pub unsafe auto trait Sync { }
Expand description
Types for which it is safe to share references between threads.
This trait is automatically implemented when the compiler determines it’s appropriate.
The precise definition is: a type T
is Sync
if and only if &T
is
Send
. In other words, if there is no possibility of
undefined behavior (including data races) when passing
&T
references between threads.
As one would expect, primitive types like u8
and f64
are all Sync
, and so are simple aggregate types containing them,
like tuples, structs and enums. More examples of basic Sync
types include “immutable” types like &T
, and those with simple
inherited mutability, such as Box<T>
, Vec<T>
and
most other collection types. (Generic parameters need to be Sync
for their container to be Sync
.)
A somewhat surprising consequence of the definition is that &mut T
is Sync
(if T
is Sync
) even though it seems like that might
provide unsynchronized mutation. The trick is that a mutable
reference behind a shared reference (that is, & &mut T
)
becomes read-only, as if it were a & &T
. Hence there is no risk
of a data race.
A shorter overview of how Sync
and Send
relate to referencing:
&T
isSend
if and only ifT
isSync
&mut T
isSend
if and only ifT
isSend
&T
and&mut T
areSync
if and only ifT
isSync
Types that are not Sync
are those that have “interior
mutability” in a non-thread-safe form, such as Cell
and RefCell
. These types allow for mutation of
their contents even through an immutable, shared reference. For
example the set
method on Cell<T>
takes &self
, so it requires
only a shared reference &Cell<T>
. The method performs no
synchronization, thus Cell
cannot be Sync
.
Another example of a non-Sync
type is the reference-counting
pointer Rc
. Given any reference &Rc<T>
, you can clone
a new Rc<T>
, modifying the reference counts in a non-atomic way.
For cases when one does need thread-safe interior mutability,
Rust provides atomic data types, as well as explicit locking via
sync::Mutex
and sync::RwLock
. These types
ensure that any mutation cannot cause data races, hence the types
are Sync
. Likewise, sync::Arc
provides a thread-safe
analogue of Rc
.
Any types with interior mutability must also use the
cell::UnsafeCell
wrapper around the value(s) which
can be mutated through a shared reference. Failing to doing this is
undefined behavior. For example, transmute
-ing
from &T
to &mut T
is invalid.
See the Nomicon for more details about Sync
.
Implementors§
impl !Sync for LocalWaker
impl !Sync for Args
impl !Sync for ArgsOs
impl Sync for CompressedResponse
impl Sync for LazyRequestBody
impl Sync for Collection
impl Sync for kvarn::shutdown::Manager
impl Sync for kvarn::prelude::Bytes
impl Sync for BytesMut
impl Sync for kvarn::prelude::utils::prelude::compact_str::Drain<'_>
impl Sync for AtomicBool
target_has_atomic_load_store="8"
only.impl Sync for AtomicI8
impl Sync for AtomicI16
impl Sync for AtomicI32
impl Sync for AtomicI64
impl Sync for AtomicIsize
impl Sync for AtomicU8
impl Sync for AtomicU16
impl Sync for AtomicU32
impl Sync for AtomicU64
impl Sync for AtomicUsize
impl Sync for Waker
impl Sync for alloc::string::Drain<'_>
impl Sync for AbortHandle
impl Sync for AtomicWaker
impl Sync for AtomicWaker
impl Sync for CCtx<'_>
impl Sync for Collector
impl Sync for DCtx<'_>
impl Sync for EcdsaKeyPair
impl Sync for GuardNoSend
impl Sync for Key
impl Sync for KeyPair
impl Sync for PrivateKey
impl Sync for PublicKey
impl Sync for Scope<'_>
impl Sync for Select<'_>
impl Sync for Unparker
impl<'a> Sync for IoSlice<'a>
impl<'a> Sync for IoSliceMut<'a>
impl<'a> Sync for CDict<'a>
impl<'a> Sync for DDict<'a>
impl<'a> Sync for Notified<'a>
impl<'a, 'b, K, Q, V, S, A> Sync for OccupiedEntryRef<'a, 'b, K, Q, V, S, A>
