sdd/atomic_shared.rs
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use super::maybe_std::AtomicPtr;
use super::ref_counted::RefCounted;
use super::{Guard, Ptr, Shared, Tag};
use std::mem::forget;
use std::panic::UnwindSafe;
use std::ptr::{null, null_mut, NonNull};
use std::sync::atomic::Ordering::{self, Acquire, Relaxed};
/// [`AtomicShared`] owns the underlying instance, and allows users to perform atomic operations
/// on the pointer to it.
#[derive(Debug)]
pub struct AtomicShared<T> {
instance_ptr: AtomicPtr<RefCounted<T>>,
}
/// A pair of [`Shared`] and [`Ptr`] of the same type.
pub type SharedPtrPair<'g, T> = (Option<Shared<T>>, Ptr<'g, T>);
impl<T: 'static> AtomicShared<T> {
/// Creates a new [`AtomicShared`] from an instance of `T`.
///
/// The type of the instance must be determined at compile-time, must not contain non-static
/// references, and must not be a non-static reference since the instance can, theoretically,
/// live as long as the process. For instance, `struct Disallowed<'l, T>(&'l T)` is not
/// allowed, because an instance of the type cannot outlive `'l` whereas the garbage collector
/// does not guarantee that the instance is dropped within `'l`.
///
/// # Examples
///
/// ```
/// use sdd::AtomicShared;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(10);
/// ```
#[inline]
pub fn new(t: T) -> Self {
Self {
instance_ptr: AtomicPtr::new(RefCounted::new_shared(t).cast_mut()),
}
}
}
impl<T> AtomicShared<T> {
/// Creates a new [`AtomicShared`] from a [`Shared`] of `T`.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Shared};
///
/// let shared: Shared<usize> = Shared::new(10);
/// let atomic_shared: AtomicShared<usize> = AtomicShared::from(shared);
/// ```
#[cfg(not(feature = "loom"))]
#[inline]
#[must_use]
pub const fn from(shared: Shared<T>) -> Self {
let ptr = shared.underlying_ptr();
forget(shared);
let instance_ptr: std::sync::atomic::AtomicPtr<RefCounted<T>> =
AtomicPtr::new(ptr.cast_mut());
Self { instance_ptr }
}
/// Creates a new [`AtomicShared`] from a [`Shared`] of `T`.
#[cfg(feature = "loom")]
#[inline]
#[must_use]
pub fn from(shared: Shared<T>) -> Self {
let ptr = shared.underlying_ptr();
forget(shared);
let instance_ptr: loom::sync::atomic::AtomicPtr<RefCounted<T>> =
AtomicPtr::new(ptr.cast_mut());
Self { instance_ptr }
}
/// Creates a null [`AtomicShared`].
///
/// # Examples
///
/// ```
/// use sdd::AtomicShared;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::null();
/// ```
#[cfg(not(feature = "loom"))]
#[inline]
#[must_use]
pub const fn null() -> Self {
let instance_ptr: std::sync::atomic::AtomicPtr<RefCounted<T>> = AtomicPtr::new(null_mut());
Self { instance_ptr }
}
/// Creates a null [`AtomicShared`].
#[cfg(feature = "loom")]
#[inline]
#[must_use]
pub fn null() -> Self {
let instance_ptr: loom::sync::atomic::AtomicPtr<RefCounted<T>> = AtomicPtr::new(null_mut());
Self { instance_ptr }
}
/// Returns `true` if the [`AtomicShared`] is null.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::null();
/// atomic_shared.update_tag_if(Tag::Both, |p| p.tag() == Tag::None, Relaxed, Relaxed);
/// assert!(atomic_shared.is_null(Relaxed));
/// ```
#[inline]
#[must_use]
pub fn is_null(&self, order: Ordering) -> bool {
Tag::unset_tag(self.instance_ptr.load(order)).is_null()
}
/// Loads a pointer value from the [`AtomicShared`].
