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// Copyright 2015 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.
//! Thread-local reference-counted boxes (the `Cc<T>` type).
//!
//! The `Cc<T>` type provides shared ownership of an immutable value.
//! Destruction is deterministic, and will occur as soon as the last owner is
//! gone. It is marked as non-sendable because it avoids the overhead of atomic
//! reference counting.
//!
//! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
//! to the box. A `Weak<T>` pointer can be upgraded to an `Cc<T>` pointer, but
//! will return `None` if the value has already been dropped.
//!
//! For example, a tree with parent pointers can be represented by putting the
//! nodes behind strong `Cc<T>` pointers, and then storing the parent pointers
//! as `Weak<T>` pointers.
//!
//! # 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`. `Cc<T>` allows us to share an `Owner` between multiple `Gadget`s,
//! and have the `Owner` remain allocated as long as any `Gadget` points at it.
//!
//! ```rust
//! use bacon_rajan_cc::{Cc, Trace, Tracer, collect_cycles};
//!
//! struct Owner {
//! name: String,
//! // ...other fields
//! }
//!
//! impl Trace for Owner {
//! // Note: nothing to trace since `Owner` doesn't own any Cc<T> things.
//! fn trace(&self, _tracer: &mut Tracer) {}
//! }
//!
//! struct Gadget {
//! id: i32,
//! owner: Cc<Owner>,
//! // ...other fields
//! }
//!
//! fn main() {
//! // Create a reference counted Owner.
//! let gadget_owner: Cc<Owner> = Cc::new(Owner {
//! name: String::from("Gadget Man"),
//! });
//!
//! // Create Gadgets belonging to gadget_owner. To increment the reference
//! // count we clone the `Cc<T>` object.
//! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
//! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
//!
//! drop(gadget_owner);
//!
//! // Despite dropping gadget_owner, we're still able to print out the name
//! // of the Owner of the Gadgets. This is because we've only dropped the
//! // reference count object, not the Owner it wraps. As long as there are
//! // other `Cc<T>` objects pointing at the same Owner, it will remain
//! // allocated. Notice that the `Cc<T>` wrapper around Gadget.owner gets
//! // automatically dereferenced for us.
//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
//!
//! // At the end of the method, gadget1 and gadget2 get destroyed, and with
//! // them the last counted references to our Owner. Gadget Man now gets
//! // destroyed as well.
//! drop(gadget1);
//! drop(gadget2);
//! collect_cycles()
//! }
//! ```
//!
//! If our requirements change, and we also need to be able to traverse from
//! Owner → Gadget, we will run into problems: an `Cc<T>` pointer from Owner
//! → Gadget introduces a cycle between the objects. This means that their
//! reference counts can never reach 0, and the objects will remain allocated: a
//! memory leak. In order to get around this, we can use `Weak<T>` pointers.
//! These pointers don't contribute to the total count.
//!
//! Rust actually makes it somewhat difficult to produce this loop in the first
//! place: in order to end up with two objects that point at each other, one of
//! them needs to be mutable. This is problematic because `Cc<T>` enforces
//! memory safety by only giving out shared references to the object it wraps,
//! and these don't allow direct mutation. We need to wrap the part of the
//! object 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. Read the `Cell`
//! documentation for more details on interior mutability.
//!
//! ```rust
//! use bacon_rajan_cc::{Cc, Weak, Trace, Tracer, collect_cycles};
//! use std::cell::RefCell;
//!
//! struct Owner {
//! name: String,
//! gadgets: RefCell<Vec<Weak<Gadget>>>,
//! // ...other fields
//! }
//!
//! impl Trace for Owner {
//! fn trace(&self, _tracer: &mut Tracer) {}
//! }
//!
//! struct Gadget {
//! id: i32,
//! owner: Cc<Owner>,
//! // ...other fields
//! }
//!
//! impl Trace for Gadget {
//! fn trace(&self, tracer: &mut Tracer) {
//! self.owner.trace(tracer);
//! }
//! }
//!
//! fn main() {
//! // Create a reference counted Owner. Note the fact that we've put the
//! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
//! // through a shared reference.
//! let gadget_owner: Cc<Owner> = Cc::new(Owner {
//! name: "Gadget Man".to_string(),
//! gadgets: RefCell::new(Vec::new()),
//! });
//!
