1134 lines
32 KiB
Rust
1134 lines
32 KiB
Rust
// Copyright 2013-2014 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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#![allow(deprecated)]
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//! Thread-local reference-counted boxes (the `Rc<T>` type).
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//!
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//! The `Rc<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 non-sendable because it avoids the overhead of atomic
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//! reference counting.
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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 `Rc<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 `Rc<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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//! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
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//! We want to have our `Gadget`s point to their `Owner`. We can't do this with
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//! unique ownership, because more than one gadget may belong to the same
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//! `Owner`. `Rc<T>` allows us to share an `Owner` between multiple `Gadget`s,
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//! and have the `Owner` remain allocated as long as any `Gadget` points at it.
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//!
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//! ```rust
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//! use std::rc::Rc;
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//!
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//! struct Owner {
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//! name: String
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//! // ...other fields
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//! }
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//!
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//! struct Gadget {
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//! id: i32,
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//! owner: Rc<Owner>
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//! // ...other fields
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//! }
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//!
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//! fn main() {
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//! // Create a reference counted Owner.
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//! let gadget_owner : Rc<Owner> = Rc::new(
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//! Owner { name: String::from("Gadget Man") }
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//! );
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//!
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//! // Create Gadgets belonging to gadget_owner. To increment the reference
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//! // count we clone the `Rc<T>` object.
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//! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
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//! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
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//!
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//! drop(gadget_owner);
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//!
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//! // Despite dropping gadget_owner, we're still able to print out the name
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//! // of the Owner of the Gadgets. This is because we've only dropped the
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//! // reference count object, not the Owner it wraps. As long as there are
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//! // other `Rc<T>` objects pointing at the same Owner, it will remain
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//! // allocated. Notice that the `Rc<T>` wrapper around Gadget.owner gets
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//! // automatically dereferenced for us.
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//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
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//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
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//!
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//! // At the end of the method, gadget1 and gadget2 get destroyed, and with
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//! // them the last counted references to our Owner. Gadget Man now gets
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//! // destroyed as well.
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//! }
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//! ```
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//!
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//! If our requirements change, and we also need to be able to traverse from
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//! Owner → Gadget, we will run into problems: an `Rc<T>` pointer from Owner
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//! → Gadget introduces a cycle between the objects. This means that their
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//! reference counts can never reach 0, and the objects will remain allocated: a
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//! memory leak. In order to get around this, we can use `Weak<T>` pointers.
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//! These pointers don't contribute to the total count.
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//!
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//! Rust actually makes it somewhat difficult to produce this loop in the first
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//! place: in order to end up with two objects that point at each other, one of
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//! them needs to be mutable. This is problematic because `Rc<T>` enforces
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//! memory safety by only giving out shared references to the object it wraps,
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//! and these don't allow direct mutation. We need to wrap the part of the
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//! object we wish to mutate in a `RefCell`, which provides *interior
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//! mutability*: a method to achieve mutability through a shared reference.
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//! `RefCell` enforces Rust's borrowing rules at runtime. Read the `Cell`
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//! documentation for more details on interior mutability.
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//!
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//! ```rust
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//! use std::rc::Rc;
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//! use std::rc::Weak;
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//! use std::cell::RefCell;
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//!
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//! struct Owner {
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//! name: String,
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//! gadgets: RefCell<Vec<Weak<Gadget>>>,
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//! // ...other fields
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//! }
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//!
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//! struct Gadget {
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//! id: i32,
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//! owner: Rc<Owner>,
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//! // ...other fields
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//! }
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//!
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//! fn main() {
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//! // Create a reference counted Owner. Note the fact that we've put the
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//! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
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//! // through a shared reference.
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//! let gadget_owner : Rc<Owner> = Rc::new(
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//! Owner {
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//! name: "Gadget Man".to_string(),
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//! gadgets: RefCell::new(Vec::new()),
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//! }
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//! );
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//!
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//! // Create Gadgets belonging to gadget_owner as before.
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//! let gadget1 = Rc::new(Gadget{id: 1, owner: gadget_owner.clone()});
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//! let gadget2 = Rc::new(Gadget{id: 2, owner: gadget_owner.clone()});
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//!
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//! // Add the Gadgets to their Owner. To do this we mutably borrow from
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//! // the RefCell holding the Owner's Gadgets.
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//! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget1));
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//! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget2));
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//!
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//! // Iterate over our Gadgets, printing their details out
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//! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
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//!
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//! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
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//! // that their object is still allocated, we need to call upgrade()
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//! // on them to turn them into a strong reference. This returns an
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//! // Option, which contains a reference to our object if it still
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//! // exists.
