1808 lines
51 KiB
Rust
1808 lines
51 KiB
Rust
// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
|
||
// file at the top-level directory of this distribution and at
|
||
// http://rust-lang.org/COPYRIGHT.
|
||
//
|
||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
||
// option. This file may not be copied, modified, or distributed
|
||
// except according to those terms.
|
||
|
||
#![allow(deprecated)]
|
||
|
||
//! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference
|
||
//! Counted'.
|
||
//!
|
||
//! The type [`Rc<T>`][`Rc`] provides shared ownership of a value of type `T`,
|
||
//! allocated in the heap. Invoking [`clone`][clone] on [`Rc`] produces a new
|
||
//! pointer to the same value in the heap. When the last [`Rc`] pointer to a
|
||
//! given value is destroyed, the pointed-to value is also destroyed.
|
||
//!
|
||
//! Shared references in Rust disallow mutation by default, and [`Rc`]
|
||
//! is no exception: you cannot generally obtain a mutable reference to
|
||
//! something inside an [`Rc`]. If you need mutability, put a [`Cell`]
|
||
//! or [`RefCell`] inside the [`Rc`]; see [an example of mutability
|
||
//! inside an Rc][mutability].
|
||
//!
|
||
//! [`Rc`] uses non-atomic reference counting. This means that overhead is very
|
||
//! low, but an [`Rc`] cannot be sent between threads, and consequently [`Rc`]
|
||
//! does not implement [`Send`][send]. As a result, the Rust compiler
|
||
//! will check *at compile time* that you are not sending [`Rc`]s between
|
||
//! threads. If you need multi-threaded, atomic reference counting, use
|
||
//! [`sync::Arc`][arc].
|
||
//!
|
||
//! The [`downgrade`][downgrade] method can be used to create a non-owning
|
||
//! [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d
|
||
//! to an [`Rc`], but this will return [`None`] if the value has
|
||
//! already been dropped.
|
||
//!
|
||
//! A cycle between [`Rc`] pointers will never be deallocated. For this reason,
|
||
//! [`Weak`] is used to break cycles. For example, a tree could have strong
|
||
//! [`Rc`] pointers from parent nodes to children, and [`Weak`] pointers from
|
||
//! children back to their parents.
|
||
//!
|
||
//! `Rc<T>` automatically dereferences to `T` (via the [`Deref`] trait),
|
||
//! so you can call `T`'s methods on a value of type [`Rc<T>`][`Rc`]. To avoid name
|
||
//! clashes with `T`'s methods, the methods of [`Rc<T>`][`Rc`] itself are [associated
|
||
//! functions][assoc], called using function-like syntax:
|
||
//!
|
||
//! ```
|
||
//! use std::rc::Rc;
|
||
//! let my_rc = Rc::new(());
|
||
//!
|
||
//! Rc::downgrade(&my_rc);
|
||
//! ```
|
||
//!
|
||
//! [`Weak<T>`][`Weak`] does not auto-dereference to `T`, because the value may have
|
||
//! already been destroyed.
|
||
//!
|
||
//! # Cloning references
|
||
//!
|
||
//! Creating a new reference from an existing reference counted pointer is done using the
|
||
//! `Clone` trait implemented for [`Rc<T>`][`Rc`] and [`Weak<T>`][`Weak`].
|
||
//!
|
||
//! ```
|
||
//! use std::rc::Rc;
|
||
//! let foo = Rc::new(vec![1.0, 2.0, 3.0]);
|
||
//! // The two syntaxes below are equivalent.
|
||
//! let a = foo.clone();
|
||
//! let b = Rc::clone(&foo);
|
||
//! // a and b both point to the same memory location as foo.
|
||
//! ```
|
||
//!
|
||
//! The `Rc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly
|
||
//! the meaning of the code. In the example above, this syntax makes it easier to see that
|
||
//! this code is creating a new reference rather than copying the whole content of foo.
|
||
//!
|
||
//! # Examples
|
||
//!
|
||
//! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
|
||
//! We want to have our `Gadget`s point to their `Owner`. We can't do this with
|
||
//! unique ownership, because more than one gadget may belong to the same
|
||
//! `Owner`. [`Rc`] allows us to share an `Owner` between multiple `Gadget`s,
|
||
//! and have the `Owner` remain allocated as long as any `Gadget` points at it.
|
||
//!
|
||
//! ```
|
||
//! use std::rc::Rc;
|
||
//!
|
||
//! struct Owner {
|
||
//! name: String,
|
||
//! // ...other fields
|
||
//! }
|
||
//!
|
||
//! struct Gadget {
|
||
//! id: i32,
|
||
//! owner: Rc<Owner>,
|
||
//! // ...other fields
|
||
//! }
|
||
//!
|
||
//! fn main() {
|
||
//! // Create a reference-counted `Owner`.
|
||
//! let gadget_owner: Rc<Owner> = Rc::new(
|
||
//! Owner {
|
||
//! name: "Gadget Man".to_string(),
|
||
//! }
|
||
//! );
|
||
//!
|
||
//! // Create `Gadget`s belonging to `gadget_owner`. Cloning the `Rc<Owner>`
|
||
//! // value gives us a new pointer to the same `Owner` value, incrementing
|
||
//! // the reference count in the process.
|
||
//! let gadget1 = Gadget {
|
||
//! id: 1,
|
||
//! owner: Rc::clone(&gadget_owner),
|
||
//! };
|
||
//! let gadget2 = Gadget {
|
||
//! id: 2,
|
||
//! owner: Rc::clone(&gadget_owner),
|
||
//! };
|
||
//!
|
||
//! // Dispose of our local variable `gadget_owner`.
|
||
//! drop(gadget_owner);
|
||
//!
|
||
//! // Despite dropping `gadget_owner`, we're still able to print out the name
|
||
//! // of the `Owner` of the `Gadget`s. This is because we've only dropped a
|
||
//! // single `Rc<Owner>`, not the `Owner` it points to. As long as there are
|
||
//! // other `Rc<Owner>` values pointing at the same `Owner`, it will remain
|
||
//! // allocated. The field projection `gadget1.owner.name` works because
|
||
//! // `Rc<Owner>` automatically dereferences to `Owner`.