//! // Create Gadgets belonging to gadget_owner as before.
//! let gadget1 = Cc::new(Gadget { id: 1, owner: gadget_owner.clone() });
//! let gadget2 = Cc::new(Gadget { id: 2, owner: gadget_owner.clone() });
//!
//! // Add the Gadgets to their Owner. To do this we mutably borrow from
//! // the RefCell holding the Owner's Gadgets.
//! gadget_owner.gadgets.borrow_mut().push(gadget1.clone().downgrade());
//! gadget_owner.gadgets.borrow_mut().push(gadget2.clone().downgrade());
//!
//! // Iterate over our Gadgets, printing their details out
//! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
//!
//! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
//! // that their object is still allocated, we need to call upgrade()
//! // on them to turn them into a strong reference. This returns an
//! // Option, which contains a reference to our object if it still
//! // exists.
//! let gadget = gadget_opt.upgrade().unwrap();
//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
//! }
//!
//! // At the end of the method, gadget_owner, gadget1 and gadget2 get
//! // destroyed. There are now no strong (`Cc<T>`) references to the gadgets.
//! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
//! // reference count on Gadget Man, so he gets destroyed as well.
//! drop((gadget_owner, gadget1, gadget2));
//! collect_cycles();
//! }
//! ```
#![deny(missing_docs)]
extern crate core;
use core::alloc::Layout;
use core::cell::Cell;
use core::cmp::Ordering;
use core::fmt;
use core::hash::{Hash, Hasher};
use core::mem::forget;
use core::ops::Deref;
use core::ptr::{self, NonNull};
use std::alloc::dealloc;
/// Tracing traits, types, and implementation.
pub mod trace;
pub use trace::{Trace, Tracer};
/// Implementation of cycle detection and collection.
pub mod collect;
pub use collect::{collect_cycles, number_of_roots_buffered};
mod cc_box_ptr;
use cc_box_ptr::CcBoxPtr;
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[doc(hidden)]
pub enum Color {
/// In use or free.
Black,
/// Possible member of a cycle.
Gray,
/// Member of a garbage cycle.
White,
/// Possible root of cycle.
Purple,
/// Candidate cycle undergoing sigma-computation. Not yet in use.
#[allow(dead_code)]
Red,
/// Candidate cycle awaiting epoch boundary. Not yet in use.
#[allow(dead_code)]
Orange,
}
#[derive(Debug)]
#[doc(hidden)]
pub struct CcBoxData {
strong: Cell<usize>,
weak: Cell<usize>,
buffered: Cell<bool>,
color: Cell<Color>,
}
impl CcBoxData {
/// Get the color of this node.
#[inline]
fn color(&self) -> Color {
self.color.get()
}
/// Return true if this node is in the buffer of possible cycle roots, false
/// otherwise.
#[inline]
fn buffered(&self) -> bool {
self.buffered.get()
}
/// Return the strong reference count.
#[inline]
fn strong(&self) -> usize {
self.strong.get()
}
/// Increment this node's strong reference count.
#[inline]
fn inc_strong(&self) {
self.strong.set(self.strong() + 1);
self.color.set(Color::Black);
}
/// Decrement this node's strong reference count.
#[inline]
fn dec_strong(&self) {
self.strong.set(self.strong() - 1);
}
/// Get this node's weak reference count, including the "strong weak"
/// reference.
#[inline]
fn weak(&self) -> usize {
self.weak.get()
}
/// Increment this node's weak reference count.
#[inline]
fn inc_weak(&self) {
self.weak.set(self.weak() + 1);
}
/// Decrement this node's weak reference count.
#[inline]
fn dec_weak(&self) {
self.weak.set(self.weak() - 1);
}
}
#[derive(Debug)]
struct CcBox<T: Trace> {
value: T,
data: CcBoxData,
}
/// A reference-counted pointer type over an immutable value.
