Import lock_api 0.3.4

And add metadata files using the following command:
get_rust_pkg.py --add3prf -v lock_api-0.3.4 -o lock_api

Test: none
Change-Id: Ia2733897fa8a889072cc873e59d8abf23d2d412f

13 files changed, 3436 insertions, 0 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
new file mode 100644
index 0000000..2ba8878
--- /dev/null
+++ b/.cargo_vcs_info.json
@@ -0,0 +1,5 @@
+{
+  "git": {
+    "sha1": "761a4d567fddde152d624c38464f4833f05c7f62"
+  }
+}
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..7cbb440
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,37 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "lock_api"
+version = "0.3.4"
+authors = ["Amanieu d'Antras <amanieu@gmail.com>"]
+description = "Wrappers to create fully-featured Mutex and RwLock types. Compatible with no_std."
+keywords = ["mutex", "rwlock", "lock", "no_std"]
+categories = ["concurrency", "no-std"]
+license = "Apache-2.0/MIT"
+repository = "https://github.com/Amanieu/parking_lot"
+[dependencies.owning_ref]
+version = "0.4"
+optional = true
+
+[dependencies.scopeguard]
+version = "1.0"
+default-features = false
+
+[dependencies.serde]
+version = "1.0.90"
+optional = true
+default-features = false
+
+[features]
+nightly = []
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..eac455f
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,22 @@
+[package]
+name = "lock_api"
+version = "0.3.4"
+authors = ["Amanieu d'Antras <amanieu@gmail.com>"]
+description = "Wrappers to create fully-featured Mutex and RwLock types. Compatible with no_std."
+license = "Apache-2.0/MIT"
+repository = "https://github.com/Amanieu/parking_lot"
+keywords = ["mutex", "rwlock", "lock", "no_std"]
+categories = ["concurrency", "no-std"]
+edition = "2018"
+
+[dependencies]
+scopeguard = { version = "1.0", default-features = false }
+owning_ref = { version = "0.4", optional = true }
+
+# Optional dependency for supporting serde.  Optional crates automatically
+# create a feature with the same name as the crate, so if you need serde
+# support, just pass "--features serde" when building this crate.
+serde = {version = "1.0.90", default-features = false, optional = true}
+
+[features]
+nightly = []
diff --git a/LICENSE b/LICENSE
new file mode 120000
index 0000000..6b579aa
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+LICENSE-APACHE
\ No newline at end of file
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..16fe87b
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,201 @@
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..40b8817
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,25 @@
+Copyright (c) 2016 The Rust Project Developers
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..b8690f7
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,19 @@
+name: "lock_api"
+description: "Wrappers to create fully-featured Mutex and RwLock types. Compatible with no_std."
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/lock_api"
+  }
+  url {
+    type: ARCHIVE
+    value: "https://static.crates.io/crates/lock_api/lock_api-0.3.4.crate"
+  }
+  version: "0.3.4"
+  license_type: NOTICE
+  last_upgrade_date {
+    year: 2020
+    month: 10
+    day: 14
+  }
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..46fc303
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1 @@
+include platform/prebuilts/rust:/OWNERS
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..6576546
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,109 @@
+// Copyright 2018 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.
+
+//! This library provides type-safe and fully-featured `Mutex` and `RwLock`
+//! types which wrap a simple raw mutex or rwlock type. This has several
+//! benefits: not only does it eliminate a large portion of the work in
+//! implementing custom lock types, it also allows users to write code which is
+//! generic with regards to different lock implementations.
+//!
+//! Basic usage of this crate is very straightforward:
+//!
+//! 1. Create a raw lock type. This should only contain the lock state, not any
+//!    data protected by the lock.
+//! 2. Implement the `RawMutex` trait for your custom lock type.
+//! 3. Export your mutex as a type alias for `lock_api::Mutex`, and
+//!    your mutex guard as a type alias for `lock_api::MutexGuard`.
+//!    See the [example](#example) below for details.
+//!
+//! This process is similar for RwLocks, except that two guards need to be
+//! exported instead of one. (Or 3 guards if your type supports upgradable read
+//! locks, see [extension traits](#extension-traits) below for details)
+//!
+//! # Example
+//!
+//! ```
+//! use lock_api::{RawMutex, Mutex, GuardSend};
+//! use std::sync::atomic::{AtomicBool, Ordering};
+//!
+//! // 1. Define our raw lock type
+//! pub struct RawSpinlock(AtomicBool);
+//!
+//! // 2. Implement RawMutex for this type
+//! unsafe impl RawMutex for RawSpinlock {
+//!     const INIT: RawSpinlock = RawSpinlock(AtomicBool::new(false));
+//!
+//!     // A spinlock guard can be sent to another thread and unlocked there
+//!     type GuardMarker = GuardSend;
+//!
+//!     fn lock(&self) {
+//!         // Note: This isn't the best way of implementing a spinlock, but it
+//!         // suffices for the sake of this example.
+//!         while !self.try_lock() {}
+//!     }
+//!
+//!     fn try_lock(&self) -> bool {
+//!         self.0
+//!             .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
+//!             .is_ok()
+//!     }
+//!
+//!     fn unlock(&self) {
+//!         self.0.store(false, Ordering::Release);
+//!     }
+//! }
+//!
+//! // 3. Export the wrappers. This are the types that your users will actually use.
+//! pub type Spinlock<T> = lock_api::Mutex<RawSpinlock, T>;
+//! pub type SpinlockGuard<'a, T> = lock_api::MutexGuard<'a, RawSpinlock, T>;
+//! ```
+//!
+//! # Extension traits
+//!
+//! In addition to basic locking & unlocking functionality, you have the option
+//! of exposing additional functionality in your lock types by implementing
+//! additional traits for it. Examples of extension features include:
+//!
+//! - Fair unlocking (`RawMutexFair`, `RawRwLockFair`)
+//! - Lock timeouts (`RawMutexTimed`, `RawRwLockTimed`)
+//! - Downgradable write locks (`RawRwLockDowngradable`)
+//! - Recursive read locks (`RawRwLockRecursive`)
+//! - Upgradable read locks (`RawRwLockUpgrade`)
+//!
+//! The `Mutex` and `RwLock` wrappers will automatically expose this additional
+//! functionality if the raw lock type implements these extension traits.
+//!
+//! # Cargo features
+//!
+//! This crate supports two cargo features:
+//!
+//! - `owning_ref`: Allows your lock types to be used with the `owning_ref` crate.
+//! - `nightly`: Enables nightly-only features. At the moment the only such
+//!   feature is `const fn` constructors for lock types.
+
+#![no_std]
+#![warn(missing_docs)]
+#![warn(rust_2018_idioms)]
+#![cfg_attr(feature = "nightly", feature(const_fn))]
+
+#[macro_use]
+extern crate scopeguard;
+
+/// Marker type which indicates that the Guard type for a lock is `Send`.
+pub struct GuardSend(());
+
+/// Marker type which indicates that the Guard type for a lock is not `Send`.
+pub struct GuardNoSend(*mut ());
+
+mod mutex;
+pub use crate::mutex::*;
+
+mod remutex;
+pub use crate::remutex::*;
+
+mod rwlock;
+pub use crate::rwlock::*;
diff --git a/src/mutex.rs b/src/mutex.rs
new file mode 100644
index 0000000..352ac31
--- /dev/null
+++ b/src/mutex.rs
@@ -0,0 +1,644 @@
+// Copyright 2018 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 core::cell::UnsafeCell;
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem;
+use core::ops::{Deref, DerefMut};
+
+#[cfg(feature = "owning_ref")]
+use owning_ref::StableAddress;
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+/// Basic operations for a mutex.
+///
+/// Types implementing this trait can be used by `Mutex` to form a safe and
+/// fully-functioning mutex type.
+///
+/// # Safety
+///
+/// Implementations of this trait must ensure that the mutex is actually
+/// exclusive: a lock can't be acquired while the mutex is already locked.
+pub unsafe trait RawMutex {
+    /// Initial value for an unlocked mutex.
+    // A “non-constant” const item is a legacy way to supply an initialized value to downstream
+    // static items. Can hopefully be replaced with `const fn new() -> Self` at some point.
+    #[allow(clippy::declare_interior_mutable_const)]
+    const INIT: Self;
+
+    /// Marker type which determines whether a lock guard should be `Send`. Use
+    /// one of the `GuardSend` or `GuardNoSend` helper types here.
+    type GuardMarker;
+
+    /// Acquires this mutex, blocking the current thread until it is able to do so.
+    fn lock(&self);
+
+    /// Attempts to acquire this mutex without blocking. Returns `true`
+    /// if the lock was successfully acquired and `false` otherwise.
+    fn try_lock(&self) -> bool;
+
+    /// Unlocks this mutex.
+    fn unlock(&self);
+}
+
+/// Additional methods for mutexes which support fair unlocking.
+///
+/// Fair unlocking means that a lock is handed directly over to the next waiting
+/// thread if there is one, without giving other threads the opportunity to
+/// "steal" the lock in the meantime. This is typically slower than unfair
+/// unlocking, but may be necessary in certain circumstances.
+pub unsafe trait RawMutexFair: RawMutex {
+    /// Unlocks this mutex using a fair unlock protocol.
+    fn unlock_fair(&self);
+
+    /// Temporarily yields the mutex to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `lock`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    fn bump(&self) {
+        self.unlock_fair();
+        self.lock();
+    }
+}
+
+/// Additional methods for mutexes which support locking with timeouts.
+///
+/// The `Duration` and `Instant` types are specified as associated types so that
+/// this trait is usable even in `no_std` environments.
+pub unsafe trait RawMutexTimed: RawMutex {
+    /// Duration type used for `try_lock_for`.
+    type Duration;
+
+    /// Instant type used for `try_lock_until`.
+    type Instant;
+
+    /// Attempts to acquire this lock until a timeout is reached.
