+++ /dev/null
-// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-//! Thread-safe reference-counting pointers.
-//!
-//! See the [`Arc<T>`][arc] documentation for more details.
-//!
-//! [arc]: struct.Arc.html
-
-use core::any::Any;
-use core::sync::atomic;
-use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
-use core::borrow;
-use core::fmt;
-use core::cmp::Ordering;
-use core::intrinsics::abort;
-use core::mem::{self, align_of_val, size_of_val};
-use core::ops::Deref;
-use core::ops::CoerceUnsized;
-use core::ptr::{self, NonNull};
-use core::marker::{Unsize, PhantomData};
-use core::hash::{Hash, Hasher};
-use core::{isize, usize};
-use core::convert::From;
-
-use alloc::{Global, Alloc, Layout, box_free, handle_alloc_error};
-use boxed::Box;
-use string::String;
-use vec::Vec;
-
-/// A soft limit on the amount of references that may be made to an `Arc`.
-///
-/// Going above this limit will abort your program (although not
-/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
-const MAX_REFCOUNT: usize = (isize::MAX) as usize;
-
-/// A sentinel value that is used for the pointer of `Weak::new()`.
-const WEAK_EMPTY: usize = 1;
-
-/// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically
-/// Reference Counted'.
-///
-/// The type `Arc<T>` provides shared ownership of a value of type `T`,
-/// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces
-/// a new pointer to the same value in the heap. When the last `Arc`
-/// pointer to a given value is destroyed, the pointed-to value is
-/// also destroyed.
-///
-/// Shared references in Rust disallow mutation by default, and `Arc` is no
-/// exception: you cannot generally obtain a mutable reference to something
-/// inside an `Arc`. If you need to mutate through an `Arc`, use
-/// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
-/// types.
-///
-/// ## Thread Safety
-///
-/// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference
-/// counting. This means that it is thread-safe. The disadvantage is that
-/// atomic operations are more expensive than ordinary memory accesses. If you
-/// are not sharing reference-counted values between threads, consider using
-/// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the
-/// compiler will catch any attempt to send an [`Rc<T>`] between threads.
-/// However, a library might choose `Arc<T>` in order to give library consumers
-/// more flexibility.
-///
-/// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements
-/// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an
-/// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at
-/// first: after all, isn't the point of `Arc<T>` thread safety? The key is
-/// this: `Arc<T>` makes it thread safe to have multiple ownership of the same
-/// data, but it doesn't add thread safety to its data. Consider
-/// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always
-/// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem:
-/// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using
-/// non-atomic operations.
-///
-/// In the end, this means that you may need to pair `Arc<T>` with some sort of
-/// [`std::sync`] type, usually [`Mutex<T>`][mutex].
-///
-/// ## Breaking cycles with `Weak`
-///
-/// The [`downgrade`][downgrade] method can be used to create a non-owning
-/// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d
-/// to an `Arc`, but this will return [`None`] if the value has already been
-/// dropped.
-///
-/// A cycle between `Arc` pointers will never be deallocated. For this reason,
-/// [`Weak`][weak] is used to break cycles. For example, a tree could have
-/// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak]
-/// pointers from children back to their parents.
-///
-/// # Cloning references
-///
-/// Creating a new reference from an existing reference counted pointer is done using the
-/// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak].
-///
-/// ```
-/// use std::sync::Arc;
-/// let foo = Arc::new(vec![1.0, 2.0, 3.0]);
-/// // The two syntaxes below are equivalent.
-/// let a = foo.clone();
-/// let b = Arc::clone(&foo);
-/// // a and b both point to the same memory location as foo.
-/// ```
-///
-/// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly
-/// the meaning of the code. In the example above, this syntax makes it easier to see that
-/// this code is creating a new reference rather than copying the whole content of foo.
-///
-/// ## `Deref` behavior
-///
-/// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait),
-/// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name
-/// clashes with `T`'s methods, the methods of `Arc<T>` itself are [associated
-/// functions][assoc], called using function-like syntax:
-///
-/// ```
-/// use std::sync::Arc;
-/// let my_arc = Arc::new(());
-///
-/// Arc::downgrade(&my_arc);
-/// ```
-///
-/// [`Weak<T>`][weak] does not auto-dereference to `T`, because the value may have
-/// already been destroyed.
-///
-/// [arc]: struct.Arc.html
-/// [weak]: struct.Weak.html
-/// [`Rc<T>`]: ../../std/rc/struct.Rc.html
-/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
-/// [mutex]: ../../std/sync/struct.Mutex.html
-/// [rwlock]: ../../std/sync/struct.RwLock.html
-/// [atomic]: ../../std/sync/atomic/index.html
-/// [`Send`]: ../../std/marker/trait.Send.html
-/// [`Sync`]: ../../std/marker/trait.Sync.html
-/// [deref]: ../../std/ops/trait.Deref.html
-/// [downgrade]: struct.Arc.html#method.downgrade
-/// [upgrade]: struct.Weak.html#method.upgrade
-/// [`None`]: ../../std/option/enum.Option.html#variant.None
-/// [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
-/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
-/// [`std::sync`]: ../../std/sync/index.html
-/// [`Arc::clone(&from)`]: #method.clone
-///
-/// # Examples
-///
-/// Sharing some immutable data between threads:
-///
-// Note that we **do not** run these tests here. The windows builders get super
-// unhappy if a thread outlives the main thread and then exits at the same time
-// (something deadlocks) so we just avoid this entirely by not running these
-// tests.
-/// ```no_run
-/// use std::sync::Arc;
-/// use std::thread;
-///
-/// let five = Arc::new(5);
-///
-/// for _ in 0..10 {
-/// let five = Arc::clone(&five);
-///
-/// thread::spawn(move || {
-/// println!("{:?}", five);
-/// });
-/// }
-/// ```
-///
-/// Sharing a mutable [`AtomicUsize`]:
-///
-/// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html
-///
-/// ```no_run
-/// use std::sync::Arc;
-/// use std::sync::atomic::{AtomicUsize, Ordering};
-/// use std::thread;
-///
-/// let val = Arc::new(AtomicUsize::new(5));
-///
-/// for _ in 0..10 {
-/// let val = Arc::clone(&val);
-///
-/// thread::spawn(move || {
-/// let v = val.fetch_add(1, Ordering::SeqCst);
-/// println!("{:?}", v);
-/// });
-/// }
-/// ```
-///
-/// See the [`rc` documentation][rc_examples] for more examples of reference
-/// counting in general.
-///
-/// [rc_examples]: ../../std/rc/index.html#examples
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Arc<T: ?Sized> {
- ptr: NonNull<ArcInner<T>>,
- phantom: PhantomData<T>,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
-
-#[unstable(feature = "coerce_unsized", issue = "27732")]
-impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
-
-/// `Weak` is a version of [`Arc`] that holds a non-owning reference to the
-/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
-/// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`.
-///
-/// Since a `Weak` reference does not count towards ownership, it will not
-/// prevent the inner value from being dropped, and `Weak` itself makes no
-/// guarantees about the value still being present and may return [`None`]
-/// when [`upgrade`]d.
-///
-/// A `Weak` pointer is useful for keeping a temporary reference to the value
-/// within [`Arc`] without extending its lifetime. It is also used to prevent
-/// circular references between [`Arc`] pointers, since mutual owning references
-/// would never allow either [`Arc`] to be dropped. For example, a tree could
-/// have strong [`Arc`] pointers from parent nodes to children, and `Weak`
-/// pointers from children back to their parents.
-///
-/// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`].
-///
-/// [`Arc`]: struct.Arc.html
-/// [`Arc::downgrade`]: struct.Arc.html#method.downgrade
-/// [`upgrade`]: struct.Weak.html#method.upgrade
-/// [`Option`]: ../../std/option/enum.Option.html
-/// [`None`]: ../../std/option/enum.Option.html#variant.None
-#[stable(feature = "arc_weak", since = "1.4.0")]
-pub struct Weak<T: ?Sized> {
- // This is a `NonNull` to allow optimizing the size of this type in enums,
- // but it is actually not truly "non-null". A `Weak::new()` will set this
- // to a sentinel value, instead of needing to allocate some space in the
- // heap.
- ptr: NonNull<ArcInner<T>>,
-}
-
-#[stable(feature = "arc_weak", since = "1.4.0")]
-unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {}
-#[stable(feature = "arc_weak", since = "1.4.0")]
-unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {}
-
-#[unstable(feature = "coerce_unsized", issue = "27732")]
-impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
-
-#[stable(feature = "arc_weak", since = "1.4.0")]
-impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- write!(f, "(Weak)")
- }
-}
-
-struct ArcInner<T: ?Sized> {
- strong: atomic::AtomicUsize,
-
- // the value usize::MAX acts as a sentinel for temporarily "locking" the
- // ability to upgrade weak pointers or downgrade strong ones; this is used
- // to avoid races in `make_mut` and `get_mut`.
- weak: atomic::AtomicUsize,
-
- data: T,
-}
-
-unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
-unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
-
-impl<T> Arc<T> {
- /// Constructs a new `Arc<T>`.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- /// ```
- #[inline]
- #[stable(feature = "rust1", since = "1.0.0")]
- pub fn new(data: T) -> Arc<T> {
- // Start the weak pointer count as 1 which is the weak pointer that's
- // held by all the strong pointers (kinda), see std/rc.rs for more info
- let x: Box<_> = box ArcInner {
- strong: atomic::AtomicUsize::new(1),
- weak: atomic::AtomicUsize::new(1),
- data,
- };
- Arc { ptr: Box::into_raw_non_null(x), phantom: PhantomData }
- }
-
- /// Returns the contained value, if the `Arc` has exactly one strong reference.
- ///
- /// Otherwise, an [`Err`][result] is returned with the same `Arc` that was
- /// passed in.
- ///
- /// This will succeed even if there are outstanding weak references.
- ///
- /// [result]: ../../std/result/enum.Result.html
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let x = Arc::new(3);
- /// assert_eq!(Arc::try_unwrap(x), Ok(3));
- ///
- /// let x = Arc::new(4);
- /// let _y = Arc::clone(&x);
- /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);
- /// ```
- #[inline]
- #[stable(feature = "arc_unique", since = "1.4.0")]
- pub fn try_unwrap(this: Self) -> Result<T, Self> {
- // See `drop` for why all these atomics are like this
- if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() {
- return Err(this);
- }
-
- atomic::fence(Acquire);
-
- unsafe {
- let elem = ptr::read(&this.ptr.as_ref().data);
-
- // Make a weak pointer to clean up the implicit strong-weak reference
- let _weak = Weak { ptr: this.ptr };
- mem::forget(this);
-
- Ok(elem)
- }
- }
-}
-
-impl<T: ?Sized> Arc<T> {
- /// Consumes the `Arc`, returning the wrapped pointer.
- ///
- /// To avoid a memory leak the pointer must be converted back to an `Arc` using
- /// [`Arc::from_raw`][from_raw].
- ///
- /// [from_raw]: struct.Arc.html#method.from_raw
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let x = Arc::new(10);
- /// let x_ptr = Arc::into_raw(x);
- /// assert_eq!(unsafe { *x_ptr }, 10);
- /// ```
- #[stable(feature = "rc_raw", since = "1.17.0")]
- pub fn into_raw(this: Self) -> *const T {
- let ptr: *const T = &*this;
- mem::forget(this);
- ptr
- }
-
- /// Constructs an `Arc` from a raw pointer.
- ///
- /// The raw pointer must have been previously returned by a call to a
- /// [`Arc::into_raw`][into_raw].
- ///
- /// This function is unsafe because improper use may lead to memory problems. For example, a
- /// double-free may occur if the function is called twice on the same raw pointer.
- ///
- /// [into_raw]: struct.Arc.html#method.into_raw
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let x = Arc::new(10);
- /// let x_ptr = Arc::into_raw(x);
- ///
- /// unsafe {
- /// // Convert back to an `Arc` to prevent leak.
- /// let x = Arc::from_raw(x_ptr);
- /// assert_eq!(*x, 10);
- ///
- /// // Further calls to `Arc::from_raw(x_ptr)` would be memory unsafe.
- /// }
- ///
- /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
- /// ```
- #[stable(feature = "rc_raw", since = "1.17.0")]
- pub unsafe fn from_raw(ptr: *const T) -> Self {
- // Align the unsized value to the end of the ArcInner.
- // Because it is ?Sized, it will always be the last field in memory.
- let align = align_of_val(&*ptr);
- let layout = Layout::new::<ArcInner<()>>();
- let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
-
- // Reverse the offset to find the original ArcInner.
- let fake_ptr = ptr as *mut ArcInner<T>;
- let arc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
-
- Arc {
- ptr: NonNull::new_unchecked(arc_ptr),
- phantom: PhantomData,
- }
- }
-
- /// Creates a new [`Weak`][weak] pointer to this value.
- ///
- /// [weak]: struct.Weak.html
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// let weak_five = Arc::downgrade(&five);
- /// ```
- #[stable(feature = "arc_weak", since = "1.4.0")]
- pub fn downgrade(this: &Self) -> Weak<T> {
- // This Relaxed is OK because we're checking the value in the CAS
- // below.
- let mut cur = this.inner().weak.load(Relaxed);
-
- loop {
- // check if the weak counter is currently "locked"; if so, spin.
- if cur == usize::MAX {
- cur = this.inner().weak.load(Relaxed);
- continue;
- }
-
- // NOTE: this code currently ignores the possibility of overflow
- // into usize::MAX; in general both Rc and Arc need to be adjusted
- // to deal with overflow.
-
- // Unlike with Clone(), we need this to be an Acquire read to
- // synchronize with the write coming from `is_unique`, so that the
- // events prior to that write happen before this read.
- match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) {
- Ok(_) => return Weak { ptr: this.ptr },
- Err(old) => cur = old,
- }
- }
- }
-
- /// Gets the number of [`Weak`][weak] pointers to this value.
- ///
- /// [weak]: struct.Weak.html
- ///
- /// # Safety
- ///
- /// This method by itself is safe, but using it correctly requires extra care.
