Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

13 files changed, 3898 insertions, 0 deletions

diff --git a/vendor/crossbeam-utils/src/atomic/atomic_cell.rs b/vendor/crossbeam-utils/src/atomic/atomic_cell.rs
new file mode 100644
index 000000000..9fed45d4c
--- /dev/null
+++ b/vendor/crossbeam-utils/src/atomic/atomic_cell.rs
@@ -0,0 +1,1124 @@
+// Necessary for implementing atomic methods for `AtomicUnit`
+#![allow(clippy::unit_arg)]
+
+use crate::primitive::sync::atomic::{self, AtomicBool};
+use core::cell::UnsafeCell;
+use core::cmp;
+use core::fmt;
+use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::sync::atomic::Ordering;
+
+use core::ptr;
+
+#[cfg(feature = "std")]
+use std::panic::{RefUnwindSafe, UnwindSafe};
+
+use super::seq_lock::SeqLock;
+
+/// A thread-safe mutable memory location.
+///
+/// This type is equivalent to [`Cell`], except it can also be shared among multiple threads.
+///
+/// Operations on `AtomicCell`s use atomic instructions whenever possible, and synchronize using
+/// global locks otherwise. You can call [`AtomicCell::<T>::is_lock_free()`] to check whether
+/// atomic instructions or locks will be used.
+///
+/// Atomic loads use the [`Acquire`] ordering and atomic stores use the [`Release`] ordering.
+///
+/// [`Cell`]: std::cell::Cell
+/// [`AtomicCell::<T>::is_lock_free()`]: AtomicCell::is_lock_free
+/// [`Acquire`]: std::sync::atomic::Ordering::Acquire
+/// [`Release`]: std::sync::atomic::Ordering::Release
+#[repr(transparent)]
+pub struct AtomicCell<T> {
+    /// The inner value.
+    ///
+    /// If this value can be transmuted into a primitive atomic type, it will be treated as such.
+    /// Otherwise, all potentially concurrent operations on this data will be protected by a global
+    /// lock.
+    ///
+    /// Using MaybeUninit to prevent code outside the cell from observing partially initialized state:
+    /// <https://github.com/crossbeam-rs/crossbeam/issues/833>
+    ///
+    /// Note:
+    /// - we'll never store uninitialized `T` due to our API only using initialized `T`.
+    /// - this `MaybeUninit` does *not* fix <https://github.com/crossbeam-rs/crossbeam/issues/315>.
+    value: UnsafeCell<MaybeUninit<T>>,
+}
+
+unsafe impl<T: Send> Send for AtomicCell<T> {}
+unsafe impl<T: Send> Sync for AtomicCell<T> {}
+
+#[cfg(feature = "std")]
+impl<T> UnwindSafe for AtomicCell<T> {}
+#[cfg(feature = "std")]
+impl<T> RefUnwindSafe for AtomicCell<T> {}
+
+impl<T> AtomicCell<T> {
+    /// Creates a new atomic cell initialized with `val`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    /// ```
+    pub const fn new(val: T) -> AtomicCell<T> {
+        AtomicCell {
+            value: UnsafeCell::new(MaybeUninit::new(val)),
+        }
+    }
+
+    /// Consumes the atomic and returns the contained value.
+    ///
+    /// This is safe because passing `self` by value guarantees that no other threads are
+    /// concurrently accessing the atomic data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    /// let v = a.into_inner();
+    ///
+    /// assert_eq!(v, 7);
+    /// ```
+    pub fn into_inner(self) -> T {
+        let this = ManuallyDrop::new(self);
+        // SAFETY:
+        // - passing `self` by value guarantees that no other threads are concurrently
+        //   accessing the atomic data
+        // - the raw pointer passed in is valid because we got it from an owned value.
+        // - `ManuallyDrop` prevents double dropping `T`
+        unsafe { this.as_ptr().read() }
+    }
+
+    /// Returns `true` if operations on values of this type are lock-free.
+    ///
+    /// If the compiler or the platform doesn't support the necessary atomic instructions,
+    /// `AtomicCell<T>` will use global locks for every potentially concurrent atomic operation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// // This type is internally represented as `AtomicUsize` so we can just use atomic
+    /// // operations provided by it.
+    /// assert_eq!(AtomicCell::<usize>::is_lock_free(), true);
+    ///
+    /// // A wrapper struct around `isize`.
+    /// struct Foo {
+    ///     bar: isize,
+    /// }
+    /// // `AtomicCell<Foo>` will be internally represented as `AtomicIsize`.
+    /// assert_eq!(AtomicCell::<Foo>::is_lock_free(), true);
+    ///
+    /// // Operations on zero-sized types are always lock-free.
+    /// assert_eq!(AtomicCell::<()>::is_lock_free(), true);
+    ///
+    /// // Very large types cannot be represented as any of the standard atomic types, so atomic
+    /// // operations on them will have to use global locks for synchronization.
+    /// assert_eq!(AtomicCell::<[u8; 1000]>::is_lock_free(), false);
+    /// ```
+    pub const fn is_lock_free() -> bool {
+        atomic_is_lock_free::<T>()
+    }
+
+    /// Stores `val` into the atomic cell.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    ///
+    /// assert_eq!(a.load(), 7);
+    /// a.store(8);
+    /// assert_eq!(a.load(), 8);
+    /// ```
+    pub fn store(&self, val: T) {
+        if mem::needs_drop::<T>() {
+            drop(self.swap(val));
+        } else {
+            unsafe {
+                atomic_store(self.as_ptr(), val);
+            }
+        }
+    }
+
+    /// Stores `val` into the atomic cell and returns the previous value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    ///
+    /// assert_eq!(a.load(), 7);
+    /// assert_eq!(a.swap(8), 7);
+    /// assert_eq!(a.load(), 8);
+    /// ```
+    pub fn swap(&self, val: T) -> T {
+        unsafe { atomic_swap(self.as_ptr(), val) }
+    }
+
+    /// Returns a raw pointer to the underlying data in this atomic cell.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(5);
+    ///
+    /// let ptr = a.as_ptr();
+    /// ```
+    #[inline]
+    pub fn as_ptr(&self) -> *mut T {
+        self.value.get() as *mut T
+    }
+}
+
+impl<T: Default> AtomicCell<T> {
+    /// Takes the value of the atomic cell, leaving `Default::default()` in its place.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(5);
+    /// let five = a.take();
+    ///
+    /// assert_eq!(five, 5);
+    /// assert_eq!(a.into_inner(), 0);
+    /// ```
+    pub fn take(&self) -> T {
+        self.swap(Default::default())
+    }
+}
+
+impl<T: Copy> AtomicCell<T> {
+    /// Loads a value from the atomic cell.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    ///
+    /// assert_eq!(a.load(), 7);
+    /// ```
+    pub fn load(&self) -> T {
+        unsafe { atomic_load(self.as_ptr()) }
+    }
+}
+
+impl<T: Copy + Eq> AtomicCell<T> {
+    /// If the current value equals `current`, stores `new` into the atomic cell.
+    ///
+    /// The return value is always the previous value. If it is equal to `current`, then the value
+    /// was updated.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(deprecated)]
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(1);
+    ///
+    /// assert_eq!(a.compare_and_swap(2, 3), 1);
+    /// assert_eq!(a.load(), 1);
+    ///
+    /// assert_eq!(a.compare_and_swap(1, 2), 1);
+    /// assert_eq!(a.load(), 2);
+    /// ```
+    // TODO: remove in the next major version.
+    #[deprecated(note = "Use `compare_exchange` instead")]
+    pub fn compare_and_swap(&self, current: T, new: T) -> T {
+        match self.compare_exchange(current, new) {
+            Ok(v) => v,
+            Err(v) => v,
+        }
+    }
+
+    /// If the current value equals `current`, stores `new` into the atomic cell.
+    ///
+    /// The return value is a result indicating whether the new value was written and containing
+    /// the previous value. On success this value is guaranteed to be equal to `current`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(1);
+    ///
+    /// assert_eq!(a.compare_exchange(2, 3), Err(1));
+    /// assert_eq!(a.load(), 1);
+    ///
+    /// assert_eq!(a.compare_exchange(1, 2), Ok(1));
+    /// assert_eq!(a.load(), 2);
+    /// ```
+    pub fn compare_exchange(&self, current: T, new: T) -> Result<T, T> {
+        unsafe { atomic_compare_exchange_weak(self.as_ptr(), current, new) }
+    }
+
+    /// Fetches the value, and applies a function to it that returns an optional
+    /// new value. Returns a `Result` of `Ok(previous_value)` if the function returned `Some(_)`, else
+    /// `Err(previous_value)`.
+    ///
+    /// Note: This may call the function multiple times if the value has been changed from other threads in
+    /// the meantime, as long as the function returns `Some(_)`, but the function will have been applied
+    /// only once to the stored value.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(7);
+    /// assert_eq!(a.fetch_update(|_| None), Err(7));
+    /// assert_eq!(a.fetch_update(|a| Some(a + 1)), Ok(7));
+    /// assert_eq!(a.fetch_update(|a| Some(a + 1)), Ok(8));
+    /// assert_eq!(a.load(), 9);
+    /// ```
+    #[inline]
+    pub fn fetch_update<F>(&self, mut f: F) -> Result<T, T>
+    where
+        F: FnMut(T) -> Option<T>,
+    {
+        let mut prev = self.load();
+        while let Some(next) = f(prev) {
+            match self.compare_exchange(prev, next) {
+                x @ Ok(_) => return x,
+                Err(next_prev) => prev = next_prev,
+            }
+        }
+        Err(prev)
+    }
+}
+
+// `MaybeUninit` prevents `T` from being dropped, so we need to implement `Drop`
+// for `AtomicCell` to avoid leaks of non-`Copy` types.
+impl<T> Drop for AtomicCell<T> {
+    fn drop(&mut self) {
+        if mem::needs_drop::<T>() {
+            // SAFETY:
+            // - the mutable reference guarantees that no other threads are concurrently accessing the atomic data
+            // - the raw pointer passed in is valid because we got it from a reference
+            // - `MaybeUninit` prevents double dropping `T`
+            unsafe {
+                self.as_ptr().drop_in_place();
+            }
+        }
+    }
+}
+
+macro_rules! impl_arithmetic {
+    ($t:ty, fallback, $example:tt) => {
+        impl AtomicCell<$t> {
+            /// Increments the current value by `val` and returns the previous value.
+            ///
+            /// The addition wraps on overflow.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_add(3), 7);
+            /// assert_eq!(a.load(), 10);
+            /// ```
+            #[inline]
+            pub fn fetch_add(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value = value.wrapping_add(val);
+                old
+            }
+
+            /// Decrements the current value by `val` and returns the previous value.
+            ///
+            /// The subtraction wraps on overflow.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_sub(3), 7);
+            /// assert_eq!(a.load(), 4);
+            /// ```
+            #[inline]
+            pub fn fetch_sub(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value = value.wrapping_sub(val);
+                old
+            }
+
+            /// Applies bitwise "and" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_and(3), 7);
+            /// assert_eq!(a.load(), 3);
+            /// ```
+            #[inline]
+            pub fn fetch_and(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value &= val;
+                old
+            }
+
+            /// Applies bitwise "nand" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_nand(3), 7);
+            /// assert_eq!(a.load(), !(7 & 3));
+            /// ```
+            #[inline]
+            pub fn fetch_nand(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value = !(old & val);
+                old
+            }
+
+            /// Applies bitwise "or" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_or(16), 7);
+            /// assert_eq!(a.load(), 23);
+            /// ```
+            #[inline]
+            pub fn fetch_or(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value |= val;
+                old
+            }
+
+            /// Applies bitwise "xor" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_xor(2), 7);
+            /// assert_eq!(a.load(), 5);
+            /// ```
+            #[inline]
+            pub fn fetch_xor(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value ^= val;
+                old
+            }
+
+            /// Compares and sets the maximum of the current value and `val`,
+            /// and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_max(2), 7);
+            /// assert_eq!(a.load(), 7);
+            /// ```
+            #[inline]
+            pub fn fetch_max(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value = cmp::max(old, val);
+                old
+            }
+
+            /// Compares and sets the minimum of the current value and `val`,
+            /// and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_min(2), 7);
+            /// assert_eq!(a.load(), 2);
+            /// ```
+            #[inline]
+            pub fn fetch_min(&self, val: $t) -> $t {
+                let _guard = lock(self.as_ptr() as usize).write();
+                let value = unsafe { &mut *(self.as_ptr()) };
+                let old = *value;
+                *value = cmp::min(old, val);
+                old
+            }
+        }
+    };
+    ($t:ty, $atomic:ty, $example:tt) => {
+        impl AtomicCell<$t> {
+            /// Increments the current value by `val` and returns the previous value.
+            ///
+            /// The addition wraps on overflow.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_add(3), 7);
+            /// assert_eq!(a.load(), 10);
+            /// ```
+            #[inline]
+            pub fn fetch_add(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_add(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value = value.wrapping_add(val);
+                    old
+                }
+            }
+
+            /// Decrements the current value by `val` and returns the previous value.
+            ///
+            /// The subtraction wraps on overflow.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_sub(3), 7);
+            /// assert_eq!(a.load(), 4);
+            /// ```
+            #[inline]
+            pub fn fetch_sub(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_sub(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value = value.wrapping_sub(val);
+                    old
+                }
+            }
+
+            /// Applies bitwise "and" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_and(3), 7);
+            /// assert_eq!(a.load(), 3);
+            /// ```
+            #[inline]
+            pub fn fetch_and(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_and(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value &= val;
+                    old
+                }
+            }
+
+            /// Applies bitwise "nand" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_nand(3), 7);
+            /// assert_eq!(a.load(), !(7 & 3));
+            /// ```
+            #[inline]
+            pub fn fetch_nand(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_nand(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value = !(old & val);
+                    old
+                }
+            }
+
+            /// Applies bitwise "or" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_or(16), 7);
+            /// assert_eq!(a.load(), 23);
+            /// ```
+            #[inline]
+            pub fn fetch_or(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_or(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value |= val;
+                    old
+                }
+            }
+
+            /// Applies bitwise "xor" to the current value and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_xor(2), 7);
+            /// assert_eq!(a.load(), 5);
+            /// ```
+            #[inline]
+            pub fn fetch_xor(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    let a = unsafe { &*(self.as_ptr() as *const $atomic) };
+                    a.fetch_xor(val, Ordering::AcqRel)
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value ^= val;
+                    old
+                }
+            }
+
+            /// Compares and sets the maximum of the current value and `val`,
+            /// and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_max(9), 7);
+            /// assert_eq!(a.load(), 9);
+            /// ```
+            #[inline]
+            pub fn fetch_max(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    // TODO: Atomic*::fetch_max requires Rust 1.45.