///
/// See the [module level documentation](./) for more details.
pub struct Cc<T: 'static + Trace> {
// FIXME #12808: strange names to try to avoid interfering with field
// accesses of the contained type via Deref
_ptr: NonNull<CcBox<T>>,
}
impl<T: Trace> Cc<T> {
/// Constructs a new `Cc<T>`.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
/// ```
pub fn new(value: T) -> Cc<T> {
unsafe {
Cc {
// 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: NonNull::new_unchecked(Box::into_raw(Box::new(CcBox {
value,
data: CcBoxData {
strong: Cell::new(1),
weak: Cell::new(1),
buffered: Cell::new(false),
color: Cell::new(Color::Black),
},
}))),
}
}
}
/// Downgrades the `Cc<T>` to a `Weak<T>` reference.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// let weak_five = five.downgrade();
/// ```
pub fn downgrade(&self) -> Weak<T> {
self.data().inc_weak();
Weak { _ptr: self._ptr }
}
}
impl<T: Trace> Cc<T> {
unsafe fn release(&mut self) {
debug_assert!(self.data().strong() == 0);
crate::drop_value(self._ptr);
self._ptr.as_ref().data().color.set(Color::Black);
// If it is in the buffer, then it will be freed later in the
// `mark_roots` procedure.
if self.data().buffered() {
return;
}
crate::cc_box_ptr::free(self._ptr);
}
fn possible_root(&mut self) {
debug_assert!(self.data().strong() > 0);
if self.data().color() == Color::Purple {
return;
}
self.data().color.set(Color::Purple);
if self.data().buffered() {
return;
}
self.data().buffered.set(true);
let ptr: NonNull<dyn CcBoxPtr> = self._ptr;
collect::add_root(ptr);
}
}
impl<T: 'static + Trace> Cc<T> {
/// Returns true if there are no other `Cc` or `Weak<T>` values that share
/// the same inner value.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc;
/// use bacon_rajan_cc::{Cc, collect_cycles};
/// {
/// let five = Cc::new(5);
/// assert_eq!(five.is_unique(), true);
///
/// let another_five = five.clone();
/// assert_eq!(five.is_unique(), false);
/// assert_eq!(another_five.is_unique(), false);
/// }
/// collect_cycles();
/// ```
#[inline]
pub fn is_unique(&self) -> bool {
self.weak_count() == 0 && self.strong_count() == 1
}
/// Unwraps the contained value if the `Cc<T>` is unique.
///
/// If the `Cc<T>` is not unique, an `Err` is returned with the same `Cc<T>`.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::{Cc, collect_cycles};
/// {
/// let x = Cc::new(3);
/// assert_eq!(x.try_unwrap(), Ok(3));
///
/// let x = Cc::new(4);
/// let _y = x.clone();
/// assert_eq!(x.try_unwrap(), Err(Cc::new(4)));
/// }
/// collect_cycles();
/// ```
#[inline]
pub fn try_unwrap(self) -> Result<T, Cc<T>> {
if self.is_unique() {
unsafe {
// Copy the contained object.
let val = ptr::read(&*self);
// Destruct the box and skip our Drop. We can ignore the
// refcounts because we know we're unique.
dealloc(self._ptr.cast().as_ptr(), Layout::new::<CcBox<T>>());
forget(self);
Ok(val)
}
} else {
Err(self)
}
}
/// Returns a mutable reference to the contained value if the `Cc<T>` is
/// unique.
///
/// Returns `None` if the `Cc<T>` is not unique.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::{Cc, collect_cycles};
/// {
/// let mut x = Cc::new(3);
/// *Cc::get_mut(&mut x).unwrap() = 4;
/// assert_eq!(*x, 4);
///
/// let _y = x.clone();
/// assert!(Cc::get_mut(&mut x).is_none());
/// }
/// collect_cycles();
/// ```
#[inline]
pub fn get_mut(&mut self) -> Option<&mut T> {
if self.is_unique() {
let inner = unsafe { self._ptr.as_mut() };
Some(&mut inner.value)
} else {
None
}
}
/// Get the number of strong references to this value.
#[inline]
pub fn strong_count(&self) -> usize {
self.data().strong()
}
/// Get the number of weak references to this value.
#[inline]
pub fn weak_count(&self) -> usize {
self.data().weak() - 1
}
}
impl<T: 'static + Clone + Trace> Cc<T> {
/// Make a mutable reference from the given `Cc<T>`.
