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helper: use crossbeam::atomic::AtomicCell for atomic floats (#56)

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* cargo.toml: add `crossbeam`

* helper: use `crossbeam::atomic::AtomicCell` for `AtomicF(32|64)`

* helper: atomic docs
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hinto-janai 2024-02-10 18:19:12 -05:00 committed by GitHub
parent 0d8f71b4c7
commit ba0f82c356
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4 changed files with 65 additions and 467 deletions
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10
Cargo.lock generated
View file

@ -369,6 +369,15 @@ dependencies = [
"libc",
]
[[package]]
name = "crossbeam"
version = "0.8.4"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "1137cd7e7fc0fb5d3c5a8678be38ec56e819125d8d7907411fe24ccb943faca8"
dependencies = [
"crossbeam-utils",
]
[[package]]
name = "crossbeam-deque"
version = "0.8.5"
@ -466,6 +475,7 @@ name = "cuprate-helper"
version = "0.1.0"
dependencies = [
"chrono",
"crossbeam",
"futures",
"libc",
"rayon",

2
Cargo.toml
View file

@ -41,6 +41,7 @@ bytes = { version = "1.5.0", default-features = false }
clap = { version = "4.4.7", default-features = false }
chrono = { version = "0.4.31", default-features = false }
crypto-bigint = { version = "0.5.5", default-features = false }
crossbeam = { version = "0.8.4", default-features = false }
curve25519-dalek = { version = "4.1.1", default-features = false }
dalek-ff-group = { git = "https://github.com/Cuprate/serai.git", rev = "a59966b", default-features = false }
dirs = { version = "5.0.1", default-features = false }
@ -74,7 +75,6 @@ proptest-derive = { version = "0.4.0" }
## TODO:
## Potential dependencies.
# arc-swap = { version = "1.6.0" } # Atomically swappable Arc<T> | https://github.com/vorner/arc-swap
# crossbeam = { version = "0.8.2" } # Channels, concurrent primitives | https://github.com/crossbeam-rs/crossbeam
# itoa = { version = "1.0.9" } # Fast integer to string formatting | https://github.com/dtolnay/itoa
# notify = { version = "6.1.1" } # Filesystem watching | https://github.com/notify-rs/notify
# once_cell = { version = "1.18.0" } # Lazy/one-time initialization | https://github.com/matklad/once_cell

9
helper/Cargo.toml
View file

@ -12,16 +12,17 @@ repository = "https://github.com/Cuprate/cuprate/tree/main/consensus"
# All features on by default.
default = ["std", "atomic", "asynch", "num", "time", "thread"]
std = []
atomic = []
atomic = ["dep:crossbeam"]
asynch = ["dep:futures", "dep:rayon"]
num = []
time = ["dep:chrono", "std"]
thread = ["std", "dep:target_os_lib"]
[dependencies]
chrono = { workspace = true, optional = true, features = ["std", "clock"] }
futures = { workspace = true, optional = true, features = ["std"] }
rayon = { workspace = true, optional = true }
crossbeam = { workspace = true, optional = true }
chrono = { workspace = true, optional = true, features = ["std", "clock"] }
futures = { workspace = true, optional = true, features = ["std"] }
rayon = { workspace = true, optional = true }
# This is kinda a stupid work around.
# [thread] needs to activate one of these libs (windows|libc)