+                    self.fetch_update(|old| Some(cmp::max(old, val))).unwrap()
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value = cmp::max(old, val);
+                    old
+                }
+            }
+
+            /// Compares and sets the minimum of the current value and `val`,
+            /// and returns the previous value.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// use crossbeam_utils::atomic::AtomicCell;
+            ///
+            #[doc = $example]
+            ///
+            /// assert_eq!(a.fetch_min(2), 7);
+            /// assert_eq!(a.load(), 2);
+            /// ```
+            #[inline]
+            pub fn fetch_min(&self, val: $t) -> $t {
+                if can_transmute::<$t, $atomic>() {
+                    // TODO: Atomic*::fetch_min requires Rust 1.45.
+                    self.fetch_update(|old| Some(cmp::min(old, val))).unwrap()
+                } else {
+                    let _guard = lock(self.as_ptr() as usize).write();
+                    let value = unsafe { &mut *(self.as_ptr()) };
+                    let old = *value;
+                    *value = cmp::min(old, val);
+                    old
+                }
+            }
+        }
+    };
+}
+
+impl_arithmetic!(u8, atomic::AtomicU8, "let a = AtomicCell::new(7u8);");
+impl_arithmetic!(i8, atomic::AtomicI8, "let a = AtomicCell::new(7i8);");
+impl_arithmetic!(u16, atomic::AtomicU16, "let a = AtomicCell::new(7u16);");
+impl_arithmetic!(i16, atomic::AtomicI16, "let a = AtomicCell::new(7i16);");
+impl_arithmetic!(u32, atomic::AtomicU32, "let a = AtomicCell::new(7u32);");
+impl_arithmetic!(i32, atomic::AtomicI32, "let a = AtomicCell::new(7i32);");
+#[cfg(not(crossbeam_no_atomic_64))]
+impl_arithmetic!(u64, atomic::AtomicU64, "let a = AtomicCell::new(7u64);");
+#[cfg(not(crossbeam_no_atomic_64))]
+impl_arithmetic!(i64, atomic::AtomicI64, "let a = AtomicCell::new(7i64);");
+#[cfg(crossbeam_no_atomic_64)]
+impl_arithmetic!(u64, fallback, "let a = AtomicCell::new(7u64);");
+#[cfg(crossbeam_no_atomic_64)]
+impl_arithmetic!(i64, fallback, "let a = AtomicCell::new(7i64);");
+// TODO: AtomicU128 is unstable
+// impl_arithmetic!(u128, atomic::AtomicU128, "let a = AtomicCell::new(7u128);");
+// impl_arithmetic!(i128, atomic::AtomicI128, "let a = AtomicCell::new(7i128);");
+impl_arithmetic!(u128, fallback, "let a = AtomicCell::new(7u128);");
+impl_arithmetic!(i128, fallback, "let a = AtomicCell::new(7i128);");
+
+impl_arithmetic!(
+    usize,
+    atomic::AtomicUsize,
+    "let a = AtomicCell::new(7usize);"
+);
+impl_arithmetic!(
+    isize,
+    atomic::AtomicIsize,
+    "let a = AtomicCell::new(7isize);"
+);
+
+impl AtomicCell<bool> {
+    /// Applies logical "and" to the current value and returns the previous value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(true);
+    ///
+    /// assert_eq!(a.fetch_and(true), true);
+    /// assert_eq!(a.load(), true);
+    ///
+    /// assert_eq!(a.fetch_and(false), true);
+    /// assert_eq!(a.load(), false);
+    /// ```
+    #[inline]
+    pub fn fetch_and(&self, val: bool) -> bool {
+        let a = unsafe { &*(self.as_ptr() as *const AtomicBool) };
+        a.fetch_and(val, Ordering::AcqRel)
+    }
+
+    /// Applies logical "nand" to the current value and returns the previous value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(true);
+    ///
+    /// assert_eq!(a.fetch_nand(false), true);
+    /// assert_eq!(a.load(), true);
+    ///
+    /// assert_eq!(a.fetch_nand(true), true);
+    /// assert_eq!(a.load(), false);
+    ///
+    /// assert_eq!(a.fetch_nand(false), false);
+    /// assert_eq!(a.load(), true);
+    /// ```
+    #[inline]
+    pub fn fetch_nand(&self, val: bool) -> bool {
+        let a = unsafe { &*(self.as_ptr() as *const AtomicBool) };
+        a.fetch_nand(val, Ordering::AcqRel)
+    }
+
+    /// Applies logical "or" to the current value and returns the previous value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(false);
+    ///
+    /// assert_eq!(a.fetch_or(false), false);
+    /// assert_eq!(a.load(), false);
+    ///
+    /// assert_eq!(a.fetch_or(true), false);
+    /// assert_eq!(a.load(), true);
+    /// ```
+    #[inline]
+    pub fn fetch_or(&self, val: bool) -> bool {
+        let a = unsafe { &*(self.as_ptr() as *const AtomicBool) };
+        a.fetch_or(val, Ordering::AcqRel)
+    }
+
+    /// Applies logical "xor" to the current value and returns the previous value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::atomic::AtomicCell;
+    ///
+    /// let a = AtomicCell::new(true);
+    ///
+    /// assert_eq!(a.fetch_xor(false), true);
+    /// assert_eq!(a.load(), true);
+    ///
+    /// assert_eq!(a.fetch_xor(true), true);
+    /// assert_eq!(a.load(), false);
+    /// ```
+    #[inline]
+    pub fn fetch_xor(&self, val: bool) -> bool {
+        let a = unsafe { &*(self.as_ptr() as *const AtomicBool) };
+        a.fetch_xor(val, Ordering::AcqRel)
+    }
+}
+
+impl<T: Default> Default for AtomicCell<T> {
+    fn default() -> AtomicCell<T> {
+        AtomicCell::new(T::default())
+    }
+}
+
+impl<T> From<T> for AtomicCell<T> {
+    #[inline]
+    fn from(val: T) -> AtomicCell<T> {
+        AtomicCell::new(val)
+    }
+}
+
+impl<T: Copy + fmt::Debug> fmt::Debug for AtomicCell<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("AtomicCell")
+            .field("value", &self.load())
+            .finish()
+    }
+}
+
+/// Returns `true` if values of type `A` can be transmuted into values of type `B`.
+const fn can_transmute<A, B>() -> bool {
+    // Sizes must be equal, but alignment of `A` must be greater or equal than that of `B`.
+    (mem::size_of::<A>() == mem::size_of::<B>()) & (mem::align_of::<A>() >= mem::align_of::<B>())
+}
+
+/// Returns a reference to the global lock associated with the `AtomicCell` at address `addr`.
+///
+/// This function is used to protect atomic data which doesn't fit into any of the primitive atomic
+/// types in `std::sync::atomic`. Operations on such atomics must therefore use a global lock.
+///
+/// However, there is not only one global lock but an array of many locks, and one of them is
+/// picked based on the given address. Having many locks reduces contention and improves
+/// scalability.
+#[inline]
+#[must_use]
+fn lock(addr: usize) -> &'static SeqLock {
+    // The number of locks is a prime number because we want to make sure `addr % LEN` gets
+    // dispersed across all locks.
+    //
+    // Note that addresses are always aligned to some power of 2, depending on type `T` in
+    // `AtomicCell<T>`. If `LEN` was an even number, then `addr % LEN` would be an even number,
+    // too, which means only half of the locks would get utilized!
+    //
+    // It is also possible for addresses to accidentally get aligned to a number that is not a
+    // power of 2. Consider this example:
+    //
+    // ```
+    // #[repr(C)]
+    // struct Foo {
+    //     a: AtomicCell<u8>,
+    //     b: u8,
+    //     c: u8,
+    // }
+    // ```
+    //
+    // Now, if we have a slice of type `&[Foo]`, it is possible that field `a` in all items gets
+    // stored at addresses that are multiples of 3. It'd be too bad if `LEN` was divisible by 3.
+    // In order to protect from such cases, we simply choose a large prime number for `LEN`.
+    const LEN: usize = 97;
+    #[allow(clippy::declare_interior_mutable_const)]
+    const L: SeqLock = SeqLock::new();
+    static LOCKS: [SeqLock; LEN] = [
+        L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L,
+        L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L,
+        L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L, L,
+        L, L, L, L, L, L, L,
+    ];
+
+    // If the modulus is a constant number, the compiler will use crazy math to transform this into
+    // a sequence of cheap arithmetic operations rather than using the slow modulo instruction.
+    &LOCKS[addr % LEN]
+}
+
+/// An atomic `()`.
+///
+/// All operations are noops.
+struct AtomicUnit;
+
+impl AtomicUnit {
+    #[inline]
+    fn load(&self, _order: Ordering) {}
+
+    #[inline]
+    fn store(&self, _val: (), _order: Ordering) {}
+
+    #[inline]
+    fn swap(&self, _val: (), _order: Ordering) {}
+
+    #[inline]
+    fn compare_exchange_weak(
+        &self,
+        _current: (),
+        _new: (),
+        _success: Ordering,
+        _failure: Ordering,
+    ) -> Result<(), ()> {
+        Ok(())
+    }
+}
+
+macro_rules! atomic {
+    // If values of type `$t` can be transmuted into values of the primitive atomic type `$atomic`,
+    // declares variable `$a` of type `$atomic` and executes `$atomic_op`, breaking out of the loop.
+    (@check, $t:ty, $atomic:ty, $a:ident, $atomic_op:expr) => {
+        if can_transmute::<$t, $atomic>() {
+            let $a: &$atomic;
+            break $atomic_op;
+        }
+    };
+
+    // If values of type `$t` can be transmuted into values of a primitive atomic type, declares
+    // variable `$a` of that type and executes `$atomic_op`. Otherwise, just executes
+    // `$fallback_op`.
+    ($t:ty, $a:ident, $atomic_op:expr, $fallback_op:expr) => {
+        loop {
+            atomic!(@check, $t, AtomicUnit, $a, $atomic_op);
+
+            atomic!(@check, $t, atomic::AtomicU8, $a, $atomic_op);
+            atomic!(@check, $t, atomic::AtomicU16, $a, $atomic_op);
+            atomic!(@check, $t, atomic::AtomicU32, $a, $atomic_op);
+            #[cfg(not(crossbeam_no_atomic_64))]
+            atomic!(@check, $t, atomic::AtomicU64, $a, $atomic_op);
+            // TODO: AtomicU128 is unstable
+            // atomic!(@check, $t, atomic::AtomicU128, $a, $atomic_op);
+
+            break $fallback_op;
+        }
+    };
+}
+
+/// Returns `true` if operations on `AtomicCell<T>` are lock-free.
+const fn atomic_is_lock_free<T>() -> bool {
+    // HACK(taiki-e): This is equivalent to `atomic! { T, _a, true, false }`, but can be used in const fn even in Rust 1.36.
+    let is_lock_free = can_transmute::<T, AtomicUnit>()
+        | can_transmute::<T, atomic::AtomicU8>()
+        | can_transmute::<T, atomic::AtomicU16>()
+        | can_transmute::<T, atomic::AtomicU32>();
+    #[cfg(not(crossbeam_no_atomic_64))]
+    let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU64>();
+    // TODO: AtomicU128 is unstable
+    // let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU128>();
+    is_lock_free
+}
+
+/// Atomically reads data from `src`.
+///
+/// This operation uses the `Acquire` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_load<T>(src: *mut T) -> T
+where
+    T: Copy,
+{
+    atomic! {
+        T, a,
+        {
+            a = &*(src as *const _ as *const _);
+            mem::transmute_copy(&a.load(Ordering::Acquire))
+        },
+        {
+            let lock = lock(src as usize);
+
+            // Try doing an optimistic read first.
+            if let Some(stamp) = lock.optimistic_read() {
+                // We need a volatile read here because other threads might concurrently modify the
+                // value. In theory, data races are *always* UB, even if we use volatile reads and
+                // discard the data when a data race is detected. The proper solution would be to
+                // do atomic reads and atomic writes, but we can't atomically read and write all
+                // kinds of data since `AtomicU8` is not available on stable Rust yet.
+                let val = ptr::read_volatile(src);
+
+                if lock.validate_read(stamp) {
+                    return val;
+                }
+            }
+
+            // Grab a regular write lock so that writers don't starve this load.
+            let guard = lock.write();
+            let val = ptr::read(src);
+            // The value hasn't been changed. Drop the guard without incrementing the stamp.
+            guard.abort();
+            val
+        }
+    }
+}
+
+/// Atomically writes `val` to `dst`.
+///
+/// This operation uses the `Release` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_store<T>(dst: *mut T, val: T) {
+    atomic! {
+        T, a,
+        {
+            a = &*(dst as *const _ as *const _);
+            a.store(mem::transmute_copy(&val), Ordering::Release);
+            mem::forget(val);
+        },
+        {
+            let _guard = lock(dst as usize).write();
+            ptr::write(dst, val);
+        }
+    }
+}
+
+/// Atomically swaps data at `dst` with `val`.
+///
+/// This operation uses the `AcqRel` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_swap<T>(dst: *mut T, val: T) -> T {
+    atomic! {
+        T, a,
+        {
+            a = &*(dst as *const _ as *const _);
+            let res = mem::transmute_copy(&a.swap(mem::transmute_copy(&val), Ordering::AcqRel));
+            mem::forget(val);
+            res
+        },
+        {
+            let _guard = lock(dst as usize).write();
+            ptr::replace(dst, val)
+        }
+    }
+}
+
+/// Atomically compares data at `dst` to `current` and, if equal byte-for-byte, exchanges data at
+/// `dst` with `new`.
+///
+/// Returns the old value on success, or the current value at `dst` on failure.
+///
+/// This operation uses the `AcqRel` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_compare_exchange_weak<T>(dst: *mut T, mut current: T, new: T) -> Result<T, T>
+where
+    T: Copy + Eq,
+{
+    atomic! {
+        T, a,
+        {
+            a = &*(dst as *const _ as *const _);
+            let mut current_raw = mem::transmute_copy(&current);
+            let new_raw = mem::transmute_copy(&new);
+
+            loop {
+                match a.compare_exchange_weak(
+                    current_raw,
+                    new_raw,
+                    Ordering::AcqRel,
+                    Ordering::Acquire,
+                ) {
+                    Ok(_) => break Ok(current),
+                    Err(previous_raw) => {
+                        let previous = mem::transmute_copy(&previous_raw);
+
+                        if !T::eq(&previous, &current) {
+                            break Err(previous);
+                        }
+
+                        // The compare-exchange operation has failed and didn't store `new`. The
+                        // failure is either spurious, or `previous` was semantically equal to
+                        // `current` but not byte-equal. Let's retry with `previous` as the new
+                        // `current`.
