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| 1 | +// SPDX-License-Identifier: GPL-2.0 |
| 2 | + |
| 3 | +//! Atomic internal implementations. |
| 4 | +//! |
| 5 | +//! Provides 1:1 mapping to the C atomic operations. |
| 6 | +
|
| 7 | +use crate::bindings; |
| 8 | +use crate::macros::paste; |
| 9 | +use core::cell::UnsafeCell; |
| 10 | + |
| 11 | +mod private { |
| 12 | + /// Sealed trait marker to disable customized impls on atomic implementation traits. |
| 13 | + pub trait Sealed {} |
| 14 | +} |
| 15 | + |
| 16 | +// `i32` and `i64` are only supported atomic implementations. |
| 17 | +impl private::Sealed for i32 {} |
| 18 | +impl private::Sealed for i64 {} |
| 19 | + |
| 20 | +/// A marker trait for types that implement atomic operations with C side primitives. |
| 21 | +/// |
| 22 | +/// This trait is sealed, and only types that have directly mapping to the C side atomics should |
| 23 | +/// impl this: |
| 24 | +/// |
| 25 | +/// - `i32` maps to `atomic_t`. |
| 26 | +/// - `i64` maps to `atomic64_t`. |
| 27 | +pub trait AtomicImpl: Sized + Send + Copy + private::Sealed { |
| 28 | + /// The type of the delta in arithmetic or logical operations. |
| 29 | + /// |
| 30 | + /// For example, in `atomic_add(ptr, v)`, it's the type of `v`. Usually it's the same type of |
| 31 | + /// [`Self`], but it may be different for the atomic pointer type. |
| 32 | + type Delta; |
| 33 | +} |
| 34 | + |
| 35 | +// `atomic_t` implements atomic operations on `i32`. |
| 36 | +impl AtomicImpl for i32 { |
| 37 | + type Delta = Self; |
| 38 | +} |
| 39 | + |
| 40 | +// `atomic64_t` implements atomic operations on `i64`. |
| 41 | +impl AtomicImpl for i64 { |
| 42 | + type Delta = Self; |
| 43 | +} |
| 44 | + |
| 45 | +/// Atomic representation. |
| 46 | +#[repr(transparent)] |
| 47 | +pub struct AtomicRepr<T: AtomicImpl>(UnsafeCell<T>); |
| 48 | + |
| 49 | +impl<T: AtomicImpl> AtomicRepr<T> { |
| 50 | + /// Creates a new atomic representation `T`. |
| 51 | + pub const fn new(v: T) -> Self { |
| 52 | + Self(UnsafeCell::new(v)) |
| 53 | + } |
| 54 | + |
| 55 | + /// Returns a pointer to the underlying `T`. |
| 56 | + /// |
| 57 | + /// # Guarantees |
| 58 | + /// |
| 59 | + /// The returned pointer is valid and properly aligned (i.e. aligned to [`align_of::<T>()`]). |
| 60 | + pub const fn as_ptr(&self) -> *mut T { |
| 61 | + // GUARANTEE: `self.0` is an `UnsafeCell<T>`, therefore the pointer returned by `.get()` |
| 62 | + // must be valid and properly aligned. |
| 63 | + self.0.get() |
| 64 | + } |
| 65 | +} |
| 66 | + |
| 67 | +// This macro generates the function signature with given argument list and return type. |
| 68 | +macro_rules! declare_atomic_method { |
| 69 | + ( |
| 70 | + $(#[doc=$doc:expr])* |
| 71 | + $func:ident($($arg:ident : $arg_type:ty),*) $(-> $ret:ty)? |
| 72 | + ) => { |
| 73 | + paste!( |
| 74 | + $(#[doc = $doc])* |
| 75 | + fn [< atomic_ $func >]($($arg: $arg_type,)*) $(-> $ret)?; |
| 76 | + ); |
| 77 | + }; |
| 78 | + ( |
| 79 | + $(#[doc=$doc:expr])* |
| 80 | + $func:ident [$variant:ident $($rest:ident)*]($($arg_sig:tt)*) $(-> $ret:ty)? |
| 81 | + ) => { |
| 82 | + paste!( |
| 83 | + declare_atomic_method!( |
| 84 | + $(#[doc = $doc])* |
| 85 | + [< $func _ $variant >]($($arg_sig)*) $(-> $ret)? |
| 86 | + ); |
| 87 | + ); |
| 88 | + |
| 89 | + declare_atomic_method!( |
