crossbeam_utils/atomic/
consume.rs

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1#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
2use crate::primitive::sync::atomic::compiler_fence;
3#[cfg(not(crossbeam_no_atomic))]
4use core::sync::atomic::Ordering;
5
6/// Trait which allows reading from primitive atomic types with "consume" ordering.
7pub trait AtomicConsume {
8    /// Type returned by `load_consume`.
9    type Val;
10
11    /// Loads a value from the atomic using a "consume" memory ordering.
12    ///
13    /// This is similar to the "acquire" ordering, except that an ordering is
14    /// only guaranteed with operations that "depend on" the result of the load.
15    /// However consume loads are usually much faster than acquire loads on
16    /// architectures with a weak memory model since they don't require memory
17    /// fence instructions.
18    ///
19    /// The exact definition of "depend on" is a bit vague, but it works as you
20    /// would expect in practice since a lot of software, especially the Linux
21    /// kernel, rely on this behavior.
22    ///
23    /// This is currently only implemented on ARM and AArch64, where a fence
24    /// can be avoided. On other architectures this will fall back to a simple
25    /// `load(Ordering::Acquire)`.
26    fn load_consume(&self) -> Self::Val;
27}
28
29#[cfg(not(crossbeam_no_atomic))]
30#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
31macro_rules! impl_consume {
32    () => {
33        #[inline]
34        fn load_consume(&self) -> Self::Val {
35            let result = self.load(Ordering::Relaxed);
36            compiler_fence(Ordering::Acquire);
37            result
38        }
39    };
40}
41
42#[cfg(not(crossbeam_no_atomic))]
43#[cfg(not(any(target_arch = "arm", target_arch = "aarch64")))]
44macro_rules! impl_consume {
45    () => {
46        #[inline]
47        fn load_consume(&self) -> Self::Val {
48            self.load(Ordering::Acquire)
49        }
50    };
51}
52
53macro_rules! impl_atomic {
54    ($atomic:ident, $val:ty) => {
55        #[cfg(not(crossbeam_no_atomic))]
56        impl AtomicConsume for core::sync::atomic::$atomic {
57            type Val = $val;
58            impl_consume!();
59        }
60        #[cfg(crossbeam_loom)]
61        impl AtomicConsume for loom::sync::atomic::$atomic {
62            type Val = $val;
63            impl_consume!();
64        }
65    };
66}
67
68impl_atomic!(AtomicBool, bool);
69impl_atomic!(AtomicUsize, usize);
70impl_atomic!(AtomicIsize, isize);
71impl_atomic!(AtomicU8, u8);
72impl_atomic!(AtomicI8, i8);
73impl_atomic!(AtomicU16, u16);
74impl_atomic!(AtomicI16, i16);
75impl_atomic!(AtomicU32, u32);
76impl_atomic!(AtomicI32, i32);
77#[cfg(not(crossbeam_no_atomic_64))]
78impl_atomic!(AtomicU64, u64);
79#[cfg(not(crossbeam_no_atomic_64))]
80impl_atomic!(AtomicI64, i64);
81
82#[cfg(not(crossbeam_no_atomic))]
83impl<T> AtomicConsume for core::sync::atomic::AtomicPtr<T> {
84    type Val = *mut T;
85    impl_consume!();
86}
87
88#[cfg(crossbeam_loom)]
89impl<T> AtomicConsume for loom::sync::atomic::AtomicPtr<T> {
90    type Val = *mut T;
91    impl_consume!();
92}
crossbeam_utils/atomic/consume.rs

crossbeam_utils/atomic/
consume.rs