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//! let gadget = gadget_opt.upgrade().unwrap();
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//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
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//! }
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//!
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//! // At the end of the method, gadget_owner, gadget1 and gadget2 get
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//! // destroyed. There are now no strong (`Rc<T>`) references to the gadgets.
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//! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
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//! // reference count on Gadget Man, they get destroyed as well.
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//! }
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//! ```
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#![stable(feature = "rust1", since = "1.0.0")]
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#[cfg(not(test))]
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use boxed::Box;
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#[cfg(test)]
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use std::boxed::Box;
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use core::borrow;
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use core::cell::Cell;
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use core::cmp::Ordering;
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use core::fmt;
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use core::hash::{Hasher, Hash};
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use core::intrinsics::{assume, abort};
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use core::marker;
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use core::marker::Unsize;
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use core::mem::{self, align_of_val, size_of_val, forget};
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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::convert::From;
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use heap::deallocate;
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struct RcBox<T: ?Sized> {
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strong: Cell<usize>,
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weak: Cell<usize>,
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value: T,
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}
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/// A reference-counted pointer type over an immutable value.
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///
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/// See the [module level documentation](./index.html) for more details.
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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 Rc<T: ?Sized> {
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// FIXME #12808: strange names to try to avoid interfering with field
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// accesses of the contained type via Deref
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_ptr: Shared<RcBox<T>>,
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> !marker::Send for Rc<T> {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> !marker::Sync for Rc<T> {}
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#[unstable(feature = "coerce_unsized", issue = "27732")]
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impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
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impl<T> Rc<T> {
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/// Constructs a new `Rc<T>`.
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///
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/// # Examples
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///
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/// ```
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/// use std::rc::Rc;
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///
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/// let five = Rc::new(5);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn new(value: T) -> Rc<T> {
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unsafe {
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Rc {
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// there is an implicit weak pointer owned by all the strong
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// pointers, which ensures that the weak destructor never frees
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// the allocation while the strong destructor is running, even
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// if the weak pointer is stored inside the strong one.
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_ptr: Shared::new(Box::into_raw(box RcBox {
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strong: Cell::new(1),
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weak: Cell::new(1),
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value: value,
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})),
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}
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}
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}
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/// Unwraps the contained value if the `Rc<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 `Rc<T>`.
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///
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/// # Examples
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///
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/// ```
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/// use std::rc::Rc;
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///
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/// let x = Rc::new(3);
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/// assert_eq!(Rc::try_unwrap(x), Ok(3));
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///
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/// let x = Rc::new(4);
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/// let _y = x.clone();
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/// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
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/// ```
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#[inline]
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#[stable(feature = "rc_unique", since = "1.4.0")]
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pub fn try_unwrap(this: Self) -> Result<T, Self> {
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if Rc::would_unwrap(&this) {
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unsafe {
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let val = ptr::read(&*this); // copy the contained object
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// Indicate to Weaks that they can't be promoted by decrememting
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// the strong count, and then remove the implicit "strong weak"
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// pointer while also handling drop logic by just crafting a
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// fake Weak.
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this.dec_strong();
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let _weak = Weak { _ptr: this._ptr };
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forget(this);
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Ok(val)
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}
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} else {
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Err(this)
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}
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}
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/// Checks if `Rc::try_unwrap` would return `Ok`.
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#[unstable(feature = "rc_would_unwrap",
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reason = "just added for niche usecase",
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issue = "28356")]
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pub fn would_unwrap(this: &Self) -> bool {
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Rc::strong_count(&this) == 1
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}
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}
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impl<T: ?Sized> Rc<T> {
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/// Downgrades the `Rc<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::rc::Rc;
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///
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/// let five = Rc::new(5);
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///
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/// let weak_five = Rc::downgrade(&five);
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/// ```
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#[stable(feature = "rc_weak", since = "1.4.0")]
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pub fn downgrade(this: &Self) -> Weak<T> {
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this.inc_weak();
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Weak { _ptr: this._ptr }
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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 = "rc_counts", reason = "not clearly useful",
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issue = "28356")]
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pub fn weak_count(this: &Self) -> usize {
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this.weak() - 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 = "rc_counts", reason = "not clearly useful",
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issue = "28356")]
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pub fn strong_count(this: &Self) -> usize {
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this.strong()
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}
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/// Returns true if there are no other `Rc` or `Weak<T>` values that share
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/// the same inner value.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(rc_counts)]
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///
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/// use std::rc::Rc;
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///
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/// let five = Rc::new(5);
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///
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/// assert!(Rc::is_unique(&five));
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/// ```
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#[inline]
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#[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
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issue = "28356")]
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pub fn is_unique(this: &Self) -> bool {
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Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
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}
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/// Returns a mutable reference to the contained value if the `Rc<T>` has
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/// one strong reference and no weak references.
