pub unsafe auto trait Send { }Expand description
Types that can be transferred across thread boundaries.
This trait is automatically implemented when the compiler determines it’s appropriate.
An example of a non-Send type is the reference-counting pointer
rc::Rc. If two threads attempt to clone Rcs that point to the same
reference-counted value, they might try to update the reference count at the
same time, which is undefined behavior because Rc doesn’t use atomic
operations. Its cousin sync::Arc does use atomic operations (incurring
some overhead) and thus is Send.
See the Nomicon for more details.
Implementations on Foreign Types
impl Send for Argument
impl Send for FormatSpec
impl Send for Alignment
impl Send for Count
impl<T> Send for Receiver<T> where
T: Send,
impl<T> Send for JoinHandle<T>
impl !Send for ArgsOs
impl<'_, T> !Send for MutexGuard<'_, T> where
T: ?Sized,
impl<T> Send for Sender<T> where
T: Send,
impl !Send for Args
impl<'a> Send for IoSliceMut<'a>
impl<'_, T> !Send for RwLockReadGuard<'_, T> where
T: ?Sized,
impl<T> Send for RwLock<T> where
T: Send + ?Sized,
impl<'a> Send for IoSlice<'a>
impl Send for Once
impl<T> Send for SyncOnceCell<T> where
T: Send,
impl<T> Send for Mutex<T> where
T: Send + ?Sized,
impl<T> Send for SyncSender<T> where
T: Send,
impl<'_, T> !Send for RwLockWriteGuard<'_, T> where
T: ?Sized,
impl<T> Send for Cell<T> where
T: Send + ?Sized,
impl<T> Send for AtomicPtr<T>
impl<'_, T> Send for Iter<'_, T> where
T: Sync,
impl<'_, T> Send for IterMut<'_, T> where
T: Send,
impl<T> !Send for *mut T where
T: ?Sized,
impl<T> !Send for *const T where
T: ?Sized,
impl<T> !Send for NonNull<T> where
T: ?Sized,
NonNull pointers are not Send because the data they reference may be aliased.
impl Send for Waker
impl<'_, T> Send for &'_ mut T where
T: Send + ?Sized,
impl<Dyn> Send for DynMetadata<Dyn> where
Dyn: ?Sized,
impl<T> Send for RefCell<T> where
T: Send + ?Sized,
impl<'_, T> Send for &'_ T where
T: Sync + ?Sized,
impl<T> !Send for Weak<T> where
T: ?Sized,
impl<T> Send for Arc<T> where
T: Sync + Send + ?Sized,
impl<T> Send for Weak<T> where
T: Sync + Send + ?Sized,
impl<T> !Send for Rc<T> where
T: ?Sized,
impl<'a, T, const CAP: usize> Send for Drain<'a, T, CAP> where
T: Send,
impl<T, O> Send for BitVec<T, O> where
T: BitStore,
O: BitOrder,
impl<'a, T, O> Send for Iter<'a, T, O> where
T: BitStore,
O: BitOrder,
&'a mut BitSlice<T, O>: Send,
impl<T, O> Send for IntoIter<T, O> where
T: BitStore + Sync,
O: BitOrder,
impl<T, O> Send for BitSlice<T, O> where
T: BitStore + Sync,
O: BitOrder,
Bit-Slice Thread Safety
This allows bit-slice references to be moved across thread boundaries only when
the underlying T element can tolerate concurrency.
All BitSlice references, shared or exclusive, are only threadsafe if the T
element type is Send, because any given bit-slice reference may only have
partial control of a memory element that is also being shared by a bit-slice
reference on another thread. As such, this is never implemented for Cell<U>,
but always implemented for AtomicU and U for a given unsigned integer type
U.
Atomic integers safely handle concurrent writes, cells do not allow concurrency
at all, so the only missing piece is &mut BitSlice<_, U: Unsigned>. This is
handled by the aliasing system that the mutable splitters employ: a mutable
reference to an unsynchronized bit-slice can only cross threads when no other
handle is able to exist to the elements it governs. Splitting a mutable
bit-slice causes the split halves to change over to either atomics or cells, so
concurrency is either safe or impossible.