diff options
Diffstat (limited to 'third_party/rust/lock_api/src/rwlock.rs')
| -rw-r--r-- | third_party/rust/lock_api/src/rwlock.rs | 2604 |
1 files changed, 2604 insertions, 0 deletions
diff --git a/third_party/rust/lock_api/src/rwlock.rs b/third_party/rust/lock_api/src/rwlock.rs new file mode 100644 index 0000000000..c972fb6c67 --- /dev/null +++ b/third_party/rust/lock_api/src/rwlock.rs @@ -0,0 +1,2604 @@ +// 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 = "arc_lock")] +use alloc::sync::Arc; +#[cfg(feature = "arc_lock")] +use core::mem::ManuallyDrop; +#[cfg(feature = "arc_lock")] +use core::ptr; + +#[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. + /// + /// # Safety + /// + /// This method may only be called if a shared lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an exclusive lock is held in the current context. + unsafe fn unlock_exclusive(&self); + + /// Checks if this `RwLock` is currently locked in any way. + #[inline] + fn is_locked(&self) -> bool { + let acquired_lock = self.try_lock_exclusive(); + if acquired_lock { + // Safety: A lock was successfully acquired above. + unsafe { + self.unlock_exclusive(); + } + } + !acquired_lock + } + + /// Check if this `RwLock` is currently exclusively locked. + fn is_locked_exclusive(&self) -> bool { + let acquired_lock = self.try_lock_shared(); + if acquired_lock { + // Safety: A shared lock was successfully acquired above. + unsafe { + self.unlock_shared(); + } + } + !acquired_lock + } +} + +/// 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. + /// + /// # Safety + /// + /// This method may only be called if a shared lock is held in the current context. + unsafe fn unlock_shared_fair(&self); + + /// Releases an exclusive lock using a fair unlock protocol. + /// + /// # Safety + /// + /// This method may only be called if an exclusive lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if a shared lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an exclusive lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an exclusive lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe fn unlock_upgradable(&self); + + /// Upgrades an upgradable lock to an exclusive lock. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe fn upgrade(&self); + + /// Attempts to upgrade an upgradable lock to an exclusive lock without + /// blocking. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe fn downgrade_upgradable(&self); + + /// Downgrades an exclusive lock to an upgradable lock. + /// + /// # Safety + /// + /// This method may only be called if an exclusive lock is held in the current context. + unsafe 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. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe fn try_upgrade_for(&self, timeout: Self::Duration) -> bool; + + /// Attempts to upgrade an upgradable lock to an exclusive lock until a + /// timeout is reached. + /// + /// # Safety + /// + /// This method may only be called if an upgradable lock is held in the current context. + unsafe 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(has_const_fn_trait_bound)] + #[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(has_const_fn_trait_bound))] + #[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() } + } + + /// Checks whether this `RwLock` is currently locked in any way. + #[inline] + pub fn is_locked(&self) -> bool { + self.raw.is_locked() + } + + /// Check if this `RwLock` is currently exclusively locked. + #[inline] + pub fn is_locked_exclusive(&self) -> bool { + self.raw.is_locked_exclusive() + } + + /// 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 + } + + /// Returns a raw pointer to the underlying data. + /// + /// This is useful when combined with `mem::forget` to hold a lock without + /// the need to maintain a `RwLockReadGuard` or `RwLockWriteGuard` object + /// alive, for example when dealing with FFI. + /// + /// # Safety + /// + /// You must ensure that there are no data races when dereferencing the + /// returned pointer, for example if the current thread logically owns a + /// `RwLockReadGuard` or `RwLockWriteGuard` but that guard has been discarded + /// using `mem::forget`. + #[inline] + pub fn data_ptr(&self) -> *mut T { + self.data.get() + } + + /// # Safety + /// + /// The lock must be held when calling this method. + #[cfg(feature = "arc_lock")] + #[inline] + unsafe fn read_guard_arc(self: &Arc<Self>) -> ArcRwLockReadGuard<R, T> { + ArcRwLockReadGuard { + rwlock: self.clone(), + marker: PhantomData, + } + } + + /// # Safety + /// + /// The lock must be held when calling this method. + #[cfg(feature = "arc_lock")] + #[inline] + unsafe fn write_guard_arc(self: &Arc<Self>) -> ArcRwLockWriteGuard<R, T> { + ArcRwLockWriteGuard { + rwlock: self.clone(), + marker: PhantomData, + } + } + + /// Locks this `RwLock` with read access, through an `Arc`. + /// + /// This method is similar to the `read` method; however, it requires the `RwLock` to be inside of an `Arc` + /// and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn read_arc(self: &Arc<Self>) -> ArcRwLockReadGuard<R, T> { + self.raw.lock_shared(); + // SAFETY: locking guarantee is upheld + unsafe { self.read_guard_arc() } + } + + /// Attempts to lock this `RwLock` with read access, through an `Arc`. + /// + /// This method is similar to the `try_read` method; however, it requires the `RwLock` to be inside of an + /// `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_arc(self: &Arc<Self>) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared() { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } else { + None + } + } + + /// Locks this `RwLock` with write access, through an `Arc`. + /// + /// This method is similar to the `write` method; however, it requires the `RwLock` to be inside of an `Arc` + /// and the resulting write guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn write_arc(self: &Arc<Self>) -> ArcRwLockWriteGuard<R, T> { + self.raw.lock_exclusive(); + // SAFETY: locking guarantee is upheld + unsafe { self.write_guard_arc() } + } + + /// Attempts to lock this `RwLock` with writ access, through an `Arc`. + /// + /// This method is similar to the `try_write` method; however, it requires the `RwLock` to be inside of an + /// `Arc` and the resulting write guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_write_arc(self: &Arc<Self>) -> Option<ArcRwLockWriteGuard<R, T>> { + if self.raw.try_lock_exclusive() { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.write_guard_arc() }) + } else { + None + } + } +} + +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 + } + } + + /// Attempts to acquire this `RwLock` with read access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_read_for` method; however, it requires the `RwLock` to be inside of an + /// `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_arc_for( + self: &Arc<Self>, + timeout: R::Duration, + ) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared_for(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } else { + None + } + } + + /// Attempts to acquire this `RwLock` with read access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_read_until` method; however, it requires the `RwLock` to be inside of + /// an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_arc_until( + self: &Arc<Self>, + timeout: R::Instant, + ) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared_until(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } else { + None + } + } + + /// Attempts to acquire this `RwLock` with write access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_write_for` method; however, it requires the `RwLock` to be inside of + /// an `Arc` and the resulting write guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_write_arc_for( + self: &Arc<Self>, + timeout: R::Duration, + ) -> Option<ArcRwLockWriteGuard<R, T>> { + if self.raw.try_lock_exclusive_for(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.write_guard_arc() }) + } else { + None + } + } + + /// Attempts to acquire this `RwLock` with read access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_write_until` method; however, it requires the `RwLock` to be inside of + /// an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_write_arc_until( + self: &Arc<Self>, + timeout: R::Instant, + ) -> Option<ArcRwLockWriteGuard<R, T>> { + if self.raw.try_lock_exclusive_until(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.write_guard_arc() }) + } 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 + } + } + + /// Locks this `RwLock` with shared read access, through an `Arc`. + /// + /// This method is similar to the `read_recursive` method; however, it requires the `RwLock` to be inside of + /// an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn read_arc_recursive(self: &Arc<Self>) -> ArcRwLockReadGuard<R, T> { + self.raw.lock_shared_recursive(); + // SAFETY: locking guarantee is upheld + unsafe { self.read_guard_arc() } + } + + /// Attempts to lock this `RwLock` with shared read access, through an `Arc`. + /// + /// This method is similar to the `try_read_recursive` method; however, it requires the `RwLock` to be inside + /// of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_recursive_arc(self: &Arc<Self>) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared_recursive() { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } 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 + } + } + + /// Attempts to lock this `RwLock` with read access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_read_recursive_for` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_arc_recursive_for( + self: &Arc<Self>, + timeout: R::Duration, + ) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared_recursive_for(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } else { + None + } + } + + /// Attempts to lock this `RwLock` with read access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_read_recursive_until` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_read_arc_recursive_until( + self: &Arc<Self>, + timeout: R::Instant, + ) -> Option<ArcRwLockReadGuard<R, T>> { + if self.raw.try_lock_shared_recursive_until(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.read_guard_arc() }) + } 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 + } + } + + /// # Safety + /// + /// The lock must be held when calling this method. + #[cfg(feature = "arc_lock")] + #[inline] + unsafe fn upgradable_guard_arc(self: &Arc<Self>) -> ArcRwLockUpgradableReadGuard<R, T> { + ArcRwLockUpgradableReadGuard { + rwlock: self.clone(), + marker: PhantomData, + } + } + + /// Locks this `RwLock` with upgradable read access, through an `Arc`. + /// + /// This method is similar to the `upgradable_read` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn upgradable_read_arc(self: &Arc<Self>) -> ArcRwLockUpgradableReadGuard<R, T> { + self.raw.lock_upgradable(); + // SAFETY: locking guarantee is upheld + unsafe { self.upgradable_guard_arc() } + } + + /// Attempts to lock this `RwLock` with upgradable read access, through an `Arc`. + /// + /// This method is similar to the `try_upgradable_read` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_upgradable_read_arc(self: &Arc<Self>) -> Option<ArcRwLockUpgradableReadGuard<R, T>> { + if self.raw.try_lock_upgradable() { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.upgradable_guard_arc() }) + } 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 + } + } + + /// Attempts to lock this `RwLock` with upgradable access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_upgradable_read_for` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_upgradable_read_arc_for( + self: &Arc<Self>, + timeout: R::Duration, + ) -> Option<ArcRwLockUpgradableReadGuard<R, T>> { + if self.raw.try_lock_upgradable_for(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.upgradable_guard_arc() }) + } else { + None + } + } + + /// Attempts to lock this `RwLock` with upgradable access until a timeout is reached, through an `Arc`. + /// + /// This method is similar to the `try_upgradable_read_until` method; however, it requires the `RwLock` to be + /// inside of an `Arc` and the resulting read guard has no lifetime requirements. + #[cfg(feature = "arc_lock")] + #[inline] + pub fn try_upgradable_read_arc_until( + self: &Arc<Self>, + timeout: R::Instant, + ) -> Option<ArcRwLockUpgradableReadGuard<R, T>> { + if self.raw.try_lock_upgradable_until(timeout) { + // SAFETY: locking guarantee is upheld + Some(unsafe { self.upgradable_guard_arc() }) + } 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)>, +} + +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. Returns the original guard 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::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<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, + { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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, + { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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> {} + +/// An RAII rwlock guard returned by the `Arc` locking operations on `RwLock`. +/// +/// This is similar to the `RwLockReadGuard` struct, except instead of using a reference to unlock the `RwLock` +/// it uses an `Arc<RwLock>`. This has several advantages, most notably that it has an `'static` lifetime. +#[cfg(feature = "arc_lock")] +#[must_use = "if unused the RwLock will immediately unlock"] +pub struct ArcRwLockReadGuard<R: RawRwLock, T: ?Sized> { + rwlock: Arc<RwLock<R, T>>, + marker: PhantomData<R::GuardMarker>, +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> ArcRwLockReadGuard<R, T> { + /// Returns a reference to the rwlock, contained in its `Arc`. + pub fn rwlock(s: &Self) -> &Arc<RwLock<R, T>> { + &s.rwlock + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally identical to the `unlocked` method on [`RwLockReadGuard`]. + #[inline] + pub fn unlocked<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + s.rwlock.raw.unlock_shared(); + } + defer!(s.rwlock.raw.lock_shared()); + f() + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockFair, T: ?Sized> ArcRwLockReadGuard<R, T> { + /// Unlocks the `RwLock` using a fair unlock protocol. + /// + /// This is functionally identical to the `unlock_fair` method on [`RwLockReadGuard`]. + #[inline] + pub fn unlock_fair(s: Self) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + s.rwlock.raw.unlock_shared_fair(); + } + + // SAFETY: ensure the Arc has its refcount decremented + let mut s = ManuallyDrop::new(s); + unsafe { ptr::drop_in_place(&mut s.rwlock) }; + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally identical to the `unlocked_fair` method on [`RwLockReadGuard`]. + #[inline] + pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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 is functionally identical to the `bump` method on [`RwLockReadGuard`]. + #[inline] + pub fn bump(s: &mut Self) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + s.rwlock.raw.bump_shared(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> Deref for ArcRwLockReadGuard<R, T> { + type Target = T; + #[inline] + fn deref(&self) -> &T { + unsafe { &*self.rwlock.data.get() } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> Drop for ArcRwLockReadGuard<R, T> { + #[inline] + fn drop(&mut self) { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + self.rwlock.raw.unlock_shared(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: fmt::Debug + ?Sized> fmt::Debug for ArcRwLockReadGuard<R, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&**self, f) + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: fmt::Display + ?Sized> fmt::Display for ArcRwLockReadGuard<R, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + (**self).fmt(f) + } +} + +/// 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)>, +} + +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::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<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, + { + // Safety: An RwLockReadGuard always holds a shared lock. + unsafe { + 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> { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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> { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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, + { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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> {} + +/// An