Struct hyper::common::sync_wrapper::SyncWrapper

#[repr(transparent)]
pub(crate) struct SyncWrapper<T>(T);

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

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>();

Tuple Fields

0: T

Implementations

impl<T> SyncWrapper<T>

pub(crate) fn new(value: T) -> Self

Creates a new SyncWrapper containing the given value.

Examples

use hyper::common::sync_wrapper::SyncWrapper;

let wrapped = SyncWrapper::new(42);

pub(crate) fn get_mut(&mut self) -> &mut T

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

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 into_inner(self) -> T

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

use hyper::common::sync_wrapper::SyncWrapper;

let mut wrapped = SyncWrapper::new(42);
assert_eq!(wrapped.into_inner(), 42);

Trait Implementations

impl<T: Send> Sync for SyncWrapper<T>