| 90 | + $(#[doc = $doc])* |
| 91 | + $func [$($rest)*]($($arg_sig)*) $(-> $ret)? |
| 92 | + ); |
| 93 | + }; |
| 94 | + ( |
| 95 | + $(#[doc=$doc:expr])* |
| 96 | + $func:ident []($($arg_sig:tt)*) $(-> $ret:ty)? |
| 97 | + ) => { |
| 98 | + declare_atomic_method!( |
| 99 | + $(#[doc = $doc])* |
| 100 | + $func($($arg_sig)*) $(-> $ret)? |
| 101 | + ); |
| 102 | + } |
| 103 | +} |
| 104 | + |
| 105 | +// This macro generates the function implementation with given argument list and return type, and it |
| 106 | +// will replace "call(...)" expression with "$ctype _ $func" to call the real C function. |
| 107 | +macro_rules! impl_atomic_method { |
| 108 | + ( |
| 109 | + ($ctype:ident) $func:ident($($arg:ident: $arg_type:ty),*) $(-> $ret:ty)? { |
| 110 | + $unsafe:tt { call($($c_arg:expr),*) } |
| 111 | + } |
| 112 | + ) => { |
| 113 | + paste!( |
| 114 | + #[inline(always)] |
| 115 | + fn [< atomic_ $func >]($($arg: $arg_type,)*) $(-> $ret)? { |
| 116 | + // TODO: Ideally we want to use the SAFETY comments written at the macro invocation |
| 117 | + // (e.g. in `declare_and_impl_atomic_methods!()`, however, since SAFETY comments |
| 118 | + // are just comments, and they are not passed to macros as tokens, therefore we |
| 119 | + // cannot use them here. One potential improvement is that if we support using |
| 120 | + // attributes as an alternative for SAFETY comments, then we can use that for macro |
| 121 | + // generating code. |
| 122 | + // |
| 123 | + // SAFETY: specified on macro invocation. |
| 124 | + $unsafe { bindings::[< $ctype _ $func >]($($c_arg,)*) } |
| 125 | + } |
| 126 | + ); |
| 127 | + }; |
| 128 | + ( |
| 129 | + ($ctype:ident) $func:ident[$variant:ident $($rest:ident)*]($($arg_sig:tt)*) $(-> $ret:ty)? { |
| 130 | + $unsafe:tt { call($($arg:tt)*) } |
| 131 | + } |
| 132 | + ) => { |
| 133 | + paste!( |
| 134 | + impl_atomic_method!( |
| 135 | + ($ctype) [< $func _ $variant >]($($arg_sig)*) $( -> $ret)? { |
| 136 | + $unsafe { call($($arg)*) } |
| 137 | + } |
| 138 | + ); |
| 139 | + ); |
| 140 | + impl_atomic_method!( |
| 141 | + ($ctype) $func [$($rest)*]($($arg_sig)*) $( -> $ret)? { |
| 142 | + $unsafe { call($($arg)*) } |
| 143 | + } |
| 144 | + ); |
| 145 | + }; |
| 146 | + ( |
| 147 | + ($ctype:ident) $func:ident[]($($arg_sig:tt)*) $( -> $ret:ty)? { |
| 148 | + $unsafe:tt { call($($arg:tt)*) } |
| 149 | + } |
| 150 | + ) => { |
| 151 | + impl_atomic_method!( |
| 152 | + ($ctype) $func($($arg_sig)*) $(-> $ret)? { |
| 153 | + $unsafe { call($($arg)*) } |
| 154 | + } |
| 155 | + ); |
| 156 | + } |
| 157 | +} |
| 158 | + |
| 159 | +// Delcares $ops trait with methods and implements the trait for `i32` and `i64`. |
| 160 | +macro_rules! declare_and_impl_atomic_methods { |
| 161 | + ($(#[$attr:meta])* $pub:vis trait $ops:ident { |
| 162 | + $( |
| 163 | + $(#[doc=$doc:expr])* |
| 164 | + fn $func:ident [$($variant:ident),*]($($arg_sig:tt)*) $( -> $ret:ty)? { |
| 165 | + $unsafe:tt { bindings::#call($($arg:tt)*) } |
| 166 | + } |
| 167 | + )* |
| 168 | + }) => { |
| 169 | + $(#[$attr])* |
| 170 | + $pub trait $ops: AtomicImpl { |
| 171 | + $( |
| 172 | + declare_atomic_method!( |
| 173 | + $(#[doc=$doc])* |
| 174 | + $func[$($variant)*]($($arg_sig)*) $(-> $ret)? |
| 175 | + ); |
| 176 | + )* |
| 177 | + } |
| 178 | + |
| 179 | + impl $ops for i32 { |
| 180 | + $( |
| 181 | + impl_atomic_method!( |
