1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408
//! Support for storing dynamically-sized types within fixed-size allocations
//!
//! - The `Value` type provides a fixed size (7 word in the current version) buffer in which a trait object
//! or array can be stored, without resorting to a heap allocation.
//! - The `Fifo` and `Stack` types provide collection types (first-in-first-out and last-in-first-out).
//!
//! # Examples
//! ## An unboxed any
//! As a quick example - The following wraps a 64-bit integer up in an inline DST using the Any trait.
//!
//! ```rust
//! # use std::any::Any;
//! # use stack_dst::Value;
//! #
//! let dst = Value::<dyn Any, ::stack_dst::buffers::Ptr2>::new_stable(1234u64, |p| p as _)
//! .ok().expect("Integer did not fit in allocation");
//! println!("dst as u64 = {:?}", dst.downcast_ref::<u64>());
//! println!("dst as i8 = {:?}", dst.downcast_ref::<i8>());
//! ```
//!
//! ## Stack-allocated closure!
//! The following snippet shows how small (`'static`) closures can be returned using this crate
//!
//! ```rust
//! # use stack_dst::Value;
//! #
//! fn make_closure(value: u64) -> Value<dyn FnMut()->String, ::stack_dst::array_buf![u64; U2]> {
//! Value::new_stable(move || format!("Hello there! value={}", value), |p| p as _)
//! .ok().expect("Closure doesn't fit")
//! }
//! let mut closure = make_closure(666);
//! assert_eq!( (&mut *closure)(), "Hello there! value=666" );
//! ```
//!
//! ## Custom allocation sizes/types
//! If you need larger alignment, you can use a different type for the backing array. (Note, that metadata uses at least one slot in the array)
//!
//! This code panics, because i128 requires 8/16 byte alignment (usually)
//! ```should_panic
//! # use stack_dst::Value;
//! # use std::any::Any;
//! let v: Value<dyn Any, ::stack_dst::buffers::U8_32> = Value::new_stable(123i128, |p| p as _).unwrap();
//! ```
//! This works, because the backing buffer has sufficient alignment
//! ```rust
//! # use stack_dst::Value;
//! # use std::any::Any;
//! let v: Value<dyn Any, ::stack_dst::array_buf![u128; U2]> = Value::new_stable(123i128, |p| p as _).unwrap();
//! ```
//!
//! # Feature flags
//! ## `alloc` (default)
//! Provides the `StackDstA::new_or_boxed` method (if `unsize` feature is active too)
//! ## `const_generics` (default)
//! Uses value/constant generics to provide a slightly nicer API (e.g. [ValueU])
//! ## `unsize` (optional)
//! Uses the nightly feature `unsize` to provide a more egonomic API (no need for the `|p| p` closures)
// //! ## `full_const_generics` (optional)
// //! Uses extended const generics to give compile time alignment errors
//!
