1209 lines
36 KiB
Rust
1209 lines
36 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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//! Threadsafe reference-counted boxes (the `Arc<T>` type).
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//!
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//! The `Arc<T>` type provides shared ownership of an immutable value.
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//! Destruction is deterministic, and will occur as soon as the last owner is
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//! gone. It is marked as `Send` because it uses atomic reference counting.
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//!
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//! If you do not need thread-safety, and just need shared ownership, consider
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//! the [`Rc<T>` type](../rc/struct.Rc.html). It is the same as `Arc<T>`, but
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//! does not use atomics, making it both thread-unsafe as well as significantly
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//! faster when updating the reference count.
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//!
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//! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
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//! to the box. A `Weak<T>` pointer can be upgraded to an `Arc<T>` pointer, but
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//! will return `None` if the value has already been dropped.
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//!
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//! For example, a tree with parent pointers can be represented by putting the
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//! nodes behind strong `Arc<T>` pointers, and then storing the parent pointers
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//! as `Weak<T>` pointers.
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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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//! ```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 = five.clone();
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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 mutable data safely between threads with a `Mutex`:
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//!
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//! ```no_run
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//! use std::sync::{Arc, Mutex};
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//! use std::thread;
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//!
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//! let five = Arc::new(Mutex::new(5));
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//!
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//! for _ in 0..10 {
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//! let five = five.clone();
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//!
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//! thread::spawn(move || {
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//! let mut number = five.lock().unwrap();
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//!
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//! *number += 1;
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//!
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//! println!("{}", *number); // prints 6
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//! });
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//! }
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//! ```
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use boxed::Box;
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use core::sync::atomic;
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use core::sync::atomic::Ordering::{Relaxed, Release, Acquire, 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::mem::{align_of_val, size_of_val};
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use core::intrinsics::abort;
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use core::mem;
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use core::mem::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::{usize, isize};
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use core::convert::From;
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use heap::deallocate;
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const MAX_REFCOUNT: usize = (isize::MAX) as usize;
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/// An atomically reference counted wrapper for shared state.
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///
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/// # Examples
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///
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/// In this example, a large vector is shared between several threads.
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/// With simple pipes, without `Arc`, a copy would have to be made for each
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/// thread.
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///
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/// When you clone an `Arc<T>`, it will create another pointer to the data and
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/// increase the reference counter.
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///
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/// ```
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/// use std::sync::Arc;
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/// use std::thread;
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///
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/// fn main() {
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/// let numbers: Vec<_> = (0..100u32).collect();
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/// let shared_numbers = Arc::new(numbers);
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///
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/// for _ in 0..10 {
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/// let child_numbers = shared_numbers.clone();
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///
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/// thread::spawn(move || {
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/// let local_numbers = &child_numbers[..];
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///
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/// // Work with the local numbers
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/// });
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/// }
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/// }
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/// ```
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#[unsafe_no_drop_flag]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Arc<T: ?Sized> {
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// FIXME #12808: strange name to try to avoid interfering with
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// field accesses of the contained type via Deref
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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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/// A weak pointer to an `Arc`.
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///
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/// Weak pointers will not keep the data inside of the `Arc` alive, and can be
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/// used to break cycles between `Arc` pointers.
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#[unsafe_no_drop_flag]
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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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// FIXME #12808: strange name to try to avoid interfering with
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// field accesses of the contained type via Deref
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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: data,
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};
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Arc { _ptr: unsafe { Shared::new(Box::into_raw(x)) } }
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}
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/// Unwraps the contained value if the `Arc<T>` has only one strong reference.
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/// This will succeed even if there are outstanding weak references.
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///
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/// Otherwise, an `Err` is returned with the same `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 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 = x.clone();
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/// assert_eq!(Arc::try_unwrap(x), Err(Arc::new(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_and_swap(1, 0, Release) != 1 {
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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 ptr = *this._ptr;
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let elem = ptr::read(&(*ptr).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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/// Downgrades the `Arc<T>` to a `Weak<T>` reference.
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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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loop {
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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 cur = this.inner().weak.load(Relaxed);
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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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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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if this.inner().weak.compare_and_swap(cur, cur + 1, Acquire) == cur {
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return Weak { _ptr: this._ptr };
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}
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}
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}
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/// Get the number of weak references to this value.
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#[inline]
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#[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
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issue = "28356")]
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pub fn weak_count(this: &Self) -> usize {
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this.inner().weak.load(SeqCst) - 1
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}
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/// Get the number of strong references to this value.
