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use core::borrow::{Borrow, BorrowMut}; use core::cmp; use core::fmt; use core::marker::PhantomData; use core::mem; use core::ptr; use core::ops::{Deref, DerefMut}; use core::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT}; use core::sync::atomic::Ordering; use alloc::boxed::Box; use guard::Guard; use crossbeam_utils::consume::AtomicConsume; /// Given ordering for the success case in a compare-exchange operation, returns the strongest /// appropriate ordering for the failure case. #[inline] fn strongest_failure_ordering(ord: Ordering) -> Ordering { use self::Ordering::*; match ord { Relaxed | Release => Relaxed, Acquire | AcqRel => Acquire, _ => SeqCst, } } /// The error returned on failed compare-and-set operation. pub struct CompareAndSetError<'g, T: 'g, P: Pointer<T>> { /// The value in the atomic pointer at the time of the failed operation. pub current: Shared<'g, T>, /// The new value, which the operation failed to store. pub new: P, } impl<'g, T: 'g, P: Pointer<T> + fmt::Debug> fmt::Debug for CompareAndSetError<'g, T, P> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("CompareAndSetError") .field("current", &self.current) .field("new", &self.new) .finish() } } /// Memory orderings for compare-and-set operations. /// /// A compare-and-set operation can have different memory orderings depending on whether it /// succeeds or fails. This trait generalizes different ways of specifying memory orderings. /// /// The two ways of specifying orderings for compare-and-set are: /// /// 1. Just one `Ordering` for the success case. In case of failure, the strongest appropriate /// ordering is chosen. /// 2. A pair of `Ordering`s. The first one is for the success case, while the second one is /// for the failure case. pub trait CompareAndSetOrdering { /// The ordering of the operation when it succeeds. fn success(&self) -> Ordering; /// The ordering of the operation when it fails. /// /// The failure ordering can't be `Release` or `AcqRel` and must be equivalent or weaker than /// the success ordering. fn failure(&self) -> Ordering; } impl CompareAndSetOrdering for Ordering { #[inline] fn success(&self) -> Ordering { *self } #[inline] fn failure(&self) -> Ordering { strongest_failure_ordering(*self) } } impl CompareAndSetOrdering for (Ordering, Ordering) { #[inline] fn success(&self) -> Ordering { self.0 } #[inline] fn failure(&self) -> Ordering { self.1 } } /// Panics if the pointer is not properly unaligned. #[inline] fn ensure_aligned<T>(raw: *const T) { assert_eq!(raw as usize & low_bits::<T>(), 0, "unaligned pointer"); } /// Returns a bitmask containing the unused least significant bits of an aligned pointer to `T`. #[inline] fn low_bits<T>() -> usize { (1 << mem::align_of::<T>().trailing_zeros()) - 1 } /// Given a tagged pointer `data`, returns the same pointer, but tagged with `tag`. /// /// `tag` is truncated to fit into the unused bits of the pointer to `T`. #[inline] fn data_with_tag<T>(data: usize, tag: usize) -> usize { (data & !low_bits::<T>()) | (tag & low_bits::<T>()) } /// Decomposes a tagged pointer `data` into the pointer and the tag. #[inline] fn decompose_data<T>(data: usize) -> (*mut T, usize) { let raw = (data & !low_bits::<T>()) as *mut T; let tag = data & low_bits::<T>(); (raw, tag) } /// An atomic pointer that can be safely shared between threads. /// /// The pointer must be properly aligned. Since it is aligned, a tag can be stored into the unused /// least significant bits of the address. More precisely, a tag should be less than `(1 << /// mem::align_of::<T>().trailing_zeros())`. /// /// Any method that loads the pointer must be passed a reference to a [`Guard`]. /// /// [`Guard`]: struct.Guard.html pub struct Atomic<T> { data: AtomicUsize, _marker: PhantomData<*mut T>, } unsafe impl<T: Send + Sync> Send for Atomic<T> {} unsafe impl<T: Send + Sync> Sync for Atomic<T> {} impl<T> Atomic<T> { /// Returns a new atomic pointer pointing to the tagged pointer `data`. fn from_usize(data: usize) -> Self { Self { data: AtomicUsize::new(data), _marker: PhantomData, } } /// Returns a new null atomic pointer. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Atomic; /// /// let a = Atomic::<i32>::null(); /// ``` #[cfg(not(feature = "nightly"))] pub fn null() -> Atomic<T> { Self { data: ATOMIC_USIZE_INIT, _marker: PhantomData, } } /// Returns a new null atomic pointer. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Atomic; /// /// let a = Atomic::<i32>::null(); /// ``` #[cfg(feature = "nightly")] pub const fn null() -> Atomic<T> { Self { data: ATOMIC_USIZE_INIT, _marker: PhantomData, } } /// Allocates `value` on the heap and returns a new atomic pointer pointing to it. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Atomic; /// /// let a = Atomic::new(1234); /// ``` pub fn new(value: T) -> Atomic<T> { Self::from(Owned::new(value)) } /// Loads a `Shared` from the atomic pointer. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// let p = a.load(SeqCst, guard); /// ``` pub fn load<'g>(&self, ord: Ordering, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.load(ord)) } } /// Loads a `Shared` from the atomic pointer using a "consume" memory ordering. /// /// This is similar to the "acquire" ordering, except that an ordering is /// only guaranteed with operations that "depend on" the result of the load. /// However consume loads are usually much faster than acquire loads on /// architectures with a weak memory model since they don't require memory /// fence instructions. /// /// The exact definition of "depend on" is a bit vague, but it works as you /// would expect in practice since a lot of software, especially the Linux /// kernel, rely on this behavior. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// let p = a.load_consume(guard); /// ``` pub fn load_consume<'g>(&self, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.load_consume()) } } /// Stores a `Shared` or `Owned` pointer into the atomic pointer. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// a.store(Shared::null(), SeqCst); /// a.store(Owned::new(1234), SeqCst); /// ``` pub fn store<'g, P: Pointer<T>>(&self, new: P, ord: Ordering) { self.data.store(new.into_usize(), ord); } /// Stores a `Shared` or `Owned` pointer into the atomic pointer, returning the previous /// `Shared`. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// let p = a.swap(Shared::null(), SeqCst, guard); /// ``` pub fn swap<'g, P: Pointer<T>>(&self, new: P, ord: Ordering, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.swap(new.into_usize(), ord)) } } /// Stores the pointer `new` (either `Shared` or `Owned`) into the atomic pointer if the current /// value is the same as `current`. The tag is also taken into account, so two pointers to the /// same object, but with different tags, will not be considered equal. /// /// The return value is a result indicating whether the new pointer was written. On success the /// pointer that was written is returned. On failure the actual current value and `new` are /// returned. /// /// This method takes a [`CompareAndSetOrdering`] argument which describes the memory /// ordering of this operation. /// /// [`CompareAndSetOrdering`]: trait.CompareAndSetOrdering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// /// let guard = &epoch::pin(); /// let mut curr = a.load(SeqCst, guard); /// let res1 = a.compare_and_set(curr, Shared::null(), SeqCst, guard); /// let res2 = a.compare_and_set(curr, Owned::new(5678), SeqCst, guard); /// ``` pub fn compare_and_set<'g, O, P>( &self, current: Shared<T>, new: P, ord: O, _: &'g Guard, ) -> Result<Shared<'g, T>, CompareAndSetError<'g, T, P>> where O: CompareAndSetOrdering, P: Pointer<T>, { let new = new.into_usize(); self.data .compare_exchange(current.into_usize(), new, ord.success(), ord.failure()) .map(|_| unsafe { Shared::from_usize(new) }) .map_err(|current| unsafe { CompareAndSetError { current: Shared::from_usize(current), new: P::from_usize(new), } }) } /// Stores the pointer `new` (either `Shared` or `Owned`) into the atomic pointer if the current /// value is the same as `current`. The tag is also taken into account, so two pointers to the /// same object, but with different tags, will not be considered equal. /// /// Unlike [`compare_and_set`], this method is allowed to spuriously fail even when comparison /// succeeds, which can result in more efficient code on some