5e251b74eb
There are a few exceptions to the rule that Arc/Rc are immutable. Rather than dig into the details, add "generally" to hint at this difference, as it's kind of a distraction at this point in the docs. Additionally, Arc's docs were slightly different here generally, so add in both the existing language and the exception. Fixes #44105
1862 lines
57 KiB
Rust
1862 lines
57 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![stable(feature = "rust1", since = "1.0.0")]
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//! Thread-safe reference-counting pointers.
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//!
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//! See the [`Arc<T>`][arc] documentation for more details.
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//!
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//! [arc]: struct.Arc.html
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use core::sync::atomic;
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use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
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use core::borrow;
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use core::fmt;
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use core::cmp::Ordering;
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use core::intrinsics::abort;
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use core::mem::{self, align_of_val, size_of_val, uninitialized};
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use core::ops::Deref;
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use core::ops::CoerceUnsized;
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use core::ptr::{self, Shared};
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use core::marker::Unsize;
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use core::hash::{Hash, Hasher};
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use core::{isize, usize};
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use core::convert::From;
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use heap::{Heap, Alloc, Layout, box_free};
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use boxed::Box;
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use string::String;
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use vec::Vec;
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/// A soft limit on the amount of references that may be made to an `Arc`.
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///
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/// Going above this limit will abort your program (although not
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/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
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const MAX_REFCOUNT: usize = (isize::MAX) as usize;
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/// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically
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/// Reference Counted'.
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///
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/// The type `Arc<T>` provides shared ownership of a value of type `T`,
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/// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces
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/// a new pointer to the same value in the heap. When the last `Arc`
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/// pointer to a given value is destroyed, the pointed-to value is
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/// also destroyed.
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///
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/// Shared references in Rust disallow mutation by default, and `Arc` is no
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/// exception: you cannot generally obtain a mutable reference to something
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/// inside an `Arc`. If you need to mutate through an `Arc`, use
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/// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
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/// types.
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///
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/// ## Thread Safety
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///
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/// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference
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/// counting This means that it is thread-safe. The disadvantage is that
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/// atomic operations are more expensive than ordinary memory accesses. If you
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/// are not sharing reference-counted values between threads, consider using
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/// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the
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/// compiler will catch any attempt to send an [`Rc<T>`] between threads.
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/// However, a library might choose `Arc<T>` in order to give library consumers
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/// more flexibility.
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///
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/// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements
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/// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an
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/// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at
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/// first: after all, isn't the point of `Arc<T>` thread safety? The key is
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/// this: `Arc<T>` makes it thread safe to have multiple ownership of the same
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/// data, but it doesn't add thread safety to its data. Consider
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/// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always
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/// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem:
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/// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using
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/// non-atomic operations.
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///
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/// In the end, this means that you may need to pair `Arc<T>` with some sort of
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/// [`std::sync`] type, usually [`Mutex<T>`][mutex].
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///
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/// ## Breaking cycles with `Weak`
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///
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/// The [`downgrade`][downgrade] method can be used to create a non-owning
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/// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d
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/// to an `Arc`, but this will return [`None`] if the value has already been
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/// dropped.
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///
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/// A cycle between `Arc` pointers will never be deallocated. For this reason,
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/// [`Weak`][weak] is used to break cycles. For example, a tree could have
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/// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak]
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/// pointers from children back to their parents.
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///
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/// # Cloning references
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///
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/// Creating a new reference from an existing reference counted pointer is done using the
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/// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak].
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///
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/// ```
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/// use std::sync::Arc;
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/// let foo = Arc::new(vec![1.0, 2.0, 3.0]);
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/// // The two syntaxes below are equivalent.
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/// let a = foo.clone();
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/// let b = Arc::clone(&foo);
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/// // a and b both point to the same memory location as foo.
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/// ```
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///
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/// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly
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/// the meaning of the code. In the example above, this syntax makes it easier to see that
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/// this code is creating a new reference rather than copying the whole content of foo.
