diff options
Diffstat (limited to 'third_party/rust/atomic_refcell')
| -rw-r--r-- | third_party/rust/atomic_refcell/.cargo-checksum.json | 1 | ||||
| -rw-r--r-- | third_party/rust/atomic_refcell/Cargo.toml | 21 | ||||
| -rw-r--r-- | third_party/rust/atomic_refcell/README.md | 2 | ||||
| -rw-r--r-- | third_party/rust/atomic_refcell/benches/basic.rs | 37 | ||||
| -rw-r--r-- | third_party/rust/atomic_refcell/src/lib.rs | 486 | ||||
| -rw-r--r-- | third_party/rust/atomic_refcell/tests/basic.rs | 156 |
6 files changed, 703 insertions, 0 deletions
diff --git a/third_party/rust/atomic_refcell/.cargo-checksum.json b/third_party/rust/atomic_refcell/.cargo-checksum.json new file mode 100644 index 0000000000..0dc5177384 --- /dev/null +++ b/third_party/rust/atomic_refcell/.cargo-checksum.json @@ -0,0 +1 @@ +{"files":{"Cargo.toml":"1191be2168fb6a9914afd20cd5a1c7ac5e612596b834a60ac495b45629805a51","README.md":"6b468f17809063c5dcee5758d1daca147d74e2297a9dc78a5e50ae13d9ea6e42","benches/basic.rs":"aba00ab044b37a7fb4e5c855cf88a323a04d6143b651717e227fdd12735602f3","src/lib.rs":"631e765b36b20ab47c7cd35fb0bf2e9b6f9c2bf2a0ab72bd67d59759ff53a71f","tests/basic.rs":"2cefa20188254d8357a595975733ad1bffb4de90933d5d9e9caa17232c1d646b"},"package":"73b5e5f48b927f04e952dedc932f31995a65a0bf65ec971c74436e51bf6e970d"}
\ No newline at end of file diff --git a/third_party/rust/atomic_refcell/Cargo.toml b/third_party/rust/atomic_refcell/Cargo.toml new file mode 100644 index 0000000000..d71703f230 --- /dev/null +++ b/third_party/rust/atomic_refcell/Cargo.toml @@ -0,0 +1,21 @@ +# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO +# +# When uploading crates to the registry Cargo will automatically +# "normalize" Cargo.toml files for maximal compatibility +# with all versions of Cargo and also rewrite `path` dependencies +# to registry (e.g., crates.io) dependencies. +# +# If you are reading this file be aware that the original Cargo.toml +# will likely look very different (and much more reasonable). +# See Cargo.toml.orig for the original contents. + +[package] +name = "atomic_refcell" +version = "0.1.8" +authors = ["Bobby Holley <bobbyholley@gmail.com>"] +description = "Threadsafe RefCell" +documentation = "https://docs.rs/atomic_refcell/" +license = "Apache-2.0/MIT" +repository = "https://github.com/bholley/atomic_refcell" + +[dependencies] diff --git a/third_party/rust/atomic_refcell/README.md b/third_party/rust/atomic_refcell/README.md new file mode 100644 index 0000000000..de72c55daa --- /dev/null +++ b/third_party/rust/atomic_refcell/README.md @@ -0,0 +1,2 @@ +# atomic_refcell +Threadsafe RefCell for Rust. diff --git a/third_party/rust/atomic_refcell/benches/basic.rs b/third_party/rust/atomic_refcell/benches/basic.rs new file mode 100644 index 0000000000..3902a98a37 --- /dev/null +++ b/third_party/rust/atomic_refcell/benches/basic.rs @@ -0,0 +1,37 @@ +#![feature(test)] + +extern crate atomic_refcell; +extern crate test; + +use atomic_refcell::AtomicRefCell; +use test::Bencher; + +#[derive(Default)] +struct Bar(u32); + +#[bench] +fn immutable_borrow(b: &mut Bencher) { + let a = AtomicRefCell::new(Bar::default()); + b.iter(|| a.borrow()); +} + +#[bench] +fn immutable_second_borrow(b: &mut Bencher) { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow(); + b.iter(|| a.borrow()); +} + +#[bench] +fn immutable_third_borrow(b: &mut Bencher) { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow(); + let _second = a.borrow(); + b.iter(|| a.borrow()); +} + +#[bench] +fn mutable_borrow(b: &mut Bencher) { + let a = AtomicRefCell::new(Bar::default()); + b.iter(|| a.borrow_mut()); +} diff --git a/third_party/rust/atomic_refcell/src/lib.rs b/third_party/rust/atomic_refcell/src/lib.rs new file mode 100644 index 0000000000..dbf599aa52 --- /dev/null +++ b/third_party/rust/atomic_refcell/src/lib.rs @@ -0,0 +1,486 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +//! Implements a container type providing RefCell-like semantics for objects +//! shared across threads. +//! +//! RwLock is traditionally considered to be the |Sync| analogue of RefCell. +//! However, for consumers that can guarantee that they will never mutably +//! borrow the contents concurrently with immutable borrows, an RwLock is +//! overkill, and has key disadvantages: +//! * Performance: Even the fastest existing implementation of RwLock (that of +//! parking_lot) performs at least two atomic operations during immutable +//! borrows. This makes mutable borrows significantly cheaper than immutable +//! borrows, leading to weird incentives when writing performance-critical +//! code. +//! * Features: Implementing AtomicRefCell on top of RwLock makes it impossible +//! to implement useful things like AtomicRef{,Mut}::map. +//! +//! As such, we re-implement RefCell semantics from scratch with a single atomic +//! reference count. The primary complication of this scheme relates to keeping +//! things in a consistent state when one thread performs an illegal borrow and +//! panics. Since an AtomicRefCell can be accessed by multiple threads, and since +//! panics are recoverable, we need to ensure that an illegal (panicking) access by +//! one thread does not lead to undefined behavior on other, still-running threads. +//! +//! So we represent things as follows: +//! * Any value with the high bit set (so half the total refcount space) indicates +//! a mutable borrow. +//! * Mutable borrows perform an atomic compare-and-swap, swapping in the high bit +//! if the current value is zero. If the current value is non-zero, the thread +//! panics and the value is left undisturbed. +//! * Immutable borrows perform an atomic increment. If the new value has the high +//! bit set, the thread panics. The incremented refcount is left as-is, since it +//! still represents a valid mutable borrow. When the mutable borrow is released, +//! the refcount is set unconditionally to zero, clearing any stray increments by +//! panicked threads. +//! +//! There are a few additional purely-academic complications to handle overflow, +//! which are documented in the implementation. +//! +//! The rest of this module is mostly derived by copy-pasting the implementation of +//! RefCell and fixing things up as appropriate. Certain non-threadsafe methods +//! have been removed. We segment the concurrency logic from the rest of the code to +//! keep the tricky parts small and easy to audit. + +#![no_std] +#![allow(unsafe_code)] +#![deny(missing_docs)] + +use core::cell::UnsafeCell; +use core::cmp; +use core::fmt; +use core::fmt::{Debug, Display}; +use core::ops::{Deref, DerefMut}; +use core::sync::atomic; +use core::sync::atomic::AtomicUsize; + +/// A threadsafe analogue to RefCell. +pub struct AtomicRefCell<T: ?Sized> { + borrow: AtomicUsize, + value: UnsafeCell<T>, +} + +/// An error returned by [`AtomicRefCell::try_borrow`](struct.AtomicRefCell.html#method.try_borrow). +pub struct BorrowError { + _private: (), +} + +impl Debug for BorrowError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("BorrowError").finish() + } +} + +impl Display for BorrowError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + Display::fmt("already mutably borrowed", f) + } +} + +/// An error returned by [`AtomicRefCell::try_borrow_mut`](struct.AtomicRefCell.html#method.try_borrow_mut). +pub struct BorrowMutError { + _private: (), +} + +impl Debug for BorrowMutError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("BorrowMutError").finish() + } +} + +impl Display for BorrowMutError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + Display::fmt("already borrowed", f) + } +} + +impl<T> AtomicRefCell<T> { + /// Creates a new `AtomicRefCell` containing `value`. + #[inline] + pub const fn new(value: T) -> AtomicRefCell<T> { + AtomicRefCell { + borrow: AtomicUsize::new(0), + value: UnsafeCell::new(value), + } + } + + /// Consumes the `AtomicRefCell`, returning the wrapped value. + #[inline] + pub fn into_inner(self) -> T { + debug_assert!(self.borrow.load(atomic::Ordering::Acquire) == 0); + self.value.into_inner() + } +} + +impl<T: ?Sized> AtomicRefCell<T> { + /// Immutably borrows the wrapped value. + #[inline] + pub fn borrow(&self) -> AtomicRef<T> { + match AtomicBorrowRef::try_new(&self.borrow) { + Ok(borrow) => AtomicRef { + value: unsafe { &*self.value.get() }, + borrow, + }, + Err(s) => panic!("{}", s), + } + } + + /// Attempts to immutably borrow the wrapped value, but instead of panicking + /// on a failed borrow, returns `Err`. + #[inline] + pub fn try_borrow(&self) -> Result<AtomicRef<T>, BorrowError> { + match AtomicBorrowRef::try_new(&self.borrow) { + Ok(borrow) => Ok(AtomicRef { + value: unsafe { &*self.value.get() }, + borrow, + }), + Err(_) => Err(BorrowError { _private: () }), + } + } + + /// Mutably borrows the wrapped value. + #[inline] + pub fn borrow_mut(&self) -> AtomicRefMut<T> { + match AtomicBorrowRefMut::try_new(&self.borrow) { + Ok(borrow) => AtomicRefMut { + value: unsafe { &mut *self.value.get() }, + borrow, + }, + Err(s) => panic!("{}", s), + } + } + + /// Attempts to mutably borrow the wrapped value, but instead of panicking + /// on a failed borrow, returns `Err`. + #[inline] + pub fn try_borrow_mut(&self) -> Result<AtomicRefMut<T>, BorrowMutError> { + match AtomicBorrowRefMut::try_new(&self.borrow) { + Ok(borrow) => Ok(AtomicRefMut { + value: unsafe { &mut *self.value.get() }, + borrow, + }), + Err(_) => Err(BorrowMutError { _private: () }), + } + } + + /// Returns a raw pointer to the underlying data in this cell. + /// + /// External synchronization is needed to avoid data races when dereferencing + /// the pointer. + #[inline] + pub fn as_ptr(&self) -> *mut T { + self.value.get() + } + + /// Returns a mutable reference to the wrapped value. + /// + /// No runtime checks take place (unless debug assertions are enabled) + /// because this call borrows `AtomicRefCell` mutably at compile-time. + #[inline] + pub fn get_mut(&mut self) -> &mut T { + debug_assert!(self.borrow.load(atomic::Ordering::Acquire) == 0); + unsafe { &mut *self.value.get() } + } +} + +// +// Core synchronization logic. Keep this section small and easy to audit. +// + +const HIGH_BIT: usize = !(::core::usize::MAX >> 1); +const MAX_FAILED_BORROWS: usize = HIGH_BIT + (HIGH_BIT >> 1); + +struct AtomicBorrowRef<'b> { + borrow: &'b AtomicUsize, +} + +impl<'b> AtomicBorrowRef<'b> { + #[inline] + fn try_new(borrow: &'b AtomicUsize) -> Result<Self, &'static str> { + let new = borrow.fetch_add(1, atomic::Ordering::Acquire) + 1; + if new & HIGH_BIT != 0 { + // If the new count has the high bit set, that almost certainly + // means there's an pre-existing mutable borrow. In that case, + // we simply leave the increment as a benign side-effect and + // return `Err`. Once the mutable borrow is released, the + // count will be reset to zero unconditionally. + // + // The overflow check here ensures that an unbounded number of + // immutable borrows during the scope of one mutable borrow + // will soundly trigger a panic (or abort) rather than UB. + Self::check_overflow(borrow, new); + Err("already mutably borrowed") + } else { + Ok(AtomicBorrowRef { borrow: borrow }) + } + } + + #[cold] + #[inline(never)] + fn check_overflow(borrow: &'b AtomicUsize, new: usize) { + if new == HIGH_BIT { + // We overflowed into the reserved upper half of the refcount + // space. Before panicking, decrement the refcount to leave things + // in a consistent immutable-borrow state. + // + // This can basically only happen if somebody forget()s AtomicRefs + // in a tight loop. + borrow.fetch_sub(1, atomic::Ordering::Release); + panic!("too many immutable borrows"); + } else if new >= MAX_FAILED_BORROWS { + // During the mutable borrow, an absurd number of threads have + // attempted to increment the refcount with immutable borrows. + // To avoid hypothetically wrapping the refcount, we abort the + // process once a certain threshold is reached. + // + // This requires billions of borrows to fail during the scope of + // one mutable borrow, and so is very unlikely to happen in a real + // program. + // + // To avoid a potential unsound state after overflowing, we make + // sure the entire process aborts. + // + // Right now, there's no stable way to do that without `std`: + // https://github.com/rust-lang/rust/issues/67952 + // As a workaround, we cause an abort by making this thread panic + // during the unwinding of another panic. + // + // On platforms where the panic strategy is already 'abort', the + // ForceAbort object here has no effect, as the program already + // panics before it is dropped. + struct ForceAbort; + impl Drop for ForceAbort { + fn drop(&mut self) { + panic!("Aborting to avoid unsound state of AtomicRefCell"); + } + } + let _abort = ForceAbort; + panic!("Too many failed borrows"); + } + } +} + +impl<'b> Drop for AtomicBorrowRef<'b> { + #[inline] + fn drop(&mut self) { + let old = self.borrow.fetch_sub(1, atomic::Ordering::Release); + // This assertion is technically incorrect in the case where another + // thread hits the hypothetical overflow case, since we might observe + // the refcount before it fixes it up (and panics). But that never will + // never happen in a real program, and this is a debug_assert! anyway. + debug_assert!(old & HIGH_BIT == 0); + } +} + +struct AtomicBorrowRefMut<'b> { + borrow: &'b AtomicUsize, +} + +impl<'b> Drop for AtomicBorrowRefMut<'b> { + #[inline] + fn drop(&mut self) { + self.borrow.store(0, atomic::Ordering::Release); + } +} + +impl<'b> AtomicBorrowRefMut<'b> { + #[inline] + fn try_new(borrow: &'b AtomicUsize) -> Result<AtomicBorrowRefMut<'b>, &'static str> { + // Use compare-and-swap to avoid corrupting the immutable borrow count + // on illegal mutable borrows. + let old = match borrow.compare_exchange( + 0, + HIGH_BIT, + atomic::Ordering::Acquire, + atomic::Ordering::Relaxed, + ) { + Ok(x) => x, + Err(x) => x, + }; + + if old == 0 { + Ok(AtomicBorrowRefMut { borrow }) + } else if old & HIGH_BIT == 0 { + Err("already immutably borrowed") + } else { + Err("already mutably borrowed") + } + } +} + +unsafe impl<T: ?Sized + Send> Send for AtomicRefCell<T> {} +unsafe impl<T: ?Sized + Send + Sync> Sync for AtomicRefCell<T> {} + +// +// End of core synchronization logic. No tricky thread stuff allowed below +// this