Trait wasmer_types::lib::std::marker::Sync 1.0.0[−][src]
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.
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
.
Implementations on Foreign Types
impl Sync for Argument
impl Sync for FormatSpec
impl Sync for Alignment
impl Sync for Count
Implementors
impl<'_, T, A> Sync for wasmer_types::lib::std::vec::Drain<'_, T, A> where
T: Sync,
A: Sync + Allocator,
1.6.0[src]NonNull
pointers are not Sync
because the data they reference may be aliased.
Auto implementors
impl !Sync for VMExternRef
impl Sync for ExportIndex
impl Sync for ExternType
impl Sync for GlobalInit
impl Sync for ImportIndex
impl Sync for Mutability
impl Sync for Infallible
impl Sync for RecvTimeoutError
impl Sync for TryRecvError
impl Sync for Atomically
impl Sync for CustomSectionIndex
impl Sync for DataInitializerLocation
impl Sync for FunctionIndex
impl Sync for FunctionType
impl Sync for GlobalIndex
impl Sync for GlobalType
impl Sync for LocalFunctionIndex
impl Sync for LocalGlobalIndex
impl Sync for LocalMemoryIndex
impl Sync for LocalTableIndex
impl Sync for MemoryIndex
impl Sync for MemoryType
impl Sync for OwnedDataInitializer
impl Sync for PageCountOutOfRange
impl Sync for SignatureIndex
impl Sync for TableIndex
impl Sync for TableInitializer
impl Sync for BorrowError
impl Sync for BorrowMutError
impl Sync for FromUtf8Error
impl Sync for FromUtf16Error
impl Sync for BarrierWaitResult
impl Sync for WaitTimeoutResult
impl Sync for PhantomPinned
impl<'a, 'b> !Sync for DebugStruct<'a, 'b>
impl<'a, 'b> !Sync for DebugTuple<'a, 'b>
impl<'a, T> Sync for ChunksExact<'a, T> where
T: Sync,
impl<'a, T> Sync for ChunksExactMut<'a, T> where
T: Sync,
impl<'a, T> Sync for RChunksExact<'a, T> where
T: Sync,
impl<'a, T> Sync for RChunksExactMut<'a, T> where
T: Sync,
impl<'a, T> Sync for RChunksMut<'a, T> where
T: Sync,
impl<'a, T, A = NonAtomically> !Sync for MemoryView<'a, T, A>
impl<'a, T, F, A> Sync for DrainFilter<'a, T, F, A> where
A: Sync,
F: Sync,
T: Sync,
impl<'a, T, P> Sync for GroupByMut<'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, const N: usize> !Sync for ArrayWindows<'a, T, N>
impl<'a, T, const N: usize> Sync for ArrayChunks<'a, T, N> where
T: Sync,
impl<'a, T, const N: usize> Sync for ArrayChunksMut<'a, T, N> where
T: Sync,
impl<'data> Sync for DataInitializer<'data>
impl<B, C> Sync for ControlFlow<B, C> where
B: Sync,
C: Sync,
impl<F> Sync for RepeatWith<F> where
F: Sync,
impl<H> Sync for BuildHasherDefault<H> where
H: Sync,
impl<I, U, F> Sync for FlatMap<I, U, F> where
F: Sync,
I: Sync,
<U as IntoIterator>::IntoIter: Sync,
impl<Idx> Sync for RangeInclusive<Idx> where
Idx: Sync,
impl<Idx> Sync for RangeToInclusive<Idx> where
Idx: Sync,
impl<K, V> Sync for BoxedSlice<K, V> where
K: Sync,
V: Sync,
impl<K, V> Sync for PrimaryMap<K, V> where
K: Sync,
V: Sync,
impl<K, V> Sync for SecondaryMap<K, V> where
K: Sync,
V: Sync,
impl<K, V> Sync for ArchivableIndexMap<K, V> where
K: Sync,
V: Sync,
impl<T> Sync for TryLockError<T> where
T: Sync,
impl<T> Sync for TrySendError<T> where
T: Sync,
impl<T> Sync for PackedOption<T> where
T: Sync,
impl<T> Sync for ExportType<T> where
T: Sync,
impl<T> Sync for ImportType<T> where
T: Sync,
impl<T> Sync for Discriminant<T>
impl<T> Sync for SyncSender<T> where
T: Send,
impl<T> Sync for PoisonError<T> where
T: Sync,
impl<T> Sync for MaybeUninit<T> where
T: Sync,
impl<T, F> Sync for Successors<T, F> where
F: Sync,
T: Sync,
impl<T: ?Sized> Sync for ManuallyDrop<T> where
T: Sync,
impl<T: ?Sized> Sync for PhantomData<T> where
T: Sync,
impl<Y, R> Sync for GeneratorState<Y, R> where
R: Sync,
Y: Sync,