+                        current = previous;
+                        current_raw = previous_raw;
+                    }
+                }
+            }
+        },
+        {
+            let guard = lock(dst as usize).write();
+
+            if T::eq(&*dst, &current) {
+                Ok(ptr::replace(dst, new))
+            } else {
+                let val = ptr::read(dst);
+                // The value hasn't been changed. Drop the guard without incrementing the stamp.
+                guard.abort();
+                Err(val)
+            }
+        }
+    }
+}
diff --git a/vendor/crossbeam-utils/src/atomic/consume.rs b/vendor/crossbeam-utils/src/atomic/consume.rs
new file mode 100644
index 000000000..277b370a5
--- /dev/null
+++ b/vendor/crossbeam-utils/src/atomic/consume.rs
@@ -0,0 +1,92 @@
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+use crate::primitive::sync::atomic::compiler_fence;
+#[cfg(not(crossbeam_no_atomic))]
+use core::sync::atomic::Ordering;
+
+/// Trait which allows reading from primitive atomic types with "consume" ordering.
+pub trait AtomicConsume {
+    /// Type returned by `load_consume`.
+    type Val;
+
+    /// Loads a value from the atomic using a "consume" memory ordering.
+    ///
+    /// This is similar to the "acquire" ordering, except that an ordering is
+    /// only guaranteed with operations that "depend on" the result of the load.
+    /// However consume loads are usually much faster than acquire loads on
+    /// architectures with a weak memory model since they don't require memory
+    /// fence instructions.
+    ///
+    /// The exact definition of "depend on" is a bit vague, but it works as you
+    /// would expect in practice since a lot of software, especially the Linux
+    /// kernel, rely on this behavior.
+    ///
+    /// This is currently only implemented on ARM and AArch64, where a fence
+    /// can be avoided. On other architectures this will fall back to a simple
+    /// `load(Ordering::Acquire)`.
+    fn load_consume(&self) -> Self::Val;
+}
+
+#[cfg(not(crossbeam_no_atomic))]
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+macro_rules! impl_consume {
+    () => {
+        #[inline]
+        fn load_consume(&self) -> Self::Val {
+            let result = self.load(Ordering::Relaxed);
+            compiler_fence(Ordering::Acquire);
+            result
+        }
+    };
+}
+
+#[cfg(not(crossbeam_no_atomic))]
+#[cfg(not(any(target_arch = "arm", target_arch = "aarch64")))]
+macro_rules! impl_consume {
+    () => {
+        #[inline]
+        fn load_consume(&self) -> Self::Val {
+            self.load(Ordering::Acquire)
+        }
+    };
+}
+
+macro_rules! impl_atomic {
+    ($atomic:ident, $val:ty) => {
+        #[cfg(not(crossbeam_no_atomic))]
+        impl AtomicConsume for core::sync::atomic::$atomic {
+            type Val = $val;
+            impl_consume!();
+        }
+        #[cfg(crossbeam_loom)]
+        impl AtomicConsume for loom::sync::atomic::$atomic {
+            type Val = $val;
+            impl_consume!();
+        }
+    };
+}
+
+impl_atomic!(AtomicBool, bool);
+impl_atomic!(AtomicUsize, usize);
+impl_atomic!(AtomicIsize, isize);
+impl_atomic!(AtomicU8, u8);
+impl_atomic!(AtomicI8, i8);
+impl_atomic!(AtomicU16, u16);
+impl_atomic!(AtomicI16, i16);
+impl_atomic!(AtomicU32, u32);
+impl_atomic!(AtomicI32, i32);
+#[cfg(not(crossbeam_no_atomic_64))]
+impl_atomic!(AtomicU64, u64);
+#[cfg(not(crossbeam_no_atomic_64))]
+impl_atomic!(AtomicI64, i64);
+
+#[cfg(not(crossbeam_no_atomic))]
+impl<T> AtomicConsume for core::sync::atomic::AtomicPtr<T> {
+    type Val = *mut T;
+    impl_consume!();
+}
+
+#[cfg(crossbeam_loom)]
+impl<T> AtomicConsume for loom::sync::atomic::AtomicPtr<T> {
+    type Val = *mut T;
+    impl_consume!();
+}
diff --git a/vendor/crossbeam-utils/src/atomic/mod.rs b/vendor/crossbeam-utils/src/atomic/mod.rs
new file mode 100644
index 000000000..38967859f
--- /dev/null
+++ b/vendor/crossbeam-utils/src/atomic/mod.rs
@@ -0,0 +1,37 @@
+//! Atomic types.
+//!
+//! * [`AtomicCell`], a thread-safe mutable memory location.
+//! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
+
+#[cfg(not(crossbeam_no_atomic_cas))]
+#[cfg(not(crossbeam_loom))]
+cfg_if::cfg_if! {
+    // Use "wide" sequence lock if the pointer width <= 32 for preventing its counter against wrap
+    // around.
+    //
+    // We are ignoring too wide architectures (pointer width >= 256), since such a system will not
+    // appear in a conceivable future.
+    //
+    // In narrow architectures (pointer width <= 16), the counter is still <= 32-bit and may be
+    // vulnerable to wrap around. But it's mostly okay, since in such a primitive hardware, the
+    // counter will not be increased that fast.
+    if #[cfg(any(target_pointer_width = "64", target_pointer_width = "128"))] {
+        mod seq_lock;
+    } else {
+        #[path = "seq_lock_wide.rs"]
+        mod seq_lock;
+    }
+}
+
+#[cfg(not(crossbeam_no_atomic_cas))]
+// We cannot provide AtomicCell under cfg(crossbeam_loom) because loom's atomic
+// types have a different in-memory representation than the underlying type.
+// TODO: The latest loom supports fences, so fallback using seqlock may be available.
+#[cfg(not(crossbeam_loom))]
+mod atomic_cell;
+mod consume;
+
+#[cfg(not(crossbeam_no_atomic_cas))]
+#[cfg(not(crossbeam_loom))]
+pub use self::atomic_cell::AtomicCell;
+pub use self::consume::AtomicConsume;
diff --git a/vendor/crossbeam-utils/src/atomic/seq_lock.rs b/vendor/crossbeam-utils/src/atomic/seq_lock.rs
new file mode 100644
index 000000000..ff8defd26
--- /dev/null
+++ b/vendor/crossbeam-utils/src/atomic/seq_lock.rs
@@ -0,0 +1,112 @@
+use core::mem;
+use core::sync::atomic::{self, AtomicUsize, Ordering};
+
+use crate::Backoff;
+
+/// A simple stamped lock.
+pub(crate) struct SeqLock {
+    /// The current state of the lock.
+    ///
+    /// All bits except the least significant one hold the current stamp. When locked, the state
+    /// equals 1 and doesn't contain a valid stamp.
+    state: AtomicUsize,
+}
+
+impl SeqLock {
+    pub(crate) const fn new() -> Self {
+        Self {
+            state: AtomicUsize::new(0),
+        }
+    }
+
+    /// If not locked, returns the current stamp.
+    ///
+    /// This method should be called before optimistic reads.
+    #[inline]
+    pub(crate) fn optimistic_read(&self) -> Option<usize> {
+        let state = self.state.load(Ordering::Acquire);
+        if state == 1 {
+            None
+        } else {
+            Some(state)
+        }
+    }
+
+    /// Returns `true` if the current stamp is equal to `stamp`.
+    ///
+    /// This method should be called after optimistic reads to check whether they are valid. The
+    /// argument `stamp` should correspond to the one returned by method `optimistic_read`.
+    #[inline]
+    pub(crate) fn validate_read(&self, stamp: usize) -> bool {
+        atomic::fence(Ordering::Acquire);
+        self.state.load(Ordering::Relaxed) == stamp
+    }
+
+    /// Grabs the lock for writing.
+    #[inline]
+    pub(crate) fn write(&'static self) -> SeqLockWriteGuard {
+        let backoff = Backoff::new();
+        loop {
+            let previous = self.state.swap(1, Ordering::Acquire);
+
+            if previous != 1 {
+                atomic::fence(Ordering::Release);
+
+                return SeqLockWriteGuard {
+                    lock: self,
+                    state: previous,
+                };
+            }
+
+            backoff.snooze();
+        }
+    }
+}
+
+/// An RAII guard that releases the lock and increments the stamp when dropped.
+pub(crate) struct SeqLockWriteGuard {
+    /// The parent lock.
+    lock: &'static SeqLock,
+
+    /// The stamp before locking.
+    state: usize,
+}
+
+impl SeqLockWriteGuard {
+    /// Releases the lock without incrementing the stamp.
+    #[inline]
+    pub(crate) fn abort(self) {
+        self.lock.state.store(self.state, Ordering::Release);
+
+        // We specifically don't want to call drop(), since that's
+        // what increments the stamp.
+        mem::forget(self);
+    }
+}
+
+impl Drop for SeqLockWriteGuard {
+    #[inline]
+    fn drop(&mut self) {
+        // Release the lock and increment the stamp.
+        self.lock
+            .state
+            .store(self.state.wrapping_add(2), Ordering::Release);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::SeqLock;
+
+    #[test]
+    fn test_abort() {
+        static LK: SeqLock = SeqLock::new();
+        let before = LK.optimistic_read().unwrap();
+        {
+            let guard = LK.write();
+            guard.abort();
+        }
+        let after = LK.optimistic_read().unwrap();
+        assert_eq!(before, after, "aborted write does not update the stamp");
+    }
+}
diff --git a/vendor/crossbeam-utils/src/atomic/seq_lock_wide.rs b/vendor/crossbeam-utils/src/atomic/seq_lock_wide.rs
new file mode 100644
index 000000000..ef5d94a45
--- /dev/null
+++ b/vendor/crossbeam-utils/src/atomic/seq_lock_wide.rs
@@ -0,0 +1,155 @@
+use core::mem;
+use core::sync::atomic::{self, AtomicUsize, Ordering};
+
+use crate::Backoff;
+
+/// A simple stamped lock.
+///
+/// The state is represented as two `AtomicUsize`: `state_hi` for high bits and `state_lo` for low
+/// bits.
+pub(crate) struct SeqLock {
+    /// The high bits of the current state of the lock.
+    state_hi: AtomicUsize,
+
+    /// The low bits of the current state of the lock.
+    ///
+    /// All bits except the least significant one hold the current stamp. When locked, the state_lo
+    /// equals 1 and doesn't contain a valid stamp.
+    state_lo: AtomicUsize,
+}
+
+impl SeqLock {
+    pub(crate) const fn new() -> Self {
+        Self {
+            state_hi: AtomicUsize::new(0),
+            state_lo: AtomicUsize::new(0),
+        }
+    }
+
+    /// If not locked, returns the current stamp.
+    ///
+    /// This method should be called before optimistic reads.
+    #[inline]
+    pub(crate) fn optimistic_read(&self) -> Option<(usize, usize)> {
+        // The acquire loads from `state_hi` and `state_lo` synchronize with the release stores in
+        // `SeqLockWriteGuard::drop`.
+        //
+        // As a consequence, we can make sure that (1) all writes within the era of `state_hi - 1`
+        // happens before now; and therefore, (2) if `state_lo` is even, all writes within the
+        // critical section of (`state_hi`, `state_lo`) happens before now.
+        let state_hi = self.state_hi.load(Ordering::Acquire);
+        let state_lo = self.state_lo.load(Ordering::Acquire);
+        if state_lo == 1 {
+            None
+        } else {
+            Some((state_hi, state_lo))
+        }
+    }
+
+    /// Returns `true` if the current stamp is equal to `stamp`.
+    ///
+    /// This method should be called after optimistic reads to check whether they are valid. The
+    /// argument `stamp` should correspond to the one returned by method `optimistic_read`.
+    #[inline]
+    pub(crate) fn validate_read(&self, stamp: (usize, usize)) -> bool {
+        // Thanks to the fence, if we're noticing any modification to the data at the critical
+        // section of `(a, b)`, then the critical section's write of 1 to state_lo should be
+        // visible.
+        atomic::fence(Ordering::Acquire);
+
+        // So if `state_lo` coincides with `stamp.1`, then either (1) we're noticing no modification
+        // to the data after the critical section of `(stamp.0, stamp.1)`, or (2) `state_lo` wrapped
+        // around.
+        //
+        // If (2) is the case, the acquire ordering ensures we see the new value of `state_hi`.
+        let state_lo = self.state_lo.load(Ordering::Acquire);
+
+        // If (2) is the case and `state_hi` coincides with `stamp.0`, then `state_hi` also wrapped
+        // around, which we give up to correctly validate the read.
+        let state_hi = self.state_hi.load(Ordering::Relaxed);
+
+        // Except for the case that both `state_hi` and `state_lo` wrapped around, the following
+        // condition implies that we're noticing no modification to the data after the critical
+        // section of `(stamp.0, stamp.1)`.
+        (state_hi, state_lo) == stamp
+    }
+
+    /// Grabs the lock for writing.
+    #[inline]
+    pub(crate) fn write(&'static self) -> SeqLockWriteGuard {
+        let backoff = Backoff::new();
+        loop {
+            let previous = self.state_lo.swap(1, Ordering::Acquire);
+
+            if previous != 1 {
+                // To synchronize with the acquire fence in `validate_read` via any modification to
+                // the data at the critical section of `(state_hi, previous)`.
+                atomic::fence(Ordering::Release);
+
+                return SeqLockWriteGuard {
+                    lock: self,
+                    state_lo: previous,
+                };
+            }
+
+            backoff.snooze();
+        }
+    }
+}
+
+/// An RAII guard that releases the lock and increments the stamp when dropped.
+pub(crate) struct SeqLockWriteGuard {
+    /// The parent lock.
+    lock: &'static SeqLock,
+
+    /// The stamp before locking.
+    state_lo: usize,
+}
+
+impl SeqLockWriteGuard {
+    /// Releases the lock without incrementing the stamp.