- /// Another thread can change the weak count at any time,
- /// including potentially between calling this method and acting on the result.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- /// let _weak_five = Arc::downgrade(&five);
- ///
- /// // This assertion is deterministic because we haven't shared
- /// // the `Arc` or `Weak` between threads.
- /// assert_eq!(1, Arc::weak_count(&five));
- /// ```
- #[inline]
- #[stable(feature = "arc_counts", since = "1.15.0")]
- pub fn weak_count(this: &Self) -> usize {
- let cnt = this.inner().weak.load(SeqCst);
- // If the weak count is currently locked, the value of the
- // count was 0 just before taking the lock.
- if cnt == usize::MAX { 0 } else { cnt - 1 }
- }
-
- /// Gets the number of strong (`Arc`) pointers to this value.
- ///
- /// # Safety
- ///
- /// This method by itself is safe, but using it correctly requires extra care.
- /// Another thread can change the strong count at any time,
- /// including potentially between calling this method and acting on the result.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- /// let _also_five = Arc::clone(&five);
- ///
- /// // This assertion is deterministic because we haven't shared
- /// // the `Arc` between threads.
- /// assert_eq!(2, Arc::strong_count(&five));
- /// ```
- #[inline]
- #[stable(feature = "arc_counts", since = "1.15.0")]
- pub fn strong_count(this: &Self) -> usize {
- this.inner().strong.load(SeqCst)
- }
-
- #[inline]
- fn inner(&self) -> &ArcInner<T> {
- // This unsafety is ok because while this arc is alive we're guaranteed
- // that the inner pointer is valid. Furthermore, we know that the
- // `ArcInner` structure itself is `Sync` because the inner data is
- // `Sync` as well, so we're ok loaning out an immutable pointer to these
- // contents.
- unsafe { self.ptr.as_ref() }
- }
-
- // Non-inlined part of `drop`.
- #[inline(never)]
- unsafe fn drop_slow(&mut self) {
- // Destroy the data at this time, even though we may not free the box
- // allocation itself (there may still be weak pointers lying around).
- ptr::drop_in_place(&mut self.ptr.as_mut().data);
-
- if self.inner().weak.fetch_sub(1, Release) == 1 {
- atomic::fence(Acquire);
- Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
- }
- }
-
- #[inline]
- #[stable(feature = "ptr_eq", since = "1.17.0")]
- /// Returns true if the two `Arc`s point to the same value (not
- /// just values that compare as equal).
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- /// let same_five = Arc::clone(&five);
- /// let other_five = Arc::new(5);
- ///
- /// assert!(Arc::ptr_eq(&five, &same_five));
- /// assert!(!Arc::ptr_eq(&five, &other_five));
- /// ```
- pub fn ptr_eq(this: &Self, other: &Self) -> bool {
- this.ptr.as_ptr() == other.ptr.as_ptr()
- }
-}
-
-impl<T: ?Sized> Arc<T> {
- // Allocates an `ArcInner<T>` with sufficient space for an unsized value
- unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> {
- // Create a fake ArcInner to find allocation size and alignment
- let fake_ptr = ptr as *mut ArcInner<T>;
-
- let layout = Layout::for_value(&*fake_ptr);
-
- let mem = Global.alloc(layout)
- .unwrap_or_else(|_| handle_alloc_error(layout));
-
- // Initialize the real ArcInner
- let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut ArcInner<T>;
-
- ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1));
- ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1));
-
- inner
- }
-
- fn from_box(v: Box<T>) -> Arc<T> {
- unsafe {
- let box_unique = Box::into_unique(v);
- let bptr = box_unique.as_ptr();
-
- let value_size = size_of_val(&*bptr);
- let ptr = Self::allocate_for_ptr(bptr);
-
- // Copy value as bytes
- ptr::copy_nonoverlapping(
- bptr as *const T as *const u8,
- &mut (*ptr).data as *mut _ as *mut u8,
- value_size);
-
- // Free the allocation without dropping its contents
- box_free(box_unique);
-
- Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
- }
- }
-}
-
-// Sets the data pointer of a `?Sized` raw pointer.
-//
-// For a slice/trait object, this sets the `data` field and leaves the rest
-// unchanged. For a sized raw pointer, this simply sets the pointer.
-unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
- ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
- ptr
-}
-
-impl<T> Arc<[T]> {
- // Copy elements from slice into newly allocated Arc<[T]>
- //
- // Unsafe because the caller must either take ownership or bind `T: Copy`
- unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> {
- let v_ptr = v as *const [T];
- let ptr = Self::allocate_for_ptr(v_ptr);
-
- ptr::copy_nonoverlapping(
- v.as_ptr(),
- &mut (*ptr).data as *mut [T] as *mut T,
- v.len());
-
- Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
- }
-}
-
-// Specialization trait used for From<&[T]>
-trait ArcFromSlice<T> {
- fn from_slice(slice: &[T]) -> Self;
-}
-
-impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
- #[inline]
- default fn from_slice(v: &[T]) -> Self {
- // Panic guard while cloning T elements.
- // In the event of a panic, elements that have been written
- // into the new ArcInner will be dropped, then the memory freed.
- struct Guard<T> {
- mem: NonNull<u8>,
- elems: *mut T,
- layout: Layout,
- n_elems: usize,
- }
-
- impl<T> Drop for Guard<T> {
- fn drop(&mut self) {
- use core::slice::from_raw_parts_mut;
-
- unsafe {
- let slice = from_raw_parts_mut(self.elems, self.n_elems);
- ptr::drop_in_place(slice);
-
- Global.dealloc(self.mem.cast(), self.layout.clone());
- }
- }
- }
-
- unsafe {
- let v_ptr = v as *const [T];
- let ptr = Self::allocate_for_ptr(v_ptr);
-
- let mem = ptr as *mut _ as *mut u8;
- let layout = Layout::for_value(&*ptr);
-
- // Pointer to first element
- let elems = &mut (*ptr).data as *mut [T] as *mut T;
-
- let mut guard = Guard{
- mem: NonNull::new_unchecked(mem),
- elems: elems,
- layout: layout,
- n_elems: 0,
- };
-
- for (i, item) in v.iter().enumerate() {
- ptr::write(elems.offset(i as isize), item.clone());
- guard.n_elems += 1;
- }
-
- // All clear. Forget the guard so it doesn't free the new ArcInner.
- mem::forget(guard);
-
- Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
- }
- }
-}
-
-impl<T: Copy> ArcFromSlice<T> for Arc<[T]> {
- #[inline]
- fn from_slice(v: &[T]) -> Self {
- unsafe { Arc::copy_from_slice(v) }
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Clone for Arc<T> {
- /// Makes a clone of the `Arc` pointer.
- ///
- /// This creates another pointer to the same inner value, increasing the
- /// strong reference count.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// Arc::clone(&five);
- /// ```
- #[inline]
- fn clone(&self) -> Arc<T> {
- // Using a relaxed ordering is alright here, as knowledge of the
- // original reference prevents other threads from erroneously deleting
- // the object.
- //
- // As explained in the [Boost documentation][1], Increasing the
- // reference counter can always be done with memory_order_relaxed: New
- // references to an object can only be formed from an existing
- // reference, and passing an existing reference from one thread to
- // another must already provide any required synchronization.
- //
- // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
- let old_size = self.inner().strong.fetch_add(1, Relaxed);
-
- // However we need to guard against massive refcounts in case someone
- // is `mem::forget`ing Arcs. If we don't do this the count can overflow
- // and users will use-after free. We racily saturate to `isize::MAX` on
- // the assumption that there aren't ~2 billion threads incrementing
- // the reference count at once. This branch will never be taken in
- // any realistic program.
- //
- // We abort because such a program is incredibly degenerate, and we
- // don't care to support it.
- if old_size > MAX_REFCOUNT {
- unsafe {
- abort();
- }
- }
-
- Arc { ptr: self.ptr, phantom: PhantomData }
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Deref for Arc<T> {
- type Target = T;
-
- #[inline]
- fn deref(&self) -> &T {
- &self.inner().data
- }
-}
-
-impl<T: Clone> Arc<T> {
- /// Makes a mutable reference into the given `Arc`.
- ///
- /// If there are other `Arc` or [`Weak`][weak] pointers to the same value,
- /// then `make_mut` will invoke [`clone`][clone] on the inner value to
- /// ensure unique ownership. This is also referred to as clone-on-write.
- ///
- /// See also [`get_mut`][get_mut], which will fail rather than cloning.
- ///
- /// [weak]: struct.Weak.html
- /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
- /// [get_mut]: struct.Arc.html#method.get_mut
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let mut data = Arc::new(5);
- ///
- /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
- /// let mut other_data = Arc::clone(&data); // Won't clone inner data
- /// *Arc::make_mut(&mut data) += 1; // Clones inner data
- /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
- /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
- ///
- /// // Now `data` and `other_data` point to different values.
- /// assert_eq!(*data, 8);
- /// assert_eq!(*other_data, 12);
- /// ```
- #[inline]
- #[stable(feature = "arc_unique", since = "1.4.0")]
- pub fn make_mut(this: &mut Self) -> &mut T {
- // Note that we hold both a strong reference and a weak reference.
- // Thus, releasing our strong reference only will not, by itself, cause
- // the memory to be deallocated.
- //
- // Use Acquire to ensure that we see any writes to `weak` that happen
- // before release writes (i.e., decrements) to `strong`. Since we hold a
- // weak count, there's no chance the ArcInner itself could be
- // deallocated.
- if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() {
- // Another strong pointer exists; clone
- *this = Arc::new((**this).clone());
- } else if this.inner().weak.load(Relaxed) != 1 {
- // Relaxed suffices in the above because this is fundamentally an
- // optimization: we are always racing with weak pointers being
- // dropped. Worst case, we end up allocated a new Arc unnecessarily.
-
- // We removed the last strong ref, but there are additional weak
- // refs remaining. We'll move the contents to a new Arc, and
- // invalidate the other weak refs.
-
- // Note that it is not possible for the read of `weak` to yield
- // usize::MAX (i.e., locked), since the weak count can only be
- // locked by a thread with a strong reference.
-
- // Materialize our own implicit weak pointer, so that it can clean
- // up the ArcInner as needed.
- let weak = Weak { ptr: this.ptr };
-
- // mark the data itself as already deallocated
- unsafe {
- // there is no data race in the implicit write caused by `read`
- // here (due to zeroing) because data is no longer accessed by
- // other threads (due to there being no more strong refs at this
- // point).
- let mut swap = Arc::new(ptr::read(&weak.ptr.as_ref().data));
- mem::swap(this, &mut swap);
- mem::forget(swap);
- }
- } else {
- // We were the sole reference of either kind; bump back up the
- // strong ref count.
- this.inner().strong.store(1, Release);
- }
-
- // As with `get_mut()`, the unsafety is ok because our reference was
- // either unique to begin with, or became one upon cloning the contents.
- unsafe {
- &mut this.ptr.as_mut().data
- }
- }
-}
-
-impl<T: ?Sized> Arc<T> {
- /// Returns a mutable reference to the inner value, if there are
- /// no other `Arc` or [`Weak`][weak] pointers to the same value.
- ///
- /// Returns [`None`][option] otherwise, because it is not safe to
- /// mutate a shared value.
- ///
- /// See also [`make_mut`][make_mut], which will [`clone`][clone]
- /// the inner value when it's shared.
- ///
- /// [weak]: struct.Weak.html
- /// [option]: ../../std/option/enum.Option.html
- /// [make_mut]: struct.Arc.html#method.make_mut
- /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let mut x = Arc::new(3);
- /// *Arc::get_mut(&mut x).unwrap() = 4;
- /// assert_eq!(*x, 4);
- ///
- /// let _y = Arc::clone(&x);
- /// assert!(Arc::get_mut(&mut x).is_none());
- /// ```
- #[inline]
- #[stable(feature = "arc_unique", since = "1.4.0")]
- pub fn get_mut(this: &mut Self) -> Option<&mut T> {
- if this.is_unique() {
- // This unsafety is ok because we're guaranteed that the pointer
- // returned is the *only* pointer that will ever be returned to T. Our
- // reference count is guaranteed to be 1 at this point, and we required
- // the Arc itself to be `mut`, so we're returning the only possible
- // reference to the inner data.
- unsafe {
- Some(&mut this.ptr.as_mut().data)
- }
- } else {
- None
- }
- }
-
- /// Determine whether this is the unique reference (including weak refs) to
- /// the underlying data.
- ///
- /// Note that this requires locking the weak ref count.
- fn is_unique(&mut self) -> bool {
- // lock the weak pointer count if we appear to be the sole weak pointer
- // holder.
- //
- // The acquire label here ensures a happens-before relationship with any
- // writes to `strong` prior to decrements of the `weak` count (via drop,
- // which uses Release).
- if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() {
- // Due to the previous acquire read, this will observe any writes to
- // `strong` that were due to upgrading weak pointers; only strong
- // clones remain, which require that the strong count is > 1 anyway.
- let unique = self.inner().strong.load(Relaxed) == 1;
-
- // The release write here synchronizes with a read in `downgrade`,
- // effectively preventing the above read of `strong` from happening
- // after the write.
- self.inner().weak.store(1, Release); // release the lock
- unique
- } else {
- false
- }
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
- /// Drops the `Arc`.
- ///
- /// This will decrement the strong reference count. If the strong reference
- /// count reaches zero then the only other references (if any) are
- /// [`Weak`][weak], so we `drop` the inner value.
- ///
- /// [weak]: struct.Weak.html
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// struct Foo;
- ///
- /// impl Drop for Foo {
- /// fn drop(&mut self) {
- /// println!("dropped!");
- /// }
- /// }
- ///
- /// let foo = Arc::new(Foo);
- /// let foo2 = Arc::clone(&foo);
- ///
- /// drop(foo); // Doesn't print anything
- /// drop(foo2); // Prints "dropped!"
