mirror of
https://github.com/tokio-rs/tokio.git
synced 2026-08-19 00:00:09 +02:00
sync: add back RwLockWriteGuard::map and RwLockWriteGuard::try_map (#3348)
This commit is contained in:
Alice Ryhl
@@ -450,7 +450,10 @@ cfg_sync! {
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pub use semaphore::{Semaphore, SemaphorePermit, OwnedSemaphorePermit};
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mod rwlock;
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pub use rwlock::{RwLock, RwLockReadGuard, RwLockWriteGuard};
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pub use rwlock::RwLock;
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pub use rwlock::read_guard::RwLockReadGuard;
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pub use rwlock::write_guard::RwLockWriteGuard;
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pub use rwlock::write_guard_mapped::RwLockMappedWriteGuard;
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mod task;
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pub(crate) use task::AtomicWaker;
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+11
-262
@@ -1,10 +1,14 @@
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use crate::sync::batch_semaphore::{Semaphore, TryAcquireError};
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use crate::sync::mutex::TryLockError;
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use std::cell::UnsafeCell;
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use std::fmt;
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use std::marker;
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use std::mem;
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use std::ops;
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pub(crate) mod read_guard;
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pub(crate) mod write_guard;
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pub(crate) mod write_guard_mapped;
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pub(crate) use read_guard::RwLockReadGuard;
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pub(crate) use write_guard::RwLockWriteGuard;
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pub(crate) use write_guard_mapped::RwLockMappedWriteGuard;
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#[cfg(not(loom))]
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const MAX_READS: usize = 32;
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@@ -80,240 +84,6 @@ pub struct RwLock<T: ?Sized> {
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c: UnsafeCell<T>,
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}
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/// RAII structure used to release the shared read access of a lock when
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/// dropped.
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///
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/// This structure is created by the [`read`] method on
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/// [`RwLock`].
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///
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/// [`read`]: method@RwLock::read
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/// [`RwLock`]: struct@RwLock
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pub struct RwLockReadGuard<'a, T: ?Sized> {
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s: &'a Semaphore,
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data: *const T,
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marker: marker::PhantomData<&'a T>,
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}
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impl<'a, T> RwLockReadGuard<'a, T> {
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/// Make a new `RwLockReadGuard` for a component of the locked data.
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///
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/// This operation cannot fail as the `RwLockReadGuard` passed in already
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/// locked the data.
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///
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/// This is an associated function that needs to be
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/// used as `RwLockReadGuard::map(...)`. A method would interfere with
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/// methods of the same name on the contents of the locked data.
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///
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/// This is an asynchronous version of [`RwLockReadGuard::map`] from the
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/// [`parking_lot` crate].
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///
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/// [`RwLockReadGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.map
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/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
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///
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/// # Examples
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///
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/// ```
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/// use tokio::sync::{RwLock, RwLockReadGuard};
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///
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/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
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/// struct Foo(u32);
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///
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/// # #[tokio::main]
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/// # async fn main() {
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/// let lock = RwLock::new(Foo(1));
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///
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/// let guard = lock.read().await;
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/// let guard = RwLockReadGuard::map(guard, |f| &f.0);
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///
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/// assert_eq!(1, *guard);
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/// # }
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/// ```
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#[inline]
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pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U>
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where
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F: FnOnce(&T) -> &U,
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{
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let data = f(&*this) as *const U;
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let s = this.s;
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// NB: Forget to avoid drop impl from being called.
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mem::forget(this);
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RwLockReadGuard {
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s,
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data,
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marker: marker::PhantomData,
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}
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}
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/// Attempts to make a new [`RwLockReadGuard`] for a component of the
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/// locked data. The original guard is returned if the closure returns
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/// `None`.
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///
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/// This operation cannot fail as the `RwLockReadGuard` passed in already
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/// locked the data.
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///
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/// This is an associated function that needs to be used as
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/// `RwLockReadGuard::try_map(..)`. A method would interfere with methods of the
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/// same name on the contents of the locked data.
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///
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/// This is an asynchronous version of [`RwLockReadGuard::try_map`] from the
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/// [`parking_lot` crate].
