Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 1144 insertions, 0 deletions

diff --git a/third_party/rust/parking_lot/src/raw_rwlock.rs b/third_party/rust/parking_lot/src/raw_rwlock.rs
new file mode 100644
index 0000000000..19b61c8144
--- /dev/null
+++ b/third_party/rust/parking_lot/src/raw_rwlock.rs
@@ -0,0 +1,1144 @@
+// Copyright 2016 Amanieu d'Antras
+//
+// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
+// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
+// http://opensource.org/licenses/MIT>, at your option. This file may not be
+// copied, modified, or distributed except according to those terms.
+
+use crate::elision::{have_elision, AtomicElisionExt};
+use crate::raw_mutex::{TOKEN_HANDOFF, TOKEN_NORMAL};
+use crate::util;
+use core::{
+    cell::Cell,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+use instant::Instant;
+use lock_api::{RawRwLock as RawRwLock_, RawRwLockUpgrade};
+use parking_lot_core::{
+    self, deadlock, FilterOp, ParkResult, ParkToken, SpinWait, UnparkResult, UnparkToken,
+};
+use std::time::Duration;
+
+// This reader-writer lock implementation is based on Boost's upgrade_mutex:
+// https://github.com/boostorg/thread/blob/fc08c1fe2840baeeee143440fba31ef9e9a813c8/include/boost/thread/v2/shared_mutex.hpp#L432
+//
+// This implementation uses 2 wait queues, one at key [addr] and one at key
+// [addr + 1]. The primary queue is used for all new waiting threads, and the
+// secondary queue is used by the thread which has acquired WRITER_BIT but is
+// waiting for the remaining readers to exit the lock.
+//
+// This implementation is fair between readers and writers since it uses the
+// order in which threads first started queuing to alternate between read phases
+// and write phases. In particular is it not vulnerable to write starvation
+// since readers will block if there is a pending writer.
+
+// There is at least one thread in the main queue.
+const PARKED_BIT: usize = 0b0001;
+// There is a parked thread holding WRITER_BIT. WRITER_BIT must be set.
+const WRITER_PARKED_BIT: usize = 0b0010;
+// A reader is holding an upgradable lock. The reader count must be non-zero and
+// WRITER_BIT must not be set.
+const UPGRADABLE_BIT: usize = 0b0100;
+// If the reader count is zero: a writer is currently holding an exclusive lock.
+// Otherwise: a writer is waiting for the remaining readers to exit the lock.
+const WRITER_BIT: usize = 0b1000;
+// Mask of bits used to count readers.
+const READERS_MASK: usize = !0b1111;
+// Base unit for counting readers.
+const ONE_READER: usize = 0b10000;
+
+// Token indicating what type of lock a queued thread is trying to acquire
+const TOKEN_SHARED: ParkToken = ParkToken(ONE_READER);
+const TOKEN_EXCLUSIVE: ParkToken = ParkToken(WRITER_BIT);
+const TOKEN_UPGRADABLE: ParkToken = ParkToken(ONE_READER | UPGRADABLE_BIT);
+
+/// Raw reader-writer lock type backed by the parking lot.
+pub struct RawRwLock {
+    state: AtomicUsize,
+}
+
+unsafe impl lock_api::RawRwLock for RawRwLock {
+    const INIT: RawRwLock = RawRwLock {
+        state: AtomicUsize::new(0),
+    };
+
+    type GuardMarker = crate::GuardMarker;
+
+    #[inline]
+    fn lock_exclusive(&self) {
+        if self
+            .state
+            .compare_exchange_weak(0, WRITER_BIT, Ordering::Acquire, Ordering::Relaxed)
+            .is_err()
+        {
+            let result = self.lock_exclusive_slow(None);
+            debug_assert!(result);
+        }
+        self.deadlock_acquire();
+    }
+
+    #[inline]
+    fn try_lock_exclusive(&self) -> bool {
+        if self
+            .state
+            .compare_exchange(0, WRITER_BIT, Ordering::Acquire, Ordering::Relaxed)
+            .is_ok()
+        {
+            self.deadlock_acquire();
+            true
+        } else {
+            false
+        }
+    }
+
+    #[inline]
+    unsafe fn unlock_exclusive(&self) {
+        self.deadlock_release();
+        if self
+            .state
+            .compare_exchange(WRITER_BIT, 0, Ordering::Release, Ordering::Relaxed)
+            .is_ok()
+        {
+            return;
+        }
+        self.unlock_exclusive_slow(false);
+    }
+
+    #[inline]
+    fn lock_shared(&self) {
+        if !self.try_lock_shared_fast(false) {
+            let result = self.lock_shared_slow(false, None);
+            debug_assert!(result);
+        }
+        self.deadlock_acquire();
+    }
+
+    #[inline]
+    fn try_lock_shared(&self) -> bool {
+        let result = if self.try_lock_shared_fast(false) {
+            true
+        } else {
+            self.try_lock_shared_slow(false)
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    unsafe fn unlock_shared(&self) {
+        self.deadlock_release();
+        let state = if have_elision() {
+            self.state.elision_fetch_sub_release(ONE_READER)
+        } else {
+            self.state.fetch_sub(ONE_READER, Ordering::Release)
+        };
+        if state & (READERS_MASK | WRITER_PARKED_BIT) == (ONE_READER | WRITER_PARKED_BIT) {
+            self.unlock_shared_slow();
+        }
+    }
+
+    #[inline]
+    fn is_locked(&self) -> bool {
+        let state = self.state.load(Ordering::Relaxed);
+        state & (WRITER_BIT | READERS_MASK) != 0
+    }
+}
+
+unsafe impl lock_api::RawRwLockFair for RawRwLock {
+    #[inline]
+    unsafe fn unlock_shared_fair(&self) {
+        // Shared unlocking is always fair in this implementation.