|
||
//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
|
||
//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
|
||
//!
|
||
//! // At the end of the function, `gadget1` and `gadget2` are destroyed, and
|
||
//! // with them the last counted references to our `Owner`. Gadget Man now
|
||
//! // gets destroyed as well.
|
||
//! }
|
||
//! ```
|
||
//!
|
||
//! If our requirements change, and we also need to be able to traverse from
|
||
//! `Owner` to `Gadget`, we will run into problems. An [`Rc`] pointer from `Owner`
|
||
//! to `Gadget` introduces a cycle between the values. This means that their
|
||
//! reference counts can never reach 0, and the values will remain allocated
|
||
//! forever: a memory leak. In order to get around this, we can use [`Weak`]
|
||
//! pointers.
|
||
//!
|
||
//! Rust actually makes it somewhat difficult to produce this loop in the first
|
||
//! place. In order to end up with two values that point at each other, one of
|
||
//! them needs to be mutable. This is difficult because [`Rc`] enforces
|
||
//! memory safety by only giving out shared references to the value it wraps,
|
||
//! and these don't allow direct mutation. We need to wrap the part of the
|
||
//! value we wish to mutate in a [`RefCell`], which provides *interior
|
||
//! mutability*: a method to achieve mutability through a shared reference.
|
||
//! [`RefCell`] enforces Rust's borrowing rules at runtime.
|
||
//!
|
||
//! ```
|
||
//! use std::rc::Rc;
|
||
//! use std::rc::Weak;
|
||
//! use std::cell::RefCell;
|
||
//!
|
||
//! struct Owner {
|
||
//! name: String,
|
||
//! gadgets: RefCell<Vec<Weak<Gadget>>>,
|
||
//! // ...other fields
|
||
//! }
|
||
//!
|
||
//! struct Gadget {
|
||
//! id: i32,
|
||
//! owner: Rc<Owner>,
|
||
//! // ...other fields
|
||
//! }
|
||
//!
|
||
//! fn main() {
|
||
//! // Create a reference-counted `Owner`. Note that we've put the `Owner`'s
|
||
//! // vector of `Gadget`s inside a `RefCell` so that we can mutate it through
|
||
//! // a shared reference.
|
||
//! let gadget_owner: Rc<Owner> = Rc::new(
|
||
//! Owner {
|
||
//! name: "Gadget Man".to_string(),
|
||
//! gadgets: RefCell::new(vec![]),
|
||
//! }
|
||
//! );
|
||
//!
|
||
//! // Create `Gadget`s belonging to `gadget_owner`, as before.
|
||
//! let gadget1 = Rc::new(
|
||
//! Gadget {
|
||
//! id: 1,
|
||
//! owner: Rc::clone(&gadget_owner),
|
||
//! }
|
||
//! );
|
||
//! let gadget2 = Rc::new(
|
||
//! Gadget {
|
||
//! id: 2,
|
||
//! owner: Rc::clone(&gadget_owner),
|
||
//! }
|
||
//! );
|
||
//!
|
||
//! // Add the `Gadget`s to their `Owner`.
|
||
//! {
|
||
//! let mut gadgets = gadget_owner.gadgets.borrow_mut();
|
||
//! gadgets.push(Rc::downgrade(&gadget1));
|
||
//! gadgets.push(Rc::downgrade(&gadget2));
|
||
//!
|
||
//! // `RefCell` dynamic borrow ends here.
|
||
//! }
|
||
//!
|
||
//! // Iterate over our `Gadget`s, printing their details out.
|
||
//! for gadget_weak in gadget_owner.gadgets.borrow().iter() {
|
||
//!
|
||
//! // `gadget_weak` is a `Weak<Gadget>`. Since `Weak` pointers can't
|
||
//! // guarantee the value is still allocated, we need to call
|
||
//! // `upgrade`, which returns an `Option<Rc<Gadget>>`.
|
||
//! //
|
||
//! // In this case we know the value still exists, so we simply
|
||
//! // `unwrap` the `Option`. In a more complicated program, you might
|
||
//! // need graceful error handling for a `None` result.
|
||
//!
|
||
//! let gadget = gadget_weak.upgrade().unwrap();
|
||
//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
|
||
//! }
|
||
//!
|
||
//! // At the end of the function, `gadget_owner`, `gadget1`, and `gadget2`
|
||
//! // are destroyed. There are now no strong (`Rc`) pointers to the
|
||
//! // gadgets, so they are destroyed. This zeroes the reference count on
|
||
//! // Gadget Man, so he gets destroyed as well.
|
||
//! }
|
||
//! ```
|
||
//!
|
||
//! [`Rc`]: struct.Rc.html
|
||
//! [`Weak`]: struct.Weak.html
|
||
//! [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
|
||
//! [`Cell`]: ../../std/cell/struct.Cell.html
|
||
//! [`RefCell`]: ../../std/cell/struct.RefCell.html
|
||
//! [send]: ../../std/marker/trait.Send.html
|
||
//! [arc]: ../../std/sync/struct.Arc.html
|
||
//! [`Deref`]: ../../std/ops/trait.Deref.html
|
||
//! [downgrade]: struct.Rc.html#method.downgrade
|
||
//! [upgrade]: struct.Weak.html#method.upgrade
|
||
//! [`None`]: ../../std/option/enum.Option.html#variant.None
|
||
//! [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
|
||
//! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable
|
||
|
||
#![stable(feature = "rust1", since = "1.0.0")]
|
||
|
||
#[cfg(not(test))]
|
||
use boxed::Box;
|
||
#[cfg(test)]
|
||
use std::boxed::Box;
|
||
|
||
use core::any::Any;
|
||
use core::borrow;
|
||
use core::cell::Cell;
|
||
use core::cmp::Ordering;
|
||
use core::fmt;
|
||
use core::hash::{Hash, Hasher};
|
||
use core::intrinsics::abort;
|
||
use core::marker;
|
||
use core::marker::{Unsize, PhantomData};
|
||
use core::mem::{self, align_of_val, forget, size_of_val, uninitialized};
|
||
use core::ops::Deref;
|
||
use core::ops::CoerceUnsized;
|
||
use core::ptr::{self, NonNull};
|
||
use core::convert::From;
|
||
|
||
use heap::{Heap, Alloc, Layout, box_free};
|
||
use string::String;
|
||
use vec::Vec;
|
||
|
||
struct RcBox<T: ?Sized> {
|
||
strong: Cell<usize>,
|
||
weak: Cell<usize>,
|
||
value: T,
|
||
}
|
||
|
||
/// A single-threaded reference-counting pointer. 'Rc' stands for 'Reference
|
||
/// Counted'.