+    fn try_lock_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to acquire this lock until a timeout is reached.
+    fn try_lock_until(&self, timeout: Self::Instant) -> bool;
+}
+
+/// A mutual exclusion primitive useful for protecting shared data
+///
+/// This mutex will block threads waiting for the lock to become available. The
+/// mutex can also be statically initialized or created via a `new`
+/// constructor. Each mutex has a type parameter which represents the data that
+/// it is protecting. The data can only be accessed through the RAII guards
+/// returned from `lock` and `try_lock`, which guarantees that the data is only
+/// ever accessed when the mutex is locked.
+pub struct Mutex<R, T: ?Sized> {
+    raw: R,
+    data: UnsafeCell<T>,
+}
+
+unsafe impl<R: RawMutex + Send, T: ?Sized + Send> Send for Mutex<R, T> {}
+unsafe impl<R: RawMutex + Sync, T: ?Sized + Send> Sync for Mutex<R, T> {}
+
+impl<R: RawMutex, T> Mutex<R, T> {
+    /// Creates a new mutex in an unlocked state ready for use.
+    #[cfg(feature = "nightly")]
+    #[inline]
+    pub const fn new(val: T) -> Mutex<R, T> {
+        Mutex {
+            raw: R::INIT,
+            data: UnsafeCell::new(val),
+        }
+    }
+
+    /// Creates a new mutex in an unlocked state ready for use.
+    #[cfg(not(feature = "nightly"))]
+    #[inline]
+    pub fn new(val: T) -> Mutex<R, T> {
+        Mutex {
+            raw: R::INIT,
+            data: UnsafeCell::new(val),
+        }
+    }
+
+    /// Consumes this mutex, returning the underlying data.
+    #[inline]
+    pub fn into_inner(self) -> T {
+        self.data.into_inner()
+    }
+}
+
+impl<R, T> Mutex<R, T> {
+    /// Creates a new mutex based on a pre-existing raw mutex.
+    ///
+    /// This allows creating a mutex in a constant context on stable Rust.
+    #[inline]
+    pub const fn const_new(raw_mutex: R, val: T) -> Mutex<R, T> {
+        Mutex {
+            raw: raw_mutex,
+            data: UnsafeCell::new(val),
+        }
+    }
+}
+
+impl<R: RawMutex, T: ?Sized> Mutex<R, T> {
+    /// # Safety
+    ///
+    /// The lock must be held when calling this method.
+    #[inline]
+    unsafe fn guard(&self) -> MutexGuard<'_, R, T> {
+        MutexGuard {
+            mutex: self,
+            marker: PhantomData,
+        }
+    }
+
+    /// Acquires a mutex, blocking the current thread until it is able to do so.
+    ///
+    /// This function will block the local thread until it is available to acquire
+    /// the mutex. Upon returning, the thread is the only thread with the mutex
+    /// held. An RAII guard is returned to allow scoped unlock of the lock. When
+    /// the guard goes out of scope, the mutex will be unlocked.
+    ///
+    /// Attempts to lock a mutex in the thread which already holds the lock will
+    /// result in a deadlock.
+    #[inline]
+    pub fn lock(&self) -> MutexGuard<'_, R, T> {
+        self.raw.lock();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.guard() }
+    }
+
+    /// Attempts to acquire this lock.
+    ///
+    /// If the lock could not be acquired at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
+    /// guard is dropped.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_lock(&self) -> Option<MutexGuard<'_, R, T>> {
+        if self.raw.try_lock() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
+    /// take place---the mutable borrow statically guarantees no locks exist.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data.get() }
+    }
+
+    /// Forcibly unlocks the mutex.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `MutexGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `MutexGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a mutex is unlocked when not locked.
+    #[inline]
+    pub unsafe fn force_unlock(&self) {
+        self.raw.unlock();
+    }
+
+    /// Returns the underlying raw mutex object.
+    ///
+    /// Note that you will most likely need to import the `RawMutex` trait from
+    /// `lock_api` to be able to call functions on the raw mutex.
+    ///
+    /// # Safety
+    ///
+    /// This method is unsafe because it allows unlocking a mutex while
+    /// still holding a reference to a `MutexGuard`.
+    #[inline]
+    pub unsafe fn raw(&self) -> &R {
+        &self.raw
+    }
+}
+
+impl<R: RawMutexFair, T: ?Sized> Mutex<R, T> {
+    /// Forcibly unlocks the mutex using a fair unlock procotol.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `MutexGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `MutexGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a mutex is unlocked when not locked.
+    #[inline]
+    pub unsafe fn force_unlock_fair(&self) {
+        self.raw.unlock_fair();
+    }
+}
+
+impl<R: RawMutexTimed, T: ?Sized> Mutex<R, T> {
+    /// Attempts to acquire this lock until a timeout is reached.
+    ///
+    /// If the lock could not be acquired before the timeout expired, then
+    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
+    /// be unlocked when the guard is dropped.
+    #[inline]
+    pub fn try_lock_for(&self, timeout: R::Duration) -> Option<MutexGuard<'_, R, T>> {
+        if self.raw.try_lock_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this lock until a timeout is reached.
+    ///
+    /// If the lock could not be acquired before the timeout expired, then
+    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
+    /// be unlocked when the guard is dropped.
+    #[inline]
+    pub fn try_lock_until(&self, timeout: R::Instant) -> Option<MutexGuard<'_, R, T>> {
+        if self.raw.try_lock_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawMutex, T: ?Sized + Default> Default for Mutex<R, T> {
+    #[inline]
+    fn default() -> Mutex<R, T> {
+        Mutex::new(Default::default())
+    }
+}
+
+impl<R: RawMutex, T> From<T> for Mutex<R, T> {
+    #[inline]
+    fn from(t: T) -> Mutex<R, T> {
+        Mutex::new(t)
+    }
+}
+
+impl<R: RawMutex, T: ?Sized + fmt::Debug> fmt::Debug for Mutex<R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.try_lock() {
+            Some(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
+            None => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+
+                f.debug_struct("Mutex")
+                    .field("data", &LockedPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+// Copied and modified from serde
+#[cfg(feature = "serde")]
+impl<R, T> Serialize for Mutex<R, T>
+where
+    R: RawMutex,
+    T: Serialize + ?Sized,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.lock().serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, R, T> Deserialize<'de> for Mutex<R, T>
+where
+    R: RawMutex,
+    T: Deserialize<'de> + ?Sized,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(Mutex::new)
+    }
+}
+
+/// An RAII implementation of a "scoped lock" of a mutex. When this structure is
+/// dropped (falls out of scope), the lock will be unlocked.
+///
+/// The data protected by the mutex can be accessed through this guard via its
+/// `Deref` and `DerefMut` implementations.
+#[must_use = "if unused the Mutex will immediately unlock"]
+pub struct MutexGuard<'a, R: RawMutex, T: ?Sized> {
+    mutex: &'a Mutex<R, T>,
+    marker: PhantomData<(&'a mut T, R::GuardMarker)>,
+}
+
+unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync for MutexGuard<'a, R, T> {}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
+    /// Returns a reference to the original `Mutex` object.
+    pub fn mutex(s: &Self) -> &'a Mutex<R, T> {
+        s.mutex
+    }
+
+    /// Makes a new `MappedMutexGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `MutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, R, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let raw = &s.mutex.raw;
+        let data = f(unsafe { &mut *s.mutex.data.get() });
+        mem::forget(s);
+        MappedMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make a new `MappedMutexGuard` for a component of the
+    /// locked data. The original guard is returned if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `MutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MutexGuard::try_map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let raw = &s.mutex.raw;
+        let data = match f(unsafe { &mut *s.mutex.data.get() }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+
+    /// Temporarily unlocks the mutex to execute the given function.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the mutex.
+    #[inline]
+    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.mutex.raw.unlock();
+        defer!(s.mutex.raw.lock());
+        f()
+    }
+}
+
+impl<'a, R: RawMutexFair + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
+    /// Unlocks the mutex using a fair unlock protocol.
+    ///
+    /// By default, mutexes are unfair and allow the current thread to re-lock
+    /// the mutex before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the mutex for a long time. This is the
+    /// default because it allows much higher throughput as it avoids forcing a
+    /// context switch on every mutex unlock. This can result in one thread
+    /// acquiring a mutex many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `MutexGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.mutex.raw.unlock_fair();
+        mem::forget(s);
+    }
+
+    /// Temporarily unlocks the mutex to execute the given function.
+    ///
+    /// The mutex is unlocked using a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the mutex.
+    #[inline]
+    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.mutex.raw.unlock_fair();
+        defer!(s.mutex.raw.lock());
+        f()
+    }
+
+    /// Temporarily yields the mutex to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `lock`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    #[inline]
+    pub fn bump(s: &mut Self) {
+        s.mutex.raw.bump();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Deref for MutexGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.mutex.data.get() }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> DerefMut for MutexGuard<'a, R, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.mutex.data.get() }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Drop for MutexGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.mutex.raw.unlock();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MutexGuard<'a, R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display for MutexGuard<'a, R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> StableAddress for MutexGuard<'a, R, T> {}
+
+/// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
+/// subfield of the protected data.
+///
+/// The main difference between `MappedMutexGuard` and `MutexGuard` is that the
+/// former doesn't support temporarily unlocking and re-locking, since that
+/// could introduce soundness issues if the locked object is modified by another
+/// thread.