///
/// This is also referred to as a copy-on-write operation because the inner
/// data is cloned if the reference count is greater than one.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let mut five = Cc::new(5);
///
/// let mut_five = five.make_unique();
/// ```
#[inline]
pub fn make_unique(&mut self) -> &mut T {
if !self.is_unique() {
*self = Cc::new((**self).clone())
}
// 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 `Cc<T>` itself to be `mut`, so we're returning the only possible
// reference to the inner value.
let inner = unsafe { self._ptr.as_mut() };
&mut inner.value
}
}
impl<T: Trace> Cc<T> {
// Returns `true` if the two `Cc`s point to the same allocation
/// (in a vein similar to [`ptr::eq`]).
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::{Cc, collect_cycles};
/// {
/// let five = Cc::new(5);
/// let same_five = Cc::clone(&five);
/// let other_five = Cc::new(5);
///
/// assert!(Cc::ptr_eq(&five, &same_five));
/// assert!(!Cc::ptr_eq(&five, &other_five));
/// }
/// collect_cycles();
/// ```
///
/// [`ptr::eq`]: core::ptr::eq
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this._ptr.as_ptr() == other._ptr.as_ptr()
}
}
impl<T: Trace> Deref for Cc<T> {
type Target = T;
#[inline(always)]
fn deref(&self) -> &T {
if self.strong_count() > 0 {
unsafe { &self._ptr.as_ref().value }
} else {
panic!("Invalid access during cycle collection");
}
}
}
impl<T: Trace> Drop for Cc<T> {
/// Drops the `Cc<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 bacon_rajan_cc::Cc;
///
/// {
/// let five = Cc::new(5);
///
/// // stuff
///
/// drop(five); // explicit drop
/// }
/// {
/// let five = Cc::new(5);
///
/// // stuff
///
/// } // implicit drop
/// ```
fn drop(&mut self) {
unsafe {
if self.data().strong() > 0 {
self.data().dec_strong();
if self.data().strong() == 0 {
self.release();
} else {
self.possible_root();
}
}
}
}
}
impl<T: Trace> Clone for Cc<T> {
/// Makes a clone of the `Cc<T>`.
///
/// When you clone an `Cc<T>`, it will create another pointer to the data and
/// increase the strong reference counter.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::{Cc, collect_cycles};
///
/// let five = Cc::new(5);
///
/// drop(five.clone());
/// collect_cycles();
/// ```
#[inline]
fn clone(&self) -> Cc<T> {
self.data().inc_strong();
Cc { _ptr: self._ptr }
}
}
impl<T: Default + Trace> Default for Cc<T> {
/// Creates a new `Cc<T>`, with the `Default` value for `T`.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let x: Cc<i32> = Default::default();
/// ```
#[inline]
fn default() -> Cc<T> {
Cc::new(Default::default())
}
}
impl<T: PartialEq + Trace> PartialEq for Cc<T> {
/// Equality for two `Cc<T>`s.
///
/// Two `Cc<T>`s are equal if their inner value are equal.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five == Cc::new(5);
/// ```
#[inline(always)]
fn eq(&self, other: &Cc<T>) -> bool {
**self == **other
}
/// Inequality for two `Cc<T>`s.
///
/// Two `Cc<T>`s are unequal if their inner value are unequal.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five != Cc::new(5);
/// ```
#[inline(always)]
fn ne(&self, other: &Cc<T>) -> bool {
**self != **other
}
}
impl<T: Eq + Trace> Eq for Cc<T> {}
impl<T: PartialOrd + Trace> PartialOrd for Cc<T> {
/// Partial comparison for two `Cc<T>`s.
///
/// The two are compared by calling `partial_cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five.partial_cmp(&Cc::new(5));
/// ```
#[inline(always)]
fn partial_cmp(&self, other: &Cc<T>) -> Option<Ordering> {
(**self).partial_cmp(&**other)
}
/// Less-than comparison for two `Cc<T>`s.
///
/// The two are compared by calling `<` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five < Cc::new(5);
/// ```
#[inline(always)]
fn lt(&self, other: &Cc<T>) -> bool {
**self < **other
}
/// 'Less-than or equal to' comparison for two `Cc<T>`s.
