12 files changed, 673 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/loom/mocked.rs b/third_party/rust/tokio/src/loom/mocked.rs
new file mode 100644
index 0000000000..367d59b43a
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/mocked.rs
@@ -0,0 +1,40 @@
+pub(crate) use loom::*;
+
+pub(crate) mod sync {
+
+    pub(crate) use loom::sync::MutexGuard;
+
+    #[derive(Debug)]
+    pub(crate) struct Mutex<T>(loom::sync::Mutex<T>);
+
+    #[allow(dead_code)]
+    impl<T> Mutex<T> {
+        #[inline]
+        pub(crate) fn new(t: T) -> Mutex<T> {
+            Mutex(loom::sync::Mutex::new(t))
+        }
+
+        #[inline]
+        pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+            self.0.lock().unwrap()
+        }
+
+        #[inline]
+        pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+            self.0.try_lock().ok()
+        }
+    }
+    pub(crate) use loom::sync::*;
+}
+
+pub(crate) mod rand {
+    pub(crate) fn seed() -> u64 {
+        1
+    }
+}
+
+pub(crate) mod sys {
+    pub(crate) fn num_cpus() -> usize {
+        2
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/mod.rs b/third_party/rust/tokio/src/loom/mod.rs
new file mode 100644
index 0000000000..5957b5377d
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/mod.rs
@@ -0,0 +1,14 @@
+//! This module abstracts over `loom` and `std::sync` depending on whether we
+//! are running tests or not.
+
+#![allow(unused)]
+
+#[cfg(not(all(test, loom)))]
+mod std;
+#[cfg(not(all(test, loom)))]
+pub(crate) use self::std::*;
+
+#[cfg(all(test, loom))]
+mod mocked;
+#[cfg(all(test, loom))]
+pub(crate) use self::mocked::*;
diff --git a/third_party/rust/tokio/src/loom/std/atomic_ptr.rs b/third_party/rust/tokio/src/loom/std/atomic_ptr.rs
new file mode 100644
index 0000000000..236645f037
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_ptr.rs
@@ -0,0 +1,34 @@
+use std::fmt;
+use std::ops::{Deref, DerefMut};
+
+/// `AtomicPtr` providing an additional `load_unsync` function.
+pub(crate) struct AtomicPtr<T> {
+    inner: std::sync::atomic::AtomicPtr<T>,
+}
+
+impl<T> AtomicPtr<T> {
+    pub(crate) fn new(ptr: *mut T) -> AtomicPtr<T> {
+        let inner = std::sync::atomic::AtomicPtr::new(ptr);
+        AtomicPtr { inner }
+    }
+}
+
+impl<T> Deref for AtomicPtr<T> {
+    type Target = std::sync::atomic::AtomicPtr<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T> DerefMut for AtomicPtr<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+impl<T> fmt::Debug for AtomicPtr<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u16.rs b/third_party/rust/tokio/src/loom/std/atomic_u16.rs
new file mode 100644
index 0000000000..c1c531208c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u16.rs
@@ -0,0 +1,44 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU16` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU16 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU16>,
+}
+
+unsafe impl Send for AtomicU16 {}
+unsafe impl Sync for AtomicU16 {}
+
+impl AtomicU16 {
+    pub(crate) const fn new(val: u16) -> AtomicU16 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU16::new(val));
+        AtomicU16 { inner }
+    }
+
+    /// Performs an unsynchronized load.
+    ///
+    /// # Safety
+    ///
+    /// All mutations must have happened before the unsynchronized load.
+    /// Additionally, there must be no concurrent mutations.