+    #[inline]
+    pub(crate) fn abort(self) {
+        self.lock.state_lo.store(self.state_lo, Ordering::Release);
+        mem::forget(self);
+    }
+}
+
+impl Drop for SeqLockWriteGuard {
+    #[inline]
+    fn drop(&mut self) {
+        let state_lo = self.state_lo.wrapping_add(2);
+
+        // Increase the high bits if the low bits wrap around.
+        //
+        // Release ordering for synchronizing with `optimistic_read`.
+        if state_lo == 0 {
+            let state_hi = self.lock.state_hi.load(Ordering::Relaxed);
+            self.lock
+                .state_hi
+                .store(state_hi.wrapping_add(1), Ordering::Release);
+        }
+
+        // Release the lock and increment the stamp.
+        //
+        // Release ordering for synchronizing with `optimistic_read`.
+        self.lock.state_lo.store(state_lo, Ordering::Release);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::SeqLock;
+
+    #[test]
+    fn test_abort() {
+        static LK: SeqLock = SeqLock::new();
+        let before = LK.optimistic_read().unwrap();
+        {
+            let guard = LK.write();
+            guard.abort();
+        }
+        let after = LK.optimistic_read().unwrap();
+        assert_eq!(before, after, "aborted write does not update the stamp");
+    }
+}
diff --git a/vendor/crossbeam-utils/src/backoff.rs b/vendor/crossbeam-utils/src/backoff.rs
new file mode 100644
index 000000000..1012f06b2
--- /dev/null
+++ b/vendor/crossbeam-utils/src/backoff.rs
@@ -0,0 +1,294 @@
+use crate::primitive::sync::atomic;
+use core::cell::Cell;
+use core::fmt;
+
+const SPIN_LIMIT: u32 = 6;
+const YIELD_LIMIT: u32 = 10;
+
+/// Performs exponential backoff in spin loops.
+///
+/// Backing off in spin loops reduces contention and improves overall performance.
+///
+/// This primitive can execute *YIELD* and *PAUSE* instructions, yield the current thread to the OS
+/// scheduler, and tell when is a good time to block the thread using a different synchronization
+/// mechanism. Each step of the back off procedure takes roughly twice as long as the previous
+/// step.
+///
+/// # Examples
+///
+/// Backing off in a lock-free loop:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicUsize;
+/// use std::sync::atomic::Ordering::SeqCst;
+///
+/// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
+///     let backoff = Backoff::new();
+///     loop {
+///         let val = a.load(SeqCst);
+///         if a.compare_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
+///             return val;
+///         }
+///         backoff.spin();
+///     }
+/// }
+/// ```
+///
+/// Waiting for an [`AtomicBool`] to become `true`:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::SeqCst;
+///
+/// fn spin_wait(ready: &AtomicBool) {
+///     let backoff = Backoff::new();
+///     while !ready.load(SeqCst) {
+///         backoff.snooze();
+///     }
+/// }
+/// ```
+///
+/// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait.
+/// Note that whoever sets the atomic variable to `true` must notify the parked thread by calling
+/// [`unpark()`]:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::SeqCst;
+/// use std::thread;
+///
+/// fn blocking_wait(ready: &AtomicBool) {
+///     let backoff = Backoff::new();
+///     while !ready.load(SeqCst) {
+///         if backoff.is_completed() {
+///             thread::park();
+///         } else {
+///             backoff.snooze();
+///         }
+///     }
+/// }
+/// ```
+///
+/// [`is_completed`]: Backoff::is_completed
+/// [`std::thread::park()`]: std::thread::park
+/// [`Condvar`]: std::sync::Condvar
+/// [`AtomicBool`]: std::sync::atomic::AtomicBool
+/// [`unpark()`]: std::thread::Thread::unpark
+pub struct Backoff {
+    step: Cell<u32>,
+}
+
+impl Backoff {
+    /// Creates a new `Backoff`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::Backoff;
+    ///
+    /// let backoff = Backoff::new();
+    /// ```
+    #[inline]
+    pub fn new() -> Self {
+        Backoff { step: Cell::new(0) }
+    }
+
+    /// Resets the `Backoff`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::Backoff;
+    ///
+    /// let backoff = Backoff::new();
+    /// backoff.reset();
+    /// ```
+    #[inline]
+    pub fn reset(&self) {
+        self.step.set(0);
+    }
+
+    /// Backs off in a lock-free loop.
+    ///
+    /// This method should be used when we need to retry an operation because another thread made
+    /// progress.
+    ///
+    /// The processor may yield using the *YIELD* or *PAUSE* instruction.
+    ///
+    /// # Examples
+    ///
+    /// Backing off in a lock-free loop:
+    ///
+    /// ```
+    /// use crossbeam_utils::Backoff;
+    /// use std::sync::atomic::AtomicUsize;
+    /// use std::sync::atomic::Ordering::SeqCst;
+    ///
+    /// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
+    ///     let backoff = Backoff::new();
+    ///     loop {
+    ///         let val = a.load(SeqCst);
+    ///         if a.compare_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
+    ///             return val;
+    ///         }
+    ///         backoff.spin();
+    ///     }
+    /// }
+    ///
+    /// let a = AtomicUsize::new(7);
+    /// assert_eq!(fetch_mul(&a, 8), 7);
+    /// assert_eq!(a.load(SeqCst), 56);
+    /// ```
+    #[inline]
+    pub fn spin(&self) {
+        for _ in 0..1 << self.step.get().min(SPIN_LIMIT) {
+            // TODO(taiki-e): once we bump the minimum required Rust version to 1.49+,
+            // use [`core::hint::spin_loop`] instead.
+            #[allow(deprecated)]
+            atomic::spin_loop_hint();
+        }
+
+        if self.step.get() <= SPIN_LIMIT {
+            self.step.set(self.step.get() + 1);
+        }
+    }
+
+    /// Backs off in a blocking loop.
+    ///
+    /// This method should be used when we need to wait for another thread to make progress.
+    ///
+    /// The processor may yield using the *YIELD* or *PAUSE* instruction and the current thread
+    /// may yield by giving up a timeslice to the OS scheduler.
+    ///
+    /// In `#[no_std]` environments, this method is equivalent to [`spin`].
+    ///
+    /// If possible, use [`is_completed`] to check when it is advised to stop using backoff and
+    /// block the current thread using a different synchronization mechanism instead.
+    ///
+    /// [`spin`]: Backoff::spin
+    /// [`is_completed`]: Backoff::is_completed
+    ///
+    /// # Examples
+    ///
+    /// Waiting for an [`AtomicBool`] to become `true`:
+    ///
+    /// ```
+    /// use crossbeam_utils::Backoff;
+    /// use std::sync::Arc;
+    /// use std::sync::atomic::AtomicBool;
+    /// use std::sync::atomic::Ordering::SeqCst;
+    /// use std::thread;
+    /// use std::time::Duration;
+    ///
+    /// fn spin_wait(ready: &AtomicBool) {
+    ///     let backoff = Backoff::new();
+    ///     while !ready.load(SeqCst) {
+    ///         backoff.snooze();
+    ///     }
+    /// }
+    ///
+    /// let ready = Arc::new(AtomicBool::new(false));
+    /// let ready2 = ready.clone();
+    ///
+    /// thread::spawn(move || {
+    ///     thread::sleep(Duration::from_millis(100));
+    ///     ready2.store(true, SeqCst);
+    /// });
+    ///
+    /// assert_eq!(ready.load(SeqCst), false);
+    /// spin_wait(&ready);
+    /// assert_eq!(ready.load(SeqCst), true);
+    /// ```
+    ///
+    /// [`AtomicBool`]: std::sync::atomic::AtomicBool
+    #[inline]
+    pub fn snooze(&self) {
+        if self.step.get() <= SPIN_LIMIT {
+            for _ in 0..1 << self.step.get() {
+                // TODO(taiki-e): once we bump the minimum required Rust version to 1.49+,
+                // use [`core::hint::spin_loop`] instead.
+                #[allow(deprecated)]
+                atomic::spin_loop_hint();
+            }
+        } else {
+            #[cfg(not(feature = "std"))]
+            for _ in 0..1 << self.step.get() {
+                // TODO(taiki-e): once we bump the minimum required Rust version to 1.49+,
+                // use [`core::hint::spin_loop`] instead.
+                #[allow(deprecated)]
+                atomic::spin_loop_hint();
+            }
+
+            #[cfg(feature = "std")]
+            ::std::thread::yield_now();
+        }
+
+        if self.step.get() <= YIELD_LIMIT {
+            self.step.set(self.step.get() + 1);
+        }
+    }
+
+    /// Returns `true` if exponential backoff has completed and blocking the thread is advised.
+    ///
+    /// # Examples
+    ///
+    /// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait:
+    ///
+    /// ```
+    /// use crossbeam_utils::Backoff;
+    /// use std::sync::Arc;
+    /// use std::sync::atomic::AtomicBool;
+    /// use std::sync::atomic::Ordering::SeqCst;
+    /// use std::thread;
+    /// use std::time::Duration;
+    ///
+    /// fn blocking_wait(ready: &AtomicBool) {
+    ///     let backoff = Backoff::new();
+    ///     while !ready.load(SeqCst) {
+    ///         if backoff.is_completed() {
+    ///             thread::park();
+    ///         } else {
+    ///             backoff.snooze();
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// let ready = Arc::new(AtomicBool::new(false));
+    /// let ready2 = ready.clone();
+    /// let waiter = thread::current();
+    ///
+    /// thread::spawn(move || {
+    ///     thread::sleep(Duration::from_millis(100));
+    ///     ready2.store(true, SeqCst);
+    ///     waiter.unpark();
+    /// });
+    ///
+    /// assert_eq!(ready.load(SeqCst), false);
+    /// blocking_wait(&ready);
+    /// assert_eq!(ready.load(SeqCst), true);
+    /// ```
+    ///
+    /// [`AtomicBool`]: std::sync::atomic::AtomicBool
+    #[inline]
+    pub fn is_completed(&self) -> bool {
+        self.step.get() > YIELD_LIMIT
+    }
+}
+
+impl fmt::Debug for Backoff {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Backoff")
+            .field("step", &self.step)
+            .field("is_completed", &self.is_completed())
+            .finish()
+    }
+}
+
+impl Default for Backoff {
+    fn default() -> Backoff {
+        Backoff::new()
+    }
+}
diff --git a/vendor/crossbeam-utils/src/cache_padded.rs b/vendor/crossbeam-utils/src/cache_padded.rs
new file mode 100644
index 000000000..822e831d1
--- /dev/null
+++ b/vendor/crossbeam-utils/src/cache_padded.rs
@@ -0,0 +1,191 @@
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+
+/// Pads and aligns a value to the length of a cache line.
+///
+/// In concurrent programming, sometimes it is desirable to make sure commonly accessed pieces of
+/// data are not placed into the same cache line. Updating an atomic value invalidates the whole
+/// cache line it belongs to, which makes the next access to the same cache line slower for other
+/// CPU cores. Use `CachePadded` to ensure updating one piece of data doesn't invalidate other
+/// cached data.
+///
+/// # Size and alignment
+///
+/// Cache lines are assumed to be N bytes long, depending on the architecture:
+///
+/// * On x86-64, aarch64, and powerpc64, N = 128.
+/// * On arm, mips, mips64, and riscv64, N = 32.
+/// * On s390x, N = 256.
+/// * On all others, N = 64.
+///
+/// Note that N is just a reasonable guess and is not guaranteed to match the actual cache line
+/// length of the machine the program is running on. On modern Intel architectures, spatial
+/// prefetcher is pulling pairs of 64-byte cache lines at a time, so we pessimistically assume that
+/// cache lines are 128 bytes long.
+///
+/// The size of `CachePadded<T>` is the smallest multiple of N bytes large enough to accommodate
+/// a value of type `T`.
+///
+/// The alignment of `CachePadded<T>` is the maximum of N bytes and the alignment of `T`.
+///
+/// # Examples
+///
+/// Alignment and padding:
+///
+/// ```
+/// use crossbeam_utils::CachePadded;
+///
+/// let array = [CachePadded::new(1i8), CachePadded::new(2i8)];
+/// let addr1 = &*array[0] as *const i8 as usize;
+/// let addr2 = &*array[1] as *const i8 as usize;
+///
+/// assert!(addr2 - addr1 >= 64);
+/// assert_eq!(addr1 % 64, 0);
+/// assert_eq!(addr2 % 64, 0);
+/// ```
+///
+/// When building a concurrent queue with a head and a tail index, it is wise to place them in
+/// different cache lines so that concurrent threads pushing and popping elements don't invalidate
+/// each other's cache lines:
+///
+/// ```
+/// use crossbeam_utils::CachePadded;
+/// use std::sync::atomic::AtomicUsize;
+///
+/// struct Queue<T> {
+///     head: CachePadded<AtomicUsize>,
+///     tail: CachePadded<AtomicUsize>,
+///     buffer: *mut T,
+/// }
+/// ```
+#[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
+// Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache
+// lines at a time, so we have to align to 128 bytes rather than 64.
+//
+// Sources:
+// - https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
+// - https://github.com/facebook/folly/blob/1b5288e6eea6df074758f877c849b6e73bbb9fbb/folly/lang/Align.h#L107
+//
+// ARM's big.LITTLE architecture has asymmetric cores and "big" cores have 128-byte cache line size.
+//
+// Sources:
+// - https://www.mono-project.com/news/2016/09/12/arm64-icache/
+//
+// powerpc64 has 128-byte cache line size.
+//
+// Sources:
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_ppc64x.go#L9
+#[cfg_attr(
+    any(
+        target_arch = "x86_64",
+        target_arch = "aarch64",
+        target_arch = "powerpc64",
+    ),
+    repr(align(128))
+)]
+// arm, mips, mips64, and riscv64 have 32-byte cache line size.
+//
+// Sources:
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_arm.go#L7
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips.go#L7
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mipsle.go#L7
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips64x.go#L9
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_riscv64.go#L7
+#[cfg_attr(
+    any(
+        target_arch = "arm",
+        target_arch = "mips",
+        target_arch = "mips64",
+        target_arch = "riscv64",
+    ),
+    repr(align(32))
+)]
+// s390x has 256-byte cache line size.
+//
+// Sources:
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_s390x.go#L7
+#[cfg_attr(target_arch = "s390x", repr(align(256)))]
+// x86 and wasm have 64-byte cache line size.
+//
+// Sources:
+// - https://github.com/golang/go/blob/dda2991c2ea0c5914714469c4defc2562a907230/src/internal/cpu/cpu_x86.go#L9
+// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_wasm.go#L7
+//
+// All others are assumed to have 64-byte cache line size.