- /// ```
- #[inline]
- fn drop(&mut self) {
- // Because `fetch_sub` is already atomic, we do not need to synchronize
- // with other threads unless we are going to delete the object. This
- // same logic applies to the below `fetch_sub` to the `weak` count.
- if self.inner().strong.fetch_sub(1, Release) != 1 {
- return;
- }
-
- // This fence is needed to prevent reordering of use of the data and
- // deletion of the data. Because it is marked `Release`, the decreasing
- // of the reference count synchronizes with this `Acquire` fence. This
- // means that use of the data happens before decreasing the reference
- // count, which happens before this fence, which happens before the
- // deletion of the data.
- //
- // As explained in the [Boost documentation][1],
- //
- // > It is important to enforce any possible access to the object in one
- // > thread (through an existing reference) to *happen before* deleting
- // > the object in a different thread. This is achieved by a "release"
- // > operation after dropping a reference (any access to the object
- // > through this reference must obviously happened before), and an
- // > "acquire" operation before deleting the object.
- //
- // In particular, while the contents of an Arc are usually immutable, it's
- // possible to have interior writes to something like a Mutex<T>. Since a
- // Mutex is not acquired when it is deleted, we can't rely on its
- // synchronization logic to make writes in thread A visible to a destructor
- // running in thread B.
- //
- // Also note that the Acquire fence here could probably be replaced with an
- // Acquire load, which could improve performance in highly-contended
- // situations. See [2].
- //
- // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
- // [2]: (https://github.com/rust-lang/rust/pull/41714)
- atomic::fence(Acquire);
-
- unsafe {
- self.drop_slow();
- }
- }
-}
-
-impl Arc<Any + Send + Sync> {
- #[inline]
- #[unstable(feature = "rc_downcast", issue = "44608")]
- /// Attempt to downcast the `Arc<Any + Send + Sync>` to a concrete type.
- ///
- /// # Examples
- ///
- /// ```
- /// #![feature(rc_downcast)]
- /// use std::any::Any;
- /// use std::sync::Arc;
- ///
- /// fn print_if_string(value: Arc<Any + Send + Sync>) {
- /// if let Ok(string) = value.downcast::<String>() {
- /// println!("String ({}): {}", string.len(), string);
- /// }
- /// }
- ///
- /// fn main() {
- /// let my_string = "Hello World".to_string();
- /// print_if_string(Arc::new(my_string));
- /// print_if_string(Arc::new(0i8));
- /// }
- /// ```
- pub fn downcast<T>(self) -> Result<Arc<T>, Self>
- where
- T: Any + Send + Sync + 'static,
- {
- if (*self).is::<T>() {
- let ptr = self.ptr.cast::<ArcInner<T>>();
- mem::forget(self);
- Ok(Arc { ptr, phantom: PhantomData })
- } else {
- Err(self)
- }
- }
-}
-
-impl<T> Weak<T> {
- /// Constructs a new `Weak<T>`, without allocating any memory.
- /// Calling [`upgrade`] on the return value always gives [`None`].
- ///
- /// [`upgrade`]: struct.Weak.html#method.upgrade
- /// [`None`]: ../../std/option/enum.Option.html#variant.None
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Weak;
- ///
- /// let empty: Weak<i64> = Weak::new();
- /// assert!(empty.upgrade().is_none());
- /// ```
- #[stable(feature = "downgraded_weak", since = "1.10.0")]
- pub fn new() -> Weak<T> {
- unsafe {
- Weak {
- ptr: NonNull::new_unchecked(WEAK_EMPTY as *mut _),
- }
- }
- }
-}
-
-impl<T: ?Sized> Weak<T> {
- /// Attempts to upgrade the `Weak` pointer to an [`Arc`], extending
- /// the lifetime of the value if successful.
- ///
- /// Returns [`None`] if the value has since been dropped.
- ///
- /// [`Arc`]: struct.Arc.html
- /// [`None`]: ../../std/option/enum.Option.html#variant.None
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// let weak_five = Arc::downgrade(&five);
- ///
- /// let strong_five: Option<Arc<_>> = weak_five.upgrade();
- /// assert!(strong_five.is_some());
- ///
- /// // Destroy all strong pointers.
- /// drop(strong_five);
- /// drop(five);
- ///
- /// assert!(weak_five.upgrade().is_none());
- /// ```
- #[stable(feature = "arc_weak", since = "1.4.0")]
- pub fn upgrade(&self) -> Option<Arc<T>> {
- // We use a CAS loop to increment the strong count instead of a
- // fetch_add because once the count hits 0 it must never be above 0.
- let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
- return None;
- } else {
- unsafe { self.ptr.as_ref() }
- };
-
- // Relaxed load because any write of 0 that we can observe
- // leaves the field in a permanently zero state (so a
- // "stale" read of 0 is fine), and any other value is
- // confirmed via the CAS below.
- let mut n = inner.strong.load(Relaxed);
-
- loop {
- if n == 0 {
- return None;
- }
-
- // See comments in `Arc::clone` for why we do this (for `mem::forget`).
- if n > MAX_REFCOUNT {
- unsafe {
- abort();
- }
- }
-
- // Relaxed is valid for the same reason it is on Arc's Clone impl
- match inner.strong.compare_exchange_weak(n, n + 1, Relaxed, Relaxed) {
- Ok(_) => return Some(Arc {
- // null checked above
- ptr: self.ptr,
- phantom: PhantomData,
- }),
- Err(old) => n = old,
- }
- }
- }
-}
-
-#[stable(feature = "arc_weak", since = "1.4.0")]
-impl<T: ?Sized> Clone for Weak<T> {
- /// Makes a clone of the `Weak` pointer that points to the same value.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::{Arc, Weak};
- ///
- /// let weak_five = Arc::downgrade(&Arc::new(5));
- ///
- /// Weak::clone(&weak_five);
- /// ```
- #[inline]
- fn clone(&self) -> Weak<T> {
- let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
- return Weak { ptr: self.ptr };
- } else {
- unsafe { self.ptr.as_ref() }
- };
- // See comments in Arc::clone() for why this is relaxed. This can use a
- // fetch_add (ignoring the lock) because the weak count is only locked
- // where are *no other* weak pointers in existence. (So we can't be
- // running this code in that case).
- let old_size = inner.weak.fetch_add(1, Relaxed);
-
- // See comments in Arc::clone() for why we do this (for mem::forget).
- if old_size > MAX_REFCOUNT {
- unsafe {
- abort();
- }
- }
-
- return Weak { ptr: self.ptr };
- }
-}
-
-#[stable(feature = "downgraded_weak", since = "1.10.0")]
-impl<T> Default for Weak<T> {
- /// Constructs a new `Weak<T>`, without allocating memory.
- /// Calling [`upgrade`] on the return value always gives [`None`].
- ///
- /// [`upgrade`]: struct.Weak.html#method.upgrade
- /// [`None`]: ../../std/option/enum.Option.html#variant.None
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Weak;
- ///
- /// let empty: Weak<i64> = Default::default();
- /// assert!(empty.upgrade().is_none());
- /// ```
- fn default() -> Weak<T> {
- Weak::new()
- }
-}
-
-#[stable(feature = "arc_weak", since = "1.4.0")]
-impl<T: ?Sized> Drop for Weak<T> {
- /// Drops the `Weak` pointer.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::{Arc, Weak};
- ///
- /// struct Foo;
- ///
- /// impl Drop for Foo {
- /// fn drop(&mut self) {
- /// println!("dropped!");
- /// }
- /// }
- ///
- /// let foo = Arc::new(Foo);
- /// let weak_foo = Arc::downgrade(&foo);
- /// let other_weak_foo = Weak::clone(&weak_foo);
- ///
- /// drop(weak_foo); // Doesn't print anything
- /// drop(foo); // Prints "dropped!"
- ///
- /// assert!(other_weak_foo.upgrade().is_none());
- /// ```
- fn drop(&mut self) {
- // If we find out that we were the last weak pointer, then its time to
- // deallocate the data entirely. See the discussion in Arc::drop() about
- // the memory orderings
- //
- // It's not necessary to check for the locked state here, because the
- // weak count can only be locked if there was precisely one weak ref,
- // meaning that drop could only subsequently run ON that remaining weak
- // ref, which can only happen after the lock is released.
- let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
- return;
- } else {
- unsafe { self.ptr.as_ref() }
- };
-
- if inner.weak.fetch_sub(1, Release) == 1 {
- atomic::fence(Acquire);
- unsafe {
- Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
- }
- }
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
- /// Equality for two `Arc`s.
- ///
- /// Two `Arc`s are equal if their inner values are equal.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five == Arc::new(5));
- /// ```
- fn eq(&self, other: &Arc<T>) -> bool {
- *(*self) == *(*other)
- }
-
- /// Inequality for two `Arc`s.
- ///
- /// Two `Arc`s are unequal if their inner values are unequal.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five != Arc::new(6));
- /// ```
- fn ne(&self, other: &Arc<T>) -> bool {
- *(*self) != *(*other)
- }
-}
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
- /// Partial comparison for two `Arc`s.
- ///
- /// The two are compared by calling `partial_cmp()` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- /// use std::cmp::Ordering;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6)));
- /// ```
- fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
- (**self).partial_cmp(&**other)
- }
-
- /// Less-than comparison for two `Arc`s.
- ///
- /// The two are compared by calling `<` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five < Arc::new(6));
- /// ```
- fn lt(&self, other: &Arc<T>) -> bool {
- *(*self) < *(*other)
- }
-
- /// 'Less than or equal to' comparison for two `Arc`s.
- ///
- /// The two are compared by calling `<=` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five <= Arc::new(5));
- /// ```
- fn le(&self, other: &Arc<T>) -> bool {
- *(*self) <= *(*other)
- }
-
- /// Greater-than comparison for two `Arc`s.
- ///
- /// The two are compared by calling `>` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five > Arc::new(4));
- /// ```
- fn gt(&self, other: &Arc<T>) -> bool {
- *(*self) > *(*other)
- }
-
- /// 'Greater than or equal to' comparison for two `Arc`s.
- ///
- /// The two are compared by calling `>=` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert!(five >= Arc::new(5));
- /// ```
- fn ge(&self, other: &Arc<T>) -> bool {
- *(*self) >= *(*other)
- }
-}
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + Ord> Ord for Arc<T> {
- /// Comparison for two `Arc`s.
- ///
- /// The two are compared by calling `cmp()` on their inner values.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- /// use std::cmp::Ordering;
- ///
- /// let five = Arc::new(5);
- ///
- /// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6)));
- /// ```
- fn cmp(&self, other: &Arc<T>) -> Ordering {
- (**self).cmp(&**other)
- }
-}
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + Eq> Eq for Arc<T> {}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- fmt::Display::fmt(&**self, f)
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- fmt::Debug::fmt(&**self, f)
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> fmt::Pointer for Arc<T> {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- fmt::Pointer::fmt(&(&**self as *const T), f)
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Default> Default for Arc<T> {
- /// Creates a new `Arc<T>`, with the `Default` value for `T`.
- ///
- /// # Examples
- ///
- /// ```
- /// use std::sync::Arc;
- ///
- /// let x: Arc<i32> = Default::default();
- /// assert_eq!(*x, 0);
- /// ```
- fn default() -> Arc<T> {
- Arc::new(Default::default())
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + Hash> Hash for Arc<T> {
- fn hash<H: Hasher>(&self, state: &mut H) {
- (**self).hash(state)
- }
-}
-
-#[stable(feature = "from_for_ptrs", since = "1.6.0")]
-impl<T> From<T> for Arc<T> {
- fn from(t: T) -> Self {
- Arc::new(t)
- }
-}
-
-#[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<'a, T: Clone> From<&'a [T]> for Arc<[T]> {
- #[inline]
- fn from(v: &[T]) -> Arc<[T]> {
- <Self as ArcFromSlice<T>>::from_slice(v)
- }
-}
-
-#[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<'a> From<&'a str> for Arc<str> {
- #[inline]
- fn from(v: &str) -> Arc<str> {
- let arc = Arc::<[u8]>::from(v.as_bytes());
- unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) }
- }
-}
-
-#[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl From<String> for Arc<str> {
- #[inline]
- fn from(v: String) -> Arc<str> {
- Arc::from(&v[..])