+        self.unlock_shared();
+    }
+
+    #[inline]
+    unsafe fn unlock_exclusive_fair(&self) {
+        self.deadlock_release();
+        if self
+            .state
+            .compare_exchange(WRITER_BIT, 0, Ordering::Release, Ordering::Relaxed)
+            .is_ok()
+        {
+            return;
+        }
+        self.unlock_exclusive_slow(true);
+    }
+
+    #[inline]
+    unsafe fn bump_shared(&self) {
+        if self.state.load(Ordering::Relaxed) & (READERS_MASK | WRITER_BIT)
+            == ONE_READER | WRITER_BIT
+        {
+            self.bump_shared_slow();
+        }
+    }
+
+    #[inline]
+    unsafe fn bump_exclusive(&self) {
+        if self.state.load(Ordering::Relaxed) & PARKED_BIT != 0 {
+            self.bump_exclusive_slow();
+        }
+    }
+}
+
+unsafe impl lock_api::RawRwLockDowngrade for RawRwLock {
+    #[inline]
+    unsafe fn downgrade(&self) {
+        let state = self
+            .state
+            .fetch_add(ONE_READER - WRITER_BIT, Ordering::Release);
+
+        // Wake up parked shared and upgradable threads if there are any
+        if state & PARKED_BIT != 0 {
+            self.downgrade_slow();
+        }
+    }
+}
+
+unsafe impl lock_api::RawRwLockTimed for RawRwLock {
+    type Duration = Duration;
+    type Instant = Instant;
+
+    #[inline]
+    fn try_lock_shared_for(&self, timeout: Self::Duration) -> bool {
+        let result = if self.try_lock_shared_fast(false) {
+            true
+        } else {
+            self.lock_shared_slow(false, util::to_deadline(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    fn try_lock_shared_until(&self, timeout: Self::Instant) -> bool {
+        let result = if self.try_lock_shared_fast(false) {
+            true
+        } else {
+            self.lock_shared_slow(false, Some(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    fn try_lock_exclusive_for(&self, timeout: Duration) -> bool {
+        let result = if self
+            .state
+            .compare_exchange_weak(0, WRITER_BIT, Ordering::Acquire, Ordering::Relaxed)
+            .is_ok()
+        {
+            true
+        } else {
+            self.lock_exclusive_slow(util::to_deadline(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    fn try_lock_exclusive_until(&self, timeout: Instant) -> bool {
+        let result = if self
+            .state
+            .compare_exchange_weak(0, WRITER_BIT, Ordering::Acquire, Ordering::Relaxed)
+            .is_ok()
+        {
+            true
+        } else {
+            self.lock_exclusive_slow(Some(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+}
+
+unsafe impl lock_api::RawRwLockRecursive for RawRwLock {
+    #[inline]
+    fn lock_shared_recursive(&self) {
+        if !self.try_lock_shared_fast(true) {
+            let result = self.lock_shared_slow(true, None);
+            debug_assert!(result);
+        }
+        self.deadlock_acquire();
+    }
+
+    #[inline]
+    fn try_lock_shared_recursive(&self) -> bool {
+        let result = if self.try_lock_shared_fast(true) {
+            true
+        } else {
+            self.try_lock_shared_slow(true)
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+}
+
+unsafe impl lock_api::RawRwLockRecursiveTimed for RawRwLock {
+    #[inline]
+    fn try_lock_shared_recursive_for(&self, timeout: Self::Duration) -> bool {
+        let result = if self.try_lock_shared_fast(true) {
+            true
+        } else {
+            self.lock_shared_slow(true, util::to_deadline(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    fn try_lock_shared_recursive_until(&self, timeout: Self::Instant) -> bool {
+        let result = if self.try_lock_shared_fast(true) {
+            true
+        } else {
+            self.lock_shared_slow(true, Some(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+}
+
+unsafe impl lock_api::RawRwLockUpgrade for RawRwLock {
+    #[inline]
+    fn lock_upgradable(&self) {
+        if !self.try_lock_upgradable_fast() {
+            let result = self.lock_upgradable_slow(None);
+            debug_assert!(result);
+        }
+        self.deadlock_acquire();
+    }
+
+    #[inline]
+    fn try_lock_upgradable(&self) -> bool {
+        let result = if self.try_lock_upgradable_fast() {
+            true
+        } else {
+            self.try_lock_upgradable_slow()
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    unsafe fn unlock_upgradable(&self) {
+        self.deadlock_release();
+        let state = self.state.load(Ordering::Relaxed);
+        if state & PARKED_BIT == 0 {
