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Diffstat (limited to 'third_party/rust/hyper/src/common/sync_wrapper.rs')
| -rw-r--r-- | third_party/rust/hyper/src/common/sync_wrapper.rs | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/third_party/rust/hyper/src/common/sync_wrapper.rs b/third_party/rust/hyper/src/common/sync_wrapper.rs new file mode 100644 index 0000000000..704d1a6712 --- /dev/null +++ b/third_party/rust/hyper/src/common/sync_wrapper.rs @@ -0,0 +1,110 @@ +/* + * This is a copy of the sync_wrapper crate. + */ + +/// A mutual exclusion primitive that relies on static type information only +/// +/// In some cases synchronization can be proven statically: whenever you hold an exclusive `&mut` +/// reference, the Rust type system ensures that no other part of the program can hold another +/// reference to the data. Therefore it is safe to access it even if the current thread obtained +/// this reference via a channel. Whenever this is the case, the overhead of allocating and locking +/// a [`Mutex`] can be avoided by using this static version. +/// +/// One example where this is often applicable is [`Future`], which requires an exclusive reference +/// for its [`poll`] method: While a given `Future` implementation may not be safe to access by +/// multiple threads concurrently, the executor can only run the `Future` on one thread at any +/// given time, making it [`Sync`] in practice as long as the implementation is `Send`. You can +/// therefore use the sync wrapper to prove that your data structure is `Sync` even though it +/// contains such a `Future`. +/// +/// # Example +/// +/// ```ignore +/// use hyper::common::sync_wrapper::SyncWrapper; +/// use std::future::Future; +/// +/// struct MyThing { +/// future: SyncWrapper<Box<dyn Future<Output = String> + Send>>, +/// } +/// +/// impl MyThing { +/// // all accesses to `self.future` now require an exclusive reference or ownership +/// } +/// +/// fn assert_sync<T: Sync>() {} +/// +/// assert_sync::<MyThing>(); +/// ``` +/// +/// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html +/// [`Future`]: https://doc.rust-lang.org/std/future/trait.Future.html +/// [`poll`]: https://doc.rust-lang.org/std/future/trait.Future.html#method.poll +/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html +#[repr(transparent)] +pub(crate) struct SyncWrapper<T>(T); + +impl<T> SyncWrapper<T> { + /// Creates a new SyncWrapper containing the given value. + /// + /// # Examples + /// + /// ```ignore + /// use hyper::common::sync_wrapper::SyncWrapper; + /// + /// let wrapped = SyncWrapper::new(42); + /// ``` + pub(crate) fn new(value: T) -> Self { + Self(value) + } + + /// Acquires a reference to the protected value. + /// + /// This is safe because it requires an exclusive reference to the wrapper. Therefore this method + /// neither panics nor does it return an error. This is in contrast to [`Mutex::get_mut`] which + /// returns an error if another thread panicked while holding the lock. It is not recommended + /// to send an exclusive reference to a potentially damaged value to another thread for further + /// processing. + /// + /// [`Mutex::get_mut`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html#method.get_mut + /// + /// # Examples + /// + /// ```ignore + /// use hyper::common::sync_wrapper::SyncWrapper; + /// + /// let mut wrapped = SyncWrapper::new(42); + /// let value = wrapped.get_mut(); + /// *value = 0; + /// assert_eq!(*wrapped.get_mut(), 0); + /// ``` + pub(crate) fn get_mut(&mut self) -> &mut T { + &mut self.0 + } + + /// Consumes this wrapper, returning the underlying data. + /// + /// This is safe because it requires ownership of the wrapper, aherefore this method will neither + /// panic nor does it return an error. This is in contrast to [`Mutex::into_inner`] which + /// returns an error if another thread panicked while holding the lock. It is not recommended + /// to send an exclusive reference to a potentially damaged value to another thread for further + /// processing. + /// + /// [`Mutex::into_inner`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html#method.into_inner + /// + /// # Examples + /// + /// ```ignore + /// use hyper::common::sync_wrapper::SyncWrapper; + /// + /// let mut wrapped = SyncWrapper::new(42); + /// assert_eq!(wrapped.into_inner(), 42); + /// ``` + #[allow(dead_code)] + pub(crate) fn into_inner(self) -> T { + self.0 + } +} + +// this is safe because the only operations permitted on this data structure require exclusive +// access or ownership +unsafe impl<T: Send> Sync for SyncWrapper<T> {} |