std/sync/mpmc/
utils.rs

1use crate::cell::Cell;
2use crate::ops::{Deref, DerefMut};
3
4/// Pads and aligns a value to the length of a cache line.
5#[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
6// Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache
7// lines at a time, so we have to align to 128 bytes rather than 64.
8//
9// Sources:
10// - https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
11// - https://github.com/facebook/folly/blob/1b5288e6eea6df074758f877c849b6e73bbb9fbb/folly/lang/Align.h#L107
12//
13// ARM's big.LITTLE architecture has asymmetric cores and "big" cores have 128-byte cache line size.
14//
15// Sources:
16// - https://www.mono-project.com/news/2016/09/12/arm64-icache/
17//
18// powerpc64 has 128-byte cache line size.
19//
20// Sources:
21// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_ppc64x.go#L9
22#[cfg_attr(
23    any(target_arch = "x86_64", target_arch = "aarch64", target_arch = "powerpc64",),
24    repr(align(128))
25)]
26// arm, mips and mips64 have 32-byte cache line size.
27//
28// Sources:
29// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_arm.go#L7
30// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips.go#L7
31// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mipsle.go#L7
32// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips64x.go#L9
33#[cfg_attr(
34    any(
35        target_arch = "arm",
36        target_arch = "mips",
37        target_arch = "mips32r6",
38        target_arch = "mips64",
39        target_arch = "mips64r6",
40    ),
41    repr(align(32))
42)]
43// s390x has 256-byte cache line size.
44//
45// Sources:
46// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_s390x.go#L7
47#[cfg_attr(target_arch = "s390x", repr(align(256)))]
48// x86, wasm and riscv have 64-byte cache line size.
49//
50// Sources:
51// - https://github.com/golang/go/blob/dda2991c2ea0c5914714469c4defc2562a907230/src/internal/cpu/cpu_x86.go#L9
52// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_wasm.go#L7
53// - https://github.com/golang/go/blob/5e31f78c8a4ed1b872ddc194f0cd1ae931b37d7e/src/internal/cpu/cpu_riscv64.go#L7
54//
55// All others are assumed to have 64-byte cache line size.
56#[cfg_attr(
57    not(any(
58        target_arch = "x86_64",
59        target_arch = "aarch64",
60        target_arch = "powerpc64",
61        target_arch = "arm",
62        target_arch = "mips",
63        target_arch = "mips32r6",
64        target_arch = "mips64",
65        target_arch = "mips64r6",
66        target_arch = "s390x",
67    )),
68    repr(align(64))
69)]
70pub struct CachePadded<T> {
71    value: T,
72}
73
74impl<T> CachePadded<T> {
75    /// Pads and aligns a value to the length of a cache line.
76    pub fn new(value: T) -> CachePadded<T> {
77        CachePadded::<T> { value }
78    }
79}
80
81impl<T> Deref for CachePadded<T> {
82    type Target = T;
83
84    fn deref(&self) -> &T {
85        &self.value
86    }
87}
88
89impl<T> DerefMut for CachePadded<T> {
90    fn deref_mut(&mut self) -> &mut T {
91        &mut self.value
92    }
93}
94
95const SPIN_LIMIT: u32 = 6;
96
97/// Performs quadratic backoff in spin loops.
98pub struct Backoff {
99    step: Cell<u32>,
100}
101
102impl Backoff {
103    /// Creates a new `Backoff`.
104    pub fn new() -> Self {
105        Backoff { step: Cell::new(0) }
106    }
107
108    /// Backs off using lightweight spinning.
109    ///
110    /// This method should be used for retrying an operation because another thread made
111    /// progress. i.e. on CAS failure.
112    #[inline]
113    pub fn spin_light(&self) {
114        let step = self.step.get().min(SPIN_LIMIT);
115        for _ in 0..step.pow(2) {
116            crate::hint::spin_loop();
117        }
118
119        self.step.set(self.step.get() + 1);
120    }
121
122    /// Backs off using heavyweight spinning.
123    ///
124    /// This method should be used in blocking loops where parking the thread is not an option.
125    #[inline]
126    pub fn spin_heavy(&self) {
127        if self.step.get() <= SPIN_LIMIT {
128            for _ in 0..self.step.get().pow(2) {
129                crate::hint::spin_loop()
130            }
131        } else {
132            crate::thread::yield_now();
133        }
134
135        self.step.set(self.step.get() + 1);
136    }
137}
std/sync/mpmc/utils.rs

std/sync/mpmc/
utils.rs