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///
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/// [`RwLockReadGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.try_map
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/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
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///
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/// # Examples
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///
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/// ```
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/// use tokio::sync::{RwLock, RwLockReadGuard};
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///
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/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
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/// struct Foo(u32);
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///
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/// # #[tokio::main]
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/// # async fn main() {
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/// let lock = RwLock::new(Foo(1));
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///
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/// let guard = lock.read().await;
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/// let guard = RwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");
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///
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/// assert_eq!(1, *guard);
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/// # }
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/// ```
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#[inline]
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pub fn try_map<F, U: ?Sized>(this: Self, f: F) -> Result<RwLockReadGuard<'a, U>, Self>
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where
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F: FnOnce(&T) -> Option<&U>,
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{
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let data = match f(&*this) {
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Some(data) => data as *const U,
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None => return Err(this),
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};
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let s = this.s;
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// NB: Forget to avoid drop impl from being called.
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mem::forget(this);
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Ok(RwLockReadGuard {
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s,
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data,
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marker: marker::PhantomData,
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})
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}
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}
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impl<'a, T: ?Sized> fmt::Debug for RwLockReadGuard<'a, T>
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where
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T: fmt::Debug,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized> fmt::Display for RwLockReadGuard<'a, T>
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where
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T: fmt::Display,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt::Display::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
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fn drop(&mut self) {
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self.s.release(1);
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}
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}
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/// RAII structure used to release the exclusive write access of a lock when
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/// dropped.
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///
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/// This structure is created by the [`write`] and method
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/// on [`RwLock`].
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///
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/// [`write`]: method@RwLock::write
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/// [`RwLock`]: struct@RwLock
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pub struct RwLockWriteGuard<'a, T: ?Sized> {
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s: &'a Semaphore,
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data: *mut T,
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marker: marker::PhantomData<&'a mut T>,
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}
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impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> {
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/// Atomically downgrades a write lock into a read lock without allowing
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/// any writers to take exclusive access of the lock in the meantime.
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///
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/// **Note:** This won't *necessarily* allow any additional readers to acquire
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/// locks, since [`RwLock`] is fair and it is possible that a writer is next
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/// in line.
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///
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/// Returns an RAII guard which will drop this read access of the `RwLock`
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/// when dropped.
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///
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/// # Examples
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///
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/// ```
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/// # use tokio::sync::RwLock;
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/// # use std::sync::Arc;
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/// #
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/// # #[tokio::main]
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/// # async fn main() {
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/// let lock = Arc::new(RwLock::new(1));
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///
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/// let n = lock.write().await;
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///
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/// let cloned_lock = lock.clone();
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/// let handle = tokio::spawn(async move {
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/// *cloned_lock.write().await = 2;
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/// });
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///
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/// let n = n.downgrade();
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/// assert_eq!(*n, 1, "downgrade is atomic");
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///
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/// drop(n);
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/// handle.await.unwrap();
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/// assert_eq!(*lock.read().await, 2, "second writer obtained write lock");
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/// # }
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/// ```
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///
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/// [`RwLock`]: struct@RwLock
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pub fn downgrade(self) -> RwLockReadGuard<'a, T> {
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let RwLockWriteGuard { s, data, .. } = self;
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// Release all but one of the permits held by the write guard
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s.release(MAX_READS - 1);
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// NB: Forget to avoid drop impl from being called.
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mem::forget(self);
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RwLockReadGuard {
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s,
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data,
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marker: marker::PhantomData,
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}
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}
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}
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impl<'a, T: ?Sized> fmt::Debug for RwLockWriteGuard<'a, T>
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where
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T: fmt::Debug,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized> fmt::Display for RwLockWriteGuard<'a, T>
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where
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T: fmt::Display,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt::Display::fmt(&**self, f)
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}
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}
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impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
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fn drop(&mut self) {
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self.s.release(MAX_READS);
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}
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}
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#[test]
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#[cfg(not(loom))]
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fn bounds() {
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@@ -351,11 +121,13 @@ unsafe impl<T> Sync for RwLock<T> where T: ?Sized + Send + Sync {}
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unsafe impl<T> Send for RwLockReadGuard<'_, T> where T: ?Sized + Sync {}
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unsafe impl<T> Sync for RwLockReadGuard<'_, T> where T: ?Sized + Send + Sync {}
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unsafe impl<T> Sync for RwLockWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
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unsafe impl<T> Sync for RwLockMappedWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
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// Safety: Stores a raw pointer to `T`, so if `T` is `Sync`, the lock guard over
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// `T` is `Send` - but since this is also provides mutable access, we need to
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// make sure that `T` is `Send` since its value can be sent across thread
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// boundaries.
