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Diffstat (limited to 'vendor/once_cell/src/race.rs')
| -rw-r--r-- | vendor/once_cell/src/race.rs | 419 |
1 files changed, 419 insertions, 0 deletions
diff --git a/vendor/once_cell/src/race.rs b/vendor/once_cell/src/race.rs new file mode 100644 index 0000000..da8a2fc --- /dev/null +++ b/vendor/once_cell/src/race.rs @@ -0,0 +1,419 @@ +//! Thread-safe, non-blocking, "first one wins" flavor of `OnceCell`. +//! +//! If two threads race to initialize a type from the `race` module, they +//! don't block, execute initialization function together, but only one of +//! them stores the result. +//! +//! This module does not require `std` feature. +//! +//! # Atomic orderings +//! +//! All types in this module use `Acquire` and `Release` +//! [atomic orderings](Ordering) for all their operations. While this is not +//! strictly necessary for types other than `OnceBox`, it is useful for users as +//! it allows them to be certain that after `get` or `get_or_init` returns on +//! one thread, any side-effects caused by the setter thread prior to them +//! calling `set` or `get_or_init` will be made visible to that thread; without +//! it, it's possible for it to appear as if they haven't happened yet from the +//! getter thread's perspective. This is an acceptable tradeoff to make since +//! `Acquire` and `Release` have very little performance overhead on most +//! architectures versus `Relaxed`. + +#[cfg(feature = "critical-section")] +use portable_atomic as atomic; +#[cfg(not(feature = "critical-section"))] +use core::sync::atomic; + +use atomic::{AtomicPtr, AtomicUsize, Ordering}; +use core::cell::UnsafeCell; +use core::marker::PhantomData; +use core::num::NonZeroUsize; +use core::ptr; + +/// A thread-safe cell which can be written to only once. +#[derive(Default, Debug)] +pub struct OnceNonZeroUsize { + inner: AtomicUsize, +} + +impl OnceNonZeroUsize { + /// Creates a new empty cell. + #[inline] + pub const fn new() -> OnceNonZeroUsize { + OnceNonZeroUsize { inner: AtomicUsize::new(0) } + } + + /// Gets the underlying value. + #[inline] + pub fn get(&self) -> Option<NonZeroUsize> { + let val = self.inner.load(Ordering::Acquire); + NonZeroUsize::new(val) + } + + /// Sets the contents of this cell to `value`. + /// + /// Returns `Ok(())` if the cell was empty and `Err(())` if it was + /// full. + #[inline] + pub fn set(&self, value: NonZeroUsize) -> Result<(), ()> { + let exchange = + self.inner.compare_exchange(0, value.get(), Ordering::AcqRel, Ordering::Acquire); + match exchange { + Ok(_) => Ok(()), + Err(_) => Err(()), + } + } + + /// Gets the contents of the cell, initializing it with `f` if the cell was + /// empty. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_init<F>(&self, f: F) -> NonZeroUsize + where + F: FnOnce() -> NonZeroUsize, + { + enum Void {} + match self.get_or_try_init(|| Ok::<NonZeroUsize, Void>(f())) { + Ok(val) => val, + Err(void) => match void {}, + } + } + + /// Gets the contents of the cell, initializing it with `f` if + /// the cell was empty. If the cell was empty and `f` failed, an + /// error is returned. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_try_init<F, E>(&self, f: F) -> Result<NonZeroUsize, E> + where + F: FnOnce() -> Result<NonZeroUsize, E>, + { + let val = self.inner.load(Ordering::Acquire); + let res = match NonZeroUsize::new(val) { + Some(it) => it, + None => { + let mut val = f()?.get(); + let exchange = + self.inner.compare_exchange(0, val, Ordering::AcqRel, Ordering::Acquire); + if let Err(old) = exchange { + val = old; + } + unsafe { NonZeroUsize::new_unchecked(val) } + } + }; + Ok(res) + } +} + +/// A thread-safe cell which can be written to only once. +#[derive(Default, Debug)] +pub struct OnceBool { + inner: OnceNonZeroUsize, +} + +impl OnceBool { + /// Creates a new empty cell. + #[inline] + pub const fn new() -> OnceBool { + OnceBool { inner: OnceNonZeroUsize::new() } + } + + /// Gets the underlying value. + #[inline] + pub fn get(&self) -> Option<bool> { + self.inner.get().map(OnceBool::from_usize) + } + + /// Sets the contents of this cell to `value`. + /// + /// Returns `Ok(())` if the cell was empty and `Err(())` if it was + /// full. + #[inline] + pub fn set(&self, value: bool) -> Result<(), ()> { + self.inner.set(OnceBool::to_usize(value)) + } + + /// Gets the contents of the cell, initializing it with `f` if the cell was + /// empty. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_init<F>(&self, f: F) -> bool + where + F: FnOnce() -> bool, + { + OnceBool::from_usize(self.inner.get_or_init(|| OnceBool::to_usize(f()))) + } + + /// Gets the contents of the cell, initializing it with `f` if + /// the cell was empty. If the cell was empty and `f` failed, an + /// error is returned. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_try_init<F, E>(&self, f: F) -> Result<bool, E> + where + F: FnOnce() -> Result<bool, E>, + { + self.inner.get_or_try_init(|| f().map(OnceBool::to_usize)).map(OnceBool::from_usize) + } + + #[inline] + fn from_usize(value: NonZeroUsize) -> bool { + value.get() == 1 + } + + #[inline] + fn to_usize(value: bool) -> NonZeroUsize { + unsafe { NonZeroUsize::new_unchecked(if value { 1 } else { 2 }) } + } +} + +/// A thread-safe cell which can be written to only once. +pub struct OnceRef<'a, T> { + inner: AtomicPtr<T>, + ghost: PhantomData<UnsafeCell<&'a T>>, +} + +// TODO: Replace UnsafeCell with SyncUnsafeCell once stabilized +unsafe impl<'a, T: Sync> Sync for OnceRef<'a, T> {} + +impl<'a, T> core::fmt::Debug for OnceRef<'a, T> { + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { + write!(f, "OnceRef({:?})", self.inner) + } +} + +impl<'a, T> Default for OnceRef<'a, T> { + fn default() -> Self { + Self::new() + } +} + +impl<'a, T> OnceRef<'a, T> { + /// Creates a new empty cell. + pub const fn new() -> OnceRef<'a, T> { + OnceRef { inner: AtomicPtr::new(ptr::null_mut()), ghost: PhantomData } + } + + /// Gets a reference to the underlying value. + pub fn get(&self) -> Option<&'a T> { + let ptr = self.inner.load(Ordering::Acquire); + unsafe { ptr.as_ref() } + } + + /// Sets the contents of this cell to `value`. + /// + /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was + /// full. + pub fn set(&self, value: &'a T) -> Result<(), ()> { + let ptr = value as *const T as *mut T; + let exchange = + self.inner.compare_exchange(ptr::null_mut(), ptr, Ordering::AcqRel, Ordering::Acquire); + match exchange { + Ok(_) => Ok(()), + Err(_) => Err(()), + } + } + + /// Gets the contents of the cell, initializing it with `f` if the cell was + /// empty. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_init<F>(&self, f: F) -> &'a T + where + F: FnOnce() -> &'a T, + { + enum Void {} + match self.get_or_try_init(|| Ok::<&'a T, Void>(f())) { + Ok(val) => val, + Err(void) => match void {}, + } + } + + /// Gets the contents of the cell, initializing it with `f` if + /// the cell was empty. If the cell was empty and `f` failed, an + /// error is returned. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&'a T, E> + where + F: FnOnce() -> Result<&'a T, E>, + { + let mut ptr = self.inner.load(Ordering::Acquire); + + if ptr.is_null() { + // TODO replace with `cast_mut` when MSRV reaches 1.65.0 (also in `set`) + ptr = f()? as *const T as *mut T; + let exchange = self.inner.compare_exchange( + ptr::null_mut(), + ptr, + Ordering::AcqRel, + Ordering::Acquire, + ); + if let Err(old) = exchange { + ptr = old; + } + } + + Ok(unsafe { &*ptr }) + } + + /// ```compile_fail + /// use once_cell::race::OnceRef; + /// + /// let mut l = OnceRef::new(); + /// + /// { + /// let y = 2; + /// let mut r = OnceRef::new(); + /// r.set(&y).unwrap(); + /// core::mem::swap(&mut l, &mut r); + /// } + /// + /// // l now contains a dangling reference to y + /// eprintln!("uaf: {}", l.get().unwrap()); + /// ``` + fn _dummy() {} +} + +#[cfg(feature = "alloc")] +pub use self::once_box::OnceBox; + +#[cfg(feature = "alloc")] +mod once_box { + use super::atomic::{AtomicPtr, Ordering}; + use core::{marker::PhantomData, ptr}; + + use alloc::boxed::Box; + + /// A thread-safe cell which can be written to only once. + pub struct OnceBox<T> { + inner: AtomicPtr<T>, + ghost: PhantomData<Option<Box<T>>>, + } + + impl<T> core::fmt::Debug for OnceBox<T> { + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { + write!(f, "OnceBox({:?})", self.inner.load(Ordering::Relaxed)) + } + } + + impl<T> Default for OnceBox<T> { + fn default() -> Self { + Self::new() + } + } + + impl<T> Drop for OnceBox<T> { + fn drop(&mut self) { + let ptr = *self.inner.get_mut(); + if !ptr.is_null() { + drop(unsafe { Box::from_raw(ptr) }) + } + } + } + + impl<T> OnceBox<T> { + /// Creates a new empty cell. + pub const fn new() -> OnceBox<T> { + OnceBox { inner: AtomicPtr::new(ptr::null_mut()), ghost: PhantomData } + } + + /// Gets a reference to the underlying value. + pub fn get(&self) -> Option<&T> { + let ptr = self.inner.load(Ordering::Acquire); + if ptr.is_null() { + return None; + } + Some(unsafe { &*ptr }) + } + + /// Sets the contents of this cell to `value`. + /// + /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was + /// full. + pub fn set(&self, value: Box<T>) -> Result<(), Box<T>> { + let ptr = Box::into_raw(value); + let exchange = self.inner.compare_exchange( + ptr::null_mut(), + ptr, + Ordering::AcqRel, + Ordering::Acquire, + ); + if exchange.is_err() { + let value = unsafe { Box::from_raw(ptr) }; + return Err(value); + } + Ok(()) + } + + /// Gets the contents of the cell, initializing it with `f` if the cell was + /// empty. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_init<F>(&self, f: F) -> &T + where + F: FnOnce() -> Box<T>, + { + enum Void {} + match self.get_or_try_init(|| Ok::<Box<T>, Void>(f())) { + Ok(val) => val, + Err(void) => match void {}, + } + } + + /// Gets the contents of the cell, initializing it with `f` if + /// the cell was empty. If the cell was empty and `f` failed, an + /// error is returned. + /// + /// If several threads concurrently run `get_or_init`, more than one `f` can + /// be called. However, all threads will return the same value, produced by + /// some `f`. + pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> + where + F: FnOnce() -> Result<Box<T>, E>, + { + let mut ptr = self.inner.load(Ordering::Acquire); + + if ptr.is_null() { + let val = f()?; + ptr = Box::into_raw(val); + let exchange = self.inner.compare_exchange( + ptr::null_mut(), + ptr, + Ordering::AcqRel, + Ordering::Acquire, + ); + if let Err(old) = exchange { + drop(unsafe { Box::from_raw(ptr) }); + ptr = old; + } + }; + Ok(unsafe { &*ptr }) + } + } + + unsafe impl<T: Sync + Send> Sync for OnceBox<T> {} + + /// ```compile_fail + /// struct S(*mut ()); + /// unsafe impl Sync for S {} + /// + /// fn share<T: Sync>(_: &T) {} + /// share(&once_cell::race::OnceBox::<S>::new()); + /// ``` + fn _dummy() {} +} |