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#[inline]
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#[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
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issue = "28356")]
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pub fn strong_count(this: &Self) -> usize {
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this.inner().strong.load(SeqCst)
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}
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#[inline]
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fn inner(&self) -> &ArcInner<T> {
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// This unsafety is ok because while this arc is alive we're guaranteed
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// that the inner pointer is valid. Furthermore, we know that the
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// `ArcInner` structure itself is `Sync` because the inner data is
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// `Sync` as well, so we're ok loaning out an immutable pointer to these
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// contents.
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unsafe { &**self._ptr }
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}
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// Non-inlined part of `drop`.
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#[inline(never)]
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unsafe fn drop_slow(&mut self) {
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let ptr = *self._ptr;
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// Destroy the data at this time, even though we may not free the box
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// allocation itself (there may still be weak pointers lying around).
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ptr::drop_in_place(&mut (*ptr).data);
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if self.inner().weak.fetch_sub(1, Release) == 1 {
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atomic::fence(Acquire);
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deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> Clone for Arc<T> {
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/// Makes a clone of the `Arc<T>`.
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///
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/// This increases the strong reference count.
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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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/// five.clone();
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/// ```
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#[inline]
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fn clone(&self) -> Arc<T> {
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// Using a relaxed ordering is alright here, as knowledge of the
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// original reference prevents other threads from erroneously deleting
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// the object.
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//
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// As explained in the [Boost documentation][1], Increasing the
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// reference counter can always be done with memory_order_relaxed: New
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// references to an object can only be formed from an existing
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// reference, and passing an existing reference from one thread to
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// another must already provide any required synchronization.
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//
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// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
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let old_size = self.inner().strong.fetch_add(1, Relaxed);
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// However we need to guard against massive refcounts in case someone
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// is `mem::forget`ing Arcs. If we don't do this the count can overflow
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// and users will use-after free. We racily saturate to `isize::MAX` on
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// the assumption that there aren't ~2 billion threads incrementing
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// the reference count at once. This branch will never be taken in
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// any realistic program.
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//
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// We abort because such a program is incredibly degenerate, and we
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// don't care to support it.
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if old_size > MAX_REFCOUNT {
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unsafe {
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abort();
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}
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}
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Arc { _ptr: self._ptr }
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> Deref for Arc<T> {
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type Target = T;
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#[inline]
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fn deref(&self) -> &T {
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&self.inner().data
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}
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}
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impl<T: Clone> Arc<T> {
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/// Make a mutable reference into the given `Arc<T>` by cloning the inner
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/// data if the `Arc<T>` doesn't have one strong reference and no weak
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/// references.
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///
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/// This is also referred to as a copy-on-write.
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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 mut data = Arc::new(5);
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///
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/// *Arc::make_mut(&mut data) += 1; // Won't clone anything
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/// let mut other_data = data.clone(); // Won't clone inner data
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/// *Arc::make_mut(&mut data) += 1; // Clones inner data
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/// *Arc::make_mut(&mut data) += 1; // Won't clone anything
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/// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
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///
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/// // Note: data and other_data now point to different numbers
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/// assert_eq!(*data, 8);
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/// assert_eq!(*other_data, 12);
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///
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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 make_mut(this: &mut Self) -> &mut T {
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// Note that we hold both a strong reference and a weak reference.
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// Thus, releasing our strong reference only will not, by itself, cause
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// the memory to be deallocated.
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//
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// Use Acquire to ensure that we see any writes to `weak` that happen
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// before release writes (i.e., decrements) to `strong`. Since we hold a
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// weak count, there's no chance the ArcInner itself could be
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// deallocated.
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if this.inner().strong.compare_and_swap(1, 0, Acquire) != 1 {
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// Another strong pointer exists; clone
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*this = Arc::new((**this).clone());
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} else if this.inner().weak.load(Relaxed) != 1 {
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// Relaxed suffices in the above because this is fundamentally an
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// optimization: we are always racing with weak pointers being
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// dropped. Worst case, we end up allocated a new Arc unnecessarily.
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// We removed the last strong ref, but there are additional weak
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// refs remaining. We'll move the contents to a new Arc, and
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// invalidate the other weak refs.
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// Note that it is not possible for the read of `weak` to yield
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// usize::MAX (i.e., locked), since the weak count can only be
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// locked by a thread with a strong reference.
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// Materialize our own implicit weak pointer, so that it can clean
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// up the ArcInner as needed.
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let weak = Weak { _ptr: this._ptr };
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// mark the data itself as already deallocated
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unsafe {
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// there is no data race in the implicit write caused by `read`
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// here (due to zeroing) because data is no longer accessed by
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// other threads (due to there being no more strong refs at this
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// point).