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///
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/// ## `Deref` behavior
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///
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/// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait),
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/// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name
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/// clashes with `T`'s methods, the methods of `Arc<T>` itself are [associated
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/// functions][assoc], called using function-like syntax:
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///
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/// ```
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/// use std::sync::Arc;
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/// let my_arc = Arc::new(());
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///
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/// Arc::downgrade(&my_arc);
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/// ```
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///
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/// [`Weak<T>`][weak] does not auto-dereference to `T`, because the value may have
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/// already been destroyed.
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///
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/// [arc]: struct.Arc.html
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/// [weak]: struct.Weak.html
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/// [`Rc<T>`]: ../../std/rc/struct.Rc.html
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/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
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/// [mutex]: ../../std/sync/struct.Mutex.html
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/// [rwlock]: ../../std/sync/struct.RwLock.html
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/// [atomic]: ../../std/sync/atomic/index.html
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/// [`Send`]: ../../std/marker/trait.Send.html
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/// [`Sync`]: ../../std/marker/trait.Sync.html
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/// [deref]: ../../std/ops/trait.Deref.html
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/// [downgrade]: struct.Arc.html#method.downgrade
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/// [upgrade]: struct.Weak.html#method.upgrade
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/// [`None`]: ../../std/option/enum.Option.html#variant.None
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/// [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
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/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
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/// [`std::sync`]: ../../std/sync/index.html
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/// [`Arc::clone(&from)`]: #method.clone
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///
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/// # Examples
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///
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/// Sharing some immutable data between threads:
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///
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// Note that we **do not** run these tests here. The windows builders get super
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// unhappy if a thread outlives the main thread and then exits at the same time
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// (something deadlocks) so we just avoid this entirely by not running these
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// tests.
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/// ```no_run
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/// use std::sync::Arc;
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/// use std::thread;
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///
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/// let five = Arc::new(5);
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///
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/// for _ in 0..10 {
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/// let five = Arc::clone(&five);
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///
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/// thread::spawn(move || {
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/// println!("{:?}", five);
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/// });
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/// }
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/// ```
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///
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/// Sharing a mutable [`AtomicUsize`]:
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///
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/// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html
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///
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/// ```no_run
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/// use std::sync::Arc;
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/// use std::sync::atomic::{AtomicUsize, Ordering};
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/// use std::thread;
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///
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/// let val = Arc::new(AtomicUsize::new(5));
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///
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/// for _ in 0..10 {
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/// let val = Arc::clone(&val);
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///
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/// thread::spawn(move || {
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/// let v = val.fetch_add(1, Ordering::SeqCst);
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/// println!("{:?}", v);
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/// });
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/// }
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/// ```
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///
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/// See the [`rc` documentation][rc_examples] for more examples of reference
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/// counting in general.
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///
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/// [rc_examples]: ../../std/rc/index.html#examples
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Arc<T: ?Sized> {
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ptr: Shared<ArcInner<T>>,
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
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#[stable(feature = "rust1", since = "1.0.0")]
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unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
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#[unstable(feature = "coerce_unsized", issue = "27732")]
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impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
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/// `Weak` is a version of [`Arc`] that holds a non-owning reference to the
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/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
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/// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`.
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///
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/// Since a `Weak` reference does not count towards ownership, it will not
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/// prevent the inner value from being dropped, and `Weak` itself makes no
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/// guarantees about the value still being present and may return [`None`]
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/// when [`upgrade`]d.
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///
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/// A `Weak` pointer is useful for keeping a temporary reference to the value
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/// within [`Arc`] without extending its lifetime. It is also used to prevent
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/// circular references between [`Arc`] pointers, since mutual owning references
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/// would never allow either [`Arc`] to be dropped. For example, a tree could
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/// have strong [`Arc`] pointers from parent nodes to children, and `Weak`
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/// pointers from children back to their parents.
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///
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/// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`].