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///
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/// Returns `None` if the `Rc<T>` is not unique.
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///
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/// # Examples
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///
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/// ```
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/// use std::rc::Rc;
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///
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/// let mut x = Rc::new(3);
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/// *Rc::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!(Rc::get_mut(&mut x).is_none());
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/// ```
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#[inline]
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#[stable(feature = "rc_unique", since = "1.4.0")]
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pub fn get_mut(this: &mut Self) -> Option<&mut T> {
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if Rc::is_unique(this) {
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let inner = unsafe { &mut **this._ptr };
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Some(&mut inner.value)
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} else {
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None
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}
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}
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}
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impl<T: Clone> Rc<T> {
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/// Make a mutable reference into the given `Rc<T>` by cloning the inner
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/// data if the `Rc<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::rc::Rc;
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///
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/// let mut data = Rc::new(5);
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///
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/// *Rc::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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/// *Rc::make_mut(&mut data) += 1; // Clones inner data
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/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
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/// *Rc::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 = "rc_unique", since = "1.4.0")]
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pub fn make_mut(this: &mut Self) -> &mut T {
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if Rc::strong_count(this) != 1 {
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// Gotta clone the data, there are other Rcs
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*this = Rc::new((**this).clone())
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} else if Rc::weak_count(this) != 0 {
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// Can just steal the data, all that's left is Weaks
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unsafe {
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let mut swap = Rc::new(ptr::read(&(**this._ptr).value));
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mem::swap(this, &mut swap);
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swap.dec_strong();
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// Remove implicit strong-weak ref (no need to craft a fake
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// Weak here -- we know other Weaks can clean up for us)
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swap.dec_weak();
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forget(swap);
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}
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}
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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
|
||
// 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.
|
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let inner = unsafe { &mut **this._ptr };
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||
&mut inner.value
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||
}
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}
|
||
|
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#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Deref for Rc<T> {
|
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type Target = T;
|
||
|
||
#[inline(always)]
|
||
fn deref(&self) -> &T {
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||
&self.inner().value
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||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Drop for Rc<T> {
|
||
/// Drops the `Rc<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::rc::Rc;
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||
///
|
||
/// {
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// // stuff
|
||
///
|
||
/// drop(five); // explicit drop
|
||
/// }
|
||
/// {
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// // stuff
|
||
///
|
||
/// } // implicit drop
|
||
/// ```
|
||
#[unsafe_destructor_blind_to_params]
|
||
fn drop(&mut self) {
|
||
unsafe {
|
||
let ptr = *self._ptr;
|
||
if !(*(&ptr as *const _ as *const *const ())).is_null() &&
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ptr as *const () as usize != mem::POST_DROP_USIZE {
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self.dec_strong();
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||
if self.strong() == 0 {
|
||
// destroy the contained object
|
||
ptr::drop_in_place(&mut (*ptr).value);
|
||
|
||
// remove the implicit "strong weak" pointer now that we've
|
||
// destroyed the contents.
|
||
self.dec_weak();
|
||
|
||
if self.weak() == 0 {
|
||
deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Clone for Rc<T> {
|
||
/// Makes a clone of the `Rc<T>`.
|
||
///
|
||
/// When you clone an `Rc<T>`, it will create another pointer to the data and
|
||
/// increase the strong reference counter.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five.clone();
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Rc<T> {
|
||
self.inc_strong();
|
||
Rc { _ptr: self._ptr }
|
||
}
|
||
}
|
||
|
||
#[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();
|
||
/// ```
|
||
#[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<T>`s.
|
||
///
|
||
/// Two `Rc<T>`s are equal if their inner value are equal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five == Rc::new(5);
|
||
/// ```
|
||
#[inline(always)]
|
||
fn eq(&self, other: &Rc<T>) -> bool {
|
||
**self == **other
|
||
}
|
||
|
||
/// Inequality for two `Rc<T>`s.
|
||
///
|
||
/// Two `Rc<T>`s are unequal if their inner value are unequal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five != Rc::new(5);
|
||
/// ```
|
||
#[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<T>`s.
|
||
///
|
||
/// The two are compared by calling `partial_cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five.partial_cmp(&Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
|
||
(**self).partial_cmp(&**other)
|
||
}
|
||
|
||
/// Less-than comparison for two `Rc<T>`s.