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(11);
/// let guard = Guard::new();
/// let ptr = atomic_shared.load(Relaxed, &guard);
/// assert_eq!(*ptr.as_ref().unwrap(), 11);
/// ```
#[inline]
#[must_use]
pub fn load<'g>(&self, order: Ordering, _guard: &'g Guard) -> Ptr<'g, T> {
Ptr::from(self.instance_ptr.load(order))
}
/// Stores the given value into the [`AtomicShared`] and returns the original value.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard, Shared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(14);
/// let guard = Guard::new();
/// let (old, tag) = atomic_shared.swap((Some(Shared::new(15)), Tag::Second), Relaxed);
/// assert_eq!(tag, Tag::None);
/// assert_eq!(*old.unwrap(), 14);
/// let (old, tag) = atomic_shared.swap((None, Tag::First), Relaxed);
/// assert_eq!(tag, Tag::Second);
/// assert_eq!(*old.unwrap(), 15);
/// let (old, tag) = atomic_shared.swap((None, Tag::None), Relaxed);
/// assert_eq!(tag, Tag::First);
/// assert!(old.is_none());
/// ```
#[inline]
pub fn swap(&self, new: (Option<Shared<T>>, Tag), order: Ordering) -> (Option<Shared<T>>, Tag) {
let desired = Tag::update_tag(
new.0.as_ref().map_or_else(null, Shared::underlying_ptr),
new.1,
)
.cast_mut();
let prev = self.instance_ptr.swap(desired, order);
let tag = Tag::into_tag(prev);
let prev_ptr = Tag::unset_tag(prev).cast_mut();
forget(new);
(NonNull::new(prev_ptr).map(Shared::from), tag)
}
/// Returns its [`Tag`].
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::null();
/// assert_eq!(atomic_shared.tag(Relaxed), Tag::None);
/// ```
#[inline]
#[must_use]
pub fn tag(&self, order: Ordering) -> Tag {
Tag::into_tag(self.instance_ptr.load(order))
}
/// Sets a new [`Tag`] if the given condition is met.
///
/// Returns `true` if the new [`Tag`] has been successfully set.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::null();
/// assert!(atomic_shared.update_tag_if(Tag::Both, |p| p.tag() == Tag::None, Relaxed, Relaxed));
/// assert_eq!(atomic_shared.tag(Relaxed), Tag::Both);
/// ```
#[inline]
pub fn update_tag_if<F: FnMut(Ptr<T>) -> bool>(
&self,
tag: Tag,
mut condition: F,
set_order: Ordering,
fetch_order: Ordering,
) -> bool {
self.instance_ptr
.fetch_update(set_order, fetch_order, |ptr| {
if condition(Ptr::from(ptr)) {
Some(Tag::update_tag(ptr, tag).cast_mut())
} else {
None
}
})
.is_ok()
}
/// Stores `new` into the [`AtomicShared`] if the current value is the same as `current`.
///
/// Returns the previously held value and the updated [`Ptr`].
///
/// # Errors
///
/// Returns `Err` with the supplied [`Shared`] and the current [`Ptr`].
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard, Shared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(17);
/// let guard = Guard::new();
///
/// let mut ptr = atomic_shared.load(Relaxed, &guard);
/// assert_eq!(*ptr.as_ref().unwrap(), 17);
///
/// atomic_shared.update_tag_if(Tag::Both, |_| true, Relaxed, Relaxed);
/// assert!(atomic_shared.compare_exchange(
/// ptr, (Some(Shared::new(18)), Tag::First), Relaxed, Relaxed, &guard).is_err());
///
/// ptr.set_tag(Tag::Both);
/// let old: Shared<usize> = atomic_shared.compare_exchange(
/// ptr,
/// (Some(Shared::new(18)), Tag::First),
/// Relaxed,
/// Relaxed,
/// &guard).unwrap().0.unwrap();
/// assert_eq!(*old, 17);
/// drop(old);
///
/// assert!(atomic_shared.compare_exchange(
/// ptr, (Some(Shared::new(19)), Tag::None), Relaxed, Relaxed, &guard).is_err());
/// assert_eq!(*ptr.as_ref().unwrap(), 17);
/// ```
#[inline]
pub fn compare_exchange<'g>(
&self,
current: Ptr<'g, T>,
new: (Option<Shared<T>>, Tag),
success: Ordering,
failure: Ordering,
_guard: &'g Guard,
) -> Result<SharedPtrPair<'g, T>, SharedPtrPair<'g, T>> {
let desired = Tag::update_tag(
new.0.as_ref().map_or_else(null, Shared::underlying_ptr),
new.1,
)
.cast_mut();
match self.instance_ptr.compare_exchange(
current.as_underlying_ptr().cast_mut(),
desired,
success,
failure,
) {
Ok(prev) => {
let prev_shared = NonNull::new(Tag::unset_tag(prev).cast_mut()).map(Shared::from);
forget(new);
Ok((prev_shared, Ptr::from(desired)))
}
Err(actual) => Err((new.0, Ptr::from(actual))),
}
}
/// Stores `new` into the [`AtomicShared`] if the current value is the same as `current`.
///
/// This method is allowed to spuriously fail even when the comparison succeeds.
///
/// Returns the previously held value and the updated [`Ptr`].
///
/// # Errors
///
/// Returns `Err` with the supplied [`Shared`] and the current [`Ptr`].