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///
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/// [`Arc`]: struct.Arc.html
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/// [`Arc::downgrade`]: struct.Arc.html#method.downgrade
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/// [`upgrade`]: struct.Weak.html#method.upgrade
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/// [`Option`]: ../../std/option/enum.Option.html
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/// [`None`]: ../../std/option/enum.Option.html#variant.None
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#[stable(feature = "arc_weak", since = "1.4.0")]
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pub struct Weak<T: ?Sized> {
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ptr: Shared<ArcInner<T>>,
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}
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#[stable(feature = "arc_weak", since = "1.4.0")]
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unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {}
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#[stable(feature = "arc_weak", since = "1.4.0")]
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unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {}
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#[unstable(feature = "coerce_unsized", issue = "27732")]
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impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
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#[stable(feature = "arc_weak", since = "1.4.0")]
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impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "(Weak)")
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}
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}
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struct ArcInner<T: ?Sized> {
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strong: atomic::AtomicUsize,
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// the value usize::MAX acts as a sentinel for temporarily "locking" the
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// ability to upgrade weak pointers or downgrade strong ones; this is used
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// to avoid races in `make_mut` and `get_mut`.
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weak: atomic::AtomicUsize,
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data: T,
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}
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unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
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unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
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impl<T> Arc<T> {
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/// Constructs a new `Arc<T>`.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::Arc;
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///
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/// let five = Arc::new(5);
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn new(data: T) -> Arc<T> {
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// Start the weak pointer count as 1 which is the weak pointer that's
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// held by all the strong pointers (kinda), see std/rc.rs for more info
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let x: Box<_> = box ArcInner {
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strong: atomic::AtomicUsize::new(1),
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weak: atomic::AtomicUsize::new(1),
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data,
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};
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Arc { ptr: Shared::from(Box::into_unique(x)) }
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}
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/// Returns the contained value, if the `Arc` has exactly one strong reference.
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///
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/// Otherwise, an [`Err`][result] is returned with the same `Arc` that was
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/// passed in.
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///
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/// This will succeed even if there are outstanding weak references.
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///
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/// [result]: ../../std/result/enum.Result.html
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::Arc;
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///
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/// let x = Arc::new(3);
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/// assert_eq!(Arc::try_unwrap(x), Ok(3));
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///
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/// let x = Arc::new(4);
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/// let _y = Arc::clone(&x);
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/// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);
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/// ```
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#[inline]
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#[stable(feature = "arc_unique", since = "1.4.0")]
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pub fn try_unwrap(this: Self) -> Result<T, Self> {
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// See `drop` for why all these atomics are like this
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if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() {
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return Err(this);
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}
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atomic::fence(Acquire);
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unsafe {
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let elem = ptr::read(&this.ptr.as_ref().data);
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// Make a weak pointer to clean up the implicit strong-weak reference
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let _weak = Weak { ptr: this.ptr };
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mem::forget(this);
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Ok(elem)
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}
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}
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}
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impl<T: ?Sized> Arc<T> {
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/// Consumes the `Arc`, returning the wrapped pointer.
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///
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/// To avoid a memory leak the pointer must be converted back to an `Arc` using
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/// [`Arc::from_raw`][from_raw].
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///
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/// [from_raw]: struct.Arc.html#method.from_raw
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::Arc;
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///
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/// let x = Arc::new(10);
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/// let x_ptr = Arc::into_raw(x);
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/// assert_eq!(unsafe { *x_ptr }, 10);
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/// ```
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#[stable(feature = "rc_raw", since = "1.17.0")]
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pub fn into_raw(this: Self) -> *const T {
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let ptr: *const T = &*this;
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mem::forget(this);
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ptr
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}
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/// Constructs an `Arc` from a raw pointer.
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///
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/// The raw pointer must have been previously returned by a call to a
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/// [`Arc::into_raw`][into_raw].
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///
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/// This function is unsafe because improper use may lead to memory problems. For example, a
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/// double-free may occur if the function is called twice on the same raw pointer.
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///
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/// [into_raw]: struct.Arc.html#method.into_raw
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::Arc;
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///
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/// let x = Arc::new(10);
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/// let x_ptr = Arc::into_raw(x);
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///
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/// unsafe {
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/// // Convert back to an `Arc` to prevent leak.
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/// let x = Arc::from_raw(x_ptr);
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/// assert_eq!(*x, 10);
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///
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/// // Further calls to `Arc::from_raw(x_ptr)` would be memory unsafe.
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/// }
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///
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/// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
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/// ```
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#[stable(feature = "rc_raw", since = "1.17.0")]
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pub unsafe fn from_raw(ptr: *const T) -> Self {
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// Align the unsized value to the end of the ArcInner.