#![cfg_attr(feature = "unsize", feature(unsize))] // needed for Unsize
#![cfg_attr(
feature = "full_const_generics",
feature(generic_const_exprs)
)]
#![cfg_attr(feature = "full_const_generics", allow(incomplete_features))]
#![no_std]
#![deny(missing_docs)]
use core::{mem, ptr, slice};
use ::core::mem::MaybeUninit;
// Internal helper
type BufSlice<T> = [MaybeUninit<T>];
#[cfg(miri)]
#[macro_use]
extern crate std;
#[cfg(feature = "alloc")]
extern crate alloc;
extern crate generic_array;
mod data_buf;
pub use self::data_buf::DataBuf;
pub use self::data_buf::Pod;
pub use fifo::Fifo;
pub use stack::Stack;
pub use value::Value;
/// Shorthand for defining a array buffer
///
/// The array size must be a typenum unsigned integer (e.g `U8`)
/// E.g. `array_buf![u8; U32]` expands to `::stack_dst::buffers::ArrayBuf<u8, ::stack_dst::buffers::n::::U32>`
#[macro_export]
macro_rules! array_buf {
($t:ty; $n:ident) => { $crate::buffers::ArrayBuf<$t, $crate::buffers::n::$n> }
}
/// Type aliases for common buffer sizes and types
///
/// Some useful suggestions
/// - [Ptr8] is the semi-standard buffer for holding a single object (a good balance of space used)
/// - [Ptr2] is suitable for storing a single pointer and its vtable
pub mod buffers {
/// A re-export of `typenum` for shorter names
pub use ::generic_array::typenum as n;
pub use self::array_buf::ArrayBuf;
#[cfg(feature="const_generics")]
pub use self::cg_array_buf::ArrayBuf as ConstArrayBuf;
mod array_buf {
use ::core::mem::MaybeUninit;
/// A buffer backing onto an array (used to provide default)
pub struct ArrayBuf<T, N>
where
N: ::generic_array::ArrayLength<MaybeUninit<T>>,
{
inner: ::generic_array::GenericArray<MaybeUninit<T>, N>,
}
impl<T, N> ::core::default::Default for ArrayBuf<T, N>
where
N: ::generic_array::ArrayLength<MaybeUninit<T>>,
{
fn default() -> Self {
ArrayBuf {
// `unwarp` won't fail, lengths match
inner: ::generic_array::GenericArray::from_exact_iter( (0 .. N::USIZE).map(|_| MaybeUninit::uninit()) ).unwrap(),
}
}
}
unsafe impl<T,N> crate::DataBuf for ArrayBuf<T, N>
where
T: crate::Pod,
N: ::generic_array::ArrayLength<MaybeUninit<T>>,
{
type Inner = T;
fn as_ref(&self) -> &[MaybeUninit<Self::Inner>] {
&self.inner
}
fn as_mut(&mut self) -> &mut [MaybeUninit<Self::Inner>] {
&mut self.inner
}
fn extend(&mut self, len: usize) -> Result<(), ()> {
if len > N::USIZE {
Err( () )
}
else {
Ok( () )
}
}
}
}
#[cfg(feature="const_generics")]
mod cg_array_buf {
/// A buffer backing onto an array (used to provide default) - using constant generics
pub struct ArrayBuf<T, const N: usize>
{
inner: [::core::mem::MaybeUninit<T>; N],
}
impl<T:, const N: usize> ::core::default::Default for ArrayBuf<T, N>
where
T: crate::Pod,
{
fn default() -> Self {
ArrayBuf {
inner: [::core::mem::MaybeUninit::uninit(); N],
}
}
}
unsafe impl<T,const N: usize> crate::DataBuf for ArrayBuf<T, N>
where
T: crate::Pod,
{
type Inner = T;
fn as_ref(&self) -> &[::core::mem::MaybeUninit<Self::Inner>] {
&self.inner
}
fn as_mut(&mut self) -> &mut [::core::mem::MaybeUninit<Self::Inner>] {
&mut self.inner
}
fn extend(&mut self, len: usize) -> Result<(), ()> {
if len > N {
Err( () )
}
else {
Ok( () )
}
}
}
}
/// 8 pointers (32/64 bytes, with pointer alignment)
pub type Ptr8 = ArrayBuf<*const (), n::U8>;
/// 64 bytes, 64-bit alignment
