Trait core::marker::Sync

#[lang = "sync"]
pub unsafe auto trait Sync { }

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.

Types that are not Sync are those that have "interior mutability" in a non-thread-safe form, such as cell::Cell and cell::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::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<T: ?Sized> !Sync for NonNull<T>

NonNull pointers are not Sync because the data they reference may be aliased.

impl<T: ?Sized> !Sync for *const T

impl<T: ?Sized> !Sync for *mut T

impl Sync for AtomicBool

impl<T> Sync for AtomicPtr<T>

impl Sync for AtomicI8

impl Sync for AtomicU8

impl Sync for AtomicI16

impl Sync for AtomicU16

impl Sync for AtomicI32

impl Sync for AtomicU32

impl Sync for AtomicI64

impl Sync for AtomicU64

impl Sync for AtomicIsize

impl Sync for AtomicUsize

impl<T: ?Sized> !Sync for Cell<T>

impl<T: ?Sized> !Sync for RefCell<T>

impl<T: ?Sized> !Sync for UnsafeCell<T>

impl<'a, T: Sync> Sync for core::slice::Iter<'a, T>

impl<'a, T: Sync> Sync for core::slice::IterMut<'a, T>

impl Sync for Waker

impl !Sync for LocalWaker

Auto implementors

impl Sync for NonZeroU8

impl Sync for NonZeroU16

impl Sync for NonZeroU32

impl Sync for NonZeroU64

impl Sync for NonZeroU128

impl Sync for NonZeroUsize

impl<T> Sync for Wrapping<T> where     T: Sync,

impl Sync for TryFromIntError

impl Sync for ParseIntError

impl Sync for ParseFloatError

impl Sync for FpCategory

impl<T> Sync for Discriminant<T>

impl<T: ?Sized> Sync for ManuallyDrop<T> where     T: Sync,

impl<T: ?Sized> Sync for PhantomData<T> where     T: Sync,

impl Sync for Pinned

impl<Idx> Sync for Range<Idx> where     Idx: Sync,

impl<Idx> Sync for RangeFrom<Idx> where     Idx: Sync,

impl Sync for RangeFull

impl<Idx> Sync for RangeTo<Idx> where     Idx: Sync,

impl<Idx> Sync for RangeInclusive<Idx> where     Idx: Sync,

impl<Idx> Sync for RangeToInclusive<Idx> where     Idx: Sync,

impl<T> Sync for Bound<T> where     T: Sync,

impl<Y, R> Sync for GeneratorState<Y, R> where     R: Sync,     Y: Sync,

impl<T> Sync for Reverse<T> where     T: Sync,

impl Sync for core::cmp::Ordering

impl Sync for TypeId

impl Sync for TryFromSliceError

impl Sync for core::ascii::EscapeDefault

impl Sync for core::sync::atomic::Ordering

impl Sync for BorrowError

impl Sync for BorrowMutError

impl<'b, T> !Sync for Ref<'b, T>

impl<'b, T> !Sync for RefMut<'b, T>

impl Sync for ParseCharError

impl Sync for CharTryFromError

impl<I> Sync for DecodeUtf16<I> where     I: Sync,

impl Sync for DecodeUtf16Error

impl Sync for UnicodeVersion

impl Sync for EscapeUnicode

impl Sync for core::char::EscapeDefault

impl Sync for EscapeDebug

impl Sync for ToLowercase

impl Sync for ToUppercase

impl<'a> !Sync for PanicInfo<'a>

impl<'a> Sync for Location<'a>

impl<'a, T: ?Sized> Sync for PinMut<'a, T> where     T: Sync,

impl<A> Sync for Repeat<A> where     A: Sync,

impl<F> Sync for RepeatWith<F> where     F: Sync,

impl<T> Sync for Empty<T> where     T: Sync,

impl<T> Sync for Once<T> where     T: Sync,

impl<T> Sync for Rev<T> where     T: Sync,

impl<I> Sync for Cloned<I> where     I: Sync,

impl<I> Sync for Cycle<I> where     I: Sync,

impl<I> Sync for StepBy<I> where     I: Sync,

impl<A, B> Sync for Chain<A, B> where     A: Sync,     B: Sync,

impl<A, B> Sync for Zip<A, B> where     A: Sync,     B: Sync,

impl<I, F> Sync for Map<I, F> where     F: Sync,     I: Sync,

impl<I, P> Sync for Filter<I, P> where     I: Sync,     P: Sync,

impl<I, F> Sync for FilterMap<I, F> where     F: Sync,     I: Sync,

impl<I> Sync for Enumerate<I> where     I: Sync,

impl<I> Sync for Peekable<I> where     I: Sync,     <I as Iterator>::Item: Sync,

impl<I, P> Sync for SkipWhile<I, P> where     I: Sync,     P: Sync,

impl<I, P> Sync for TakeWhile<I, P> where     I: Sync,     P: Sync,

impl<I> Sync for Skip<I> where     I: Sync,

impl<I> Sync for Take<I> where     I: Sync,

impl<I, St, F> Sync for Scan<I, St, F> where     F: Sync,     I: Sync,     St: Sync,

impl<I, U, F> Sync for FlatMap<I, U, F> where     F: Sync,     I: Sync,     <U as IntoIterator>::IntoIter: Sync,

impl<I> Sync for Flatten<I> where     I: Sync,     <<I as Iterator>::Item as IntoIterator>::IntoIter: Sync,