|
||
///
|
||
/// See the [module-level documentation](./index.html) for more details.
|
||
///
|
||
/// The inherent methods of `Rc` are all associated functions, which means
|
||
/// that you have to call them as e.g. [`Rc::get_mut(&mut value)`][get_mut] instead of
|
||
/// `value.get_mut()`. This avoids conflicts with methods of the inner
|
||
/// type `T`.
|
||
///
|
||
/// [get_mut]: #method.get_mut
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
pub struct Rc<T: ?Sized> {
|
||
ptr: NonNull<RcBox<T>>,
|
||
phantom: PhantomData<T>,
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> !marker::Send for Rc<T> {}
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> !marker::Sync for Rc<T> {}
|
||
|
||
#[unstable(feature = "coerce_unsized", issue = "27732")]
|
||
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
|
||
|
||
impl<T> Rc<T> {
|
||
/// Constructs a new `Rc<T>`.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// ```
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
pub fn new(value: T) -> Rc<T> {
|
||
Rc {
|
||
// there is an implicit weak pointer owned by all the strong
|
||
// pointers, which ensures that the weak destructor never frees
|
||
// the allocation while the strong destructor is running, even
|
||
// if the weak pointer is stored inside the strong one.
|
||
ptr: Box::into_raw_non_null(box RcBox {
|
||
strong: Cell::new(1),
|
||
weak: Cell::new(1),
|
||
value,
|
||
}),
|
||
phantom: PhantomData,
|
||
}
|
||
}
|
||
|
||
/// Returns the contained value, if the `Rc` has exactly one strong reference.
|
||
///
|
||
/// Otherwise, an [`Err`][result] is returned with the same `Rc` that was
|
||
/// passed in.
|
||
///
|
||
/// This will succeed even if there are outstanding weak references.
|
||
///
|
||
/// [result]: ../../std/result/enum.Result.html
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new(3);
|
||
/// assert_eq!(Rc::try_unwrap(x), Ok(3));
|
||
///
|
||
/// let x = Rc::new(4);
|
||
/// let _y = Rc::clone(&x);
|
||
/// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_unique", since = "1.4.0")]
|
||
pub fn try_unwrap(this: Self) -> Result<T, Self> {
|
||
if Rc::strong_count(&this) == 1 {
|
||
unsafe {
|
||
let val = ptr::read(&*this); // copy the contained object
|
||
|
||
// Indicate to Weaks that they can't be promoted by decrementing
|
||
// the strong count, and then remove the implicit "strong weak"
|
||
// pointer while also handling drop logic by just crafting a
|
||
// fake Weak.
|
||
this.dec_strong();
|
||
let _weak = Weak { ptr: this.ptr };
|
||
forget(this);
|
||
Ok(val)
|
||
}
|
||
} else {
|
||
Err(this)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> Rc<T> {
|
||
/// Consumes the `Rc`, returning the wrapped pointer.
|
||
///
|
||
/// To avoid a memory leak the pointer must be converted back to an `Rc` using
|
||
/// [`Rc::from_raw`][from_raw].
|
||
///
|
||
/// [from_raw]: struct.Rc.html#method.from_raw
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new(10);
|
||
/// let x_ptr = Rc::into_raw(x);
|
||
/// assert_eq!(unsafe { *x_ptr }, 10);
|
||
/// ```
|
||
#[stable(feature = "rc_raw", since = "1.17.0")]
|
||
pub fn into_raw(this: Self) -> *const T {
|
||
let ptr: *const T = &*this;
|
||
mem::forget(this);
|
||
ptr
|
||
}
|
||
|
||
/// Constructs an `Rc` from a raw pointer.
|
||
///
|
||
/// The raw pointer must have been previously returned by a call to a
|
||
/// [`Rc::into_raw`][into_raw].
|
||
///
|
||
/// This function is unsafe because improper use may lead to memory problems. For example, a
|
||
/// double-free may occur if the function is called twice on the same raw pointer.
|
||
///
|
||
/// [into_raw]: struct.Rc.html#method.into_raw
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new(10);
|
||
/// let x_ptr = Rc::into_raw(x);
|
||
///
|
||
/// unsafe {
|
||
/// // Convert back to an `Rc` to prevent leak.
|
||
/// let x = Rc::from_raw(x_ptr);
|
||
/// assert_eq!(*x, 10);
|
||
///
|
||
/// // Further calls to `Rc::from_raw(x_ptr)` would be memory unsafe.
|
||
/// }
|
||
///
|
||
/// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
|
||
/// ```
|
||
#[stable(feature = "rc_raw", since = "1.17.0")]
|
||
pub unsafe fn from_raw(ptr: *const T) -> Self {
|
||
// Align the unsized value to the end of the RcBox.
|
||
// Because it is ?Sized, it will always be the last field in memory.
|
||
let align = align_of_val(&*ptr);
|
||
let layout = Layout::new::<RcBox<()>>();
|
||
let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
|
||
|
||
// Reverse the offset to find the original RcBox.
|
||
let fake_ptr = ptr as *mut RcBox<T>;
|
||
let rc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
|
||
|
||
Rc {
|
||
ptr: NonNull::new_unchecked(rc_ptr),
|
||
phantom: PhantomData,
|
||
}
|
||
}
|
||
|
||
/// Creates a new [`Weak`][weak] pointer to this value.