pub type U64_8 = ArrayBuf<u64, n::U8>;
/// 32 bytes, 8-bit alignment
pub type U8_32 = ArrayBuf<u8, n::U32>;
/// 16 bytes, 64-bit alignment
pub type U64_2 = ArrayBuf<u64, n::U2>;
/// 16 pointers (64/128 bytes, with pointer alignment)
pub type Ptr16 = ArrayBuf<*const (), n::U16>;
/// Two pointers, useful for wrapping a pointer along with a vtable
pub type Ptr2 = ArrayBuf<*const (), n::U2>;
/// One pointer, can only store the vtable
pub type Ptr1 = ArrayBuf<*const (), n::U1>;
/// Dyanamically allocated buffer with 8-byte alignment
#[cfg(feature="alloc")]
pub type U64Vec = ::alloc::vec::Vec<::core::mem::MaybeUninit<u64>>;
/// Dyanamically allocated buffer with 1-byte alignment
#[cfg(feature="alloc")]
pub type U8Vec = ::alloc::vec::Vec<::core::mem::MaybeUninit<u8>>;
/// Dyanamically allocated buffer with pointer alignment
#[cfg(feature="alloc")]
pub type PtrVec = ::alloc::vec::Vec<::core::mem::MaybeUninit<*const ()>>;
}
/// Implementation of the FIFO list structure
pub mod fifo;
/// Implementation of the LIFO stack structure
pub mod stack;
/// Implementation of the single-value structure
pub mod value;
#[cfg(feature = "const_generics")]
/// A single dynamically-sized value stored in a `usize` aligned buffer
///
/// ```
/// let v = ::stack_dst::ValueU::<[u8], 16>::new_stable([1,2,3], |v| v);
/// ```
pub type ValueU<T /*: ?Sized*/, const N: usize /* = {8+1}*/> = Value<T, buffers::ConstArrayBuf<usize, N>>;
#[cfg(feature = "const_generics")]
/// A single LIFO stack of DSTs using a `usize` aligned buffer
///
/// ```
/// let mut stack = ::stack_dst::StackU::<[u8], 16>::new();
/// stack.push_copied(&[1]);
/// ```
pub type StackU<T /*: ?Sized*/, const N: usize /* = 16*/> = Stack<T, buffers::ConstArrayBuf<usize, N>>;
#[cfg(feature = "const_generics")]
/// A FIFO queue of DSTs using a `usize` aligned buffer
///
/// ```
/// let mut queue = ::stack_dst::FifoU::<[u8], 16>::new();
/// queue.push_copied(&[1]);
/// ```
pub type FifoU<T /*: ?Sized*/, const N: usize /* = {8+1}*/> = Fifo<T, buffers::ConstArrayBuf<usize, N>>;
fn decompose_pointer<T: ?Sized>(mut ptr: *const T) -> (*const (), usize, [usize; 3]) {
let addr = ptr as *const ();
let rv = mem_as_slice(&mut ptr);
let mut vals = [0; 3];
assert!(
rv[0] == addr as usize,
"BUG: Pointer layout is not (data_ptr, info...)"
);
vals[..rv.len()-1].copy_from_slice(&rv[1..]);
(addr, rv.len()-1, vals,)
}
fn mem_as_slice<T>(ptr: &mut T) -> &mut [usize] {
assert!(mem::size_of::<T>() % mem::size_of::<usize>() == 0);
assert!(mem::align_of::<T>() % mem::align_of::<usize>() == 0);
let words = mem::size_of::<T>() / mem::size_of::<usize>();
// SAFE: Points to valid memory (a raw pointer)
unsafe { slice::from_raw_parts_mut(ptr as *mut _ as *mut usize, words) }
}
/// Re-construct a fat pointer
unsafe fn make_fat_ptr<T: ?Sized, W: Pod>(data_ptr: *mut (), meta_vals: &BufSlice<W>) -> *mut T {
#[repr(C)]
#[derive(Copy,Clone)]
struct Raw {
ptr: *const (),
meta: [usize; 4],
}
union Inner<T: ?Sized> {
ptr: *mut T,
raw: Raw,
}
let mut rv = Inner { raw: Raw { ptr: data_ptr, meta: [0; 4] } };
assert!(meta_vals.len() * mem::size_of::<W>() % mem::size_of::<usize>() == 0);
assert!(meta_vals.len() * mem::size_of::<W>() <= 4 * mem::size_of::<usize>());
ptr::copy(
meta_vals.as_ptr() as *const u8,
rv.raw.meta.as_mut_ptr() as *mut u8,