+    pub(crate) unsafe fn unsync_load(&self) -> u16 {
+        *(*self.inner.get()).get_mut()
+    }
+}
+
+impl Deref for AtomicU16 {
+    type Target = std::sync::atomic::AtomicU16;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU16 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u32.rs b/third_party/rust/tokio/src/loom/std/atomic_u32.rs
new file mode 100644
index 0000000000..61f95fb30c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u32.rs
@@ -0,0 +1,34 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU32` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU32 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU32>,
+}
+
+unsafe impl Send for AtomicU32 {}
+unsafe impl Sync for AtomicU32 {}
+
+impl AtomicU32 {
+    pub(crate) const fn new(val: u32) -> AtomicU32 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU32::new(val));
+        AtomicU32 { inner }
+    }
+}
+
+impl Deref for AtomicU32 {
+    type Target = std::sync::atomic::AtomicU32;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU32 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u64.rs b/third_party/rust/tokio/src/loom/std/atomic_u64.rs
new file mode 100644
index 0000000000..113992d977
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u64.rs
@@ -0,0 +1,78 @@
+//! Implementation of an atomic u64 cell. On 64 bit platforms, this is a
+//! re-export of `AtomicU64`. On 32 bit platforms, this is implemented using a
+//! `Mutex`.
+
+// `AtomicU64` can only be used on targets with `target_has_atomic` is 64 or greater.
+// Once `cfg_target_has_atomic` feature is stable, we can replace it with
+// `#[cfg(target_has_atomic = "64")]`.
+// Refs: https://github.com/rust-lang/rust/tree/master/src/librustc_target
+cfg_has_atomic_u64! {
+    pub(crate) use std::sync::atomic::AtomicU64;
+}
+
+cfg_not_has_atomic_u64! {
+    use crate::loom::sync::Mutex;
+    use std::sync::atomic::Ordering;
+
+    #[derive(Debug)]
+    pub(crate) struct AtomicU64 {
+        inner: Mutex<u64>,
+    }
+
+    impl AtomicU64 {
+        pub(crate) fn new(val: u64) -> Self {
+            Self {
+                inner: Mutex::new(val),
+            }
+        }
+
+        pub(crate) fn load(&self, _: Ordering) -> u64 {
+            *self.inner.lock()
+        }
+
+        pub(crate) fn store(&self, val: u64, _: Ordering) {
+            *self.inner.lock() = val;
+        }
+
+        pub(crate) fn fetch_add(&self, val: u64, _: Ordering) -> u64 {
+            let mut lock = self.inner.lock();
+            let prev = *lock;
+            *lock = prev + val;
+            prev
+        }
+
+        pub(crate) fn fetch_or(&self, val: u64, _: Ordering) -> u64 {
+            let mut lock = self.inner.lock();
+            let prev = *lock;
+            *lock = prev | val;
+            prev
+        }
+
+        pub(crate) fn compare_exchange(
+            &self,
+            current: u64,
+            new: u64,
+            _success: Ordering,
+            _failure: Ordering,
+        ) -> Result<u64, u64> {
+            let mut lock = self.inner.lock();
+
+            if *lock == current {
+                *lock = new;
+                Ok(current)
+            } else {
+                Err(*lock)
+            }
+        }
+
+        pub(crate) fn compare_exchange_weak(
+            &self,
+            current: u64,
+            new: u64,
+            success: Ordering,
+            failure: Ordering,
+        ) -> Result<u64, u64> {
+            self.compare_exchange(current, new, success, failure)
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u8.rs b/third_party/rust/tokio/src/loom/std/atomic_u8.rs
new file mode 100644
index 0000000000..408aea338c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u8.rs
@@ -0,0 +1,34 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU8` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU8 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU8>,
+}
+
+unsafe impl Send for AtomicU8 {}
+unsafe impl Sync for AtomicU8 {}
+
+impl AtomicU8 {
+    pub(crate) const fn new(val: u8) -> AtomicU8 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU8::new(val));
+        AtomicU8 { inner }
+    }
+}
+
+impl Deref for AtomicU8 {
+    type Target = std::sync::atomic::AtomicU8;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU8 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_usize.rs b/third_party/rust/tokio/src/loom/std/atomic_usize.rs
new file mode 100644
index 0000000000..0d5f36e431
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_usize.rs
@@ -0,0 +1,56 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops;
+
+/// `AtomicUsize` providing an additional `load_unsync` function.