///
/// The two are compared by calling `<=` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five <= Cc::new(5);
/// ```
#[inline(always)]
fn le(&self, other: &Cc<T>) -> bool {
**self <= **other
}
/// Greater-than comparison for two `Cc<T>`s.
///
/// The two are compared by calling `>` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five > Cc::new(5);
/// ```
#[inline(always)]
fn gt(&self, other: &Cc<T>) -> bool {
**self > **other
}
/// 'Greater-than or equal to' comparison for two `Cc<T>`s.
///
/// The two are compared by calling `>=` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five >= Cc::new(5);
/// ```
#[inline(always)]
fn ge(&self, other: &Cc<T>) -> bool {
**self >= **other
}
}
impl<T: Ord + Trace> Ord for Cc<T> {
/// Comparison for two `Cc<T>`s.
///
/// The two are compared by calling `cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let five = Cc::new(5);
///
/// five.partial_cmp(&Cc::new(5));
/// ```
#[inline]
fn cmp(&self, other: &Cc<T>) -> Ordering {
(**self).cmp(&**other)
}
}
// FIXME (#18248) Make `T` `Sized?`
impl<T: Hash + Trace> Hash for Cc<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
(**self).hash(state);
}
}
impl<T: fmt::Display + Trace> fmt::Display for Cc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
impl<T: fmt::Debug + Trace> fmt::Debug for Cc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
impl<T: Trace> fmt::Pointer for Cc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Pointer::fmt(&self._ptr, f)
}
}
/// A weak version of `Cc<T>`.
///
/// Weak references do not count when determining if the inner value should be
/// dropped.
///
/// See the [module level documentation](./) for more.
pub struct Weak<T: Trace> {
// FIXME #12808: strange names to try to avoid interfering with
// field accesses of the contained type via Deref
_ptr: NonNull<CcBox<T>>,
}
impl<T: Trace> Weak<T> {
/// Upgrades a weak reference to a strong reference.
///
/// Upgrades the `Weak<T>` reference to an `Cc<T>`, if possible.
///
/// Returns `None` if there were no strong references and the data was
/// destroyed.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::{Cc, collect_cycles};
///
/// let five = Cc::new(5);
///
/// let weak_five = five.downgrade();
///
/// let strong_five: Option<Cc<_>> = weak_five.upgrade();
/// drop((five, weak_five, strong_five));
/// collect_cycles();
/// ```
pub fn upgrade(&self) -> Option<Cc<T>> {
if self.data().strong() == 0 {
None
} else {
self.data().inc_strong();
Some(Cc { _ptr: self._ptr })
}
}
}
impl<T: Trace> Drop for Weak<T> {
/// Drops the `Weak<T>`.
///
/// This will decrement the weak reference count.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// {
/// let five = Cc::new(5);
/// let weak_five = five.downgrade();
///
/// // stuff
///
/// drop(weak_five); // explicit drop
/// }
/// {
/// let five = Cc::new(5);
/// let weak_five = five.downgrade();
///
/// // stuff
///
/// } // implicit drop
/// ```
fn drop(&mut self) {
unsafe {
if self.data().weak() > 0 {
self.data().dec_weak();
// The weak count starts at 1, and will only go to zero if all
// the strong pointers have disappeared.
if self.data().weak() == 0 {
dealloc(self._ptr.cast().as_ptr(), Layout::new::<CcBox<T>>())
}
}
}
}
}
impl<T: Trace> Clone for Weak<T> {
/// Makes a clone of the `Weak<T>`.
///
/// This increases the weak reference count.
///
/// # Examples
///
/// ```
/// use bacon_rajan_cc::Cc;
///
/// let weak_five = Cc::new(5).downgrade();
///
/// weak_five.clone();
/// ```
#[inline]
fn clone(&self) -> Weak<T> {
self.data().inc_weak();
Weak { _ptr: self._ptr }
}
}
impl<T: fmt::Debug + Trace> fmt::Debug for Weak<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "(Weak)")
}
}
impl<T: Trace> Trace for Cc<T> {
fn trace(&self, tracer: &mut Tracer) {
tracer(self._ptr);
}
}
impl<T: Trace> Trace for Weak<T> {
fn trace(&self, _tracer: &mut Tracer) {
// Weak references should not be traced.