point. +// + +impl<T: Clone> Clone for AtomicRefCell<T> { + #[inline] + fn clone(&self) -> AtomicRefCell<T> { + AtomicRefCell::new(self.borrow().clone()) + } +} + +impl<T: Default> Default for AtomicRefCell<T> { + #[inline] + fn default() -> AtomicRefCell<T> { + AtomicRefCell::new(Default::default()) + } +} + +impl<T: ?Sized + PartialEq> PartialEq for AtomicRefCell<T> { + #[inline] + fn eq(&self, other: &AtomicRefCell<T>) -> bool { + *self.borrow() == *other.borrow() + } +} + +impl<T: ?Sized + Eq> Eq for AtomicRefCell<T> {} + +impl<T: ?Sized + PartialOrd> PartialOrd for AtomicRefCell<T> { + #[inline] + fn partial_cmp(&self, other: &AtomicRefCell<T>) -> Option<cmp::Ordering> { + self.borrow().partial_cmp(&*other.borrow()) + } +} + +impl<T: ?Sized + Ord> Ord for AtomicRefCell<T> { + #[inline] + fn cmp(&self, other: &AtomicRefCell<T>) -> cmp::Ordering { + self.borrow().cmp(&*other.borrow()) + } +} + +impl<T> From<T> for AtomicRefCell<T> { + fn from(t: T) -> AtomicRefCell<T> { + AtomicRefCell::new(t) + } +} + +impl<'b> Clone for AtomicBorrowRef<'b> { + #[inline] + fn clone(&self) -> AtomicBorrowRef<'b> { + AtomicBorrowRef::try_new(self.borrow).unwrap() + } +} + +/// A wrapper type for an immutably borrowed value from an `AtomicRefCell<T>`. +pub struct AtomicRef<'b, T: ?Sized + 'b> { + value: &'b T, + borrow: AtomicBorrowRef<'b>, +} + +impl<'b, T: ?Sized> Deref for AtomicRef<'b, T> { + type Target = T; + + #[inline] + fn deref(&self) -> &T { + self.value + } +} + +impl<'b, T: ?Sized> AtomicRef<'b, T> { + /// Copies an `AtomicRef`. + #[inline] + pub fn clone(orig: &AtomicRef<'b, T>) -> AtomicRef<'b, T> { + AtomicRef { + value: orig.value, + borrow: orig.borrow.clone(), + } + } + + /// Make a new `AtomicRef` for a component of the borrowed data. + #[inline] + pub fn map<U: ?Sized, F>(orig: AtomicRef<'b, T>, f: F) -> AtomicRef<'b, U> + where + F: FnOnce(&T) -> &U, + { + AtomicRef { + value: f(orig.value), + borrow: orig.borrow, + } + } + + /// Make a new `AtomicRef` for an optional component of the borrowed data. + #[inline] + pub fn filter_map<U: ?Sized, F>(orig: AtomicRef<'b, T>, f: F) -> Option<AtomicRef<'b, U>> + where + F: FnOnce(&T) -> Option<&U>, + { + Some(AtomicRef { + value: f(orig.value)?, + borrow: orig.borrow, + }) + } +} + +impl<'b, T: ?Sized> AtomicRefMut<'b, T> { + /// Make a new `AtomicRefMut` for a component of the borrowed data, e.g. an enum + /// variant. + #[inline] + pub fn map<U: ?Sized, F>(orig: AtomicRefMut<'b, T>, f: F) -> AtomicRefMut<'b, U> + where + F: FnOnce(&mut T) -> &mut U, + { + AtomicRefMut { + value: f(orig.value), + borrow: orig.borrow, + } + } + + /// Make a new `AtomicRefMut` for an optional component of the borrowed data. + #[inline] + pub fn filter_map<U: ?Sized, F>(orig: AtomicRefMut<'b, T>, f: F) -> Option<AtomicRefMut<'b, U>> + where + F: FnOnce(&mut T) -> Option<&mut U>, + { + Some(AtomicRefMut { + value: f(orig.value)?, + borrow: orig.borrow, + }) + } +} + +/// A wrapper type for a mutably borrowed value from an `AtomicRefCell<T>`. +pub struct AtomicRefMut<'b, T: ?Sized + 'b> { + value: &'b mut T, + borrow: AtomicBorrowRefMut<'b>, +} + +impl<'b, T: ?Sized> Deref for AtomicRefMut<'b, T> { + type Target = T; + + #[inline] + fn deref(&self) -> &T { + self.value + } +} + +impl<'b, T: ?Sized> DerefMut for AtomicRefMut<'b, T> { + #[inline] + fn deref_mut(&mut self) -> &mut T { + self.value + } +} + +impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRef<'b, T> { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + self.value.fmt(f) + } +} + +impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRefMut<'b, T> { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + self.value.fmt(f) + } +} + +impl<T: ?Sized + Debug> Debug for AtomicRefCell<T> { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + write!