diff options
Diffstat (limited to 'vendor/tokio/src/sync/rwlock/write_guard.rs')
| -rw-r--r-- | vendor/tokio/src/sync/rwlock/write_guard.rs | 240 |
1 files changed, 240 insertions, 0 deletions
diff --git a/vendor/tokio/src/sync/rwlock/write_guard.rs b/vendor/tokio/src/sync/rwlock/write_guard.rs new file mode 100644 index 000000000..865a121ed --- /dev/null +++ b/vendor/tokio/src/sync/rwlock/write_guard.rs @@ -0,0 +1,240 @@ +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`] method +/// on [`RwLock`]. +/// +/// [`write`]: method@crate::sync::RwLock::write +/// [`RwLock`]: struct@crate::sync::RwLock +pub struct RwLockWriteGuard<'a, T: ?Sized> { + pub(super) permits_acquired: u32, + 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; + let permits_acquired = this.permits_acquired; + // NB: Forget to avoid drop impl from being called. + mem::forget(this); + RwLockMappedWriteGuard { + permits_acquired, + 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; + let permits_acquired = this.permits_acquired; + // NB: Forget to avoid drop impl from being called. + mem::forget(this); + Ok(RwLockMappedWriteGuard { + permits_acquired, + 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((self.permits_acquired - 1) as usize); + // 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(self.permits_acquired as usize); + } +} |