|
||
///
|
||
/// [weak]: struct.Weak.html
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
/// ```
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub fn downgrade(this: &Self) -> Weak<T> {
|
||
this.inc_weak();
|
||
Weak { ptr: this.ptr }
|
||
}
|
||
|
||
/// Gets the number of [`Weak`][weak] pointers to this value.
|
||
///
|
||
/// [weak]: struct.Weak.html
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let _weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// assert_eq!(1, Rc::weak_count(&five));
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_counts", since = "1.15.0")]
|
||
pub fn weak_count(this: &Self) -> usize {
|
||
this.weak() - 1
|
||
}
|
||
|
||
/// Gets the number of strong (`Rc`) pointers to this value.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let _also_five = Rc::clone(&five);
|
||
///
|
||
/// assert_eq!(2, Rc::strong_count(&five));
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_counts", since = "1.15.0")]
|
||
pub fn strong_count(this: &Self) -> usize {
|
||
this.strong()
|
||
}
|
||
|
||
/// Returns true if there are no other `Rc` or [`Weak`][weak] pointers to
|
||
/// this inner value.
|
||
///
|
||
/// [weak]: struct.Weak.html
|
||
#[inline]
|
||
fn is_unique(this: &Self) -> bool {
|
||
Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
|
||
}
|
||
|
||
/// Returns a mutable reference to the inner value, if there are
|
||
/// no other `Rc` or [`Weak`][weak] pointers to the same value.
|
||
///
|
||
/// Returns [`None`] 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
|
||
/// [`None`]: ../../std/option/enum.Option.html#variant.None
|
||
/// [make_mut]: struct.Rc.html#method.make_mut
|
||
/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut x = Rc::new(3);
|
||
/// *Rc::get_mut(&mut x).unwrap() = 4;
|
||
/// assert_eq!(*x, 4);
|
||
///
|
||
/// let _y = Rc::clone(&x);
|
||
/// assert!(Rc::get_mut(&mut x).is_none());
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_unique", since = "1.4.0")]
|
||
pub fn get_mut(this: &mut Self) -> Option<&mut T> {
|
||
if Rc::is_unique(this) {
|
||
unsafe {
|
||
Some(&mut this.ptr.as_mut().value)
|
||
}
|
||
} else {
|
||
None
|
||
}
|
||
}
|
||
|
||
#[inline]
|
||
#[stable(feature = "ptr_eq", since = "1.17.0")]
|
||
/// Returns true if the two `Rc`s point to the same value (not
|
||
/// just values that compare as equal).
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let same_five = Rc::clone(&five);
|
||
/// let other_five = Rc::new(5);
|
||
///
|
||
/// assert!(Rc::ptr_eq(&five, &same_five));
|
||
/// assert!(!Rc::ptr_eq(&five, &other_five));
|
||
/// ```
|
||
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
|
||
this.ptr.as_ptr() == other.ptr.as_ptr()
|
||
}
|
||
}
|
||
|
||
impl<T: Clone> Rc<T> {
|
||
/// Makes a mutable reference into the given `Rc`.
|
||
///
|
||
/// If there are other `Rc` 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.Rc.html#method.get_mut
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut data = Rc::new(5);
|
||
///
|
||
/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
|
||
/// let mut other_data = Rc::clone(&data); // Won't clone inner data
|
||
/// *Rc::make_mut(&mut data) += 1; // Clones inner data
|
||
/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
|
||
/// *Rc::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 = "rc_unique", since = "1.4.0")]
|
||
pub fn make_mut(this: &mut Self) -> &mut T {
|
||
if Rc::strong_count(this) != 1 {
|
||
// Gotta clone the data, there are other Rcs
|
||
*this = Rc::new((**this).clone())
|
||
} else if Rc::weak_count(this) != 0 {
|
||
// Can just steal the data, all that's left is Weaks
|
||
unsafe {
|
||
let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value));
|
||
mem::swap(this, &mut swap);
|
||
swap.dec_strong();
|
||
// Remove implicit strong-weak ref (no need to craft a fake
|
||
// Weak here -- we know other Weaks can clean up for us)
|
||
swap.dec_weak();
|
||
forget(swap);
|
||
}
|
||
}
|
||
// 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 `Rc<T>` itself to be `mut`, so we're returning the only possible
|
||
// reference to the inner value.
|
||
unsafe {
|
||
&mut this.ptr.as_mut().value
|
||
}
|
||
}
|
||
}
|
||
|
||
impl Rc<Any> {
|
||
#[inline]
|
||
#[unstable(feature = "rc_downcast", issue = "44608")]
|
||
/// Attempt to downcast the `Rc<Any>` to a concrete type.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(rc_downcast)]
|
||
/// use std::any::Any;
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// fn print_if_string(value: Rc<Any>) {
|
||
/// if let Ok(string) = value.downcast::<String>() {
|
||
/// println!("String ({}): {}", string.len(), string);
|
||
/// }
|
||
/// }
|
||
///
|
||
/// fn main() {
|
||
/// let my_string = "Hello World".to_string();
|
||
/// print_if_string(Rc::new(my_string));
|
||
/// print_if_string(Rc::new(0i8));
|
||
/// }
|
||
/// ```
|
||
pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<Any>> {
|
||
if (*self).is::<T>() {
|
||
// avoid the pointer arithmetic in from_raw
|
||
unsafe {
|
||
let raw: *const RcBox<Any> = self.ptr.as_ptr();
|
||
forget(self);
|
||
Ok(Rc {
|
||
ptr: NonNull::new_unchecked(raw as *const RcBox<T> as *mut _),
|
||
phantom: PhantomData,
|
||
})
|
||
}
|
||
} else {
|
||
Err(self)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> Rc<T> {
|
||
// Allocates an `RcBox<T>` with sufficient space for an unsized value
|
||
unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
|
||
// Create a fake RcBox to find allocation size and alignment
|
||
let fake_ptr = ptr as *mut RcBox<T>;
|
||
|
||
let layout = Layout::for_value(&*fake_ptr);
|
||
|
||
let mem = Heap.alloc(layout)
|
||
.unwrap_or_else(|e| Heap.oom(e));
|
||
|
||
// Initialize the real RcBox
|
||
let inner = set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>;
|
||
|
||
ptr::write(&mut (*inner).strong, Cell::new(1));
|
||
ptr::write(&mut (*inner).weak, Cell::new(1));
|
||
|
||
inner
|
||
}
|
||
|
||
fn from_box(v: Box<T>) -> Rc<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).value as *mut _ as *mut u8,
|
||
value_size);
|
||
|
||
// Free the allocation without dropping its contents
|
||
box_free(bptr);
|
||
|
||
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
|
||
}
|
||
}
|
||
}
|
||
|
||
// Sets the data pointer of a `?Sized` raw pointer.