+            if self
+                .state
+                .compare_exchange_weak(
+                    state,
+                    state - (ONE_READER | UPGRADABLE_BIT),
+                    Ordering::Release,
+                    Ordering::Relaxed,
+                )
+                .is_ok()
+            {
+                return;
+            }
+        }
+        self.unlock_upgradable_slow(false);
+    }
+
+    #[inline]
+    unsafe fn upgrade(&self) {
+        let state = self.state.fetch_sub(
+            (ONE_READER | UPGRADABLE_BIT) - WRITER_BIT,
+            Ordering::Acquire,
+        );
+        if state & READERS_MASK != ONE_READER {
+            let result = self.upgrade_slow(None);
+            debug_assert!(result);
+        }
+    }
+
+    #[inline]
+    unsafe fn try_upgrade(&self) -> bool {
+        if self
+            .state
+            .compare_exchange_weak(
+                ONE_READER | UPGRADABLE_BIT,
+                WRITER_BIT,
+                Ordering::Acquire,
+                Ordering::Relaxed,
+            )
+            .is_ok()
+        {
+            true
+        } else {
+            self.try_upgrade_slow()
+        }
+    }
+}
+
+unsafe impl lock_api::RawRwLockUpgradeFair for RawRwLock {
+    #[inline]
+    unsafe fn unlock_upgradable_fair(&self) {
+        self.deadlock_release();
+        let state = self.state.load(Ordering::Relaxed);
+        if state & PARKED_BIT == 0 {
+            if self
+                .state
+                .compare_exchange_weak(
+                    state,
+                    state - (ONE_READER | UPGRADABLE_BIT),
+                    Ordering::Release,
+                    Ordering::Relaxed,
+                )
+                .is_ok()
+            {
+                return;
+            }
+        }
+        self.unlock_upgradable_slow(false);
+    }
+
+    #[inline]
+    unsafe fn bump_upgradable(&self) {
+        if self.state.load(Ordering::Relaxed) == ONE_READER | UPGRADABLE_BIT | PARKED_BIT {
+            self.bump_upgradable_slow();
+        }
+    }
+}
+
+unsafe impl lock_api::RawRwLockUpgradeDowngrade for RawRwLock {
+    #[inline]
+    unsafe fn downgrade_upgradable(&self) {
+        let state = self.state.fetch_sub(UPGRADABLE_BIT, Ordering::Relaxed);
+
+        // Wake up parked upgradable threads if there are any
+        if state & PARKED_BIT != 0 {
+            self.downgrade_slow();
+        }
+    }
+
+    #[inline]
+    unsafe fn downgrade_to_upgradable(&self) {
+        let state = self.state.fetch_add(
+            (ONE_READER | UPGRADABLE_BIT) - WRITER_BIT,
+            Ordering::Release,
+        );
+
+        // Wake up parked shared threads if there are any
+        if state & PARKED_BIT != 0 {
+            self.downgrade_to_upgradable_slow();
+        }
+    }
+}
+
+unsafe impl lock_api::RawRwLockUpgradeTimed for RawRwLock {
+    #[inline]
+    fn try_lock_upgradable_until(&self, timeout: Instant) -> bool {
+        let result = if self.try_lock_upgradable_fast() {
+            true
+        } else {
+            self.lock_upgradable_slow(Some(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    fn try_lock_upgradable_for(&self, timeout: Duration) -> bool {
+        let result = if self.try_lock_upgradable_fast() {
+            true
+        } else {
+            self.lock_upgradable_slow(util::to_deadline(timeout))
+        };
+        if result {
+            self.deadlock_acquire();
+        }
+        result
+    }
+
+    #[inline]
+    unsafe fn try_upgrade_until(&self, timeout: Instant) -> bool {
+        let state = self.state.fetch_sub(
+            (ONE_READER | UPGRADABLE_BIT) - WRITER_BIT,
+            Ordering::Relaxed,
+        );
+        if state & READERS_MASK == ONE_READER {
+            true
+        } else {
+            self.upgrade_slow(Some(timeout))
+        }
+    }
+
+    #[inline]
+    unsafe fn try_upgrade_for(&self, timeout: Duration) -> bool {
+        let state = self.state.fetch_sub(
+            (ONE_READER | UPGRADABLE_BIT) - WRITER_BIT,
+            Ordering::Relaxed,
+        );
+        if state & READERS_MASK == ONE_READER {
+            true
+        } else {
+            self.upgrade_slow(util::to_deadline(timeout))
+        }
+    }
+}
+
+impl RawRwLock {
+    #[inline(always)]
+    fn try_lock_shared_fast(&self, recursive: bool) -> bool {
+        let state = self.state.load(Ordering::Relaxed);
+
+        // We can't allow grabbing a shared lock if there is a writer, even if
+        // the writer is still waiting for the remaining readers to exit.