+#[cfg_attr(
+    not(any(
+        target_arch = "x86_64",
+        target_arch = "aarch64",
+        target_arch = "powerpc64",
+        target_arch = "arm",
+        target_arch = "mips",
+        target_arch = "mips64",
+        target_arch = "riscv64",
+        target_arch = "s390x",
+    )),
+    repr(align(64))
+)]
+pub struct CachePadded<T> {
+    value: T,
+}
+
+unsafe impl<T: Send> Send for CachePadded<T> {}
+unsafe impl<T: Sync> Sync for CachePadded<T> {}
+
+impl<T> CachePadded<T> {
+    /// Pads and aligns a value to the length of a cache line.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::CachePadded;
+    ///
+    /// let padded_value = CachePadded::new(1);
+    /// ```
+    pub const fn new(t: T) -> CachePadded<T> {
+        CachePadded::<T> { value: t }
+    }
+
+    /// Returns the inner value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::CachePadded;
+    ///
+    /// let padded_value = CachePadded::new(7);
+    /// let value = padded_value.into_inner();
+    /// assert_eq!(value, 7);
+    /// ```
+    pub fn into_inner(self) -> T {
+        self.value
+    }
+}
+
+impl<T> Deref for CachePadded<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.value
+    }
+}
+
+impl<T> DerefMut for CachePadded<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.value
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("CachePadded")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+impl<T> From<T> for CachePadded<T> {
+    fn from(t: T) -> Self {
+        CachePadded::new(t)
+    }
+}
diff --git a/vendor/crossbeam-utils/src/lib.rs b/vendor/crossbeam-utils/src/lib.rs
new file mode 100644
index 000000000..191c5a17d
--- /dev/null
+++ b/vendor/crossbeam-utils/src/lib.rs
@@ -0,0 +1,104 @@
+//! Miscellaneous tools for concurrent programming.
+//!
+//! ## Atomics
+//!
+//! * [`AtomicCell`], a thread-safe mutable memory location.
+//! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
+//!
+//! ## Thread synchronization
+//!
+//! * [`Parker`], a thread parking primitive.
+//! * [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
+//! * [`WaitGroup`], for synchronizing the beginning or end of some computation.
+//!
+//! ## Utilities
+//!
+//! * [`Backoff`], for exponential backoff in spin loops.
+//! * [`CachePadded`], for padding and aligning a value to the length of a cache line.
+//! * [`scope`], for spawning threads that borrow local variables from the stack.
+//!
+//! [`AtomicCell`]: atomic::AtomicCell
+//! [`AtomicConsume`]: atomic::AtomicConsume
+//! [`Parker`]: sync::Parker
+//! [`ShardedLock`]: sync::ShardedLock
+//! [`WaitGroup`]: sync::WaitGroup
+//! [`scope`]: thread::scope
+
+#![doc(test(
+    no_crate_inject,
+    attr(
+        deny(warnings, rust_2018_idioms),
+        allow(dead_code, unused_assignments, unused_variables)
+    )
+))]
+#![warn(
+    missing_docs,
+    missing_debug_implementations,
+    rust_2018_idioms,
+    unreachable_pub
+)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(crossbeam_loom)]
+#[allow(unused_imports)]
+mod primitive {
+    pub(crate) mod sync {
+        pub(crate) mod atomic {
+            pub(crate) use loom::sync::atomic::spin_loop_hint;
+            pub(crate) use loom::sync::atomic::{
+                AtomicBool, AtomicI16, AtomicI32, AtomicI64, AtomicI8, AtomicIsize, AtomicU16,
+                AtomicU32, AtomicU64, AtomicU8, AtomicUsize,
+            };
+
+            // FIXME: loom does not support compiler_fence at the moment.
+            // https://github.com/tokio-rs/loom/issues/117
+            // we use fence as a stand-in for compiler_fence for the time being.
+            // this may miss some races since fence is stronger than compiler_fence,
+            // but it's the best we can do for the time being.
+            pub(crate) use loom::sync::atomic::fence as compiler_fence;
+        }
+        pub(crate) use loom::sync::{Arc, Condvar, Mutex};
+    }
+}
+#[cfg(not(crossbeam_loom))]
+#[allow(unused_imports)]
+mod primitive {
+    pub(crate) mod sync {
+        pub(crate) mod atomic {
+            pub(crate) use core::sync::atomic::compiler_fence;
+            // TODO(taiki-e): once we bump the minimum required Rust version to 1.49+,
+            // use [`core::hint::spin_loop`] instead.
+            #[allow(deprecated)]
+            pub(crate) use core::sync::atomic::spin_loop_hint;
+            #[cfg(not(crossbeam_no_atomic))]
+            pub(crate) use core::sync::atomic::{
+                AtomicBool, AtomicI16, AtomicI32, AtomicI8, AtomicIsize, AtomicU16, AtomicU32,
+                AtomicU8, AtomicUsize,
+            };
+            #[cfg(not(crossbeam_no_atomic_64))]
+            pub(crate) use core::sync::atomic::{AtomicI64, AtomicU64};
+        }
+
+        #[cfg(feature = "std")]
+        pub(crate) use std::sync::{Arc, Condvar, Mutex};
+    }
+}
+
+pub mod atomic;
+
+mod cache_padded;
+pub use crate::cache_padded::CachePadded;
+
+mod backoff;
+pub use crate::backoff::Backoff;
+
+use cfg_if::cfg_if;
+
+cfg_if! {
+    if #[cfg(feature = "std")] {
+        pub mod sync;
+
+        #[cfg(not(crossbeam_loom))]
+        pub mod thread;
+    }
+}
diff --git a/vendor/crossbeam-utils/src/sync/mod.rs b/vendor/crossbeam-utils/src/sync/mod.rs
new file mode 100644
index 000000000..eeb740c2c
--- /dev/null
+++ b/vendor/crossbeam-utils/src/sync/mod.rs
@@ -0,0 +1,15 @@
+//! Thread synchronization primitives.
+//!
+//! * [`Parker`], a thread parking primitive.
+//! * [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
+//! * [`WaitGroup`], for synchronizing the beginning or end of some computation.
+
+mod parker;
+#[cfg(not(crossbeam_loom))]
+mod sharded_lock;
+mod wait_group;
+
+pub use self::parker::{Parker, Unparker};
+#[cfg(not(crossbeam_loom))]
+pub use self::sharded_lock::{ShardedLock, ShardedLockReadGuard, ShardedLockWriteGuard};
+pub use self::wait_group::WaitGroup;
diff --git a/vendor/crossbeam-utils/src/sync/parker.rs b/vendor/crossbeam-utils/src/sync/parker.rs
new file mode 100644
index 000000000..531f5a5fc
--- /dev/null
+++ b/vendor/crossbeam-utils/src/sync/parker.rs
@@ -0,0 +1,411 @@
+use crate::primitive::sync::atomic::AtomicUsize;
+use crate::primitive::sync::{Arc, Condvar, Mutex};
+use core::sync::atomic::Ordering::SeqCst;
+use std::fmt;
+use std::marker::PhantomData;
+use std::time::{Duration, Instant};
+
+/// A thread parking primitive.
+///
+/// Conceptually, each `Parker` has an associated token which is initially not present:
+///
+/// * The [`park`] method blocks the current thread unless or until the token is available, at
+///   which point it automatically consumes the token.
+///
+/// * The [`park_timeout`] and [`park_deadline`] methods work the same as [`park`], but block for
+///   a specified maximum time.
+///
+/// * The [`unpark`] method atomically makes the token available if it wasn't already. Because the
+///   token is initially absent, [`unpark`] followed by [`park`] will result in the second call
+///   returning immediately.
+///
+/// In other words, each `Parker` acts a bit like a spinlock that can be locked and unlocked using
+/// [`park`] and [`unpark`].
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_utils::sync::Parker;
+///
+/// let p = Parker::new();
+/// let u = p.unparker().clone();
+///
+/// // Make the token available.
+/// u.unpark();
+/// // Wakes up immediately and consumes the token.
+/// p.park();
+///
+/// thread::spawn(move || {
+///     thread::sleep(Duration::from_millis(500));
+///     u.unpark();
+/// });
+///
+/// // Wakes up when `u.unpark()` provides the token.
+/// p.park();
+/// ```
+///
+/// [`park`]: Parker::park
+/// [`park_timeout`]: Parker::park_timeout
+/// [`park_deadline`]: Parker::park_deadline
+/// [`unpark`]: Unparker::unpark
+pub struct Parker {
+    unparker: Unparker,
+    _marker: PhantomData<*const ()>,
+}
+
+unsafe impl Send for Parker {}
+
+impl Default for Parker {
+    fn default() -> Self {
+        Self {
+            unparker: Unparker {
+                inner: Arc::new(Inner {
+                    state: AtomicUsize::new(EMPTY),
+                    lock: Mutex::new(()),
+                    cvar: Condvar::new(),
+                }),
+            },
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl Parker {
+    /// Creates a new `Parker`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// ```
+    ///
+    pub fn new() -> Parker {
+        Self::default()
+    }
+
+    /// Blocks the current thread until the token is made available.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let u = p.unparker().clone();
+    ///
+    /// // Make the token available.
+    /// u.unpark();
+    ///
+    /// // Wakes up immediately and consumes the token.
+    /// p.park();
+    /// ```
+    pub fn park(&self) {
+        self.unparker.inner.park(None);
+    }
+
+    /// Blocks the current thread until the token is made available, but only for a limited time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::time::Duration;
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    ///
+    /// // Waits for the token to become available, but will not wait longer than 500 ms.
+    /// p.park_timeout(Duration::from_millis(500));
+    /// ```
+    pub fn park_timeout(&self, timeout: Duration) {
+        self.park_deadline(Instant::now() + timeout)
+    }
+
+    /// Blocks the current thread until the token is made available, or until a certain deadline.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::time::{Duration, Instant};
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let deadline = Instant::now() + Duration::from_millis(500);
+    ///
+    /// // Waits for the token to become available, but will not wait longer than 500 ms.
+    /// p.park_deadline(deadline);
+    /// ```
+    pub fn park_deadline(&self, deadline: Instant) {
+        self.unparker.inner.park(Some(deadline))
+    }
+
+    /// Returns a reference to an associated [`Unparker`].
+    ///
+    /// The returned [`Unparker`] doesn't have to be used by reference - it can also be cloned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let u = p.unparker().clone();
+    ///
+    /// // Make the token available.
+    /// u.unpark();
+    /// // Wakes up immediately and consumes the token.
+    /// p.park();
+    /// ```
+    ///
+    /// [`park`]: Parker::park
+    /// [`park_timeout`]: Parker::park_timeout
+    pub fn unparker(&self) -> &Unparker {
+        &self.unparker
+    }
+
+    /// Converts a `Parker` into a raw pointer.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let raw = Parker::into_raw(p);
+    /// # let _ = unsafe { Parker::from_raw(raw) };
+    /// ```
+    pub fn into_raw(this: Parker) -> *const () {
+        Unparker::into_raw(this.unparker)
+    }
+
+    /// Converts a raw pointer into a `Parker`.
+    ///
+    /// # Safety
+    ///
+    /// This method is safe to use only with pointers returned by [`Parker::into_raw`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let raw = Parker::into_raw(p);
+    /// let p = unsafe { Parker::from_raw(raw) };
+    /// ```
+    pub unsafe fn from_raw(ptr: *const ()) -> Parker {
+        Parker {
+            unparker: Unparker::from_raw(ptr),
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl fmt::Debug for Parker {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Parker { .. }")
+    }
+}
+
+/// Unparks a thread parked by the associated [`Parker`].
+pub struct Unparker {
+    inner: Arc<Inner>,
+}
+
+unsafe impl Send for Unparker {}
+unsafe impl Sync for Unparker {}
+
+impl Unparker {
+    /// Atomically makes the token available if it is not already.
+    ///
+    /// This method will wake up the thread blocked on [`park`] or [`park_timeout`], if there is
+    /// any.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::thread;
+    /// use std::time::Duration;
+    /// use crossbeam_utils::sync::Parker;
+    ///
+    /// let p = Parker::new();
+    /// let u = p.unparker().clone();
+    ///
+    /// thread::spawn(move || {
+    ///     thread::sleep(Duration::from_millis(500));
+    ///     u.unpark();
+    /// });
+    ///
+    /// // Wakes up when `u.unpark()` provides the token.
+    /// p.park();
+    /// ```
+    ///
+    /// [`park`]: Parker::park
+    /// [`park_timeout`]: Parker::park_timeout
+    pub fn unpark(&self) {
+        self.inner.unpark()
+    }
+
+    /// Converts an `Unparker` into a raw pointer.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::{Parker, Unparker};
+    ///
+    /// let p = Parker::new();
+    /// let u = p.unparker().clone();
+    /// let raw = Unparker::into_raw(u);
+    /// # let _ = unsafe { Unparker::from_raw(raw) };
+    /// ```
+    pub fn into_raw(this: Unparker) -> *const () {
+        Arc::into_raw(this.inner) as *const ()
+    }
+
+    /// Converts a raw pointer into an `Unparker`.
+    ///
+    /// # Safety
+    ///
+    /// This method is safe to use only with pointers returned by [`Unparker::into_raw`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::{Parker, Unparker};
+    ///
+    /// let p = Parker::new();
+    /// let u = p.unparker().clone();
+    ///
+    /// let raw = Unparker::into_raw(u);
+    /// let u = unsafe { Unparker::from_raw(raw) };
+    /// ```
+    pub unsafe fn from_raw(ptr: *const ()) -> Unparker {
+        Unparker {
+            inner: Arc::from_raw(ptr as *const Inner),
+        }
+    }
+}
+
+impl fmt::Debug for Unparker {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Unparker { .. }")
+    }
+}
+
+impl Clone for Unparker {
+    fn clone(&self) -> Unparker {
+        Unparker {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+const EMPTY: usize = 0;
+const PARKED: usize = 1;
+const NOTIFIED: usize = 2;
+
+struct Inner {
+    state: AtomicUsize,
+    lock: Mutex<()>,
+    cvar: Condvar,
+}
+
+impl Inner {
+    fn park(&self, deadline: Option<Instant>) {
+        // If we were previously notified then we consume this notification and return quickly.
+        if self
+            .state
+            .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+            .is_ok()
+        {
+            return;
+        }
+
+        // If the timeout is zero, then there is no need to actually block.