platforms. The return value is a /// result indicating whether the new pointer was written. On success the pointer that was /// written is returned. On failure the actual current value and `new` are returned. /// /// This method takes a [`CompareAndSetOrdering`] argument which describes the memory /// ordering of this operation. /// /// [`compare_and_set`]: struct.Atomic.html#method.compare_and_set /// [`CompareAndSetOrdering`]: trait.CompareAndSetOrdering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// /// let mut new = Owned::new(5678); /// let mut ptr = a.load(SeqCst, guard); /// loop { /// match a.compare_and_set_weak(ptr, new, SeqCst, guard) { /// Ok(p) => { /// ptr = p; /// break; /// } /// Err(err) => { /// ptr = err.current; /// new = err.new; /// } /// } /// } /// /// let mut curr = a.load(SeqCst, guard); /// loop { /// match a.compare_and_set_weak(curr, Shared::null(), SeqCst, guard) { /// Ok(_) => break, /// Err(err) => curr = err.current, /// } /// } /// ``` pub fn compare_and_set_weak<'g, O, P>( &self, current: Shared<T>, new: P, ord: O, _: &'g Guard, ) -> Result<Shared<'g, T>, CompareAndSetError<'g, T, P>> where O: CompareAndSetOrdering, P: Pointer<T>, { let new = new.into_usize(); self.data .compare_exchange_weak(current.into_usize(), new, ord.success(), ord.failure()) .map(|_| unsafe { Shared::from_usize(new) }) .map_err(|current| unsafe { CompareAndSetError { current: Shared::from_usize(current), new: P::from_usize(new), } }) } /// Bitwise "and" with the current tag. /// /// Performs a bitwise "and" operation on the current tag and the argument `val`, and sets the /// new tag to the result. Returns the previous pointer. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::<i32>::from(Shared::null().with_tag(3)); /// let guard = &epoch::pin(); /// assert_eq!(a.fetch_and(2, SeqCst, guard).tag(), 3); /// assert_eq!(a.load(SeqCst, guard).tag(), 2); /// ``` pub fn fetch_and<'g>(&self, val: usize, ord: Ordering, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.fetch_and(val | !low_bits::<T>(), ord)) } } /// Bitwise "or" with the current tag. /// /// Performs a bitwise "or" operation on the current tag and the argument `val`, and sets the /// new tag to the result. Returns the previous pointer. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::<i32>::from(Shared::null().with_tag(1)); /// let guard = &epoch::pin(); /// assert_eq!(a.fetch_or(2, SeqCst, guard).tag(), 1); /// assert_eq!(a.load(SeqCst, guard).tag(), 3); /// ``` pub fn fetch_or<'g>(&self, val: usize, ord: Ordering, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.fetch_or(val & low_bits::<T>(), ord)) } } /// Bitwise "xor" with the current tag. /// /// Performs a bitwise "xor" operation on the current tag and the argument `val`, and sets the /// new tag to the result. Returns the previous pointer. /// /// This method takes an [`Ordering`] argument which describes the memory ordering of this /// operation. /// /// [`Ordering`]: https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Shared}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::<i32>::from(Shared::null().with_tag(1)); /// let guard = &epoch::pin(); /// assert_eq!(a.fetch_xor(3, SeqCst, guard).tag(), 1); /// assert_eq!(a.load(SeqCst, guard).tag(), 2); /// ``` pub fn fetch_xor<'g>(&self, val: usize, ord: Ordering, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.data.fetch_xor(val & low_bits::<T>(), ord)) } } } impl<T> fmt::Debug for Atomic<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let data = self.data.load(Ordering::SeqCst); let (raw, tag) = decompose_data::<T>(data); f.debug_struct("Atomic") .field("raw", &raw) .field("tag", &tag) .finish() } } impl<T> fmt::Pointer for Atomic<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let data = self.data.load(Ordering::SeqCst); let (raw, _) = decompose_data::<T>(data); fmt::Pointer::fmt(&raw, f) } } impl<T> Clone for Atomic<T> { /// Returns a copy of the atomic value. /// /// Note that a `Relaxed` load is used here. If you need synchronization, use it with other /// atomics or fences. fn clone(&self) -> Self { let data = self.data.load(Ordering::Relaxed); Atomic::from_usize(data) } } impl<T> Default for Atomic<T> { fn default() -> Self { Atomic::null() } } impl<T> From<Owned<T>> for Atomic<T> { /// Returns a new atomic pointer pointing to `owned`. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{Atomic, Owned}; /// /// let a = Atomic::<i32>::from(Owned::new(1234)); /// ``` fn from(owned: Owned<T>) -> Self { let data = owned.data; mem::forget(owned); Self::from_usize(data) } } impl<T> From<Box<T>> for Atomic<T> { fn from(b: Box<T>) -> Self { Self::from(Owned::from(b)) } } impl<T> From<T> for Atomic<T> { fn from(t: T) -> Self { Self::new(t) } } impl<'g, T> From<Shared<'g, T>> for Atomic<T> { /// Returns a new atomic pointer pointing to `ptr`. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{Atomic, Shared}; /// /// let a = Atomic::<i32>::from(Shared::<i32>::null()); /// ``` fn from(ptr: Shared<'g, T>) -> Self { Self::from_usize(ptr.data) } } impl<T> From<*const T> for Atomic<T> { /// Returns a new atomic pointer pointing to `raw`. /// /// # Examples /// /// ``` /// use std::ptr; /// use crossbeam_epoch::Atomic; /// /// let a = Atomic::<i32>::from(ptr::null::<i32>()); /// ``` fn from(raw: *const T) -> Self { Self::from_usize(raw as usize) } } /// A trait for either `Owned` or `Shared` pointers. pub trait Pointer<T> { /// Returns the machine representation of the pointer. fn into_usize(self) -> usize; /// Returns a new pointer pointing to the tagged pointer `data`. unsafe fn from_usize(data: usize) -> Self; } /// An owned heap-allocated object. /// /// This type is very similar to `Box<T>`. /// /// The pointer must be properly aligned. Since it is aligned, a tag can be stored into the unused /// least significant bits of the address. pub struct Owned<T> { data: usize, _marker: PhantomData<Box<T>>, } impl<T> Pointer<T> for Owned<T> { #[inline] fn into_usize(self) -> usize { let data = self.data; mem::forget(self); data } /// Returns a new pointer pointing to the tagged pointer `data`. /// /// # Panics /// /// Panics if the data is zero in debug mode. #[inline] unsafe fn from_usize(data: usize) -> Self { debug_assert!(data != 0, "converting zero into `Owned`"); Owned { data: data, _marker: PhantomData, } } } impl<T> Owned<T> { /// Allocates `value` on the heap and returns a new owned pointer pointing to it. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Owned; /// /// let o = Owned::new(1234); /// ``` pub fn new(value: T) -> Owned<T> { Self::from(Box::new(value)) } /// Returns a new owned pointer pointing to `raw`. /// /// This function is unsafe because improper use may lead to memory problems. Argument `raw` /// must be a valid pointer. Also, a double-free may occur if the function is called twice on /// the same raw pointer. /// /// # Panics /// /// Panics if `raw` is not properly aligned. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Owned; /// /// let o = unsafe { Owned::from_raw(Box::into_raw(Box::new(1234))) }; /// ``` pub unsafe fn from_raw(raw: *mut T) -> Owned<T> { ensure_aligned(raw); Self::from_usize(raw as usize) } /// Converts the owned pointer into a [`Shared`]. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Owned}; /// /// let o = Owned::new(1234); /// let guard = &epoch::pin(); /// let p = o.into_shared(guard); /// ``` /// /// [`Shared`]: struct.Shared.html pub fn into_shared<'g>(self, _: &'g Guard) -> Shared<'g, T> { unsafe { Shared::from_usize(self.into_usize()) } } /// Converts the owned pointer into a `Box`. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Owned}; /// /// let o = Owned::new(1234); /// let b: Box<i32> = o.into_box(); /// assert_eq!(*b, 1234); /// ``` pub fn into_box(self) -> Box<T> { let (raw, _) = decompose_data::<T>(self.data); mem::forget(self); unsafe { Box::from_raw(raw) } } /// Returns the tag stored within the pointer. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Owned; /// /// assert_eq!(Owned::new(1234).tag(), 0); /// ``` pub fn tag(&self) -> usize { let (_, tag) = decompose_data::<T>(self.data); tag } /// Returns the same pointer, but tagged with `tag`. `tag` is truncated to be fit into the /// unused bits of the pointer to `T`. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Owned; /// /// let o = Owned::new(0u64); /// assert_eq!(o.tag(), 0); /// let o = o.with_tag(2); /// assert_eq!