+        if state & WRITER_BIT != 0 {
+            // To allow recursive locks, we make an exception and allow readers
+            // to skip ahead of a pending writer to avoid deadlocking, at the
+            // cost of breaking the fairness guarantees.
+            if !recursive || state & READERS_MASK == 0 {
+                return false;
+            }
+        }
+
+        // Use hardware lock elision to avoid cache conflicts when multiple
+        // readers try to acquire the lock. We only do this if the lock is
+        // completely empty since elision handles conflicts poorly.
+        if have_elision() && state == 0 {
+            self.state
+                .elision_compare_exchange_acquire(0, ONE_READER)
+                .is_ok()
+        } else if let Some(new_state) = state.checked_add(ONE_READER) {
+            self.state
+                .compare_exchange_weak(state, new_state, Ordering::Acquire, Ordering::Relaxed)
+                .is_ok()
+        } else {
+            false
+        }
+    }
+
+    #[cold]
+    fn try_lock_shared_slow(&self, recursive: bool) -> bool {
+        let mut state = self.state.load(Ordering::Relaxed);
+        loop {
+            // This mirrors the condition in try_lock_shared_fast
+            if state & WRITER_BIT != 0 {
+                if !recursive || state & READERS_MASK == 0 {
+                    return false;
+                }
+            }
+            if have_elision() && state == 0 {
+                match self.state.elision_compare_exchange_acquire(0, ONE_READER) {
+                    Ok(_) => return true,
+                    Err(x) => state = x,
+                }
+            } else {
+                match self.state.compare_exchange_weak(
+                    state,
+                    state
+                        .checked_add(ONE_READER)
+                        .expect("RwLock reader count overflow"),
+                    Ordering::Acquire,
+                    Ordering::Relaxed,
+                ) {
+                    Ok(_) => return true,
+                    Err(x) => state = x,
+                }
+            }
+        }
+    }
+
+    #[inline(always)]
+    fn try_lock_upgradable_fast(&self) -> bool {
+        let state = self.state.load(Ordering::Relaxed);
+
+        // We can't grab an upgradable lock if there is already a writer or
+        // upgradable reader.
+        if state & (WRITER_BIT | UPGRADABLE_BIT) != 0 {
+            return false;
+        }
+
+        if let Some(new_state) = state.checked_add(ONE_READER | UPGRADABLE_BIT) {
+            self.state
+                .compare_exchange_weak(state, new_state, Ordering::Acquire, Ordering::Relaxed)
+                .is_ok()
+        } else {
+            false
+        }
+    }
+
+    #[cold]
+    fn try_lock_upgradable_slow(&self) -> bool {
+        let mut state = self.state.load(Ordering::Relaxed);
+        loop {
+            // This mirrors the condition in try_lock_upgradable_fast
+            if state & (WRITER_BIT | UPGRADABLE_BIT) != 0 {
+                return false;
+            }
+
+            match self.state.compare_exchange_weak(
+                state,
+                state
+                    .checked_add(ONE_READER | UPGRADABLE_BIT)
+                    .expect("RwLock reader count overflow"),
+                Ordering::Acquire,
+                Ordering::Relaxed,
+            ) {
+                Ok(_) => return true,
+                Err(x) => state = x,
+            }
+        }
+    }
+
+    #[cold]
+    fn lock_exclusive_slow(&self, timeout: Option<Instant>) -> bool {
+        let try_lock = |state: &mut usize| {
+            loop {
+                if *state & (WRITER_BIT | UPGRADABLE_BIT) != 0 {
+                    return false;
+                }
+
+                // Grab WRITER_BIT if it isn't set, even if there are parked threads.
