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use crate::sync::rwlock::RwLock;
use std::marker::PhantomData;
use std::sync::Arc;
use std::{fmt, mem, ops, ptr};
/// Owned RAII structure used to release the exclusive write access of a lock when
/// dropped.
///
/// This structure is created by [mapping] an [`OwnedRwLockWriteGuard`]. It is a
/// separate type from `OwnedRwLockWriteGuard` to disallow downgrading a mapped
/// guard, since doing so can cause undefined behavior.
///
/// [mapping]: method@crate::sync::OwnedRwLockWriteGuard::map
/// [`OwnedRwLockWriteGuard`]: struct@crate::sync::OwnedRwLockWriteGuard
#[clippy::has_significant_drop]
pub struct OwnedRwLockMappedWriteGuard<T: ?Sized, U: ?Sized = T> {
// When changing the fields in this struct, make sure to update the
// `skip_drop` method.
#[cfg(all(tokio_unstable, feature = "tracing"))]
pub(super) resource_span: tracing::Span,
pub(super) permits_acquired: u32,
pub(super) lock: Arc<RwLock<T>>,
pub(super) data: *mut U,
pub(super) _p: PhantomData<T>,
}
#[allow(dead_code)] // Unused fields are still used in Drop.
struct Inner<T: ?Sized, U: ?Sized> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
permits_acquired: u32,
lock: Arc<RwLock<T>>,
data: *const U,
}
impl<T: ?Sized, U: ?Sized> OwnedRwLockMappedWriteGuard<T, U> {
fn skip_drop(self) -> Inner<T, U> {
let me = mem::ManuallyDrop::new(self);
// SAFETY: This duplicates the values in every field of the guard, then
// forgets the originals, so in the end no value is duplicated.
unsafe {
Inner {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: ptr::read(&me.resource_span),
permits_acquired: me.permits_acquired,
lock: ptr::read(&me.lock),
data: me.data,
}
}
}
/// Makes a new `OwnedRwLockMappedWriteGuard` for a component of the locked
/// data.
///
/// This operation cannot fail as the `OwnedRwLockMappedWriteGuard` passed
/// in already locked the data.
///
/// This is an associated function that needs to be used as
/// `OwnedRwLockWriteGuard::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, OwnedRwLockWriteGuard};
///
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// struct Foo(u32);
///
/// # #[tokio::main]
/// # async fn main() {
/// let lock = Arc::new(RwLock::new(Foo(1)));
///
/// {
/// let lock = Arc::clone(&lock);
/// let mut mapped = OwnedRwLockWriteGuard::map(lock.write_owned().await, |f| &mut f.0);
/// *mapped = 2;
/// }
///
/// assert_eq!(Foo(2), *lock.read().await);
/// # }
/// ```
#[inline]
pub fn map<F, V: ?Sized>(mut this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, V>
where
F: FnOnce(&mut U) -> &mut V,
{
let data = f(&mut *this) as *mut V;
let this = this.skip_drop();
OwnedRwLockMappedWriteGuard {
permits_acquired: this.permits_acquired,
lock: this.lock,
data,
_p: PhantomData,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: this.resource_span,
}
}
/// Attempts to make a new `OwnedRwLockMappedWriteGuard` for a component
/// of the locked data. The original guard is returned if the closure
/// returns `None`.
///
/// This operation cannot fail as the `OwnedRwLockMappedWriteGuard` passed
/// in already locked the data.
///
/// This is an associated function that needs to be
/// used as `OwnedRwLockMappedWriteGuard::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, OwnedRwLockWriteGuard};
///
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// struct Foo(u32);
///
/// # #[tokio::main]
/// # async fn main() {
/// let lock = Arc::new(RwLock::new(Foo(1)));
///
/// {
/// let guard = Arc::clone(&lock).write_owned().await;
/// let mut guard = OwnedRwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
/// *guard = 2;
/// }
///
/// assert_eq!(Foo(2), *lock.read().await);
/// # }
/// ```
#[inline]
pub fn try_map<F, V: ?Sized>(
mut this: Self,
f: F,
) -> Result<OwnedRwLockMappedWriteGuard<T, V>, Self>
where
F: FnOnce(&mut U) -> Option<&mut V>,
{
let data = match f(&mut *this) {
Some(data) => data as *mut V,
None => return Err(this),
};
let this = this.skip_drop();
Ok(OwnedRwLockMappedWriteGuard {
permits_acquired: this.permits_acquired,
lock: this.lock,
data,
_p: PhantomData,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: this.resource_span,
})
}
/// Returns a reference to the original `Arc<RwLock>`.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
/// use tokio::sync::{
/// RwLock,
/// OwnedRwLockWriteGuard,
/// OwnedRwLockMappedWriteGuard,
/// };
///
/// # #[tokio::main]
/// # async fn main() {
/// let lock = Arc::new(RwLock::new(1));
///
/// let guard = lock.clone().write_owned().await;
/// let guard = OwnedRwLockWriteGuard::map(guard, |x| x);
/// assert!(Arc::ptr_eq(&lock, OwnedRwLockMappedWriteGuard::rwlock(&guard)));
/// # }
/// ```
pub fn rwlock(this: &Self) -> &Arc<RwLock<T>> {
&this.lock
}
}
impl<T: ?Sized, U: ?Sized> ops::Deref for OwnedRwLockMappedWriteGuard<T, U> {
type Target = U;
fn deref(&self) -> &U {
unsafe { &*self.data }
}
}
impl<T: ?Sized, U: ?Sized> ops::DerefMut for OwnedRwLockMappedWriteGuard<T, U> {
fn deref_mut(&mut self) -> &mut U {
unsafe { &mut *self.data }
}
}
impl<T: ?Sized, U: ?Sized> fmt::Debug for OwnedRwLockMappedWriteGuard<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 OwnedRwLockMappedWriteGuard<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 OwnedRwLockMappedWriteGuard<T, U> {
fn drop(&mut self) {
self.lock.s.release(self.permits_acquired as usize);
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
write_locked = false,
write_locked.op = "override",
)
});
}
}