use core::fmt;
use core::mem;
use core::ops::{Deref, DerefMut};
use core::ptr;
cfg_if! {
if #[cfg(feature = "nightly")] {
macro_rules! nightly_inner {
() => (
#[derive(Clone)]
#[repr(align(64))]
pub(crate) struct Inner<T> {
value: T,
}
)
}
nightly_inner!();
impl<T> Inner<T> {
pub(crate) fn new(t: T) -> Inner<T> {
Self {
value: t
}
}
}
impl<T> Deref for Inner<T> {
type Target = T;
fn deref(&self) -> &T {
&self.value
}
}
impl<T> DerefMut for Inner<T> {
fn deref_mut(&mut self) -> &mut T {
&mut self.value
}
}
} else {
use core::marker::PhantomData;
struct Inner<T> {
bytes: [u8; 64],
_marker: ([T; 0], PhantomData<T>),
}
impl<T> Inner<T> {
fn new(t: T) -> Inner<T> {
assert!(mem::size_of::<T>() <= mem::size_of::<Self>());
assert!(mem::align_of::<T>() <= mem::align_of::<Self>());
unsafe {
let mut inner: Self = mem::uninitialized();
let p: *mut T = &mut *inner;
ptr::write(p, t);
inner
}
}
}
impl<T> Deref for Inner<T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*(self.bytes.as_ptr() as *const T) }
}
}
impl<T> DerefMut for Inner<T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *(self.bytes.as_ptr() as *mut T) }
}
}
impl<T> Drop for CachePadded<T> {
fn drop(&mut self) {
let p: *mut T = self.deref_mut();
unsafe {
ptr::drop_in_place(p);
}
}
}
impl<T: Clone> Clone for Inner<T> {
fn clone(&self) -> Inner<T> {
let val = self.deref().clone();
Self::new(val)
}
}
}
}
pub struct CachePadded<T> {
inner: Inner<T>,
}
unsafe impl<T: Send> Send for CachePadded<T> {}
unsafe impl<T: Sync> Sync for CachePadded<T> {}
impl<T> CachePadded<T> {
pub fn new(t: T) -> CachePadded<T> {
CachePadded::<T> { inner: Inner::new(t) }
}
}
impl<T> Deref for CachePadded<T> {
type Target = T;
fn deref(&self) -> &T {
self.inner.deref()
}
}
impl<T> DerefMut for CachePadded<T> {
fn deref_mut(&mut self) -> &mut T {
self.inner.deref_mut()
}
}
impl<T: Default> Default for CachePadded<T> {
fn default() -> Self {
Self::new(Default::default())
}
}
impl<T: Clone> Clone for CachePadded<T> {
fn clone(&self) -> Self {
CachePadded { inner: self.inner.clone() }
}
}
impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let inner: &T = &*self;
write!(f, "CachePadded {{ {:?} }}", inner)
}
}
impl<T> From<T> for CachePadded<T> {
fn from(t: T) -> Self {
CachePadded::new(t)
}
}
#[cfg(test)]
mod test {
use super::*;
use std::cell::Cell;
#[test]
fn store_u64() {
let x: CachePadded<u64> = CachePadded::new(17);
assert_eq!(*x, 17);
}
#[test]
fn store_pair() {
let x: CachePadded<(u64, u64)> = CachePadded::new((17, 37));
assert_eq!(x.0, 17);
assert_eq!(x.1, 37);
}
#[test]
fn distance() {
let arr = [CachePadded::new(17u8), CachePadded::new(37u8)];
let a = &*arr[0] as *const u8;
let b = &*arr[1] as *const u8;
assert!(unsafe { a.offset(64) } <= b);
}
#[test]
fn different_sizes() {
CachePadded::new(17u8);
CachePadded::new(17u16);
CachePadded::new(17u32);
CachePadded::new([17u64; 0]);
CachePadded::new([17u64; 1]);
CachePadded::new([17u64; 2]);
CachePadded::new([17u64; 3]);
CachePadded::new([17u64; 4]);
CachePadded::new([17u64; 5]);
CachePadded::new([17u64; 6]);
CachePadded::new([17u64; 7]);
CachePadded::new([17u64; 8]);
}
cfg_if! {
if #[cfg(feature = "nightly")] {
#[test]
fn large() {
let a = [17u64; 9];
let b = CachePadded::new(a);
assert!(mem::size_of_val(&a) <= mem::size_of_val(&b));
}
} else {
#[test]
#[should_panic]
fn large() {
CachePadded::new([17u64; 9]);
}
}
}
#[test]
fn debug() {
assert_eq!(
format!("{:?}", CachePadded::new(17u64)),
"CachePadded { 17 }"
);
}
#[test]
fn drops() {
let count = Cell::new(0);
struct Foo<'a>(&'a Cell<usize>);
impl<'a> Drop for Foo<'a> {
fn drop(&mut self) {
self.0.set(self.0.get() + 1);
}
}
let a = CachePadded::new(Foo(&count));
let b = CachePadded::new(Foo(&count));
assert_eq!(count.get(), 0);
drop(a);
assert_eq!(count.get(), 1);
drop(b);
assert_eq!(count.get(), 2);
}
#[test]
fn clone() {
let a = CachePadded::new(17);
let b = a.clone();
assert_eq!(*a, *b);
}
#[test]
fn runs_custom_clone() {
let count = Cell::new(0);
struct Foo<'a>(&'a Cell<usize>);
impl<'a> Clone for Foo<'a> {
fn clone(&self) -> Foo<'a> {
self.0.set(self.0.get() + 1);
Foo::<'a>(self.0)
}
}
let a = CachePadded::new(Foo(&count));
a.clone();
assert_eq!(count.get(), 1);
}
}