+                match self.state.compare_exchange_weak(
+                    *state,
+                    *state | WRITER_BIT,
+                    Ordering::Acquire,
+                    Ordering::Relaxed,
+                ) {
+                    Ok(_) => return true,
+                    Err(x) => *state = x,
+                }
+            }
+        };
+
+        // Step 1: grab exclusive ownership of WRITER_BIT
+        let timed_out = !self.lock_common(
+            timeout,
+            TOKEN_EXCLUSIVE,
+            try_lock,
+            WRITER_BIT | UPGRADABLE_BIT,
+        );
+        if timed_out {
+            return false;
+        }
+
+        // Step 2: wait for all remaining readers to exit the lock.
+        self.wait_for_readers(timeout, 0)
+    }
+
+    #[cold]
+    fn unlock_exclusive_slow(&self, force_fair: bool) {
+        // There are threads to unpark. Try to unpark as many as we can.
+        let callback = |mut new_state, result: UnparkResult| {
+            // If we are using a fair unlock then we should keep the
+            // rwlock locked and hand it off to the unparked threads.
+            if result.unparked_threads != 0 && (force_fair || result.be_fair) {
+                if result.have_more_threads {
+                    new_state |= PARKED_BIT;
+                }
+                self.state.store(new_state, Ordering::Release);
+                TOKEN_HANDOFF
+            } else {
+                // Clear the parked bit if there are no more parked threads.
+                if result.have_more_threads {
+                    self.state.store(PARKED_BIT, Ordering::Release);
+                } else {
+                    self.state.store(0, Ordering::Release);
+                }
+                TOKEN_NORMAL
+            }
+        };
+        // SAFETY: `callback` does not panic or call into any function of `parking_lot`.
+        unsafe {
+            self.wake_parked_threads(0, callback);
+        }
+    }
+
+    #[cold]
+    fn lock_shared_slow(&self, recursive: bool, timeout: Option<Instant>) -> bool {
+        let try_lock = |state: &mut usize| {
+            let mut spinwait_shared = SpinWait::new();
+            loop {
+                // Use hardware lock elision to avoid cache conflicts when multiple
+                // readers try to acquire the lock. We only do this if the lock is
+                // completely empty since elision handles conflicts poorly.
+                if have_elision() && *state == 0 {
+                    match self.state.elision_compare_exchange_acquire(0, ONE_READER) {
+                        Ok(_) => return true,
+                        Err(x) => *state = x,
+                    }
+                }
+
+                // This is the same condition as try_lock_shared_fast
+                if *state & WRITER_BIT != 0 {
+                    if !recursive || *state & READERS_MASK == 0 {
+                        return false;
+                    }
+                }
+
+                if self
+                    .state
+                    .compare_exchange_weak(
+                        *state,
+                        state
+                            .checked_add(ONE_READER)
+                            .expect("RwLock reader count overflow"),
+                        Ordering::Acquire,
+                        Ordering::Relaxed,
+                    )
+                    .is_ok()
+                {
+                    return true;
+                }
+
+                // If there is high contention on the reader count then we want
+                // to leave some time between attempts to acquire the lock to
+                // let other threads make progress.
+                spinwait_shared.spin_no_yield();
+                *state = self.state.load(Ordering::Relaxed);
+            }
+        };
+        self.lock_common(timeout, TOKEN_SHARED, try_lock, WRITER_BIT)
+    }
+
+    #[cold]
+    fn unlock_shared_slow(&self) {
+        // At this point WRITER_PARKED_BIT is set and READER_MASK is empty. We
+        // just need to wake up a potentially sleeping pending writer.
+        // Using the 2nd key at addr + 1
+        let addr = self as *const _ as usize + 1;
+        let callback = |_result: UnparkResult| {
+            // Clear the WRITER_PARKED_BIT here since there can only be one
+            // parked writer thread.
+            self.state.fetch_and(!WRITER_PARKED_BIT, Ordering::Relaxed);
+            TOKEN_NORMAL
+        };
+        // SAFETY:
+        //   * `addr` is an address we control.
+        //   * `callback` does not panic or call into any function of `parking_lot`.