impl<I> Sync for Fuse<I> where     I: Sync,

impl<I, F> Sync for Inspect<I, F> where     F: Sync,     I: Sync,

impl<'a, A> Sync for core::option::Iter<'a, A> where     A: Sync,

impl<'a, A> Sync for core::option::IterMut<'a, A> where     A: Sync,

impl<A> Sync for core::option::IntoIter<A> where     A: Sync,

impl Sync for NoneError

impl<T> Sync for Option<T> where     T: Sync,

impl !Sync for TraitObject

impl<'a, T> Sync for core::result::Iter<'a, T> where     T: Sync,

impl<'a, T> Sync for core::result::IterMut<'a, T> where     T: Sync,

impl<T> Sync for core::result::IntoIter<T> where     T: Sync,

impl<T, E> Sync for Result<T, E> where     E: Sync,     T: Sync,

impl<'a, T, P> Sync for core::slice::Split<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for SplitMut<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for core::slice::RSplit<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for RSplitMut<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for core::slice::SplitN<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for core::slice::RSplitN<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for SplitNMut<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T, P> Sync for RSplitNMut<'a, T, P> where     P: Sync,     T: Sync,

impl<'a, T> Sync for Windows<'a, T> where     T: Sync,

impl<'a, T> Sync for Chunks<'a, T> where     T: Sync,

impl<'a, T> Sync for ChunksMut<'a, T> where     T: Sync,

impl<'a, T> Sync for ExactChunks<'a, T> where     T: Sync,

impl<'a, T> Sync for ExactChunksMut<'a, T> where     T: Sync,

impl Sync for ParseBoolError

impl Sync for Utf8Error

impl<'a> Sync for Chars<'a>

impl<'a> Sync for CharIndices<'a>

impl<'a> Sync for Bytes<'a>

impl<'a, P> Sync for core::str::Split<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for core::str::RSplit<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for SplitTerminator<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for RSplitTerminator<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for core::str::SplitN<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for core::str::RSplitN<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for MatchIndices<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for RMatchIndices<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for Matches<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a, P> Sync for RMatches<'a, P> where     <P as Pattern<'a>>::Searcher: Sync,

impl<'a> Sync for Lines<'a>

impl<'a> Sync for LinesAny<'a>

impl<'a> Sync for SplitWhitespace<'a>

impl<'a> Sync for SplitAsciiWhitespace<'a>

impl<'a> Sync for EncodeUtf16<'a>

impl<'a> Sync for CharSearcher<'a>

impl<'a, 'b> Sync for CharSliceSearcher<'a, 'b>

impl<'a, F> Sync for CharPredicateSearcher<'a, F> where     F: Sync,

impl<'a, 'b> Sync for StrSearcher<'a, 'b>

impl Sync for SearchStep

impl Sync for Utf8Lossy

impl<'a> Sync for Utf8LossyChunksIter<'a>

impl<'a> Sync for Utf8LossyChunk<'a>

impl Sync for SipHasher

impl<H> Sync for BuildHasherDefault<H> where     H: Sync,

impl<'a, 'b> !Sync for DebugStruct<'a, 'b>

impl<'a, 'b> !Sync for DebugTuple<'a, 'b>

impl<'a, 'b> !Sync for DebugSet<'a, 'b>

impl<'a, 'b> !Sync for DebugList<'a, 'b>

impl<'a, 'b> !Sync for DebugMap<'a, 'b>

impl Sync for Error

impl<'a> !Sync for Formatter<'a>

impl<'a> !Sync for Arguments<'a>

impl Sync for Alignment

impl Sync for Duration

impl<'a, T> !Sync for FutureObj<'a, T>

impl<'a, T> !Sync for LocalFutureObj<'a, T>

impl<'a> !Sync for Context<'a>

impl Sync for SpawnErrorKind

impl !Sync for SpawnObjError

impl !Sync for SpawnLocalObjError

impl<T> Sync for Poll<T> where     T: Sync,

impl !Sync for Excess

impl Sync for Layout

impl Sync for LayoutErr

impl Sync for AllocErr

impl Sync for CannotReallocInPlace

impl Sync for __m64

impl Sync for __m128i

impl Sync for __m128

impl Sync for __m128d

impl Sync for __m256i

impl Sync for __m256

impl Sync for __m256d

impl Sync for CpuidResult

impl Sync for float64x1_t

impl Sync for float64x2_t

impl Sync for int8x4_t

impl Sync for uint8x4_t

impl Sync for int16x2_t

impl Sync for uint16x2_t

impl Sync for int8x8_t

impl Sync for uint8x8_t

impl Sync for poly8x8_t

impl Sync for int16x4_t

impl Sync for uint16x4_t

impl Sync for poly16x4_t

impl Sync for int32x2_t

impl Sync for uint32x2_t

impl Sync for float32x2_t

impl Sync for int64x1_t

impl Sync for uint64x1_t

impl Sync for int8x16_t

impl Sync for uint8x16_t

impl Sync for poly8x16_t

impl Sync for int16x8_t

impl Sync for uint16x8_t

impl Sync for poly16x8_t

impl Sync for int32x4_t

impl Sync for uint32x4_t

impl Sync for float32x4_t

impl Sync for int64x2_t

impl Sync for uint64x2_t

impl Sync for i8x16

impl Sync for vector_signed_long

impl Sync for vector_unsigned_long

impl Sync for vector_bool_long

impl Sync for vector_double