|
||
//
|
||
// For a slice/trait object, this sets the `data` field and leaves the rest
|
||
// unchanged. For a sized raw pointer, this simply sets the pointer.
|
||
unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
|
||
ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
|
||
ptr
|
||
}
|
||
|
||
impl<T> Rc<[T]> {
|
||
// Copy elements from slice into newly allocated Rc<[T]>
|
||
//
|
||
// Unsafe because the caller must either take ownership or bind `T: Copy`
|
||
unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> {
|
||
let v_ptr = v as *const [T];
|
||
let ptr = Self::allocate_for_ptr(v_ptr);
|
||
|
||
ptr::copy_nonoverlapping(
|
||
v.as_ptr(),
|
||
&mut (*ptr).value as *mut [T] as *mut T,
|
||
v.len());
|
||
|
||
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
|
||
}
|
||
}
|
||
|
||
trait RcFromSlice<T> {
|
||
fn from_slice(slice: &[T]) -> Self;
|
||
}
|
||
|
||
impl<T: Clone> RcFromSlice<T> for Rc<[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 RcBox 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).value 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 RcBox.
|
||
forget(guard);
|
||
|
||
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: Copy> RcFromSlice<T> for Rc<[T]> {
|
||
#[inline]
|
||
fn from_slice(v: &[T]) -> Self {
|
||
unsafe { Rc::copy_from_slice(v) }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Deref for Rc<T> {
|
||
type Target = T;
|
||
|
||
#[inline(always)]
|
||
fn deref(&self) -> &T {
|
||
&self.inner().value
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
|
||
/// Drops the `Rc`.
|
||
///
|
||
/// 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::rc::Rc;
|
||
///
|
||
/// struct Foo;
|
||
///
|
||
/// impl Drop for Foo {
|
||
/// fn drop(&mut self) {
|
||
/// println!("dropped!");
|
||
/// }
|
||
/// }
|
||
///
|
||
/// let foo = Rc::new(Foo);
|
||
/// let foo2 = Rc::clone(&foo);
|
||
///
|
||
/// drop(foo); // Doesn't print anything
|
||
/// drop(foo2); // Prints "dropped!"
|
||
/// ```
|
||
fn drop(&mut self) {
|
||
unsafe {
|
||
let ptr = self.ptr.as_ptr();
|
||
|
||
self.dec_strong();
|
||
if self.strong() == 0 {
|
||
// destroy the contained object
|
||
ptr::drop_in_place(self.ptr.as_mut());
|
||
|
||
// remove the implicit "strong weak" pointer now that we've
|
||
// destroyed the contents.
|
||
self.dec_weak();
|
||
|
||
if self.weak() == 0 {
|
||
Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr));
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Clone for Rc<T> {
|
||
/// Makes a clone of the `Rc` pointer.
|
||
///
|
||
/// This creates another pointer to the same inner value, increasing the
|
||
/// strong reference count.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// Rc::clone(&five);
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Rc<T> {
|
||
self.inc_strong();
|
||
Rc { ptr: self.ptr, phantom: PhantomData }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: Default> Default for Rc<T> {
|
||
/// Creates a new `Rc<T>`, with the `Default` value for `T`.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x: Rc<i32> = Default::default();
|
||
/// assert_eq!(*x, 0);
|
||
/// ```
|
||
#[inline]
|
||
fn default() -> Rc<T> {
|
||
Rc::new(Default::default())
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
|
||
/// Equality for two `Rc`s.
|
||
///
|
||
/// Two `Rc`s are equal if their inner values are equal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five == Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn eq(&self, other: &Rc<T>) -> bool {
|
||
**self == **other
|
||
}
|
||
|
||
/// Inequality for two `Rc`s.
|
||
///
|
||
/// Two `Rc`s are unequal if their inner values are unequal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five != Rc::new(6));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn ne(&self, other: &Rc<T>) -> bool {
|
||
**self != **other
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Eq> Eq for Rc<T> {}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
|
||
/// Partial comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `partial_cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
/// use std::cmp::Ordering;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6)));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
|
||
(**self).partial_cmp(&**other)
|
||
}
|
||
|
||
/// Less-than comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `<` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five < Rc::new(6));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn lt(&self, other: &Rc<T>) -> bool {
|
||
**self < **other
|
||
}
|
||
|
||
/// 'Less than or equal to' comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `<=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five <= Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn le(&self, other: &Rc<T>) -> bool {
|
||
**self <= **other
|
||
}
|
||
|
||
/// Greater-than comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `>` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five > Rc::new(4));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn gt(&self, other: &Rc<T>) -> bool {
|
||
**self > **other
|
||
}
|
||
|
||
/// 'Greater than or equal to' comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `>=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five >= Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn ge(&self, other: &Rc<T>) -> bool {
|
||
**self >= **other
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Ord> Ord for Rc<T> {
|
||
/// Comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
/// use std::cmp::Ordering;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));
|
||
/// ```
|
||
#[inline]
|
||
fn cmp(&self, other: &Rc<T>) -> Ordering {
|
||
(**self).cmp(&**other)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Hash> Hash for Rc<T> {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
(**self).hash(state);
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + fmt::Display> fmt::Display for Rc<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 Rc<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 Rc<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
||
fmt::Pointer::fmt(&(&**self as *const T), f)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "from_for_ptrs", since = "1.6.0")]
|
||
impl<T> From<T> for Rc<T> {
|
||
fn from(t: T) -> Self {
|
||
Rc::new(t)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<'a, T: Clone> From<&'a [T]> for Rc<[T]> {
|
||
#[inline]
|
||
fn from(v: &[T]) -> Rc<[T]> {
|
||
<Self as RcFromSlice<T>>::from_slice(v)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<'a> From<&'a str> for Rc<str> {
|
||
#[inline]
|
||
fn from(v: &str) -> Rc<str> {
|
||
let rc = Rc::<[u8]>::from(v.as_bytes());
|
||
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl From<String> for Rc<str> {
|
||
#[inline]
|
||
fn from(v: String) -> Rc<str> {
|
||
Rc::from(&v[..])
