|
| 1 | +use crate::marker::{PointerLike, Unpin}; |
| 2 | +use crate::ops::{CoerceUnsized, DispatchFromDyn}; |
| 3 | +use crate::pin::Pin; |
| 4 | +use crate::{fmt, ptr}; |
| 5 | + |
| 6 | +/// This type provides a way to opt-out of typical aliasing rules; |
| 7 | +/// specifically, `&mut UnsafePinned<T>` is not guaranteed to be a unique pointer. |
| 8 | +/// |
| 9 | +/// However, even if you define your type like `pub struct Wrapper(UnsafePinned<...>)`, it is still |
| 10 | +/// very risky to have an `&mut Wrapper` that aliases anything else. Many functions that work |
| 11 | +/// generically on `&mut T` assume that the memory that stores `T` is uniquely owned (such as |
| 12 | +/// `mem::swap`). In other words, while having aliasing with `&mut Wrapper` is not immediate |
| 13 | +/// Undefined Behavior, it is still unsound to expose such a mutable reference to code you do not |
| 14 | +/// control! Techniques such as pinning via [`Pin`] are needed to ensure soundness. |
| 15 | +/// |
| 16 | +/// Similar to [`UnsafeCell`](crate::cell::UnsafeCell), `UnsafePinned` will not usually show up in |
| 17 | +/// the public API of a library. It is an internal implementation detail of libraries that need to |
| 18 | +/// support aliasing mutable references. |
| 19 | +/// |
| 20 | +/// Further note that this does *not* lift the requirement that shared references must be read-only! |
| 21 | +/// Use `UnsafeCell` for that. |
| 22 | +/// |
| 23 | +/// This type blocks niches the same way `UnsafeCell` does. |
| 24 | +#[cfg_attr(not(bootstrap), lang = "unsafe_pinned")] |
| 25 | +#[repr(transparent)] |
| 26 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 27 | +pub struct UnsafePinned<T: ?Sized> { |
| 28 | + value: T, |
| 29 | +} |
| 30 | + |
| 31 | +/// When this type is used, that almost certainly means safe APIs need to use pinning to avoid the |
| 32 | +/// aliases from becoming invalidated. Therefore let's mark this as `!Unpin`. You can always opt |
| 33 | +/// back in to `Unpin` with an `impl` block, provided your API is still sound while unpinned. |
| 34 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 35 | +impl<T: ?Sized> !Unpin for UnsafePinned<T> {} |
| 36 | + |
| 37 | +/// The type is `Copy` when `T` is to avoid people assuming that `Copy` implies there is no |
| 38 | +/// `UnsafePinned` anywhere. (This is an issue with `UnsafeCell`: people use `Copy` bounds to mean |
| 39 | +/// `Freeze`.) Given that there is no `unsafe impl Copy for ...`, this is also the option that |
| 40 | +/// leaves the user more choices (as they can always wrap this in a `!Copy` type). |
| 41 | +// FIXME(unsafe_pinned): this may be unsound or a footgun? |
| 42 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 43 | +impl<T: Copy> Copy for UnsafePinned<T> {} |
| 44 | + |
| 45 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 46 | +impl<T: Copy> Clone for UnsafePinned<T> { |
| 47 | + fn clone(&self) -> Self { |
| 48 | + *self |
| 49 | + } |
| 50 | +} |
| 51 | + |
| 52 | +// `Send` and `Sync` are inherited from `T`. This is similar to `SyncUnsafeCell`, since |
| 53 | +// we eventually concluded that `UnsafeCell` implicitly making things `!Sync` is sometimes |
| 54 | +// unergonomic. A type that needs to be `!Send`/`!Sync` should really have an explicit |
| 55 | +// opt-out itself, e.g. via an `PhantomData<*mut T>` or (one day) via `impl !Send`/`impl !Sync`. |
| 56 | + |
| 57 | +impl<T> UnsafePinned<T> { |
| 58 | + /// Constructs a new instance of `UnsafePinned` which will wrap the specified value. |
| 59 | + /// |
| 60 | + /// All access to the inner value through `&UnsafePinned<T>` or `&mut UnsafePinned<T>` or |
| 61 | + /// `Pin<&mut UnsafePinned<T>>` requires `unsafe` code. |
| 62 | + #[inline(always)] |
| 63 | + #[must_use] |
| 64 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 65 | + pub const fn new(value: T) -> Self { |
| 66 | + UnsafePinned { value } |
| 67 | + } |
| 68 | + |
| 69 | + /// Unwraps the value, consuming this `UnsafePinned`. |
| 70 | + #[inline(always)] |
| 71 | + #[must_use] |
| 72 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 73 | + #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 74 | + pub const fn into_inner(self) -> T { |
| 75 | + self.value |
| 76 | + } |
| 77 | +} |
| 78 | + |
| 79 | +impl<T: ?Sized> UnsafePinned<T> { |
| 80 | + /// Get read-write access to the contents of a pinned `UnsafePinned`. |
| 81 | + #[inline(always)] |
| 82 | + #[must_use] |
| 83 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 84 | + pub const fn get_mut_pinned(self: Pin<&mut Self>) -> *mut T { |
| 85 | + // SAFETY: we're not using `get_unchecked_mut` to unpin anything |
| 86 | + unsafe { self.get_unchecked_mut() }.get_mut_unchecked() |
| 87 | + } |
| 88 | + |
| 89 | + /// Get read-write access to the contents of an `UnsafePinned`. |
| 90 | + /// |