|
||
///
|
||
/// The two are compared by calling `<` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five < Rc::new(5);
|
||
/// ```
|
||
#[inline(always)]
|
||
fn lt(&self, other: &Rc<T>) -> bool {
|
||
**self < **other
|
||
}
|
||
|
||
/// 'Less-than or equal to' comparison for two `Rc<T>`s.
|
||
///
|
||
/// The two are compared by calling `<=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five <= Rc::new(5);
|
||
/// ```
|
||
#[inline(always)]
|
||
fn le(&self, other: &Rc<T>) -> bool {
|
||
**self <= **other
|
||
}
|
||
|
||
/// Greater-than comparison for two `Rc<T>`s.
|
||
///
|
||
/// The two are compared by calling `>` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five > Rc::new(5);
|
||
/// ```
|
||
#[inline(always)]
|
||
fn gt(&self, other: &Rc<T>) -> bool {
|
||
**self > **other
|
||
}
|
||
|
||
/// 'Greater-than or equal to' comparison for two `Rc<T>`s.
|
||
///
|
||
/// The two are compared by calling `>=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// 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<T>`s.
|
||
///
|
||
/// The two are compared by calling `cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// five.partial_cmp(&Rc::new(5));
|
||
/// ```
|
||
#[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> fmt::Pointer for Rc<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
||
fmt::Pointer::fmt(&*self._ptr, 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)
|
||
}
|
||
}
|
||
|
||
/// A weak version of `Rc<T>`.
|
||
///
|
||
/// Weak references do not count when determining if the inner value should be
|
||
/// dropped.
|
||
///
|
||
/// See the [module level documentation](./index.html) for more.
|
||
#[unsafe_no_drop_flag]
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub struct Weak<T: ?Sized> {
|
||
// FIXME #12808: strange names to try to avoid interfering with
|
||
// field accesses of the contained type via Deref
|
||
_ptr: Shared<RcBox<T>>,
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> !marker::Send for Weak<T> {}
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
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: ?Sized> Weak<T> {
|
||
/// Upgrades a weak reference to a strong reference.
|
||
///
|
||
/// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
|
||
///
|
||
/// Returns `None` if there were no strong references and the data was
|
||
/// destroyed.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// let strong_five: Option<Rc<_>> = weak_five.upgrade();
|
||
/// ```
|
||
#[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 })
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Drop for Weak<T> {
|
||
/// Drops the `Weak<T>`.
|
||
///
|
||
/// This will decrement the weak reference count.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// {
|
||
/// let five = Rc::new(5);
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// // stuff
|
||
///
|
||
/// drop(weak_five); // explicit drop
|
||
/// }
|
||
/// {
|
||
/// let five = Rc::new(5);
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// // stuff
|
||
///
|
||
/// } // implicit drop
|
||
/// ```
|
||
fn drop(&mut self) {
|
||
unsafe {
|
||
let ptr = *self._ptr;
|
||
if !(*(&ptr as *const _ as *const *const ())).is_null() &&
|
||
ptr as *const () as usize != mem::POST_DROP_USIZE {
|
||
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 {
|
||
deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_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::rc::Rc;
|
||
///
|
||
/// let weak_five = Rc::downgrade(&Rc::new(5));
|
||
///
|
||
/// weak_five.clone();
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Weak<T> {
|
||
self.inc_weak();
|
||
Weak { _ptr: self._ptr }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
||
write!(f, "(Weak)")
|
||
}
|
||
}
|
||
|
||
// 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 {
|
||
// Safe to assume this here, as if it weren't true, we'd be breaking
|
||
// the contract anyway.
|
||
// This allows the null check to be elided in the destructor if we
|
||
// manipulated the reference count in the same function.
|
||
assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
|
||
&(**self._ptr)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
|
||
#[inline(always)]
|
||
fn inner(&self) -> &RcBox<T> {
|
||
unsafe {
|
||
// Safe to assume this here, as if it weren't true, we'd be breaking
|
||
// the contract anyway.
|
||
// This allows the null check to be elided in the destructor if we
|
||
// manipulated the reference count in the same function.
|
||
assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
|
||
&(**self._ptr)
|
||
}
|
||
}
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::{Rc, Weak};
|
||
use std::boxed::Box;
|
||
use std::cell::RefCell;
|
||
use std::option::Option;
|
||
use std::option::Option::{Some, None};
|
||
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(0u32);
|
||
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(0u32);
|
||
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 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);
|
||
}
|
||
}
|
||
|
||
#[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
|
||
}
|
||
}
|