+#[must_use = "if unused the Mutex will immediately unlock"]
+pub struct MappedMutexGuard<'a, R: RawMutex, T: ?Sized> {
+    raw: &'a R,
+    data: *mut T,
+    marker: PhantomData<&'a mut T>,
+}
+
+unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync
+    for MappedMutexGuard<'a, R, T>
+{
+}
+unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Send for MappedMutexGuard<'a, R, T> where
+    R::GuardMarker: Send
+{
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MappedMutexGuard<'a, R, T> {
+    /// Makes a new `MappedMutexGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `MappedMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedMutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, R, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let raw = s.raw;
+        let data = f(unsafe { &mut *s.data });
+        mem::forget(s);
+        MappedMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make a new `MappedMutexGuard` for a component of the
+    /// locked data. The original guard is returned if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `MappedMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedMutexGuard::try_map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let raw = s.raw;
+        let data = match f(unsafe { &mut *s.data }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+}
+
+impl<'a, R: RawMutexFair + 'a, T: ?Sized + 'a> MappedMutexGuard<'a, R, T> {
+    /// Unlocks the mutex using a fair unlock protocol.
+    ///
+    /// By default, mutexes are unfair and allow the current thread to re-lock
+    /// the mutex before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the mutex for a long time. This is the
+    /// default because it allows much higher throughput as it avoids forcing a
+    /// context switch on every mutex unlock. This can result in one thread
+    /// acquiring a mutex many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `MutexGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.raw.unlock_fair();
+        mem::forget(s);
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Deref for MappedMutexGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> DerefMut for MappedMutexGuard<'a, R, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Drop for MappedMutexGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.raw.unlock();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MappedMutexGuard<'a, R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawMutex + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for MappedMutexGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> StableAddress for MappedMutexGuard<'a, R, T> {}
diff --git a/src/remutex.rs b/src/remutex.rs
new file mode 100644
index 0000000..bdfcc40
--- /dev/null
+++ b/src/remutex.rs
@@ -0,0 +1,740 @@
+// Copyright 2018 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::{
+    mutex::{RawMutex, RawMutexFair, RawMutexTimed},
+    GuardNoSend,
+};
+use core::{
+    cell::{Cell, UnsafeCell},
+    fmt,
+    marker::PhantomData,
+    mem,
+    num::NonZeroUsize,
+    ops::Deref,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+
+#[cfg(feature = "owning_ref")]
+use owning_ref::StableAddress;
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+/// Helper trait which returns a non-zero thread ID.
+///
+/// The simplest way to implement this trait is to return the address of a
+/// thread-local variable.
+///
+/// # Safety
+///
+/// Implementations of this trait must ensure that no two active threads share
+/// the same thread ID. However the ID of a thread that has exited can be
+/// re-used since that thread is no longer active.
+pub unsafe trait GetThreadId {
+    /// Initial value.
+    // A “non-constant” const item is a legacy way to supply an initialized value to downstream
+    // static items. Can hopefully be replaced with `const fn new() -> Self` at some point.
+    #[allow(clippy::declare_interior_mutable_const)]
+    const INIT: Self;
+
+    /// Returns a non-zero thread ID which identifies the current thread of
+    /// execution.
+    fn nonzero_thread_id(&self) -> NonZeroUsize;
+}
+
+struct RawReentrantMutex<R, G> {
+    owner: AtomicUsize,
+    lock_count: Cell<usize>,
+    mutex: R,
+    get_thread_id: G,
+}
+
+impl<R: RawMutex, G: GetThreadId> RawReentrantMutex<R, G> {
+    #[inline]
+    fn lock_internal<F: FnOnce() -> bool>(&self, try_lock: F) -> bool {
+        let id = self.get_thread_id.nonzero_thread_id().get();
+        if self.owner.load(Ordering::Relaxed) == id {
+            self.lock_count.set(
+                self.lock_count
+                    .get()
+                    .checked_add(1)
+                    .expect("ReentrantMutex lock count overflow"),
+            );
+        } else {
+            if !try_lock() {
+                return false;
+            }
+            self.owner.store(id, Ordering::Relaxed);
+            debug_assert_eq!(self.lock_count.get(), 0);
+            self.lock_count.set(1);
+        }
+        true
+    }
+
+    #[inline]
+    fn lock(&self) {
+        self.lock_internal(|| {
+            self.mutex.lock();
+            true
+        });
+    }
+
+    #[inline]
+    fn try_lock(&self) -> bool {
+        self.lock_internal(|| self.mutex.try_lock())
+    }
+
+    #[inline]
+    fn unlock(&self) {
+        let lock_count = self.lock_count.get() - 1;
+        self.lock_count.set(lock_count);
+        if lock_count == 0 {
+            self.owner.store(0, Ordering::Relaxed);
+            self.mutex.unlock();
+        }
+    }
+}
+
+impl<R: RawMutexFair, G: GetThreadId> RawReentrantMutex<R, G> {
+    #[inline]
+    fn unlock_fair(&self) {
+        let lock_count = self.lock_count.get() - 1;
+        self.lock_count.set(lock_count);
+        if lock_count == 0 {
+            self.owner.store(0, Ordering::Relaxed);
+            self.mutex.unlock_fair();
+        }
+    }
+
+    #[inline]
+    fn bump(&self) {
+        if self.lock_count.get() == 1 {
+            let id = self.owner.load(Ordering::Relaxed);
+            self.owner.store(0, Ordering::Relaxed);
+            self.mutex.bump();
+            self.owner.store(id, Ordering::Relaxed);
+        }
+    }
+}
+
+impl<R: RawMutexTimed, G: GetThreadId> RawReentrantMutex<R, G> {
+    #[inline]
+    fn try_lock_until(&self, timeout: R::Instant) -> bool {
+        self.lock_internal(|| self.mutex.try_lock_until(timeout))
+    }
+
+    #[inline]
+    fn try_lock_for(&self, timeout: R::Duration) -> bool {
+        self.lock_internal(|| self.mutex.try_lock_for(timeout))
+    }
+}
+
+/// A mutex which can be recursively locked by a single thread.
+///
+/// This type is identical to `Mutex` except for the following points:
+///
+/// - Locking multiple times from the same thread will work correctly instead of
+///   deadlocking.
+/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
+///   Use a `RefCell` if you need this.
+///
+/// See [`Mutex`](struct.Mutex.html) for more details about the underlying mutex
+/// primitive.
+pub struct ReentrantMutex<R, G, T: ?Sized> {
+    raw: RawReentrantMutex<R, G>,
+    data: UnsafeCell<T>,
+}
+
+unsafe impl<R: RawMutex + Send, G: GetThreadId + Send, T: ?Sized + Send> Send
+    for ReentrantMutex<R, G, T>
+{
+}
+unsafe impl<R: RawMutex + Sync, G: GetThreadId + Sync, T: ?Sized + Send> Sync
+    for ReentrantMutex<R, G, T>
+{
+}
+
+impl<R: RawMutex, G: GetThreadId, T> ReentrantMutex<R, G, T> {
+    /// Creates a new reentrant mutex in an unlocked state ready for use.
+    #[cfg(feature = "nightly")]
+    #[inline]
+    pub const fn new(val: T) -> ReentrantMutex<R, G, T> {
+        ReentrantMutex {
+            data: UnsafeCell::new(val),
+            raw: RawReentrantMutex {
+                owner: AtomicUsize::new(0),
+                lock_count: Cell::new(0),
+                mutex: R::INIT,
+                get_thread_id: G::INIT,
+            },
+        }
+    }
+
+    /// Creates a new reentrant mutex in an unlocked state ready for use.
+    #[cfg(not(feature = "nightly"))]
+    #[inline]
+    pub fn new(val: T) -> ReentrantMutex<R, G, T> {
+        ReentrantMutex {
+            data: UnsafeCell::new(val),
+            raw: RawReentrantMutex {
+                owner: AtomicUsize::new(0),
+                lock_count: Cell::new(0),
+                mutex: R::INIT,
+                get_thread_id: G::INIT,
+            },
+        }
+    }
+
+    /// Consumes this mutex, returning the underlying data.
+    #[inline]
+    pub fn into_inner(self) -> T {
+        self.data.into_inner()
+    }
+}
+
+impl<R, G, T> ReentrantMutex<R, G, T> {
+    /// Creates a new reentrant mutex based on a pre-existing raw mutex and a
+    /// helper to get the thread ID.
+    ///
+    /// This allows creating a reentrant mutex in a constant context on stable
+    /// Rust.
+    #[inline]
+    pub const fn const_new(raw_mutex: R, get_thread_id: G, val: T) -> ReentrantMutex<R, G, T> {
+        ReentrantMutex {
+            data: UnsafeCell::new(val),
+            raw: RawReentrantMutex {
+                owner: AtomicUsize::new(0),
+                lock_count: Cell::new(0),
+                mutex: raw_mutex,
+                get_thread_id,
+            },
+        }
+    }
+}
+
+impl<R: RawMutex, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
+    /// # Safety
+    ///
+    /// The lock must be held when calling this method.
+    #[inline]
+    unsafe fn guard(&self) -> ReentrantMutexGuard<'_, R, G, T> {
+        ReentrantMutexGuard {
+            remutex: &self,
+            marker: PhantomData,
+        }
+    }
+
+    /// Acquires a reentrant mutex, blocking the current thread until it is able
+    /// to do so.
+    ///
+    /// If the mutex is held by another thread then this function will block the
+    /// local thread until it is available to acquire the mutex. If the mutex is
+    /// already held by the current thread then this function will increment the
+    /// lock reference count and return immediately. Upon returning,
+    /// the thread is the only thread with the mutex held. An RAII guard is
+    /// returned to allow scoped unlock of the lock. When the guard goes out of
+    /// scope, the mutex will be unlocked.
+    #[inline]
+    pub fn lock(&self) -> ReentrantMutexGuard<'_, R, G, T> {
+        self.raw.lock();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.guard() }
+    }
+
+    /// Attempts to acquire this lock.
+    ///
+    /// If the lock could not be acquired at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
+    /// guard is dropped.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_lock(&self) -> Option<ReentrantMutexGuard<'_, R, G, T>> {
+        if self.raw.try_lock() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `ReentrantMutex` mutably, no actual locking needs to
+    /// take place---the mutable borrow statically guarantees no locks exist.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data.get() }
+    }
+
+    /// Forcibly unlocks the mutex.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `ReentrantMutexGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `ReentrantMutexGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a mutex is unlocked when not locked.