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard, Shared, Tag};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(17);
/// let guard = Guard::new();
///
/// let mut ptr = atomic_shared.load(Relaxed, &guard);
/// assert_eq!(*ptr.as_ref().unwrap(), 17);
///
/// while let Err((_, actual)) = atomic_shared.compare_exchange_weak(
/// ptr,
/// (Some(Shared::new(18)), Tag::First),
/// Relaxed,
/// Relaxed,
/// &guard) {
/// ptr = actual;
/// }
///
/// let mut ptr = atomic_shared.load(Relaxed, &guard);
/// assert_eq!(*ptr.as_ref().unwrap(), 18);
/// ```
#[inline]
pub fn compare_exchange_weak<'g>(
&self,
current: Ptr<'g, T>,
new: (Option<Shared<T>>, Tag),
success: Ordering,
failure: Ordering,
_guard: &'g Guard,
) -> Result<SharedPtrPair<'g, T>, SharedPtrPair<'g, T>> {
let desired = Tag::update_tag(
new.0.as_ref().map_or_else(null, Shared::underlying_ptr),
new.1,
)
.cast_mut();
match self.instance_ptr.compare_exchange_weak(
current.as_underlying_ptr().cast_mut(),
desired,
success,
failure,
) {
Ok(prev) => {
let prev_shared = NonNull::new(Tag::unset_tag(prev).cast_mut()).map(Shared::from);
forget(new);
Ok((prev_shared, Ptr::from(desired)))
}
Err(actual) => Err((new.0, Ptr::from(actual))),
}
}
/// Clones `self` including tags.
///
/// If `self` is not supposed to be an `AtomicShared::null`, this will never return an
/// `AtomicShared::null`.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(59);
/// let guard = Guard::new();
/// let atomic_shared_clone = atomic_shared.clone(Relaxed, &guard);
/// let ptr = atomic_shared_clone.load(Relaxed, &guard);
/// assert_eq!(*ptr.as_ref().unwrap(), 59);
/// ```
#[inline]
#[must_use]
pub fn clone(&self, order: Ordering, guard: &Guard) -> AtomicShared<T> {
self.get_shared(order, guard)
.map_or_else(Self::null, |s| Self::from(s))
}
/// Tries to create a [`Shared`] out of `self`.
///
/// If `self` is not supposed to be an `AtomicShared::null`, this will never return `None`.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Guard, Shared};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(47);
/// let guard = Guard::new();
/// let shared: Shared<usize> = atomic_shared.get_shared(Relaxed, &guard).unwrap();
/// assert_eq!(*shared, 47);
/// ```
#[inline]
#[must_use]
pub fn get_shared(&self, order: Ordering, _guard: &Guard) -> Option<Shared<T>> {
let mut ptr = Tag::unset_tag(self.instance_ptr.load(order));
while !ptr.is_null() {
if unsafe { (*ptr).try_add_ref(Acquire) } {
return NonNull::new(ptr.cast_mut()).map(Shared::from);
}
ptr = Tag::unset_tag(self.instance_ptr.load(order));
}
None
}
/// Converts `self` into a [`Shared`].
///
/// Returns `None` if `self` did not hold a strong reference.
///
/// # Examples
///
/// ```
/// use sdd::{AtomicShared, Shared};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let atomic_shared: AtomicShared<usize> = AtomicShared::new(55);
/// let shared: Shared<usize> = atomic_shared.into_shared(Relaxed).unwrap();
/// assert_eq!(*shared, 55);
/// ```
#[inline]
#[must_use]
pub fn into_shared(self, order: Ordering) -> Option<Shared<T>> {
let ptr = self.instance_ptr.swap(null_mut(), order);
if let Some(underlying_ptr) = NonNull::new(Tag::unset_tag(ptr).cast_mut()) {
return Some(Shared::from(underlying_ptr));
}
None
}
}
impl<T> Clone for AtomicShared<T> {
#[inline]
fn clone(&self) -> AtomicShared<T> {
self.clone(Acquire, &Guard::new())
}
}
impl<T> Default for AtomicShared<T> {
#[inline]
fn default() -> Self {
Self::null()
}
}
impl<T> Drop for AtomicShared<T> {
#[inline]
fn drop(&mut self) {
if let Some(ptr) = NonNull::new(Tag::unset_tag(self.instance_ptr.load(Relaxed)).cast_mut())
{
drop(Shared::from(ptr));
}
}
}
unsafe impl<T: Send> Send for AtomicShared<T> {}
unsafe impl<T: Sync> Sync for AtomicShared<T> {}
impl<T: UnwindSafe> UnwindSafe for AtomicShared<T> {}