Merging upstream version 1.72.1+dfsg1.

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

14 files changed, 536 insertions, 169 deletions

diff --git a/vendor/tokio/src/loom/std/atomic_ptr.rs b/vendor/tokio/src/loom/std/atomic_ptr.rs
deleted file mode 100644
index 236645f03..000000000
--- a/vendor/tokio/src/loom/std/atomic_ptr.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-use std::fmt;
-use std::ops::{Deref, DerefMut};
-
-/// `AtomicPtr` providing an additional `load_unsync` function.
-pub(crate) struct AtomicPtr<T> {
-    inner: std::sync::atomic::AtomicPtr<T>,
-}
-
-impl<T> AtomicPtr<T> {
-    pub(crate) fn new(ptr: *mut T) -> AtomicPtr<T> {
-        let inner = std::sync::atomic::AtomicPtr::new(ptr);
-        AtomicPtr { inner }
-    }
-}
-
-impl<T> Deref for AtomicPtr<T> {
-    type Target = std::sync::atomic::AtomicPtr<T>;
-
-    fn deref(&self) -> &Self::Target {
-        &self.inner
-    }
-}
-
-impl<T> DerefMut for AtomicPtr<T> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.inner
-    }
-}
-
-impl<T> fmt::Debug for AtomicPtr<T> {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.deref().fmt(fmt)
-    }
-}
diff --git a/vendor/tokio/src/loom/std/atomic_u16.rs b/vendor/tokio/src/loom/std/atomic_u16.rs
index c1c531208..c9e105c19 100644
--- a/vendor/tokio/src/loom/std/atomic_u16.rs
+++ b/vendor/tokio/src/loom/std/atomic_u16.rs
@@ -2,7 +2,7 @@ use std::cell::UnsafeCell;
 use std::fmt;
 use std::ops::Deref;
 
-/// `AtomicU16` providing an additional `load_unsync` function.
+/// `AtomicU16` providing an additional `unsync_load` function.
 pub(crate) struct AtomicU16 {
     inner: UnsafeCell<std::sync::atomic::AtomicU16>,
 }
@@ -23,7 +23,7 @@ impl AtomicU16 {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> u16 {
-        *(*self.inner.get()).get_mut()
+        core::ptr::read(self.inner.get() as *const u16)
     }
 }
 
diff --git a/vendor/tokio/src/loom/std/atomic_u32.rs b/vendor/tokio/src/loom/std/atomic_u32.rs
index 61f95fb30..ee0d2d380 100644
--- a/vendor/tokio/src/loom/std/atomic_u32.rs
+++ b/vendor/tokio/src/loom/std/atomic_u32.rs
@@ -2,7 +2,7 @@ use std::cell::UnsafeCell;
 use std::fmt;
 use std::ops::Deref;
 
-/// `AtomicU32` providing an additional `load_unsync` function.
+/// `AtomicU32` providing an additional `unsync_load` function.
 pub(crate) struct AtomicU32 {
     inner: UnsafeCell<std::sync::atomic::AtomicU32>,
 }
@@ -15,6 +15,16 @@ impl AtomicU32 {
         let inner = UnsafeCell::new(std::sync::atomic::AtomicU32::new(val));
         AtomicU32 { inner }
     }
+
+    /// Performs an unsynchronized load.
+    ///
+    /// # Safety
+    ///
+    /// All mutations must have happened before the unsynchronized load.
+    /// Additionally, there must be no concurrent mutations.
+    pub(crate) unsafe fn unsync_load(&self) -> u32 {
+        core::ptr::read(self.inner.get() as *const u32)
+    }
 }
 
 impl Deref for AtomicU32 {
diff --git a/vendor/tokio/src/loom/std/atomic_u64.rs b/vendor/tokio/src/loom/std/atomic_u64.rs
index 7eb457a24..ce391be3e 100644
--- a/vendor/tokio/src/loom/std/atomic_u64.rs
+++ b/vendor/tokio/src/loom/std/atomic_u64.rs
@@ -2,74 +2,18 @@
 //! re-export of `AtomicU64`. On 32 bit platforms, this is implemented using a
 //! `Mutex`.
 