+        if let Some(deadline) = deadline {
+            if deadline <= Instant::now() {
+                return;
+            }
+        }
+
+        // Otherwise we need to coordinate going to sleep.
+        let mut m = self.lock.lock().unwrap();
+
+        match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
+            Ok(_) => {}
+            // Consume this notification to avoid spurious wakeups in the next park.
+            Err(NOTIFIED) => {
+                // We must read `state` here, even though we know it will be `NOTIFIED`. This is
+                // because `unpark` may have been called again since we read `NOTIFIED` in the
+                // `compare_exchange` above. We must perform an acquire operation that synchronizes
+                // with that `unpark` to observe any writes it made before the call to `unpark`. To
+                // do that we must read from the write it made to `state`.
+                let old = self.state.swap(EMPTY, SeqCst);
+                assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+                return;
+            }
+            Err(n) => panic!("inconsistent park_timeout state: {}", n),
+        }
+
+        loop {
+            // Block the current thread on the conditional variable.
+            m = match deadline {
+                None => self.cvar.wait(m).unwrap(),
+                Some(deadline) => {
+                    let now = Instant::now();
+                    if now < deadline {
+                        // We could check for a timeout here, in the return value of wait_timeout,
+                        // but in the case that a timeout and an unpark arrive simultaneously, we
+                        // prefer to report the former.
+                        self.cvar.wait_timeout(m, deadline - now).unwrap().0
+                    } else {
+                        // We've timed out; swap out the state back to empty on our way out
+                        match self.state.swap(EMPTY, SeqCst) {
+                            NOTIFIED | PARKED => return,
+                            n => panic!("inconsistent park_timeout state: {}", n),
+                        };
+                    }
+                }
+            };
+
+            if self
+                .state
+                .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+                .is_ok()
+            {
+                // got a notification
+                return;
+            }
+
+            // Spurious wakeup, go back to sleep. Alternatively, if we timed out, it will be caught
+            // in the branch above, when we discover the deadline is in the past
+        }
+    }
+
+    pub(crate) fn unpark(&self) {
+        // To ensure the unparked thread will observe any writes we made before this call, we must
+        // perform a release operation that `park` can synchronize with. To do that we must write
+        // `NOTIFIED` even if `state` is already `NOTIFIED`. That is why this must be a swap rather
+        // than a compare-and-swap that returns if it reads `NOTIFIED` on failure.
+        match self.state.swap(NOTIFIED, SeqCst) {
+            EMPTY => return,    // no one was waiting
+            NOTIFIED => return, // already unparked
+            PARKED => {}        // gotta go wake someone up
+            _ => panic!("inconsistent state in unpark"),
+        }
+
+        // There is a period between when the parked thread sets `state` to `PARKED` (or last
+        // checked `state` in the case of a spurious wakeup) and when it actually waits on `cvar`.
+        // If we were to notify during this period it would be ignored and then when the parked
+        // thread went to sleep it would never wake up. Fortunately, it has `lock` locked at this
+        // stage so we can acquire `lock` to wait until it is ready to receive the notification.
+        //
+        // Releasing `lock` before the call to `notify_one` means that when the parked thread wakes
+        // it doesn't get woken only to have to wait for us to release `lock`.
+        drop(self.lock.lock().unwrap());
+        self.cvar.notify_one();
+    }
+}
diff --git a/vendor/crossbeam-utils/src/sync/sharded_lock.rs b/vendor/crossbeam-utils/src/sync/sharded_lock.rs
new file mode 100644
index 000000000..692653447
--- /dev/null
+++ b/vendor/crossbeam-utils/src/sync/sharded_lock.rs
@@ -0,0 +1,630 @@
+use std::cell::UnsafeCell;
+use std::collections::HashMap;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::ops::{Deref, DerefMut};
+use std::panic::{RefUnwindSafe, UnwindSafe};
+use std::sync::{LockResult, PoisonError, TryLockError, TryLockResult};
+use std::sync::{Mutex, RwLock, RwLockReadGuard, RwLockWriteGuard};
+use std::thread::{self, ThreadId};
+
+use crate::CachePadded;
+use once_cell::sync::Lazy;
+
+/// The number of shards per sharded lock. Must be a power of two.
+const NUM_SHARDS: usize = 8;
+
+/// A shard containing a single reader-writer lock.
+struct Shard {
+    /// The inner reader-writer lock.
+    lock: RwLock<()>,
+
+    /// The write-guard keeping this shard locked.
+    ///
+    /// Write operations will lock each shard and store the guard here. These guards get dropped at
+    /// the same time the big guard is dropped.
+    write_guard: UnsafeCell<Option<RwLockWriteGuard<'static, ()>>>,
+}
+
+/// A sharded reader-writer lock.
+///
+/// This lock is equivalent to [`RwLock`], except read operations are faster and write operations
+/// are slower.
+///
+/// A `ShardedLock` is internally made of a list of *shards*, each being a [`RwLock`] occupying a
+/// single cache line. Read operations will pick one of the shards depending on the current thread
+/// and lock it. Write operations need to lock all shards in succession.
+///
+/// By splitting the lock into shards, concurrent read operations will in most cases choose
+/// different shards and thus update different cache lines, which is good for scalability. However,
+/// write operations need to do more work and are therefore slower than usual.
+///
+/// The priority policy of the lock is dependent on the underlying operating system's
+/// implementation, and this type does not guarantee that any particular policy will be used.
+///
+/// # Poisoning
+///
+/// A `ShardedLock`, like [`RwLock`], will become poisoned on a panic. Note that it may only be
+/// poisoned if a panic occurs while a write operation is in progress. If a panic occurs in any
+/// read operation, the lock will not be poisoned.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::sync::ShardedLock;
+///
+/// let lock = ShardedLock::new(5);
+///
+/// // Any number of read locks can be held at once.
+/// {
+///     let r1 = lock.read().unwrap();
+///     let r2 = lock.read().unwrap();
+///     assert_eq!(*r1, 5);
+///     assert_eq!(*r2, 5);
+/// } // Read locks are dropped at this point.
+///
+/// // However, only one write lock may be held.
+/// {
+///     let mut w = lock.write().unwrap();
+///     *w += 1;
+///     assert_eq!(*w, 6);
+/// } // Write lock is dropped here.
+/// ```
+///
+/// [`RwLock`]: std::sync::RwLock
+pub struct ShardedLock<T: ?Sized> {
+    /// A list of locks protecting the internal data.
+    shards: Box<[CachePadded<Shard>]>,
+
+    /// The internal data.
+    value: UnsafeCell<T>,
+}
+
+unsafe impl<T: ?Sized + Send> Send for ShardedLock<T> {}
+unsafe impl<T: ?Sized + Send + Sync> Sync for ShardedLock<T> {}
+
+impl<T: ?Sized> UnwindSafe for ShardedLock<T> {}
+impl<T: ?Sized> RefUnwindSafe for ShardedLock<T> {}
+
+impl<T> ShardedLock<T> {
+    /// Creates a new sharded reader-writer lock.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let lock = ShardedLock::new(5);
+    /// ```
+    pub fn new(value: T) -> ShardedLock<T> {
+        ShardedLock {
+            shards: (0..NUM_SHARDS)
+                .map(|_| {
+                    CachePadded::new(Shard {
+                        lock: RwLock::new(()),
+                        write_guard: UnsafeCell::new(None),
+                    })
+                })
+                .collect::<Box<[_]>>(),
+            value: UnsafeCell::new(value),
+        }
+    }
+
+    /// Consumes this lock, returning the underlying data.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let lock = ShardedLock::new(String::new());
+    /// {
+    ///     let mut s = lock.write().unwrap();
+    ///     *s = "modified".to_owned();
+    /// }
+    /// assert_eq!(lock.into_inner().unwrap(), "modified");
+    /// ```
+    pub fn into_inner(self) -> LockResult<T> {
+        let is_poisoned = self.is_poisoned();
+        let inner = self.value.into_inner();
+
+        if is_poisoned {
+            Err(PoisonError::new(inner))
+        } else {
+            Ok(inner)
+        }
+    }
+}
+
+impl<T: ?Sized> ShardedLock<T> {
+    /// Returns `true` if the lock is poisoned.
+    ///
+    /// If another thread can still access the lock, it may become poisoned at any time. A `false`
+    /// result should not be trusted without additional synchronization.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let lock = Arc::new(ShardedLock::new(0));
+    /// let c_lock = lock.clone();
+    ///
+    /// let _ = thread::spawn(move || {
+    ///     let _lock = c_lock.write().unwrap();
+    ///     panic!(); // the lock gets poisoned
+    /// }).join();
+    /// assert_eq!(lock.is_poisoned(), true);
+    /// ```
+    pub fn is_poisoned(&self) -> bool {
+        self.shards[0].lock.is_poisoned()
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the lock mutably, no actual locking needs to take place.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let mut lock = ShardedLock::new(0);
+    /// *lock.get_mut().unwrap() = 10;
+    /// assert_eq!(*lock.read().unwrap(), 10);
+    /// ```
+    pub fn get_mut(&mut self) -> LockResult<&mut T> {
+        let is_poisoned = self.is_poisoned();
+        let inner = unsafe { &mut *self.value.get() };
+
+        if is_poisoned {
+            Err(PoisonError::new(inner))
+        } else {
+            Ok(inner)
+        }
+    }
+
+    /// Attempts to acquire this lock with shared read access.
+    ///
+    /// If the access could not be granted at this time, an error is returned. Otherwise, a guard
+    /// is returned which will release the shared access when it is dropped. This method does not
+    /// provide any guarantees with respect to the ordering of whether contentious readers or
+    /// writers will acquire the lock first.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let lock = ShardedLock::new(1);
+    ///
+    /// match lock.try_read() {
+    ///     Ok(n) => assert_eq!(*n, 1),
+    ///     Err(_) => unreachable!(),
+    /// };
+    /// ```
+    pub fn try_read(&self) -> TryLockResult<ShardedLockReadGuard<'_, T>> {
+        // Take the current thread index and map it to a shard index. Thread indices will tend to
+        // distribute shards among threads equally, thus reducing contention due to read-locking.
+        let current_index = current_index().unwrap_or(0);
+        let shard_index = current_index & (self.shards.len() - 1);
+
+        match self.shards[shard_index].lock.try_read() {
+            Ok(guard) => Ok(ShardedLockReadGuard {
+                lock: self,
+                _guard: guard,
+                _marker: PhantomData,
+            }),
+            Err(TryLockError::Poisoned(err)) => {
+                let guard = ShardedLockReadGuard {
+                    lock: self,
+                    _guard: err.into_inner(),
+                    _marker: PhantomData,
+                };
+                Err(TryLockError::Poisoned(PoisonError::new(guard)))
+            }
+            Err(TryLockError::WouldBlock) => Err(TryLockError::WouldBlock),
+        }
+    }
+
+    /// Locks with shared read access, blocking the current thread until it can be acquired.
+    ///
+    /// The calling thread will be blocked until there are no more writers which hold the lock.
+    /// There may be other readers currently inside the lock when this method returns. This method
+    /// does not provide any guarantees with respect to the ordering of whether contentious readers
+    /// or writers will acquire the lock first.
+    ///
+    /// Returns a guard which will release the shared access when dropped.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Panics
+    ///
+    /// This method might panic when called if the lock is already held by the current thread.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    /// use std::sync::Arc;
+    /// use std::thread;
+    ///
+    /// let lock = Arc::new(ShardedLock::new(1));
+    /// let c_lock = lock.clone();
+    ///
+    /// let n = lock.read().unwrap();
+    /// assert_eq!(*n, 1);
+    ///
+    /// thread::spawn(move || {
+    ///     let r = c_lock.read();
+    ///     assert!(r.is_ok());
+    /// }).join().unwrap();
+    /// ```
+    pub fn read(&self) -> LockResult<ShardedLockReadGuard<'_, T>> {
+        // Take the current thread index and map it to a shard index. Thread indices will tend to
+        // distribute shards among threads equally, thus reducing contention due to read-locking.
+        let current_index = current_index().unwrap_or(0);
+        let shard_index = current_index & (self.shards.len() - 1);
+
+        match self.shards[shard_index].lock.read() {
+            Ok(guard) => Ok(ShardedLockReadGuard {
+                lock: self,
+                _guard: guard,
+                _marker: PhantomData,
+            }),
+            Err(err) => Err(PoisonError::new(ShardedLockReadGuard {
+                lock: self,
+                _guard: err.into_inner(),
+                _marker: PhantomData,
+            })),
+        }
+    }
+
+    /// Attempts to acquire this lock with exclusive write access.
+    ///
+    /// If the access could not be granted at this time, an error is returned. Otherwise, a guard
+    /// is returned which will release the exclusive access when it is dropped. This method does
+    /// not provide any guarantees with respect to the ordering of whether contentious readers or
+    /// writers will acquire the lock first.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let lock = ShardedLock::new(1);
+    ///
+    /// let n = lock.read().unwrap();
+    /// assert_eq!(*n, 1);
+    ///
+    /// assert!(lock.try_write().is_err());
+    /// ```
+    pub fn try_write(&self) -> TryLockResult<ShardedLockWriteGuard<'_, T>> {
+        let mut poisoned = false;
+        let mut blocked = None;
+
+        // Write-lock each shard in succession.
+        for (i, shard) in self.shards.iter().enumerate() {
+            let guard = match shard.lock.try_write() {
+                Ok(guard) => guard,
+                Err(TryLockError::Poisoned(err)) => {
+                    poisoned = true;
+                    err.into_inner()
+                }
+                Err(TryLockError::WouldBlock) => {
+                    blocked = Some(i);
+                    break;
+                }
+            };
+
+            // Store the guard into the shard.
+            unsafe {
+                let guard: RwLockWriteGuard<'static, ()> = mem::transmute(guard);
+                let dest: *mut _ = shard.write_guard.get();
+                *dest = Some(guard);
+            }
+        }
+
+        if let Some(i) = blocked {
+            // Unlock the shards in reverse order of locking.
+            for shard in self.shards[0..i].iter().rev() {
+                unsafe {
+                    let dest: *mut _ = shard.write_guard.get();
+                    let guard = mem::replace(&mut *dest, None);
+                    drop(guard);
+                }
+            }
+            Err(TryLockError::WouldBlock)
+        } else if poisoned {
+            let guard = ShardedLockWriteGuard {
+                lock: self,
+                _marker: PhantomData,
+            };
+            Err(TryLockError::Poisoned(PoisonError::new(guard)))
+        } else {
+            Ok(ShardedLockWriteGuard {
+                lock: self,
+                _marker: PhantomData,
+            })
+        }
+    }
+
+    /// Locks with exclusive write access, blocking the current thread until it can be acquired.