(o.tag(), 2); /// ``` pub fn with_tag(self, tag: usize) -> Owned<T> { let data = self.into_usize(); unsafe { Self::from_usize(data_with_tag::<T>(data, tag)) } } } impl<T> Drop for Owned<T> { fn drop(&mut self) { let (raw, _) = decompose_data::<T>(self.data); unsafe { drop(Box::from_raw(raw)); } } } impl<T> fmt::Debug for Owned<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let (raw, tag) = decompose_data::<T>(self.data); f.debug_struct("Owned") .field("raw", &raw) .field("tag", &tag) .finish() } } impl<T: Clone> Clone for Owned<T> { fn clone(&self) -> Self { Owned::new((**self).clone()).with_tag(self.tag()) } } impl<T> Deref for Owned<T> { type Target = T; fn deref(&self) -> &T { let (raw, _) = decompose_data::<T>(self.data); unsafe { &*raw } } } impl<T> DerefMut for Owned<T> { fn deref_mut(&mut self) -> &mut T { let (raw, _) = decompose_data::<T>(self.data); unsafe { &mut *raw } } } impl<T> From<T> for Owned<T> { fn from(t: T) -> Self { Owned::new(t) } } impl<T> From<Box<T>> for Owned<T> { /// Returns a new owned pointer pointing to `b`. /// /// # Panics /// /// Panics if the pointer (the `Box`) is not properly aligned. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Owned; /// /// let o = unsafe { Owned::from_raw(Box::into_raw(Box::new(1234))) }; /// ``` fn from(b: Box<T>) -> Self { unsafe { Self::from_raw(Box::into_raw(b)) } } } impl<T> Borrow<T> for Owned<T> { fn borrow(&self) -> &T { &**self } } impl<T> BorrowMut<T> for Owned<T> { fn borrow_mut(&mut self) -> &mut T { &mut **self } } impl<T> AsRef<T> for Owned<T> { fn as_ref(&self) -> &T { &**self } } impl<T> AsMut<T> for Owned<T> { fn as_mut(&mut self) -> &mut T { &mut **self } } /// A pointer to an object protected by the epoch GC. /// /// The pointer is valid for use only during the lifetime `'g`. /// /// The pointer must be properly aligned. Since it is aligned, a tag can be stored into the unused /// least significant bits of the address. pub struct Shared<'g, T: 'g> { data: usize, _marker: PhantomData<(&'g (), *const T)>, } impl<'g, T> Clone for Shared<'g, T> { fn clone(&self) -> Self { Shared { data: self.data, _marker: PhantomData, } } } impl<'g, T> Copy for Shared<'g, T> {} impl<'g, T> Pointer<T> for Shared<'g, T> { #[inline] fn into_usize(self) -> usize { self.data } #[inline] unsafe fn from_usize(data: usize) -> Self { Shared { data: data, _marker: PhantomData, } } } impl<'g, T> Shared<'g, T> { /// Returns a new null pointer. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Shared; /// /// let p = Shared::<i32>::null(); /// assert!(p.is_null()); /// ``` pub fn null() -> Shared<'g, T> { Shared { data: 0, _marker: PhantomData, } } /// Returns `true` if the pointer is null. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::null(); /// let guard = &epoch::pin(); /// assert!(a.load(SeqCst, guard).is_null()); /// a.store(Owned::new(1234), SeqCst); /// assert!(!a.load(SeqCst, guard).is_null()); /// ``` pub fn is_null(&self) -> bool { self.as_raw().is_null() } /// Converts the pointer to a raw pointer (without the tag). /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let o = Owned::new(1234); /// let raw = &*o as *const _; /// let a = Atomic::from(o); /// /// let guard = &epoch::pin(); /// let p = a.load(SeqCst, guard); /// assert_eq!(p.as_raw(), raw); /// ``` pub fn as_raw(&self) -> *const T { let (raw, _) = decompose_data::<T>(self.data); raw } /// Dereferences the pointer. /// /// Returns a reference to the pointee that is valid during the lifetime `'g`. /// /// # Safety /// /// Dereferencing a pointer is unsafe because it could be pointing to invalid memory. /// /// Another concern is the possiblity of data races due to lack of proper synchronization. /// For example, consider the following scenario: /// /// 1. A thread creates a new object: `a.store(Owned::new(10), Relaxed)` /// 2. Another thread reads it: `*a.load(Relaxed, guard).as_ref().unwrap()` /// /// The problem is that relaxed orderings don't synchronize initialization of the object with /// the read from the second thread. This is a data race. A possible solution would be to use /// `Release` and `Acquire` orderings. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// let p = a.load(SeqCst, guard); /// unsafe { /// assert_eq!