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

1 files changed, 1632 insertions, 0 deletions

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>
+{
+}