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// Because it is ?Sized, it will always be the last field in memory.
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let align = align_of_val(&*ptr);
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let layout = Layout::new::<ArcInner<()>>();
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let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
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// Reverse the offset to find the original ArcInner.
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let fake_ptr = ptr as *mut ArcInner<T>;
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let arc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
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Arc {
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ptr: Shared::new_unchecked(arc_ptr),
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}
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}
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/// Creates a new [`Weak`][weak] pointer to this value.
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///
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/// [weak]: struct.Weak.html
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::Arc;
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///
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/// let five = Arc::new(5);
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///
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/// let weak_five = Arc::downgrade(&five);
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/// ```
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#[stable(feature = "arc_weak", since = "1.4.0")]
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pub fn downgrade(this: &Self) -> Weak<T> {
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// This Relaxed is OK because we're checking the value in the CAS
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// below.
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let mut cur = this.inner().weak.load(Relaxed);
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loop {
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// check if the weak counter is currently "locked"; if so, spin.
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if cur == usize::MAX {
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cur = this.inner().weak.load(Relaxed);
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continue;
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}
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// NOTE: this code currently ignores the possibility of overflow
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// into usize::MAX; in general both Rc and Arc need to be adjusted
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// to deal with overflow.
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// Unlike with Clone(), we need this to be an Acquire read to
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// synchronize with the write coming from `is_unique`, so that the
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// events prior to that write happen before this read.
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match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) {
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Ok(_) => return Weak { ptr: this.ptr },
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Err(old) => cur = old,
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}
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}
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}
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/// Gets the number of [`Weak`][weak] pointers to this value.
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///
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/// [weak]: struct.Weak.html
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///
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/// # Safety
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///
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/// This method by itself is safe, but using it correctly requires extra care.
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/// Another thread can change the weak count at any time,
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/// including potentially between calling this method and acting on the result.
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///
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/// # Examples
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///
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/// ```
|
|
/// 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) {
|
|
let ptr = self.ptr.as_ptr();
|
|
|
|
// 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);
|
|
Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr))
|
|
}
|
|
}
|
|
|
|
#[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 = Heap.alloc(layout)
|
|
.unwrap_or_else(|e| Heap.oom(e));
|
|
|
|
// Initialize the real ArcInner
|
|
let inner = set_data_ptr(ptr as *mut T, mem) 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 bptr = Box::into_raw(v);
|
|
|
|
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(bptr);
|
|
|
|
Arc { ptr: Shared::new_unchecked(ptr) }
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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: Shared::new_unchecked(ptr) }
|
|
}
|
|
}
|
|
|
|
// 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: *mut 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);
|
|
|
|
Heap.dealloc(self.mem, 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: 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: Shared::new_unchecked(ptr) }
|
|
}
|
|
}
|
|
}
|
|
|
|
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 }
|
|
}
|
|
}
|
|
|
|
#[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<T> Weak<T> {
|
|
/// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
|
|
/// it. 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: Shared::from(Box::into_unique(box ArcInner {
|
|
strong: atomic::AtomicUsize::new(0),
|
|
weak: atomic::AtomicUsize::new(1),
|
|
data: uninitialized(),
|
|
})),
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
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 = self.inner();
|
|
|
|
// 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 { ptr: self.ptr }),
|
|
Err(old) => n = old,
|
|
}
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn inner(&self) -> &ArcInner<T> {
|
|
// See comments above for why this is "safe"
|
|
unsafe { self.ptr.as_ref() }
|
|
}
|
|
}
|
|
|
|
#[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> {
|
|
// 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 = self.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>`, allocating memory for `T` without initializing
|
|
/// it. 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) {
|
|
let ptr = self.ptr.as_ptr();
|
|
|
|
// 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.
|
|
if self.inner().weak.fetch_sub(1, Release) == 1 {
|
|
atomic::fence(Acquire);
|
|
unsafe {
|
|
Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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.ptr, 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> {
|
|
unsafe { mem::transmute(<Arc<[u8]>>::from(v.as_bytes())) }
|
|
}
|
|
}
|
|
|
|
#[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]);
|
|
}
|
|
}
|
|
|
|
#[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
|
|
}
|
|
}
|