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/*
* 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>();
/// ```
///
#[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.
///
///
/// # 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.
///
///
/// # 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> {}