- }
-}
-
-#[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<T: ?Sized> From<Box<T>> for Arc<T> {
- #[inline]
- fn from(v: Box<T>) -> Arc<T> {
- Arc::from_box(v)
- }
-}
-
-#[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<T> From<Vec<T>> for Arc<[T]> {
- #[inline]
- fn from(mut v: Vec<T>) -> Arc<[T]> {
- unsafe {
- let arc = Arc::copy_from_slice(&v);
-
- // Allow the Vec to free its memory, but not destroy its contents
- v.set_len(0);
-
- arc
- }
- }
-}
-
-#[cfg(test)]
-mod tests {
- use std::boxed::Box;
- use std::clone::Clone;
- use std::sync::mpsc::channel;
- use std::mem::drop;
- use std::ops::Drop;
- use std::option::Option;
- use std::option::Option::{None, Some};
- use std::sync::atomic;
- use std::sync::atomic::Ordering::{Acquire, SeqCst};
- use std::thread;
- use std::sync::Mutex;
- use std::convert::From;
-
- use super::{Arc, Weak};
- use vec::Vec;
-
- struct Canary(*mut atomic::AtomicUsize);
-
- impl Drop for Canary {
- fn drop(&mut self) {
- unsafe {
- match *self {
- Canary(c) => {
- (*c).fetch_add(1, SeqCst);
- }
- }
- }
- }
- }
-
- #[test]
- #[cfg_attr(target_os = "emscripten", ignore)]
- fn manually_share_arc() {
- let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
- let arc_v = Arc::new(v);
-
- let (tx, rx) = channel();
-
- let _t = thread::spawn(move || {
- let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
- assert_eq!((*arc_v)[3], 4);
- });
-
- tx.send(arc_v.clone()).unwrap();
-
- assert_eq!((*arc_v)[2], 3);
- assert_eq!((*arc_v)[4], 5);
- }
-
- #[test]
- fn test_arc_get_mut() {
- let mut x = Arc::new(3);
- *Arc::get_mut(&mut x).unwrap() = 4;
- assert_eq!(*x, 4);
- let y = x.clone();
- assert!(Arc::get_mut(&mut x).is_none());
- drop(y);
- assert!(Arc::get_mut(&mut x).is_some());
- let _w = Arc::downgrade(&x);
- assert!(Arc::get_mut(&mut x).is_none());
- }
-
- #[test]
- fn try_unwrap() {
- let x = Arc::new(3);
- assert_eq!(Arc::try_unwrap(x), Ok(3));
- let x = Arc::new(4);
- let _y = x.clone();
- assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
- let x = Arc::new(5);
- let _w = Arc::downgrade(&x);
- assert_eq!(Arc::try_unwrap(x), Ok(5));
- }
-
- #[test]
- fn into_from_raw() {
- let x = Arc::new(box "hello");
- let y = x.clone();
-
- let x_ptr = Arc::into_raw(x);
- drop(y);
- unsafe {
- assert_eq!(**x_ptr, "hello");
-
- let x = Arc::from_raw(x_ptr);
- assert_eq!(**x, "hello");
-
- assert_eq!(Arc::try_unwrap(x).map(|x| *x), Ok("hello"));
- }
- }
-
- #[test]
- fn test_into_from_raw_unsized() {
- use std::fmt::Display;
- use std::string::ToString;
-
- let arc: Arc<str> = Arc::from("foo");
-
- let ptr = Arc::into_raw(arc.clone());
- let arc2 = unsafe { Arc::from_raw(ptr) };
-
- assert_eq!(unsafe { &*ptr }, "foo");
- assert_eq!(arc, arc2);
-
- let arc: Arc<Display> = Arc::new(123);
-
- let ptr = Arc::into_raw(arc.clone());
- let arc2 = unsafe { Arc::from_raw(ptr) };
-
- assert_eq!(unsafe { &*ptr }.to_string(), "123");
- assert_eq!(arc2.to_string(), "123");
- }
-
- #[test]
- fn test_cowarc_clone_make_mut() {
- let mut cow0 = Arc::new(75);
- let mut cow1 = cow0.clone();
- let mut cow2 = cow1.clone();
-
- assert!(75 == *Arc::make_mut(&mut cow0));
- assert!(75 == *Arc::make_mut(&mut cow1));
- assert!(75 == *Arc::make_mut(&mut cow2));
-
- *Arc::make_mut(&mut cow0) += 1;
- *Arc::make_mut(&mut cow1) += 2;
- *Arc::make_mut(&mut cow2) += 3;
-
- assert!(76 == *cow0);
- assert!(77 == *cow1);
- assert!(78 == *cow2);
-
- // none should point to the same backing memory
- assert!(*cow0 != *cow1);
- assert!(*cow0 != *cow2);
- assert!(*cow1 != *cow2);
- }
-
- #[test]
- fn test_cowarc_clone_unique2() {
- let mut cow0 = Arc::new(75);
- let cow1 = cow0.clone();
- let cow2 = cow1.clone();
-
- assert!(75 == *cow0);
- assert!(75 == *cow1);
- assert!(75 == *cow2);
-
- *Arc::make_mut(&mut cow0) += 1;
- assert!(76 == *cow0);
- assert!(75 == *cow1);
- assert!(75 == *cow2);
-
- // cow1 and cow2 should share the same contents
- // cow0 should have a unique reference
- assert!(*cow0 != *cow1);
- assert!(*cow0 != *cow2);
- assert!(*cow1 == *cow2);
- }
-
- #[test]
- fn test_cowarc_clone_weak() {
- let mut cow0 = Arc::new(75);
- let cow1_weak = Arc::downgrade(&cow0);
-
- assert!(75 == *cow0);
- assert!(75 == *cow1_weak.upgrade().unwrap());
-
- *Arc::make_mut(&mut cow0) += 1;
-
- assert!(76 == *cow0);
- assert!(cow1_weak.upgrade().is_none());
- }
-
- #[test]
- fn test_live() {
- let x = Arc::new(5);
- let y = Arc::downgrade(&x);
- assert!(y.upgrade().is_some());
- }
-
- #[test]
- fn test_dead() {
- let x = Arc::new(5);
- let y = Arc::downgrade(&x);
- drop(x);
- assert!(y.upgrade().is_none());
- }
-
- #[test]
- fn weak_self_cyclic() {
- struct Cycle {
- x: Mutex<Option<Weak<Cycle>>>,
- }
-
- let a = Arc::new(Cycle { x: Mutex::new(None) });
- let b = Arc::downgrade(&a.clone());
- *a.x.lock().unwrap() = Some(b);
-
- // hopefully we don't double-free (or leak)...
- }
-
- #[test]
- fn drop_arc() {
- let mut canary = atomic::AtomicUsize::new(0);
- let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
- drop(x);
- assert!(canary.load(Acquire) == 1);
- }
-
- #[test]
- fn drop_arc_weak() {
- let mut canary = atomic::AtomicUsize::new(0);
- let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
- let arc_weak = Arc::downgrade(&arc);
- assert!(canary.load(Acquire) == 0);
- drop(arc);
- assert!(canary.load(Acquire) == 1);
- drop(arc_weak);
- }
-
- #[test]
- fn test_strong_count() {
- let a = Arc::new(0);
- assert!(Arc::strong_count(&a) == 1);
- let w = Arc::downgrade(&a);
- assert!(Arc::strong_count(&a) == 1);
- let b = w.upgrade().expect("");
- assert!(Arc::strong_count(&b) == 2);
- assert!(Arc::strong_count(&a) == 2);
- drop(w);
- drop(a);
- assert!(Arc::strong_count(&b) == 1);
- let c = b.clone();
- assert!(Arc::strong_count(&b) == 2);
- assert!(Arc::strong_count(&c) == 2);
- }
-
- #[test]
- fn test_weak_count() {
- let a = Arc::new(0);
- assert!(Arc::strong_count(&a) == 1);
- assert!(Arc::weak_count(&a) == 0);
- let w = Arc::downgrade(&a);
- assert!(Arc::strong_count(&a) == 1);
- assert!(Arc::weak_count(&a) == 1);
- let x = w.clone();
- assert!(Arc::weak_count(&a) == 2);
- drop(w);
- drop(x);
- assert!(Arc::strong_count(&a) == 1);
- assert!(Arc::weak_count(&a) == 0);
- let c = a.clone();
- assert!(Arc::strong_count(&a) == 2);
- assert!(Arc::weak_count(&a) == 0);
- let d = Arc::downgrade(&c);
- assert!(Arc::weak_count(&c) == 1);
- assert!(Arc::strong_count(&c) == 2);
-
- drop(a);
- drop(c);
- drop(d);
- }
-
- #[test]
- fn show_arc() {
- let a = Arc::new(5);
- assert_eq!(format!("{:?}", a), "5");
- }
-
- // Make sure deriving works with Arc<T>
- #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
- struct Foo {
- inner: Arc<i32>,
- }
-
- #[test]
- fn test_unsized() {
- let x: Arc<[i32]> = Arc::new([1, 2, 3]);
- assert_eq!(format!("{:?}", x), "[1, 2, 3]");
- let y = Arc::downgrade(&x.clone());
- drop(x);
- assert!(y.upgrade().is_none());
- }
-
- #[test]
- fn test_from_owned() {
- let foo = 123;
- let foo_arc = Arc::from(foo);
- assert!(123 == *foo_arc);
- }
-
- #[test]
- fn test_new_weak() {
- let foo: Weak<usize> = Weak::new();
- assert!(foo.upgrade().is_none());
- }
-
- #[test]
- fn test_ptr_eq() {
- let five = Arc::new(5);
- let same_five = five.clone();
- let other_five = Arc::new(5);
-
- assert!(Arc::ptr_eq(&five, &same_five));
- assert!(!Arc::ptr_eq(&five, &other_five));
- }
-
- #[test]
- #[cfg_attr(target_os = "emscripten", ignore)]
- fn test_weak_count_locked() {
- let mut a = Arc::new(atomic::AtomicBool::new(false));
- let a2 = a.clone();
- let t = thread::spawn(move || {
- for _i in 0..1000000 {
- Arc::get_mut(&mut a);
- }
- a.store(true, SeqCst);
- });
-
- while !a2.load(SeqCst) {
- let n = Arc::weak_count(&a2);
- assert!(n < 2, "bad weak count: {}", n);
- }
- t.join().unwrap();
- }
-
- #[test]
- fn test_from_str() {
- let r: Arc<str> = Arc::from("foo");
-
- assert_eq!(&r[..], "foo");
- }
-
- #[test]
- fn test_copy_from_slice() {
- let s: &[u32] = &[1, 2, 3];
- let r: Arc<[u32]> = Arc::from(s);
-
- assert_eq!(&r[..], [1, 2, 3]);
- }
-
- #[test]
- fn test_clone_from_slice() {
- #[derive(Clone, Debug, Eq, PartialEq)]
- struct X(u32);
-
- let s: &[X] = &[X(1), X(2), X(3)];
- let r: Arc<[X]> = Arc::from(s);
-
- assert_eq!(&r[..], s);
- }
-
- #[test]
- #[should_panic]
- fn test_clone_from_slice_panic() {
- use std::string::{String, ToString};
-
- struct Fail(u32, String);
-
- impl Clone for Fail {
- fn clone(&self) -> Fail {
- if self.0 == 2 {
- panic!();
- }
- Fail(self.0, self.1.clone())
- }
- }
-
- let s: &[Fail] = &[
- Fail(0, "foo".to_string()),
- Fail(1, "bar".to_string()),
- Fail(2, "baz".to_string()),
- ];
-
- // Should panic, but not cause memory corruption
- let _r: Arc<[Fail]> = Arc::from(s);
- }
-
- #[test]
- fn test_from_box() {
- let b: Box<u32> = box 123;
- let r: Arc<u32> = Arc::from(b);
-
- assert_eq!(*r, 123);
- }
-
- #[test]
- fn test_from_box_str() {
- use std::string::String;
-
- let s = String::from("foo").into_boxed_str();
- let r: Arc<str> = Arc::from(s);
-
- assert_eq!(&r[..], "foo");
- }
-
- #[test]
- fn test_from_box_slice() {
- let s = vec![1, 2, 3].into_boxed_slice();
- let r: Arc<[u32]> = Arc::from(s);
-
- assert_eq!(&r[..], [1, 2, 3]);
- }
-
- #[test]
- fn test_from_box_trait() {
- use std::fmt::Display;
- use std::string::ToString;
-
- let b: Box<Display> = box 123;
- let r: Arc<Display> = Arc::from(b);
-
- assert_eq!(r.to_string(), "123");
- }
-
- #[test]
- fn test_from_box_trait_zero_sized() {
- use std::fmt::Debug;
-
- let b: Box<Debug> = box ();
- let r: Arc<Debug> = Arc::from(b);
-
- assert_eq!(format!("{:?}", r), "()");
- }
-
- #[test]
- fn test_from_vec() {
- let v = vec![1, 2, 3];
- let r: Arc<[u32]> = Arc::from(v);
-
- assert_eq!(&r[..], [1, 2, 3]);
- }
-
- #[test]
- fn test_downcast() {
- use std::any::Any;
-
- let r1: Arc<Any + Send + Sync> = Arc::new(i32::max_value());
- let r2: Arc<Any + Send + Sync> = Arc::new("abc");
-
- assert!(r1.clone().downcast::<u32>().is_err());
-
- let r1i32 = r1.downcast::<i32>();
- assert!(r1i32.is_ok());
- assert_eq!(r1i32.unwrap(), Arc::new(i32::max_value()));
-
- assert!(r2.clone().downcast::<i32>().is_err());
-
- let r2str = r2.downcast::<&'static str>();
- assert!(r2str.is_ok());
- assert_eq!(r2str.unwrap(), Arc::new("abc"));
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
- fn borrow(&self) -> &T {
- &**self
- }
-}
-
-#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
-impl<T: ?Sized> AsRef<T> for Arc<T> {
- fn as_ref(&self) -> &T {
- &**self
- }
-}
//!
//! ## Atomically reference counted pointers
//!
-//! The [`Arc`](arc/index.html) type is the threadsafe equivalent of the `Rc`
+//! The [`Arc`](sync/index.html) type is the threadsafe equivalent of the `Rc`
//! type. It provides all the same functionality of `Rc`, except it requires
//! that the contained type `T` is shareable. Additionally, `Arc<T>` is itself
//! sendable while `Rc<T>` is not.
mod boxed_test;
pub mod collections;
#[cfg(target_has_atomic = "ptr")]
-pub mod arc;
+pub mod sync;
pub mod rc;
pub mod raw_vec;
--- /dev/null
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+//! Thread-safe reference-counting pointers.
+//!
+//! See the [`Arc<T>`][arc] documentation for more details.
+//!
+//! [arc]: struct.Arc.html
+
+use core::any::Any;
+use core::sync::atomic;
+use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
+use core::borrow;
+use core::fmt;
+use core::cmp::Ordering;
+use core::intrinsics::abort;
+use core::mem::{self, align_of_val, size_of_val};
+use core::ops::Deref;
+use core::ops::CoerceUnsized;
+use core::ptr::{self, NonNull};
+use core::marker::{Unsize, PhantomData};
+use core::hash::{Hash, Hasher};
+use core::{isize, usize};
+use core::convert::From;
+
+use alloc::{Global, Alloc, Layout, box_free, handle_alloc_error};
+use boxed::Box;
+use string::String;
+use vec::Vec;
+
+/// A soft limit on the amount of references that may be made to an `Arc`.
+///
+/// Going above this limit will abort your program (although not
+/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
+const MAX_REFCOUNT: usize = (isize::MAX) as usize;
+
+/// A sentinel value that is used for the pointer of `Weak::new()`.