+        unsafe {
+            parking_lot_core::unpark_one(addr, callback);
+        }
+    }
+
+    #[cold]
+    fn lock_upgradable_slow(&self, timeout: Option<Instant>) -> bool {
+        let try_lock = |state: &mut usize| {
+            let mut spinwait_shared = SpinWait::new();
+            loop {
+                if *state & (WRITER_BIT | UPGRADABLE_BIT) != 0 {
+                    return false;
+                }
+
+                if self
+                    .state
+                    .compare_exchange_weak(
+                        *state,
+                        state
+                            .checked_add(ONE_READER | UPGRADABLE_BIT)
+                            .expect("RwLock reader count overflow"),
+                        Ordering::Acquire,
+                        Ordering::Relaxed,
+                    )
+                    .is_ok()
+                {
+                    return true;
+                }
+
+                // If there is high contention on the reader count then we want
+                // to leave some time between attempts to acquire the lock to
+                // let other threads make progress.
+                spinwait_shared.spin_no_yield();
+                *state = self.state.load(Ordering::Relaxed);
+            }
+        };
+        self.lock_common(
+            timeout,
+            TOKEN_UPGRADABLE,
+            try_lock,
+            WRITER_BIT | UPGRADABLE_BIT,
+        )
+    }
+
+    #[cold]
+    fn unlock_upgradable_slow(&self, force_fair: bool) {
+        // Just release the lock if there are no parked threads.
+        let mut state = self.state.load(Ordering::Relaxed);
+        while state & PARKED_BIT == 0 {
+            match self.state.compare_exchange_weak(
+                state,
+                state - (ONE_READER | UPGRADABLE_BIT),
+                Ordering::Release,
+                Ordering::Relaxed,
+            ) {
+                Ok(_) => return,
+                Err(x) => state = x,
+            }
+        }
+
+        // There are threads to unpark. Try to unpark as many as we can.
+        let callback = |new_state, result: UnparkResult| {
+            // If we are using a fair unlock then we should keep the
+            // rwlock locked and hand it off to the unparked threads.
+            let mut state = self.state.load(Ordering::Relaxed);
+            if force_fair || result.be_fair {
+                // Fall back to normal unpark on overflow. Panicking is
+                // not allowed in parking_lot callbacks.
+                while let Some(mut new_state) =
+                    (state - (ONE_READER | UPGRADABLE_BIT)).checked_add(new_state)
+                {
+                    if result.have_more_threads {
+                        new_state |= PARKED_BIT;
+                    } else {
+                        new_state &= !PARKED_BIT;
+                    }
+                    match self.state.compare_exchange_weak(
+                        state,
+                        new_state,
+                        Ordering::Relaxed,
+                        Ordering::Relaxed,
+                    ) {
+                        Ok(_) => return TOKEN_HANDOFF,
+                        Err(x) => state = x,
+                    }
+                }
+            }
+
+            // Otherwise just release the upgradable lock and update PARKED_BIT.
+            loop {
+                let mut new_state = state - (ONE_READER | UPGRADABLE_BIT);
+                if result.have_more_threads {
+                    new_state |= PARKED_BIT;
+                } else {
+                    new_state &= !PARKED_BIT;
+                }
+                match self.state.compare_exchange_weak(
+                    state,
+                    new_state,
+                    Ordering::Relaxed,
+                    Ordering::Relaxed,
+                ) {
+                    Ok(_) => return TOKEN_NORMAL,
+                    Err(x) => state = x,
+                }
+            }
+        };
+        // SAFETY: `callback` does not panic or call into any function of `parking_lot`.
+        unsafe {
+            self.wake_parked_threads(0, callback);
+        }
+    }
+
+    #[cold]
+    fn try_upgrade_slow(&self) -> bool {
+        let mut state = self.state.load(Ordering::Relaxed);
+        loop {
+            if state & READERS_MASK != ONE_READER {
+                return false;
+            }
+            match self.state.compare_exchange_weak(
+                state,
+                state - (ONE_READER | UPGRADABLE_BIT) + WRITER_BIT,
+                Ordering::Relaxed,
+                Ordering::Relaxed,
+            ) {
+                Ok(_) => return true,
+                Err(x) => state = x,
+            }
+        }
+    }
+
+    #[cold]
+    fn upgrade_slow(&self, timeout: Option<Instant>) -> bool {
+        self.wait_for_readers(timeout, ONE_READER | UPGRADABLE_BIT)
+    }
+
+    #[cold]
+    fn downgrade_slow(&self) {
+        // We only reach this point if PARKED_BIT is set.
+        let callback = |_, result: UnparkResult| {
+            // Clear the parked bit if there no more parked threads
+            if !result.have_more_threads {
+                self.state.fetch_and(!PARKED_BIT, Ordering::Relaxed);
+            }
+            TOKEN_NORMAL
+        };
+        // SAFETY: `callback` does not panic or call into any function of `parking_lot`.
