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// Copyright 2018 Theodore Cipicchio // // 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. //! Stack-like dynamic memory pool with double-ended allocation support. //! //! # Table of Contents //! //! - [Overview](#overview) //! - [Crate Features](#crate-features) //! - [Examples](#examples) //! - [Memory Management](#memory-management) //! - [Buffer Types](#buffer-types) //! - [Macros and Functions for Handling Buffers](#macros-and-functions-for-handling-buffers) //! - [Data Alignment](#data-alignment) //! - [`Buffer` and `Tracking` Alignments](#buffer-and-tracking-alignments) //! - [Alignment of Allocated Arrays](#alignment-of-allocated-arrays) //! - [Cache Alignment](#cache-alignment) //! - [Memory Overhead](#memory-overhead) //! - [Limitations](#limitations) //! - [Mutability Notes](#mutability-notes) //! //! # Overview //! //! [`Scratchpad`] provides a method for quick and safe dynamic allocations of //! arbitrary types without relying on the global heap (e.g. using [`Box`] or //! [`Vec`]). Allocations are made from a fixed-size region of memory in a //! stack-like fashion using two separate stacks (one for each end of the //! allocation buffer) to allow different types of allocations with possibly //! overlapping lifecycles to be made from each end. //! //! Groups of allocations are partitioned using [`Marker`] objects. Markers //! can be set at the [front][`mark_front()`] or [back][`mark_back()`] of a //! scratchpad. Allocations can be made from either a front or back marker as //! long as it is the most-recently created active marker of that type (e.g. //! creating and allocating from a back marker still allows you to allocate //! from the most recent front marker, but creating a new front marker blocks //! allocations from previous front markers until the newer front marker is //! dropped). //! //! No memory is actually freed until the marker is dropped (although an //! item's [`Drop`] implementation is still called if necessary when the //! allocation is dropped). Markers can be dropped in any order, but the //! memory is not made available for reuse until any subsequently set markers //! of the same type (front versus back) have also been dropped. This behavior //! allows allocations and frees to be performed relatively quickly. //! //! Some cases for which [`Scratchpad`] can be useful include: //! //! - **Short-term dynamic allocations.** A function may need to allocate a //! variable amount of memory for a relatively short amount of time. Rust //! currently does not provide anything analogous to the `alloca()` function //! in C (which also has its own pitfalls), and using the global heap can be //! slow and introduce fragmentation if other allocations are made before //! the short-term allocation is freed. Additionally, if each thread has its //! own scratchpad, overhead incurred from synchronization between threads //! can be eliminated. //! - **Grouped allocation lifecycles.** Some applications may incorporate //! some cycle in which they allocate an arbitrary amount of data that can //! be freed all at once after some period of time. One such case is with //! video games, where static data for a level may be allocated and persist //! only for the duration in which the level is active. Such allocations can //! be made by setting a marker for the level and dropping it when the level //! is unloaded. Other allocations with overlapping lifecycles, such as //! those persisting across levels, or temporary allocations needed while //! loading into one end of the scratchpad, can also be set at the other end //! of the same scratchpad at the same time. //! //! # Crate Features //! //! The following optional features can be set when building this crate: //! //! - **`std`**: Allows [`Box`] to be used as the storage type for allocations //! and marker tracking. Enabled by default; can be disabled to build the //! crate with `#![no_std]`. //! - **`unstable`**: Enables unstable toolchain features (requires a nightly //! compiler). Disabled by default. Enabling this feature includes: //! - [`ByteData`] trait implementations for `u128`/`i128`. //! - Declaration of the function [`Scratchpad::new()`] as `const`. //! - Support for using [`Box`] as the storage type for allocations and //! marker tracking, regardless of whether the `std` feature is enabled //! (`alloc` library is used if `std` is disabled). //! //! # Examples //! //! Applications can create per-thread scratchpads for temporary allocations //! using thread-local variables, reducing fragmentation of the global memory //! heap and improving performance. The following example shows how one might //! use temporary storage to interface with a third-party library within some //! abstraction layer: //! //! ``` //! #[macro_use] //! extern crate scratchpad; //! //! use scratchpad::{CacheAligned, Scratchpad}; //! use scratchpad::uninitialized_boxed_slice_for_bytes; //! use std::mem::{size_of, uninitialized}; //! use std::os::raw::c_void; //! //! /// Thread-local scratchpad size, in bytes (1 MB). //! const THREAD_LOCAL_SCRATCHPAD_SIZE: usize = 1024 * 1024; //! /// Maximum thread-local scratchpad allocation marker count. //! const THREAD_LOCAL_SCRATCHPAD_MAX_MARKERS: usize = 8; //! //! /// Buffer type for thread-local scratchpad allocations. By using //! /// `CacheAligned`, we avoid false sharing of cache lines between threads. //! type ThreadLocalScratchBuffer = Box<[CacheAligned]>; //! //! /// Buffer type for tracking of thread-local scratchpad markers (each //! /// marker requires a `usize` value). //! type ThreadLocalScratchTracking = array_type_for_markers!( //! CacheAligned, //! THREAD_LOCAL_SCRATCHPAD_MAX_MARKERS, //! ); //! //! thread_local! { //! /// Thread-local scratchpad. The initial contents of the allocation //! /// buffer and marker tracking buffer are ignored, so we can create //! /// them as uninitialized. //! pub static THREAD_LOCAL_SCRATCHPAD: Scratchpad< //! ThreadLocalScratchBuffer, //! ThreadLocalScratchTracking, //! > = unsafe { Scratchpad::new( //! uninitialized_boxed_slice_for_bytes(THREAD_LOCAL_SCRATCHPAD_SIZE), //! uninitialized(), //! ) }; //! } //! //! /// Rust bindings for part of some fictional third-party API written in //! /// C/C++. //! pub mod libfoo { //! use std::os::raw::c_void; //! //! #[repr(C)] //! pub enum SequenceType { //! Integer, //! Float, //! Double, //! } //! //! #[derive(Debug, PartialEq)] //! #[repr(C)] //! pub enum SequenceResult { //! Red, //! Green, //! Blue, //! } //! //! #[repr(C)] //! pub struct SequenceParameters { //! pub data_type: SequenceType, //! pub data_count: usize, //! pub data: *const c_void, //! } //! //! pub unsafe extern "C" fn process_sequences( //! sequence_count: usize, //! sequences: *const SequenceParameters, //! ) -> SequenceResult { //! // ... //! # SequenceResult::Red //! } //! } //! //! /// Our abstraction of `libfoo::process_sequences()`, in which we only //! /// ever work with `f32` data. //! pub fn process_float_sequences<I, E, S>( //! sequences: I, //! ) -> Result<libfoo::SequenceResult, scratchpad::Error> //! where //! I: IntoIterator<Item = S, IntoIter = E>, //! E: ExactSizeIterator<Item = S>, //! S: AsRef<[f32]>, //! { //! THREAD_LOCAL_SCRATCHPAD.with(|scratchpad| { //! // We need an array of `libfoo::SequenceParameters` structs for //! // the call to `libfoo::process_sequences()`. //! let mut sequences = sequences.into_iter(); //! let sequences_len = sequences.len(); //! //! let marker = scratchpad.mark_front()?; //! let foo_sequences = marker.allocate_array_with( //! sequences_len, //! |index| { //! let data = sequences.next().unwrap(); //! let data_ref = data.as_ref(); //! libfoo::SequenceParameters { //! data_type: libfoo::SequenceType::Float, //! data_count: data_ref.len(), //! data: data_ref.as_ptr() as *const c_void, //! } //! } //! )?; //! //! Ok(unsafe { libfoo::process_sequences( //! sequences_len, //! foo_sequences.as_ptr(), //! ) }) //! //! // The marker is dropped as it goes out of scope, freeing the //! // allocated memory. //! }) //! } //! //! fn main() { //! let sequence_a = [2.22f32, 9.99f32, -1234.56f32]; //! let sequence_b = [-1.0f32, 8.8f32, 27.0f32, 0.03f32]; //! let sequence_c = [88.0f32]; //! let sequences = [&sequence_a[..], &sequence_b[..], &sequence_c[..]]; //! assert_eq!