-pub(crate) use self::imp::AtomicU64;
-
 // `AtomicU64` can only be used on targets with `target_has_atomic` is 64 or greater.
 // Once `cfg_target_has_atomic` feature is stable, we can replace it with
 // `#[cfg(target_has_atomic = "64")]`.
 // Refs: https://github.com/rust-lang/rust/tree/master/src/librustc_target
-#[cfg(not(any(target_arch = "arm", target_arch = "mips", target_arch = "powerpc")))]
-mod imp {
-    pub(crate) use std::sync::atomic::AtomicU64;
+cfg_has_atomic_u64! {
+    #[path = "atomic_u64_native.rs"]
+    mod imp;
 }
 
-#[cfg(any(target_arch = "arm", target_arch = "mips", target_arch = "powerpc"))]
-mod imp {
-    use crate::loom::sync::Mutex;
-    use std::sync::atomic::Ordering;
-
-    #[derive(Debug)]
-    pub(crate) struct AtomicU64 {
-        inner: Mutex<u64>,
-    }
-
-    impl AtomicU64 {
-        pub(crate) fn new(val: u64) -> Self {
-            Self {
-                inner: Mutex::new(val),
-            }
-        }
-
-        pub(crate) fn load(&self, _: Ordering) -> u64 {
-            *self.inner.lock()
-        }
-
-        pub(crate) fn store(&self, val: u64, _: Ordering) {
-            *self.inner.lock() = val;
-        }
-
-        pub(crate) fn fetch_or(&self, val: u64, _: Ordering) -> u64 {
-            let mut lock = self.inner.lock();
-            let prev = *lock;
-            *lock = prev | val;
-            prev
-        }
-
-        pub(crate) fn compare_exchange(
-            &self,
-            current: u64,
-            new: u64,
-            _success: Ordering,
-            _failure: Ordering,
-        ) -> Result<u64, u64> {
-            let mut lock = self.inner.lock();
-
-            if *lock == current {
-                *lock = new;
-                Ok(current)
-            } else {
-                Err(*lock)
-            }
-        }
-
-        pub(crate) fn compare_exchange_weak(
-            &self,
-            current: u64,
-            new: u64,
-            success: Ordering,
-            failure: Ordering,
-        ) -> Result<u64, u64> {
-            self.compare_exchange(current, new, success, failure)
-        }
-    }
+cfg_not_has_atomic_u64! {
+    #[path = "atomic_u64_as_mutex.rs"]
+    mod imp;
 }
+
+pub(crate) use imp::{AtomicU64, StaticAtomicU64};
diff --git a/vendor/tokio/src/loom/std/atomic_u64_as_mutex.rs b/vendor/tokio/src/loom/std/atomic_u64_as_mutex.rs
new file mode 100644
index 000000000..9b3b6fac6
--- /dev/null
+++ b/vendor/tokio/src/loom/std/atomic_u64_as_mutex.rs
@@ -0,0 +1,76 @@
+use crate::loom::sync::Mutex;
+use std::sync::atomic::Ordering;
+
+cfg_has_const_mutex_new! {
+    #[path = "atomic_u64_static_const_new.rs"]
+    mod static_macro;
+}
+
+cfg_not_has_const_mutex_new! {
+    #[path = "atomic_u64_static_once_cell.rs"]
+    mod static_macro;
+}
+
+pub(crate) use static_macro::StaticAtomicU64;
+
+#[derive(Debug)]
+pub(crate) struct AtomicU64 {
+    inner: Mutex<u64>,
+}
+
+impl AtomicU64 {
+    pub(crate) fn load(&self, _: Ordering) -> u64 {
+        *self.inner.lock()
+    }
+
+    pub(crate) fn store(&self, val: u64, _: Ordering) {
+        *self.inner.lock() = val;
+    }
+
+    pub(crate) fn fetch_add(&self, val: u64, _: Ordering) -> u64 {
+        let mut lock = self.inner.lock();
+        let prev = *lock;
+        *lock = prev + val;
+        prev
+    }
+
+    pub(crate) fn fetch_or(&self, val: u64, _: Ordering) -> u64 {
+        let mut lock = self.inner.lock();
+        let prev = *lock;
+        *lock = prev | val;
+        prev
+    }
+
+    pub(crate) fn compare_exchange(
+        &self,
+        current: u64,
+        new: u64,
+        _success: Ordering,
+        _failure: Ordering,
+    ) -> Result<u64, u64> {
+        let mut lock = self.inner.lock();
+
+        if *lock == current {
+            *lock = new;
+            Ok(current)
+        } else {
+            Err(*lock)
+        }
+    }
+
+    pub(crate) fn compare_exchange_weak(
+        &self,
+        current: u64,
+        new: u64,
+        success: Ordering,
+        failure: Ordering,
+    ) -> Result<u64, u64> {