}
}
impl<T: Trace> Trace for CcBox<T> {
fn trace(&self, tracer: &mut Tracer) {
Trace::trace(&self.value, tracer);
}
}
impl<T: Trace> Cc<T> {
#[inline(always)]
fn data(&self) -> &CcBoxData {
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.
&self._ptr.as_ref().data
}
}
}
impl<T: Trace> Weak<T> {
#[inline(always)]
fn data(&self) -> &CcBoxData {
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.
// We specifically avoid taking a reference to the CcBox because
// it will cover the containing T and there may already be a mutable
// reference to it on the stack because we can end up being called
// from the drop method of strong Cc<T> to the same data.
// The standard library does the same sort of thing using `WeakInner`
&(*self._ptr.as_ptr()).data
}
}
}
// We implement CcBoxPtr on CcBox so we can add and operate on type erased CcBox's
// added to the ROOTS table
impl<T: Trace> CcBoxPtr for CcBox<T> {
#[inline(always)]
fn data(&self) -> &CcBoxData {
&self.data
}
}
unsafe fn deallocate(ptr: NonNull<dyn CcBoxPtr>) {
dealloc(ptr.cast().as_ptr(), Layout::for_value(ptr.as_ref()));
}
pub(crate) unsafe fn drop_value(ptr: NonNull<dyn CcBoxPtr>) {
ptr::drop_in_place(ptr.as_ptr());
}
#[cfg(test)]
mod tests {
use core::cell::RefCell;
use super::{collect_cycles, Cc, Trace, Tracer, Weak};
// Tests copied from `Rc<T>`.
#[test]
fn test_clone() {
{
let x = Cc::new(RefCell::new(5));
let y = x.clone();
*x.borrow_mut() = 20;
assert_eq!(*y.borrow(), 20);
}
collect_cycles();
}
#[test]
fn test_simple() {
let x = Cc::new(5);
assert_eq!(*x, 5);
}
#[test]
fn test_simple_clone() {
{
let x = Cc::new(5);
let y = x.clone();
assert_eq!(*x, 5);
assert_eq!(*y, 5);
}
collect_cycles();
}
#[test]
fn test_destructor() {
let x: Cc<Box<_>> = Cc::new(Box::new(5));
assert_eq!(**x, 5);
}
#[test]
fn test_live() {
{
let x = Cc::new(5);
let y = x.downgrade();
assert!(y.upgrade().is_some());
}
collect_cycles();
}
#[test]
fn test_dead() {
let x = Cc::new(5);
let y = x.downgrade();
drop(x);
assert!(y.upgrade().is_none());
}
#[test]
fn weak_self_cyclic() {
{
struct Cycle {
x: RefCell<Option<Weak<Cycle>>>,
}
impl Trace for Cycle {
fn trace(&self, _: &mut Tracer) {}
}
let a = Cc::new(Cycle {
x: RefCell::new(None),
});
let b = a.clone().downgrade();
*a.x.borrow_mut() = Some(b);
}
collect_cycles();
// hopefully we don't double-free (or leak)...