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unsafe impl<T> Send for RwLockWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
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unsafe impl<T> Send for RwLockMappedWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
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impl<T: ?Sized> RwLock<T> {
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/// Creates a new instance of an `RwLock<T>` which is unlocked.
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@@ -437,7 +209,6 @@ impl<T: ?Sized> RwLock<T> {
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/// drop(n);
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///}
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/// ```
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///
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pub async fn read(&self) -> RwLockReadGuard<'_, T> {
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self.s.acquire(1).await.unwrap_or_else(|_| {
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// The semaphore was closed. but, we never explicitly close it, and we have a
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@@ -500,8 +271,8 @@ impl<T: ?Sized> RwLock<T> {
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/// Locks this `RwLock` with exclusive write access, causing the current
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/// task to yield until the lock has been acquired.
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///
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/// The calling task will yield while other writers or readers
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/// currently have access to the lock.
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/// The calling task will yield while other writers or readers currently
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/// have access to the lock.
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///
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/// Returns an RAII guard which will drop the write access of this `RwLock`
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/// when dropped.
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@@ -602,28 +373,6 @@ impl<T: ?Sized> RwLock<T> {
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}
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}
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impl<T: ?Sized> ops::Deref for RwLockReadGuard<'_, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { &*self.data }
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}
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}
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impl<T: ?Sized> ops::Deref for RwLockWriteGuard<'_, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { &*self.data }
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}
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}
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impl<T: ?Sized> ops::DerefMut for RwLockWriteGuard<'_, T> {
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fn deref_mut(&mut self) -> &mut T {
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unsafe { &mut *self.data }
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}
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}
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impl<T> From<T> for RwLock<T> {
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fn from(s: T) -> Self {
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Self::new(s)
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@@ -0,0 +1,156 @@
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use crate::sync::batch_semaphore::Semaphore;
|
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use std::fmt;
|
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use std::marker;
|
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use std::mem;
|
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use std::ops;
|
||||
|
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/// RAII structure used to release the shared read access of a lock when
|
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/// dropped.
|
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///
|
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/// This structure is created by the [`read`] method on
|
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/// [`RwLock`].
|
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///
|
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/// [`read`]: method@crate::sync::RwLock::read
|
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/// [`RwLock`]: struct@crate::sync::RwLock
|
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pub struct RwLockReadGuard<'a, T: ?Sized> {
|
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pub(super) s: &'a Semaphore,
|
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pub(super) data: *const T,
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pub(super) marker: marker::PhantomData<&'a T>,
|
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}
|
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|
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impl<'a, T> RwLockReadGuard<'a, T> {
|
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/// Make a new `RwLockReadGuard` 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockReadGuard::map`] from the
|
||||
/// [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockReadGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.map
|
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/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
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/// # Examples
|
||||
///
|
||||
/// ```
|
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/// use tokio::sync::{RwLock, RwLockReadGuard};
|
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///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
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///
|
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/// # #[tokio::main]
|