+pub(crate) struct AtomicUsize {
+    inner: UnsafeCell<std::sync::atomic::AtomicUsize>,
+}
+
+unsafe impl Send for AtomicUsize {}
+unsafe impl Sync for AtomicUsize {}
+
+impl AtomicUsize {
+    pub(crate) const fn new(val: usize) -> AtomicUsize {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicUsize::new(val));
+        AtomicUsize { inner }
+    }
+
+    /// Performs an unsynchronized load.
+    ///
+    /// # Safety
+    ///
+    /// All mutations must have happened before the unsynchronized load.
+    /// Additionally, there must be no concurrent mutations.
+    pub(crate) unsafe fn unsync_load(&self) -> usize {
+        *(*self.inner.get()).get_mut()
+    }
+
+    pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {
+        // safety: we have mutable access
+        f(unsafe { (*self.inner.get()).get_mut() })
+    }
+}
+
+impl ops::Deref for AtomicUsize {
+    type Target = std::sync::atomic::AtomicUsize;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl ops::DerefMut for AtomicUsize {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // safety: we hold `&mut self`
+        unsafe { &mut *self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicUsize {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/mod.rs b/third_party/rust/tokio/src/loom/std/mod.rs
new file mode 100644
index 0000000000..0c70bee74e
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/mod.rs
@@ -0,0 +1,108 @@
+#![cfg_attr(any(not(feature = "full"), loom), allow(unused_imports, dead_code))]
+
+mod atomic_ptr;
+mod atomic_u16;
+mod atomic_u32;
+mod atomic_u64;
+mod atomic_u8;
+mod atomic_usize;
+mod mutex;
+#[cfg(feature = "parking_lot")]
+mod parking_lot;
+mod unsafe_cell;
+
+pub(crate) mod cell {
+    pub(crate) use super::unsafe_cell::UnsafeCell;
+}
+
+#[cfg(any(
+    feature = "net",
+    feature = "process",
+    feature = "signal",
+    feature = "sync",
+))]
+pub(crate) mod future {
+    pub(crate) use crate::sync::AtomicWaker;
+}
+
+pub(crate) mod hint {
+    pub(crate) use std::hint::spin_loop;
+}
+
+pub(crate) mod rand {
+    use std::collections::hash_map::RandomState;
+    use std::hash::{BuildHasher, Hash, Hasher};
+    use std::sync::atomic::AtomicU32;
+    use std::sync::atomic::Ordering::Relaxed;
+
+    static COUNTER: AtomicU32 = AtomicU32::new(1);
+
+    pub(crate) fn seed() -> u64 {
+        let rand_state = RandomState::new();
+
+        let mut hasher = rand_state.build_hasher();
+
+        // Hash some unique-ish data to generate some new state
+        COUNTER.fetch_add(1, Relaxed).hash(&mut hasher);
+
+        // Get the seed
+        hasher.finish()
+    }
+}
+
+pub(crate) mod sync {
+    pub(crate) use std::sync::{Arc, Weak};
+
+    // Below, make sure all the feature-influenced types are exported for
+    // internal use. Note however that some are not _currently_ named by
+    // consuming code.