( //! process_float_sequences(&sequences).unwrap(), //! libfoo::SequenceResult::Red, //! ); //! } //! ``` //! //! # Memory Management //! //! ## Buffer Types //! //! The backing data structures used for allocation storage and marker //! tracking are declared in the generic parameters of the [`Scratchpad`] //! type. This allows a fair degree of control over the memory usage of the //! scratchpad itself. //! //! The allocation storage type is provided by the `BufferT` generic //! parameter, which is constrained by the [`Buffer`] trait. Allocation //! storage must be a contiguous region of memory, such as a static array, //! boxed slice, or mutable slice reference. Array element types are //! constrained to types that implement the [`ByteData`] trait; by default, //! this only includes basic integer types and the [`CacheAligned`] struct //! provided by this crate. //! //! The marker tracking buffer type is provided by the `TrackingT` generic //! parameter, which is constrained by the [`Tracking`] trait. This type must //! allow storage and retrieval of a fixed number of `usize` values. Unlike //! [`Buffer`], there is no restriction on how the values are stored so long //! as they can be set and subsequently retrieved by index. Any type //! implementing [`Buffer`] also implements [`Tracking`] by default. //! //! ## Macros and Functions for Handling Buffers //! //! Writing out the math needed to determine the number of elements needed for //! an array or boxed slice of a specific byte capacity or marker tracking //! capacity can be tedious and error-prone. This crate provides some macros //! and functions to help reduce the amount of work needed for declaring //! buffers based on their byte capacity or marker capacity: //! //! - [`array_type_for_bytes!()`] and [`array_type_for_markers!()`] can be //! used to declare static array types based on their capacity. //! - [`cache_aligned_zeroed_for_bytes!()`] and //! [`cache_aligned_zeroed_for_markers!()`] provide shorthand for creating //! static arrays of [`CacheAligned`] elements with their contents zeroed //! out. The expansion of this macro is a constant expression. //! - [`uninitialized_boxed_slice_for_bytes()`] and //! [`uninitialized_boxed_slice_for_markers()`] can be used to allocate //! memory for a boxed slice of a given capacity without initializing its //! contents. //! //! Some lower level macros and functions are also available if needed: //! //! - [`array_len_for_bytes!()`] and [`array_len_for_markers!()`] return the //! number of elements needed for a static array with a given capacity. The //! results are constant expressions that can be evaluated at compile-time. //! - [`cache_aligned_zeroed!()`] provides shorthand for creating a //! [`CacheAligned`] value with its contents zeroed out. //! - [`uninitialized_boxed_slice()`] allocates a boxed slice of a given //! number of elements without initializing its contents. //! //! # Data Alignment //! //! [`Scratchpad`] properly handles the alignment requirements of allocated //! objects by padding the offset of the allocation within the allocation //! buffer. This can result in some amount of wasted space if mixing //! allocations of types that have different alignment requirements. This //! waste can be minimized if necessary by grouping allocations based on their //! alignment requirements or by using separate scratchpads for different //! alignments. //! //! ## `Buffer` and `Tracking` Alignments //! //! The alignment of the allocation buffer and marker tracking themselves are //! determined by the element type of the corresponding slice or array used, //! as specified by the generic parameters of the [`Scratchpad`] type and the //! parameters of [`Scratchpad::new()`]. If the alignment of the buffer itself //! doesn't match the alignment needed for the first allocation made, the //! allocation will be offset from the start of the buffer as needed, //! resulting in wasted space. //! //! To avoid this, use an element type for the buffer's slice or array that //! provides at least the same alignment as that which will be needed for //! allocations. For most types, a slice or array of `u64` elements should //! provide sufficient alignment to avoid any initial wasted space. //! //! Allocations that require non-standard alignments may require defining a //! custom [`ByteData`] type with an appropriate `#[repr(align)]` attribute to //! avoid any wasted space at the start of the allocation buffer. For example, //! a [`Scratchpad`] guaranteeing a minimum initial alignment of 16 bytes for //! SIMD allocations can be created as follows: //! //! ``` //! use std::mem::uninitialized; //! use scratchpad::{ByteData, Scratchpad}; //! //! #[repr(align(16))] //! struct Aligned16([u32; 4]); //! //! unsafe impl ByteData for Aligned16 {} //! //! let scratchpad = Scratchpad::<[Aligned16; 1024], [usize; 4]>::new( //! unsafe { uninitialized() }, //! unsafe { uninitialized() }, //! ); //! ``` //! //! ## Alignment of Allocated Arrays //! //! When allocating a dynamically sized array from a [`Marker`][`Marker`] //! (i.e. using one of the `allocate_array*()` methods), the array is *only* //! guaranteed to be aligned based on the requirements of the element type. //! This means that, for example, it is unsafe to use an array of `u8` values //! as a buffer in which `f32` values will be written to or read from //! directly. It is strongly recommended that you only use arrays allocated //! from a marker as the element type specified, or that the array is //! allocated using an element type whose alignment is at least as large as //! the data it will contain. //! //! ## Cache Alignment //! //! Applications may prefer to keep data aligned to cache lines to avoid //! performance issues (e.g. multiple cache line loads for data crossing cache //! line boundaries, false sharing). The crate provides a simple data type, //! [`CacheAligned`], that can be used as the backing type for both allocation //! buffers and marker tracking. Simply providing an array or slice of //! [`CacheAligned`] objects instead of a built-in integer type will help //! ensure cache alignment of the buffer. The size of a single //! [`CacheAligned`] element will always match its alignment. //! //! This crate uses 64 bytes as the assumed cache line alignment, regardless //! of the build target. While the actual cache line alignment can vary //! between processors, 64 bytes is generally assumed to be a "safe" target. //! This value is exported in the [`CACHE_ALIGNMENT`] constant for //! applications that wish to reference it. //! //! # Memory Overhead //! //! Creating a marker requires a single `usize` value (4 bytes on platforms //! using 32-bit pointers, 8 bytes if using 64-bit pointers) within the //! scratchpad's tracking buffer. When using a slice or array for marker //! tracking, this memory is allocated up-front, so the footprint of the //! [`Scratchpad`] does not change after the scratchpad is created. //! //! Each [`Marker`] instance itself contains a reference back to its //! [`Scratchpad`] and its index within the scratchpad. This comes out to 8 //! bytes on platforms with 32-bit pointers and 16 bytes on platforms with //! 