| 182 | + (atomic) $func[$($variant)*]($($arg_sig)*) $(-> $ret)? { |
| 183 | + $unsafe { call($($arg)*) } |
| 184 | + } |
| 185 | + ); |
| 186 | + )* |
| 187 | + } |
| 188 | + |
| 189 | + impl $ops for i64 { |
| 190 | + $( |
| 191 | + impl_atomic_method!( |
| 192 | + (atomic64) $func[$($variant)*]($($arg_sig)*) $(-> $ret)? { |
| 193 | + $unsafe { call($($arg)*) } |
| 194 | + } |
| 195 | + ); |
| 196 | + )* |
| 197 | + } |
| 198 | + } |
| 199 | +} |
| 200 | + |
| 201 | +declare_and_impl_atomic_methods!( |
| 202 | + /// Basic atomic operations |
| 203 | + pub trait AtomicBasicOps { |
| 204 | + /// Atomic read (load). |
| 205 | + fn read[acquire](a: &AtomicRepr<Self>) -> Self { |
| 206 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. |
| 207 | + unsafe { bindings::#call(a.as_ptr().cast()) } |
| 208 | + } |
| 209 | + |
| 210 | + /// Atomic set (store). |
| 211 | + fn set[release](a: &AtomicRepr<Self>, v: Self) { |
| 212 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. |
| 213 | + unsafe { bindings::#call(a.as_ptr().cast(), v) } |
| 214 | + } |
| 215 | + } |
| 216 | +); |
| 217 | + |
| 218 | +declare_and_impl_atomic_methods!( |
| 219 | + /// Exchange and compare-and-exchange atomic operations |
| 220 | + pub trait AtomicExchangeOps { |
| 221 | + /// Atomic exchange. |
| 222 | + /// |
| 223 | + /// Atomically updates `*a` to `v` and returns the old value. |
| 224 | + fn xchg[acquire, release, relaxed](a: &AtomicRepr<Self>, v: Self) -> Self { |
| 225 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. |
| 226 | + unsafe { bindings::#call(a.as_ptr().cast(), v) } |
| 227 | + } |
| 228 | + |
| 229 | + /// Atomic compare and exchange. |
| 230 | + /// |
| 231 | + /// If `*a` == `*old`, atomically updates `*a` to `new`. Otherwise, `*a` is not |
| 232 | + /// modified, `*old` is updated to the current value of `*a`. |
| 233 | + /// |
| 234 | + /// Return `true` if the update of `*a` occurred, `false` otherwise. |
| 235 | + fn try_cmpxchg[acquire, release, relaxed]( |
| 236 | + a: &AtomicRepr<Self>, old: &mut Self, new: Self |
| 237 | + ) -> bool { |
| 238 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. `core::ptr::from_mut(old)` |
| 239 | + // is valid and properly aligned. |
| 240 | + unsafe { bindings::#call(a.as_ptr().cast(), core::ptr::from_mut(old), new) } |
| 241 | + } |
| 242 | + } |
| 243 | +); |
| 244 | + |
| 245 | +declare_and_impl_atomic_methods!( |
| 246 | + /// Atomic arithmetic operations |
| 247 | + pub trait AtomicArithmeticOps { |
| 248 | + /// Atomic add (wrapping). |
| 249 | + /// |
| 250 | + /// Atomically updates `*a` to `(*a).wrapping_add(v)`. |
| 251 | + fn add[](a: &AtomicRepr<Self>, v: Self::Delta) { |
| 252 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. |
| 253 | + unsafe { bindings::#call(v, a.as_ptr().cast()) } |
| 254 | + } |
| 255 | + |
| 256 | + /// Atomic fetch and add (wrapping). |
| 257 | + /// |
| 258 | + /// Atomically updates `*a` to `(*a).wrapping_add(v)`, and returns the value of `*a` |
| 259 | + /// before the update. |
| 260 | + fn fetch_add[acquire, release, relaxed](a: &AtomicRepr<Self>, v: Self::Delta) -> Self { |
| 261 | + // SAFETY: `a.as_ptr()` is valid and properly aligned. |
| 262 | + unsafe { bindings::#call(v, a.as_ptr().cast()) } |
| 263 | + } |
| 264 | + } |
| 265 | +); |
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