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Rollup merge of #52759 - stjepang:impl-send-sync-for-joinhandle, r=TimNN

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Impl Send & Sync for JoinHandle

This is just a cosmetic change - it slightly relaxes and clarifies the public API without effectively promising any new guarantees.

Currently we have [these auto trait implementations](https://doc.rust-lang.org/nightly/std/thread/struct.JoinHandle.html#synthetic-implementations):

```rust
impl<T: Send> Send for JoinHandle<T> {}
impl<T: Sync> Sync for JoinHandle<T> {}
```

Bound `T: Send` doesn't make much sense because `JoinHandle<T>` can be created only when `T: Send`. Note that [`JoinHandle::<T>::join`](https://doc.rust-lang.org/nightly/std/thread/struct.JoinHandle.html#method.join) doesn't require `T: Send` so why should the `Send` impl?

And the `Sync` impl doesn't need `T: Sync` because `JoinHandle<T>` cannot even share `T` - it can only send it to the thread that calls `join`.
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kennytm 2018-07-28 16:24:59 +08:00 committed by GitHub
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5
src/libstd/thread/mod.rs
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@ -1276,6 +1276,11 @@ impl<T> JoinInner<T> {
#[stable(feature = "rust1", since = "1.0.0")]
pub struct JoinHandle<T>(JoinInner<T>);
#[stable(feature = "joinhandle_impl_send_sync", since = "1.29.0")]
unsafe impl<T> Send for JoinHandle<T> {}
#[stable(feature = "joinhandle_impl_send_sync", since = "1.29.0")]
unsafe impl<T> Sync for JoinHandle<T> {}
impl<T> JoinHandle<T> {
/// Extracts a handle to the underlying thread.
///