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/// # async fn main() {
|
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/// let lock = RwLock::new(Foo(1));
|
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///
|
||||
/// let guard = lock.read().await;
|
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/// let guard = RwLockReadGuard::map(guard, |f| &f.0);
|
||||
///
|
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/// assert_eq!(1, *guard);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U>
|
||||
where
|
||||
F: FnOnce(&T) -> &U,
|
||||
{
|
||||
let data = f(&*this) as *const U;
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
RwLockReadGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
}
|
||||
}
|
||||
|
||||
/// Attempts to make a new [`RwLockReadGuard`] for a component of the
|
||||
/// locked data. The original guard is returned 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockReadGuard::try_map`] from the
|
||||
/// [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockReadGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.try_map
|
||||
/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use tokio::sync::{RwLock, RwLockReadGuard};
|
||||
///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
||||
///
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = RwLock::new(Foo(1));
|
||||
///
|
||||
/// let guard = lock.read().await;
|
||||
/// let guard = RwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");
|
||||
///
|
||||
/// assert_eq!(1, *guard);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn try_map<F, U: ?Sized>(this: Self, f: F) -> Result<RwLockReadGuard<'a, U>, Self>
|
||||
where
|
||||
F: FnOnce(&T) -> Option<&U>,
|
||||
{
|
||||
let data = match f(&*this) {
|
||||
Some(data) => data as *const U,
|
||||
None => return Err(this),
|
||||
};
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
Ok(RwLockReadGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
})
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> ops::Deref for RwLockReadGuard<'_, T> {
|
||||
type Target = T;
|
||||
|
||||
fn deref(&self) -> &T {
|
||||
unsafe { &*self.data }
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Debug for RwLockReadGuard<'a, T>
|
||||
where
|
||||
T: fmt::Debug,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Debug::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Display for RwLockReadGuard<'a, T>
|
||||
where
|
||||
T: fmt::Display,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Display::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
|
||||
fn drop(&mut self) {
|
||||
self.s.release(1);
|
||||
}
|
||||
}
|
||||
@@ -0,0 +1,235 @@
|
||||
use crate::sync::batch_semaphore::Semaphore;
|
||||
use crate::sync::rwlock::read_guard::RwLockReadGuard;
|
||||
use crate::sync::rwlock::write_guard_mapped::RwLockMappedWriteGuard;
|
||||
use std::fmt;
|
||||
use std::marker;
|
||||
use std::mem;
|
||||
use std::ops;
|
||||
|
||||
/// RAII structure used to release the exclusive write access of a lock when
|
||||
/// dropped.
|
||||
///
|
||||
/// This structure is created by the [`write`] and method
|
||||
/// on [`RwLock`].
|
||||
///
|
||||
/// [`write`]: method@crate::sync::RwLock::write
|
||||
/// [`RwLock`]: struct@crate::sync::RwLock
|
||||
pub struct RwLockWriteGuard<'a, T: ?Sized> {
|
||||
pub(super) s: &'a Semaphore,
|
||||
pub(super) data: *mut T,
|
||||
pub(super) marker: marker::PhantomData<&'a mut T>,
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> {
|
||||
/// Make a new [`RwLockMappedWriteGuard`] 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockWriteGuard::map`] from the
|
||||
/// [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
|
||||
/// [`RwLockWriteGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.map
|
||||
/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use tokio::sync::{RwLock, RwLockWriteGuard};
|
||||
///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
||||
///
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = RwLock::new(Foo(1));
|
||||
///
|
||||
/// {
|
||||
/// let mut mapped = RwLockWriteGuard::map(lock.write().await, |f| &mut f.0);
|
||||
/// *mapped = 2;
|
||||
/// }
|
||||
///
|
||||
/// assert_eq!(Foo(2), *lock.read().await);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn map<F, U: ?Sized>(mut this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>
|
||||
where
|
||||
F: FnOnce(&mut T) -> &mut U,
|
||||
{
|
||||
let data = f(&mut *this) as *mut U;
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
RwLockMappedWriteGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
}
|
||||
}
|
||||
|
||||
/// Attempts to make a new [`RwLockMappedWriteGuard`] for a component of
|
||||
/// the locked data. The original guard is returned 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockWriteGuard::try_map`] from
|
||||
/// the [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
|
||||
/// [`RwLockWriteGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.try_map
|
||||
/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use tokio::sync::{RwLock, RwLockWriteGuard};
|
||||
///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
||||
///
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = RwLock::new(Foo(1));
|
||||
///
|
||||
/// {
|
||||
/// let guard = lock.write().await;
|
||||
/// let mut guard = RwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
|
||||
/// *guard = 2;
|
||||
/// }
|
||||
///
|
||||
/// assert_eq!(Foo(2), *lock.read().await);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn try_map<F, U: ?Sized>(
|
||||
mut this: Self,
|
||||
f: F,
|
||||
) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
|
||||
where
|
||||
F: FnOnce(&mut T) -> Option<&mut U>,
|
||||
{
|
||||
let data = match f(&mut *this) {
|
||||
Some(data) => data as *mut U,
|
||||
None => return Err(this),
|
||||
};
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
Ok(RwLockMappedWriteGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
})
|
||||
}
|
||||
|
||||
/// Converts this `RwLockWriteGuard` into an `RwLockMappedWriteGuard`. This
|
||||
/// method can be used to store a non-mapped guard in a struct field that
|
||||
/// expects a mapped guard.