+const WEAK_EMPTY: usize = 1;
+
+/// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically
+/// Reference Counted'.
+///
+/// The type `Arc<T>` provides shared ownership of a value of type `T`,
+/// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces
+/// a new pointer to the same value in the heap. When the last `Arc`
+/// pointer to a given value is destroyed, the pointed-to value is
+/// also destroyed.
+///
+/// Shared references in Rust disallow mutation by default, and `Arc` is no
+/// exception: you cannot generally obtain a mutable reference to something
+/// inside an `Arc`. If you need to mutate through an `Arc`, use
+/// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
+/// types.
+///
+/// ## Thread Safety
+///
+/// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference
+/// counting. This means that it is thread-safe. The disadvantage is that
+/// atomic operations are more expensive than ordinary memory accesses. If you
+/// are not sharing reference-counted values between threads, consider using
+/// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the
+/// compiler will catch any attempt to send an [`Rc<T>`] between threads.
+/// However, a library might choose `Arc<T>` in order to give library consumers
+/// more flexibility.
+///
+/// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements
+/// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an
+/// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at
+/// first: after all, isn't the point of `Arc<T>` thread safety? The key is
+/// this: `Arc<T>` makes it thread safe to have multiple ownership of the same
+/// data, but it doesn't add thread safety to its data. Consider
+/// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always
+/// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem:
+/// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using
+/// non-atomic operations.
+///
+/// In the end, this means that you may need to pair `Arc<T>` with some sort of
+/// [`std::sync`] type, usually [`Mutex<T>`][mutex].
+///
+/// ## Breaking cycles with `Weak`
+///
+/// The [`downgrade`][downgrade] method can be used to create a non-owning
+/// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d
+/// to an `Arc`, but this will return [`None`] if the value has already been
+/// dropped.
+///
+/// A cycle between `Arc` pointers will never be deallocated. For this reason,
+/// [`Weak`][weak] is used to break cycles. For example, a tree could have
+/// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak]
+/// pointers from children back to their parents.
+///
+/// # Cloning references
+///
+/// Creating a new reference from an existing reference counted pointer is done using the
+/// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak].
+///
+/// ```
+/// use std::sync::Arc;
+/// let foo = Arc::new(vec![1.0, 2.0, 3.0]);
+/// // The two syntaxes below are equivalent.
+/// let a = foo.clone();
+/// let b = Arc::clone(&foo);
+/// // a and b both point to the same memory location as foo.
+/// ```
+///
+/// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly
+/// the meaning of the code. In the example above, this syntax makes it easier to see that
+/// this code is creating a new reference rather than copying the whole content of foo.
+///
+/// ## `Deref` behavior
+///
+/// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait),
+/// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name
+/// clashes with `T`'s methods, the methods of `Arc<T>` itself are [associated
+/// functions][assoc], called using function-like syntax:
+///
+/// ```
+/// use std::sync::Arc;
+/// let my_arc = Arc::new(());
+///
+/// Arc::downgrade(&my_arc);
+/// ```
+///
+/// [`Weak<T>`][weak] does not auto-dereference to `T`, because the value may have
+/// already been destroyed.
+///
+/// [arc]: struct.Arc.html
+/// [weak]: struct.Weak.html
+/// [`Rc<T>`]: ../../std/rc/struct.Rc.html
+/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
+/// [mutex]: ../../std/sync/struct.Mutex.html
+/// [rwlock]: ../../std/sync/struct.RwLock.html
+/// [atomic]: ../../std/sync/atomic/index.html
+/// [`Send`]: ../../std/marker/trait.Send.html
+/// [`Sync`]: ../../std/marker/trait.Sync.html
+/// [deref]: ../../std/ops/trait.Deref.html
+/// [downgrade]: struct.Arc.html#method.downgrade
+/// [upgrade]: struct.Weak.html#method.upgrade
+/// [`None`]: ../../std/option/enum.Option.html#variant.None
+/// [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
+/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
+/// [`std::sync`]: ../../std/sync/index.html
+/// [`Arc::clone(&from)`]: #method.clone
+///
+/// # Examples
+///
+/// Sharing some immutable data between threads:
+///
+// Note that we **do not** run these tests here. The windows builders get super
+// unhappy if a thread outlives the main thread and then exits at the same time
+// (something deadlocks) so we just avoid this entirely by not running these
+// tests.
+/// ```no_run
+/// use std::sync::Arc;
+/// use std::thread;
+///
+/// let five = Arc::new(5);
+///
+/// for _ in 0..10 {
+/// let five = Arc::clone(&five);
+///
+/// thread::spawn(move || {
+/// println!("{:?}", five);
+/// });
+/// }
+/// ```
+///
+/// Sharing a mutable [`AtomicUsize`]:
+///
+/// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html
+///
+/// ```no_run
+/// use std::sync::Arc;
+/// use std::sync::atomic::{AtomicUsize, Ordering};
+/// use std::thread;
+///
+/// let val = Arc::new(AtomicUsize::new(5));
+///
+/// for _ in 0..10 {
+/// let val = Arc::clone(&val);
+///
+/// thread::spawn(move || {
+/// let v = val.fetch_add(1, Ordering::SeqCst);
+/// println!("{:?}", v);
+/// });
+/// }
+/// ```
+///
+/// See the [`rc` documentation][rc_examples] for more examples of reference
+/// counting in general.
+///
+/// [rc_examples]: ../../std/rc/index.html#examples
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Arc<T: ?Sized> {
+ ptr: NonNull<ArcInner<T>>,
+ phantom: PhantomData<T>,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
+
+#[unstable(feature = "coerce_unsized", issue = "27732")]
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
+
+/// `Weak` is a version of [`Arc`] that holds a non-owning reference to the
+/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
+/// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`.
+///
+/// Since a `Weak` reference does not count towards ownership, it will not
+/// prevent the inner value from being dropped, and `Weak` itself makes no
+/// guarantees about the value still being present and may return [`None`]
+/// when [`upgrade`]d.
+///
+/// A `Weak` pointer is useful for keeping a temporary reference to the value
+/// within [`Arc`] without extending its lifetime. It is also used to prevent
+/// circular references between [`Arc`] pointers, since mutual owning references
+/// would never allow either [`Arc`] to be dropped. For example, a tree could
+/// have strong [`Arc`] pointers from parent nodes to children, and `Weak`
+/// pointers from children back to their parents.
+///
+/// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`].
+///
+/// [`Arc`]: struct.Arc.html
+/// [`Arc::downgrade`]: struct.Arc.html#method.downgrade
+/// [`upgrade`]: struct.Weak.html#method.upgrade
+/// [`Option`]: ../../std/option/enum.Option.html
+/// [`None`]: ../../std/option/enum.Option.html#variant.None
+#[stable(feature = "arc_weak", since = "1.4.0")]
+pub struct Weak<T: ?Sized> {
+ // This is a `NonNull` to allow optimizing the size of this type in enums,
+ // but it is actually not truly "non-null". A `Weak::new()` will set this
+ // to a sentinel value, instead of needing to allocate some space in the
+ // heap.
+ ptr: NonNull<ArcInner<T>>,
+}
+
+#[stable(feature = "arc_weak", since = "1.4.0")]
+unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {}
+#[stable(feature = "arc_weak", since = "1.4.0")]
+unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {}
+
+#[unstable(feature = "coerce_unsized", issue = "27732")]
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
+
+#[stable(feature = "arc_weak", since = "1.4.0")]
+impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ write!(f, "(Weak)")
+ }
+}
+
+struct ArcInner<T: ?Sized> {
+ strong: atomic::AtomicUsize,
+
+ // the value usize::MAX acts as a sentinel for temporarily "locking" the
+ // ability to upgrade weak pointers or downgrade strong ones; this is used
+ // to avoid races in `make_mut` and `get_mut`.
+ weak: atomic::AtomicUsize,
+
+ data: T,
+}
+
+unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
+unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
+
+impl<T> Arc<T> {
+ /// Constructs a new `Arc<T>`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn new(data: T) -> Arc<T> {
+ // Start the weak pointer count as 1 which is the weak pointer that's
+ // held by all the strong pointers (kinda), see std/rc.rs for more info
+ let x: Box<_> = box ArcInner {
+ strong: atomic::AtomicUsize::new(1),
+ weak: atomic::AtomicUsize::new(1),
+ data,
+ };
+ Arc { ptr: Box::into_raw_non_null(x), phantom: PhantomData }
+ }
+
+ /// Returns the contained value, if the `Arc` has exactly one strong reference.
+ ///
+ /// Otherwise, an [`Err`][result] is returned with the same `Arc` that was
+ /// passed in.
+ ///
+ /// This will succeed even if there are outstanding weak references.
+ ///
+ /// [result]: ../../std/result/enum.Result.html
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let x = Arc::new(3);
+ /// assert_eq!(Arc::try_unwrap(x), Ok(3));
+ ///
+ /// let x = Arc::new(4);
+ /// let _y = Arc::clone(&x);
+ /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);
+ /// ```
+ #[inline]
+ #[stable(feature = "arc_unique", since = "1.4.0")]
+ pub fn try_unwrap(this: Self) -> Result<T, Self> {
+ // See `drop` for why all these atomics are like this
+ if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() {
+ return Err(this);
+ }
+
+ atomic::fence(Acquire);
+
+ unsafe {
+ let elem = ptr::read(&this.ptr.as_ref().data);
+
+ // Make a weak pointer to clean up the implicit strong-weak reference
+ let _weak = Weak { ptr: this.ptr };
+ mem::forget(this);
+
+ Ok(elem)
+ }
+ }
+}
+
+impl<T: ?Sized> Arc<T> {
+ /// Consumes the `Arc`, returning the wrapped pointer.
+ ///
+ /// To avoid a memory leak the pointer must be converted back to an `Arc` using
+ /// [`Arc::from_raw`][from_raw].
+ ///
+ /// [from_raw]: struct.Arc.html#method.from_raw
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let x = Arc::new(10);
+ /// let x_ptr = Arc::into_raw(x);
+ /// assert_eq!(unsafe { *x_ptr }, 10);
+ /// ```
+ #[stable(feature = "rc_raw", since = "1.17.0")]
+ pub fn into_raw(this: Self) -> *const T {
+ let ptr: *const T = &*this;
+ mem::forget(this);
+ ptr
+ }
+
+ /// Constructs an `Arc` from a raw pointer.
+ ///
+ /// The raw pointer must have been previously returned by a call to a
+ /// [`Arc::into_raw`][into_raw].
+ ///
+ /// This function is unsafe because improper use may lead to memory problems. For example, a
+ /// double-free may occur if the function is called twice on the same raw pointer.
+ ///
+ /// [into_raw]: struct.Arc.html#method.into_raw
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let x = Arc::new(10);
+ /// let x_ptr = Arc::into_raw(x);
+ ///
+ /// unsafe {
+ /// // Convert back to an `Arc` to prevent leak.
+ /// let x = Arc::from_raw(x_ptr);
+ /// assert_eq!(*x, 10);
+ ///
+ /// // Further calls to `Arc::from_raw(x_ptr)` would be memory unsafe.
+ /// }
+ ///
+ /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
+ /// ```
+ #[stable(feature = "rc_raw", since = "1.17.0")]
+ pub unsafe fn from_raw(ptr: *const T) -> Self {
+ // Align the unsized value to the end of the ArcInner.
+ // Because it is ?Sized, it will always be the last field in memory.
+ let align = align_of_val(&*ptr);
+ let layout = Layout::new::<ArcInner<()>>();
+ let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
+
+ // Reverse the offset to find the original ArcInner.
+ let fake_ptr = ptr as *mut ArcInner<T>;
+ let arc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
+
+ Arc {
+ ptr: NonNull::new_unchecked(arc_ptr),
+ phantom: PhantomData,
+ }
+ }
+
+ /// Creates a new [`Weak`][weak] pointer to this value.
+ ///
+ /// [weak]: struct.Weak.html
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// let weak_five = Arc::downgrade(&five);
+ /// ```
+ #[stable(feature = "arc_weak", since = "1.4.0")]
+ pub fn downgrade(this: &Self) -> Weak<T> {
+ // This Relaxed is OK because we're checking the value in the CAS
+ // below.
+ let mut cur = this.inner().weak.load(Relaxed);
+
+ loop {
+ // check if the weak counter is currently "locked"; if so, spin.
+ if cur == usize::MAX {
+ cur = this.inner().weak.load(Relaxed);
+ continue;
+ }
+
+ // NOTE: this code currently ignores the possibility of overflow
+ // into usize::MAX; in general both Rc and Arc need to be adjusted
+ // to deal with overflow.
+
+ // Unlike with Clone(), we need this to be an Acquire read to
+ // synchronize with the write coming from `is_unique`, so that the
+ // events prior to that write happen before this read.
+ match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) {
+ Ok(_) => return Weak { ptr: this.ptr },
+ Err(old) => cur = old,
+ }
+ }
+ }
+
+ /// Gets the number of [`Weak`][weak] pointers to this value.
+ ///
+ /// [weak]: struct.Weak.html
+ ///
+ /// # Safety
+ ///
+ /// This method by itself is safe, but using it correctly requires extra care.
+ /// Another thread can change the weak count at any time,
+ /// including potentially between calling this method and acting on the result.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ /// let _weak_five = Arc::downgrade(&five);
+ ///
+ /// // This assertion is deterministic because we haven't shared
+ /// // the `Arc` or `Weak` between threads.
+ /// assert_eq!(1, Arc::weak_count(&five));
+ /// ```
+ #[inline]
+ #[stable(feature = "arc_counts", since = "1.15.0")]
+ pub fn weak_count(this: &Self) -> usize {
+ let cnt = this.inner().weak.load(SeqCst);
+ // If the weak count is currently locked, the value of the
+ // count was 0 just before taking the lock.
+ if cnt == usize::MAX { 0 } else { cnt - 1 }
+ }
+
+ /// Gets the number of strong (`Arc`) pointers to this value.