+        unsafe {
+            self.wake_parked_threads(ONE_READER, callback);
+        }
+    }
+
+    #[cold]
+    fn downgrade_to_upgradable_slow(&self) {
+        // We only reach this point if PARKED_BIT is set.
+        let callback = |_, result: UnparkResult| {
+            // Clear the parked bit if there no more parked threads
+            if !result.have_more_threads {
+                self.state.fetch_and(!PARKED_BIT, Ordering::Relaxed);
+            }
+            TOKEN_NORMAL
+        };
+        // SAFETY: `callback` does not panic or call into any function of `parking_lot`.
+        unsafe {
+            self.wake_parked_threads(ONE_READER | UPGRADABLE_BIT, callback);
+        }
+    }
+
+    #[cold]
+    unsafe fn bump_shared_slow(&self) {
+        self.unlock_shared();
+        self.lock_shared();
+    }
+
+    #[cold]
+    fn bump_exclusive_slow(&self) {
+        self.deadlock_release();
+        self.unlock_exclusive_slow(true);
+        self.lock_exclusive();
+    }
+
+    #[cold]
+    fn bump_upgradable_slow(&self) {
+        self.deadlock_release();
+        self.unlock_upgradable_slow(true);
+        self.lock_upgradable();
+    }
+
+    /// Common code for waking up parked threads after releasing WRITER_BIT or
+    /// UPGRADABLE_BIT.
+    ///
+    /// # Safety
+    ///
+    /// `callback` must uphold the requirements of the `callback` parameter to
+    /// `parking_lot_core::unpark_filter`. Meaning no panics or calls into any function in
+    /// `parking_lot`.
+    #[inline]
+    unsafe fn wake_parked_threads(
+        &self,
+        new_state: usize,
+        callback: impl FnOnce(usize, UnparkResult) -> UnparkToken,
+    ) {
+        // We must wake up at least one upgrader or writer if there is one,
+        // otherwise they may end up parked indefinitely since unlock_shared
+        // does not call wake_parked_threads.
+        let new_state = Cell::new(new_state);
+        let addr = self as *const _ as usize;
+        let filter = |ParkToken(token)| {
+            let s = new_state.get();
+
+            // If we are waking up a writer, don't wake anything else.
+            if s & WRITER_BIT != 0 {
+                return FilterOp::Stop;
+            }
+
+            // Otherwise wake *all* readers and one upgrader/writer.
+            if token & (UPGRADABLE_BIT | WRITER_BIT) != 0 && s & UPGRADABLE_BIT != 0 {
+                // Skip writers and upgradable readers if we already have
+                // a writer/upgradable reader.
+                FilterOp::Skip
+            } else {
+                new_state.set(s + token);
+                FilterOp::Unpark
+            }
+        };
+        let callback = |result| callback(new_state.get(), result);
+        // SAFETY:
+        // * `addr` is an address we control.
+        // * `filter` does not panic or call into any function of `parking_lot`.
+        // * `callback` safety responsibility is on caller
+        parking_lot_core::unpark_filter(addr, filter, callback);
+    }
+
+    // Common code for waiting for readers to exit the lock after acquiring
+    // WRITER_BIT.
+    #[inline]
+    fn wait_for_readers(&self, timeout: Option<Instant>, prev_value: usize) -> bool {
+        // At this point WRITER_BIT is already set, we just need to wait for the
+        // remaining readers to exit the lock.
+        let mut spinwait = SpinWait::new();
+        let mut state = self.state.load(Ordering::Acquire);
+        while state & READERS_MASK != 0 {
+            // Spin a few times to wait for readers to exit
+            if spinwait.spin() {
+                state = self.state.load(Ordering::Acquire);
+                continue;
+            }
+
+            // Set the parked bit
+            if state & WRITER_PARKED_BIT == 0 {
+                if let Err(x) = self.state.compare_exchange_weak(
+                    state,
+                    state | WRITER_PARKED_BIT,
+                    Ordering::Relaxed,
+                    Ordering::Relaxed,
+                ) {
+                    state = x;
+                    continue;
+                }
+            }
+
+            // Park our thread until we are woken up by an unlock
+            // Using the 2nd key at addr + 1
+            let addr = self as *const _ as usize + 1;
+            let validate = || {
+                let state = self.state.load(Ordering::Relaxed);
+                state & READERS_MASK != 0 && state & WRITER_PARKED_BIT != 0
+            };
+            let before_sleep = || {};
+            let timed_out = |_, _| {};
+            // SAFETY:
+            //   * `addr` is an address we control.
+            //   * `validate`/`timed_out` does not panic or call into any function of `parking_lot`.
+            //   * `before_sleep` does not call `park`, nor does it panic.