511
helper/src/atomic.rs
View file

@ -3,488 +3,75 @@
//! `#[no_std]` compatible.
//---------------------------------------------------------------------------------------------------- Use
use core::sync::atomic::{AtomicU32, AtomicU64, Ordering};
use crossbeam::atomic::AtomicCell;
#[allow(unused_imports)] // docs
use std::sync::atomic::{Ordering, Ordering::Acquire, Ordering::Release};
//---------------------------------------------------------------------------------------------------- Atomic Float
// An AtomicF(32|64) implementation.
//
// This internally uses [AtomicU(32|64)], where the
// u(32|64) is the bit pattern of the internal float.
//
// This uses [.to_bits()] and [from_bits()] to
// convert between actual floats, and the bit
// representations for storage.
//
// Using `UnsafeCell<float>` is also viable,
// and would allow for a `const fn new(f: float) -> Self`
// except that becomes problematic with NaN's and infinites:
// - <https://github.com/rust-lang/rust/issues/73328>
// - <https://github.com/rust-lang/rfcs/pull/3514>
//
// This is most likely safe(?) but... instead of risking UB,
// this just uses the Atomic unsigned integer as the inner
// type instead of transmuting from `UnsafeCell`.
//
// This creates the types:
// - `AtomicF32`
// - `AtomicF64`
//
// Originally taken from:
// <https://github.com/hinto-janai/sansan/blob/1f6680b2d08ff5fbf4f090178ea5233d4cf9056f/src/atomic.rs>
macro_rules! impl_atomic_f {
(
$atomic_float:ident, // Name of the new float type
$atomic_float_lit:literal, // Literal name of new float type
$float:ident, // The target float (f32/f64)
$unsigned:ident, // The underlying unsigned type
$atomic_unsigned:ident, // The underlying unsigned atomic type
$bits_0:literal, // Bit pattern for 0.0
$bits_025:literal, // Bit pattern for 0.25
$bits_050:literal, // Bit pattern for 0.50
$bits_075:literal, // Bit pattern for 0.75
$bits_1:literal, // Bit pattern for 1.0
) => {
/// An atomic float.
///
/// ## Portability
/// [Quoting the std library: ](<https://doc.rust-lang.org/1.70.0/std/primitive.f32.html#method.to_bits)>
/// "See from_bits for some discussion of the portability of this operation (there are almost no issues)."
///
/// ## Compile-time failure
/// This internal functions `std` uses will panic _at compile time_
/// if the bit transmutation operations it uses are not available
/// on the build target, aka, if it compiles we're probably safe.
#[repr(transparent)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "bincode", derive(bincode::Encode, bincode::Decode))]
pub struct $atomic_float($atomic_unsigned);
/// Compile-time assertion that our floats are
/// lock-free for the target we're building for.
const _: () = {
assert!(
AtomicCell::<f32>::is_lock_free(),
"32-bit atomics are not supported on this build target."
);
impl $atomic_float {
/// Representation of `0.0` as bits, can be inputted into [`Self::from_bits`].
pub const BITS_0: $unsigned = $bits_0;
/// Representation of `0.25` as bits, can be inputted into [`Self::from_bits`].
pub const BITS_0_25: $unsigned = $bits_025;
/// Representation of `0.50` as bits, can be inputted into [`Self::from_bits`].
pub const BITS_0_50: $unsigned = $bits_050;
/// Representation of `0.75` as bits, can be inputted into [`Self::from_bits`].
pub const BITS_0_75: $unsigned = $bits_075;
/// Representation of `1.0` as bits, can be inputted into [`Self::from_bits`].
pub const BITS_0_100: $unsigned = $bits_1;
assert!(
AtomicCell::<f64>::is_lock_free(),
"64-bit atomics are not supported on this build target."
);
};
#[allow(clippy::declare_interior_mutable_const)]
// FIXME:
// Seems like `std` internals has some unstable cfg options that
// allow interior mutable consts to be defined without clippy complaining:
// <https://doc.rust-lang.org/1.70.0/src/core/sync/atomic.rs.html#3013>.
//
/// `0.0`, returned by [`Self::default`].
pub const DEFAULT: Self = Self($atomic_unsigned::new($bits_0));
// SOMEDAY: use a custom float that implements `Eq`
// so that `compare_exchange()`, `fetch_*()` work.