impl<'a, 'i, K, S, M> Sync for Iter<'i, K, S, M>
impl<'a, 'i, K, V> Sync for Iter<'i, K, V>
impl<'a, 'i, K, V, S, M> Sync for Iter<'i, K, V, S, M>
impl<'a, 'i, K, V, S, M> Sync for IterMut<'i, K, V, S, M>
impl<'a, K, V> Sync for OccupiedEntry<'a, K, V>
impl<'a, K, V> Sync for Ref<'a, K, V>
impl<'a, K, V> Sync for RefMulti<'a, K, V>
impl<'a, K, V> Sync for RefMut<'a, K, V>
impl<'a, K, V> Sync for RefMutMulti<'a, K, V>
impl<'a, K, V> Sync for VacantEntry<'a, K, V>
impl<'a, R, G, T> Sync for MappedReentrantMutexGuard<'a, R, G, T>
impl<'a, R, G, T> Sync for ReentrantMutexGuard<'a, R, G, T>
impl<'a, R, T> Sync for MappedMutexGuard<'a, R, T>
impl<'a, R, T> Sync for MappedRwLockReadGuard<'a, R, T>
impl<'a, R, T> Sync for MappedRwLockWriteGuard<'a, R, T>
impl<'a, R, T> Sync for MutexGuard<'a, R, T>
impl<'a, R, T> Sync for RwLockUpgradableReadGuard<'a, R, T>
impl<'a, T> Sync for kvarn::prelude::utils::prelude::header::Drain<'a, T>where
T: Sync,
impl<'a, T> Sync for kvarn::prelude::utils::prelude::header::Iter<'a, T>where
T: Sync,
impl<'a, T> Sync for kvarn::prelude::utils::prelude::header::IterMut<'a, T>where
T: Sync,
impl<'a, T> Sync for ValueDrain<'a, T>where
T: Sync,
impl<'a, T> Sync for ValueIterMut<'a, T>where
T: Sync,
impl<'a, T> Sync for ArcBorrow<'a, T>
impl<'a, T> Sync for Drain<'a, T>where
T: Sync + Array,
impl<'a, T> Sync for MappedMutexGuard<'a, T>
impl<'a, T> Sync for OnceRef<'a, T>where
T: Sync,
impl<A, B> Sync for ArcUnion<A, B>
impl<Dyn> Sync for DynMetadata<Dyn>where
Dyn: ?Sized,
impl<Fut> Sync for FuturesUnordered<Fut>
impl<Fut> Sync for IntoIter<Fut>
impl<Fut> Sync for IterPinMut<'_, Fut>where
Fut: Sync,
impl<Fut> Sync for IterPinRef<'_, Fut>where
Fut: Sync,
impl<H, T> Sync for ThinArc<H, T>
impl<Id> Sync for DecapsulationKey<Id>where
Id: AlgorithmIdentifier,
impl<Id> Sync for EncapsulationKey<Id>where
Id: AlgorithmIdentifier,
impl<K, S> Sync for OwningIter<K, S>
impl<K, V, S> Sync for Cache<K, V, S>
impl<K, V, S> Sync for OwningIter<K, V, S>
impl<K, V, S> Sync for SegmentedCache<K, V, S>
impl<K, V, S, A> Sync for OccupiedEntry<'_, K, V, S, A>
impl<K, V, S, A> Sync for RawOccupiedEntryMut<'_, K, V, S, A>
impl<R, G> Sync for RawReentrantMutex<R, G>
impl<R, G, T> Sync for ReentrantMutex<R, G, T>
impl<R, T> Sync for Mutex<R, T>
impl<R, T> Sync for RwLock<R, T>
impl<R, T> Sync for RwLockReadGuard<'_, R, T>
impl<R, T> Sync for RwLockWriteGuard<'_, R, T>
impl<S, C> Sync for IoUring<S, C>where
S: EntryMarker,
C: EntryMarker,
impl<T> !Sync for *const Twhere
T: ?Sized,
impl<T> !Sync for *mut Twhere
T: ?Sized,
impl<T> !Sync for Cell<T>where
T: ?Sized,
impl<T> !Sync for kvarn::prelude::utils::prelude::compact_str::core::cell::OnceCell<T>
impl<T> !Sync for RefCell<T>where
T: ?Sized,
impl<T> !Sync for UnsafeCell<T>where
T: ?Sized,
impl<T> !Sync for NonNull<T>where
T: ?Sized,
NonNull
pointers are not Sync
because the data they reference may be aliased.
impl<T> !Sync for std::sync::mpsc::Receiver<T>
impl<T> Sync for kvarn::prelude::Mutex<T>
impl<T> Sync for kvarn::prelude::RwLock<T>
impl<T> Sync for SyncUnsafeCell<T>
impl<T> Sync for NonZero<T>where
T: ZeroablePrimitive + Sync,
impl<T> Sync for ChunksExactMut<'_, T>where
T: Sync,
impl<T> Sync for ChunksMut<'_, T>where
T: Sync,
impl<T> Sync for kvarn::prelude::utils::prelude::compact_str::core::slice::Iter<'_, T>where
T: Sync,
impl<T> Sync for kvarn::prelude::utils::prelude::compact_str::core::slice::IterMut<'_, T>where
T: Sync,
impl<T> Sync for RChunksExactMut<'_, T>where
T: Sync,
impl<T> Sync for RChunksMut<'_, T>where
T: Sync,
impl<T> Sync for AtomicPtr<T>
target_has_atomic_load_store="ptr"
only.impl<T> Sync for Exclusive<T>where
T: ?Sized,
impl<T> Sync for ThinBox<T>
ThinBox<T>
is Sync
if T
is Sync
because the data is owned.