+ ///
+ /// # Safety
+ ///
+ /// This method by itself is safe, but using it correctly requires extra care.
+ /// Another thread can change the strong count at any time,
+ /// including potentially between calling this method and acting on the result.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ /// let _also_five = Arc::clone(&five);
+ ///
+ /// // This assertion is deterministic because we haven't shared
+ /// // the `Arc` between threads.
+ /// assert_eq!(2, Arc::strong_count(&five));
+ /// ```
+ #[inline]
+ #[stable(feature = "arc_counts", since = "1.15.0")]
+ pub fn strong_count(this: &Self) -> usize {
+ this.inner().strong.load(SeqCst)
+ }
+
+ #[inline]
+ fn inner(&self) -> &ArcInner<T> {
+ // This unsafety is ok because while this arc is alive we're guaranteed
+ // that the inner pointer is valid. Furthermore, we know that the
+ // `ArcInner` structure itself is `Sync` because the inner data is
+ // `Sync` as well, so we're ok loaning out an immutable pointer to these
+ // contents.
+ unsafe { self.ptr.as_ref() }
+ }
+
+ // Non-inlined part of `drop`.
+ #[inline(never)]
+ unsafe fn drop_slow(&mut self) {
+ // Destroy the data at this time, even though we may not free the box
+ // allocation itself (there may still be weak pointers lying around).
+ ptr::drop_in_place(&mut self.ptr.as_mut().data);
+
+ if self.inner().weak.fetch_sub(1, Release) == 1 {
+ atomic::fence(Acquire);
+ Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
+ }
+ }
+
+ #[inline]
+ #[stable(feature = "ptr_eq", since = "1.17.0")]
+ /// Returns true if the two `Arc`s point to the same value (not
+ /// just values that compare as equal).
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ /// let same_five = Arc::clone(&five);
+ /// let other_five = Arc::new(5);
+ ///
+ /// assert!(Arc::ptr_eq(&five, &same_five));
+ /// assert!(!Arc::ptr_eq(&five, &other_five));
+ /// ```
+ pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+ this.ptr.as_ptr() == other.ptr.as_ptr()
+ }
+}
+
+impl<T: ?Sized> Arc<T> {
+ // Allocates an `ArcInner<T>` with sufficient space for an unsized value
+ unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> {
+ // Create a fake ArcInner to find allocation size and alignment
+ let fake_ptr = ptr as *mut ArcInner<T>;
+
+ let layout = Layout::for_value(&*fake_ptr);
+
+ let mem = Global.alloc(layout)
+ .unwrap_or_else(|_| handle_alloc_error(layout));
+
+ // Initialize the real ArcInner
+ let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut ArcInner<T>;
+
+ ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1));
+ ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1));
+
+ inner
+ }
+
+ fn from_box(v: Box<T>) -> Arc<T> {
+ unsafe {
+ let box_unique = Box::into_unique(v);
+ let bptr = box_unique.as_ptr();
+
+ let value_size = size_of_val(&*bptr);
+ let ptr = Self::allocate_for_ptr(bptr);
+
+ // Copy value as bytes
+ ptr::copy_nonoverlapping(
+ bptr as *const T as *const u8,
+ &mut (*ptr).data as *mut _ as *mut u8,
+ value_size);
+
+ // Free the allocation without dropping its contents
+ box_free(box_unique);
+
+ Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
+ }
+ }
+}
+
+// Sets the data pointer of a `?Sized` raw pointer.
+//
+// For a slice/trait object, this sets the `data` field and leaves the rest
+// unchanged. For a sized raw pointer, this simply sets the pointer.
+unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
+ ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
+ ptr
+}
+
+impl<T> Arc<[T]> {
+ // Copy elements from slice into newly allocated Arc<[T]>
+ //
+ // Unsafe because the caller must either take ownership or bind `T: Copy`
+ unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> {
+ let v_ptr = v as *const [T];
+ let ptr = Self::allocate_for_ptr(v_ptr);
+
+ ptr::copy_nonoverlapping(
+ v.as_ptr(),
+ &mut (*ptr).data as *mut [T] as *mut T,
+ v.len());
+
+ Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
+ }
+}
+
+// Specialization trait used for From<&[T]>
+trait ArcFromSlice<T> {
+ fn from_slice(slice: &[T]) -> Self;
+}
+
+impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
+ #[inline]
+ default fn from_slice(v: &[T]) -> Self {
+ // Panic guard while cloning T elements.
+ // In the event of a panic, elements that have been written
+ // into the new ArcInner will be dropped, then the memory freed.
+ struct Guard<T> {
+ mem: NonNull<u8>,
+ elems: *mut T,
+ layout: Layout,
+ n_elems: usize,
+ }
+
+ impl<T> Drop for Guard<T> {
+ fn drop(&mut self) {
+ use core::slice::from_raw_parts_mut;
+
+ unsafe {
+ let slice = from_raw_parts_mut(self.elems, self.n_elems);
+ ptr::drop_in_place(slice);
+
+ Global.dealloc(self.mem.cast(), self.layout.clone());
+ }
+ }
+ }
+
+ unsafe {
+ let v_ptr = v as *const [T];
+ let ptr = Self::allocate_for_ptr(v_ptr);
+
+ let mem = ptr as *mut _ as *mut u8;
+ let layout = Layout::for_value(&*ptr);
+
+ // Pointer to first element
+ let elems = &mut (*ptr).data as *mut [T] as *mut T;
+
+ let mut guard = Guard{
+ mem: NonNull::new_unchecked(mem),
+ elems: elems,
+ layout: layout,
+ n_elems: 0,
+ };
+
+ for (i, item) in v.iter().enumerate() {
+ ptr::write(elems.offset(i as isize), item.clone());
+ guard.n_elems += 1;
+ }
+
+ // All clear. Forget the guard so it doesn't free the new ArcInner.
+ mem::forget(guard);
+
+ Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
+ }
+ }
+}
+
+impl<T: Copy> ArcFromSlice<T> for Arc<[T]> {
+ #[inline]
+ fn from_slice(v: &[T]) -> Self {
+ unsafe { Arc::copy_from_slice(v) }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Clone for Arc<T> {
+ /// Makes a clone of the `Arc` pointer.
+ ///
+ /// This creates another pointer to the same inner value, increasing the
+ /// strong reference count.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// Arc::clone(&five);
+ /// ```
+ #[inline]
+ fn clone(&self) -> Arc<T> {
+ // Using a relaxed ordering is alright here, as knowledge of the
+ // original reference prevents other threads from erroneously deleting
+ // the object.
+ //
+ // As explained in the [Boost documentation][1], Increasing the
+ // reference counter can always be done with memory_order_relaxed: New
+ // references to an object can only be formed from an existing
+ // reference, and passing an existing reference from one thread to
+ // another must already provide any required synchronization.
+ //
+ // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+ let old_size = self.inner().strong.fetch_add(1, Relaxed);
+
+ // However we need to guard against massive refcounts in case someone
+ // is `mem::forget`ing Arcs. If we don't do this the count can overflow
+ // and users will use-after free. We racily saturate to `isize::MAX` on
+ // the assumption that there aren't ~2 billion threads incrementing
+ // the reference count at once. This branch will never be taken in
+ // any realistic program.
+ //
+ // We abort because such a program is incredibly degenerate, and we
+ // don't care to support it.
+ if old_size > MAX_REFCOUNT {
+ unsafe {
+ abort();
+ }
+ }
+
+ Arc { ptr: self.ptr, phantom: PhantomData }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Deref for Arc<T> {
+ type Target = T;
+
+ #[inline]
+ fn deref(&self) -> &T {
+ &self.inner().data
+ }
+}
+
+impl<T: Clone> Arc<T> {
+ /// Makes a mutable reference into the given `Arc`.
+ ///
+ /// If there are other `Arc` or [`Weak`][weak] pointers to the same value,
+ /// then `make_mut` will invoke [`clone`][clone] on the inner value to
+ /// ensure unique ownership. This is also referred to as clone-on-write.
+ ///
+ /// See also [`get_mut`][get_mut], which will fail rather than cloning.
+ ///
+ /// [weak]: struct.Weak.html
+ /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
+ /// [get_mut]: struct.Arc.html#method.get_mut
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let mut data = Arc::new(5);
+ ///
+ /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
+ /// let mut other_data = Arc::clone(&data); // Won't clone inner data
+ /// *Arc::make_mut(&mut data) += 1; // Clones inner data
+ /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
+ /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
+ ///
+ /// // Now `data` and `other_data` point to different values.
+ /// assert_eq!(*data, 8);
+ /// assert_eq!(*other_data, 12);
+ /// ```
+ #[inline]
+ #[stable(feature = "arc_unique", since = "1.4.0")]
+ pub fn make_mut(this: &mut Self) -> &mut T {
+ // Note that we hold both a strong reference and a weak reference.
+ // Thus, releasing our strong reference only will not, by itself, cause
+ // the memory to be deallocated.
+ //
+ // Use Acquire to ensure that we see any writes to `weak` that happen
+ // before release writes (i.e., decrements) to `strong`. Since we hold a
+ // weak count, there's no chance the ArcInner itself could be
+ // deallocated.
+ if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() {
+ // Another strong pointer exists; clone
+ *this = Arc::new((**this).clone());
+ } else if this.inner().weak.load(Relaxed) != 1 {
+ // Relaxed suffices in the above because this is fundamentally an
+ // optimization: we are always racing with weak pointers being
+ // dropped. Worst case, we end up allocated a new Arc unnecessarily.
+
+ // We removed the last strong ref, but there are additional weak
+ // refs remaining. We'll move the contents to a new Arc, and
+ // invalidate the other weak refs.
+
+ // Note that it is not possible for the read of `weak` to yield
+ // usize::MAX (i.e., locked), since the weak count can only be
+ // locked by a thread with a strong reference.
+
+ // Materialize our own implicit weak pointer, so that it can clean
+ // up the ArcInner as needed.
+ let weak = Weak { ptr: this.ptr };
+
+ // mark the data itself as already deallocated
+ unsafe {
+ // there is no data race in the implicit write caused by `read`
+ // here (due to zeroing) because data is no longer accessed by
+ // other threads (due to there being no more strong refs at this
+ // point).
+ let mut swap = Arc::new(ptr::read(&weak.ptr.as_ref().data));
+ mem::swap(this, &mut swap);
+ mem::forget(swap);
+ }
+ } else {
+ // We were the sole reference of either kind; bump back up the
+ // strong ref count.
+ this.inner().strong.store(1, Release);
+ }
+
+ // As with `get_mut()`, the unsafety is ok because our reference was
+ // either unique to begin with, or became one upon cloning the contents.
+ unsafe {
+ &mut this.ptr.as_mut().data
+ }
+ }
+}
+
+impl<T: ?Sized> Arc<T> {
+ /// Returns a mutable reference to the inner value, if there are
+ /// no other `Arc` or [`Weak`][weak] pointers to the same value.
+ ///
+ /// Returns [`None`][option] otherwise, because it is not safe to
+ /// mutate a shared value.
+ ///
+ /// See also [`make_mut`][make_mut], which will [`clone`][clone]
+ /// the inner value when it's shared.
+ ///
+ /// [weak]: struct.Weak.html
+ /// [option]: ../../std/option/enum.Option.html
+ /// [make_mut]: struct.Arc.html#method.make_mut
+ /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let mut x = Arc::new(3);
+ /// *Arc::get_mut(&mut x).unwrap() = 4;
+ /// assert_eq!(*x, 4);
+ ///
+ /// let _y = Arc::clone(&x);
+ /// assert!(Arc::get_mut(&mut x).is_none());
+ /// ```
+ #[inline]
+ #[stable(feature = "arc_unique", since = "1.4.0")]
+ pub fn get_mut(this: &mut Self) -> Option<&mut T> {
+ if this.is_unique() {
+ // This unsafety is ok because we're guaranteed that the pointer
+ // returned is the *only* pointer that will ever be returned to T. Our
+ // reference count is guaranteed to be 1 at this point, and we required
+ // the Arc itself to be `mut`, so we're returning the only possible
+ // reference to the inner data.
+ unsafe {
+ Some(&mut this.ptr.as_mut().data)
+ }
+ } else {
+ None
+ }
+ }
+
+ /// Determine whether this is the unique reference (including weak refs) to
+ /// the underlying data.
+ ///
+ /// Note that this requires locking the weak ref count.
+ fn is_unique(&mut self) -> bool {
+ // lock the weak pointer count if we appear to be the sole weak pointer
+ // holder.
+ //
+ // The acquire label here ensures a happens-before relationship with any
+ // writes to `strong` prior to decrements of the `weak` count (via drop,
+ // which uses Release).
+ if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() {
+ // Due to the previous acquire read, this will observe any writes to
+ // `strong` that were due to upgrading weak pointers; only strong
+ // clones remain, which require that the strong count is > 1 anyway.
+ let unique = self.inner().strong.load(Relaxed) == 1;
+
+ // The release write here synchronizes with a read in `downgrade`,
+ // effectively preventing the above read of `strong` from happening
+ // after the write.
+ self.inner().weak.store(1, Release); // release the lock
+ unique
+ } else {
+ false
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
+ /// Drops the `Arc`.
+ ///
+ /// This will decrement the strong reference count. If the strong reference
+ /// count reaches zero then the only other references (if any) are
+ /// [`Weak`][weak], so we `drop` the inner value.
+ ///
+ /// [weak]: struct.Weak.html
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// struct Foo;
+ ///
+ /// impl Drop for Foo {
+ /// fn drop(&mut self) {
+ /// println!("dropped!");
+ /// }
+ /// }
+ ///
+ /// let foo = Arc::new(Foo);
+ /// let foo2 = Arc::clone(&foo);
+ ///
+ /// drop(foo); // Doesn't print anything
+ /// drop(foo2); // Prints "dropped!"