64-bit pointers. //! //! Individual allocations have effectively no overhead. Each [`Allocation`] //! instance itself only contains a reference to the allocated type, whose //! size can vary depending on whether the allocation is a single item or an //! array of items. //! //! # Limitations //! //! - Due to a lack of support in Rust for generically implementing traits for //! any size of a static array of a given type, the [`Buffer`] trait (and, //! by association, [`Tracking`] trait) is only implemented for a limited //! number of array sizes. Mutable slice references and boxed slices do not //! have this restriction, so they can be used for unsupported array sizes. //! - Using large static arrays as buffers can cause the program stack to //! overflow while creating a scratchpad, particularly in debug builds. //! Using [`Scratchpad::static_new()`] instead of [`Scratchpad::new()`] can //! help avoid such issues, and using either boxed slices or slice //! references of externally owned arrays for storage can help avoid such //! issues entirely. //! //! # Mutability Notes //! //! [`Scratchpad`] uses internal mutability when allocating and freeing //! memory, with allocation methods operating on immutable [`Scratchpad`] and //! [`Marker`] references. This is necessary to cleanly allow for multiple //! concurrent allocations, as Rust's mutable borrowing restrictions would //! otherwise prevent such behavior. Allocation and free operations do not //! have any side effect on other existing allocations, so there are no //! special considerations necessary by the user. //! //! [`Allocation`]: struct.Allocation.html //! [`array_len_for_bytes!()`]: macro.array_len_for_bytes.html //! [`array_len_for_markers!()`]: macro.array_len_for_markers.html //! [`array_type_for_bytes!()`]: macro.array_type_for_bytes.html //! [`array_type_for_markers!()`]: macro.array_type_for_markers.html //! [`Box`]: https://doc.rust-lang.org/alloc/boxed/index.html //! [`Buffer`]: trait.Buffer.html //! [`ByteData`]: trait.ByteData.html //! [`cache_aligned_zeroed!()`]: macro.cache_aligned_zeroed.html //! [`cache_aligned_zeroed_for_bytes!()`]: macro.cache_aligned_zeroed_for_bytes.html //! [`cache_aligned_zeroed_for_markers!()`]: macro.cache_aligned_zeroed_for_markers.html //! [`CACHE_ALIGNMENT`]: constant.CACHE_ALIGNMENT.html //! [`CacheAligned`]: struct.CacheAligned.html //! [`Drop`]: https://doc.rust-lang.org/core/ops/trait.Drop.html //! [`mark_back()`]: struct.Scratchpad.html#method.mark_back //! [`mark_front()`]: struct.Scratchpad.html#method.mark_front //! [`Marker`]: trait.Marker.html //! [`Scratchpad`]: struct.Scratchpad.html //! [`Scratchpad::new()`]: struct.Scratchpad.html#method.new //! [`Tracking`]: trait.Tracking.html //! [`uninitialized_boxed_slice()`]: fn.uninitialized_boxed_slice.html //! [`uninitialized_boxed_slice_for_bytes()`]: fn.uninitialized_boxed_slice_for_bytes.html //! [`uninitialized_boxed_slice_for_markers()`]: fn.uninitialized_boxed_slice_for_markers.html //! [`Vec`]: https://doc.rust-lang.org/alloc/vec/index.html #![cfg_attr(not(feature = "std"), no_std)] #![cfg_attr(all(feature = "unstable", not(feature = "std")), feature(alloc))] #![cfg_attr(feature = "unstable", feature(const_fn))] #[cfg(all(feature = "unstable", not(feature = "std")))] extern crate alloc; #[cfg(feature = "std")] extern crate core; #[cfg(test)] extern crate arrayvec; use core::fmt; use core::ptr; use core::slice; use core::cell::{RefCell, UnsafeCell}; use core::marker::PhantomData; use core::mem::{align_of, forget, uninitialized}; use core::ops::{Deref, DerefMut}; #[cfg(feature = "std")] use std::boxed::Box; #[cfg(feature = "std")] use std::vec::Vec; #[cfg(all(feature = "unstable", not(feature = "std")))] use alloc::boxed::Box; #[cfg(all(feature = "unstable", not(feature = "std")))] use alloc::vec::Vec; // Re-export `size_of()` for easier use with our exported macros. pub use core::mem::size_of; /// Returns the minimum number of elements of a given type necessary for /// storage of a given byte count. The actual supported byte count may be /// larger due to padding. /// /// # Examples /// /// ``` /// #[macro_use] /// extern crate scratchpad; /// /// # fn main() { /// assert_eq!(array_len_for_bytes!(u64, 32), 4); /// # } /// ``` #[macro_export] macro_rules! array_len_for_bytes { ($element:ty, $bytes:expr) => { ($bytes + $crate::size_of::<$element>() - 1) / $crate::size_of::<$element>() }; ($element:ty, $bytes:expr,) => { array_len_for_bytes!($element, $bytes) }; } /// Declares a static array of the specified element type that is large enough /// for storage of a given byte count. The actual supported byte count may be /// larger due to padding. /// /// # Examples /// /// ``` /// #[macro_use] /// extern crate scratchpad; /// /// // `BufferType` is the same as `[u64; 4]`. /// type BufferType = array_type_for_bytes!(u64, 32); /// /// # fn main() { /// let buffer: BufferType = [1, 2, 3, 4]; /// # } /// ``` #[macro_export] macro_rules! array_type_for_bytes { ($element:ty, $bytes:expr) => { [$element; array_len_for_bytes!($element, $bytes)] }; ($element:ty, $bytes:expr,) => { array_type_for_bytes!($element, $bytes) }; } /// Returns the minimum number of elements of a given type necessary for /// tracking of at least the specified number of [allocation markers]. The /// actual supported marker count may be larger due to padding. /// /// # Examples /// /// ``` /// #[macro_use] /// extern crate scratchpad; /// /// use scratchpad::CacheAligned; /// /// # fn main() { /// let len = array_len_for_markers!(CacheAligned, 16); /// /// #[cfg(target_pointer_width = "32")] /// assert_eq!(len, 1); /// /// #[cfg(target_pointer_width = "64")] /// assert_eq!(len, 2); /// # } /// ``` /// /// [allocation markers]: trait.Marker.html #[macro_export] macro_rules! array_len_for_markers { ($element:ty, $marker_count:expr) => { array_len_for_bytes!( $element, $marker_count * $crate::size_of::<usize>(), ) }; ($element:ty, $marker_count:expr,) => { array_len_for_markers!($element, $marker_count) }; } /// Declares a static array of the specified element type that is large enough /// for storage of at least the specified number of [allocation markers]. The /// actual supported marker count may be larger due to padding. /// /// # Examples /// /// ``` /// #[macro_use] /// extern crate scratchpad; /// /// use scratchpad::{CacheAligned, Error, Scratchpad}; /// /// // `BufferType` is the same as `[CacheAligned; 1]` on targets using 32-bit /// // pointers and `[CacheAligned; 2]` on targets using 64-bit pointers. /// type BufferType = array_type_for_markers!(CacheAligned, 16); /// /// # fn main() { /// #[cfg(target_pointer_width = "32")] /// let buffer: BufferType = [CacheAligned([1; 64])]; /// /// #[cfg(target_pointer_width = "64")] /// let buffer: BufferType = [CacheAligned([1; 64]), CacheAligned([2; 64])]; /// /// // Regardless of the target pointer size, the capacity of 16 markers is /// // still the same. /// let scratchpad = Scratchpad::new([0u64; 1], buffer); /// let mut markers = Vec::new(); /// for _ in 0..16 { /// markers.push(scratchpad.mark_front().unwrap()); /// } /// /// assert_eq!(scratchpad.mark_front().unwrap_err(), Error::MarkerLimit); /// # } /// ``` /// /// [allocation markers]: trait.Marker.html #[macro_export] macro_rules! array_type_for_markers { ($element:ty, $marker_count:expr) => { [$element; array_len_for_markers!($element, $marker_count)] }; ($element:ty, $marker_count:expr,) => { array_type_for_markers!($element, $marker_count) }; } /// Creates a [`CacheAligned`] instance whose contents are zeroed-out. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// # fn main() { /// let zeroed = cache_aligned_zeroed!(); /// for i in 0..zeroed.0.len() { /// assert_eq!(zeroed.0[i], 0); /// } /// # } /// ``` #[macro_export] macro_rules! cache_aligned_zeroed { () => { $crate::CacheAligned([0; $crate::CACHE_ALIGNMENT]) }; } /// Creates an array of zeroed-out [`CacheAligned`] values large enough for /// storage of the given byte count. The actual supported byte count may be /// larger due to padding. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// # fn main() { /// let zeroed = cache_aligned_zeroed_for_bytes!(256); /// for element in &zeroed { /// for i in 0..element.0.len() { /// assert_eq!(element.0[i], 0); /// } /// } /// # } /// ``` #[macro_export] macro_rules! cache_aligned_zeroed_for_bytes { ($bytes:expr) => { [ cache_aligned_zeroed!(); array_len_for_bytes!($crate::CacheAligned, $bytes) ] }; ($bytes:expr,) => { cache_aligned_zeroed_for_bytes!($bytes) }; } /// Creates an array of zeroed-out [`CacheAligned`] values large enough for /// storage of at least the specified number of [allocation markers]. The /// actual supported marker count may be larger due to padding. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// # fn main() { /// let zeroed = cache_aligned_zeroed_for_markers!(32); /// for element in &zeroed { /// for i in 0..element.0.len() { /// assert_eq!(element.0[i], 0); /// } /// } /// # } /// ``` /// /// [allocation markers]: trait.Marker.html #[macro_export] macro_rules! cache_aligned_zeroed_for_markers { ($marker_count:expr) => { [ cache_aligned_zeroed!(); array_len_for_markers!($crate::CacheAligned, $marker_count) ] }; ($marker_count:expr,) => { cache_aligned_zeroed_for_markers!($marker_count) }; } /// Assumed cache line byte alignment. /// /// This may vary from the actual cache line alignment, which can vary between /// processors types, including those of the same architecture. 64 bytes is /// typically assumed to be a "safe" target to ensure cache alignment. /// /// Note that since the `repr(align)` attribute doesn't support named /// constants, this value is duplicated in the declaration of /// [`CacheAligned`], so it must be updated in both locations if changed. /// /// [`CacheAligned`]: struct.CacheAligned.html pub const CACHE_ALIGNMENT: usize = 64; /// [`Scratchpad`] allocation errors. /// /// [`Scratchpad`]: struct.Scratchpad.html #[derive(Debug, PartialEq)] pub enum Error { /// Maximum number of scratchpad markers are currently set. MarkerLimit, /// Allocation cannot be made because the marker is not the most-recently /// created active marker. MarkerLocked, /// Insufficient space in the scratchpad buffer for the allocation. InsufficientMemory, /// Integer overflow detected (typically due to a very large size or /// alignment). Overflow, } impl fmt::Display for Error { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match self { &Error::MarkerLimit => { write!(f, "scratchpad marker limit reached") } &Error::MarkerLocked => { write!(f, "marker is not the most recent active marker") } &Error::InsufficientMemory => { write!(f, "insufficient allocation buffer space") } &Error::Overflow => write!(f, "integer overflow"), } } } #[cfg(feature = "std")] impl std::error::Error for Error { fn description(&self) -> &str { match self { &Error::MarkerLimit => "scratchpad marker limit reached", &Error::MarkerLocked => { "marker is not the most recent active marker" } &Error::InsufficientMemory => { "insufficient allocation buffer space" } &Error::Overflow => "integer overflow", } } } /// Cache-aligned storage for [`Buffer`] and [`Tracking`] use. /// /// Internally, this simply wraps a `u8` array to ensure cache alignment. /// Arrays and slices of this type can be used directly for either /// [`Scratchpad`] storage or marker tracking. /// /// The alignment and size of `CacheAligned` are determined by the /// [`CACHE_ALIGNMENT`] constant. /// /// [`Buffer`]: trait.Buffer.html /// [`CACHE_ALIGNMENT`]: constant.CACHE_ALIGNMENT.html /// [`Scratchpad`]: struct.Scratchpad.html /// [`Tracking`]: trait.Tracking.html #[derive(Clone, Copy)] #[repr(align(64))] pub struct CacheAligned(pub [u8; CACHE_ALIGNMENT]); impl fmt::Debug for CacheAligned { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "CacheAligned {{ ... }}") } } /// Trait for types that can be safely used as the backing data type for /// storage of arbitrary data. /// /// `ByteData` is implemented by default for all basic integer types as well /// as the [`CacheAligned`] struct provided by this crate. /// /// # Safety /// /// This trait is used to help constrain implementations of the [`Buffer`] /// trait to known types that are considered "safe" to use as the backing /// storage type of a buffer. To properly implement this trait, the type /// should have the following characteristics: /// /// - Allow arbitrary bytes within instances of the type to be left /// uninitialized without any possible side effects (outside of attempts to /// explicitly read those bytes). In particular, types should not have /// [`Drop`] trait implementations that rely on the data to be in any /// particular state. /// - Allow arbitrary bytes within instances of the type to be written to with /// arbitrary values without affecting other bytes. /// - Allow previously written bytes to be read back regardless of whether /// other bytes have been written to yet (only bytes that have been /// explicitly written to are expected to be read back). /// /// [`Buffer`]: trait.Buffer.html /// [`CacheAligned`]: struct.CacheAligned.html /// [`Drop`]: https://doc.rust-lang.org/core/ops/trait.Drop.html pub unsafe trait ByteData: Sized {} unsafe impl ByteData for u8 {} unsafe impl ByteData for u16 {} unsafe impl ByteData for u32 {} unsafe impl ByteData for u64 {} #[cfg(feature = "nightly")] unsafe impl ByteData for u128 {} unsafe impl ByteData for usize {} unsafe impl ByteData for i8 {} unsafe impl ByteData for i16 {} unsafe impl ByteData for i32 {} unsafe impl ByteData for i64 {} #[cfg(feature = "nightly")] unsafe impl ByteData for i128 {} unsafe impl ByteData for isize {} unsafe impl ByteData for CacheAligned {} /// Trait for [`Scratchpad`] buffer types. /// /// `Buffer` objects contain the memory from which [`Scratchpad`] allocations /// are made. [`Scratchpad`] handles all bookkeeping, so a buffer only needs /// to provide methods for raw access of the buffer memory. /// /// [`Scratchpad`]: struct.Scratchpad.html pub trait Buffer { /// Returns a byte slice of the buffer contents. fn as_bytes(&self) -> &[u8]; /// Returns a mutable byte slice of the buffer contents. fn as_bytes_mut(&mut self) -> &mut [u8]; } /// [`Buffer`] sub-trait for static arrays. /// /// This trait is used specifically to restrict the implementation of /// [`Scratchpad::static_new()`] to static array buffers. /// /// # Safety /// /// [`Scratchpad::static_new()`] leaves instances of this type **entirely** /// uninitialized, so implementing it is fundamentally unsafe. It should only /// be implemented by static arrays of [`ByteData`] types. /// /// [`Buffer`]: trait.Buffer.html /// [`ByteData`]: trait.ByteData.html /// [`Scratchpad::static_new()`]: struct.Scratchpad.html#method.static_new pub unsafe trait StaticBuffer: Buffer {} impl<'a, T> Buffer for &'a mut [T] where T: ByteData, { #[inline] fn as_bytes(&self) -> &[u8] { unsafe { slice::from_raw_parts( self.as_ptr() as *const u8, self.len() * size_of::<T>(), ) } } #[inline] fn as_bytes_mut(&mut self) -> &mut [u8] { unsafe { slice::from_raw_parts_mut( self.as_mut_ptr() as *mut u8, self.len() * size_of::<T>(), ) } } } #[cfg(any(feature = "std", feature = "unstable"))] impl<T> Buffer for Box<[T]> where T: ByteData, { #[inline] fn as_bytes(&self) -> &[u8] { let data = self.as_ref(); unsafe { slice::from_raw_parts( data.as_ptr() as *const u8, data.len() * size_of::<T>(), ) } } #[inline] fn as_bytes_mut(&mut self) -> &mut [u8] { let data = self.as_mut(); unsafe { slice::from_raw_parts_mut( data.as_mut_ptr() as *mut u8, data.len() * size_of::<T>(), ) } } } /// Macro for generating `Buffer` implementations for static arrays. macro_rules! generate_buffer_impl { ($size:expr) => { impl<T> Buffer for [T; $size] where T: ByteData, { #[inline] fn as_bytes(&self) -> &[u8] { let data = &self[..]; unsafe { slice::from_raw_parts ( data.as_ptr() as *const u8, data.len() * size_of::<T>(), ) } } #[inline] fn as_bytes_mut(&mut self) -> &mut [u8] { let data = &mut self[..]; unsafe { slice::from_raw_parts_mut ( data.as_mut_ptr() as *mut u8, data.len() * size_of::<T>(), ) } } } unsafe impl<T> StaticBuffer for [T; $size] where T: ByteData, {} }; ($size:expr, $($other:tt)*) => { generate_buffer_impl!($size); generate_buffer_impl!($($other)*); }; () => {}; } generate_buffer_impl!(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); generate_buffer_impl!(11, 12, 13, 14, 15, 16, 17, 18, 19, 20); generate_buffer_impl!(21, 22, 23, 24, 25, 26, 27, 28, 29, 30); generate_buffer_impl!(31, 32, 33, 34, 35, 36, 37, 38, 39, 40); generate_buffer_impl!(41, 42, 43, 44, 45, 46, 47, 48, 49, 50); generate_buffer_impl!(51, 52, 53, 54, 55, 56, 57, 58, 59, 60); generate_buffer_impl!(61, 62, 63, 64); generate_buffer_impl!(0x80, 0x100, 0x200, 0x400, 0x800, 0x1000, 0x2000); generate_buffer_impl!(0x4000, 0x8000, 0x10000, 0x20000, 0x40000, 0x80000); generate_buffer_impl!