|
||||
///
|
||||
/// This is equivalent to calling `RwLockWriteGuard::map(guard, |me| me)`.
|
||||
#[inline]
|
||||
pub fn into_mapped(this: Self) -> RwLockMappedWriteGuard<'a, T> {
|
||||
RwLockWriteGuard::map(this, |me| me)
|
||||
}
|
||||
|
||||
/// Atomically downgrades a write lock into a read lock without allowing
|
||||
/// any writers to take exclusive access of the lock in the meantime.
|
||||
///
|
||||
/// **Note:** This won't *necessarily* allow any additional readers to acquire
|
||||
/// locks, since [`RwLock`] is fair and it is possible that a writer is next
|
||||
/// in line.
|
||||
///
|
||||
/// Returns an RAII guard which will drop this read access of the `RwLock`
|
||||
/// when dropped.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// # use tokio::sync::RwLock;
|
||||
/// # use std::sync::Arc;
|
||||
/// #
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = Arc::new(RwLock::new(1));
|
||||
///
|
||||
/// let n = lock.write().await;
|
||||
///
|
||||
/// let cloned_lock = lock.clone();
|
||||
/// let handle = tokio::spawn(async move {
|
||||
/// *cloned_lock.write().await = 2;
|
||||
/// });
|
||||
///
|
||||
/// let n = n.downgrade();
|
||||
/// assert_eq!(*n, 1, "downgrade is atomic");
|
||||
///
|
||||
/// drop(n);
|
||||
/// handle.await.unwrap();
|
||||
/// assert_eq!(*lock.read().await, 2, "second writer obtained write lock");
|
||||
/// # }
|
||||
/// ```
|
||||
///
|
||||
/// [`RwLock`]: struct@crate::sync::RwLock
|
||||
pub fn downgrade(self) -> RwLockReadGuard<'a, T> {
|
||||
let RwLockWriteGuard { s, data, .. } = self;
|
||||
|
||||
// Release all but one of the permits held by the write guard
|
||||
s.release(super::MAX_READS - 1);
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(self);
|
||||
RwLockReadGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> ops::Deref for RwLockWriteGuard<'_, T> {
|
||||
type Target = T;
|
||||
|
||||
fn deref(&self) -> &T {
|
||||
unsafe { &*self.data }
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> ops::DerefMut for RwLockWriteGuard<'_, T> {
|
||||
fn deref_mut(&mut self) -> &mut T {
|
||||
unsafe { &mut *self.data }
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Debug for RwLockWriteGuard<'a, T>
|
||||
where
|
||||
T: fmt::Debug,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Debug::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Display for RwLockWriteGuard<'a, T>
|
||||
where
|
||||
T: fmt::Display,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Display::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
|
||||
fn drop(&mut self) {
|
||||
self.s.release(super::MAX_READS);
|
||||
}
|
||||
}
|
||||
@@ -0,0 +1,171 @@
|
||||
use crate::sync::batch_semaphore::Semaphore;
|
||||
use std::fmt;
|
||||
use std::marker;
|
||||
use std::mem;
|
||||
use std::ops;
|
||||
|
||||
/// RAII structure used to release the exclusive write access of a lock when
|
||||
/// dropped.
|
||||
///
|
||||
/// This structure is created by [mapping] an [`RwLockWriteGuard`]. It is a
|
||||
/// separate type from `RwLockWriteGuard` to disallow downgrading a mapped
|
||||
/// guard, since doing so can cause undefined behavior.
