# Trait core::marker::Sync 1.0.0 [−] [src]

    #[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 `&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

- [src]
  `impl<T: Sync + ?Sized> Sync for Unique<T>`
- [src]
  `impl<T: ?Sized> !Sync for NonNull<T>`
- [src]
  `impl<T: ?Sized> !Sync for *const T`
- [src]
  `impl<T: ?Sized> !Sync for *mut T`
- [src]
  `impl Sync for AtomicBool`
- [src]
  `impl<T> Sync for AtomicPtr<T>`
- [src]
  `impl Sync for AtomicI8`
- [src]
  `impl Sync for AtomicU8`
- [src]
  `impl Sync for AtomicI16`
- [src]
  `impl Sync for AtomicU16`
- [src]
  `impl Sync for AtomicI32`
- [src]
  `impl Sync for AtomicU32`
- [src]
  `impl Sync for AtomicI64`
- [src]
  `impl Sync for AtomicU64`
- [src]
  `impl Sync for AtomicIsize`
- [src]
  `impl Sync for AtomicUsize`
- [src]
  `impl<T> !Sync for Cell<T>`
- [src]
  `impl<T: ?Sized> !Sync for RefCell<T>`
- [src]
  `impl<T: ?Sized> !Sync for UnsafeCell<T>`
- [src]
  `impl<'a, T: Sync> Sync for core::slice::Iter<'a, T>`
- [src]
  `impl<'a, T: Sync> Sync for core::slice::IterMut<'a, T>`

## Auto implementors

- `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> Sync for ManuallyDrop<T> where
  T: Sync,`
- `impl<T> Sync for NonZero<T> where
  T: Sync,`
- `impl<T: ?Sized> Sync for PhantomData<T> where
  T: Sync,`
- `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<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 Infallible`
- `impl Sync for TypeId`
- `impl Sync for TryFromSliceError`
- `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 Sync for EscapeUnicode`
- `impl Sync for EscapeDefault`
- `impl Sync for EscapeDebug`
- `impl<I> Sync for DecodeUtf8<I> where
  I: Sync,`
- `impl Sync for InvalidSequence`
- `impl<'a> !Sync for PanicInfo<'a>`
- `impl<'a> Sync for Location<'a>`
- `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 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 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 SipHasher`
- `impl Sync for SipHasher13`
- `impl Sync for SipHasher24`
- `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`

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