#[inline]
/// Create a new atomic float.
///
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.new>
pub fn new(f: $float) -> Self {
// FIXME: Update to const when available.
// <https://doc.rust-lang.org/1.70.0/src/core/num/f32.rs.html#998>
//
// `transmute()` here would be safe (`to_bits()` is doing this)
// although checking for NaN's and infinites are non-`const`...
// so we can't can't `transmute()` even though it would allow
// this function to be `const`.
Self($atomic_unsigned::new(f.to_bits()))
}
/// An atomic [`f32`].
///
/// This is an alias for
/// [`crossbeam::atomic::AtomicCell<f32>`](https://docs.rs/crossbeam/latest/crossbeam/atomic/struct.AtomicCell.html).
///
/// Note that there are no [`Ordering`] parameters,
/// atomic loads use [`Acquire`],
/// and atomic stores use [`Release`].
pub type AtomicF32 = AtomicCell<f32>;
#[inline]
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.into_inner>
pub fn into_inner(self) -> $float {
$float::from_bits(self.0.into_inner())
}
#[inline]
/// Create a new atomic float, from the unsigned bit representation.
pub const fn from_bits(bits: $unsigned) -> Self {
Self($atomic_unsigned::new(bits))
}
#[inline]
/// Store a float inside the atomic.
///
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.store>
pub fn store(&self, f: $float, ordering: Ordering) {
self.0.store(f.to_bits(), ordering);
}
#[inline]
/// Store a bit representation of a float inside the atomic.
pub fn store_bits(&self, bits: $unsigned, ordering: Ordering) {
self.0.store(bits, ordering);
}
#[inline]
/// Load the internal float from the atomic.
///
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.load>
pub fn load(&self, ordering: Ordering) -> $float {
// FIXME: Update to const when available.
// <https://doc.rust-lang.org/1.70.0/src/core/num/f32.rs.html#1088>
$float::from_bits(self.0.load(ordering))
}
#[inline]
/// Load the internal bit representation of the float from the atomic.
pub fn load_bits(&self, ordering: Ordering) -> $unsigned {
self.0.load(ordering)
}
#[inline]
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.swap>
pub fn swap(&self, val: $float, ordering: Ordering) -> $float {
$float::from_bits(self.0.swap($float::to_bits(val), ordering))
}
#[inline]
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.compare_exchange>
pub fn compare_exchange(
&self,
current: $float,
new: $float,
success: Ordering,
failure: Ordering,
) -> Result<$float, $float> {
match self
.0
.compare_exchange(current.to_bits(), new.to_bits(), success, failure)
{
Ok(b) => Ok($float::from_bits(b)),
Err(b) => Err($float::from_bits(b)),
}
}
#[inline]
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.compare_exchange_weak>
pub fn compare_exchange_weak(
&self,
current: $float,
new: $float,
success: Ordering,
failure: Ordering,
) -> Result<$float, $float> {
match self.0.compare_exchange_weak(
current.to_bits(),
new.to_bits(),
success,
failure,
) {
Ok(b) => Ok($float::from_bits(b)),
Err(b) => Err($float::from_bits(b)),
}
}
//------------------------------------------------------------------ fetch_*()
// These are tricky to implement because we must
// operate on the _numerical_ value and not the
// bit representations.
//
// This means using some type of CAS,
// which comes with the regular tradeoffs...
// The (private) function using CAS to implement `fetch_*()` operations.
//
// This is function body used in all the below `fetch_*()` functions.
fn fetch_update_unwrap<F>(&self, ordering: Ordering, mut update: F) -> $float
where
F: FnMut($float) -> $float,
{
// Since it's a CAS, we need a second ordering for failures,
// this will take the user input and return an appropriate order.
let second_order = match ordering {
Ordering::Release | Ordering::Relaxed => Ordering::Relaxed,
Ordering::Acquire | Ordering::AcqRel => Ordering::Acquire,
Ordering::SeqCst => Ordering::SeqCst,
// Ordering is #[non_exhaustive], so we must do this.
ordering => ordering,
};
// SAFETY:
// unwrap is safe since `fetch_update()` only panics
