Auto merge of #45267 - oconnor663:rwlock_send, r=alexcrichton

bors · bors · commit 31bbe57c7911 · 2017-11-01T04:32:15.000Z
remove the `T: Sync` requirement for `RwLock<T>: Send` That requirement makes sense for containers like `Arc` that don't uniquely own their contents, but `RwLock` is not one of those. This restriction was added in 380d23b, but it's not clear why. @hniksic and I [were discussing this on reddit](https://www.reddit.com/r/rust/comments/763o7r/blog_posts_introducing_lockfree_rust_comparing/dobcvbm/). I might be totally wrong about this change being sound, but I'm super curious to find out :)
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
@@ -82,7 +82,7 @@ pub struct RwLock<T: ?Sized> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Send + Sync> Send for RwLock<T> {}
+unsafe impl<T: ?Sized + Send> Send for RwLock<T> {}
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
 

Original file line number	Diff line number	Diff line change
`@@ -82,7 +82,7 @@ pub struct RwLock<T: ?Sized> {`
`82`	`82`	`}`
`83`	`83`
`84`	`84`	`#[stable(feature = "rust1", since = "1.0.0")]`
`85`		`-unsafe impl<T: ?Sized + Send + Sync> Send for RwLock<T> {}`
	`85`	`+unsafe impl<T: ?Sized + Send> Send for RwLock<T> {}`
`86`	`86`	`#[stable(feature = "rust1", since = "1.0.0")]`
`87`	`87`	`unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}`
`88`	`88`