+
+    #[cfg(feature = "parking_lot")]
+    #[allow(unused_imports)]
+    pub(crate) use crate::loom::std::parking_lot::{
+        Condvar, Mutex, MutexGuard, RwLock, RwLockReadGuard, WaitTimeoutResult,
+    };
+
+    #[cfg(not(feature = "parking_lot"))]
+    #[allow(unused_imports)]
+    pub(crate) use std::sync::{Condvar, MutexGuard, RwLock, RwLockReadGuard, WaitTimeoutResult};
+
+    #[cfg(not(feature = "parking_lot"))]
+    pub(crate) use crate::loom::std::mutex::Mutex;
+
+    pub(crate) mod atomic {
+        pub(crate) use crate::loom::std::atomic_ptr::AtomicPtr;
+        pub(crate) use crate::loom::std::atomic_u16::AtomicU16;
+        pub(crate) use crate::loom::std::atomic_u32::AtomicU32;
+        pub(crate) use crate::loom::std::atomic_u64::AtomicU64;
+        pub(crate) use crate::loom::std::atomic_u8::AtomicU8;
+        pub(crate) use crate::loom::std::atomic_usize::AtomicUsize;
+
+        pub(crate) use std::sync::atomic::{fence, AtomicBool, Ordering};
+    }
+}
+
+pub(crate) mod sys {
+    #[cfg(feature = "rt-multi-thread")]
+    pub(crate) fn num_cpus() -> usize {
+        usize::max(1, num_cpus::get())
+    }
+
+    #[cfg(not(feature = "rt-multi-thread"))]
+    pub(crate) fn num_cpus() -> usize {
+        1
+    }
+}
+
+pub(crate) mod thread {
+    #[inline]
+    pub(crate) fn yield_now() {
+        std::hint::spin_loop();
+    }
+
+    #[allow(unused_imports)]
+    pub(crate) use std::thread::{
+        current, panicking, park, park_timeout, sleep, spawn, Builder, JoinHandle, LocalKey,
+        Result, Thread, ThreadId,
+    };
+}
diff --git a/third_party/rust/tokio/src/loom/std/mutex.rs b/third_party/rust/tokio/src/loom/std/mutex.rs
new file mode 100644
index 0000000000..3f686e0a78
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/mutex.rs
@@ -0,0 +1,31 @@
+use std::sync::{self, MutexGuard, TryLockError};
+
+/// Adapter for `std::Mutex` that removes the poisoning aspects
+/// from its api.
+#[derive(Debug)]
+pub(crate) struct Mutex<T: ?Sized>(sync::Mutex<T>);
+
+#[allow(dead_code)]
+impl<T> Mutex<T> {
+    #[inline]
+    pub(crate) fn new(t: T) -> Mutex<T> {
+        Mutex(sync::Mutex::new(t))
+    }
+
+    #[inline]
+    pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+        match self.0.lock() {
+            Ok(guard) => guard,
+            Err(p_err) => p_err.into_inner(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        match self.0.try_lock() {
+            Ok(guard) => Some(guard),
+            Err(TryLockError::Poisoned(p_err)) => Some(p_err.into_inner()),
+            Err(TryLockError::WouldBlock) => None,
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/parking_lot.rs b/third_party/rust/tokio/src/loom/std/parking_lot.rs
new file mode 100644
index 0000000000..034a0ce69a
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/parking_lot.rs
@@ -0,0 +1,184 @@
+//! A minimal adaption of the `parking_lot` synchronization primitives to the
+//! equivalent `std::sync` types.
+//!
+//! This can be extended to additional types/methods as required.
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::sync::LockResult;
+use std::time::Duration;
+
+// All types in this file are marked with PhantomData to ensure that
+// parking_lot's send_guard feature does not leak through and affect when Tokio
+// types are Send.
+//
+// See <https://github.com/tokio-rs/tokio/pull/4359> for more info.