}
#[test]
fn is_unique() {
{
let x = Cc::new(3);
assert!(x.is_unique());
let y = x.clone();
assert!(!x.is_unique());
drop(y);
assert!(x.is_unique());
let w = x.downgrade();
assert!(!x.is_unique());
drop(w);
assert!(x.is_unique());
}
collect_cycles();
}
#[test]
fn test_strong_count() {
{
let a = Cc::new(0u32);
assert!(a.strong_count() == 1);
let w = a.downgrade();
assert!(a.strong_count() == 1);
let b = w.upgrade().expect("upgrade of live rc failed");
assert!(b.strong_count() == 2);
assert!(b.strong_count() == 2);
drop(w);
drop(a);
assert!(b.strong_count() == 1);
let c = b.clone();
assert!(b.strong_count() == 2);
assert!(c.strong_count() == 2);
}
collect_cycles();
}
#[test]
fn test_weak_count() {
{
let a = Cc::new(0u32);
assert!(a.strong_count() == 1);
assert!(a.weak_count() == 0);
let w = a.downgrade();
assert!(a.strong_count() == 1);
assert!(a.weak_count() == 1);
drop(w);
assert!(a.strong_count() == 1);
assert!(a.weak_count() == 0);
let c = a.clone();
assert!(a.strong_count() == 2);
assert!(a.weak_count() == 0);
drop(c);
}
collect_cycles();
}
#[test]
fn try_unwrap() {
{
let x = Cc::new(3);
assert_eq!(x.try_unwrap(), Ok(3));
let x = Cc::new(4);
let _y = x.clone();
assert_eq!(x.try_unwrap(), Err(Cc::new(4)));
let x = Cc::new(5);
let _w = x.downgrade();
assert_eq!(x.try_unwrap(), Err(Cc::new(5)));
}
collect_cycles();
}
#[test]
fn get_mut() {
{
let mut x = Cc::new(3);
*x.get_mut().unwrap() = 4;
assert_eq!(*x, 4);
let y = x.clone();
assert!(x.get_mut().is_none());
drop(y);
assert!(x.get_mut().is_some());
let _w = x.downgrade();
assert!(x.get_mut().is_none());
}
collect_cycles();
}
#[test]
fn test_cowrc_clone_make_unique() {
{
let mut cow0 = Cc::new(75);
let mut cow1 = cow0.clone();
let mut cow2 = cow1.clone();
assert!(75 == *cow0.make_unique());
assert!(75 == *cow1.make_unique());
assert!(75 == *cow2.make_unique());
*cow0.make_unique() += 1;
*cow1.make_unique() += 2;
*cow2.make_unique() += 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);
}
collect_cycles();
}
#[test]
fn test_cowrc_clone_unique2() {
{
let mut cow0 = Cc::new(75);
let cow1 = cow0.clone();
let cow2 = cow1.clone();
assert!(75 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
*cow0.make_unique() += 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);
}
collect_cycles();
}
#[test]
fn test_cowrc_clone_weak() {
{
let mut cow0 = Cc::new(75);
let cow1_weak = cow0.downgrade();
assert!(75 == *cow0);
assert!(75 == *cow1_weak.upgrade().unwrap());
*cow0.make_unique() += 1;
assert!(76 == *cow0);
assert!(cow1_weak.upgrade().is_none());
}
collect_cycles();
}
#[test]
fn test_show() {
let foo = Cc::new(75);
assert_eq!(format!("{:?}", foo), "75");
}
#[cfg(not(all(target_os = "macos", miri)))]
#[test]
fn test_map() {
let mut map = std::collections::HashMap::new();
map.insert("Foo".to_string(), 4);
let x = Cc::new(map);
assert_eq!(x.get("Foo"), Some(&4));
}
#[test]
fn list_cycle() {
use std::cell::RefCell;
struct List(Vec<Cc<RefCell<List>>>);
impl Trace for List {
fn trace(&self, tracer: &mut Tracer) {
self.0.trace(tracer);
}
}
{
let a = Cc::new(RefCell::new(List(Vec::new())));
let b = Cc::new(RefCell::new(List(Vec::new())));
{
let mut a = a.borrow_mut();
a.0.push(b.clone());
}
{
let mut b = b.borrow_mut();
b.0.push(a.clone());
}
}
collect_cycles();
}
#[test]
fn test_retain_weak() {
let retained_weak_a;
{
struct A {
x: Cc<RefCell<Option<A>>>,
}
struct WeakA {
_x: Weak<RefCell<Option<A>>>,
}
impl A {
fn downgrade(this: &Self) -> WeakA {
WeakA {
_x: Cc::downgrade(&this.x),
}
}
}
impl Clone for A {
fn clone(&self) -> Self {
A { x: self.x.clone() }
}
}
impl Trace for A {