+    ///
+    /// The calling thread will be blocked until there are no more writers which hold the lock.
+    /// There may be other readers currently inside the lock when this method returns. This method
+    /// does not provide any guarantees with respect to the ordering of whether contentious readers
+    /// or writers will acquire the lock first.
+    ///
+    /// Returns a guard which will release the exclusive access when dropped.
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+    /// operation panics.
+    ///
+    /// # Panics
+    ///
+    /// This method might panic when called if the lock is already held by the current thread.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::ShardedLock;
+    ///
+    /// let lock = ShardedLock::new(1);
+    ///
+    /// let mut n = lock.write().unwrap();
+    /// *n = 2;
+    ///
+    /// assert!(lock.try_read().is_err());
+    /// ```
+    pub fn write(&self) -> LockResult<ShardedLockWriteGuard<'_, T>> {
+        let mut poisoned = false;
+
+        // Write-lock each shard in succession.
+        for shard in self.shards.iter() {
+            let guard = match shard.lock.write() {
+                Ok(guard) => guard,
+                Err(err) => {
+                    poisoned = true;
+                    err.into_inner()
+                }
+            };
+
+            // Store the guard into the shard.
+            unsafe {
+                let guard: RwLockWriteGuard<'_, ()> = guard;
+                let guard: RwLockWriteGuard<'static, ()> = mem::transmute(guard);
+                let dest: *mut _ = shard.write_guard.get();
+                *dest = Some(guard);
+            }
+        }
+
+        if poisoned {
+            Err(PoisonError::new(ShardedLockWriteGuard {
+                lock: self,
+                _marker: PhantomData,
+            }))
+        } else {
+            Ok(ShardedLockWriteGuard {
+                lock: self,
+                _marker: PhantomData,
+            })
+        }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for ShardedLock<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.try_read() {
+            Ok(guard) => f
+                .debug_struct("ShardedLock")
+                .field("data", &&*guard)
+                .finish(),
+            Err(TryLockError::Poisoned(err)) => f
+                .debug_struct("ShardedLock")
+                .field("data", &&**err.get_ref())
+                .finish(),
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+                f.debug_struct("ShardedLock")
+                    .field("data", &LockedPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+impl<T: Default> Default for ShardedLock<T> {
+    fn default() -> ShardedLock<T> {
+        ShardedLock::new(Default::default())
+    }
+}
+
+impl<T> From<T> for ShardedLock<T> {
+    fn from(t: T) -> Self {
+        ShardedLock::new(t)
+    }
+}
+
+/// A guard used to release the shared read access of a [`ShardedLock`] when dropped.
+pub struct ShardedLockReadGuard<'a, T: ?Sized> {
+    lock: &'a ShardedLock<T>,
+    _guard: RwLockReadGuard<'a, ()>,
+    _marker: PhantomData<RwLockReadGuard<'a, T>>,
+}
+
+unsafe impl<T: ?Sized + Sync> Sync for ShardedLockReadGuard<'_, T> {}
+
+impl<T: ?Sized> Deref for ShardedLockReadGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.lock.value.get() }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ShardedLockReadGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ShardedLockReadGuard")
+            .field("lock", &self.lock)
+            .finish()
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for ShardedLockReadGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+/// A guard used to release the exclusive write access of a [`ShardedLock`] when dropped.
+pub struct ShardedLockWriteGuard<'a, T: ?Sized> {
+    lock: &'a ShardedLock<T>,
+    _marker: PhantomData<RwLockWriteGuard<'a, T>>,
+}
+
+unsafe impl<T: ?Sized + Sync> Sync for ShardedLockWriteGuard<'_, T> {}
+
+impl<T: ?Sized> Drop for ShardedLockWriteGuard<'_, T> {
+    fn drop(&mut self) {
+        // Unlock the shards in reverse order of locking.
+        for shard in self.lock.shards.iter().rev() {
+            unsafe {
+                let dest: *mut _ = shard.write_guard.get();
+                let guard = mem::replace(&mut *dest, None);
+                drop(guard);
+            }
+        }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ShardedLockWriteGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ShardedLockWriteGuard")
+            .field("lock", &self.lock)
+            .finish()
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for ShardedLockWriteGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+impl<T: ?Sized> Deref for ShardedLockWriteGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.lock.value.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for ShardedLockWriteGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.lock.value.get() }
+    }
+}
+
+/// Returns a `usize` that identifies the current thread.
+///
+/// Each thread is associated with an 'index'. While there are no particular guarantees, indices
+/// usually tend to be consecutive numbers between 0 and the number of running threads.
+///
+/// Since this function accesses TLS, `None` might be returned if the current thread's TLS is
+/// tearing down.
+#[inline]
+fn current_index() -> Option<usize> {
+    REGISTRATION.try_with(|reg| reg.index).ok()
+}
+
+/// The global registry keeping track of registered threads and indices.
+struct ThreadIndices {
+    /// Mapping from `ThreadId` to thread index.
+    mapping: HashMap<ThreadId, usize>,
+
+    /// A list of free indices.
+    free_list: Vec<usize>,
+
+    /// The next index to allocate if the free list is empty.
+    next_index: usize,
+}
+
+static THREAD_INDICES: Lazy<Mutex<ThreadIndices>> = Lazy::new(|| {
+    Mutex::new(ThreadIndices {
+        mapping: HashMap::new(),
+        free_list: Vec::new(),
+        next_index: 0,
+    })
+});
+
+/// A registration of a thread with an index.
+///
+/// When dropped, unregisters the thread and frees the reserved index.
+struct Registration {
+    index: usize,
+    thread_id: ThreadId,
+}
+
+impl Drop for Registration {
+    fn drop(&mut self) {
+        let mut indices = THREAD_INDICES.lock().unwrap();
+        indices.mapping.remove(&self.thread_id);
+        indices.free_list.push(self.index);
+    }
+}
+
+thread_local! {
+    static REGISTRATION: Registration = {
+        let thread_id = thread::current().id();
+        let mut indices = THREAD_INDICES.lock().unwrap();
+
+        let index = match indices.free_list.pop() {
+            Some(i) => i,
+            None => {
+                let i = indices.next_index;
+                indices.next_index += 1;
+                i
+            }
+        };
+        indices.mapping.insert(thread_id, index);
+
+        Registration {
+            index,
+            thread_id,
+        }
+    };
+}
diff --git a/vendor/crossbeam-utils/src/sync/wait_group.rs b/vendor/crossbeam-utils/src/sync/wait_group.rs
new file mode 100644
index 000000000..4206ee42b
--- /dev/null
+++ b/vendor/crossbeam-utils/src/sync/wait_group.rs
@@ -0,0 +1,146 @@
+// Necessary for using `Mutex<usize>` for conditional variables
+#![allow(clippy::mutex_atomic)]
+
+use crate::primitive::sync::{Arc, Condvar, Mutex};
+use std::fmt;
+
+/// Enables threads to synchronize the beginning or end of some computation.
+///
+/// # Wait groups vs barriers
+///
+/// `WaitGroup` is very similar to [`Barrier`], but there are a few differences:
+///
+/// * [`Barrier`] needs to know the number of threads at construction, while `WaitGroup` is cloned to
+///   register more threads.
+///
+/// * A [`Barrier`] can be reused even after all threads have synchronized, while a `WaitGroup`
+///   synchronizes threads only once.
+///
+/// * All threads wait for others to reach the [`Barrier`]. With `WaitGroup`, each thread can choose
+///   to either wait for other threads or to continue without blocking.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::sync::WaitGroup;
+/// use std::thread;
+///
+/// // Create a new wait group.
+/// let wg = WaitGroup::new();
+///
+/// for _ in 0..4 {
+///     // Create another reference to the wait group.
+///     let wg = wg.clone();
+///
+///     thread::spawn(move || {
+///         // Do some work.
+///
+///         // Drop the reference to the wait group.
+///         drop(wg);
+///     });
+/// }
+///
+/// // Block until all threads have finished their work.
+/// wg.wait();
+/// ```
+///
+/// [`Barrier`]: std::sync::Barrier
+pub struct WaitGroup {
+    inner: Arc<Inner>,
+}
+
+/// Inner state of a `WaitGroup`.
+struct Inner {
+    cvar: Condvar,
+    count: Mutex<usize>,
+}
+
+impl Default for WaitGroup {
+    fn default() -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                cvar: Condvar::new(),
+                count: Mutex::new(1),
+            }),
+        }
+    }
+}
+
+impl WaitGroup {
+    /// Creates a new wait group and returns the single reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::WaitGroup;
+    ///
+    /// let wg = WaitGroup::new();
+    /// ```
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Drops this reference and waits until all other references are dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::sync::WaitGroup;
+    /// use std::thread;
+    ///
+    /// let wg = WaitGroup::new();
+    ///
+    /// thread::spawn({
+    ///     let wg = wg.clone();
+    ///     move || {
+    ///         // Block until both threads have reached `wait()`.
+    ///         wg.wait();
+    ///     }
+    /// });
+    ///
+    /// // Block until both threads have reached `wait()`.
+    /// wg.wait();
+    /// ```
+    pub fn wait(self) {
+        if *self.inner.count.lock().unwrap() == 1 {
+            return;
+        }
+
+        let inner = self.inner.clone();
+        drop(self);
+
+        let mut count = inner.count.lock().unwrap();
+        while *count > 0 {
+            count = inner.cvar.wait(count).unwrap();
+        }
+    }
+}
+
+impl Drop for WaitGroup {
+    fn drop(&mut self) {
+        let mut count = self.inner.count.lock().unwrap();
+        *count -= 1;
+
+        if *count == 0 {
+            self.inner.cvar.notify_all();
+        }
+    }
+}
+
+impl Clone for WaitGroup {
+    fn clone(&self) -> WaitGroup {
+        let mut count = self.inner.count.lock().unwrap();
+        *count += 1;
+
+        WaitGroup {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl fmt::Debug for WaitGroup {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let count: &usize = &*self.inner.count.lock().unwrap();
+        f.debug_struct("WaitGroup").field("count", count).finish()
+    }
+}
diff --git a/vendor/crossbeam-utils/src/thread.rs b/vendor/crossbeam-utils/src/thread.rs
new file mode 100644
index 000000000..f1086d9ec
--- /dev/null
+++ b/vendor/crossbeam-utils/src/thread.rs
@@ -0,0 +1,587 @@
+//! Threads that can borrow variables from the stack.
+//!
+//! Create a scope when spawned threads need to access variables on the stack:
+//!
+//! ```
+//! use crossbeam_utils::thread;
+//!
+//! let people = vec![
+//!     "Alice".to_string(),
+//!     "Bob".to_string(),
+//!     "Carol".to_string(),
+//! ];
+//!
+//! thread::scope(|s| {
+//!     for person in &people {
+//!         s.spawn(move |_| {
+//!             println!("Hello, {}!", person);
+//!         });
+//!     }
+//! }).unwrap();
+//! ```
+//!
+//! # Why scoped threads?
+//!
+//! Suppose we wanted to re-write the previous example using plain threads:
+//!
+//! ```compile_fail,E0597
+//! use std::thread;
+//!
+//! let people = vec![
+//!     "Alice".to_string(),
+//!     "Bob".to_string(),
+//!     "Carol".to_string(),
+//! ];
+//!
+//! let mut threads = Vec::new();
+//!
+//! for person in &people {
+//!     threads.push(thread::spawn(move || {
+//!         println!("Hello, {}!", person);
+//!     }));
+//! }
+//!
+//! for thread in threads {
+//!     thread.join().unwrap();
+//! }
+//! ```
+//!
+//! This doesn't work because the borrow checker complains about `people` not living long enough:
+//!
+//! ```text
+//! error[E0597]: `people` does not live long enough
+//!   --> src/main.rs:12:20
+//!    |
+//! 12 |     for person in &people {
+//!    |                    ^^^^^^ borrowed value does not live long enough
+//! ...
+//! 21 | }
+//!    | - borrowed value only lives until here
+//!    |
+//!    = note: borrowed value must be valid for the static lifetime...
+//! ```
+//!
+//! The problem here is that spawned threads are not allowed to borrow variables on stack because
+//! the compiler cannot prove they will be joined before `people` is destroyed.
+//!
+//! Scoped threads are a mechanism to guarantee to the compiler that spawned threads will be joined
+//! before the scope ends.
+//!
+//! # How scoped threads work
+//!
+//! If a variable is borrowed by a thread, the thread must complete before the variable is
+//! destroyed. Threads spawned using [`std::thread::spawn`] can only borrow variables with the
+//! `'static` lifetime because the borrow checker cannot be sure when the thread will complete.
+//!
+//! A scope creates a clear boundary between variables outside the scope and threads inside the
+//! scope. Whenever a scope spawns a thread, it promises to join the thread before the scope ends.
+//! This way we guarantee to the borrow checker that scoped threads only live within the scope and
+//! can safely access variables outside it.
+//!
+//! # Nesting scoped threads
+//!
+//! Sometimes scoped threads need to spawn more threads within the same scope. This is a little
+//! tricky because argument `s` lives *inside* the invocation of `thread::scope()` and as such
+//! cannot be borrowed by scoped threads:
+//!
+//! ```compile_fail,E0373,E0521
+//! use crossbeam_utils::thread;
+//!
+//! thread::scope(|s| {
+//!     s.spawn(|_| {
+//!         // Not going to compile because we're trying to borrow `s`,
+//!         // which lives *inside* the scope! :(
+//!         s.spawn(|_| println!("nested thread"));
+//!     });
+//! });
+//! ```
+//!
+//! Fortunately, there is a solution. Every scoped thread is passed a reference to its scope as an
+//! argument, which can be used for spawning nested threads:
+//!
+//! ```
+//! use crossbeam_utils::thread;
+//!
+//! thread::scope(|s| {
+//!     // Note the `|s|` here.
+//!     s.spawn(|s| {
+//!         // Yay, this works because we're using a fresh argument `s`! :)
+//!         s.spawn(|_| println!("nested thread"));
+//!     });
+//! }).unwrap();
+//! ```
+
+use std::fmt;
+use std::io;
+use std::marker::PhantomData;
+use std::mem;
+use std::panic;
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+use crate::sync::WaitGroup;
+use cfg_if::cfg_if;
+
+type SharedVec<T> = Arc<Mutex<Vec<T>>>;
+type SharedOption<T> = Arc<Mutex<Option<T>>>;
+
+/// Creates a new scope for spawning threads.