+        self.compare_exchange(current, new, success, failure)
+    }
+}
+
+impl Default for AtomicU64 {
+    fn default() -> AtomicU64 {
+        AtomicU64::new(u64::default())
+    }
+}
diff --git a/vendor/tokio/src/loom/std/atomic_u64_native.rs b/vendor/tokio/src/loom/std/atomic_u64_native.rs
new file mode 100644
index 000000000..08adb2862
--- /dev/null
+++ b/vendor/tokio/src/loom/std/atomic_u64_native.rs
@@ -0,0 +1,4 @@
+pub(crate) use std::sync::atomic::{AtomicU64, Ordering};
+
+/// Alias `AtomicU64` to `StaticAtomicU64`
+pub(crate) type StaticAtomicU64 = AtomicU64;
diff --git a/vendor/tokio/src/loom/std/atomic_u64_static_const_new.rs b/vendor/tokio/src/loom/std/atomic_u64_static_const_new.rs
new file mode 100644
index 000000000..a4215342b
--- /dev/null
+++ b/vendor/tokio/src/loom/std/atomic_u64_static_const_new.rs
@@ -0,0 +1,12 @@
+use super::AtomicU64;
+use crate::loom::sync::Mutex;
+
+pub(crate) type StaticAtomicU64 = AtomicU64;
+
+impl AtomicU64 {
+    pub(crate) const fn new(val: u64) -> Self {
+        Self {
+            inner: Mutex::const_new(val),
+        }
+    }
+}
diff --git a/vendor/tokio/src/loom/std/atomic_u64_static_once_cell.rs b/vendor/tokio/src/loom/std/atomic_u64_static_once_cell.rs
new file mode 100644
index 000000000..40c6172a5
--- /dev/null
+++ b/vendor/tokio/src/loom/std/atomic_u64_static_once_cell.rs
@@ -0,0 +1,57 @@
+use super::AtomicU64;
+use crate::loom::sync::{atomic::Ordering, Mutex};
+use crate::util::once_cell::OnceCell;
+
+pub(crate) struct StaticAtomicU64 {
+    init: u64,
+    cell: OnceCell<Mutex<u64>>,
+}
+
+impl AtomicU64 {
+    pub(crate) fn new(val: u64) -> Self {
+        Self {
+            inner: Mutex::new(val),
+        }
+    }
+}
+
+impl StaticAtomicU64 {
+    pub(crate) const fn new(val: u64) -> StaticAtomicU64 {
+        StaticAtomicU64 {
+            init: val,
+            cell: OnceCell::new(),
+        }
+    }
+
+    pub(crate) fn load(&self, order: Ordering) -> u64 {
+        *self.inner().lock()
+    }
+
+    pub(crate) fn fetch_add(&self, val: u64, order: Ordering) -> u64 {
+        let mut lock = self.inner().lock();
+        let prev = *lock;
+        *lock = prev + val;
+        prev
+    }
+
+    pub(crate) fn compare_exchange_weak(
+        &self,
+        current: u64,
+        new: u64,
+        _success: Ordering,
+        _failure: Ordering,
+    ) -> Result<u64, u64> {
+        let mut lock = self.inner().lock();
+
+        if *lock == current {
+            *lock = new;
+            Ok(current)
+        } else {
+            Err(*lock)
+        }
+    }
+
+    fn inner(&self) -> &Mutex<u64> {
+        self.cell.get(|| Mutex::new(self.init))
+    }
+}
diff --git a/vendor/tokio/src/loom/std/atomic_u8.rs b/vendor/tokio/src/loom/std/atomic_u8.rs
deleted file mode 100644
index 408aea338..000000000
--- a/vendor/tokio/src/loom/std/atomic_u8.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-use std::cell::UnsafeCell;
-use std::fmt;
-use std::ops::Deref;
-
-/// `AtomicU8` providing an additional `load_unsync` function.
-pub(crate) struct AtomicU8 {
-    inner: UnsafeCell<std::sync::atomic::AtomicU8>,
-}
-
-unsafe impl Send for AtomicU8 {}
-unsafe impl Sync for AtomicU8 {}
-
-impl AtomicU8 {
-    pub(crate) const fn new(val: u8) -> AtomicU8 {
-        let inner = UnsafeCell::new(std::sync::atomic::AtomicU8::new(val));
-        AtomicU8 { inner }
-    }
-}
-
-impl Deref for AtomicU8 {
-    type Target = std::sync::atomic::AtomicU8;
-
-    fn deref(&self) -> &Self::Target {
-        // safety: it is always safe to access `&self` fns on the inner value as
-        // we never perform unsafe mutations.
-        unsafe { &*self.inner.get() }
-    }
-}
-
-impl fmt::Debug for AtomicU8 {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.deref().fmt(fmt)
-    }
-}
diff --git a/vendor/tokio/src/loom/std/atomic_usize.rs b/vendor/tokio/src/loom/std/atomic_usize.rs
index 0d5f36e43..c5503a2c1 100644
--- a/vendor/tokio/src/loom/std/atomic_usize.rs
+++ b/vendor/tokio/src/loom/std/atomic_usize.rs
@@ -2,7 +2,7 @@ use std::cell::UnsafeCell;
 use std::fmt;
 use std::ops;
 