+    #[inline]
+    pub unsafe fn force_unlock(&self) {
+        self.raw.unlock();
+    }
+
+    /// Returns the underlying raw mutex object.
+    ///
+    /// Note that you will most likely need to import the `RawMutex` trait from
+    /// `lock_api` to be able to call functions on the raw mutex.
+    ///
+    /// # Safety
+    ///
+    /// This method is unsafe because it allows unlocking a mutex while
+    /// still holding a reference to a `ReentrantMutexGuard`.
+    #[inline]
+    pub unsafe fn raw(&self) -> &R {
+        &self.raw.mutex
+    }
+}
+
+impl<R: RawMutexFair, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
+    /// Forcibly unlocks the mutex using a fair unlock protocol.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `ReentrantMutexGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `ReentrantMutexGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a mutex is unlocked when not locked.
+    #[inline]
+    pub unsafe fn force_unlock_fair(&self) {
+        self.raw.unlock_fair();
+    }
+}
+
+impl<R: RawMutexTimed, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
+    /// Attempts to acquire this lock until a timeout is reached.
+    ///
+    /// If the lock could not be acquired before the timeout expired, then
+    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
+    /// be unlocked when the guard is dropped.
+    #[inline]
+    pub fn try_lock_for(&self, timeout: R::Duration) -> Option<ReentrantMutexGuard<'_, R, G, T>> {
+        if self.raw.try_lock_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this lock until a timeout is reached.
+    ///
+    /// If the lock could not be acquired before the timeout expired, then
+    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
+    /// be unlocked when the guard is dropped.
+    #[inline]
+    pub fn try_lock_until(&self, timeout: R::Instant) -> Option<ReentrantMutexGuard<'_, R, G, T>> {
+        if self.raw.try_lock_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawMutex, G: GetThreadId, T: ?Sized + Default> Default for ReentrantMutex<R, G, T> {
+    #[inline]
+    fn default() -> ReentrantMutex<R, G, T> {
+        ReentrantMutex::new(Default::default())
+    }
+}
+
+impl<R: RawMutex, G: GetThreadId, T> From<T> for ReentrantMutex<R, G, T> {
+    #[inline]
+    fn from(t: T) -> ReentrantMutex<R, G, T> {
+        ReentrantMutex::new(t)
+    }
+}
+
+impl<R: RawMutex, G: GetThreadId, T: ?Sized + fmt::Debug> fmt::Debug for ReentrantMutex<R, G, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.try_lock() {
+            Some(guard) => f
+                .debug_struct("ReentrantMutex")
+                .field("data", &&*guard)
+                .finish(),
+            None => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+
+                f.debug_struct("ReentrantMutex")
+                    .field("data", &LockedPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+// Copied and modified from serde
+#[cfg(feature = "serde")]
+impl<R, G, T> Serialize for ReentrantMutex<R, G, T>
+where
+    R: RawMutex,
+    G: GetThreadId,
+    T: Serialize + ?Sized,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.lock().serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, R, G, T> Deserialize<'de> for ReentrantMutex<R, G, T>
+where
+    R: RawMutex,
+    G: GetThreadId,
+    T: Deserialize<'de> + ?Sized,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(ReentrantMutex::new)
+    }
+}
+
+/// An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure
+/// is dropped (falls out of scope), the lock will be unlocked.
+///
+/// The data protected by the mutex can be accessed through this guard via its
+/// `Deref` implementation.
+#[must_use = "if unused the ReentrantMutex will immediately unlock"]
+pub struct ReentrantMutexGuard<'a, R: RawMutex, G: GetThreadId, T: ?Sized> {
+    remutex: &'a ReentrantMutex<R, G, T>,
+    marker: PhantomData<(&'a T, GuardNoSend)>,
+}
+
+unsafe impl<'a, R: RawMutex + Sync + 'a, G: GetThreadId + Sync + 'a, T: ?Sized + Sync + 'a> Sync
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> ReentrantMutexGuard<'a, R, G, T> {
+    /// Returns a reference to the original `ReentrantMutex` object.
+    pub fn remutex(s: &Self) -> &'a ReentrantMutex<R, G, T> {
+        s.remutex
+    }
+
+    /// Makes a new `MappedReentrantMutexGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `ReentrantMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `ReentrantMutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedReentrantMutexGuard<'a, R, G, U>
+    where
+        F: FnOnce(&T) -> &U,
+    {
+        let raw = &s.remutex.raw;
+        let data = f(unsafe { &*s.remutex.data.get() });
+        mem::forget(s);
+        MappedReentrantMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedReentrantMutexGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `ReentrantMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `ReentrantMutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(
+        s: Self,
+        f: F,
+    ) -> Result<MappedReentrantMutexGuard<'a, R, G, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let raw = &s.remutex.raw;
+        let data = match f(unsafe { &mut *s.remutex.data.get() }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedReentrantMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+
+    /// Temporarily unlocks the mutex to execute the given function.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the mutex.
+    #[inline]
+    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.remutex.raw.unlock();
+        defer!(s.remutex.raw.lock());
+        f()
+    }
+}
+
+impl<'a, R: RawMutexFair + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
+    ReentrantMutexGuard<'a, R, G, T>
+{
+    /// Unlocks the mutex using a fair unlock protocol.
+    ///
+    /// By default, mutexes are unfair and allow the current thread to re-lock
+    /// the mutex before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the mutex for a long time. This is the
+    /// default because it allows much higher throughput as it avoids forcing a
+    /// context switch on every mutex unlock. This can result in one thread
+    /// acquiring a mutex many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `ReentrantMutexGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.remutex.raw.unlock_fair();
+        mem::forget(s);
+    }
+
+    /// Temporarily unlocks the mutex to execute the given function.
+    ///
+    /// The mutex is unlocked a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the mutex.
+    #[inline]
+    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.remutex.raw.unlock_fair();
+        defer!(s.remutex.raw.lock());
+        f()
+    }
+
+    /// Temporarily yields the mutex to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `lock`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    #[inline]
+    pub fn bump(s: &mut Self) {
+        s.remutex.raw.bump();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Deref
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.remutex.data.get() }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Drop
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+    #[inline]
+    fn drop(&mut self) {
+        self.remutex.raw.unlock();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> StableAddress
+    for ReentrantMutexGuard<'a, R, G, T>
+{
+}
+
+/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
+/// subfield of the protected data.
+///
+/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
+/// former doesn't support temporarily unlocking and re-locking, since that
+/// could introduce soundness issues if the locked object is modified by another
+/// thread.
+#[must_use = "if unused the ReentrantMutex will immediately unlock"]
+pub struct MappedReentrantMutexGuard<'a, R: RawMutex, G: GetThreadId, T: ?Sized> {
+    raw: &'a RawReentrantMutex<R, G>,
+    data: *const T,
+    marker: PhantomData<&'a T>,
+}
+
+unsafe impl<'a, R: RawMutex + Sync + 'a, G: GetThreadId + Sync + 'a, T: ?Sized + Sync + 'a> Sync
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
+    MappedReentrantMutexGuard<'a, R, G, T>
+{
+    /// Makes a new `MappedReentrantMutexGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `MappedReentrantMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedReentrantMutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedReentrantMutexGuard<'a, R, G, U>
+    where
+        F: FnOnce(&T) -> &U,
+    {
+        let raw = s.raw;
+        let data = f(unsafe { &*s.data });
+        mem::forget(s);
+        MappedReentrantMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedReentrantMutexGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `MappedReentrantMutexGuard` passed
+    /// in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedReentrantMutexGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(
+        s: Self,
+        f: F,
+    ) -> Result<MappedReentrantMutexGuard<'a, R, G, U>, Self>
+    where
+        F: FnOnce(&T) -> Option<&U>,
+    {
+        let raw = s.raw;
+        let data = match f(unsafe { &*s.data }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedReentrantMutexGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+}
+
+impl<'a, R: RawMutexFair + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
+    MappedReentrantMutexGuard<'a, R, G, T>
+{
+    /// Unlocks the mutex using a fair unlock protocol.
+    ///
+    /// By default, mutexes are unfair and allow the current thread to re-lock
+    /// the mutex before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the mutex for a long time. This is the
+    /// default because it allows much higher throughput as it avoids forcing a
+    /// context switch on every mutex unlock. This can result in one thread
+    /// acquiring a mutex many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `ReentrantMutexGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.raw.unlock_fair();
+        mem::forget(s);
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Deref
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Drop
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+    #[inline]
+    fn drop(&mut self) {
+        self.raw.unlock();
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> StableAddress
+    for MappedReentrantMutexGuard<'a, R, G, T>
+{
+}
diff --git a/src/rwlock.rs b/src/rwlock.rs
new file mode 100644
index 0000000..892ba52
--- /dev/null
+++ b/src/rwlock.rs
@@ -0,0 +1,1632 @@
+// 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 core::cell::UnsafeCell;
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem;
+use core::ops::{Deref, DerefMut};
+
+#[cfg(feature = "owning_ref")]
+use owning_ref::StableAddress;
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+/// Basic operations for a reader-writer lock.
+///
+/// Types implementing this trait can be used by `RwLock` to form a safe and
+/// fully-functioning `RwLock` type.
+///
+/// # Safety
+///
+/// Implementations of this trait must ensure that the `RwLock` is actually
+/// exclusive: an exclusive lock can't be acquired while an exclusive or shared
+/// lock exists, and a shared lock can't be acquire while an exclusive lock
+/// exists.
+pub unsafe trait RawRwLock {
+    /// Initial value for an unlocked `RwLock`.
+    // A “non-constant” const item is a legacy way to supply an initialized value to downstream
+    // static items. Can hopefully be replaced with `const fn new() -> Self` at some point.
+    #[allow(clippy::declare_interior_mutable_const)]
+    const INIT: Self;
+
+    /// Marker type which determines whether a lock guard should be `Send`. Use
+    /// one of the `GuardSend` or `GuardNoSend` helper types here.