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let mut swap = Arc::new(ptr::read(&(**weak._ptr).data));
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mem::swap(this, &mut swap);
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mem::forget(swap);
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}
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} else {
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// We were the sole reference of either kind; bump back up the
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// strong ref count.
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this.inner().strong.store(1, Release);
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}
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// As with `get_mut()`, the unsafety is ok because our reference was
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// either unique to begin with, or became one upon cloning the contents.
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unsafe {
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let inner = &mut **this._ptr;
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&mut inner.data
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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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/// Returns a mutable reference to the contained value if the `Arc<T>` has
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/// one strong reference and no weak references.
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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 mut x = Arc::new(3);
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/// *Arc::get_mut(&mut x).unwrap() = 4;
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/// assert_eq!(*x, 4);
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///
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/// let _y = x.clone();
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/// assert!(Arc::get_mut(&mut x).is_none());
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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 get_mut(this: &mut Self) -> Option<&mut T> {
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if this.is_unique() {
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// This unsafety is ok because we're guaranteed that the pointer
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// returned is the *only* pointer that will ever be returned to T. Our
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// reference count is guaranteed to be 1 at this point, and we required
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// the Arc itself to be `mut`, so we're returning the only possible
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// reference to the inner data.
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unsafe {
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let inner = &mut **this._ptr;
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Some(&mut inner.data)
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}
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} else {
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None
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}
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}
|
|
|
|
/// 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_and_swap(1, usize::MAX, Acquire) == 1 {
|
|
// 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")]
|
|
impl<T: ?Sized> Drop for Arc<T> {
|
|
/// Drops the `Arc<T>`.
|
|
///
|
|
/// This will decrement the strong reference count. If the strong reference
|
|
/// count becomes zero and the only other references are `Weak<T>` ones,
|
|
/// `drop`s the inner value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// {
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// // stuff
|
|
///
|
|
/// drop(five); // explicit drop
|
|
/// }
|
|
/// {
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// // stuff
|
|
///
|
|
/// } // implicit drop
|
|
/// ```
|
|
#[unsafe_destructor_blind_to_params]
|
|
#[inline]
|
|
fn drop(&mut self) {
|
|
// This structure has #[unsafe_no_drop_flag], so this drop glue may run
|
|
// more than once (but it is guaranteed to be zeroed after the first if
|
|
// it's run more than once)
|
|
let thin = *self._ptr as *const ();
|
|
|
|
if thin as usize == mem::POST_DROP_USIZE {
|
|
return;
|
|
}
|
|
|
|
// 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.
|
|
//
|
|
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
|
|
atomic::fence(Acquire);
|
|
|
|
unsafe {
|
|
self.drop_slow();
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Weak<T> {
|
|
/// Upgrades a weak reference to a strong reference.
|
|
///
|
|
/// Upgrades the `Weak<T>` reference to an `Arc<T>`, if possible.
|
|
///
|
|
/// Returns `None` if there were no strong references and the data was
|
|
/// destroyed.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// let weak_five = Arc::downgrade(&five);
|
|
///
|
|
/// let strong_five: Option<Arc<_>> = weak_five.upgrade();
|
|
/// ```
|
|
#[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();
|
|
loop {
|
|
// 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 n = inner.strong.load(Relaxed);
|
|
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
|
|
let old = inner.strong.compare_and_swap(n, n + 1, Relaxed);
|
|
if old == n {
|
|
return Some(Arc { _ptr: self._ptr });
|
|
}
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn inner(&self) -> &ArcInner<T> {
|
|
// See comments above for why this is "safe"
|
|
unsafe { &**self._ptr }
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "arc_weak", since = "1.4.0")]
|
|
impl<T: ?Sized> Clone for Weak<T> {
|
|
/// Makes a clone of the `Weak<T>`.
|
|
///
|
|
/// This increases the weak reference count.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let weak_five = Arc::downgrade(&Arc::new(5));
|
|
///
|
|
/// weak_five.clone();
|
|
/// ```
|
|
#[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 = "arc_weak", since = "1.4.0")]
|
|
impl<T: ?Sized> Drop for Weak<T> {
|
|
/// Drops the `Weak<T>`.
