# 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 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>` | [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>` | [src]

- `impl Sync for Waker` | [src]

- `impl !Sync for LocalWaker` | [src]

## 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<'a, T: ?Sized> Sync for PinMut<'a, T> where T: Sync,` |

- `impl<T> 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<I> Sync for DecodeUtf8<I> where I: Sync,` |

- `impl Sync for InvalidSequence` |

- `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> 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 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> !Sync for Context<'a>` |

- `impl !Sync for TaskObj` |

- `impl Sync for SpawnErrorKind` |

- `impl !Sync for SpawnObjError` |

- `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 CollectionAllocErr` |

- `impl Sync for i8x16` |

- `impl Sync for u8x16` |

- `impl Sync for m8x16` |

- `impl Sync for i16x8` |

- `impl Sync for u16x8` |

- `impl Sync for m16x8` |

- `impl Sync for i32x4` |

- `impl Sync for u32x4` |

- `impl Sync for f32x4` |

- `impl Sync for m32x4` |

- `impl Sync for i64x2` |

- `impl Sync for u64x2` |

- `impl Sync for f64x2` |

- `impl Sync for m64x2` |

- `impl Sync for i8x2` |

- `impl Sync for u8x2` |

- `impl Sync for m8x2` |

- `impl Sync for i8x32` |

- `impl Sync for u8x32` |

- `impl Sync for m8x32` |

- `impl Sync for i16x16` |

- `impl Sync for u16x16` |

- `impl Sync for m16x16` |

- `impl Sync for i32x8` |

- `impl Sync for u32x8` |

- `impl Sync for f32x8` |

- `impl Sync for m32x8` |

- `impl Sync for i64x4` |

- `impl Sync for u64x4` |

- `impl Sync for f64x4` |

- `impl Sync for m64x4` |

- `impl Sync for i16x2` |

- `impl Sync for u16x2` |

- `impl Sync for m16x2` |

- `impl Sync for i8x4` |

- `impl Sync for u8x4` |

- `impl Sync for m8x4` |

- `impl Sync for i8x64` |

- `impl Sync for u8x64` |

- `impl Sync for m1x64` |

- `impl Sync for i16x32` |

- `impl Sync for u16x32` |

- `impl Sync for m1x32` |

- `impl Sync for i32x16` |

- `impl Sync for u32x16` |

- `impl Sync for f32x16` |

- `impl Sync for m1x16` |

- `impl Sync for i64x8` |

- `impl Sync for u64x8` |

- `impl Sync for f64x8` |

- `impl Sync for m1x8` |

- `impl Sync for i8x8` |

- `impl Sync for u8x8` |

- `impl Sync for m8x8` |

- `impl Sync for i16x4` |

- `impl Sync for u16x4` |

- `impl Sync for m16x4` |

- `impl Sync for i32x2` |

- `impl Sync for u32x2` |

- `impl Sync for m32x2` |

- `impl Sync for f32x2` |

- `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 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` |

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