fn trace(&self, tracer: &mut Tracer) {
self.x.trace(tracer);
}
}
let a = A {
x: Cc::new(RefCell::new(None)),
};
*a.x.borrow_mut() = Some(a.clone());
retained_weak_a = A::downgrade(&a);
}
collect_cycles();
let _x = retained_weak_a;
}
#[test]
fn test_no_leak_with_double_indirection() {
use crate::collect::*;
#[derive(Debug, Clone)]
struct S {
ty: Cc<Cc<i32>>,
}
// If either of the drops below is missing, we don't get a leak
let ty = Cc::new(5);
drop(ty.clone());
let s = S { ty: Cc::new(ty) };
drop(s.ty.clone());
// if collect_cycles() is called before s is dropped, we don't get a leak
std::mem::drop(s);
collect_cycles();
}
#[test]
fn test_double_visit_scan_black() {
let count = std::rc::Rc::new(std::cell::Cell::new(0));
struct A {
count: std::rc::Rc<std::cell::Cell<i32>>,
next_op: Cc<RefCell<Option<A>>>,
}
impl Clone for A {
fn clone(&self) -> Self {
self.count.set(self.count.get() + 1);
A {
count: self.count.clone(),
next_op: self.next_op.clone(),
}
}
}
impl Trace for A {
fn trace(&self, tracer: &mut Tracer) {
self.next_op.trace(tracer);
}
}
impl A {
fn new(count: std::rc::Rc<std::cell::Cell<i32>>, next_op: Option<A>) -> A {
count.set(count.get() + 1);
A {
count,
next_op: Cc::new(RefCell::new(next_op)),
}
}
}
impl Drop for A {
fn drop(&mut self) {
self.count.set(self.count.get() - 1);
}
}
{
let q;
{
let z = A::new(count.clone(), None);
let y = A::new(count.clone(), Some(z.clone()));
let x = A::new(count.clone(), Some(y));
*z.next_op.borrow_mut() = Some(x.clone());
q = x;
}
collect_cycles();
*q.next_op.borrow_mut() = None;
}
collect_cycles();
assert_eq!(count.get(), 0);
}
#[test]
fn extra_free() {
struct Env {
pub closures: Vec<Cc<RefCell<Clos>>>,
pub next: Option<Cc<Env>>,
}
impl Trace for Env {
fn trace(&self, tracer: &mut Tracer) {
self.closures.trace(tracer);
self.next.trace(tracer);
}
}
struct Clos {
pub env: Cc<Env>,
}
impl Trace for Clos {
fn trace(&self, tracer: &mut Tracer) {
self.env.trace(tracer);
}
}
let live_env = {
let base_env = Cc::new(Env {
closures: vec![],
next: None,
});
let env_a = Cc::new(Env {
closures: vec![Cc::new(RefCell::new(Clos {
env: base_env.clone(),
}))],
next: Some(base_env.clone()),
});
let circular_env = Cc::new(Env {
closures: vec![Cc::new(RefCell::new(Clos {
env: base_env.clone(),
}))],
next: Some(env_a.clone()),
});
circular_env.closures[0].replace(Clos {
env: circular_env.clone(),
});
let live_env = Cc::new(Env {
closures: vec![],
next: Some(env_a.clone()),
});
drop(base_env); // don't need the stack ref
drop(env_a); // don't need the stack ref
collect_cycles();
drop(circular_env); // cycle root
collect_cycles(); // <- incorrectly? frees env_a.
// mark_gray decrements env_a and does
// not reinstate (it's the root of the
// black region). collect_white frees
// circular_env, which decrements env_a
// again - to zero and frees it...
live_env
};
if let Some(a) = &live_env.next {
assert_eq!(a.closures.len(), 1);
}
drop(live_env);
collect_cycles();
}
#[test]
fn weak_cycle() {
type Owner = RefCell<Option<Weak<Gadget>>>;
struct Gadget {
owner: Cc<Owner>,
}
impl Trace for Gadget {
fn trace(&self, tracer: &mut Tracer) {
self.owner.trace(tracer);
}
}
let gadget_owner = Cc::new(RefCell::new(None));
let gadget = Cc::new(Gadget {
owner: gadget_owner.clone(),
});
*gadget_owner.borrow_mut() = Some(gadget.clone().downgrade());
drop(gadget_owner);
drop(gadget);
collect_cycles();
}
#[test]
fn clone_drop_collect() {
struct A {
a: Cc<i32>,
}
impl Trace for A {
fn trace(&self, tracer: &mut Tracer) {
self.a.trace(tracer);
}
}
let a = Cc::new(A { a: Cc::new(1) });
let b = Cc::clone(&a);
drop(b);
collect_cycles();
}
}