cap * elem_size,
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new_alloc_size,
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align)
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};
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// If allocate or reallocate fail, we'll get `null` back
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if ptr.is_null() { oom() }
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self.ptr = Unique::new(ptr as *mut _);
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self.cap = new_cap;
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}
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}
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/// Shrinks the allocation down to the specified amount. If the given amount
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/// is 0, actually completely deallocates.
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///
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/// # Panics
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///
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/// Panics if the given amount is *larger* than the current capacity.
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///
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/// # Aborts
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///
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/// Aborts on OOM.
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pub fn shrink_to_fit(&mut self, amount: usize) {
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let elem_size = mem::size_of::<T>();
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let align = mem::align_of::<T>();
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// Set the `cap` because they might be about to promote to a `Box<[T]>`
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if elem_size == 0 {
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self.cap = amount;
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return;
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}
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// This check is my waterloo; it's the only thing Vec wouldn't have to do.
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assert!(self.cap >= amount, "Tried to shrink to a larger capacity");
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if amount == 0 {
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mem::replace(self, RawVec::new());
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} else if self.cap != amount {
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unsafe {
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// Overflow check is unnecessary as the vector is already at
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// least this large.
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let ptr = heap::reallocate(self.ptr() as *mut _,
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self.cap * elem_size,
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amount * elem_size,
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align);
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if ptr.is_null() { oom() }
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self.ptr = Unique::new(ptr as *mut _);
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}
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self.cap = amount;
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}
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}
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/// Converts the entire buffer into `Box<[T]>`.
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///
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/// While it is not *strictly* Undefined Behaviour to call
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/// this procedure while some of the RawVec is unintialized,
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/// it cetainly makes it trivial to trigger it.
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///
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/// Note that this will correctly reconstitute any `cap` changes
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/// that may have been performed. (see description of type for details)
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pub unsafe fn into_box(self) -> Box<[T]> {
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// NOTE: not calling `cap()` here, actually using the real `cap` field!
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let slice = slice::from_raw_parts_mut(self.ptr(), self.cap);
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let output: Box<[T]> = Box::from_raw(slice);
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mem::forget(self);
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output
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}
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/// This is a stupid name in the hopes that someone will find this in the
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/// not too distant future and remove it with the rest of
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/// #[unsafe_no_drop_flag]
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pub fn unsafe_no_drop_flag_needs_drop(&self) -> bool {
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self.cap != mem::POST_DROP_USIZE
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}
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}
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impl<T> Drop for RawVec<T> {
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/// Frees the memory owned by the RawVec *without* trying to Drop its contents.
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fn drop(&mut self) {
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let elem_size = mem::size_of::<T>();
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if elem_size != 0 && self.cap != 0 && self.unsafe_no_drop_flag_needs_drop() {
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let align = mem::align_of::<T>();
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|
||||
let num_bytes = elem_size * self.cap;
|
||||
unsafe {
|
||||
heap::deallocate(*self.ptr as *mut _, num_bytes, align);
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
|
||||
// We need to guarantee the following:
|
||||
// * We don't ever allocate `> isize::MAX` byte-size objects
|
||||
// * We don't overflow `usize::MAX` and actually allocate too little
|
||||
//
|
||||
// On 64-bit we just need to check for overflow since trying to allocate
|
||||
// `> isize::MAX` bytes will surely fail. On 32-bit we need to add an extra
|
||||
// guard for this in case we're running on a platform which can use all 4GB in
|
||||
// user-space. e.g. PAE or x32
|
||||
|
||||
#[inline]
|
||||
#[cfg(target_pointer_width = "64")]
|
||||
fn alloc_guard(_alloc_size: usize) { }
|
||||
|
||||
#[inline]
|
||||
#[cfg(target_pointer_width = "32")]
|
||||
fn alloc_guard(alloc_size: usize) {
|
||||
assert!(alloc_size <= ::core::isize::MAX as usize, "capacity overflow");
|
||||
}
|
||||
Reference in New Issue
Block a user