-/// `AtomicUsize` providing an additional `load_unsync` function.
+/// `AtomicUsize` providing an additional `unsync_load` function.
 pub(crate) struct AtomicUsize {
     inner: UnsafeCell<std::sync::atomic::AtomicUsize>,
 }
@@ -23,7 +23,7 @@ impl AtomicUsize {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> usize {
-        *(*self.inner.get()).get_mut()
+        core::ptr::read(self.inner.get() as *const usize)
     }
 
     pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {
diff --git a/vendor/tokio/src/loom/std/barrier.rs b/vendor/tokio/src/loom/std/barrier.rs
new file mode 100644
index 000000000..a3f0ca0ab
--- /dev/null
+++ b/vendor/tokio/src/loom/std/barrier.rs
@@ -0,0 +1,217 @@
+//! A `Barrier` that provides `wait_timeout`.
+//!
+//! This implementation mirrors that of the Rust standard library.
+
+use crate::loom::sync::{Condvar, Mutex};
+use std::fmt;
+use std::time::{Duration, Instant};
+
+/// A barrier enables multiple threads to synchronize the beginning
+/// of some computation.
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::{Arc, Barrier};
+/// use std::thread;
+///
+/// let mut handles = Vec::with_capacity(10);
+/// let barrier = Arc::new(Barrier::new(10));
+/// for _ in 0..10 {
+///     let c = Arc::clone(&barrier);
+///     // The same messages will be printed together.
+///     // You will NOT see any interleaving.
+///     handles.push(thread::spawn(move|| {
+///         println!("before wait");
+///         c.wait();
+///         println!("after wait");
+///     }));
+/// }
+/// // Wait for other threads to finish.
+/// for handle in handles {
+///     handle.join().unwrap();
+/// }
+/// ```
+pub(crate) struct Barrier {
+    lock: Mutex<BarrierState>,
+    cvar: Condvar,
+    num_threads: usize,
+}
+
+// The inner state of a double barrier
+struct BarrierState {
+    count: usize,
+    generation_id: usize,
+}
+
+/// A `BarrierWaitResult` is returned by [`Barrier::wait()`] when all threads
+/// in the [`Barrier`] have rendezvoused.
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::Barrier;
+///
+/// let barrier = Barrier::new(1);
+/// let barrier_wait_result = barrier.wait();
+/// ```
+pub(crate) struct BarrierWaitResult(bool);
+
+impl fmt::Debug for Barrier {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Barrier").finish_non_exhaustive()
+    }
+}
+
+impl Barrier {
+    /// Creates a new barrier that can block a given number of threads.
+    ///
+    /// A barrier will block `n`-1 threads which call [`wait()`] and then wake
+    /// up all threads at once when the `n`th thread calls [`wait()`].
+    ///
+    /// [`wait()`]: Barrier::wait
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Barrier;
+    ///
+    /// let barrier = Barrier::new(10);
+    /// ```
+    #[must_use]
+    pub(crate) fn new(n: usize) -> Barrier {
+        Barrier {
+            lock: Mutex::new(BarrierState {
+                count: 0,
+                generation_id: 0,
+            }),
+            cvar: Condvar::new(),
+            num_threads: n,
+        }
+    }
+
+    /// Blocks the current thread until all threads have rendezvoused here.
+    ///
+    /// Barriers are re-usable after all threads have rendezvoused once, and can
+    /// be used continuously.
+    ///
+    /// A single (arbitrary) thread will receive a [`BarrierWaitResult`] that
+    /// returns `true` from [`BarrierWaitResult::is_leader()`] when returning
+    /// from this function, and all other threads will receive a result that
+    /// will return `false` from [`BarrierWaitResult::is_leader()`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::{Arc, Barrier};
+    /// use std::thread;
+    ///
+    /// let mut handles = Vec::with_capacity(10);
+    /// let barrier = Arc::new(Barrier::new(10));
+    /// for _ in 0..10 {
+    ///     let c = Arc::clone(&barrier);
+    ///     // The same messages will be printed together.