(0x100000, 0x200000, 0x400000, 0x800000, 0x1000000); generate_buffer_impl!(0x2000000, 0x4000000, 0x8000000, 0x10000000); generate_buffer_impl!(0x20000000, 0x40000000); /// Trait for [`Scratchpad`] allocation tracking containers. /// /// Each [`Marker`] is tracked within a [`Scratchpad`] using only a single /// `usize` value per allocation. Actual storage of such values can be /// implemented in any manner (memory does not need to be contiguous, for /// instance). /// /// [`Scratchpad`] and [`Marker`] will never call [`get()`] for a given index /// if [`set()`] has not been previously called for the same index, so values /// can be left uninitialized prior to [`set()`] calls. /// /// [`get()`]: #method.get.html /// [`Marker`]: trait.Marker.html /// [`Scratchpad`]: struct.Scratchpad.html /// [`set()`]: #method.set.html pub trait Tracking: Sized { /// Returns the total number of allocations that can be stored in this /// container. fn capacity(&self) -> usize; /// Stores a value at the specified index. fn set(&mut self, index: usize, value: usize); /// Retrieves the value from the specified index. fn get(&self, index: usize) -> usize; } impl<T> Tracking for T where T: Buffer, { #[inline] fn capacity(&self) -> usize { self.as_bytes().len() / size_of::<usize>() } #[inline] fn set(&mut self, index: usize, value: usize) { let bytes = self.as_bytes_mut(); let contents = unsafe { slice::from_raw_parts_mut( bytes.as_mut_ptr() as *mut usize, bytes.len() / size_of::<usize>(), ) }; contents[index] = value; } #[inline] fn get(&self, index: usize) -> usize { let bytes = self.as_bytes(); let contents = unsafe { slice::from_raw_parts( bytes.as_ptr() as *const usize, bytes.len() / size_of::<usize>(), ) }; contents[index] } } /// Front and back stacks for `Marker` tracking (used internally). struct MarkerStacks<TrackingT> where TrackingT: Tracking, { /// Stack data. data: TrackingT, /// Front stack offset. front: usize, /// Back stack offset. back: usize, } impl<TrackingT> fmt::Debug for MarkerStacks<TrackingT> where TrackingT: Tracking, { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "MarkerStacks {{ ... }}") } } /// Scratchpad [`Marker`] allocation. /// /// Markers implement the [`Deref`] and [`DerefMut`] traits, allowing the data /// to be dereferenced explicitly using the unary `*` operator (e.g. /// `*allocation`) or implicitly by the compiler under various circumstances. /// /// An allocation is statically bound to the lifetime of the [`Marker`] from /// which it is allocated, ensuring that no dangling references can be left /// when the [`Marker`] is dropped. /// /// [`Marker`]: trait.Marker.html /// [`Deref`]: https://doc.rust-lang.org/core/ops/trait.Deref.html /// [`DerefMut`]: https://doc.rust-lang.org/core/ops/trait.DerefMut.html pub struct Allocation<'marker, 't, T> where T: 't + ?Sized, { /// Allocation data. data: &'t mut T, /// Dummy reference for ensuring the allocation does not outlive the /// `Marker` from which it was allocated. _phantom: PhantomData<&'marker ()>, } impl<'marker, 't, T> Allocation<'marker, 't, T> where T: 't + Sized, { /// Moves the value out of the `Allocation`. /// /// Note that this is only implemented for [`Sized`] value types. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let x = { /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new( /// [0], /// [0], /// ); /// let marker = scratchpad.mark_front().unwrap(); /// let allocation = marker.allocate(3.14159).unwrap(); /// /// allocation.unwrap() /// }; /// /// // Value was moved out of the allocation, so it can now outlive the /// // scratchpad in which it was initially created. /// assert_eq!(x, 3.14159); /// ``` /// /// [`Sized`]: https://doc.rust-lang.org/core/marker/trait.Sized.html pub fn unwrap(self) -> T { unsafe { let value = ptr::read(self.data); forget(self); value } } } impl<'marker, 't, T> Deref for Allocation<'marker, 't, T> where T: 't + ?Sized, { type Target = T; #[inline] fn deref(&self) -> &T { self.data } } impl<'marker, 't, T> DerefMut for Allocation<'marker, 't, T> where T: 't + ?Sized, { #[inline] fn deref_mut(&mut self) -> &mut T { self.data } } impl<'marker, 't, T> Drop for Allocation<'marker, 't, T> where T: 't + ?Sized, { #[inline] fn drop(&mut self) { unsafe { ptr::drop_in_place(self.data) }; } } impl<'marker, 't, T> fmt::Debug for Allocation<'marker, 't, T> where T: 't + ?Sized + fmt::Debug, { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "Allocation {{ data: {:?} }}", self.data) } } /// [`Scratchpad`] allocation marker implementation trait. /// /// This provides the shared interface for the [`MarkerFront`] and /// [`MarkerBack`] types. /// /// [`MarkerBack`]: struct.MarkerBack.html /// [`MarkerFront`]: struct.MarkerFront.html /// [`Scratchpad`]: struct.Scratchpad.html pub trait Marker { /// Allocates space for the given value, moving it into the allocation. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate(3.14159).unwrap(); /// assert_eq!(*x, 3.14159); /// ``` fn allocate<'marker, 't, T>( &'marker self, value: T, ) -> Result<Allocation<'marker, 't, T>, Error> { unsafe { self.allocate_uninitialized::<T>().map(|allocation| { ptr::write(allocation.data, value); allocation }) } } /// Allocates space for a value, initializing it to its default. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_default::<f64>().unwrap(); /// assert_eq!(*x, 0.0); /// ``` fn allocate_default<'marker, 't, T: Default>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { self.allocate(Default::default()) } /// Allocates uninitialized space for the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let mut x = unsafe { marker.allocate_uninitialized().unwrap() }; /// *x = 3.14159; /// assert_eq!(*x, 3.14159); /// ``` unsafe fn allocate_uninitialized<'marker, 't, T>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { let data = self.allocate_memory(align_of::<T>(), size_of::<T>(), 1)?; Ok(Allocation { data: &mut *(data as *mut T), _phantom: PhantomData, }) } /// Allocates space for an array, initializing each element with the given /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array(3, 3.14159).unwrap(); /// assert_eq!(*x, [3.14159, 3.14159, 3.14159]); /// ``` fn allocate_array<'marker, 't, T: Clone>( &'marker self, len: usize, value: T, ) -> Result<Allocation<'marker, 't, [T]>, Error> { unsafe { self.allocate_array_uninitialized(len).map(|allocation| { debug_assert_eq!(allocation.data.len(), len); for element in allocation.data.iter_mut() { ptr::write(element, value.clone()); } allocation }) } } /// Allocates space for an array, initializing each element to its default /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array_default::<f64>(3).unwrap(); /// assert_eq!(*x, [0.0, 0.0, 0.0]); /// ``` fn allocate_array_default<'marker, 't, T: Default>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { unsafe { self.allocate_array_uninitialized(len).map(|allocation| { debug_assert_eq!(allocation.data.len(), len); for element in allocation.data.iter_mut() { ptr::write(element, Default::default()); } allocation }) } } /// Allocates space for an array, initializing each element with the /// result of a function. /// /// The function `func` takes a single parameter containing the index of /// the element being initialized. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array_with(3, |index| index as f64).unwrap(); /// assert_eq!(*x, [0.0, 1.0, 2.0]); /// ``` fn allocate_array_with<'marker, 't, T, F: FnMut(usize) -> T>( &'marker self, len: usize, mut func: F, ) -> Result<Allocation<'marker, 't, [T]>, Error> { unsafe { self.allocate_array_uninitialized(len).map(|allocation| { debug_assert_eq!(allocation.data.len(), len); for (index, element) in allocation.data.iter_mut().enumerate() { ptr::write(element, func(index)); } allocation }) } } /// Allocates uninitialized space for an array of the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let mut x = unsafe { /// marker.allocate_array_uninitialized(3).unwrap() /// }; /// x[0] = 3.14159; /// x[1] = 4.14159; /// x[2] = 5.14159; /// assert_eq!