1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
use std::alloc::Layout;
use std::future::Future;
use std::pin::Pin;
use std::ptr::NonNull;
use crate::arena::raw_arena::RawArena;
use super::alloc;
use super::ptr_byte_add;
use super::ptr_byte_sub;
/// In debug mode we use a signature to ensure that raw pointers are pointing to the correct
/// shape of arena object.
#[cfg(debug_assertions)]
const SIGNATURE: usize = 0x8877665544332211;
pub struct ArenaUniqueReservation<T>(NonNull<ArenaBoxData<T>>);
impl<T> Drop for ArenaUniqueReservation<T> {
fn drop(&mut self) {
panic!("A reservation must be completed or forgotten")
}
}
pub struct ArenaBox<T: 'static> {
ptr: NonNull<ArenaBoxData<T>>,
}
impl<T> Unpin for ArenaBox<T> {}
struct ArenaBoxData<T> {
#[cfg(debug_assertions)]
signature: usize,
arena_data: NonNull<ArenaUniqueData<T>>,
data: T,
}
impl<T: 'static> ArenaBox<T> {
/// Offset of the `ptr` field within the `ArenaBox` struct.
const PTR_OFFSET: usize = memoffset::offset_of!(ArenaBox<T>, ptr);
/// Constructs a `NonNull` reference to `ArenaBoxData` from a raw pointer to `T`.
#[inline(always)]
unsafe fn data_from_ptr(ptr: NonNull<T>) -> NonNull<ArenaBoxData<T>> {
ptr_byte_sub(ptr, Self::PTR_OFFSET)
}
/// Obtains a raw pointer to `T` from a `NonNull` reference to `ArenaBoxData`.
#[inline(always)]
unsafe fn ptr_from_data(ptr: NonNull<ArenaBoxData<T>>) -> NonNull<T> {
ptr_byte_add(ptr, Self::PTR_OFFSET)
}
/// Transforms an `ArenaBox` into a raw pointer to `T` and forgets it.
///
/// # Safety
///
/// This function returns a raw pointer without managing the memory, potentially leading to
/// memory leaks if the pointer is not properly handled or deallocated.
#[inline(always)]
pub fn into_raw(mut alloc: ArenaBox<T>) -> NonNull<T> {
let ptr = NonNull::from(alloc.data_mut());
std::mem::forget(alloc);
unsafe { Self::ptr_from_data(ptr) }
}
/// Constructs an `ArenaBox` from a raw pointer to the contained data.
///
/// # Safety
///
/// This function safely constructs an `ArenaBox` from a raw pointer, assuming the pointer is
/// valid and properly aligned. Misuse may lead to undefined behavior, memory unsafety, or data corruption.
#[inline(always)]
pub unsafe fn from_raw(ptr: NonNull<T>) -> ArenaBox<T> {
let ptr = Self::data_from_ptr(ptr);
#[cfg(debug_assertions)]
debug_assert_eq!(ptr.as_ref().signature, SIGNATURE);
ArenaBox { ptr }
}
}
// This Box cannot be sent between threads
static_assertions::assert_not_impl_any!(ArenaBox<()>: Send, Sync);
impl<T> ArenaBox<T> {
#[inline(always)]
fn data(&self) -> &ArenaBoxData<T> {
unsafe { self.ptr.as_ref() }
}
#[inline(always)]
fn data_mut(&mut self) -> &mut ArenaBoxData<T> {
unsafe { self.ptr.as_mut() }
}
}
impl<T> Drop for ArenaBox<T> {
#[inline(always)]
fn drop(&mut self) {
unsafe {
ArenaUnique::delete(self.ptr);
}
}
}
impl<T> std::ops::Deref for ArenaBox<T> {
type Target = T;
#[inline(always)]
fn deref(&self) -> &Self::Target {
&self.data().data
}
}
impl<T> std::convert::AsRef<T> for ArenaBox<T> {
#[inline(always)]
fn as_ref(&self) -> &T {
&self.data().data
}
}
impl<T> std::ops::DerefMut for ArenaBox<T> {
#[inline(always)]
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.data_mut().data
}
}
impl<T> std::convert::AsMut<T> for ArenaBox<T> {
#[inline(always)]
fn as_mut(&mut self) -> &mut T {
&mut self.data_mut().data
}
}
impl<F, R> std::future::Future for ArenaBox<F>
where
F: Future<Output = R>,
{
type Output = R;
#[inline(always)]
fn poll(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<Self::Output> {
unsafe { F::poll(Pin::new_unchecked(&mut self.data_mut().data), cx) }
}
}
/// An arena-based unique ownership container allowing allocation
/// and deallocation of objects with exclusive ownership semantics.
///
/// `ArenaUnique` provides exclusive ownership semantics similar to
/// a `Box`. It utilizes a `RawArena` for allocation and
/// deallocation of objects, maintaining the sole ownership of the
/// allocated data and enabling safe cleanup when the `ArenaUnique`
/// instance is dropped.