+    ///     // You will NOT see any interleaving.
+    ///     handles.push(thread::spawn(move|| {
+    ///         println!("before wait");
+    ///         c.wait();
+    ///         println!("after wait");
+    ///     }));
+    /// }
+    /// // Wait for other threads to finish.
+    /// for handle in handles {
+    ///     handle.join().unwrap();
+    /// }
+    /// ```
+    pub(crate) fn wait(&self) -> BarrierWaitResult {
+        let mut lock = self.lock.lock();
+        let local_gen = lock.generation_id;
+        lock.count += 1;
+        if lock.count < self.num_threads {
+            // We need a while loop to guard against spurious wakeups.
+            // https://en.wikipedia.org/wiki/Spurious_wakeup
+            while local_gen == lock.generation_id {
+                lock = self.cvar.wait(lock).unwrap();
+            }
+            BarrierWaitResult(false)
+        } else {
+            lock.count = 0;
+            lock.generation_id = lock.generation_id.wrapping_add(1);
+            self.cvar.notify_all();
+            BarrierWaitResult(true)
+        }
+    }
+
+    /// Blocks the current thread until all threads have rendezvoused here for
+    /// at most `timeout` duration.
+    pub(crate) fn wait_timeout(&self, timeout: Duration) -> Option<BarrierWaitResult> {
+        // This implementation mirrors `wait`, but with each blocking operation
+        // replaced by a timeout-amenable alternative.
+
+        let deadline = Instant::now() + timeout;
+
+        // Acquire `self.lock` with at most `timeout` duration.
+        let mut lock = loop {
+            if let Some(guard) = self.lock.try_lock() {
+                break guard;
+            } else if Instant::now() > deadline {
+                return None;
+            } else {
+                std::thread::yield_now();
+            }
+        };
+
+        // Shrink the `timeout` to account for the time taken to acquire `lock`.
+        let timeout = deadline.saturating_duration_since(Instant::now());
+
+        let local_gen = lock.generation_id;
+        lock.count += 1;
+        if lock.count < self.num_threads {
+            // We need a while loop to guard against spurious wakeups.
+            // https://en.wikipedia.org/wiki/Spurious_wakeup
+            while local_gen == lock.generation_id {
+                let (guard, timeout_result) = self.cvar.wait_timeout(lock, timeout).unwrap();
+                lock = guard;
+                if timeout_result.timed_out() {
+                    return None;
+                }
+            }
+            Some(BarrierWaitResult(false))
+        } else {
+            lock.count = 0;
+            lock.generation_id = lock.generation_id.wrapping_add(1);
+            self.cvar.notify_all();
+            Some(BarrierWaitResult(true))
+        }
+    }
+}
+
+impl fmt::Debug for BarrierWaitResult {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BarrierWaitResult")
+            .field("is_leader", &self.is_leader())
+            .finish()
+    }
+}
+
+impl BarrierWaitResult {
+    /// Returns `true` if this thread is the "leader thread" for the call to
+    /// [`Barrier::wait()`].
+    ///
+    /// Only one thread will have `true` returned from their result, all other
+    /// threads will have `false` returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Barrier;
+    ///
+    /// let barrier = Barrier::new(1);
+    /// let barrier_wait_result = barrier.wait();
+    /// println!("{:?}", barrier_wait_result.is_leader());
+    /// ```
+    #[must_use]
+    pub(crate) fn is_leader(&self) -> bool {
+        self.0
+    }
+}
diff --git a/vendor/tokio/src/loom/std/mod.rs b/vendor/tokio/src/loom/std/mod.rs
index b29cbeeb8..0a732791f 100644
--- a/vendor/tokio/src/loom/std/mod.rs
+++ b/vendor/tokio/src/loom/std/mod.rs
@@ -1,11 +1,10 @@
 #![cfg_attr(any(not(feature = "full"), loom), allow(unused_imports, dead_code))]
 