|
|
///
|
|
/// This will decrement the weak reference count.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// {
|
|
/// let five = Arc::new(5);
|
|
/// let weak_five = Arc::downgrade(&five);
|
|
///
|
|
/// // stuff
|
|
///
|
|
/// drop(weak_five); // explicit drop
|
|
/// }
|
|
/// {
|
|
/// let five = Arc::new(5);
|
|
/// let weak_five = Arc::downgrade(&five);
|
|
///
|
|
/// // stuff
|
|
///
|
|
/// } // implicit drop
|
|
/// ```
|
|
fn drop(&mut self) {
|
|
let ptr = *self._ptr;
|
|
let thin = ptr as *const ();
|
|
|
|
// see comments above for why this check is here
|
|
if thin as usize == mem::POST_DROP_USIZE {
|
|
return;
|
|
}
|
|
|
|
// 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 { deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr)) }
|
|
}
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
|
|
/// Equality for two `Arc<T>`s.
|
|
///
|
|
/// Two `Arc<T>`s are equal if their inner value are equal.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five == Arc::new(5);
|
|
/// ```
|
|
fn eq(&self, other: &Arc<T>) -> bool {
|
|
*(*self) == *(*other)
|
|
}
|
|
|
|
/// Inequality for two `Arc<T>`s.
|
|
///
|
|
/// Two `Arc<T>`s are unequal if their inner value are unequal.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five != Arc::new(5);
|
|
/// ```
|
|
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<T>`s.
|
|
///
|
|
/// The two are compared by calling `partial_cmp()` on their inner values.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five.partial_cmp(&Arc::new(5));
|
|
/// ```
|
|
fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
|
|
(**self).partial_cmp(&**other)
|
|
}
|
|
|
|
/// Less-than comparison for two `Arc<T>`s.
|
|
///
|
|
/// The two are compared by calling `<` on their inner values.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five < Arc::new(5);
|
|
/// ```
|
|
fn lt(&self, other: &Arc<T>) -> bool {
|
|
*(*self) < *(*other)
|
|
}
|
|
|
|
/// 'Less-than or equal to' comparison for two `Arc<T>`s.
|
|
///
|
|
/// The two are compared by calling `<=` on their inner values.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five <= Arc::new(5);
|
|
/// ```
|
|
fn le(&self, other: &Arc<T>) -> bool {
|
|
*(*self) <= *(*other)
|
|
}
|
|
|
|
/// Greater-than comparison for two `Arc<T>`s.
|
|
///
|
|
/// The two are compared by calling `>` on their inner values.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// five > Arc::new(5);
|
|
/// ```
|
|
fn gt(&self, other: &Arc<T>) -> bool {
|
|
*(*self) > *(*other)
|
|
}
|
|
|
|
/// 'Greater-than or equal to' comparison for two `Arc<T>`s.
|
|
///
|
|
/// The two are compared by calling `>=` on their inner values.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::sync::Arc;
|
|
///
|
|
/// let five = Arc::new(5);
|
|
///
|
|
/// 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> {
|
|
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> 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> {
|
|
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)
|
|
}
|
|
}
|
|
|
|
impl<T> Weak<T> {
|
|
/// Constructs a new `Weak<T>` without an accompanying instance of T.
|
|
///
|
|
/// This allocates memory for T, but does not initialize it. Calling
|
|
/// Weak<T>::upgrade() on the return value always gives None.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(downgraded_weak)]
|
|
///
|
|
/// use std::sync::Weak;
|
|
///
|
|
/// let empty: Weak<i64> = Weak::new();
|
|
/// ```
|
|
#[unstable(feature = "downgraded_weak",
|
|
reason = "recently added",
|
|
issue = "30425")]
|
|
pub fn new() -> Weak<T> {
|
|
unsafe {
|
|
Weak { _ptr: Shared::new(Box::into_raw(box ArcInner {
|
|
strong: atomic::AtomicUsize::new(0),
|
|
weak: atomic::AtomicUsize::new(1),
|
|
data: uninitialized(),
|
|
}))}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
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::{Some, None};
|
|
use std::sync::atomic;
|
|
use std::sync::atomic::Ordering::{Acquire, SeqCst};
|
|
use std::thread;
|
|
use std::vec::Vec;
|
|
use super::{Arc, Weak};
|
|
use std::sync::Mutex;
|
|
use std::convert::From;
|
|
|
|
struct Canary(*mut atomic::AtomicUsize);
|
|
|
|
impl Drop for Canary {
|
|
fn drop(&mut self) {
|
|
unsafe {
|
|
match *self {
|
|
Canary(c) => {
|
|
(*c).fetch_add(1, SeqCst);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
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 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(0u32);
|
|
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(0u32);
|
|
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(5u32);
|
|
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());
|
|
}
|
|
}
|
|
|
|
#[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
|
|
}
|
|
}
|