|
||||
///
|
||||
/// [mapping]: method@crate::sync::RwLockWriteGuard::map
|
||||
/// [`RwLockWriteGuard`]: struct@crate::sync::RwLockWriteGuard
|
||||
pub struct RwLockMappedWriteGuard<'a, T: ?Sized> {
|
||||
pub(super) s: &'a Semaphore,
|
||||
pub(super) data: *mut T,
|
||||
pub(super) marker: marker::PhantomData<&'a mut T>,
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> RwLockMappedWriteGuard<'a, T> {
|
||||
/// Make a new `RwLockMappedWriteGuard` for a component of the locked data.
|
||||
///
|
||||
/// This operation cannot fail as the `RwLockMappedWriteGuard` 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockWriteGuard::map`] from the
|
||||
/// [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockWriteGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.map
|
||||
/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use tokio::sync::{RwLock, RwLockWriteGuard};
|
||||
///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
||||
///
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = RwLock::new(Foo(1));
|
||||
///
|
||||
/// {
|
||||
/// let mut mapped = RwLockWriteGuard::map(lock.write().await, |f| &mut f.0);
|
||||
/// *mapped = 2;
|
||||
/// }
|
||||
///
|
||||
/// assert_eq!(Foo(2), *lock.read().await);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn map<F, U: ?Sized>(mut this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>
|
||||
where
|
||||
F: FnOnce(&mut T) -> &mut U,
|
||||
{
|
||||
let data = f(&mut *this) as *mut U;
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
RwLockMappedWriteGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
}
|
||||
}
|
||||
|
||||
/// Attempts to make a new [`RwLockMappedWriteGuard`] for a component of
|
||||
/// the locked data. The original guard is returned if the closure returns
|
||||
/// `None`.
|
||||
///
|
||||
/// This operation cannot fail as the `RwLockMappedWriteGuard` 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.
|
||||
///
|
||||
/// This is an asynchronous version of [`RwLockWriteGuard::try_map`] from
|
||||
/// the [`parking_lot` crate].
|
||||
///
|
||||
/// [`RwLockWriteGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.try_map
|
||||
/// [`parking_lot` crate]: https://crates.io/crates/parking_lot
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use tokio::sync::{RwLock, RwLockWriteGuard};
|
||||
///
|
||||
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
|
||||
/// struct Foo(u32);
|
||||
///
|
||||
/// # #[tokio::main]
|
||||
/// # async fn main() {
|
||||
/// let lock = RwLock::new(Foo(1));
|
||||
///
|
||||
/// {
|
||||
/// let guard = lock.write().await;
|
||||
/// let mut guard = RwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
|
||||
/// *guard = 2;
|
||||
/// }
|
||||
///
|
||||
/// assert_eq!(Foo(2), *lock.read().await);
|
||||
/// # }
|
||||
/// ```
|
||||
#[inline]
|
||||
pub fn try_map<F, U: ?Sized>(
|
||||
mut this: Self,
|
||||
f: F,
|
||||
) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
|
||||
where
|
||||
F: FnOnce(&mut T) -> Option<&mut U>,
|
||||
{
|
||||
let data = match f(&mut *this) {
|
||||
Some(data) => data as *mut U,
|
||||
None => return Err(this),
|
||||
};
|
||||
let s = this.s;
|
||||
// NB: Forget to avoid drop impl from being called.
|
||||
mem::forget(this);
|
||||
Ok(RwLockMappedWriteGuard {
|
||||
s,
|
||||
data,
|
||||
marker: marker::PhantomData,
|
||||
})
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> ops::Deref for RwLockMappedWriteGuard<'_, T> {
|
||||
type Target = T;
|
||||
|
||||
fn deref(&self) -> &T {
|
||||
unsafe { &*self.data }
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> ops::DerefMut for RwLockMappedWriteGuard<'_, T> {
|
||||
fn deref_mut(&mut self) -> &mut T {
|
||||
unsafe { &mut *self.data }
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Debug for RwLockMappedWriteGuard<'a, T>
|
||||
where
|
||||
T: fmt::Debug,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Debug::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> fmt::Display for RwLockMappedWriteGuard<'a, T>
|
||||
where
|
||||
T: fmt::Display,
|
||||
{
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Display::fmt(&**self, f)
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, T: ?Sized> Drop for RwLockMappedWriteGuard<'a, T> {
|
||||
fn drop(&mut self) {
|
||||
self.s.release(super::MAX_READS);
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user