-mod atomic_ptr;
 mod atomic_u16;
 mod atomic_u32;
 mod atomic_u64;
-mod atomic_u8;
 mod atomic_usize;
+mod barrier;
 mod mutex;
 #[cfg(feature = "parking_lot")]
 mod parking_lot;
@@ -25,6 +24,10 @@ pub(crate) mod future {
     pub(crate) use crate::sync::AtomicWaker;
 }
 
+pub(crate) mod hint {
+    pub(crate) use std::hint::spin_loop;
+}
+
 pub(crate) mod rand {
     use std::collections::hash_map::RandomState;
     use std::hash::{BuildHasher, Hash, Hasher};
@@ -67,24 +70,41 @@ pub(crate) mod sync {
     pub(crate) use crate::loom::std::mutex::Mutex;
 
     pub(crate) mod atomic {
-        pub(crate) use crate::loom::std::atomic_ptr::AtomicPtr;
         pub(crate) use crate::loom::std::atomic_u16::AtomicU16;
         pub(crate) use crate::loom::std::atomic_u32::AtomicU32;
-        pub(crate) use crate::loom::std::atomic_u64::AtomicU64;
-        pub(crate) use crate::loom::std::atomic_u8::AtomicU8;
+        pub(crate) use crate::loom::std::atomic_u64::{AtomicU64, StaticAtomicU64};
         pub(crate) use crate::loom::std::atomic_usize::AtomicUsize;
 
-        pub(crate) use std::sync::atomic::{fence, AtomicBool, Ordering};
-        // TODO: once we bump MSRV to 1.49+, use `hint::spin_loop` instead.
-        #[allow(deprecated)]
-        pub(crate) use std::sync::atomic::spin_loop_hint;
+        pub(crate) use std::sync::atomic::{fence, AtomicBool, AtomicPtr, AtomicU8, Ordering};
     }
+
+    pub(crate) use super::barrier::Barrier;
 }
 