+ /// ```
+ #[inline]
+ fn drop(&mut self) {
+ // Because `fetch_sub` is already atomic, we do not need to synchronize
+ // with other threads unless we are going to delete the object. This
+ // same logic applies to the below `fetch_sub` to the `weak` count.
+ if self.inner().strong.fetch_sub(1, Release) != 1 {
+ return;
+ }
+
+ // This fence is needed to prevent reordering of use of the data and
+ // deletion of the data. Because it is marked `Release`, the decreasing
+ // of the reference count synchronizes with this `Acquire` fence. This
+ // means that use of the data happens before decreasing the reference
+ // count, which happens before this fence, which happens before the
+ // deletion of the data.
+ //
+ // As explained in the [Boost documentation][1],
+ //
+ // > It is important to enforce any possible access to the object in one
+ // > thread (through an existing reference) to *happen before* deleting
+ // > the object in a different thread. This is achieved by a "release"
+ // > operation after dropping a reference (any access to the object
+ // > through this reference must obviously happened before), and an
+ // > "acquire" operation before deleting the object.
+ //
+ // In particular, while the contents of an Arc are usually immutable, it's
+ // possible to have interior writes to something like a Mutex<T>. Since a
+ // Mutex is not acquired when it is deleted, we can't rely on its
+ // synchronization logic to make writes in thread A visible to a destructor
+ // running in thread B.
+ //
+ // Also note that the Acquire fence here could probably be replaced with an
+ // Acquire load, which could improve performance in highly-contended
+ // situations. See [2].
+ //
+ // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+ // [2]: (https://github.com/rust-lang/rust/pull/41714)
+ atomic::fence(Acquire);
+
+ unsafe {
+ self.drop_slow();
+ }
+ }
+}
+
+impl Arc<Any + Send + Sync> {
+ #[inline]
+ #[unstable(feature = "rc_downcast", issue = "44608")]
+ /// Attempt to downcast the `Arc<Any + Send + Sync>` to a concrete type.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(rc_downcast)]
+ /// use std::any::Any;
+ /// use std::sync::Arc;
+ ///
+ /// fn print_if_string(value: Arc<Any + Send + Sync>) {
+ /// if let Ok(string) = value.downcast::<String>() {
+ /// println!("String ({}): {}", string.len(), string);
+ /// }
+ /// }
+ ///
+ /// fn main() {
+ /// let my_string = "Hello World".to_string();
+ /// print_if_string(Arc::new(my_string));
+ /// print_if_string(Arc::new(0i8));
+ /// }
+ /// ```
+ pub fn downcast<T>(self) -> Result<Arc<T>, Self>
+ where
+ T: Any + Send + Sync + 'static,
+ {
+ if (*self).is::<T>() {
+ let ptr = self.ptr.cast::<ArcInner<T>>();
+ mem::forget(self);
+ Ok(Arc { ptr, phantom: PhantomData })
+ } else {
+ Err(self)
+ }
+ }
+}
+
+impl<T> Weak<T> {
+ /// Constructs a new `Weak<T>`, without allocating any memory.
+ /// Calling [`upgrade`] on the return value always gives [`None`].
+ ///
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html#variant.None
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Weak;
+ ///
+ /// let empty: Weak<i64> = Weak::new();
+ /// assert!(empty.upgrade().is_none());
+ /// ```
+ #[stable(feature = "downgraded_weak", since = "1.10.0")]
+ pub fn new() -> Weak<T> {
+ unsafe {
+ Weak {
+ ptr: NonNull::new_unchecked(WEAK_EMPTY as *mut _),
+ }
+ }
+ }
+}
+
+impl<T: ?Sized> Weak<T> {
+ /// Attempts to upgrade the `Weak` pointer to an [`Arc`], extending
+ /// the lifetime of the value if successful.
+ ///
+ /// Returns [`None`] if the value has since been dropped.
+ ///
+ /// [`Arc`]: struct.Arc.html
+ /// [`None`]: ../../std/option/enum.Option.html#variant.None
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// let weak_five = Arc::downgrade(&five);
+ ///
+ /// let strong_five: Option<Arc<_>> = weak_five.upgrade();
+ /// assert!(strong_five.is_some());
+ ///
+ /// // Destroy all strong pointers.
+ /// drop(strong_five);
+ /// drop(five);
+ ///
+ /// assert!(weak_five.upgrade().is_none());
+ /// ```
+ #[stable(feature = "arc_weak", since = "1.4.0")]
+ pub fn upgrade(&self) -> Option<Arc<T>> {
+ // We use a CAS loop to increment the strong count instead of a
+ // fetch_add because once the count hits 0 it must never be above 0.
+ let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
+ return None;
+ } else {
+ unsafe { self.ptr.as_ref() }
+ };
+
+ // Relaxed load because any write of 0 that we can observe
+ // leaves the field in a permanently zero state (so a
+ // "stale" read of 0 is fine), and any other value is
+ // confirmed via the CAS below.
+ let mut n = inner.strong.load(Relaxed);
+
+ loop {
+ if n == 0 {
+ return None;
+ }
+
+ // See comments in `Arc::clone` for why we do this (for `mem::forget`).
+ if n > MAX_REFCOUNT {
+ unsafe {
+ abort();
+ }
+ }
+
+ // Relaxed is valid for the same reason it is on Arc's Clone impl
+ match inner.strong.compare_exchange_weak(n, n + 1, Relaxed, Relaxed) {
+ Ok(_) => return Some(Arc {
+ // null checked above
+ ptr: self.ptr,
+ phantom: PhantomData,
+ }),
+ Err(old) => n = old,
+ }
+ }
+ }
+}
+
+#[stable(feature = "arc_weak", since = "1.4.0")]
+impl<T: ?Sized> Clone for Weak<T> {
+ /// Makes a clone of the `Weak` pointer that points to the same value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::{Arc, Weak};
+ ///
+ /// let weak_five = Arc::downgrade(&Arc::new(5));
+ ///
+ /// Weak::clone(&weak_five);
+ /// ```
+ #[inline]
+ fn clone(&self) -> Weak<T> {
+ let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
+ return Weak { ptr: self.ptr };
+ } else {
+ unsafe { self.ptr.as_ref() }
+ };
+ // See comments in Arc::clone() for why this is relaxed. This can use a
+ // fetch_add (ignoring the lock) because the weak count is only locked
+ // where are *no other* weak pointers in existence. (So we can't be
+ // running this code in that case).
+ let old_size = inner.weak.fetch_add(1, Relaxed);
+
+ // See comments in Arc::clone() for why we do this (for mem::forget).
+ if old_size > MAX_REFCOUNT {
+ unsafe {
+ abort();
+ }
+ }
+
+ return Weak { ptr: self.ptr };
+ }
+}
+
+#[stable(feature = "downgraded_weak", since = "1.10.0")]
+impl<T> Default for Weak<T> {
+ /// Constructs a new `Weak<T>`, without allocating memory.
+ /// Calling [`upgrade`] on the return value always gives [`None`].
+ ///
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html#variant.None
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Weak;
+ ///
+ /// let empty: Weak<i64> = Default::default();
+ /// assert!(empty.upgrade().is_none());
+ /// ```
+ fn default() -> Weak<T> {
+ Weak::new()
+ }
+}
+
+#[stable(feature = "arc_weak", since = "1.4.0")]
+impl<T: ?Sized> Drop for Weak<T> {
+ /// Drops the `Weak` pointer.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::{Arc, Weak};
+ ///
+ /// struct Foo;
+ ///
+ /// impl Drop for Foo {
+ /// fn drop(&mut self) {
+ /// println!("dropped!");
+ /// }
+ /// }
+ ///
+ /// let foo = Arc::new(Foo);
+ /// let weak_foo = Arc::downgrade(&foo);
+ /// let other_weak_foo = Weak::clone(&weak_foo);
+ ///
+ /// drop(weak_foo); // Doesn't print anything
+ /// drop(foo); // Prints "dropped!"
+ ///
+ /// assert!(other_weak_foo.upgrade().is_none());
+ /// ```
+ fn drop(&mut self) {
+ // If we find out that we were the last weak pointer, then its time to
+ // deallocate the data entirely. See the discussion in Arc::drop() about
+ // the memory orderings
+ //
+ // It's not necessary to check for the locked state here, because the
+ // weak count can only be locked if there was precisely one weak ref,
+ // meaning that drop could only subsequently run ON that remaining weak
+ // ref, which can only happen after the lock is released.
+ let inner = if self.ptr.as_ptr() as *const u8 as usize == WEAK_EMPTY {
+ return;
+ } else {
+ unsafe { self.ptr.as_ref() }
+ };
+
+ if inner.weak.fetch_sub(1, Release) == 1 {
+ atomic::fence(Acquire);
+ unsafe {
+ Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
+ }
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
+ /// Equality for two `Arc`s.
+ ///
+ /// Two `Arc`s are equal if their inner values are equal.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five == Arc::new(5));
+ /// ```
+ fn eq(&self, other: &Arc<T>) -> bool {
+ *(*self) == *(*other)
+ }
+
+ /// Inequality for two `Arc`s.
+ ///
+ /// Two `Arc`s are unequal if their inner values are unequal.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five != Arc::new(6));
+ /// ```
+ fn ne(&self, other: &Arc<T>) -> bool {
+ *(*self) != *(*other)
+ }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
+ /// Partial comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `partial_cmp()` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ /// use std::cmp::Ordering;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6)));
+ /// ```
+ fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
+ (**self).partial_cmp(&**other)
+ }
+
+ /// Less-than comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `<` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five < Arc::new(6));
+ /// ```
+ fn lt(&self, other: &Arc<T>) -> bool {
+ *(*self) < *(*other)
+ }
+
+ /// 'Less than or equal to' comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `<=` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five <= Arc::new(5));
+ /// ```
+ fn le(&self, other: &Arc<T>) -> bool {
+ *(*self) <= *(*other)
+ }
+
+ /// Greater-than comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `>` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five > Arc::new(4));
+ /// ```
+ fn gt(&self, other: &Arc<T>) -> bool {
+ *(*self) > *(*other)
+ }
+
+ /// 'Greater than or equal to' comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `>=` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert!(five >= Arc::new(5));
+ /// ```
+ fn ge(&self, other: &Arc<T>) -> bool {
+ *(*self) >= *(*other)
+ }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Ord> Ord for Arc<T> {
+ /// Comparison for two `Arc`s.
+ ///
+ /// The two are compared by calling `cmp()` on their inner values.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ /// use std::cmp::Ordering;
+ ///
+ /// let five = Arc::new(5);
+ ///
+ /// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6)));
+ /// ```
+ fn cmp(&self, other: &Arc<T>) -> Ordering {
+ (**self).cmp(&**other)
+ }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Eq> Eq for Arc<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ fmt::Display::fmt(&**self, f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ fmt::Debug::fmt(&**self, f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> fmt::Pointer for Arc<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ fmt::Pointer::fmt(&(&**self as *const T), f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Default> Default for Arc<T> {
+ /// Creates a new `Arc<T>`, with the `Default` value for `T`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::Arc;
+ ///
+ /// let x: Arc<i32> = Default::default();
+ /// assert_eq!(*x, 0);
+ /// ```
+ fn default() -> Arc<T> {
+ Arc::new(Default::default())
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Hash> Hash for Arc<T> {
+ fn hash<H: Hasher>(&self, state: &mut H) {
+ (**self).hash(state)
+ }
+}
+
+#[stable(feature = "from_for_ptrs", since = "1.6.0")]
+impl<T> From<T> for Arc<T> {
+ fn from(t: T) -> Self {
+ Arc::new(t)
+ }
+}
+
+#[stable(feature = "shared_from_slice", since = "1.21.0")]
+impl<'a, T: Clone> From<&'a [T]> for Arc<[T]> {
+ #[inline]
+ fn from(v: &[T]) -> Arc<[T]> {
+ <Self as ArcFromSlice<T>>::from_slice(v)
+ }
+}
+
+#[stable(feature = "shared_from_slice", since = "1.21.0")]
+impl<'a> From<&'a str> for Arc<str> {
+ #[inline]
+ fn from(v: &str) -> Arc<str> {
+ let arc = Arc::<[u8]>::from(v.as_bytes());
+ unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) }
+ }
+}
+
+#[stable(feature = "shared_from_slice", since = "1.21.0")]
+impl From<String> for Arc<str> {
+ #[inline]
+ fn from(v: String) -> Arc<str> {
+ Arc::from(&v[..])
