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use crate::sync::atomic::Atomic;
#[cfg(test)]
use crate::sync::ResourceSignature;
use std::sync::atomic::Ordering;
/// A raw pointer type which can be safely shared between threads.
pub struct AtomicPtr<T> {
inner: Atomic<*mut T>,
}
impl<T> Default for AtomicPtr<T> {
fn default() -> Self {
Self::new(std::ptr::null_mut())
}
}
impl<T> From<*mut T> for AtomicPtr<T> {
fn from(p: *mut T) -> Self {
Self::new(p)
}
}
impl<T> std::fmt::Debug for AtomicPtr<T> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
std::fmt::Debug::fmt(unsafe { &self.raw_load() }, f)
}
}
impl<T> std::fmt::Pointer for AtomicPtr<T> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
std::fmt::Pointer::fmt(unsafe { &self.raw_load() }, f)
}
}
// Atomic operations make it safe to Send + Sync this shared raw pointer (establishing the safety of
// *using* the raw pointer is still up to the caller)
unsafe impl<T> Send for AtomicPtr<T> {}
unsafe impl<T> Sync for AtomicPtr<T> {}
impl<T> AtomicPtr<T> {
/// Creates a new `AtomicPtr`.
#[track_caller]
pub const fn new(v: *mut T) -> Self {
Self { inner: Atomic::new(v) }
}
/// Returns a mutable reference to the underlying pointer.
pub fn get_mut(&mut self) -> &mut *mut T {
self.inner.get_mut()
}
/// Consumes the atomic and returns the contained value.
pub fn into_inner(self) -> *mut T {
self.inner.into_inner()
}
/// Loads a value from the pointer.
pub fn load(&self, order: Ordering) -> *mut T {
self.inner.load(order)
}
/// Stores a value into the pointer.
pub fn store(&self, val: *mut T, order: Ordering) {
self.inner.store(val, order)
}
/// Stores a value into the atomic pointer, returning the previous value.
pub fn swap(&self, val: *mut T, order: Ordering) -> *mut T {
self.inner.swap(val, order)
}
/// Fetches the value, and applies a function to it that returns an optional new value.
/// Returns a `Result` of `Ok(previous_value)` if the function returned `Some(_)`, else
/// `Err(previous_value)`.
pub fn try_update(
&self,
set_order: Ordering,
fetch_order: Ordering,
mut f: impl FnMut(*mut T) -> Option<*mut T>,
) -> Result<*mut T, *mut T> {
let mut prev = self.load(fetch_order);
while let Some(next) = f(prev) {
match self.compare_exchange_weak(prev, next, set_order, fetch_order) {
x @ Ok(_) => return x,
Err(next_prev) => prev = next_prev,
}
}
Err(prev)
}
/// Fetches the value, and applies a function to it that returns an optional new value.
///
/// Since Rust 1.95 this is an alias for [`try_update`](Self::try_update). Deprecated since
/// Rust 1.99.
pub fn fetch_update<F>(&self, set_order: Ordering, fetch_order: Ordering, f: F) -> Result<*mut T, *mut T>
where
F: FnMut(*mut T) -> Option<*mut T>,
{
self.try_update(set_order, fetch_order, f)
}
/// Fetches the value, applies a function to it that returns a new value, and stores the new
/// value. Returns the previous value.
pub fn update(&self, set_order: Ordering, fetch_order: Ordering, mut f: impl FnMut(*mut T) -> *mut T) -> *mut T {
let mut prev = self.load(fetch_order);
loop {
match self.compare_exchange_weak(prev, f(prev), set_order, fetch_order) {
Ok(x) => break x,
Err(next_prev) => prev = next_prev,
}
}
}
/// Stores a value into the atomic pointer if the current value is the same as the
/// `current` value.
#[deprecated(since = "0.0.6", note = "Use `compare_exchange` or `compare_exchange_weak` instead")]
pub fn compare_and_swap(&self, current: *mut T, new: *mut T, order: Ordering) -> *mut T {
match self.compare_exchange(current, new, order, order) {
Ok(v) => v,
Err(v) => v,
}
}
/// Stores a value into the atomic pointer if the current value is the same as the
/// `current` value.