///
/// This container guarantees exclusive access to the allocated data
/// within the arena, allowing single-threaded operations while
/// efficiently managing memory and ensuring cleanup on drop.
pub struct ArenaUnique<T> {
ptr: NonNull<ArenaUniqueData<T>>,
}
// The arena itself may not be shared so that we can guarantee all [`RawArena`]
// access happens on the owning thread.
static_assertions::assert_not_impl_any!(ArenaUnique<()>: Send, Sync);
struct ArenaUniqueData<T> {
raw_arena: RawArena<ArenaBoxData<T>>,
alive: bool,
}
impl<T> ArenaUnique<T> {
/// Returns the constant overhead per allocation to assist with making allocations
/// page-aligned.
pub const fn overhead() -> usize {
Self::allocation_size() - std::mem::size_of::<T>()
}
/// Returns the size of each allocation.
pub const fn allocation_size() -> usize {
RawArena::<ArenaBoxData<T>>::allocation_size()
}
pub fn with_capacity(capacity: usize) -> Self {
unsafe {
let ptr = alloc();
std::ptr::write(
ptr.as_ptr(),
ArenaUniqueData {
raw_arena: RawArena::with_capacity(capacity),
alive: true,
},
);
Self { ptr }
}
}
#[cold]
#[inline(never)]
unsafe fn drop_data(data: NonNull<ArenaUniqueData<T>>) {
let data = data.as_ptr();
std::ptr::drop_in_place(data);
std::alloc::dealloc(data as _, Layout::new::<ArenaUniqueData<T>>());
}
/// Deletes the data associated with an `ArenaBox` from the arena. If this is the last
/// allocation for the arena and the arena has been dropped, de-allocate everything.
#[inline(always)]
unsafe fn delete(data: NonNull<ArenaBoxData<T>>) {
let arena_data = data.as_ref().arena_data;
let arena = arena_data.as_ref();
if arena.raw_arena.recycle(data) && !arena.alive {
Self::drop_data(arena_data)
}
}
/// Allocates a new data instance of type `T` within the arena, encapsulating it within an `ArenaBox`.
///
/// This method creates a new instance of type `T` within the `RawArena`. The provided `data`
/// is initialized within the arena, and an `ArenaBox` is returned to manage this allocated data.
/// The `ArenaBox` serves as a reference to the allocated data within the arena, providing safe access
/// and management of the stored value.
///
/// # Safety
///
/// The provided `data` is allocated within the arena and managed by the `ArenaBox`. Improper handling
/// or misuse of the returned `ArenaBox` pointer may lead to memory leaks or memory unsafety.
///
/// # Example
///
/// ```rust
/// # use deno_core::arena::ArenaUnique;
///
/// // Define a struct that will be allocated within the arena
/// struct MyStruct {
/// data: usize,
/// }
///
/// // Create a new instance of ArenaUnique with a specified base capacity
/// let arena: ArenaUnique<MyStruct> = ArenaUnique::with_capacity(16);
///
/// // Allocate a new MyStruct instance within the arena
/// let data_instance = MyStruct { data: 42 };
/// let allocated_box = arena.allocate(data_instance);
///
/// // Now, allocated_box can be used as a managed reference to the allocated data
/// assert_eq!(allocated_box.data, 42); // Validate the data stored in the allocated box
/// ```
pub fn allocate(&self, data: T) -> ArenaBox<T> {
let ptr = unsafe {
let this = self.ptr.as_ptr();
let ptr = (*this).raw_arena.allocate();
std::ptr::write(
ptr.as_ptr(),
ArenaBoxData {
#[cfg(debug_assertions)]
signature: SIGNATURE,
arena_data: self.ptr,
data,
},
);
ptr
};
ArenaBox { ptr }
}
/// Attempt to reserve space in this arena.
///
/// # Safety
///
/// Reservations must be either completed or forgotten, and must be provided to the same
/// arena that created them.
#[inline(always)]
pub unsafe fn reserve_space(&self) -> Option<ArenaUniqueReservation<T>> {
let this = &mut *self.ptr.as_ptr();
let ptr = this.raw_arena.allocate_if_space()?;
Some(ArenaUniqueReservation(ptr))
}
/// Forget a reservation.
///
/// # Safety
///
/// Reservations must be either completed or forgotten, and must be provided to the same
/// arena that created them.
pub unsafe fn forget_reservation(
&self,
reservation: ArenaUniqueReservation<T>,
) {
let ptr = reservation.0;
std::mem::forget(reservation);
let this = self.ptr.as_ptr();
(*this).raw_arena.recycle_without_drop(ptr);
}
/// Complete a reservation.
///
/// # Safety
///
/// Reservations must be either completed or forgotten, and must be provided to the same
/// arena that created them.
#[inline(always)]
pub unsafe fn complete_reservation(
&self,
reservation: ArenaUniqueReservation<T>,
data: T,
) -> ArenaBox<T> {
let ptr = reservation.0;
std::mem::forget(reservation);
let ptr = {
std::ptr::write(
ptr.as_ptr(),
ArenaBoxData {
#[cfg(debug_assertions)]
signature: SIGNATURE,
arena_data: self.ptr,
data,
},
);
ptr
};
ArenaBox { ptr }
}
}
impl<T> Drop for ArenaUnique<T> {
fn drop(&mut self) {
unsafe {
let this = self.ptr.as_mut();
if this.raw_arena.allocated() == 0 {
Self::drop_data(self.ptr);
} else {
this.alive = false;
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::cell::RefCell;
#[test]
fn test_raw() {
let arena: ArenaUnique<RefCell<usize>> = ArenaUnique::with_capacity(16);
let arc = arena.allocate(Default::default());
let raw = ArenaBox::into_raw(arc);
_ = unsafe { ArenaBox::from_raw(raw) };
}
#[test]
fn test_allocate_drop_box_first() {
let arena: ArenaUnique<RefCell<usize>> = ArenaUnique::with_capacity(16);
let alloc = arena.allocate(Default::default());
*alloc.borrow_mut() += 1;
drop(alloc);
drop(arena);
}
#[test]
fn test_allocate_drop_arena_first() {
let arena: ArenaUnique<RefCell<usize>> = ArenaUnique::with_capacity(16);
let alloc = arena.allocate(Default::default());
*alloc.borrow_mut() += 1;
drop(arena);
drop(alloc);
}
}