 pub(crate) mod sys {
     #[cfg(feature = "rt-multi-thread")]
     pub(crate) fn num_cpus() -> usize {
-        usize::max(1, num_cpus::get())
+        const ENV_WORKER_THREADS: &str = "TOKIO_WORKER_THREADS";
+
+        match std::env::var(ENV_WORKER_THREADS) {
+            Ok(s) => {
+                let n = s.parse().unwrap_or_else(|e| {
+                    panic!(
+                        "\"{}\" must be usize, error: {}, value: {}",
+                        ENV_WORKER_THREADS, e, s
+                    )
+                });
+                assert!(n > 0, "\"{}\" cannot be set to 0", ENV_WORKER_THREADS);
+                n
+            }
+            Err(std::env::VarError::NotPresent) => usize::max(1, num_cpus::get()),
+            Err(std::env::VarError::NotUnicode(e)) => {
+                panic!(
+                    "\"{}\" must be valid unicode, error: {:?}",
+                    ENV_WORKER_THREADS, e
+                )
+            }
+        }
     }
 
     #[cfg(not(feature = "rt-multi-thread"))]
@@ -93,4 +113,15 @@ pub(crate) mod sys {
     }
 }
 
-pub(crate) use std::thread;
+pub(crate) mod thread {
+    #[inline]
+    pub(crate) fn yield_now() {
+        std::hint::spin_loop();
+    }
+
+    #[allow(unused_imports)]
+    pub(crate) use std::thread::{
+        current, panicking, park, park_timeout, sleep, spawn, AccessError, Builder, JoinHandle,
+        LocalKey, Result, Thread, ThreadId,
+    };
+}
diff --git a/vendor/tokio/src/loom/std/mutex.rs b/vendor/tokio/src/loom/std/mutex.rs
index bf14d6242..076f78611 100644
--- a/vendor/tokio/src/loom/std/mutex.rs
+++ b/vendor/tokio/src/loom/std/mutex.rs
@@ -1,7 +1,7 @@
 use std::sync::{self, MutexGuard, TryLockError};
 
 /// Adapter for `std::Mutex` that removes the poisoning aspects
-// from its api
+/// from its api.
 #[derive(Debug)]
 pub(crate) struct Mutex<T: ?Sized>(sync::Mutex<T>);
 
@@ -13,6 +13,12 @@ impl<T> Mutex<T> {
     }
 
     #[inline]
+    #[cfg(not(tokio_no_const_mutex_new))]
+    pub(crate) const fn const_new(t: T) -> Mutex<T> {
+        Mutex(sync::Mutex::new(t))
+    }
+
+    #[inline]
     pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
         match self.0.lock() {
             Ok(guard) => guard,
diff --git a/vendor/tokio/src/loom/std/parking_lot.rs b/vendor/tokio/src/loom/std/parking_lot.rs
index 8448bed53..e3af258d1 100644
--- a/vendor/tokio/src/loom/std/parking_lot.rs
+++ b/vendor/tokio/src/loom/std/parking_lot.rs
@@ -3,83 +3,143 @@
 //!
 //! This can be extended to additional types/methods as required.
 
+use std::fmt;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
 use std::sync::LockResult;
 use std::time::Duration;
 
+// All types in this file are marked with PhantomData to ensure that
+// parking_lot's send_guard feature does not leak through and affect when Tokio
+// types are Send.
+//
+// See <https://github.com/tokio-rs/tokio/pull/4359> for more info.
+
 // Types that do not need wrapping
-pub(crate) use parking_lot::{MutexGuard, RwLockReadGuard, RwLockWriteGuard, WaitTimeoutResult};
+pub(crate) use parking_lot::WaitTimeoutResult;
+
+#[derive(Debug)]
+pub(crate) struct Mutex<T: ?Sized>(PhantomData<std::sync::Mutex<T>>, parking_lot::Mutex<T>);
+
+#[derive(Debug)]
+pub(crate) struct RwLock<T>(PhantomData<std::sync::RwLock<T>>, parking_lot::RwLock<T>);
+
+#[derive(Debug)]
+pub(crate) struct Condvar(PhantomData<std::sync::Condvar>, parking_lot::Condvar);
 
-/// Adapter for `parking_lot::Mutex` to the `std::sync::Mutex` interface.
 #[derive(Debug)]
-pub(crate) struct Mutex<T: ?Sized>(parking_lot::Mutex<T>);
+pub(crate) struct MutexGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::MutexGuard<'a, T>>,
+    parking_lot::MutexGuard<'a, T>,
+);
 