+    type GuardMarker;
+
+    /// Acquires a shared lock, blocking the current thread until it is able to do so.
+    fn lock_shared(&self);
+
+    /// Attempts to acquire a shared lock without blocking.
+    fn try_lock_shared(&self) -> bool;
+
+    /// Releases a shared lock.
+    fn unlock_shared(&self);
+
+    /// Acquires an exclusive lock, blocking the current thread until it is able to do so.
+    fn lock_exclusive(&self);
+
+    /// Attempts to acquire an exclusive lock without blocking.
+    fn try_lock_exclusive(&self) -> bool;
+
+    /// Releases an exclusive lock.
+    fn unlock_exclusive(&self);
+}
+
+/// Additional methods for RwLocks which support fair unlocking.
+///
+/// Fair unlocking means that a lock is handed directly over to the next waiting
+/// thread if there is one, without giving other threads the opportunity to
+/// "steal" the lock in the meantime. This is typically slower than unfair
+/// unlocking, but may be necessary in certain circumstances.
+pub unsafe trait RawRwLockFair: RawRwLock {
+    /// Releases a shared lock using a fair unlock protocol.
+    fn unlock_shared_fair(&self);
+
+    /// Releases an exclusive lock using a fair unlock protocol.
+    fn unlock_exclusive_fair(&self);
+
+    /// Temporarily yields a shared lock to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_shared_fair` followed
+    /// by `lock_shared`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    fn bump_shared(&self) {
+        self.unlock_shared_fair();
+        self.lock_shared();
+    }
+
+    /// Temporarily yields an exclusive lock to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_exclusive_fair` followed
+    /// by `lock_exclusive`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    fn bump_exclusive(&self) {
+        self.unlock_exclusive_fair();
+        self.lock_exclusive();
+    }
+}
+
+/// Additional methods for RwLocks which support atomically downgrading an
+/// exclusive lock to a shared lock.
+pub unsafe trait RawRwLockDowngrade: RawRwLock {
+    /// Atomically downgrades an exclusive lock into a shared lock without
+    /// allowing any thread to take an exclusive lock in the meantime.
+    fn downgrade(&self);
+}
+
+/// Additional methods for RwLocks which support locking with timeouts.
+///
+/// The `Duration` and `Instant` types are specified as associated types so that
+/// this trait is usable even in `no_std` environments.
+pub unsafe trait RawRwLockTimed: RawRwLock {
+    /// Duration type used for `try_lock_for`.
+    type Duration;
+
+    /// Instant type used for `try_lock_until`.
+    type Instant;
+
+    /// Attempts to acquire a shared lock until a timeout is reached.
+    fn try_lock_shared_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to acquire a shared lock until a timeout is reached.
+    fn try_lock_shared_until(&self, timeout: Self::Instant) -> bool;
+
+    /// Attempts to acquire an exclusive lock until a timeout is reached.
+    fn try_lock_exclusive_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to acquire an exclusive lock until a timeout is reached.
+    fn try_lock_exclusive_until(&self, timeout: Self::Instant) -> bool;
+}
+
+/// Additional methods for RwLocks which support recursive read locks.
+///
+/// These are guaranteed to succeed without blocking if
+/// another read lock is held at the time of the call. This allows a thread
+/// to recursively lock a `RwLock`. However using this method can cause
+/// writers to starve since readers no longer block if a writer is waiting
+/// for the lock.
+pub unsafe trait RawRwLockRecursive: RawRwLock {
+    /// Acquires a shared lock without deadlocking in case of a recursive lock.
+    fn lock_shared_recursive(&self);
+
+    /// Attempts to acquire a shared lock without deadlocking in case of a recursive lock.
+    fn try_lock_shared_recursive(&self) -> bool;
+}
+
+/// Additional methods for RwLocks which support recursive read locks and timeouts.
+pub unsafe trait RawRwLockRecursiveTimed: RawRwLockRecursive + RawRwLockTimed {
+    /// Attempts to acquire a shared lock until a timeout is reached, without
+    /// deadlocking in case of a recursive lock.
+    fn try_lock_shared_recursive_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to acquire a shared lock until a timeout is reached, without
+    /// deadlocking in case of a recursive lock.
+    fn try_lock_shared_recursive_until(&self, timeout: Self::Instant) -> bool;
+}
+
+/// Additional methods for RwLocks which support atomically upgrading a shared
+/// lock to an exclusive lock.
+///
+/// This requires acquiring a special "upgradable read lock" instead of a
+/// normal shared lock. There may only be one upgradable lock at any time,
+/// otherwise deadlocks could occur when upgrading.
+pub unsafe trait RawRwLockUpgrade: RawRwLock {
+    /// Acquires an upgradable lock, blocking the current thread until it is able to do so.
+    fn lock_upgradable(&self);
+
+    /// Attempts to acquire an upgradable lock without blocking.
+    fn try_lock_upgradable(&self) -> bool;
+
+    /// Releases an upgradable lock.
+    fn unlock_upgradable(&self);
+
+    /// Upgrades an upgradable lock to an exclusive lock.
+    fn upgrade(&self);
+
+    /// Attempts to upgrade an upgradable lock to an exclusive lock without
+    /// blocking.
+    fn try_upgrade(&self) -> bool;
+}
+
+/// Additional methods for RwLocks which support upgradable locks and fair
+/// unlocking.
+pub unsafe trait RawRwLockUpgradeFair: RawRwLockUpgrade + RawRwLockFair {
+    /// Releases an upgradable lock using a fair unlock protocol.
+    fn unlock_upgradable_fair(&self);
+
+    /// Temporarily yields an upgradable lock to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_upgradable_fair` followed
+    /// by `lock_upgradable`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    fn bump_upgradable(&self) {
+        self.unlock_upgradable_fair();
+        self.lock_upgradable();
+    }
+}
+
+/// Additional methods for RwLocks which support upgradable locks and lock
+/// downgrading.
+pub unsafe trait RawRwLockUpgradeDowngrade: RawRwLockUpgrade + RawRwLockDowngrade {
+    /// Downgrades an upgradable lock to a shared lock.
+    fn downgrade_upgradable(&self);
+
+    /// Downgrades an exclusive lock to an upgradable lock.
+    fn downgrade_to_upgradable(&self);
+}
+
+/// Additional methods for RwLocks which support upgradable locks and locking
+/// with timeouts.
+pub unsafe trait RawRwLockUpgradeTimed: RawRwLockUpgrade + RawRwLockTimed {
+    /// Attempts to acquire an upgradable lock until a timeout is reached.
+    fn try_lock_upgradable_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to acquire an upgradable lock until a timeout is reached.
+    fn try_lock_upgradable_until(&self, timeout: Self::Instant) -> bool;
+
+    /// Attempts to upgrade an upgradable lock to an exclusive lock until a
+    /// timeout is reached.
+    fn try_upgrade_for(&self, timeout: Self::Duration) -> bool;
+
+    /// Attempts to upgrade an upgradable lock to an exclusive lock until a
+    /// timeout is reached.
+    fn try_upgrade_until(&self, timeout: Self::Instant) -> bool;
+}
+
+/// A reader-writer lock
+///
+/// This type of lock allows a number of readers or at most one writer at any
+/// point in time. The write portion of this lock typically allows modification
+/// of the underlying data (exclusive access) and the read portion of this lock
+/// typically allows for read-only access (shared access).
+///
+/// The type parameter `T` represents the data that this lock protects. It is
+/// required that `T` satisfies `Send` to be shared across threads and `Sync` to
+/// allow concurrent access through readers. The RAII guards returned from the
+/// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
+/// to allow access to the contained of the lock.
+pub struct RwLock<R, T: ?Sized> {
+    raw: R,
+    data: UnsafeCell<T>,
+}
+
+// Copied and modified from serde
+#[cfg(feature = "serde")]
+impl<R, T> Serialize for RwLock<R, T>
+where
+    R: RawRwLock,
+    T: Serialize + ?Sized,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.read().serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, R, T> Deserialize<'de> for RwLock<R, T>
+where
+    R: RawRwLock,
+    T: Deserialize<'de> + ?Sized,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(RwLock::new)
+    }
+}
+
+unsafe impl<R: RawRwLock + Send, T: ?Sized + Send> Send for RwLock<R, T> {}
+unsafe impl<R: RawRwLock + Sync, T: ?Sized + Send + Sync> Sync for RwLock<R, T> {}
+
+impl<R: RawRwLock, T> RwLock<R, T> {
+    /// Creates a new instance of an `RwLock<T>` which is unlocked.
+    #[cfg(feature = "nightly")]
+    #[inline]
+    pub const fn new(val: T) -> RwLock<R, T> {
+        RwLock {
+            data: UnsafeCell::new(val),
+            raw: R::INIT,
+        }
+    }
+
+    /// Creates a new instance of an `RwLock<T>` which is unlocked.
+    #[cfg(not(feature = "nightly"))]
+    #[inline]
+    pub fn new(val: T) -> RwLock<R, T> {
+        RwLock {
+            data: UnsafeCell::new(val),
+            raw: R::INIT,
+        }
+    }
+
+    /// Consumes this `RwLock`, returning the underlying data.
+    #[inline]
+    #[allow(unused_unsafe)]
+    pub fn into_inner(self) -> T {
+        unsafe { self.data.into_inner() }
+    }
+}
+
+impl<R, T> RwLock<R, T> {
+    /// Creates a new new instance of an `RwLock<T>` based on a pre-existing
+    /// `RawRwLock<T>`.
+    ///
+    /// This allows creating a `RwLock<T>` in a constant context on stable
+    /// Rust.