(p.deref(), &1234); /// } /// ``` pub unsafe fn deref(&self) -> &'g T { &*self.as_raw() } /// Converts the pointer to a reference. /// /// Returns `None` if the pointer is null, or else a reference to the object wrapped in `Some`. /// /// # Safety /// /// Dereferencing a pointer is unsafe because it could be pointing to invalid memory. /// /// Another concern is the possiblity of data races due to lack of proper synchronization. /// For example, consider the following scenario: /// /// 1. A thread creates a new object: `a.store(Owned::new(10), Relaxed)` /// 2. Another thread reads it: `*a.load(Relaxed, guard).as_ref().unwrap()` /// /// The problem is that relaxed orderings don't synchronize initialization of the object with /// the read from the second thread. This is a data race. A possible solution would be to use /// `Release` and `Acquire` orderings. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// let guard = &epoch::pin(); /// let p = a.load(SeqCst, guard); /// unsafe { /// assert_eq!(p.as_ref(), Some(&1234)); /// } /// ``` pub unsafe fn as_ref(&self) -> Option<&'g T> { self.as_raw().as_ref() } /// Takes ownership of the pointee. /// /// # Panics /// /// Panics if this pointer is null, but only in debug mode. /// /// # Safety /// /// This method may be called only if the pointer is valid and nobody else is holding a /// reference to the same object. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(1234); /// unsafe { /// let guard = &epoch::unprotected(); /// let p = a.load(SeqCst, guard); /// drop(p.into_owned()); /// } /// ``` pub unsafe fn into_owned(self) -> Owned<T> { debug_assert!( self.as_raw() != ptr::null(), "converting a null `Shared` into `Owned`" ); Owned::from_usize(self.data) } /// Returns the tag stored within the pointer. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic, Owned}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::<u64>::from(Owned::new(0u64).with_tag(2)); /// let guard = &epoch::pin(); /// let p = a.load(SeqCst, guard); /// assert_eq!(p.tag(), 2); /// ``` pub fn tag(&self) -> usize { let (_, tag) = decompose_data::<T>(self.data); tag } /// Returns the same pointer, but tagged with `tag`. `tag` is truncated to be fit into the /// unused bits of the pointer to `T`. /// /// # Examples /// /// ``` /// use crossbeam_epoch::{self as epoch, Atomic}; /// use std::sync::atomic::Ordering::SeqCst; /// /// let a = Atomic::new(0u64); /// let guard = &epoch::pin(); /// let p1 = a.load(SeqCst, guard); /// let p2 = p1.with_tag(2); /// /// assert_eq!(p1.tag(), 0); /// assert_eq!(p2.tag(), 2); /// assert_eq!(p1.as_raw(), p2.as_raw()); /// ``` pub fn with_tag(&self, tag: usize) -> Shared<'g, T> { unsafe { Self::from_usize(data_with_tag::<T>(self.data, tag)) } } } impl<'g, T> From<*const T> for Shared<'g, T> { /// Returns a new pointer pointing to `raw`. /// /// # Panics /// /// Panics if `raw` is not properly aligned. /// /// # Examples /// /// ``` /// use crossbeam_epoch::Shared; /// /// let p = unsafe { Shared::from(Box::into_raw(Box::new(1234)) as *const _) }; /// assert!(!p.is_null()); /// ``` fn from(raw: *const T) -> Self { ensure_aligned(raw); unsafe { Self::from_usize(raw as usize) } } } impl<'g, T> PartialEq<Shared<'g, T>> for Shared<'g, T> { fn eq(&self, other: &Self) -> bool { self.data == other.data } } impl<'g, T> Eq for Shared<'g, T> {} impl<'g, T> PartialOrd<Shared<'g, T>> for Shared<'g, T> { fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> { self.data.partial_cmp(&other.data) } } impl<'g, T> Ord for Shared<'g, T> { fn cmp(&self, other: &Self) -> cmp::Ordering { self.data.cmp(&other.data) } } impl<'g, T> fmt::Debug for Shared<'g, T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let (raw, tag) = decompose_data::<T>(self.data); f.debug_struct("Shared") .field("raw", &raw) .field("tag", &tag) .finish() } } impl<'g, T> fmt::Pointer for Shared<'g, T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Pointer::fmt(&self.as_raw(), f) } } impl<'g, T> Default for Shared<'g, T> { fn default() -> Self { Shared::null() } } #[cfg(test)] mod tests { use super::Shared; #[test] fn valid_tag_i8() { Shared::<i8>::null().with_tag(0); } #[test] fn valid_tag_i64() { Shared::<i64>::null().with_tag(7); } }