+ }
+}
+
+#[stable(feature = "shared_from_slice", since = "1.21.0")]
+impl<T: ?Sized> From<Box<T>> for Arc<T> {
+ #[inline]
+ fn from(v: Box<T>) -> Arc<T> {
+ Arc::from_box(v)
+ }
+}
+
+#[stable(feature = "shared_from_slice", since = "1.21.0")]
+impl<T> From<Vec<T>> for Arc<[T]> {
+ #[inline]
+ fn from(mut v: Vec<T>) -> Arc<[T]> {
+ unsafe {
+ let arc = Arc::copy_from_slice(&v);
+
+ // Allow the Vec to free its memory, but not destroy its contents
+ v.set_len(0);
+
+ arc
+ }
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use std::boxed::Box;
+ use std::clone::Clone;
+ use std::sync::mpsc::channel;
+ use std::mem::drop;
+ use std::ops::Drop;
+ use std::option::Option;
+ use std::option::Option::{None, Some};
+ use std::sync::atomic;
+ use std::sync::atomic::Ordering::{Acquire, SeqCst};
+ use std::thread;
+ use std::sync::Mutex;
+ use std::convert::From;
+
+ use super::{Arc, Weak};
+ use vec::Vec;
+
+ struct Canary(*mut atomic::AtomicUsize);
+
+ impl Drop for Canary {
+ fn drop(&mut self) {
+ unsafe {
+ match *self {
+ Canary(c) => {
+ (*c).fetch_add(1, SeqCst);
+ }
+ }
+ }
+ }
+ }
+
+ #[test]
+ #[cfg_attr(target_os = "emscripten", ignore)]
+ fn manually_share_arc() {
+ let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+ let arc_v = Arc::new(v);
+
+ let (tx, rx) = channel();
+
+ let _t = thread::spawn(move || {
+ let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
+ assert_eq!((*arc_v)[3], 4);
+ });
+
+ tx.send(arc_v.clone()).unwrap();
+
+ assert_eq!((*arc_v)[2], 3);
+ assert_eq!((*arc_v)[4], 5);
+ }
+
+ #[test]
+ fn test_arc_get_mut() {
+ let mut x = Arc::new(3);
+ *Arc::get_mut(&mut x).unwrap() = 4;
+ assert_eq!(*x, 4);
+ let y = x.clone();
+ assert!(Arc::get_mut(&mut x).is_none());
+ drop(y);
+ assert!(Arc::get_mut(&mut x).is_some());
+ let _w = Arc::downgrade(&x);
+ assert!(Arc::get_mut(&mut x).is_none());
+ }
+
+ #[test]
+ fn try_unwrap() {
+ let x = Arc::new(3);
+ assert_eq!(Arc::try_unwrap(x), Ok(3));
+ let x = Arc::new(4);
+ let _y = x.clone();
+ assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
+ let x = Arc::new(5);
+ let _w = Arc::downgrade(&x);
+ assert_eq!(Arc::try_unwrap(x), Ok(5));
+ }
+
+ #[test]
+ fn into_from_raw() {
+ let x = Arc::new(box "hello");
+ let y = x.clone();
+
+ let x_ptr = Arc::into_raw(x);
+ drop(y);
+ unsafe {
+ assert_eq!(**x_ptr, "hello");
+
+ let x = Arc::from_raw(x_ptr);
+ assert_eq!(**x, "hello");
+
+ assert_eq!(Arc::try_unwrap(x).map(|x| *x), Ok("hello"));
+ }
+ }
+
+ #[test]
+ fn test_into_from_raw_unsized() {
+ use std::fmt::Display;
+ use std::string::ToString;
+
+ let arc: Arc<str> = Arc::from("foo");
+
+ let ptr = Arc::into_raw(arc.clone());
+ let arc2 = unsafe { Arc::from_raw(ptr) };
+
+ assert_eq!(unsafe { &*ptr }, "foo");
+ assert_eq!(arc, arc2);
+
+ let arc: Arc<Display> = Arc::new(123);
+
+ let ptr = Arc::into_raw(arc.clone());
+ let arc2 = unsafe { Arc::from_raw(ptr) };
+
+ assert_eq!(unsafe { &*ptr }.to_string(), "123");
+ assert_eq!(arc2.to_string(), "123");
+ }
+
+ #[test]
+ fn test_cowarc_clone_make_mut() {
+ let mut cow0 = Arc::new(75);
+ let mut cow1 = cow0.clone();
+ let mut cow2 = cow1.clone();
+
+ assert!(75 == *Arc::make_mut(&mut cow0));
+ assert!(75 == *Arc::make_mut(&mut cow1));
+ assert!(75 == *Arc::make_mut(&mut cow2));
+
+ *Arc::make_mut(&mut cow0) += 1;
+ *Arc::make_mut(&mut cow1) += 2;
+ *Arc::make_mut(&mut cow2) += 3;
+
+ assert!(76 == *cow0);
+ assert!(77 == *cow1);
+ assert!(78 == *cow2);
+
+ // none should point to the same backing memory
+ assert!(*cow0 != *cow1);
+ assert!(*cow0 != *cow2);
+ assert!(*cow1 != *cow2);
+ }
+
+ #[test]
+ fn test_cowarc_clone_unique2() {
+ let mut cow0 = Arc::new(75);
+ let cow1 = cow0.clone();
+ let cow2 = cow1.clone();
+
+ assert!(75 == *cow0);
+ assert!(75 == *cow1);
+ assert!(75 == *cow2);
+
+ *Arc::make_mut(&mut cow0) += 1;
+ assert!(76 == *cow0);
+ assert!(75 == *cow1);
+ assert!(75 == *cow2);
+
+ // cow1 and cow2 should share the same contents
+ // cow0 should have a unique reference
+ assert!(*cow0 != *cow1);
+ assert!(*cow0 != *cow2);
+ assert!(*cow1 == *cow2);
+ }
+
+ #[test]
+ fn test_cowarc_clone_weak() {
+ let mut cow0 = Arc::new(75);
+ let cow1_weak = Arc::downgrade(&cow0);
+
+ assert!(75 == *cow0);
+ assert!(75 == *cow1_weak.upgrade().unwrap());
+
+ *Arc::make_mut(&mut cow0) += 1;
+
+ assert!(76 == *cow0);
+ assert!(cow1_weak.upgrade().is_none());
+ }
+
+ #[test]
+ fn test_live() {
+ let x = Arc::new(5);
+ let y = Arc::downgrade(&x);
+ assert!(y.upgrade().is_some());
+ }
+
+ #[test]
+ fn test_dead() {
+ let x = Arc::new(5);
+ let y = Arc::downgrade(&x);
+ drop(x);
+ assert!(y.upgrade().is_none());
+ }
+
+ #[test]
+ fn weak_self_cyclic() {
+ struct Cycle {
+ x: Mutex<Option<Weak<Cycle>>>,
+ }
+
+ let a = Arc::new(Cycle { x: Mutex::new(None) });
+ let b = Arc::downgrade(&a.clone());
+ *a.x.lock().unwrap() = Some(b);
+
+ // hopefully we don't double-free (or leak)...
+ }
+
+ #[test]
+ fn drop_arc() {
+ let mut canary = atomic::AtomicUsize::new(0);
+ let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
+ drop(x);
+ assert!(canary.load(Acquire) == 1);
+ }
+
+ #[test]
+ fn drop_arc_weak() {
+ let mut canary = atomic::AtomicUsize::new(0);
+ let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
+ let arc_weak = Arc::downgrade(&arc);
+ assert!(canary.load(Acquire) == 0);
+ drop(arc);
+ assert!(canary.load(Acquire) == 1);
+ drop(arc_weak);
+ }
+
+ #[test]
+ fn test_strong_count() {
+ let a = Arc::new(0);
+ assert!(Arc::strong_count(&a) == 1);
+ let w = Arc::downgrade(&a);
+ assert!(Arc::strong_count(&a) == 1);
+ let b = w.upgrade().expect("");
+ assert!(Arc::strong_count(&b) == 2);
+ assert!(Arc::strong_count(&a) == 2);
+ drop(w);
+ drop(a);
+ assert!(Arc::strong_count(&b) == 1);
+ let c = b.clone();
+ assert!(Arc::strong_count(&b) == 2);
+ assert!(Arc::strong_count(&c) == 2);
+ }
+
+ #[test]
+ fn test_weak_count() {
+ let a = Arc::new(0);
+ assert!(Arc::strong_count(&a) == 1);
+ assert!(Arc::weak_count(&a) == 0);
+ let w = Arc::downgrade(&a);
+ assert!(Arc::strong_count(&a) == 1);
+ assert!(Arc::weak_count(&a) == 1);
+ let x = w.clone();
+ assert!(Arc::weak_count(&a) == 2);
+ drop(w);
+ drop(x);
+ assert!(Arc::strong_count(&a) == 1);
+ assert!(Arc::weak_count(&a) == 0);
+ let c = a.clone();
+ assert!(Arc::strong_count(&a) == 2);
+ assert!(Arc::weak_count(&a) == 0);
+ let d = Arc::downgrade(&c);
+ assert!(Arc::weak_count(&c) == 1);
+ assert!(Arc::strong_count(&c) == 2);
+
+ drop(a);
+ drop(c);
+ drop(d);
+ }
+
+ #[test]
+ fn show_arc() {
+ let a = Arc::new(5);
+ assert_eq!(format!("{:?}", a), "5");
+ }
+
+ // Make sure deriving works with Arc<T>
+ #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
+ struct Foo {
+ inner: Arc<i32>,
+ }
+
+ #[test]
+ fn test_unsized() {
+ let x: Arc<[i32]> = Arc::new([1, 2, 3]);
+ assert_eq!(format!("{:?}", x), "[1, 2, 3]");
+ let y = Arc::downgrade(&x.clone());
+ drop(x);
+ assert!(y.upgrade().is_none());
+ }
+
+ #[test]
+ fn test_from_owned() {
+ let foo = 123;
+ let foo_arc = Arc::from(foo);
+ assert!(123 == *foo_arc);
+ }
+
+ #[test]
+ fn test_new_weak() {
+ let foo: Weak<usize> = Weak::new();
+ assert!(foo.upgrade().is_none());
+ }
+
+ #[test]
+ fn test_ptr_eq() {
+ let five = Arc::new(5);
+ let same_five = five.clone();
+ let other_five = Arc::new(5);
+
+ assert!(Arc::ptr_eq(&five, &same_five));
+ assert!(!Arc::ptr_eq(&five, &other_five));
+ }
+
+ #[test]
+ #[cfg_attr(target_os = "emscripten", ignore)]
+ fn test_weak_count_locked() {
+ let mut a = Arc::new(atomic::AtomicBool::new(false));
+ let a2 = a.clone();
+ let t = thread::spawn(move || {
+ for _i in 0..1000000 {
+ Arc::get_mut(&mut a);
+ }
+ a.store(true, SeqCst);
+ });
+
+ while !a2.load(SeqCst) {
+ let n = Arc::weak_count(&a2);
+ assert!(n < 2, "bad weak count: {}", n);
+ }
+ t.join().unwrap();
+ }
+
+ #[test]
+ fn test_from_str() {
+ let r: Arc<str> = Arc::from("foo");
+
+ assert_eq!(&r[..], "foo");
+ }
+
+ #[test]
+ fn test_copy_from_slice() {
+ let s: &[u32] = &[1, 2, 3];
+ let r: Arc<[u32]> = Arc::from(s);
+
+ assert_eq!(&r[..], [1, 2, 3]);
+ }
+
+ #[test]
+ fn test_clone_from_slice() {
+ #[derive(Clone, Debug, Eq, PartialEq)]
+ struct X(u32);
+
+ let s: &[X] = &[X(1), X(2), X(3)];
+ let r: Arc<[X]> = Arc::from(s);
+
+ assert_eq!(&r[..], s);
+ }
+
+ #[test]
+ #[should_panic]
+ fn test_clone_from_slice_panic() {
+ use std::string::{String, ToString};
+
+ struct Fail(u32, String);
+
+ impl Clone for Fail {
+ fn clone(&self) -> Fail {
+ if self.0 == 2 {
+ panic!();
+ }
+ Fail(self.0, self.1.clone())
+ }
+ }
+
+ let s: &[Fail] = &[
+ Fail(0, "foo".to_string()),
+ Fail(1, "bar".to_string()),
+ Fail(2, "baz".to_string()),
+ ];
+
+ // Should panic, but not cause memory corruption
+ let _r: Arc<[Fail]> = Arc::from(s);
+ }
+
+ #[test]
+ fn test_from_box() {
+ let b: Box<u32> = box 123;
+ let r: Arc<u32> = Arc::from(b);
+
+ assert_eq!(*r, 123);
+ }
+
+ #[test]
+ fn test_from_box_str() {
+ use std::string::String;
+
+ let s = String::from("foo").into_boxed_str();
+ let r: Arc<str> = Arc::from(s);
+
+ assert_eq!(&r[..], "foo");
+ }
+
+ #[test]
+ fn test_from_box_slice() {
+ let s = vec![1, 2, 3].into_boxed_slice();
+ let r: Arc<[u32]> = Arc::from(s);
+
+ assert_eq!(&r[..], [1, 2, 3]);
+ }
+
+ #[test]
+ fn test_from_box_trait() {
+ use std::fmt::Display;
+ use std::string::ToString;
+
+ let b: Box<Display> = box 123;
+ let r: Arc<Display> = Arc::from(b);
+
+ assert_eq!(r.to_string(), "123");
+ }
+
+ #[test]
+ fn test_from_box_trait_zero_sized() {
+ use std::fmt::Debug;
+
+ let b: Box<Debug> = box ();
+ let r: Arc<Debug> = Arc::from(b);
+
+ assert_eq!(format!("{:?}", r), "()");
+ }
+
+ #[test]
+ fn test_from_vec() {
+ let v = vec![1, 2, 3];
+ let r: Arc<[u32]> = Arc::from(v);
+
+ assert_eq!(&r[..], [1, 2, 3]);
+ }
+
+ #[test]
+ fn test_downcast() {
+ use std::any::Any;
+
+ let r1: Arc<Any + Send + Sync> = Arc::new(i32::max_value());
+ let r2: Arc<Any + Send + Sync> = Arc::new("abc");
+
+ assert!(r1.clone().downcast::<u32>().is_err());
+
+ let r1i32 = r1.downcast::<i32>();
+ assert!(r1i32.is_ok());
+ assert_eq!(r1i32.unwrap(), Arc::new(i32::max_value()));
+
+ assert!(r2.clone().downcast::<i32>().is_err());
+
+ let r2str = r2.downcast::<&'static str>();
+ assert!(r2str.is_ok());
+ assert_eq!(r2str.unwrap(), Arc::new("abc"));
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
+ fn borrow(&self) -> &T {
+ &**self
+ }
+}
+
+#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
+impl<T: ?Sized> AsRef<T> for Arc<T> {
+ fn as_ref(&self) -> &T {
+ &**self
+ }
+}
#[cfg(target_has_atomic = "ptr")]
mod if_arc {
use super::*;
- use arc::Arc;
use core::marker::PhantomData;
use core::mem;
use core::ptr::{self, NonNull};
+ use sync::Arc;
/// A way of waking up a specific task.
///
#![stable(feature = "rust1", since = "1.0.0")]
#[stable(feature = "rust1", since = "1.0.0")]
-pub use alloc_crate::arc::{Arc, Weak};
+pub use alloc_crate::sync::{Arc, Weak};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::sync::atomic;
projects / rust.git / commitdiff