(*x, [3.14159, 4.14159, 5.14159]); /// ``` unsafe fn allocate_array_uninitialized<'marker, 't, T>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { let data = self.allocate_memory(align_of::<T>(), size_of::<T>(), len)?; Ok(Allocation { data: slice::from_raw_parts_mut(data as *mut T, len), _phantom: PhantomData, }) } /// Allocates a block of memory of a given size and alignment. /// /// If successful, returns a tuple containing the allocation address and /// allocation index. /// /// **_This is intended primarily for use by the internal implementation /// of this trait, and is not safe for use by external code. Its signature /// and behavior are not guaranteed to be consistent across versions of /// this crate._** #[doc(hidden)] unsafe fn allocate_memory( &self, alignment: usize, size: usize, len: usize, ) -> Result<*mut u8, Error>; } /// [`Scratchpad`] marker for allocations from the front of the allocation /// buffer. /// /// A `MarkerFront` is created when calling the [`mark_front()`] method on a /// [`Scratchpad`] instance. Object allocations can only be made from the most /// recently created `MarkerFront` or [`MarkerBack`] that is still active. /// /// Markers are statically bound to the lifetime of the [`Scratchpad`] from /// which they are created, ensuring that no dangling references are left when /// the [`Scratchpad`] is dropped. /// /// This struct wraps [`Marker`] trait methods to avoid the need to import /// [`Marker`] into scope. /// /// [`mark_front()`]: struct.Scratchpad.html#method.mark_front /// [`Marker`]: trait.Marker.html /// [`MarkerBack`]: struct.MarkerBack.html /// [`Scratchpad`]: struct.Scratchpad.html #[derive(Debug)] pub struct MarkerFront<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { /// `Scratchpad` in which the allocation is tracked. scratchpad: &'scratchpad Scratchpad<BufferT, TrackingT>, /// Marker index. index: usize, } impl<'scratchpad, BufferT, TrackingT> Marker for MarkerFront<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { unsafe fn allocate_memory( &self, alignment: usize, size: usize, len: usize, ) -> Result<*mut u8, Error> { // Make sure the marker is the top-most front marker (no allocations // are allowed if a more-recently created front marker is still // active). let mut markers = self.scratchpad.markers.borrow_mut(); if markers.front != self.index + 1 { return Err(Error::MarkerLocked); } let alignment_mask = alignment - 1; debug_assert_eq!(alignment & alignment_mask, 0); // Pad the allocation size to match the requested alignment. let size = size.checked_add(alignment_mask).ok_or(Error::Overflow)? & !alignment_mask; let size = size * len; // Compute the buffer range needed to accommodate the allocation size // and alignment. let buffer = (*self.scratchpad.buffer.get()).as_bytes_mut(); let buffer_end_offset = if markers.back == markers.data.capacity() { buffer.len() } else { markers.data.get(markers.back) }; let buffer_start = buffer.as_mut_ptr() as usize; let buffer_end = buffer_start + buffer_end_offset; let start = buffer_start + markers.data.get(self.index); debug_assert!(start <= buffer_end); let start = start.checked_add(alignment_mask).ok_or(Error::Overflow)? & !alignment_mask; let end = start.checked_add(size).ok_or(Error::Overflow)?; if end > buffer_end { return Err(Error::InsufficientMemory); } // Update this marker's offset and return the allocation. markers.data.set(self.index, end - buffer_start); Ok(start as *mut u8) } } impl<'scratchpad, BufferT, TrackingT> MarkerFront<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { /// Allocates space for the given value, moving it into the allocation. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate(3.14159).unwrap(); /// assert_eq!(*x, 3.14159); /// ``` #[inline(always)] pub fn allocate<'marker, 't, T>( &'marker self, value: T, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate(self, value) } /// Allocates space for a value, initializing it to its default. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_default::<f64>().unwrap(); /// assert_eq!(*x, 0.0); /// ``` #[inline(always)] pub fn allocate_default<'marker, 't, T: Default>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate_default(self) } /// Allocates uninitialized space for the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let mut x = unsafe { marker.allocate_uninitialized().unwrap() }; /// *x = 3.14159; /// assert_eq!(*x, 3.14159); /// ``` #[inline(always)] pub unsafe fn allocate_uninitialized<'marker, 't, T>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate_uninitialized(self) } /// Allocates space for an array, initializing each element with the given /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array(3, 3.14159).unwrap(); /// assert_eq!(*x, [3.14159, 3.14159, 3.14159]); /// ``` #[inline(always)] pub fn allocate_array<'marker, 't, T: Clone>( &'marker self, len: usize, value: T, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array(self, len, value) } /// Allocates space for an array, initializing each element to its default /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array_default::<f64>(3).unwrap(); /// assert_eq!(*x, [0.0, 0.0, 0.0]); /// ``` #[inline(always)] pub fn allocate_array_default<'marker, 't, T: Default>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_default(self, len) } /// Allocates space for an array, initializing each element with the /// result of a function. /// /// The function `func` takes a single parameter containing the index of /// the element being initialized. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let x = marker.allocate_array_with(3, |index| index as f64).unwrap(); /// assert_eq!(*x, [0.0, 1.0, 2.0]); /// ``` #[inline(always)] pub fn allocate_array_with<'marker, 't, T, F: FnMut(usize) -> T>( &'marker self, len: usize, func: F, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_with(self, len, func) } /// Allocates uninitialized space for an array of the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_front().unwrap(); /// /// let mut x = unsafe { /// marker.allocate_array_uninitialized(3).unwrap() /// }; /// x[0] = 3.14159; /// x[1] = 4.14159; /// x[2] = 5.14159; /// assert_eq!(*x, [3.14159, 4.14159, 5.14159]); /// ``` #[inline(always)] pub unsafe fn allocate_array_uninitialized<'marker, 't, T>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_uninitialized(self, len) } } impl<'scratchpad, BufferT, TrackingT> Drop for MarkerFront<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { fn drop(&mut self) { let mut markers = self.scratchpad.markers.borrow_mut(); let mut front = markers.front; debug_assert!(self.index < front); let mut last_index = front - 1; if self.index < last_index { // Markers created after this marker still exist, so flag it as // unused so it can be freed later. markers.data.set(self.index, core::usize::MAX); return; } // Pop the marker entry off the marker stack as well all other unused // marker slots at the end of the stack. loop { front = last_index; if front == 0 { break; } last_index -= 1; if markers.data.get(last_index) != core::usize::MAX { break; } } markers.front = front; } } /// [`Scratchpad`] marker for allocations from the back of the allocation /// buffer. /// /// A `MarkerBack` is created when calling the [`mark_back()`] method on a /// [`Scratchpad`] instance. Object allocations can only be made from the most /// recently created [`MarkerFront`] or `MarkerBack` that is still active. /// /// Markers are statically bound to the lifetime of the [`Scratchpad`] from /// which they are created, ensuring that no dangling references are left when /// the [`Scratchpad`] is dropped. /// /// This struct wraps [`Marker`] trait methods to avoid the need to import /// [`Marker`] into scope. /// /// [`mark_back()`]: struct.Scratchpad.html#method.mark_back /// [`Marker`]: trait.Marker.html /// [`MarkerFront`]: struct.MarkerFront.html /// [`Scratchpad`]: struct.Scratchpad.html #[derive(Debug)] pub struct MarkerBack<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { /// `Scratchpad` in which the allocation is tracked. scratchpad: &'scratchpad Scratchpad<BufferT, TrackingT>, /// Marker index. index: usize, } impl<'scratchpad, BufferT, TrackingT> Marker for MarkerBack<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { unsafe fn allocate_memory( &self, alignment: usize, size: usize, len: usize, ) -> Result<*mut u8, Error> { // Make sure the marker is the bottom-most back marker (no allocations // are allowed if a more-recently created back marker is still // active). let mut markers = self.scratchpad.markers.borrow_mut(); if markers.back != self.index { return Err(Error::MarkerLocked); } let alignment_mask = alignment - 1; debug_assert_eq!