+    #[inline]
+    pub const fn const_new(raw_rwlock: R, val: T) -> RwLock<R, T> {
+        RwLock {
+            data: UnsafeCell::new(val),
+            raw: raw_rwlock,
+        }
+    }
+}
+
+impl<R: RawRwLock, T: ?Sized> RwLock<R, T> {
+    /// # Safety
+    ///
+    /// The lock must be held when calling this method.
+    #[inline]
+    unsafe fn read_guard(&self) -> RwLockReadGuard<'_, R, T> {
+        RwLockReadGuard {
+            rwlock: self,
+            marker: PhantomData,
+        }
+    }
+
+    /// # Safety
+    ///
+    /// The lock must be held when calling this method.
+    #[inline]
+    unsafe fn write_guard(&self) -> RwLockWriteGuard<'_, R, T> {
+        RwLockWriteGuard {
+            rwlock: self,
+            marker: PhantomData,
+        }
+    }
+
+    /// Locks this `RwLock` 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.
+    ///
+    /// Note that attempts to recursively acquire a read lock on a `RwLock` when
+    /// the current thread already holds one may result in a deadlock.
+    ///
+    /// Returns an RAII guard which will release this thread's shared access
+    /// once it is dropped.
+    #[inline]
+    pub fn read(&self) -> RwLockReadGuard<'_, R, T> {
+        self.raw.lock_shared();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.read_guard() }
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access.
+    ///
+    /// If the access could not be granted at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned which will release the shared access
+    /// when it is dropped.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_read(&self) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Locks this `RwLock` with exclusive write access, blocking the current
+    /// thread until it can be acquired.
+    ///
+    /// This function will not return while other writers or other readers
+    /// currently have access to the lock.
+    ///
+    /// Returns an RAII guard which will drop the write access of this `RwLock`
+    /// when dropped.
+    #[inline]
+    pub fn write(&self) -> RwLockWriteGuard<'_, R, T> {
+        self.raw.lock_exclusive();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.write_guard() }
+    }
+
+    /// Attempts to lock this `RwLock` with exclusive write access.
+    ///
+    /// If the lock could not be acquired at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned which will release the lock when
+    /// it is dropped.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_write(&self) -> Option<RwLockWriteGuard<'_, R, T>> {
+        if self.raw.try_lock_exclusive() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.write_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `RwLock` mutably, no actual locking needs to
+    /// take place---the mutable borrow statically guarantees no locks exist.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data.get() }
+    }
+
+    /// Forcibly unlocks a read lock.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `RwLockReadGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `RwLockReadGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a rwlock is read-unlocked when not read-locked.
+    #[inline]
+    pub unsafe fn force_unlock_read(&self) {
+        self.raw.unlock_shared();
+    }
+
+    /// Forcibly unlocks a write lock.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `RwLockWriteGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `RwLockWriteGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a rwlock is write-unlocked when not write-locked.
+    #[inline]
+    pub unsafe fn force_unlock_write(&self) {
+        self.raw.unlock_exclusive();
+    }
+
+    /// Returns the underlying raw reader-writer lock object.
+    ///
+    /// Note that you will most likely need to import the `RawRwLock` trait from
+    /// `lock_api` to be able to call functions on the raw
+    /// reader-writer lock.
+    ///
+    /// # Safety
+    ///
+    /// This method is unsafe because it allows unlocking a mutex while
+    /// still holding a reference to a lock guard.
+    pub unsafe fn raw(&self) -> &R {
+        &self.raw
+    }
+}
+
+impl<R: RawRwLockFair, T: ?Sized> RwLock<R, T> {
+    /// Forcibly unlocks a read lock using a fair unlock procotol.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `RwLockReadGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `RwLockReadGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a rwlock is read-unlocked when not read-locked.
+    #[inline]
+    pub unsafe fn force_unlock_read_fair(&self) {
+        self.raw.unlock_shared_fair();
+    }
+
+    /// Forcibly unlocks a write lock using a fair unlock procotol.
+    ///
+    /// This is useful when combined with `mem::forget` to hold a lock without
+    /// the need to maintain a `RwLockWriteGuard` object alive, for example when
+    /// dealing with FFI.
+    ///
+    /// # Safety
+    ///
+    /// This method must only be called if the current thread logically owns a
+    /// `RwLockWriteGuard` but that guard has be discarded using `mem::forget`.
+    /// Behavior is undefined if a rwlock is write-unlocked when not write-locked.
+    #[inline]
+    pub unsafe fn force_unlock_write_fair(&self) {
+        self.raw.unlock_exclusive_fair();
+    }
+}
+
+impl<R: RawRwLockTimed, T: ?Sized> RwLock<R, T> {
+    /// Attempts to acquire this `RwLock` with shared read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    #[inline]
+    pub fn try_read_for(&self, timeout: R::Duration) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    #[inline]
+    pub fn try_read_until(&self, timeout: R::Instant) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with exclusive write access until a
+    /// timeout is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the exclusive access when it is dropped.
+    #[inline]
+    pub fn try_write_for(&self, timeout: R::Duration) -> Option<RwLockWriteGuard<'_, R, T>> {
+        if self.raw.try_lock_exclusive_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.write_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with exclusive write access until a
+    /// timeout is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the exclusive access when it is dropped.
+    #[inline]
+    pub fn try_write_until(&self, timeout: R::Instant) -> Option<RwLockWriteGuard<'_, R, T>> {
+        if self.raw.try_lock_exclusive_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.write_guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawRwLockRecursive, T: ?Sized> RwLock<R, T> {
+    /// Locks this `RwLock` 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.
+    ///
+    /// Unlike `read`, this method is guaranteed to succeed without blocking if
+    /// another read lock is held at the time of the call. This allows a thread
+    /// to recursively lock a `RwLock`. However using this method can cause
+    /// writers to starve since readers no longer block if a writer is waiting
+    /// for the lock.
+    ///
+    /// Returns an RAII guard which will release this thread's shared access
+    /// once it is dropped.
+    #[inline]
+    pub fn read_recursive(&self) -> RwLockReadGuard<'_, R, T> {
+        self.raw.lock_shared_recursive();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.read_guard() }
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access.
+    ///
+    /// If the access could not be granted at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned which will release the shared access
+    /// when it is dropped.
+    ///
+    /// This method is guaranteed to succeed if another read lock is held at the
+    /// time of the call. See the documentation for `read_recursive` for details.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_read_recursive(&self) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared_recursive() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawRwLockRecursiveTimed, T: ?Sized> RwLock<R, T> {
+    /// Attempts to acquire this `RwLock` with shared read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    ///
+    /// This method is guaranteed to succeed without blocking if another read
+    /// lock is held at the time of the call. See the documentation for
+    /// `read_recursive` for details.
+    #[inline]
+    pub fn try_read_recursive_for(
+        &self,
+        timeout: R::Duration,
+    ) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared_recursive_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    #[inline]
+    pub fn try_read_recursive_until(
+        &self,
+        timeout: R::Instant,
+    ) -> Option<RwLockReadGuard<'_, R, T>> {
+        if self.raw.try_lock_shared_recursive_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.read_guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawRwLockUpgrade, T: ?Sized> RwLock<R, T> {
+    /// # Safety
+    ///
+    /// The lock must be held when calling this method.
+    #[inline]
+    unsafe fn upgradable_guard(&self) -> RwLockUpgradableReadGuard<'_, R, T> {
+        RwLockUpgradableReadGuard {
+            rwlock: self,
+            marker: PhantomData,
+        }
+    }
+
+    /// Locks this `RwLock` with upgradable read access, blocking the current thread
+    /// until it can be acquired.
+    ///
+    /// The calling thread will be blocked until there are no more writers or other
+    /// upgradable reads which hold the lock. There may be other readers currently
+    /// inside the lock when this method returns.
+    ///
+    /// Returns an RAII guard which will release this thread's shared access
+    /// once it is dropped.
+    #[inline]
+    pub fn upgradable_read(&self) -> RwLockUpgradableReadGuard<'_, R, T> {
+        self.raw.lock_upgradable();
+        // SAFETY: The lock is held, as required.
+        unsafe { self.upgradable_guard() }
+    }
+
+    /// Attempts to acquire this `RwLock` with upgradable read access.
+    ///
+    /// If the access could not be granted at this time, then `None` is returned.
+    /// Otherwise, an RAII guard is returned which will release the shared access
+    /// when it is dropped.
+    ///
+    /// This function does not block.
+    #[inline]
+    pub fn try_upgradable_read(&self) -> Option<RwLockUpgradableReadGuard<'_, R, T>> {
+        if self.raw.try_lock_upgradable() {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.upgradable_guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawRwLockUpgradeTimed, T: ?Sized> RwLock<R, T> {
+    /// Attempts to acquire this `RwLock` with upgradable read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    #[inline]
+    pub fn try_upgradable_read_for(
+        &self,
+        timeout: R::Duration,
+    ) -> Option<RwLockUpgradableReadGuard<'_, R, T>> {
+        if self.raw.try_lock_upgradable_for(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.upgradable_guard() })
+        } else {
+            None
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with upgradable read access until a timeout
+    /// is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// `None` is returned. Otherwise, an RAII guard is returned which will
+    /// release the shared access when it is dropped.
+    #[inline]
+    pub fn try_upgradable_read_until(
+        &self,
+        timeout: R::Instant,
+    ) -> Option<RwLockUpgradableReadGuard<'_, R, T>> {
+        if self.raw.try_lock_upgradable_until(timeout) {
+            // SAFETY: The lock is held, as required.
+            Some(unsafe { self.upgradable_guard() })
+        } else {
+            None
+        }
+    }
+}
+
+impl<R: RawRwLock, T: ?Sized + Default> Default for RwLock<R, T> {
+    #[inline]
+    fn default() -> RwLock<R, T> {
+        RwLock::new(Default::default())
+    }
+}
+
+impl<R: RawRwLock, T> From<T> for RwLock<R, T> {
+    #[inline]
+    fn from(t: T) -> RwLock<R, T> {
+        RwLock::new(t)
+    }
+}
+
+impl<R: RawRwLock, T: ?Sized + fmt::Debug> fmt::Debug for RwLock<R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.try_read() {
+            Some(guard) => f.debug_struct("RwLock").field("data", &&*guard).finish(),
+            None => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+
+                f.debug_struct("RwLock")
+                    .field("data", &LockedPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+/// RAII structure used to release the shared read access of a lock when
+/// dropped.