| 91 | + /// You should usually be using `get_mut_pinned` instead to explicitly track the fact that this |
| 92 | + /// memory is "pinned" due to there being aliases. |
| 93 | + #[inline(always)] |
| 94 | + #[must_use] |
| 95 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 96 | + pub const fn get_mut_unchecked(&mut self) -> *mut T { |
| 97 | + ptr::from_mut(self) as *mut T |
| 98 | + } |
| 99 | + |
| 100 | + /// Get read-only access to the contents of a shared `UnsafePinned`. |
| 101 | + /// |
| 102 | + /// Note that `&UnsafePinned<T>` is read-only if `&T` is read-only. This means that if there is |
| 103 | + /// mutation of the `T`, future reads from the `*const T` returned here are UB! Use |
| 104 | + /// [`UnsafeCell`] if you also need interior mutability. |
| 105 | + /// |
| 106 | + /// [`UnsafeCell`]: crate::cell::UnsafeCell |
| 107 | + /// |
| 108 | + /// ```rust,no_run |
| 109 | + /// #![feature(unsafe_pinned)] |
| 110 | + /// use std::pin::UnsafePinned; |
| 111 | + /// |
| 112 | + /// unsafe { |
| 113 | + /// let mut x = UnsafePinned::new(0); |
| 114 | + /// let ptr = x.get(); // read-only pointer, assumes immutability |
| 115 | + /// x.get_mut_unchecked().write(1); |
| 116 | + /// ptr.read(); // UB! |
| 117 | + /// } |
| 118 | + /// ``` |
| 119 | + #[inline(always)] |
| 120 | + #[must_use] |
| 121 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 122 | + pub const fn get(&self) -> *const T { |
| 123 | + ptr::from_ref(self) as *const T |
| 124 | + } |
| 125 | + |
| 126 | + /// Gets an immutable pointer to the wrapped value. |
| 127 | + /// |
| 128 | + /// The difference from [`get`] is that this function accepts a raw pointer, which is useful to |
| 129 | + /// avoid the creation of temporary references. |
| 130 | + /// |
| 131 | + /// [`get`]: UnsafePinned::get |
| 132 | + #[inline(always)] |
| 133 | + #[must_use] |
| 134 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 135 | + pub const fn raw_get(this: *const Self) -> *const T { |
| 136 | + this as *const T |
| 137 | + } |
| 138 | + |
| 139 | + /// Gets a mutable pointer to the wrapped value. |
| 140 | + /// |
| 141 | + /// The difference from [`get_mut_pinned`] and [`get_mut_unchecked`] is that this function |
| 142 | + /// accepts a raw pointer, which is useful to avoid the creation of temporary references. |
| 143 | + /// |
| 144 | + /// [`get_mut_pinned`]: UnsafePinned::get_mut_pinned |
| 145 | + /// [`get_mut_unchecked`]: UnsafePinned::get_mut_unchecked |
| 146 | + #[inline(always)] |
| 147 | + #[must_use] |
| 148 | + #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 149 | + pub const fn raw_get_mut(this: *mut Self) -> *mut T { |
| 150 | + this as *mut T |
| 151 | + } |
| 152 | +} |
| 153 | + |
| 154 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 155 | +impl<T: Default> Default for UnsafePinned<T> { |
| 156 | + /// Creates an `UnsafePinned`, with the `Default` value for T. |
| 157 | + fn default() -> Self { |
| 158 | + UnsafePinned::new(T::default()) |
| 159 | + } |
| 160 | +} |
| 161 | + |
| 162 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 163 | +impl<T> From<T> for UnsafePinned<T> { |
| 164 | + /// Creates a new `UnsafePinned<T>` containing the given value. |
| 165 | + fn from(value: T) -> Self { |
| 166 | + UnsafePinned::new(value) |
| 167 | + } |
| 168 | +} |
| 169 | + |
| 170 | +#[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 171 | +impl<T: ?Sized> fmt::Debug for UnsafePinned<T> { |
| 172 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 173 | + f.debug_struct("UnsafePinned").finish_non_exhaustive() |
| 174 | + } |
| 175 | +} |
| 176 | + |
| 177 | +#[unstable(feature = "coerce_unsized", issue = "18598")] |
| 178 | +// #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 179 | +impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafePinned<U>> for UnsafePinned<T> {} |
| 180 | + |
| 181 | +// Allow types that wrap `UnsafePinned` to also implement `DispatchFromDyn` |
| 182 | +// and become dyn-compatible method receivers. |
| 183 | +// Note that currently `UnsafePinned` itself cannot be a method receiver |
| 184 | +// because it does not implement Deref. |
| 185 | +// In other words: |
| 186 | +// `self: UnsafePinned<&Self>` won't work |
| 187 | +// `self: UnsafePinned<Self>` becomes possible |
| 188 | +// FIXME(unsafe_pinned) this logic is copied from UnsafeCell, is it still sound? |
| 189 | +#[unstable(feature = "dispatch_from_dyn", issue = "none")] |
| 190 | +// #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 191 | +impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafePinned<U>> for UnsafePinned<T> {} |
| 192 | + |
| 193 | +#[unstable(feature = "pointer_like_trait", issue = "none")] |
| 194 | +// #[unstable(feature = "unsafe_pinned", issue = "125735")] |
| 195 | +impl<T: PointerLike> PointerLike for UnsafePinned<T> {} |
| 196 | + |
| 197 | +// FIXME(unsafe_pinned): impl PinCoerceUnsized for UnsafePinned<T>? |
0 commit comments