(alignment & alignment_mask, 0); // Pad the allocation size to match the requested alignment. let size = size.checked_add(alignment_mask).ok_or(Error::Overflow)? & !alignment_mask; let size = size * len; // Compute the buffer range needed to accommodate the allocation size // and alignment. let buffer = (*self.scratchpad.buffer.get()).as_bytes_mut(); let buffer_start = buffer.as_mut_ptr() as usize; let buffer_end = buffer_start + markers.data.get(self.index); let start_min = if markers.front == 0 { buffer_start } else { buffer_start + markers.data.get(markers.front - 1) }; debug_assert!(start_min <= buffer_end); let start = buffer_end.checked_sub(size).ok_or(Error::Overflow)? & !alignment_mask; if start < start_min { return Err(Error::InsufficientMemory); } // Update this marker's offset and return the allocation. markers.data.set(self.index, start - buffer_start); Ok(start as *mut u8) } } impl<'scratchpad, BufferT, TrackingT> MarkerBack<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { /// Allocates space for the given value, moving it into the allocation. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let x = marker.allocate(3.14159).unwrap(); /// assert_eq!(*x, 3.14159); /// ``` #[inline(always)] pub fn allocate<'marker, 't, T>( &'marker self, value: T, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate(self, value) } /// Allocates space for a value, initializing it to its default. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let x = marker.allocate_default::<f64>().unwrap(); /// assert_eq!(*x, 0.0); /// ``` #[inline(always)] pub fn allocate_default<'marker, 't, T: Default>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate_default(self) } /// Allocates uninitialized space for the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let mut x = unsafe { marker.allocate_uninitialized().unwrap() }; /// *x = 3.14159; /// assert_eq!(*x, 3.14159); /// ``` #[inline(always)] pub unsafe fn allocate_uninitialized<'marker, 't, T>( &'marker self, ) -> Result<Allocation<'marker, 't, T>, Error> { Marker::allocate_uninitialized(self) } /// Allocates space for an array, initializing each element with the given /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let x = marker.allocate_array(3, 3.14159).unwrap(); /// assert_eq!(*x, [3.14159, 3.14159, 3.14159]); /// ``` #[inline(always)] pub fn allocate_array<'marker, 't, T: Clone>( &'marker self, len: usize, value: T, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array(self, len, value) } /// Allocates space for an array, initializing each element to its default /// value. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let x = marker.allocate_array_default::<f64>(3).unwrap(); /// assert_eq!(*x, [0.0, 0.0, 0.0]); /// ``` #[inline(always)] pub fn allocate_array_default<'marker, 't, T: Default>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_default(self, len) } /// Allocates space for an array, initializing each element with the /// result of a function. /// /// The function `func` takes a single parameter containing the index of /// the element being initialized. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let x = marker.allocate_array_with(3, |index| index as f64).unwrap(); /// assert_eq!(*x, [0.0, 1.0, 2.0]); /// ``` #[inline(always)] pub fn allocate_array_with<'marker, 't, T, F: FnMut(usize) -> T>( &'marker self, len: usize, func: F, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_with(self, len, func) } /// Allocates uninitialized space for an array of the given type. /// /// # Safety /// /// Since memory for the allocated data is uninitialized, it can /// potentially be in an invalid state for a given type, leading to /// undefined program behavior. It is recommended that one of the safe /// `allocate*()` methods are used instead if possible. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 3], [usize; 1]>::new([0; 3], [0]); /// let marker = scratchpad.mark_back().unwrap(); /// /// let mut x = unsafe { /// marker.allocate_array_uninitialized(3).unwrap() /// }; /// x[0] = 3.14159; /// x[1] = 4.14159; /// x[2] = 5.14159; /// assert_eq!(*x, [3.14159, 4.14159, 5.14159]); /// ``` #[inline(always)] pub unsafe fn allocate_array_uninitialized<'marker, 't, T>( &'marker self, len: usize, ) -> Result<Allocation<'marker, 't, [T]>, Error> { Marker::allocate_array_uninitialized(self, len) } } impl<'scratchpad, BufferT, TrackingT> Drop for MarkerBack<'scratchpad, BufferT, TrackingT> where BufferT: 'scratchpad + Buffer, TrackingT: 'scratchpad + Tracking, { fn drop(&mut self) { let mut markers = self.scratchpad.markers.borrow_mut(); let mut back = markers.back; debug_assert!(self.index >= back); if self.index > back { // Markers created after this marker still exist, so flag it as // unused so it can be freed later. markers.data.set(self.index, core::usize::MAX); return; } // Pop the marker entry off the marker stack as well all other unused // marker slots at the end of the stack. let capacity = markers.data.capacity(); loop { back += 1; if back == capacity { break; } if markers.data.get(back) != core::usize::MAX { break; } } markers.back = back; } } /// Stack-like dynamic memory pool with double-ended allocation support. /// /// `Scratchpad` manages dynamic allocations from a fixed-size region of /// memory in a stack-like manner. Allocations can be made simultaneously from /// either the "front" or "back" of the scratchpad by setting a [`Marker`] /// using either [`mark_front()`][`mark_front()`] (returning a /// [`MarkerFront`]) or [`mark_back()`][`mark_back()`] (returning a /// [`MarkerBack`]). Multiple markers can be set, but only the most-recently /// set marker of a given type that is still active can be used to allocate /// objects. /// /// Individual allocations can be made from the marker, but no memory is /// actually freed back into the pool until the marker is dropped, where all /// the memory allocated through the marker is released at once. If the marker /// is not the most-recently set active marker of its type, its memory will /// simply be flagged as unused until all markers of the same type that were /// created after it are also dropped, at which point the memory will be once /// again made available for allocations. /// /// `Scratchpad`, [`Marker`] implementations, and [`Allocation`] all make use /// of static lifetimes to ensure that an object cannot be used after the /// object from which it was created is dropped (an allocation cannot outlive /// its marker, and a marker cannot outlive its scratchpad). /// /// *See also the [crate-level documentation](index.html) for more detailed /// information about how `Scratchpad` works and can be used.* /// /// [`Allocation`]: struct.Allocation.html /// [`mark_back()`]: #method.mark_back /// [`mark_front()`]: #method.mark_front /// [`Marker`]: trait.Marker.html /// [`MarkerBack`]: struct.MarkerBack.html /// [`MarkerFront`]: struct.MarkerFront.html pub struct Scratchpad<BufferT, TrackingT> where BufferT: Buffer, TrackingT: Tracking, { /// Buffer from which allocations are made. buffer: UnsafeCell<BufferT>, /// Dual stack containing the offsets of each active marker. If a marker /// not at the end of one of the stacks is freed, its offset is set to /// `core::usize::MAX` to indicate it is no longer active until the /// allocations that came after it (in the same stack) have also been /// freed. markers: RefCell<MarkerStacks<TrackingT>>, } impl<BufferT, TrackingT> Scratchpad<BufferT, TrackingT> where BufferT: Buffer, TrackingT: Tracking, { /// Creates a new scratchpad instance. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// use scratchpad::Scratchpad; /// use std::mem::uninitialized; /// /// # fn main() { /// // Creates a scratchpad that can hold up to 256 bytes of data and up /// // to 4 allocation markers. The initial contents of each buffer are /// // ignored, so we can provide uninitialized data in order to reduce /// // the runtime overhead of creating a scratchpad. /// let scratchpad = unsafe { Scratchpad::new( /// uninitialized::<array_type_for_bytes!(u64, 256)>(), /// uninitialized::<array_type_for_markers!(usize, 4)>(), /// ) }; /// # } /// ``` #[inline(always)] #[cfg(feature = "unstable")] pub const fn new(buffer: BufferT, tracking: TrackingT) -> Self { Scratchpad { buffer: UnsafeCell::new(buffer), markers: RefCell::new(MarkerStacks { data: tracking, front: 0, back: core::usize::MAX, // Lazy initialization. }), } } /// Creates a new scratchpad instance. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// use scratchpad::Scratchpad; /// use std::mem::uninitialized; /// /// # fn main() { /// // Creates a scratchpad that can hold up to 256 bytes of data and up /// // to 4 allocation markers. The initial contents of each buffer are /// // ignored, so we can provide uninitialized data in order to reduce /// // the runtime overhead of creating a scratchpad. /// let scratchpad = unsafe { Scratchpad::new( /// uninitialized::<array_type_for_bytes!(u64, 256)>(), /// uninitialized::<array_type_for_markers!(usize, 4)>(), /// ) }; /// # } /// ``` #[inline(always)] #[cfg(not(feature = "unstable"))] pub fn new(buffer: BufferT, tracking: TrackingT) -> Self { Scratchpad { buffer: UnsafeCell::new(buffer), markers: RefCell::new(MarkerStacks { back: tracking.capacity(), data: tracking, front: 0, }), } } } impl<BufferT, TrackingT> Scratchpad<BufferT, TrackingT> where BufferT: StaticBuffer, TrackingT: Tracking + StaticBuffer, { /// Creates a new instance for scratchpad types backed entirely by static /// arrays without initializing array memory. /// /// Since static array [`Buffer`] and [`Tracking`] types are owned by the /// scratchpad, and their sizes are known ahead of time to the scratchpad /// type, scratchpads using only static arrays for storage can be created /// without having to provide any parameters. /// /// Note that this cannot be `const` as there is no support in Rust for /// creating uninitialized values in `const` code. [`Scratchpad::new()`] /// must be used with the `unstable` crate feature enabled if `const` code /// is required. /// /// # Examples /// /// ``` /// # #[macro_use] /// # extern crate scratchpad; /// use scratchpad::Scratchpad; /// /// # fn main() { /// // Creates a scratchpad that can hold up to 256 bytes of data and up /// // to 4 allocation markers. /// let scratchpad = Scratchpad::< /// array_type_for_bytes!(u64, 256), /// array_type_for_markers!(usize, 4), /// >::static_new(); /// # } /// ``` /// /// [`Buffer`]: trait.Buffer.html /// [`Tracking`]: trait.Tracking.html /// [`Scratchpad::new()`]: #method.new #[inline(always)] pub fn static_new() -> Self { Scratchpad { buffer: unsafe { uninitialized() }, markers: RefCell::new(MarkerStacks { data: unsafe { uninitialized() }, front: 0, back: size_of::<TrackingT>() / size_of::<usize>(), }), } } } impl<BufferT, TrackingT> Scratchpad<BufferT, TrackingT> where BufferT: Buffer, TrackingT: Tracking, { /// Creates a marker at the front of the allocation buffer for subsequent /// allocations. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// /// let marker = scratchpad.mark_front().unwrap(); /// // `marker` can now be used for allocations... /// ``` pub fn mark_front<'scratchpad>( &'scratchpad self, ) -> Result<MarkerFront<'scratchpad, BufferT, TrackingT>, Error> { let mut markers = self.markers.borrow_mut(); // `markers.back` is lazy-initialized when the "unstable" feature is // enabled so that `Scratchpad::new()` can be a `const` function. #[cfg(feature = "unstable")] { if markers.back == core::usize::MAX { markers.back = markers.data.capacity(); } } let index = markers.front; if index == markers.back { return Err(Error::MarkerLimit); } let buffer_offset = if index == 0 { 0 } else { markers.data.get(index - 1) }; markers.data.set(index, buffer_offset); markers.front = index + 1; Ok(MarkerFront { scratchpad: self, index, }) } /// Creates a marker at the back of the allocation buffer for subsequent /// allocations. /// /// # Examples /// /// ``` /// use scratchpad::Scratchpad; /// /// let scratchpad = Scratchpad::<[u64; 1], [usize; 1]>::new([0], [0]); /// /// let marker = scratchpad.mark_back().unwrap(); /// // `marker` can now be used for allocations... /// ``` pub fn mark_back<'scratchpad>( &'scratchpad self, ) -> Result<MarkerBack<'scratchpad, BufferT, TrackingT>, Error> { let mut markers = self.markers.borrow_mut(); // `markers.back` is lazy-initialized when the "unstable" feature is // enabled so that `Scratchpad::new()` can be a `const` function. #[cfg(feature = "unstable")] { if markers.back == core::usize::MAX { markers.back = markers.data.capacity(); } } let mut index = markers.back; if index == markers.front { return Err(Error::MarkerLimit); } let buffer_offset = if index == markers.data.capacity() { unsafe { (*self.buffer.get()).as_bytes().len() } } else { markers.data.get(index) }; index -= 1; markers.data.set(index, buffer_offset); markers.back = index; Ok(MarkerBack { scratchpad: self, index, }) } } impl<BufferT, TrackingT> fmt::Debug for Scratchpad<BufferT, TrackingT> where BufferT: Buffer, TrackingT: Tracking, { #[inline] fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!( f, "Scratchpad {{ buffer.len = {}, markers: {:?} }}", unsafe { &*self.buffer.get() }.as_bytes().len(), self.markers.borrow(), ) } } /// Returns a boxed slice of a given length whose data is uninitialized. /// /// # Safety /// /// The contents of the boxed slice are left uninitialized; reading from and /// writing to the slice contents can trigger [undefined behavior] if not /// careful. /// /// # Examples /// /// ``` /// use scratchpad::uninitialized_boxed_slice; /// /// let buffer = unsafe { uninitialized_boxed_slice::<u32>(32) }; /// assert_eq!(buffer.len(), 32); /// ``` /// /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html #[cfg(any(feature = "std", feature = "unstable"))] pub unsafe fn uninitialized_boxed_slice<T>(len: usize) -> Box<[T]> where T: ByteData, { let mut buffer = Vec::with_capacity(len); buffer.set_len(len); buffer.into_boxed_slice() } /// Returns a boxed slice of uninitialized data large enough to hold at least /// the specified number of bytes. /// /// # Safety /// /// The contents of the boxed slice are left uninitialized; reading from and /// writing to the slice contents can trigger [undefined behavior] if not /// careful. /// /// # Examples /// /// ``` /// use scratchpad::uninitialized_boxed_slice_for_bytes; /// /// let buffer = unsafe { uninitialized_boxed_slice_for_bytes::<u32>(32) }; /// assert_eq!(buffer.len(), 8); /// ``` /// /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html #[cfg(any(feature = "std", feature = "unstable"))] pub unsafe fn uninitialized_boxed_slice_for_bytes<T>(bytes: usize) -> Box<[T]> where T: ByteData, { uninitialized_boxed_slice(array_len_for_bytes!(T, bytes)) } /// Returns a boxed slice of uninitialized data large enough for tracking of /// at least the specified number of [allocation markers]. /// /// # Safety /// /// The contents of the boxed slice are left uninitialized; reading from and /// writing to the slice contents can trigger [undefined behavior] if not /// careful. /// /// # Examples /// /// ``` /// use scratchpad::uninitialized_boxed_slice_for_markers; /// /// let buffer = unsafe { /// uninitialized_boxed_slice_for_markers::<usize>(32) /// }; /// assert_eq!(buffer.len(), 32); /// ``` /// /// [allocation markers]: trait.Marker.html /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html #[cfg(any(feature = "std", feature = "unstable"))] pub unsafe fn uninitialized_boxed_slice_for_markers<T>( marker_count: usize, ) -> Box<[T]> where T: ByteData, { uninitialized_boxed_slice(array_len_for_markers!(T, marker_count)) } #[cfg(test)] mod tests;