1 files changed, 170 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs b/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs
new file mode 100644
index 0000000000..27b71bd988
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs
@@ -0,0 +1,170 @@
+use crate::sync::rwlock::RwLock;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::mem::ManuallyDrop;
+use std::ops;
+use std::sync::Arc;
+
+/// Owned RAII structure used to release the shared read access of a lock when
+/// dropped.
+///
+/// This structure is created by the [`read_owned`] method on
+/// [`RwLock`].
+///
+/// [`read_owned`]: method@crate::sync::RwLock::read_owned
+/// [`RwLock`]: struct@crate::sync::RwLock
+pub struct OwnedRwLockReadGuard<T: ?Sized, U: ?Sized = T> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    // ManuallyDrop allows us to destructure into this field without running the destructor.
+    pub(super) lock: ManuallyDrop<Arc<RwLock<T>>>,
+    pub(super) data: *const U,
+    pub(super) _p: PhantomData<T>,
+}
+
+impl<T: ?Sized, U: ?Sized> OwnedRwLockReadGuard<T, U> {
+    /// Makes a new `OwnedRwLockReadGuard` for a component of the locked data.
+    /// This operation cannot fail as the `OwnedRwLockReadGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `OwnedRwLockReadGuard::map(...)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// let guard = lock.read_owned().await;
+    /// let guard = OwnedRwLockReadGuard::map(guard, |f| &f.0);
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, V: ?Sized>(mut this: Self, f: F) -> OwnedRwLockReadGuard<T, V>
+    where
+        F: FnOnce(&U) -> &V,
+    {
+        let data = f(&*this) as *const V;
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        OwnedRwLockReadGuard {
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make a new [`OwnedRwLockReadGuard`] for a component of the
+    /// locked data. The original guard is returned if the closure returns
+    /// `None`.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockReadGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `OwnedRwLockReadGuard::try_map(..)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// let guard = lock.read_owned().await;
+    /// let guard = OwnedRwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, V: ?Sized>(mut this: Self, f: F) -> Result<OwnedRwLockReadGuard<T, V>, Self>
+    where
+        F: FnOnce(&U) -> Option<&V>,
+    {
+        let data = match f(&*this) {
+            Some(data) => data as *const V,
+            None => return Err(this),
+        };
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(OwnedRwLockReadGuard {
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> ops::Deref for OwnedRwLockReadGuard<T, U> {
+    type Target = U;
+
+    fn deref(&self) -> &U {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Debug for OwnedRwLockReadGuard<T, U>
+where
+    U: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Display for OwnedRwLockReadGuard<T, U>
+where
+    U: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Drop for OwnedRwLockReadGuard<T, U> {
+    fn drop(&mut self) {
+        self.lock.s.release(1);
+        unsafe { ManuallyDrop::drop(&mut self.lock) };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "sub",
+            )
+        });
+    }
+}