+#[must_use = "if unused the RwLock will immediately unlock"]
+pub struct RwLockReadGuard<'a, R: RawRwLock, T: ?Sized> {
+    rwlock: &'a RwLock<R, T>,
+    marker: PhantomData<(&'a T, R::GuardMarker)>,
+}
+
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for RwLockReadGuard<'a, R, T> {}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> RwLockReadGuard<'a, R, T> {
+    /// Returns a reference to the original reader-writer lock object.
+    pub fn rwlock(s: &Self) -> &'a RwLock<R, T> {
+        s.rwlock
+    }
+
+    /// Make a new `MappedRwLockReadGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `RwLockReadGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockReadGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedRwLockReadGuard<'a, R, U>
+    where
+        F: FnOnce(&T) -> &U,
+    {
+        let raw = &s.rwlock.raw;
+        let data = f(unsafe { &*s.rwlock.data.get() });
+        mem::forget(s);
+        MappedRwLockReadGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedRwLockReadGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `RwLockReadGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockReadGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedRwLockReadGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&T) -> Option<&U>,
+    {
+        let raw = &s.rwlock.raw;
+        let data = match f(unsafe { &*s.rwlock.data.get() }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedRwLockReadGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// The `RwLock` is unlocked a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_shared();
+        defer!(s.rwlock.raw.lock_shared());
+        f()
+    }
+}
+
+impl<'a, R: RawRwLockFair + 'a, T: ?Sized + 'a> RwLockReadGuard<'a, R, T> {
+    /// Unlocks the `RwLock` using a fair unlock protocol.
+    ///
+    /// By default, `RwLock` is unfair and allow the current thread to re-lock
+    /// the `RwLock` before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the `RwLock` for a long time. This is
+    /// the default because it allows much higher throughput as it avoids
+    /// forcing a context switch on every `RwLock` unlock. This can result in one
+    /// thread acquiring a `RwLock` many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `RwLockReadGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.rwlock.raw.unlock_shared_fair();
+        mem::forget(s);
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// The `RwLock` is unlocked a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_shared_fair();
+        defer!(s.rwlock.raw.lock_shared());
+        f()
+    }
+
+    /// Temporarily yields the `RwLock` to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `read`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    #[inline]
+    pub fn bump(s: &mut Self) {
+        s.rwlock.raw.bump_shared();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Deref for RwLockReadGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.rwlock.data.get() }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Drop for RwLockReadGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.rwlock.raw.unlock_shared();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for RwLockReadGuard<'a, R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for RwLockReadGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> StableAddress for RwLockReadGuard<'a, R, T> {}
+
+/// RAII structure used to release the exclusive write access of a lock when
+/// dropped.
+#[must_use = "if unused the RwLock will immediately unlock"]
+pub struct RwLockWriteGuard<'a, R: RawRwLock, T: ?Sized> {
+    rwlock: &'a RwLock<R, T>,
+    marker: PhantomData<(&'a mut T, R::GuardMarker)>,
+}
+
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for RwLockWriteGuard<'a, R, T> {}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> RwLockWriteGuard<'a, R, T> {
+    /// Returns a reference to the original reader-writer lock object.
+    pub fn rwlock(s: &Self) -> &'a RwLock<R, T> {
+        s.rwlock
+    }
+
+    /// Make a new `MappedRwLockWriteGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `RwLockWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockWriteGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedRwLockWriteGuard<'a, R, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let raw = &s.rwlock.raw;
+        let data = f(unsafe { &mut *s.rwlock.data.get() });
+        mem::forget(s);
+        MappedRwLockWriteGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedRwLockWriteGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `RwLockWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockWriteGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedRwLockWriteGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let raw = &s.rwlock.raw;
+        let data = match f(unsafe { &mut *s.rwlock.data.get() }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedRwLockWriteGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_exclusive();
+        defer!(s.rwlock.raw.lock_exclusive());
+        f()
+    }
+}
+
+impl<'a, R: RawRwLockDowngrade + 'a, T: ?Sized + 'a> RwLockWriteGuard<'a, R, T> {
+    /// Atomically downgrades a write lock into a read lock without allowing any
+    /// writers to take exclusive access of the lock in the meantime.
+    ///
+    /// Note that if there are any writers currently waiting to take the lock
+    /// then other readers may not be able to acquire the lock even if it was
+    /// downgraded.
+    pub fn downgrade(s: Self) -> RwLockReadGuard<'a, R, T> {
+        s.rwlock.raw.downgrade();
+        let rwlock = s.rwlock;
+        mem::forget(s);
+        RwLockReadGuard {
+            rwlock,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, R: RawRwLockUpgradeDowngrade + 'a, T: ?Sized + 'a> RwLockWriteGuard<'a, R, T> {
+    /// Atomically downgrades a write lock into an upgradable read lock without allowing any
+    /// writers to take exclusive access of the lock in the meantime.
+    ///
+    /// Note that if there are any writers currently waiting to take the lock
+    /// then other readers may not be able to acquire the lock even if it was
+    /// downgraded.
+    pub fn downgrade_to_upgradable(s: Self) -> RwLockUpgradableReadGuard<'a, R, T> {
+        s.rwlock.raw.downgrade_to_upgradable();
+        let rwlock = s.rwlock;
+        mem::forget(s);
+        RwLockUpgradableReadGuard {
+            rwlock,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, R: RawRwLockFair + 'a, T: ?Sized + 'a> RwLockWriteGuard<'a, R, T> {
+    /// Unlocks the `RwLock` using a fair unlock protocol.
+    ///
+    /// By default, `RwLock` is unfair and allow the current thread to re-lock
+    /// the `RwLock` before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the `RwLock` for a long time. This is
+    /// the default because it allows much higher throughput as it avoids
+    /// forcing a context switch on every `RwLock` unlock. This can result in one
+    /// thread acquiring a `RwLock` many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `RwLockWriteGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.rwlock.raw.unlock_exclusive_fair();
+        mem::forget(s);
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// The `RwLock` is unlocked a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_exclusive_fair();
+        defer!(s.rwlock.raw.lock_exclusive());
+        f()
+    }
+
+    /// Temporarily yields the `RwLock` to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `write`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    #[inline]
+    pub fn bump(s: &mut Self) {
+        s.rwlock.raw.bump_exclusive();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Deref for RwLockWriteGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.rwlock.data.get() }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> DerefMut for RwLockWriteGuard<'a, R, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.rwlock.data.get() }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Drop for RwLockWriteGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.rwlock.raw.unlock_exclusive();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for RwLockWriteGuard<'a, R, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for RwLockWriteGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> StableAddress for RwLockWriteGuard<'a, R, T> {}
+
+/// RAII structure used to release the upgradable read access of a lock when
+/// dropped.
+#[must_use = "if unused the RwLock will immediately unlock"]
+pub struct RwLockUpgradableReadGuard<'a, R: RawRwLockUpgrade, T: ?Sized> {
+    rwlock: &'a RwLock<R, T>,
+    marker: PhantomData<(&'a T, R::GuardMarker)>,
+}
+
+unsafe impl<'a, R: RawRwLockUpgrade + 'a, T: ?Sized + Sync + 'a> Sync
+    for RwLockUpgradableReadGuard<'a, R, T>
+{
+}
+
+impl<'a, R: RawRwLockUpgrade + 'a, T: ?Sized + 'a> RwLockUpgradableReadGuard<'a, R, T> {
+    /// Returns a reference to the original reader-writer lock object.
+    pub fn rwlock(s: &Self) -> &'a RwLock<R, T> {
+        s.rwlock
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_upgradable();
+        defer!(s.rwlock.raw.lock_upgradable());
+        f()
+    }
+
+    /// Atomically upgrades an upgradable read lock lock into a exclusive write lock,
+    /// blocking the current thread until it can be acquired.
+    pub fn upgrade(s: Self) -> RwLockWriteGuard<'a, R, T> {
+        s.rwlock.raw.upgrade();
+        let rwlock = s.rwlock;
+        mem::forget(s);
+        RwLockWriteGuard {
+            rwlock,
+            marker: PhantomData,
+        }
+    }
+
+    /// Tries to atomically upgrade an upgradable read lock into a exclusive write lock.
+    ///
+    /// If the access could not be granted at this time, then the current guard is returned.
+    pub fn try_upgrade(s: Self) -> Result<RwLockWriteGuard<'a, R, T>, Self> {
+        if s.rwlock.raw.try_upgrade() {
+            let rwlock = s.rwlock;
+            mem::forget(s);
+            Ok(RwLockWriteGuard {
+                rwlock,
+                marker: PhantomData,
+            })
+        } else {
+            Err(s)
+        }
+    }
+}
+
+impl<'a, R: RawRwLockUpgradeFair + 'a, T: ?Sized + 'a> RwLockUpgradableReadGuard<'a, R, T> {
+    /// Unlocks the `RwLock` using a fair unlock protocol.
+    ///
+    /// By default, `RwLock` is unfair and allow the current thread to re-lock
+    /// the `RwLock` before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the `RwLock` for a long time. This is
+    /// the default because it allows much higher throughput as it avoids
+    /// forcing a context switch on every `RwLock` unlock. This can result in one
+    /// thread acquiring a `RwLock` many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `RwLockUpgradableReadGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.rwlock.raw.unlock_upgradable_fair();
+        mem::forget(s);
+    }
+
+    /// Temporarily unlocks the `RwLock` to execute the given function.
+    ///
+    /// The `RwLock` is unlocked a fair unlock protocol.