///
/// The return value is a result indicating whether the new value was written and
/// containing the previous value. On success this value is guaranteed to be equal to
/// `current`.
pub fn compare_exchange(
&self,
current: *mut T,
new: *mut T,
success: Ordering,
failure: Ordering,
) -> Result<*mut T, *mut T> {
self.inner
.try_update(success, failure, |val| (val == current).then_some(new))
}
/// Stores a value into the atomic pointer if the current value is the same as the
/// `current` value.
///
/// Unlike [`AtomicPtr::compare_exchange`], this function is allowed to spuriously fail
/// even when the comparison succeeds, which can result in more efficient code on some
/// platforms. The return value is a result indicating whether the new value was written
/// and containing the previous value.
// TODO actually produce spurious failures
pub fn compare_exchange_weak(
&self,
current: *mut T,
new: *mut T,
success: Ordering,
failure: Ordering,
) -> Result<*mut T, *mut T> {
self.compare_exchange(current, new, success, failure)
}
/// Offsets the pointer's address by adding `val` (in units of `T`). Returns the previous
/// pointer.
///
/// This operation wraps around on overflow, like `<*mut T>::wrapping_add`.
pub fn fetch_ptr_add(&self, val: usize, order: Ordering) -> *mut T {
self.fetch_byte_add(val.wrapping_mul(std::mem::size_of::<T>()), order)
}
/// Offsets the pointer's address by subtracting `val` (in units of `T`). Returns the previous
/// pointer.
///
/// This operation wraps around on overflow, like `<*mut T>::wrapping_sub`.
pub fn fetch_ptr_sub(&self, val: usize, order: Ordering) -> *mut T {
self.fetch_byte_sub(val.wrapping_mul(std::mem::size_of::<T>()), order)
}
/// Offsets the pointer's address by adding `val` bytes. Returns the previous pointer.
///
/// This operation wraps around on overflow, like `<*mut T>::wrapping_byte_add`.
pub fn fetch_byte_add(&self, val: usize, order: Ordering) -> *mut T {
self.inner
.try_update(order, order, |old| Some(old.wrapping_byte_add(val)))
.unwrap()
}
/// Offsets the pointer's address by subtracting `val` bytes. Returns the previous pointer.
///
/// This operation wraps around on overflow, like `<*mut T>::wrapping_byte_sub`.
pub fn fetch_byte_sub(&self, val: usize, order: Ordering) -> *mut T {
self.inner
.try_update(order, order, |old| Some(old.wrapping_byte_sub(val)))
.unwrap()
}
/// Bitwise "or" of the pointer's address with `val`, keeping the pointer's provenance.
/// Returns the previous pointer.
pub fn fetch_or(&self, val: usize, order: Ordering) -> *mut T {
self.inner
.try_update(order, order, |old| Some(old.map_addr(|addr| addr | val)))
.unwrap()
}
/// Bitwise "and" of the pointer's address with `val`, keeping the pointer's provenance.
/// Returns the previous pointer.
pub fn fetch_and(&self, val: usize, order: Ordering) -> *mut T {
self.inner
.try_update(order, order, |old| Some(old.map_addr(|addr| addr & val)))
.unwrap()
}
/// Bitwise "xor" of the pointer's address with `val`, keeping the pointer's provenance.
/// Returns the previous pointer.
pub fn fetch_xor(&self, val: usize, order: Ordering) -> *mut T {
self.inner
.try_update(order, order, |old| Some(old.map_addr(|addr| addr ^ val)))
.unwrap()
}
/// Load the atomic value directly without triggering any Shuttle context switches.
///
/// # Safety
///
/// Shuttle does not consider potential concurrent interleavings of this function call,
/// and so it should be used when those interleavings aren't important (primarily in
/// debugging scenarios where we might want to just print this atomic's value).
pub unsafe fn raw_load(&self) -> *mut T {
self.inner.raw_load()
}
#[cfg(test)]
pub(crate) fn signature(&self) -> ResourceSignature {
self.inner.signature()
}
}