meta_vals.len() * mem::size_of::<W>()
);
let rv = rv.ptr;
assert_eq!(rv as *const (), data_ptr as *const ());
rv
}
/// Write metadata (abstraction around `ptr::copy`)
fn store_metadata<W: Pod>(dst: &mut BufSlice<W>, meta_words: &[usize]) {
let n_bytes = meta_words.len() * mem::size_of::<usize>();
assert!(n_bytes <= dst.len() * mem::size_of::<W>(),
"nbytes [{}] <= dst.len() [{}] * sizeof [{}]", n_bytes, dst.len(), mem::size_of::<W>());
unsafe {
ptr::copy(
meta_words.as_ptr() as *const u8,
dst.as_mut_ptr() as *mut u8,
n_bytes,
);
}
}
fn round_to_words<T>(len: usize) -> usize {
(len + mem::size_of::<T>() - 1) / mem::size_of::<T>()
}
/// Calls a provided function to get a fat pointer version of `v` (and checks that the returned pointer is sane)
fn check_fat_pointer<U, T: ?Sized>(v: &U, get_ref: impl FnOnce(&U) -> &T) -> &T {
let ptr: &T = get_ref(v);
assert_eq!(
ptr as *const _ as *const u8, v as *const _ as *const u8,
"MISUSE: Closure returned different pointer"
);
assert_eq!(
mem::size_of_val(ptr),
mem::size_of::<U>(),
"MISUSE: Closure returned a subset pointer"
);
ptr
}
/// Push items to a list using a generator function to get the items
/// - `meta` - Metadata slot (must be 1 usize long)
/// - `data` - Data slot, must be at least `count * sizeof(T)` long
/// - `count` - Number of items to insert
/// - `gen` - Generator function (is passed the current index)
/// - `reset_slot` - A slot updated with `reset_value` when a panic happens before push is complete
/// - `reset_value` - Value used in `reset_slot`
///
/// This provides a panic-safe push as long as `reset_slot` and `reset_value` undo the allocation operation
unsafe fn list_push_gen<T, W: Pod>(meta: &mut BufSlice<W>, data: &mut BufSlice<W>, count: usize, mut gen: impl FnMut(usize)->T, reset_slot: &mut usize, reset_value: usize)
{
/// Helper to drop/zero all pushed items, and reset data structure state if there's a panic
struct PanicState<'a, T>(*mut T, usize, &'a mut usize, usize);
impl<'a, T> ::core::ops::Drop for PanicState<'a, T> {
fn drop(&mut self) {
if self.0.is_null() {
return ;
}
// Reset the state of the data structure (leaking items)
*self.2 = self.3;
// Drop all partially-populated items
unsafe {
while self.1 != 0 {
ptr::drop_in_place(&mut *self.0);
ptr::write_bytes(self.0 as *mut u8, 0, mem::size_of::<T>());
self.0 = self.0.offset(1);
self.1 -= 1;
}
}
}
}
let mut ptr = data.as_mut_ptr() as *mut T;
let mut clr = PanicState(ptr, 0, reset_slot, reset_value);
for i in 0 .. count {
let val = gen(i);
ptr::write(ptr, val);
ptr = ptr.offset(1);
clr.1 += 1;
}
clr.0 = ptr::null_mut(); // Prevent drops and prevent reset
// Save the length once everything has been written
crate::store_metadata(meta, &[count]);
}
/// Marker trait used to check alignment
pub unsafe trait AlignmentValid {
#[doc(hidden)]
fn check();
}
#[cfg(feature = "full_const_generics")]
unsafe impl<S, L> AlignmentValid for (S, L)
where
[(); mem::align_of::<L>() - mem::align_of::<S>()]: Sized,
{
fn check() {}
}
#[cfg(not(feature = "full_const_generics"))]
unsafe impl<S, L> AlignmentValid for (S, L) {
fn check() {
assert!(
mem::align_of::<S>() <= mem::align_of::<L>(),
"TODO: Enforce alignment >{} (requires {})",
mem::align_of::<L>(),
mem::align_of::<S>()
);
}
}
/*
#[cfg(doctest)]
#[doc=include_str!("../README.md")]
pub mod readme {
}
*/