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<T: ?Sized> From<Box<T>> for Rc<T> {
|
||
#[inline]
|
||
fn from(v: Box<T>) -> Rc<T> {
|
||
Rc::from_box(v)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<T> From<Vec<T>> for Rc<[T]> {
|
||
#[inline]
|
||
fn from(mut v: Vec<T>) -> Rc<[T]> {
|
||
unsafe {
|
||
let rc = Rc::copy_from_slice(&v);
|
||
|
||
// Allow the Vec to free its memory, but not destroy its contents
|
||
v.set_len(0);
|
||
|
||
rc
|
||
}
|
||
}
|
||
}
|
||
|
||
/// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
|
||
/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
|
||
/// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.
|
||
///
|
||
/// Since a `Weak` reference does not count towards ownership, it will not
|
||
/// prevent the inner value from being dropped, and `Weak` itself makes no
|
||
/// guarantees about the value still being present and may return [`None`]
|
||
/// when [`upgrade`]d.
|
||
///
|
||
/// A `Weak` pointer is useful for keeping a temporary reference to the value
|
||
/// within [`Rc`] without extending its lifetime. It is also used to prevent
|
||
/// circular references between [`Rc`] pointers, since mutual owning references
|
||
/// would never allow either [`Rc`] to be dropped. For example, a tree could
|
||
/// have strong [`Rc`] pointers from parent nodes to children, and `Weak`
|
||
/// pointers from children back to their parents.
|
||
///
|
||
/// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
|
||
///
|
||
/// [`Rc`]: struct.Rc.html
|
||
/// [`Rc::downgrade`]: struct.Rc.html#method.downgrade
|
||
/// [`upgrade`]: struct.Weak.html#method.upgrade
|
||
/// [`Option`]: ../../std/option/enum.Option.html
|
||
/// [`None`]: ../../std/option/enum.Option.html#variant.None
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub struct Weak<T: ?Sized> {
|
||
ptr: NonNull<RcBox<T>>,
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> !marker::Send for Weak<T> {}
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> !marker::Sync for Weak<T> {}
|
||
|
||
#[unstable(feature = "coerce_unsized", issue = "27732")]
|
||
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
|
||
|
||
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
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::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: Box::into_raw_non_null(box RcBox {
|
||
strong: Cell::new(0),
|
||
weak: Cell::new(1),
|
||
value: uninitialized(),
|
||
}),
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> Weak<T> {
|
||
/// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending
|
||
/// the lifetime of the value if successful.
|
||
///
|
||
/// Returns [`None`] if the value has since been dropped.
|
||
///
|
||
/// [`Rc`]: struct.Rc.html
|
||
/// [`None`]: ../../std/option/enum.Option.html
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// let strong_five: Option<Rc<_>> = 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 = "rc_weak", since = "1.4.0")]
|
||
pub fn upgrade(&self) -> Option<Rc<T>> {
|
||
if self.strong() == 0 {
|
||
None
|
||
} else {
|
||
self.inc_strong();
|
||
Some(Rc { ptr: self.ptr, phantom: PhantomData })
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> Drop for Weak<T> {
|
||
/// Drops the `Weak` pointer.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// struct Foo;
|
||
///
|
||
/// impl Drop for Foo {
|
||
/// fn drop(&mut self) {
|
||
/// println!("dropped!");
|
||
/// }
|
||
/// }
|
||
///
|
||
/// let foo = Rc::new(Foo);
|
||
/// let weak_foo = Rc::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) {
|
||
unsafe {
|
||
let ptr = self.ptr.as_ptr();
|
||
|
||
self.dec_weak();
|
||
// the weak count starts at 1, and will only go to zero if all
|
||
// the strong pointers have disappeared.
|
||
if self.weak() == 0 {
|
||
Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr));
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_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::rc::{Rc, Weak};
|
||
///
|
||
/// let weak_five = Rc::downgrade(&Rc::new(5));
|
||
///
|
||
/// Weak::clone(&weak_five);
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Weak<T> {
|
||
self.inc_weak();
|
||
Weak { ptr: self.ptr }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
||
write!(f, "(Weak)")
|
||
}
|
||
}
|
||
|
||
#[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
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Weak;
|
||
///
|
||
/// let empty: Weak<i64> = Default::default();
|
||
/// assert!(empty.upgrade().is_none());
|
||
/// ```
|
||
fn default() -> Weak<T> {
|
||
Weak::new()
|
||
}
|
||
}
|
||
|
||
// NOTE: We checked_add here to deal with mem::forget safety. In particular
|
||
// if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
|
||
// you can free the allocation while outstanding Rcs (or Weaks) exist.
|
||
// We abort because this is such a degenerate scenario that we don't care about
|
||
// what happens -- no real program should ever experience this.
|
||
//
|
||
// This should have negligible overhead since you don't actually need to
|
||
// clone these much in Rust thanks to ownership and move-semantics.
