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use crate::sync::rwlock::owned_read_guard::OwnedRwLockReadGuard;
use crate::sync::rwlock::owned_write_guard_mapped::OwnedRwLockMappedWriteGuard;
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 the [`write_owned`] method
/// on [`RwLock`].
///
/// [`write_owned`]: method@crate::sync::RwLock::write_owned
/// [`RwLock`]: struct@crate::sync::RwLock
#[clippy::has_significant_drop]
pub struct OwnedRwLockWriteGuard<T: ?Sized> {
// 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 T,
pub(super) _p: PhantomData<T>,
}
#[allow(dead_code)] // Unused fields are still used in Drop.
struct Inner<T: ?Sized> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
permits_acquired: u32,
lock: Arc<RwLock<T>>,
data: *const T,
}
impl<T: ?Sized> OwnedRwLockWriteGuard<T> {
fn skip_drop(self) -> Inner<T> {
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 `OwnedRwLockWriteGuard` 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, U: ?Sized>(mut this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, U>
where
F: FnOnce(&mut T) -> &mut U,
{
let data = f(&mut *this) as *mut U;
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,
}
}
/// Makes a new [`OwnedRwLockReadGuard`] for a component of the locked data.
///
/// This operation cannot fail as the `OwnedRwLockWriteGuard` passed in already
/// locked the data.
///
/// This is an associated function that needs to be used as
/// `OwnedRwLockWriteGuard::downgrade_map(..)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
///
/// Inside of `f`, you retain exclusive access to the data, despite only being given a `&T`. Handing out a
/// `&mut T` would result in unsoundness, as you could use interior mutability.
///
/// # 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 mapped = OwnedRwLockWriteGuard::downgrade_map(guard, |f| &f.0);
/// let foo = lock.read_owned().await;
/// assert_eq!(foo.0, *mapped);
/// # }
/// ```
#[inline]
pub fn downgrade_map<F, U: ?Sized>(this: Self, f: F) -> OwnedRwLockReadGuard<T, U>
where
F: FnOnce(&T) -> &U,
{
let data = f(&*this) as *const U;
let this = this.skip_drop();
let guard = OwnedRwLockReadGuard {
lock: this.lock,
data,
_p: PhantomData,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: this.resource_span,
};
// Release all but one of the permits held by the write guard
let to_release = (this.permits_acquired - 1) as usize;
guard.lock.s.release(to_release);
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
write_locked = false,
write_locked.op = "override",
)
});
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
current_readers = 1,
current_readers.op = "add",
)
});
guard
}
/// 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 `OwnedRwLockWriteGuard` passed in
/// already locked the data.
///
/// This is an associated function that needs to be
/// used as `OwnedRwLockWriteGuard::try_map(...)`. A method would interfere
/// with methods of the same name on the contents of the locked data.
///
/// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
///
/// # 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, U: ?Sized>(
mut this: Self,
f: F,
) -> Result<OwnedRwLockMappedWriteGuard<T, U>, Self>
where
F: FnOnce(&mut T) -> Option<&mut U>,
{
let data = match f(&mut *this) {
Some(data) => data as *mut U,
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,
})
}
/// 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 `OwnedRwLockWriteGuard` passed in already
/// locked the data.
///
/// This is an associated function that needs to be
/// used as `OwnedRwLockWriteGuard::try_downgrade_map(...)`. A method would interfere with
/// methods of the same name on the contents of the locked data.
///
/// Inside of `f`, you retain exclusive access to the data, despite only being given a `&T`. Handing out a
/// `&mut T` would result in unsoundness, as you could use interior mutability.
///
/// If this function returns `Err(...)`, the lock is never unlocked nor downgraded.
///
/// # 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 guard = OwnedRwLockWriteGuard::try_downgrade_map(guard, |f| Some(&f.0)).expect("should not fail");
/// let foo = lock.read_owned().await;
/// assert_eq!(foo.0, *guard);
/// # }
/// ```
#[inline]
pub fn try_downgrade_map<F, U: ?Sized>(
this: Self,
f: F,
) -> Result<OwnedRwLockReadGuard<T, U>, Self>
where
F: FnOnce(&T) -> Option<&U>,
{
let data = match f(&*this) {
Some(data) => data as *const U,
None => return Err(this),
};
let this = this.skip_drop();
let guard = OwnedRwLockReadGuard {
lock: this.lock,
data,
_p: PhantomData,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: this.resource_span,
};
// Release all but one of the permits held by the write guard
let to_release = (this.permits_acquired - 1) as usize;
guard.lock.s.release(to_release);
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
write_locked = false,
write_locked.op = "override",
)
});
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
current_readers = 1,
current_readers.op = "add",
)
});
Ok(guard)
}
/// Converts this `OwnedRwLockWriteGuard` into an
/// `OwnedRwLockMappedWriteGuard`. This method can be used to store a
/// non-mapped guard in a struct field that expects a mapped guard.
///
/// This is equivalent to calling `OwnedRwLockWriteGuard::map(guard, |me| me)`.
#[inline]
pub fn into_mapped(this: Self) -> OwnedRwLockMappedWriteGuard<T> {
Self::map(this, |me| me)
}
/// Atomically downgrades a write lock into a read lock without allowing
/// any writers to take exclusive access of the lock in the meantime.
///
/// **Note:** This won't *necessarily* allow any additional readers to acquire
/// locks, since [`RwLock`] is fair and it is possible that a writer is next
/// in line.
///
/// Returns an RAII guard which will drop this read access of the `RwLock`
/// when dropped.
///
/// # Examples
///
/// ```
/// # use tokio::sync::RwLock;
/// # use std::sync::Arc;
/// #
/// # #[tokio::main]
/// # async fn main() {
/// let lock = Arc::new(RwLock::new(1));
///
/// let n = lock.clone().write_owned().await;
///
/// let cloned_lock = lock.clone();
/// let handle = tokio::spawn(async move {
/// *cloned_lock.write_owned().await = 2;
/// });
///
/// let n = n.downgrade();
/// assert_eq!(*n, 1, "downgrade is atomic");
///
/// drop(n);
/// handle.await.unwrap();
/// assert_eq!(*lock.read().await, 2, "second writer obtained write lock");
/// # }
/// ```
pub fn downgrade(self) -> OwnedRwLockReadGuard<T> {
let this = self.skip_drop();
let guard = OwnedRwLockReadGuard {
lock: this.lock,
data: this.data,
_p: PhantomData,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: this.resource_span,
};
// Release all but one of the permits held by the write guard
let to_release = (this.permits_acquired - 1) as usize;
guard.lock.s.release(to_release);
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
write_locked = false,
write_locked.op = "override",
)
});
#[cfg(all(tokio_unstable, feature = "tracing"))]
guard.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
current_readers = 1,
current_readers.op = "add",
)
});
guard
}
}
impl<T: ?Sized> ops::Deref for OwnedRwLockWriteGuard<T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.data }
}
}
impl<T: ?Sized> ops::DerefMut for OwnedRwLockWriteGuard<T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.data }
}
}
impl<T: ?Sized> fmt::Debug for OwnedRwLockWriteGuard<T>
where
T: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
impl<T: ?Sized> fmt::Display for OwnedRwLockWriteGuard<T>
where
T: fmt::Display,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
impl<T: ?Sized> Drop for OwnedRwLockWriteGuard<T> {
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",
)
});
}
}