+    ///
+    /// This is safe because `&mut` guarantees that there exist no other
+    /// references to the data protected by the `RwLock`.
+    #[inline]
+    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
+    where
+        F: FnOnce() -> U,
+    {
+        s.rwlock.raw.unlock_upgradable_fair();
+        defer!(s.rwlock.raw.lock_upgradable());
+        f()
+    }
+
+    /// Temporarily yields the `RwLock` to a waiting thread if there is one.
+    ///
+    /// This method is functionally equivalent to calling `unlock_fair` followed
+    /// by `upgradable_read`, however it can be much more efficient in the case where there
+    /// are no waiting threads.
+    #[inline]
+    pub fn bump(s: &mut Self) {
+        s.rwlock.raw.bump_upgradable();
+    }
+}
+
+impl<'a, R: RawRwLockUpgradeDowngrade + 'a, T: ?Sized + 'a> RwLockUpgradableReadGuard<'a, R, T> {
+    /// Atomically downgrades an upgradable read lock lock into a shared read lock
+    /// without allowing any writers to take exclusive access of the lock in the
+    /// meantime.
+    ///
+    /// Note that if there are any writers currently waiting to take the lock
+    /// then other readers may not be able to acquire the lock even if it was
+    /// downgraded.
+    pub fn downgrade(s: Self) -> RwLockReadGuard<'a, R, T> {
+        s.rwlock.raw.downgrade_upgradable();
+        let rwlock = s.rwlock;
+        mem::forget(s);
+        RwLockReadGuard {
+            rwlock,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, R: RawRwLockUpgradeTimed + 'a, T: ?Sized + 'a> RwLockUpgradableReadGuard<'a, R, T> {
+    /// Tries to atomically upgrade an upgradable read lock into a exclusive
+    /// write lock, until a timeout is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// the current guard is returned.
+    pub fn try_upgrade_for(
+        s: Self,
+        timeout: R::Duration,
+    ) -> Result<RwLockWriteGuard<'a, R, T>, Self> {
+        if s.rwlock.raw.try_upgrade_for(timeout) {
+            let rwlock = s.rwlock;
+            mem::forget(s);
+            Ok(RwLockWriteGuard {
+                rwlock,
+                marker: PhantomData,
+            })
+        } else {
+            Err(s)
+        }
+    }
+
+    /// Tries to atomically upgrade an upgradable read lock into a exclusive
+    /// write lock, until a timeout is reached.
+    ///
+    /// If the access could not be granted before the timeout expires, then
+    /// the current guard is returned.
+    #[inline]
+    pub fn try_upgrade_until(
+        s: Self,
+        timeout: R::Instant,
+    ) -> Result<RwLockWriteGuard<'a, R, T>, Self> {
+        if s.rwlock.raw.try_upgrade_until(timeout) {
+            let rwlock = s.rwlock;
+            mem::forget(s);
+            Ok(RwLockWriteGuard {
+                rwlock,
+                marker: PhantomData,
+            })
+        } else {
+            Err(s)
+        }
+    }
+}
+
+impl<'a, R: RawRwLockUpgrade + 'a, T: ?Sized + 'a> Deref for RwLockUpgradableReadGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.rwlock.data.get() }
+    }
+}
+
+impl<'a, R: RawRwLockUpgrade + 'a, T: ?Sized + 'a> Drop for RwLockUpgradableReadGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.rwlock.raw.unlock_upgradable();
+    }
+}
+
+impl<'a, R: RawRwLockUpgrade + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug
+    for RwLockUpgradableReadGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawRwLockUpgrade + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for RwLockUpgradableReadGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawRwLockUpgrade + 'a, T: ?Sized + 'a> StableAddress
+    for RwLockUpgradableReadGuard<'a, R, T>
+{
+}
+
+/// An RAII read lock guard returned by `RwLockReadGuard::map`, which can point to a
+/// subfield of the protected data.
+///
+/// The main difference between `MappedRwLockReadGuard` and `RwLockReadGuard` is that the
+/// former doesn't support temporarily unlocking and re-locking, since that
+/// could introduce soundness issues if the locked object is modified by another
+/// thread.
+#[must_use = "if unused the RwLock will immediately unlock"]
+pub struct MappedRwLockReadGuard<'a, R: RawRwLock, T: ?Sized> {
+    raw: &'a R,
+    data: *const T,
+    marker: PhantomData<&'a T>,
+}
+
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for MappedRwLockReadGuard<'a, R, T> {}
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Send for MappedRwLockReadGuard<'a, R, T> where
+    R::GuardMarker: Send
+{
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> MappedRwLockReadGuard<'a, R, T> {
+    /// Make a new `MappedRwLockReadGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `MappedRwLockReadGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedRwLockReadGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedRwLockReadGuard<'a, R, U>
+    where
+        F: FnOnce(&T) -> &U,
+    {
+        let raw = s.raw;
+        let data = f(unsafe { &*s.data });
+        mem::forget(s);
+        MappedRwLockReadGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedRwLockReadGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `MappedRwLockReadGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedRwLockReadGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedRwLockReadGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&T) -> Option<&U>,
+    {
+        let raw = s.raw;
+        let data = match f(unsafe { &*s.data }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedRwLockReadGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+}
+
+impl<'a, R: RawRwLockFair + 'a, T: ?Sized + 'a> MappedRwLockReadGuard<'a, R, T> {
+    /// Unlocks the `RwLock` using a fair unlock protocol.
+    ///
+    /// By default, `RwLock` is unfair and allow the current thread to re-lock
+    /// the `RwLock` before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the `RwLock` for a long time. This is
+    /// the default because it allows much higher throughput as it avoids
+    /// forcing a context switch on every `RwLock` unlock. This can result in one
+    /// thread acquiring a `RwLock` many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `MappedRwLockReadGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.raw.unlock_shared_fair();
+        mem::forget(s);
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Deref for MappedRwLockReadGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Drop for MappedRwLockReadGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.raw.unlock_shared();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug
+    for MappedRwLockReadGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for MappedRwLockReadGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> StableAddress
+    for MappedRwLockReadGuard<'a, R, T>
+{
+}
+
+/// An RAII write lock guard returned by `RwLockWriteGuard::map`, which can point to a
+/// subfield of the protected data.
+///
+/// The main difference between `MappedRwLockWriteGuard` and `RwLockWriteGuard` is that the
+/// former doesn't support temporarily unlocking and re-locking, since that
+/// could introduce soundness issues if the locked object is modified by another
+/// thread.
+#[must_use = "if unused the RwLock will immediately unlock"]
+pub struct MappedRwLockWriteGuard<'a, R: RawRwLock, T: ?Sized> {
+    raw: &'a R,
+    data: *mut T,
+    marker: PhantomData<&'a mut T>,
+}
+
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync
+    for MappedRwLockWriteGuard<'a, R, T>
+{
+}
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Send for MappedRwLockWriteGuard<'a, R, T> where
+    R::GuardMarker: Send
+{
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T> {
+    /// Make a new `MappedRwLockWriteGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `MappedRwLockWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedRwLockWriteGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedRwLockWriteGuard<'a, R, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let raw = s.raw;
+        let data = f(unsafe { &mut *s.data });
+        mem::forget(s);
+        MappedRwLockWriteGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+
+    /// Attempts to make  a new `MappedRwLockWriteGuard` for a component of the
+    /// locked data. The original guard is return if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the `MappedRwLockWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `MappedRwLockWriteGuard::map(...)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    #[inline]
+    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedRwLockWriteGuard<'a, R, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let raw = s.raw;
+        let data = match f(unsafe { &mut *s.data }) {
+            Some(data) => data,
+            None => return Err(s),
+        };
+        mem::forget(s);
+        Ok(MappedRwLockWriteGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        })
+    }
+}
+
+impl<'a, R: RawRwLockDowngrade + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T> {
+    /// Atomically downgrades a write lock into a read lock without allowing any
+    /// writers to take exclusive access of the lock in the meantime.
+    ///
+    /// Note that if there are any writers currently waiting to take the lock
+    /// then other readers may not be able to acquire the lock even if it was
+    /// downgraded.
+    #[deprecated(
+        since = "0.3.3",
+        note = "This function is unsound and will be removed in the future, see issue #198"
+    )]
+    pub fn downgrade(s: Self) -> MappedRwLockReadGuard<'a, R, T> {
+        s.raw.downgrade();
+        let raw = s.raw;
+        let data = s.data;
+        mem::forget(s);
+        MappedRwLockReadGuard {
+            raw,
+            data,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, R: RawRwLockFair + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T> {
+    /// Unlocks the `RwLock` using a fair unlock protocol.
+    ///
+    /// By default, `RwLock` is unfair and allow the current thread to re-lock
+    /// the `RwLock` before another has the chance to acquire the lock, even if
+    /// that thread has been blocked on the `RwLock` for a long time. This is
+    /// the default because it allows much higher throughput as it avoids
+    /// forcing a context switch on every `RwLock` unlock. This can result in one
+    /// thread acquiring a `RwLock` many more times than other threads.
+    ///
+    /// However in some cases it can be beneficial to ensure fairness by forcing
+    /// the lock to pass on to a waiting thread if there is one. This is done by
+    /// using this method instead of dropping the `MappedRwLockWriteGuard` normally.
+    #[inline]
+    pub fn unlock_fair(s: Self) {
+        s.raw.unlock_exclusive_fair();
+        mem::forget(s);
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Deref for MappedRwLockWriteGuard<'a, R, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> DerefMut for MappedRwLockWriteGuard<'a, R, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Drop for MappedRwLockWriteGuard<'a, R, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.raw.unlock_exclusive();
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug
+    for MappedRwLockWriteGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, R: RawRwLock + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
+    for MappedRwLockWriteGuard<'a, R, T>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(feature = "owning_ref")]
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> StableAddress
+    for MappedRwLockWriteGuard<'a, R, T>
+{
+}