RAII rwlock guard returned by the `Arc` locking operations on `RwLock`. +/// This is similar to the `RwLockWriteGuard` struct, except instead of using a reference to unlock the `RwLock` +/// it uses an `Arc<RwLock>`. This has several advantages, most notably that it has an `'static` lifetime. +#[cfg(feature = "arc_lock")] +#[must_use = "if unused the RwLock will immediately unlock"] +pub struct ArcRwLockWriteGuard<R: RawRwLock, T: ?Sized> { + rwlock: Arc<RwLock<R, T>>, + marker: PhantomData<R::GuardMarker>, +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> ArcRwLockWriteGuard<R, T> { + /// Returns a reference to the rwlock, contained in its `Arc`. + pub fn rwlock(s: &Self) -> &Arc<RwLock<R, T>> { + &s.rwlock + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally equivalent to the `unlocked` method on [`RwLockWriteGuard`]. + #[inline] + pub fn unlocked<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockWriteGuard always holds a shared lock. + unsafe { + s.rwlock.raw.unlock_exclusive(); + } + defer!(s.rwlock.raw.lock_exclusive()); + f() + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockDowngrade, T: ?Sized> ArcRwLockWriteGuard<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. + /// + /// This is functionally equivalent to the `downgrade` method on [`RwLockWriteGuard`]. + pub fn downgrade(s: Self) -> ArcRwLockReadGuard<R, T> { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + s.rwlock.raw.downgrade(); + } + + // SAFETY: prevent the arc's refcount from changing using ManuallyDrop and ptr::read + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + ArcRwLockReadGuard { + rwlock, + marker: PhantomData, + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgradeDowngrade, T: ?Sized> ArcRwLockWriteGuard<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. + /// + /// This is functionally identical to the `downgrade_to_upgradable` method on [`RwLockWriteGuard`]. + pub fn downgrade_to_upgradable(s: Self) -> ArcRwLockUpgradableReadGuard<R, T> { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + s.rwlock.raw.downgrade_to_upgradable(); + } + + // SAFETY: same as above + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + ArcRwLockUpgradableReadGuard { + rwlock, + marker: PhantomData, + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockFair, T: ?Sized> ArcRwLockWriteGuard<R, T> { + /// Unlocks the `RwLock` using a fair unlock protocol. + /// + /// This is functionally equivalent to the `unlock_fair` method on [`RwLockWriteGuard`]. + #[inline] + pub fn unlock_fair(s: Self) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + s.rwlock.raw.unlock_exclusive_fair(); + } + + // SAFETY: prevent the Arc from leaking memory + let mut s = ManuallyDrop::new(s); + unsafe { ptr::drop_in_place(&mut s.rwlock) }; + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally equivalent to the `unlocked_fair` method on [`RwLockWriteGuard`]. + #[inline] + pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + 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 the `bump` method on [`RwLockWriteGuard`]. + #[inline] + pub fn bump(s: &mut Self) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + s.rwlock.raw.bump_exclusive(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> Deref for ArcRwLockWriteGuard<R, T> { + type Target = T; + #[inline] + fn deref(&self) -> &T { + unsafe { &*self.rwlock.data.get() } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> DerefMut for ArcRwLockWriteGuard<R, T> { + #[inline] + fn deref_mut(&mut self) -> &mut T { + unsafe { &mut *self.rwlock.data.get() } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: ?Sized> Drop for ArcRwLockWriteGuard<R, T> { + #[inline] + fn drop(&mut self) { + // Safety: An RwLockWriteGuard always holds an exclusive lock. + unsafe { + self.rwlock.raw.unlock_exclusive(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: fmt::Debug + ?Sized> fmt::Debug for ArcRwLockWriteGuard<R, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&**self, f) + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLock, T: fmt::Display + ?Sized> fmt::Display for ArcRwLockWriteGuard<R, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + (**self).fmt(f) + } +} + +/// 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, + { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { 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) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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, + { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { 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> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { 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) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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 rwlock guard returned by the `Arc` locking operations on `RwLock`. +/// This is similar to the `RwLockUpgradableReadGuard` struct, except instead of using a reference to unlock the +/// `RwLock` it uses an `Arc<RwLock>`. This has several advantages, most notably that it has an `'static` +/// lifetime. +#[cfg(feature = "arc_lock")] +#[must_use = "if unused the RwLock will immediately unlock"] +pub struct ArcRwLockUpgradableReadGuard<R: RawRwLockUpgrade, T: ?Sized> { + rwlock: Arc<RwLock<R, T>>, + marker: PhantomData<R::GuardMarker>, +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgrade, T: ?Sized> ArcRwLockUpgradableReadGuard<R, T> { + /// Returns a reference to the rwlock, contained in its original `Arc`. + pub fn rwlock(s: &Self) -> &Arc<RwLock<R, T>> { + &s.rwlock + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally identical to the `unlocked` method on [`RwLockUpgradableReadGuard`]. + #[inline] + pub fn unlocked<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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) -> ArcRwLockWriteGuard<R, T> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + s.rwlock.raw.upgrade(); + } + + // SAFETY: avoid incrementing or decrementing the refcount using ManuallyDrop and reading the Arc out + // of the struct + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + ArcRwLockWriteGuard { + 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<ArcRwLockWriteGuard<R, T>, Self> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { s.rwlock.raw.try_upgrade() } { + // SAFETY: same as above + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + Ok(ArcRwLockWriteGuard { + rwlock, + marker: PhantomData, + }) + } else { + Err(s) + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgradeFair, T: ?Sized> ArcRwLockUpgradableReadGuard<R, T> { + /// Unlocks the `RwLock` using a fair unlock protocol. + /// + /// This is functionally identical to the `unlock_fair` method on [`RwLockUpgradableReadGuard`]. + #[inline] + pub fn unlock_fair(s: Self) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + s.rwlock.raw.unlock_upgradable_fair(); + } + + // SAFETY: make sure we decrement the refcount properly + let mut s = ManuallyDrop::new(s); + unsafe { ptr::drop_in_place(&mut s.rwlock) }; + } + + /// Temporarily unlocks the `RwLock` to execute the given function. + /// + /// This is functionally equivalent to the `unlocked_fair` method on [`RwLockUpgradableReadGuard`]. + #[inline] + pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U + where + F: FnOnce() -> U, + { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + 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 `bump` on [`RwLockUpgradableReadGuard`]. + #[inline] + pub fn bump(s: &mut Self) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + s.rwlock.raw.bump_upgradable(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgradeDowngrade, T: ?Sized> ArcRwLockUpgradableReadGuard<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) -> ArcRwLockReadGuard<R, T> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + s.rwlock.raw.downgrade_upgradable(); + } + + // SAFETY: use ManuallyDrop and ptr::read to ensure the refcount is not changed + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + ArcRwLockReadGuard { + rwlock, + marker: PhantomData, + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgradeTimed, T: ?Sized> ArcRwLockUpgradableReadGuard<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<ArcRwLockWriteGuard<R, T>, Self> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { s.rwlock.raw.try_upgrade_for(timeout) } { + // SAFETY: same as above + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + Ok(ArcRwLockWriteGuard { + 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<ArcRwLockWriteGuard<R, T>, Self> { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + if unsafe { s.rwlock.raw.try_upgrade_until(timeout) } { + // SAFETY: same as above + let s = ManuallyDrop::new(s); + let rwlock = unsafe { ptr::read(&s.rwlock) }; + + Ok(ArcRwLockWriteGuard { + rwlock, + marker: PhantomData, + }) + } else { + Err(s) + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgrade, T: ?Sized> Deref for ArcRwLockUpgradableReadGuard<R, T> { + type Target = T; + #[inline] + fn deref(&self) -> &T { + unsafe { &*self.rwlock.data.get() } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgrade, T: ?Sized> Drop for ArcRwLockUpgradableReadGuard<R, T> { + #[inline] + fn drop(&mut self) { + // Safety: An RwLockUpgradableReadGuard always holds an upgradable lock. + unsafe { + self.rwlock.raw.unlock_upgradable(); + } + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgrade, T: fmt::Debug + ?Sized> fmt::Debug + for ArcRwLockUpgradableReadGuard<R, T> +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&**self, f) + } +} + +#[cfg(feature = "arc_lock")] +impl<R: RawRwLockUpgrade, T: fmt::Display + ?Sized> fmt::Display + for ArcRwLockUpgradableReadGuard<R, T> +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + (**self).fmt(f) + } +} + +/// 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 + Sync + '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::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<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) { + // Safety: A MappedRwLockReadGuard always holds a shared lock. + unsafe { + 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) { + // Safety: A MappedRwLockReadGuard always holds a shared lock. + unsafe { + 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 + Send + '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::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<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: 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) { + // Safety: A MappedRwLockWriteGuard always holds an exclusive lock. + unsafe { + 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) { + // Safety: A MappedRwLockWriteGuard always holds an exclusive lock. + unsafe { + 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> +{ +} |