maitake_sync/util/
cache_pad.rs

1use core::{
2    fmt,
3    ops::{Deref, DerefMut},
4};
5
6pub use self::inner::CachePadded;
7
8/// When configured not to pad to cache alignment, just provide a no-op wrapper struct
9/// This feature is useful for platforms with no data cache, such as many Cortex-M
10/// targets.
11#[cfg(feature = "no-cache-pad")]
12mod inner {
13    /// Aligns the wrapped value to the size of a cache line.
14    ///
15    /// This is used to avoid [false sharing] for values that may be
16    /// accessed concurrently.
17    ///
18    /// # Size/Alignment
19    ///
20    /// The size and alignment of this type depends on the target architecture,
21    /// and on whether or not the `no-cache-pad` feature flag is enabled.
22    ///
23    /// When the `no-cache-pad` crate feature flag is enabled, this is simply a
24    /// no-op wrapper struct. This is intended for use on useful for platforms
25    /// with no data cache, such as many Cortex-M targets.
26    ///
27    /// In other cases, this type is always aligned to the size of a cache line,
28    /// based on the target architecture. On `x86_64`/`aarch64`, a cache line is
29    /// 128 bytes. On all other targets, a cache line is assumed to 64 bytes
30    /// long. This type's size will always be a multiple of the cache line size;
31    /// if the wrapped type is longer than the alignment of a cache line, then
32    /// this type will be padded to multiple cache lines.
33    ///
34    /// [false sharing]: https://en.wikipedia.org/wiki/False_sharing
35    #[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
36    pub struct CachePadded<T>(pub(super) T);
37}
38
39/// When not inhibited, determine cache alignment based on target architecture.
40/// Align to 128 bytes on 64-bit x86/ARM targets, otherwise align to 64 bytes.
41#[cfg(not(feature = "no-cache-pad"))]
42mod inner {
43    /// Aligns the wrapped value to the size of a cache line.
44    ///
45    /// This is used to avoid [false sharing] for values that may be
46    /// accessed concurrently.
47    ///
48    /// # Size/Alignment
49    ///
50    /// The size and alignment of this type depends on the target architecture,
51    /// and on whether or not the `no-cache-pad` feature flag is enabled.
52    ///
53    /// When the `no-cache-pad` crate feature flag is enabled, this is simply a
54    /// no-op wrapper struct. This is intended for use on useful for platforms
55    /// with no data cache, such as many Cortex-M targets.
56    ///
57    /// In other cases, this type is always aligned to the size of a cache line,
58    /// based on the target architecture. On `x86_64`/`aarch64`, a cache line is
59    /// 128 bytes. On all other targets, a cache line is assumed to 64 bytes
60    /// long. This type's size will always be a multiple of the cache line size;
61    /// if the wrapped type is longer than the alignment of a cache line, then
62    /// this type will be padded to multiple cache lines.
63    ///
64    /// [false sharing]: https://en.wikipedia.org/wiki/False_sharing
65    #[cfg_attr(any(target_arch = "x86_64", target_arch = "aarch64"), repr(align(128)))]
66    #[cfg_attr(
67        not(any(target_arch = "x86_64", target_arch = "aarch64")),
68        repr(align(64))
69    )]
70    #[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
71    pub struct CachePadded<T>(pub(super) T);
72}
73
74// === impl CachePadded ===
75
76impl<T> CachePadded<T> {
77    /// Pads `value` to the length of a cache line.
78    pub const fn new(value: T) -> Self {
79        Self(value)
80    }
81
82    /// Unwraps the inner value and returns it.
83    pub fn into_inner(self) -> T {
84        self.0
85    }
86}
87
88impl<T> Deref for CachePadded<T> {
89    type Target = T;
90
91    #[inline]
92    fn deref(&self) -> &T {
93        &self.0
94    }
95}
96
97impl<T> DerefMut for CachePadded<T> {
98    #[inline]
99    fn deref_mut(&mut self) -> &mut T {
100        &mut self.0
101    }
102}
103
104impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
105    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
106        self.0.fmt(f)
107    }
108}
maitake_sync/util/cache_pad.rs

maitake_sync/util/
cache_pad.rs