|
||
|
||
#[doc(hidden)]
|
||
trait RcBoxPtr<T: ?Sized> {
|
||
fn inner(&self) -> &RcBox<T>;
|
||
|
||
#[inline]
|
||
fn strong(&self) -> usize {
|
||
self.inner().strong.get()
|
||
}
|
||
|
||
#[inline]
|
||
fn inc_strong(&self) {
|
||
self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
|
||
}
|
||
|
||
#[inline]
|
||
fn dec_strong(&self) {
|
||
self.inner().strong.set(self.strong() - 1);
|
||
}
|
||
|
||
#[inline]
|
||
fn weak(&self) -> usize {
|
||
self.inner().weak.get()
|
||
}
|
||
|
||
#[inline]
|
||
fn inc_weak(&self) {
|
||
self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
|
||
}
|
||
|
||
#[inline]
|
||
fn dec_weak(&self) {
|
||
self.inner().weak.set(self.weak() - 1);
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
|
||
#[inline(always)]
|
||
fn inner(&self) -> &RcBox<T> {
|
||
unsafe {
|
||
self.ptr.as_ref()
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
|
||
#[inline(always)]
|
||
fn inner(&self) -> &RcBox<T> {
|
||
unsafe {
|
||
self.ptr.as_ref()
|
||
}
|
||
}
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::{Rc, Weak};
|
||
use std::boxed::Box;
|
||
use std::cell::RefCell;
|
||
use std::option::Option;
|
||
use std::option::Option::{None, Some};
|
||
use std::result::Result::{Err, Ok};
|
||
use std::mem::drop;
|
||
use std::clone::Clone;
|
||
use std::convert::From;
|
||
|
||
#[test]
|
||
fn test_clone() {
|
||
let x = Rc::new(RefCell::new(5));
|
||
let y = x.clone();
|
||
*x.borrow_mut() = 20;
|
||
assert_eq!(*y.borrow(), 20);
|
||
}
|
||
|
||
#[test]
|
||
fn test_simple() {
|
||
let x = Rc::new(5);
|
||
assert_eq!(*x, 5);
|
||
}
|
||
|
||
#[test]
|
||
fn test_simple_clone() {
|
||
let x = Rc::new(5);
|
||
let y = x.clone();
|
||
assert_eq!(*x, 5);
|
||
assert_eq!(*y, 5);
|
||
}
|
||
|
||
#[test]
|
||
fn test_destructor() {
|
||
let x: Rc<Box<_>> = Rc::new(box 5);
|
||
assert_eq!(**x, 5);
|
||
}
|
||
|
||
#[test]
|
||
fn test_live() {
|
||
let x = Rc::new(5);
|
||
let y = Rc::downgrade(&x);
|
||
assert!(y.upgrade().is_some());
|
||
}
|
||
|
||
#[test]
|
||
fn test_dead() {
|
||
let x = Rc::new(5);
|
||
let y = Rc::downgrade(&x);
|
||
drop(x);
|
||
assert!(y.upgrade().is_none());
|
||
}
|
||
|
||
#[test]
|
||
fn weak_self_cyclic() {
|
||
struct Cycle {
|
||
x: RefCell<Option<Weak<Cycle>>>,
|
||
}
|
||
|
||
let a = Rc::new(Cycle { x: RefCell::new(None) });
|
||
let b = Rc::downgrade(&a.clone());
|
||
*a.x.borrow_mut() = Some(b);
|
||
|
||
// hopefully we don't double-free (or leak)...
|
||
}
|
||
|
||
#[test]
|
||
fn is_unique() {
|
||
let x = Rc::new(3);
|
||
assert!(Rc::is_unique(&x));
|
||
let y = x.clone();
|
||
assert!(!Rc::is_unique(&x));
|
||
drop(y);
|
||
assert!(Rc::is_unique(&x));
|
||
let w = Rc::downgrade(&x);
|
||
assert!(!Rc::is_unique(&x));
|
||
drop(w);
|
||
assert!(Rc::is_unique(&x));
|
||
}
|
||
|
||
#[test]
|
||
fn test_strong_count() {
|
||
let a = Rc::new(0);
|
||
assert!(Rc::strong_count(&a) == 1);
|
||
let w = Rc::downgrade(&a);
|
||
assert!(Rc::strong_count(&a) == 1);
|
||
let b = w.upgrade().expect("upgrade of live rc failed");
|
||
assert!(Rc::strong_count(&b) == 2);
|
||
assert!(Rc::strong_count(&a) == 2);
|
||
drop(w);
|
||
drop(a);
|
||
assert!(Rc::strong_count(&b) == 1);
|
||
let c = b.clone();
|
||
assert!(Rc::strong_count(&b) == 2);
|
||
assert!(Rc::strong_count(&c) == 2);
|
||
}
|
||
|
||
#[test]
|
||
fn test_weak_count() {
|
||
let a = Rc::new(0);
|
||
assert!(Rc::strong_count(&a) == 1);
|
||
assert!(Rc::weak_count(&a) == 0);
|
||
let w = Rc::downgrade(&a);
|
||
assert!(Rc::strong_count(&a) == 1);
|
||
assert!(Rc::weak_count(&a) == 1);
|
||
drop(w);
|
||
assert!(Rc::strong_count(&a) == 1);
|
||
assert!(Rc::weak_count(&a) == 0);
|
||
let c = a.clone();
|
||
assert!(Rc::strong_count(&a) == 2);
|
||
assert!(Rc::weak_count(&a) == 0);
|
||
drop(c);
|
||
}
|
||
|
||
#[test]
|
||
fn try_unwrap() {
|
||
let x = Rc::new(3);
|
||
assert_eq!(Rc::try_unwrap(x), Ok(3));
|
||
let x = Rc::new(4);
|
||
let _y = x.clone();
|
||
assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
|
||
let x = Rc::new(5);
|
||
let _w = Rc::downgrade(&x);
|
||
assert_eq!(Rc::try_unwrap(x), Ok(5));
|
||
}
|
||
|
||
#[test]
|
||
fn into_from_raw() {
|
||
let x = Rc::new(box "hello");
|
||
let y = x.clone();
|
||
|
||
let x_ptr = Rc::into_raw(x);
|
||
drop(y);
|
||
unsafe {
|
||
assert_eq!(**x_ptr, "hello");
|
||
|
||
let x = Rc::from_raw(x_ptr);
|
||
assert_eq!(**x, "hello");
|
||
|
||
assert_eq!(Rc::try_unwrap(x).map(|x| *x), Ok("hello"));
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_into_from_raw_unsized() {
|
||
