Avoid `thread::panicking()` in non-poisoning methods of `Mutex` and `RwLock`

`Mutex::lock()` and `RwLock::write()` are poison-guarded against panics,
in that they set the poison flag if a panic occurs while they're locked.
But if we're already in a panic (`thread::panicking()`), they leave the
poison flag alone.

That check is a bit of a waste for methods that never set the poison
flag though, namely `get_mut()`, `into_inner()`, and `RwLock::read()`.
These use-cases are now split to avoid that unnecessary call.

1 files changed, 4 insertions, 4 deletions

diff --git a/library/std/src/sync/rwlock.rs b/library/std/src/sync/rwlock.rs
index 4f1b4bedaab..9517e7e1f03 100644
--- a/library/std/src/sync/rwlock.rs
+++ b/library/std/src/sync/rwlock.rs
@@ -434,7 +434,7 @@ impl<T: ?Sized> RwLock<T> {
         T: Sized,
     {
         let data = self.data.into_inner();
-        poison::map_result(self.poison.borrow(), |_| data)
+        poison::map_result(self.poison.borrow(), |()| data)
     }
 
     /// Returns a mutable reference to the underlying data.
@@ -461,7 +461,7 @@ impl<T: ?Sized> RwLock<T> {
     #[stable(feature = "rwlock_get_mut", since = "1.6.0")]
     pub fn get_mut(&mut self) -> LockResult<&mut T> {
         let data = self.data.get_mut();
-        poison::map_result(self.poison.borrow(), |_| data)
+        poison::map_result(self.poison.borrow(), |()| data)
     }
 }
 
@@ -510,13 +510,13 @@ impl<T> From<T> for RwLock<T> {
 
 impl<'rwlock, T: ?Sized> RwLockReadGuard<'rwlock, T> {
     unsafe fn new(lock: &'rwlock RwLock<T>) -> LockResult<RwLockReadGuard<'rwlock, T>> {
-        poison::map_result(lock.poison.borrow(), |_| RwLockReadGuard { lock })
+        poison::map_result(lock.poison.borrow(), |()| RwLockReadGuard { lock })
     }
 }
 
 impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
     unsafe fn new(lock: &'rwlock RwLock<T>) -> LockResult<RwLockWriteGuard<'rwlock, T>> {
-        poison::map_result(lock.poison.borrow(), |guard| RwLockWriteGuard { lock, poison: guard })
+        poison::map_result(lock.poison.guard(), |guard| RwLockWriteGuard { lock, poison: guard })
     }
 }