 #[derive(Debug)]
-pub(crate) struct RwLock<T>(parking_lot::RwLock<T>);
+pub(crate) struct RwLockReadGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockReadGuard<'a, T>>,
+    parking_lot::RwLockReadGuard<'a, T>,
+);
 
-/// Adapter for `parking_lot::Condvar` to the `std::sync::Condvar` interface.
 #[derive(Debug)]
-pub(crate) struct Condvar(parking_lot::Condvar);
+pub(crate) struct RwLockWriteGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockWriteGuard<'a, T>>,
+    parking_lot::RwLockWriteGuard<'a, T>,
+);
 
 impl<T> Mutex<T> {
     #[inline]
     pub(crate) fn new(t: T) -> Mutex<T> {
-        Mutex(parking_lot::Mutex::new(t))
+        Mutex(PhantomData, parking_lot::Mutex::new(t))
     }
 
     #[inline]
-    #[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
     #[cfg_attr(docsrs, doc(cfg(all(feature = "parking_lot",))))]
     pub(crate) const fn const_new(t: T) -> Mutex<T> {
-        Mutex(parking_lot::const_mutex(t))
+        Mutex(PhantomData, parking_lot::const_mutex(t))
     }
 
     #[inline]
     pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
-        self.0.lock()
+        MutexGuard(PhantomData, self.1.lock())
     }
 
     #[inline]
     pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
-        self.0.try_lock()
+        self.1
+            .try_lock()
+            .map(|guard| MutexGuard(PhantomData, guard))
     }
 
     #[inline]
     pub(crate) fn get_mut(&mut self) -> &mut T {
-        self.0.get_mut()
+        self.1.get_mut()
     }
 
     // Note: Additional methods `is_poisoned` and `into_inner`, can be
     // provided here as needed.
 }
 
+impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
+    }
+}
+
 impl<T> RwLock<T> {
     pub(crate) fn new(t: T) -> RwLock<T> {
-        RwLock(parking_lot::RwLock::new(t))
+        RwLock(PhantomData, parking_lot::RwLock::new(t))
     }
 
     pub(crate) fn read(&self) -> LockResult<RwLockReadGuard<'_, T>> {
-        Ok(self.0.read())
+        Ok(RwLockReadGuard(PhantomData, self.1.read()))
     }
 
     pub(crate) fn write(&self) -> LockResult<RwLockWriteGuard<'_, T>> {
-        Ok(self.0.write())
+        Ok(RwLockWriteGuard(PhantomData, self.1.write()))
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockReadGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockWriteGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for RwLockWriteGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
     }
 }
 
 impl Condvar {
     #[inline]
     pub(crate) fn new() -> Condvar {
-        Condvar(parking_lot::Condvar::new())
+        Condvar(PhantomData, parking_lot::Condvar::new())
     }
 
     #[inline]
     pub(crate) fn notify_one(&self) {
-        self.0.notify_one();
+        self.1.notify_one();
     }
 
     #[inline]
     pub(crate) fn notify_all(&self) {
-        self.0.notify_all();
+        self.1.notify_all();
     }
 
     #[inline]
@@ -87,7 +147,7 @@ impl Condvar {
         &self,
         mut guard: MutexGuard<'a, T>,
     ) -> LockResult<MutexGuard<'a, T>> {
-        self.0.wait(&mut guard);
+        self.1.wait(&mut guard.1);
         Ok(guard)
     }
 
@@ -97,10 +157,28 @@ impl Condvar {
         mut guard: MutexGuard<'a, T>,
         timeout: Duration,
     ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
-        let wtr = self.0.wait_for(&mut guard, timeout);
+        let wtr = self.1.wait_for(&mut guard.1, timeout);
         Ok((guard, wtr))
     }
 
     // Note: Additional methods `wait_timeout_ms`, `wait_timeout_until`,
     // `wait_until` can be provided here as needed.
 }
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}