+
+// Types that do not need wrapping
+pub(crate) use parking_lot::WaitTimeoutResult;
+
+#[derive(Debug)]
+pub(crate) struct Mutex<T: ?Sized>(PhantomData<std::sync::Mutex<T>>, parking_lot::Mutex<T>);
+
+#[derive(Debug)]
+pub(crate) struct RwLock<T>(PhantomData<std::sync::RwLock<T>>, parking_lot::RwLock<T>);
+
+#[derive(Debug)]
+pub(crate) struct Condvar(PhantomData<std::sync::Condvar>, parking_lot::Condvar);
+
+#[derive(Debug)]
+pub(crate) struct MutexGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::MutexGuard<'a, T>>,
+    parking_lot::MutexGuard<'a, T>,
+);
+
+#[derive(Debug)]
+pub(crate) struct RwLockReadGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockReadGuard<'a, T>>,
+    parking_lot::RwLockReadGuard<'a, T>,
+);
+
+#[derive(Debug)]
+pub(crate) struct RwLockWriteGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockWriteGuard<'a, T>>,
+    parking_lot::RwLockWriteGuard<'a, T>,
+);
+
+impl<T> Mutex<T> {
+    #[inline]
+    pub(crate) fn new(t: T) -> Mutex<T> {
+        Mutex(PhantomData, parking_lot::Mutex::new(t))
+    }
+
+    #[inline]
+    #[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "parking_lot",))))]
+    pub(crate) const fn const_new(t: T) -> Mutex<T> {
+        Mutex(PhantomData, parking_lot::const_mutex(t))
+    }
+
+    #[inline]
+    pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+        MutexGuard(PhantomData, self.1.lock())
+    }
+
+    #[inline]
+    pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        self.1
+            .try_lock()
+            .map(|guard| MutexGuard(PhantomData, guard))
+    }
+
+    #[inline]
+    pub(crate) fn get_mut(&mut self) -> &mut T {
+        self.1.get_mut()
+    }
+
+    // Note: Additional methods `is_poisoned` and `into_inner`, can be
+    // provided here as needed.
+}
+
+impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
+    }
+}
+
+impl<T> RwLock<T> {
+    pub(crate) fn new(t: T) -> RwLock<T> {
+        RwLock(PhantomData, parking_lot::RwLock::new(t))
+    }
+
+    pub(crate) fn read(&self) -> LockResult<RwLockReadGuard<'_, T>> {
+        Ok(RwLockReadGuard(PhantomData, self.1.read()))
+    }
+
+    pub(crate) fn write(&self) -> LockResult<RwLockWriteGuard<'_, T>> {
+        Ok(RwLockWriteGuard(PhantomData, self.1.write()))
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockReadGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockWriteGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for RwLockWriteGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
+    }
+}
+
+impl Condvar {
+    #[inline]
+    pub(crate) fn new() -> Condvar {
+        Condvar(PhantomData, parking_lot::Condvar::new())
+    }
+
+    #[inline]
+    pub(crate) fn notify_one(&self) {
+        self.1.notify_one();
+    }
+
+    #[inline]
+    pub(crate) fn notify_all(&self) {
+        self.1.notify_all();
+    }
+
+    #[inline]
+    pub(crate) fn wait<'a, T>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+    ) -> LockResult<MutexGuard<'a, T>> {
+        self.1.wait(&mut guard.1);
+        Ok(guard)
+    }
+
+    #[inline]
+    pub(crate) fn wait_timeout<'a, T>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        timeout: Duration,
+    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
+        let wtr = self.1.wait_for(&mut guard.1, timeout);
+        Ok((guard, wtr))
+    }
+
+    // Note: Additional methods `wait_timeout_ms`, `wait_timeout_until`,
+    // `wait_until` can be provided here as needed.
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/unsafe_cell.rs b/third_party/rust/tokio/src/loom/std/unsafe_cell.rs
new file mode 100644
index 0000000000..66c1d7943e
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/unsafe_cell.rs
@@ -0,0 +1,16 @@
+#[derive(Debug)]
+pub(crate) struct UnsafeCell<T>(std::cell::UnsafeCell<T>);
+
+impl<T> UnsafeCell<T> {
+    pub(crate) const fn new(data: T) -> UnsafeCell<T> {
+        UnsafeCell(std::cell::UnsafeCell::new(data))
+    }
+
+    pub(crate) fn with<R>(&self, f: impl FnOnce(*const T) -> R) -> R {
+        f(self.0.get())
+    }
+
+    pub(crate) fn with_mut<R>(&self, f: impl FnOnce(*mut T) -> R) -> R {
+        f(self.0.get())
+    }
+}