use std::fmt::Display;
|
||
use std::string::ToString;
|
||
|
||
let rc: Rc<str> = Rc::from("foo");
|
||
|
||
let ptr = Rc::into_raw(rc.clone());
|
||
let rc2 = unsafe { Rc::from_raw(ptr) };
|
||
|
||
assert_eq!(unsafe { &*ptr }, "foo");
|
||
assert_eq!(rc, rc2);
|
||
|
||
let rc: Rc<Display> = Rc::new(123);
|
||
|
||
let ptr = Rc::into_raw(rc.clone());
|
||
let rc2 = unsafe { Rc::from_raw(ptr) };
|
||
|
||
assert_eq!(unsafe { &*ptr }.to_string(), "123");
|
||
assert_eq!(rc2.to_string(), "123");
|
||
}
|
||
|
||
#[test]
|
||
fn get_mut() {
|
||
let mut x = Rc::new(3);
|
||
*Rc::get_mut(&mut x).unwrap() = 4;
|
||
assert_eq!(*x, 4);
|
||
let y = x.clone();
|
||
assert!(Rc::get_mut(&mut x).is_none());
|
||
drop(y);
|
||
assert!(Rc::get_mut(&mut x).is_some());
|
||
let _w = Rc::downgrade(&x);
|
||
assert!(Rc::get_mut(&mut x).is_none());
|
||
}
|
||
|
||
#[test]
|
||
fn test_cowrc_clone_make_unique() {
|
||
let mut cow0 = Rc::new(75);
|
||
let mut cow1 = cow0.clone();
|
||
let mut cow2 = cow1.clone();
|
||
|
||
assert!(75 == *Rc::make_mut(&mut cow0));
|
||
assert!(75 == *Rc::make_mut(&mut cow1));
|
||
assert!(75 == *Rc::make_mut(&mut cow2));
|
||
|
||
*Rc::make_mut(&mut cow0) += 1;
|
||
*Rc::make_mut(&mut cow1) += 2;
|
||
*Rc::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_cowrc_clone_unique2() {
|
||
let mut cow0 = Rc::new(75);
|
||
let cow1 = cow0.clone();
|
||
let cow2 = cow1.clone();
|
||
|
||
assert!(75 == *cow0);
|
||
assert!(75 == *cow1);
|
||
assert!(75 == *cow2);
|
||
|
||
*Rc::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_cowrc_clone_weak() {
|
||
let mut cow0 = Rc::new(75);
|
||
let cow1_weak = Rc::downgrade(&cow0);
|
||
|
||
assert!(75 == *cow0);
|
||
assert!(75 == *cow1_weak.upgrade().unwrap());
|
||
|
||
*Rc::make_mut(&mut cow0) += 1;
|
||
|
||
assert!(76 == *cow0);
|
||
assert!(cow1_weak.upgrade().is_none());
|
||
}
|
||
|
||
#[test]
|
||
fn test_show() {
|
||
let foo = Rc::new(75);
|
||
assert_eq!(format!("{:?}", foo), "75");
|
||
}
|
||
|
||
#[test]
|
||
fn test_unsized() {
|
||
let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
|
||
assert_eq!(foo, foo.clone());
|
||
}
|
||
|
||
#[test]
|
||
fn test_from_owned() {
|
||
let foo = 123;
|
||
let foo_rc = Rc::from(foo);
|
||
assert!(123 == *foo_rc);
|
||
}
|
||
|
||
#[test]
|
||
fn test_new_weak() {
|
||
let foo: Weak<usize> = Weak::new();
|
||
assert!(foo.upgrade().is_none());
|
||
}
|
||
|
||
#[test]
|
||
fn test_ptr_eq() {
|
||
let five = Rc::new(5);
|
||
let same_five = five.clone();
|
||
let other_five = Rc::new(5);
|
||
|
||
assert!(Rc::ptr_eq(&five, &same_five));
|
||
assert!(!Rc::ptr_eq(&five, &other_five));
|
||
}
|
||
|
||
#[test]
|
||
fn test_from_str() {
|
||
let r: Rc<str> = Rc::from("foo");
|
||
|
||
assert_eq!(&r[..], "foo");
|
||
}
|
||
|
||
#[test]
|
||
fn test_copy_from_slice() {
|
||
let s: &[u32] = &[1, 2, 3];
|
||
let r: Rc<[u32]> = Rc::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: Rc<[X]> = Rc::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: Rc<[Fail]> = Rc::from(s);
|
||
}
|
||
|
||
#[test]
|
||
fn test_from_box() {
|
||
let b: Box<u32> = box 123;
|
||
let r: Rc<u32> = Rc::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: Rc<str> = Rc::from(s);
|
||
|
||
assert_eq!(&r[..], "foo");
|
||
}
|
||
|
||
#[test]
|
||
fn test_from_box_slice() {
|
||
let s = vec![1, 2, 3].into_boxed_slice();
|
||
let r: Rc<[u32]> = Rc::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: Rc<Display> = Rc::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: Rc<Debug> = Rc::from(b);
|
||
|
||
assert_eq!(format!("{:?}", r), "()");
|
||
}
|
||
|
||
#[test]
|
||
fn test_from_vec() {
|
||
let v = vec![1, 2, 3];
|
||
let r: Rc<[u32]> = Rc::from(v);
|
||
|
||
assert_eq!(&r[..], [1, 2, 3]);
|
||
}
|
||
|
||
#[test]
|
||
fn test_downcast() {
|
||
use std::any::Any;
|
||
|
||
let r1: Rc<Any> = Rc::new(i32::max_value());
|
||
let r2: Rc<Any> = Rc::new("abc");
|
||
|
||
assert!(r1.clone().downcast::<u32>().is_err());
|
||
|
||
let r1i32 = r1.downcast::<i32>();
|
||
assert!(r1i32.is_ok());
|
||
assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value()));
|
||
|
||
assert!(r2.clone().downcast::<i32>().is_err());
|
||
|
||
let r2str = r2.downcast::<&'static str>();
|
||
assert!(r2str.is_ok());
|
||
assert_eq!(r2str.unwrap(), Rc::new("abc"));
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
|
||
fn borrow(&self) -> &T {
|
||
&**self
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
|
||
impl<T: ?Sized> AsRef<T> for Rc<T> {
|
||
fn as_ref(&self) -> &T {
|
||
&**self
|
||
}
|
||
}
|