(f, "AtomicRefCell {{ ... }}") + } +} diff --git a/third_party/rust/atomic_refcell/tests/basic.rs b/third_party/rust/atomic_refcell/tests/basic.rs new file mode 100644 index 0000000000..a37833085d --- /dev/null +++ b/third_party/rust/atomic_refcell/tests/basic.rs @@ -0,0 +1,156 @@ +extern crate atomic_refcell; + +use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut}; + +#[derive(Debug)] +struct Foo { + u: u32, +} + +#[derive(Debug)] +struct Bar { + f: Foo, +} + +impl Default for Bar { + fn default() -> Self { + Bar { f: Foo { u: 42 } } + } +} + +// FIXME(bholley): Add tests to exercise this in concurrent scenarios. + +#[test] +fn immutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow(); + let _second = a.borrow(); +} + +#[test] +fn try_immutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.try_borrow().unwrap(); + let _second = a.try_borrow().unwrap(); +} + +#[test] +fn mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _ = a.borrow_mut(); +} + +#[test] +fn try_mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _ = a.try_borrow_mut().unwrap(); +} + +#[test] +fn get_mut() { + let mut a = AtomicRefCell::new(Bar::default()); + let _ = a.get_mut(); +} + +#[test] +fn interleaved() { + let a = AtomicRefCell::new(Bar::default()); + { + let _ = a.borrow_mut(); + } + { + let _first = a.borrow(); + let _second = a.borrow(); + } + { + let _ = a.borrow_mut(); + } +} + +#[test] +fn try_interleaved() { + let a = AtomicRefCell::new(Bar::default()); + { + let _ = a.try_borrow_mut().unwrap(); + } + { + let _first = a.try_borrow().unwrap(); + let _second = a.try_borrow().unwrap(); + let _ = a.try_borrow_mut().unwrap_err(); + } + { + let _first = a.try_borrow_mut().unwrap(); + let _ = a.try_borrow().unwrap_err(); + } +} + +#[test] +#[should_panic(expected = "already immutably borrowed")] +fn immutable_then_mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow(); + let _second = a.borrow_mut(); +} + +#[test] +fn immutable_then_try_mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow(); + let _second = a.try_borrow_mut().unwrap_err(); +} + +#[test] +#[should_panic(expected = "already mutably borrowed")] +fn mutable_then_immutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow_mut(); + let _second = a.borrow(); +} + +#[test] +fn mutable_then_try_immutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow_mut(); + let _second = a.try_borrow().unwrap_err(); +} + +#[test] +#[should_panic(expected = "already mutably borrowed")] +fn double_mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow_mut(); + let _second = a.borrow_mut(); +} + +#[test] +fn mutable_then_try_mutable() { + let a = AtomicRefCell::new(Bar::default()); + let _first = a.borrow_mut(); + let _second = a.try_borrow_mut().unwrap_err(); +} + +#[test] +fn map() { + let a = AtomicRefCell::new(Bar::default()); + let b = a.borrow(); + assert_eq!(b.f.u, 42); + let c = AtomicRef::map(b, |x| &x.f); + assert_eq!(c.u, 42); + let d = AtomicRef::map(c, |x| &x.u); + assert_eq!(*d, 42); +} + +#[test] +fn map_mut() { + let a = AtomicRefCell::new(Bar::default()); + let mut b = a.borrow_mut(); + assert_eq!(b.f.u, 42); + b.f.u = 43; + let mut c = AtomicRefMut::map(b, |x| &mut x.f); + assert_eq!(c.u, 43); + c.u = 44; + let mut d = AtomicRefMut::map(c, |x| &mut x.u); + assert_eq!(*d, 44); + *d = 45; + assert_eq!(*d, 45); +} |