+            let park_result = unsafe {
+                parking_lot_core::park(
+                    addr,
+                    validate,
+                    before_sleep,
+                    timed_out,
+                    TOKEN_EXCLUSIVE,
+                    timeout,
+                )
+            };
+            match park_result {
+                // We still need to re-check the state if we are unparked
+                // since a previous writer timing-out could have allowed
+                // another reader to sneak in before we parked.
+                ParkResult::Unparked(_) | ParkResult::Invalid => {
+                    state = self.state.load(Ordering::Acquire);
+                    continue;
+                }
+
+                // Timeout expired
+                ParkResult::TimedOut => {
+                    // We need to release WRITER_BIT and revert back to
+                    // our previous value. We also wake up any threads that
+                    // might be waiting on WRITER_BIT.
+                    let state = self.state.fetch_add(
+                        prev_value.wrapping_sub(WRITER_BIT | WRITER_PARKED_BIT),
+                        Ordering::Relaxed,
+                    );
+                    if state & PARKED_BIT != 0 {
+                        let callback = |_, result: UnparkResult| {
+                            // Clear the parked bit if there no more parked threads
+                            if !result.have_more_threads {
+                                self.state.fetch_and(!PARKED_BIT, Ordering::Relaxed);
+                            }
+                            TOKEN_NORMAL
+                        };
+                        // SAFETY: `callback` does not panic or call any function of `parking_lot`.
+                        unsafe {
+                            self.wake_parked_threads(ONE_READER | UPGRADABLE_BIT, callback);
+                        }
+                    }
+                    return false;
+                }
+            }
+        }
+        true
+    }
+
+    /// Common code for acquiring a lock
+    #[inline]
+    fn lock_common(
+        &self,
+        timeout: Option<Instant>,
+        token: ParkToken,
+        mut try_lock: impl FnMut(&mut usize) -> bool,
+        validate_flags: usize,
+    ) -> bool {
+        let mut spinwait = SpinWait::new();
+        let mut state = self.state.load(Ordering::Relaxed);
+        loop {
+            // Attempt to grab the lock
+            if try_lock(&mut state) {
+                return true;
+            }
+
+            // If there are no parked threads, try spinning a few times.
+            if state & (PARKED_BIT | WRITER_PARKED_BIT) == 0 && spinwait.spin() {
+                state = self.state.load(Ordering::Relaxed);
+                continue;
+            }
+
+            // Set the parked bit
+            if state & PARKED_BIT == 0 {
+                if let Err(x) = self.state.compare_exchange_weak(
+                    state,
+                    state | PARKED_BIT,
+                    Ordering::Relaxed,
+                    Ordering::Relaxed,
+                ) {
+                    state = x;
+                    continue;
+                }
+            }
+
+            // Park our thread until we are woken up by an unlock
+            let addr = self as *const _ as usize;
+            let validate = || {
+                let state = self.state.load(Ordering::Relaxed);
+                state & PARKED_BIT != 0 && (state & validate_flags != 0)
+            };
+            let before_sleep = || {};
+            let timed_out = |_, was_last_thread| {
+                // Clear the parked bit if we were the last parked thread
+                if was_last_thread {
+                    self.state.fetch_and(!PARKED_BIT, Ordering::Relaxed);
+                }
+            };
+
+            // SAFETY:
+            // * `addr` is an address we control.
+            // * `validate`/`timed_out` does not panic or call into any function of `parking_lot`.
+            // * `before_sleep` does not call `park`, nor does it panic.
+            let park_result = unsafe {
+                parking_lot_core::park(addr, validate, before_sleep, timed_out, token, timeout)
+            };
+            match park_result {
+                // The thread that unparked us passed the lock on to us
+                // directly without unlocking it.
+                ParkResult::Unparked(TOKEN_HANDOFF) => return true,
+
+                // We were unparked normally, try acquiring the lock again
+                ParkResult::Unparked(_) => (),
+
+                // The validation function failed, try locking again
+                ParkResult::Invalid => (),
+
+                // Timeout expired
+                ParkResult::TimedOut => return false,
+            }
+
+            // Loop back and try locking again
+            spinwait.reset();
+            state = self.state.load(Ordering::Relaxed);
+        }
+    }
+
+    #[inline]
+    fn deadlock_acquire(&self) {
+        unsafe { deadlock::acquire_resource(self as *const _ as usize) };
+        unsafe { deadlock::acquire_resource(self as *const _ as usize + 1) };
+    }
+
+    #[inline]
+    fn deadlock_release(&self) {
+        unsafe { deadlock::release_resource(self as *const _ as usize) };
+        unsafe { deadlock::release_resource(self as *const _ as usize + 1) };
+    }
+}