// if the closure we pass it returns `None`.
// As seen below, we're passing a `Some`.
//
// <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_update>
self.fetch_update(ordering, second_order, |f| Some(update(f)))
.unwrap()
}
#[inline]
/// This function is implemented with [`Self::fetch_update`], and is not 100% equivalent to
/// <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_add>.
///
/// In particular, this method will not circumvent the [ABA Problem](https://en.wikipedia.org/wiki/ABA_problem).
///
/// Other than this not actually being atomic, all other behaviors are the same.
pub fn fetch_add(&self, val: $float, order: Ordering) -> $float {
self.fetch_update_unwrap(order, |f| f + val)
}
#[inline]
/// This function is implemented with [`Self::fetch_update`], and is not 100% equivalent to
/// <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_sub>.
///
/// In particular, this method will not circumvent the [ABA Problem](https://en.wikipedia.org/wiki/ABA_problem).
///
/// Other than this not actually being atomic, all other behaviors are the same.
pub fn fetch_sub(&self, val: $float, order: Ordering) -> $float {
self.fetch_update_unwrap(order, |f| f - val)
}
#[inline]
/// This function is implemented with [`Self::fetch_update`], and is not 100% equivalent to
/// <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_max>.
///
/// In particular, this method will not circumvent the [ABA Problem](https://en.wikipedia.org/wiki/ABA_problem).
///
/// Other than this not actually being atomic, all other behaviors are the same.
pub fn fetch_max(&self, val: $float, order: Ordering) -> $float {
self.fetch_update_unwrap(order, |f| f.max(val))
}
#[inline]
/// This function is implemented with [`Self::fetch_update`], and is not 100% equivalent to
/// <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_min>.
///
/// In particular, this method will not circumvent the [ABA Problem](https://en.wikipedia.org/wiki/ABA_problem).
///
/// Other than this not actually being atomic, all other behaviors are the same.
pub fn fetch_min(&self, val: $float, order: Ordering) -> $float {
self.fetch_update_unwrap(order, |f| f.min(val))
}
#[inline]
/// Equivalent to <https://doc.rust-lang.org/1.70.0/std/sync/atomic/struct.AtomicUsize.html#method.fetch_update>
pub fn fetch_update<F>(
&self,
set_order: Ordering,
fetch_order: Ordering,
mut f: F,
) -> Result<$float, $float>
where
F: FnMut($float) -> Option<$float>,
{
// Very unreadable closure...
//
// Basically this is converting:
// `f(f32) -> Option<f32>` into `f(u32) -> Option<u32>`
// so the internal atomic `fetch_update` can work.
let f = |bits: $unsigned| f($float::from_bits(bits)).map(|f| $float::to_bits(f));
match self.0.fetch_update(set_order, fetch_order, f) {
Ok(b) => Ok($float::from_bits(b)),
Err(b) => Err($float::from_bits(b)),
}
}
#[inline]
/// Set the internal float from the atomic, using [`Ordering::Release`].
pub fn set(&self, f: $float) {
self.store(f, Ordering::Release);
}
#[inline]
/// Get the internal float from the atomic, using [`Ordering::Acquire`].
pub fn get(&self) -> $float {
self.load(Ordering::Acquire)
}
}
impl From<$float> for $atomic_float {
/// Calls [`Self::new`]
fn from(float: $float) -> Self {
Self::new(float)
}
}
impl Default for $atomic_float {
/// Returns `0.0`.
fn default() -> Self {
Self::DEFAULT
}
}
impl std::fmt::Debug for $atomic_float {
/// This prints the internal float value, using [`Ordering::Acquire`].
///
/// # Panics
/// This panics on NaN or subnormal float inputs.
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_tuple($atomic_float_lit)
.field(&self.0.load(Ordering::Acquire))
.finish()
}
}
};
}
impl_atomic_f! {
AtomicF64,
"AtomicF64",
f64,
u64,
AtomicU64,
0,
4598175219545276416,
4602678819172646912,
4604930618986332160,
4607182418800017408,
}
impl_atomic_f! {
AtomicF32,
"AtomicF32",
f32,
u32,
AtomicU32,
0,
1048576000,
1056964608,
1061158912,
1065353216,
}
/// An atomic [`f64`].
///
/// This is an alias for
/// [`crossbeam::atomic::AtomicCell<f64>`](https://docs.rs/crossbeam/latest/crossbeam/atomic/struct.AtomicCell.html).