+///
+/// All child threads that haven't been manually joined will be automatically joined just before
+/// this function invocation ends. If all joined threads have successfully completed, `Ok` is
+/// returned with the return value of `f`. If any of the joined threads has panicked, an `Err` is
+/// returned containing errors from panicked threads. Note that if panics are implemented by
+/// aborting the process, no error is returned; see the notes of [std::panic::catch_unwind].
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::thread;
+///
+/// let var = vec![1, 2, 3];
+///
+/// thread::scope(|s| {
+///     s.spawn(|_| {
+///         println!("A child thread borrowing `var`: {:?}", var);
+///     });
+/// }).unwrap();
+/// ```
+pub fn scope<'env, F, R>(f: F) -> thread::Result<R>
+where
+    F: FnOnce(&Scope<'env>) -> R,
+{
+    let wg = WaitGroup::new();
+    let scope = Scope::<'env> {
+        handles: SharedVec::default(),
+        wait_group: wg.clone(),
+        _marker: PhantomData,
+    };
+
+    // Execute the scoped function, but catch any panics.
+    let result = panic::catch_unwind(panic::AssertUnwindSafe(|| f(&scope)));
+
+    // Wait until all nested scopes are dropped.
+    drop(scope.wait_group);
+    wg.wait();
+
+    // Join all remaining spawned threads.
+    let panics: Vec<_> = scope
+        .handles
+        .lock()
+        .unwrap()
+        // Filter handles that haven't been joined, join them, and collect errors.
+        .drain(..)
+        .filter_map(|handle| handle.lock().unwrap().take())
+        .filter_map(|handle| handle.join().err())
+        .collect();
+
+    // If `f` has panicked, resume unwinding.
+    // If any of the child threads have panicked, return the panic errors.
+    // Otherwise, everything is OK and return the result of `f`.
+    match result {
+        Err(err) => panic::resume_unwind(err),
+        Ok(res) => {
+            if panics.is_empty() {
+                Ok(res)
+            } else {
+                Err(Box::new(panics))
+            }
+        }
+    }
+}
+
+/// A scope for spawning threads.
+pub struct Scope<'env> {
+    /// The list of the thread join handles.
+    handles: SharedVec<SharedOption<thread::JoinHandle<()>>>,
+
+    /// Used to wait until all subscopes all dropped.
+    wait_group: WaitGroup,
+
+    /// Borrows data with invariant lifetime `'env`.
+    _marker: PhantomData<&'env mut &'env ()>,
+}
+
+unsafe impl Sync for Scope<'_> {}
+
+impl<'env> Scope<'env> {
+    /// Spawns a scoped thread.
+    ///
+    /// This method is similar to the [`spawn`] function in Rust's standard library. The difference
+    /// is that this thread is scoped, meaning it's guaranteed to terminate before the scope exits,
+    /// allowing it to reference variables outside the scope.
+    ///
+    /// The scoped thread is passed a reference to this scope as an argument, which can be used for
+    /// spawning nested threads.
+    ///
+    /// The returned [handle](ScopedJoinHandle) can be used to manually
+    /// [join](ScopedJoinHandle::join) the thread before the scope exits.
+    ///
+    /// This will create a thread using default parameters of [`ScopedThreadBuilder`], if you want to specify the
+    /// stack size or the name of the thread, use this API instead.
+    ///
+    /// [`spawn`]: std::thread::spawn
+    ///
+    /// # Panics
+    ///
+    /// Panics if the OS fails to create a thread; use [`ScopedThreadBuilder::spawn`]
+    /// to recover from such errors.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     let handle = s.spawn(|_| {
+    ///         println!("A child thread is running");
+    ///         42
+    ///     });
+    ///
+    ///     // Join the thread and retrieve its result.
+    ///     let res = handle.join().unwrap();
+    ///     assert_eq!(res, 42);
+    /// }).unwrap();
+    /// ```
+    pub fn spawn<'scope, F, T>(&'scope self, f: F) -> ScopedJoinHandle<'scope, T>
+    where
+        F: FnOnce(&Scope<'env>) -> T,
+        F: Send + 'env,
+        T: Send + 'env,
+    {
+        self.builder()
+            .spawn(f)
+            .expect("failed to spawn scoped thread")
+    }
+
+    /// Creates a builder that can configure a thread before spawning.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     s.builder()
+    ///         .spawn(|_| println!("A child thread is running"))
+    ///         .unwrap();
+    /// }).unwrap();
+    /// ```
+    pub fn builder<'scope>(&'scope self) -> ScopedThreadBuilder<'scope, 'env> {
+        ScopedThreadBuilder {
+            scope: self,
+            builder: thread::Builder::new(),
+        }
+    }
+}
+
+impl fmt::Debug for Scope<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Scope { .. }")
+    }
+}
+
+/// Configures the properties of a new thread.
+///
+/// The two configurable properties are:
+///
+/// - [`name`]: Specifies an [associated name for the thread][naming-threads].
+/// - [`stack_size`]: Specifies the [desired stack size for the thread][stack-size].
+///
+/// The [`spawn`] method will take ownership of the builder and return an [`io::Result`] of the
+/// thread handle with the given configuration.
+///
+/// The [`Scope::spawn`] method uses a builder with default configuration and unwraps its return
+/// value. You may want to use this builder when you want to recover from a failure to launch a
+/// thread.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::thread;
+///
+/// thread::scope(|s| {
+///     s.builder()
+///         .spawn(|_| println!("Running a child thread"))
+///         .unwrap();
+/// }).unwrap();
+/// ```
+///
+/// [`name`]: ScopedThreadBuilder::name
+/// [`stack_size`]: ScopedThreadBuilder::stack_size
+/// [`spawn`]: ScopedThreadBuilder::spawn
+/// [`io::Result`]: std::io::Result
+/// [naming-threads]: std::thread#naming-threads
+/// [stack-size]: std::thread#stack-size
+#[derive(Debug)]
+pub struct ScopedThreadBuilder<'scope, 'env> {
+    scope: &'scope Scope<'env>,
+    builder: thread::Builder,
+}
+
+impl<'scope, 'env> ScopedThreadBuilder<'scope, 'env> {
+    /// Sets the name for the new thread.
+    ///
+    /// The name must not contain null bytes (`\0`).
+    ///
+    /// For more information about named threads, see [here][naming-threads].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    /// use std::thread::current;
+    ///
+    /// thread::scope(|s| {
+    ///     s.builder()
+    ///         .name("my thread".to_string())
+    ///         .spawn(|_| assert_eq!(current().name(), Some("my thread")))
+    ///         .unwrap();
+    /// }).unwrap();
+    /// ```
+    ///
+    /// [naming-threads]: std::thread#naming-threads
+    pub fn name(mut self, name: String) -> ScopedThreadBuilder<'scope, 'env> {
+        self.builder = self.builder.name(name);
+        self
+    }
+
+    /// Sets the size of the stack for the new thread.
+    ///
+    /// The stack size is measured in bytes.
+    ///
+    /// For more information about the stack size for threads, see [here][stack-size].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     s.builder()
+    ///         .stack_size(32 * 1024)
+    ///         .spawn(|_| println!("Running a child thread"))
+    ///         .unwrap();
+    /// }).unwrap();
+    /// ```
+    ///
+    /// [stack-size]: std::thread#stack-size
+    pub fn stack_size(mut self, size: usize) -> ScopedThreadBuilder<'scope, 'env> {
+        self.builder = self.builder.stack_size(size);
+        self
+    }
+
+    /// Spawns a scoped thread with this configuration.
+    ///
+    /// The scoped thread is passed a reference to this scope as an argument, which can be used for
+    /// spawning nested threads.
+    ///
+    /// The returned handle can be used to manually join the thread before the scope exits.
+    ///
+    /// # Errors
+    ///
+    /// Unlike the [`Scope::spawn`] method, this method yields an
+    /// [`io::Result`] to capture any failure to create the thread at
+    /// the OS level.
+    ///
+    /// [`io::Result`]: std::io::Result
+    ///
+    /// # Panics
+    ///
+    /// Panics if a thread name was set and it contained null bytes.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     let handle = s.builder()
+    ///         .spawn(|_| {
+    ///             println!("A child thread is running");
+    ///             42
+    ///         })
+    ///         .unwrap();
+    ///
+    ///     // Join the thread and retrieve its result.
+    ///     let res = handle.join().unwrap();
+    ///     assert_eq!(res, 42);
+    /// }).unwrap();
+    /// ```
+    pub fn spawn<F, T>(self, f: F) -> io::Result<ScopedJoinHandle<'scope, T>>
+    where
+        F: FnOnce(&Scope<'env>) -> T,
+        F: Send + 'env,
+        T: Send + 'env,
+    {
+        // The result of `f` will be stored here.
+        let result = SharedOption::default();
+
+        // Spawn the thread and grab its join handle and thread handle.
+        let (handle, thread) = {
+            let result = Arc::clone(&result);
+
+            // A clone of the scope that will be moved into the new thread.
+            let scope = Scope::<'env> {
+                handles: Arc::clone(&self.scope.handles),
+                wait_group: self.scope.wait_group.clone(),
+                _marker: PhantomData,
+            };
+
+            // Spawn the thread.
+            let handle = {
+                let closure = move || {
+                    // Make sure the scope is inside the closure with the proper `'env` lifetime.
+                    let scope: Scope<'env> = scope;
+
+                    // Run the closure.
+                    let res = f(&scope);
+
+                    // Store the result if the closure didn't panic.
+                    *result.lock().unwrap() = Some(res);
+                };
+
+                // Allocate `closure` on the heap and erase the `'env` bound.
+                let closure: Box<dyn FnOnce() + Send + 'env> = Box::new(closure);
+                let closure: Box<dyn FnOnce() + Send + 'static> =
+                    unsafe { mem::transmute(closure) };
+
+                // Finally, spawn the closure.
+                self.builder.spawn(closure)?
+            };
+
+            let thread = handle.thread().clone();
+            let handle = Arc::new(Mutex::new(Some(handle)));
+            (handle, thread)
+        };
+
+        // Add the handle to the shared list of join handles.
+        self.scope.handles.lock().unwrap().push(Arc::clone(&handle));
+
+        Ok(ScopedJoinHandle {
+            handle,
+            result,
+            thread,
+            _marker: PhantomData,
+        })
+    }
+}
+
+unsafe impl<T> Send for ScopedJoinHandle<'_, T> {}
+unsafe impl<T> Sync for ScopedJoinHandle<'_, T> {}
+
+/// A handle that can be used to join its scoped thread.
+///
+/// This struct is created by the [`Scope::spawn`] method and the
+/// [`ScopedThreadBuilder::spawn`] method.
+pub struct ScopedJoinHandle<'scope, T> {
+    /// A join handle to the spawned thread.
+    handle: SharedOption<thread::JoinHandle<()>>,
+
+    /// Holds the result of the inner closure.
+    result: SharedOption<T>,
+
+    /// A handle to the the spawned thread.
+    thread: thread::Thread,
+
+    /// Borrows the parent scope with lifetime `'scope`.
+    _marker: PhantomData<&'scope ()>,
+}
+
+impl<T> ScopedJoinHandle<'_, T> {
+    /// Waits for the thread to finish and returns its result.
+    ///
+    /// If the child thread panics, an error is returned. Note that if panics are implemented by
+    /// aborting the process, no error is returned; see the notes of [std::panic::catch_unwind].
+    ///
+    /// # Panics
+    ///
+    /// This function may panic on some platforms if a thread attempts to join itself or otherwise
+    /// may create a deadlock with joining threads.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     let handle1 = s.spawn(|_| println!("I'm a happy thread :)"));
+    ///     let handle2 = s.spawn(|_| panic!("I'm a sad thread :("));
+    ///
+    ///     // Join the first thread and verify that it succeeded.
+    ///     let res = handle1.join();
+    ///     assert!(res.is_ok());
+    ///
+    ///     // Join the second thread and verify that it panicked.
+    ///     let res = handle2.join();
+    ///     assert!(res.is_err());
+    /// }).unwrap();
+    /// ```
+    pub fn join(self) -> thread::Result<T> {
+        // Take out the handle. The handle will surely be available because the root scope waits
+        // for nested scopes before joining remaining threads.
+        let handle = self.handle.lock().unwrap().take().unwrap();
+
+        // Join the thread and then take the result out of its inner closure.
+        handle
+            .join()
+            .map(|()| self.result.lock().unwrap().take().unwrap())
+    }
+
+    /// Returns a handle to the underlying thread.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_utils::thread;
+    ///
+    /// thread::scope(|s| {
+    ///     let handle = s.spawn(|_| println!("A child thread is running"));
+    ///     println!("The child thread ID: {:?}", handle.thread().id());
+    /// }).unwrap();
+    /// ```
+    pub fn thread(&self) -> &thread::Thread {
+        &self.thread
+    }
+}
+
+cfg_if! {
+    if #[cfg(unix)] {
+        use std::os::unix::thread::{JoinHandleExt, RawPthread};
+
+        impl<T> JoinHandleExt for ScopedJoinHandle<'_, T> {
+            fn as_pthread_t(&self) -> RawPthread {
+                // Borrow the handle. The handle will surely be available because the root scope waits
+                // for nested scopes before joining remaining threads.
+                let handle = self.handle.lock().unwrap();
+                handle.as_ref().unwrap().as_pthread_t()
+            }
+            fn into_pthread_t(self) -> RawPthread {
+                self.as_pthread_t()
+            }
+        }
+    } else if #[cfg(windows)] {
+        use std::os::windows::io::{AsRawHandle, IntoRawHandle, RawHandle};
+
+        impl<T> AsRawHandle for ScopedJoinHandle<'_, T> {
+            fn as_raw_handle(&self) -> RawHandle {
+                // Borrow the handle. The handle will surely be available because the root scope waits
+                // for nested scopes before joining remaining threads.
+                let handle = self.handle.lock().unwrap();
+                handle.as_ref().unwrap().as_raw_handle()
+            }
+        }
+
+        impl<T> IntoRawHandle for ScopedJoinHandle<'_, T> {
+            fn into_raw_handle(self) -> RawHandle {
+                self.as_raw_handle()
+            }
+        }
+    }
+}
+
+impl<T> fmt::Debug for ScopedJoinHandle<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("ScopedJoinHandle { .. }")
+    }
+}