///
/// Note that there are no [`Ordering`] parameters,
/// atomic loads use [`Acquire`],
/// and atomic stores use [`Release`].
pub type AtomicF64 = AtomicCell<f64>;
//---------------------------------------------------------------------------------------------------- TESTS
#[cfg(test)]
mod tests {
use super::*;
// These tests come in pairs, `f32|f64`.
//
// If changing one, update the other as well.
//
// `macro_rules!()` + `paste!()` could do this automatically,
// but that might be more trouble than it's worth...
#[test]
// Tests the varying fetch, swap, and compare functions.
fn f32_functions() {
// Tests `AtomicF32`.
fn f32() {
let float = AtomicF32::new(5.0);
let ordering = Ordering::SeqCst;
// Loads/Stores
assert_eq!(float.swap(1.0, ordering), 5.0);
assert_eq!(float.load(ordering), 1.0);
float.store(2.0, ordering);
assert_eq!(float.load(ordering), 2.0);
// CAS
assert_eq!(
float.compare_exchange(2.0, 5.0, ordering, ordering),
Ok(2.0)
);
assert_eq!(
float.fetch_update(ordering, ordering, |f| Some(f * 3.0)),
Ok(5.0)
);
assert_eq!(float.get(), 15.0);
loop {
if let Ok(float) = float.compare_exchange_weak(15.0, 2.0, ordering, ordering) {
assert_eq!(float, 15.0);
break;
}
}
// `fetch_*()` functions
assert_eq!(float.fetch_add(1.0, ordering), 2.0);
assert_eq!(float.fetch_sub(1.0, ordering), 3.0);
assert_eq!(float.fetch_max(5.0, ordering), 2.0);
assert_eq!(float.fetch_min(0.0, ordering), 5.0);
assert_eq!(float.swap(1.0), 5.0);
assert_eq!(float.load(), 1.0);
float.store(2.0);
assert_eq!(float.load(), 2.0);
}
#[test]
fn f64_functions() {
// Tests `AtomicF64`.
fn f64() {
let float = AtomicF64::new(5.0);
let ordering = Ordering::SeqCst;
assert_eq!(float.swap(1.0, ordering), 5.0);
assert_eq!(float.load(ordering), 1.0);
float.store(2.0, ordering);
assert_eq!(float.load(ordering), 2.0);
assert_eq!(
float.compare_exchange(2.0, 5.0, ordering, ordering),
Ok(2.0)
);
assert_eq!(
float.fetch_update(ordering, ordering, |f| Some(f * 3.0)),
Ok(5.0)
);
assert_eq!(float.get(), 15.0);
loop {
if let Ok(float) = float.compare_exchange_weak(15.0, 2.0, ordering, ordering) {
assert_eq!(float, 15.0);
break;
}
}
assert_eq!(float.fetch_add(1.0, ordering), 2.0);
assert_eq!(float.fetch_sub(1.0, ordering), 3.0);
assert_eq!(float.fetch_max(5.0, ordering), 2.0);
assert_eq!(float.fetch_min(0.0, ordering), 5.0);
}
#[test]
fn f32_bits() {
assert_eq!(AtomicF32::default().get(), 0.00);
assert_eq!(AtomicF32::from_bits(AtomicF32::BITS_0).get(), 0.00);
assert_eq!(AtomicF32::from_bits(AtomicF32::BITS_0_25).get(), 0.25);
assert_eq!(AtomicF32::from_bits(AtomicF32::BITS_0_50).get(), 0.50);
assert_eq!(AtomicF32::from_bits(AtomicF32::BITS_0_75).get(), 0.75);
assert_eq!(AtomicF32::from_bits(AtomicF32::BITS_0_100).get(), 1.00);
}
#[test]
fn f64_bits() {
assert_eq!(AtomicF64::default().get(), 0.00);
assert_eq!(AtomicF64::from_bits(AtomicF64::BITS_0).get(), 0.00);
assert_eq!(AtomicF64::from_bits(AtomicF64::BITS_0_25).get(), 0.25);
assert_eq!(AtomicF64::from_bits(AtomicF64::BITS_0_50).get(), 0.50);
assert_eq!(AtomicF64::from_bits(AtomicF64::BITS_0_75).get(), 0.75);
assert_eq!(AtomicF64::from_bits(AtomicF64::BITS_0_100).get(), 1.00);
}
#[test]
fn f32_0_to_100() {
let mut i = 0.0;
let f = AtomicF32::new(0.0);
while i < 100.0 {
f.set(i);
assert_eq!(f.get(), i);
i += 0.1;
}
}
#[test]
fn f64_0_to_100() {
let mut i = 0.0;
let f = AtomicF64::new(0.0);
while i < 100.0 {
f.set(i);
assert_eq!(f.get(), i);
i += 0.1;
}
}
#[test]
fn f32_irregular() {
assert!(AtomicF32::new(f32::NAN).get().is_nan());
assert_eq!(AtomicF32::new(f32::INFINITY).get(), f32::INFINITY);
assert_eq!(AtomicF32::new(f32::NEG_INFINITY).get(), f32::NEG_INFINITY);
}
#[test]
fn f64_irregular() {
assert!(AtomicF64::new(f64::NAN).get().is_nan());
assert_eq!(AtomicF64::new(f64::INFINITY).get(), f64::INFINITY);
assert_eq!(AtomicF64::new(f64::NEG_INFINITY).get(), f64::NEG_INFINITY);
// Loads/Stores
assert_eq!(float.swap(1.0), 5.0);
assert_eq!(float.load(), 1.0);
float.store(2.0);
assert_eq!(float.load(), 2.0);
}
}