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Change MappedRwLock types to allow owned data
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@eira-fransham
eira-fransham committed Aug 24, 2021
1 parent cc4858e commit 5dda2cd
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Showing 3 changed files with 196 additions and 132 deletions.
4 changes: 2 additions & 2 deletions core/src/spinwait.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,14 +6,14 @@
// copied, modified, or distributed except according to those terms.

use crate::thread_parker;
use std::sync::atomic::spin_loop_hint;
use std::hint;

// Wastes some CPU time for the given number of iterations,
// using a hint to indicate to the CPU that we are spinning.
#[inline]
fn cpu_relax(iterations: u32) {
for _ in 0..iterations {
spin_loop_hint()
hint::spin_loop()
}
}

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98 changes: 53 additions & 45 deletions lock_api/src/mutex.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -499,7 +499,7 @@ impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
s.mutex
}

/// Makes a new `OwnedMappedMutexGuard` for a component of the locked data.
/// Makes a new `MappedMutexGuard` for a component of the locked data.
///
/// This operation cannot fail as the `MutexGuard` passed
/// in already locked the mutex.
Expand All @@ -508,7 +508,7 @@ impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
/// used as `MutexGuard::map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn map<U: 'a, F>(s: Self, f: F) -> OwnedMappedMutexGuard<'a, R, U>
pub fn map<U, F>(s: Self, f: F) -> MappedMutexGuard<'a, R, U>
where
F: FnOnce(&'a mut T) -> U,
{
Expand All @@ -517,14 +517,14 @@ impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
mem::forget(s);

let data = f(data);
OwnedMappedMutexGuard {
MappedMutexGuard {
raw,
data,
marker: PhantomData,
}
}

/// Attempts to make a new `OwnedMappedMutexGuard` for a component of the
/// Attempts to make a new `MappedMutexGuard` for a component of the
/// locked data. The original guard is returned if the closure returns `None`.
///
/// This operation cannot fail as the `MutexGuard` passed
Expand All @@ -534,21 +534,23 @@ impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
/// used as `MutexGuard::try_map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn try_map<U: 'a, F>(s: Self, f: F) -> Result<OwnedMappedMutexGuard<'a, R, U>, Self>
pub fn try_map<U, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
where
F: FnOnce(&'a mut T) -> Option<U>,
{
let s = mem::ManuallyDrop::new(s);

let raw = &s.mutex.raw;
let data = unsafe { &mut *s.mutex.data.get() };

let data = match f(data) {
Some(data) => data,
None => return Err(mem::ManuallyDrop::into_inner(s)),
None => return Err(s),
};

Ok(OwnedMappedMutexGuard {
// We use `mem::forget` instead of `ManuallyDrop` because we want to drop `self` if
// `f` panicks. This is safe, as `self` must outlive the `&'a mut T` reference.
mem::forget(s);

Ok(MappedMutexGuard {
raw,
data,
marker: PhantomData,
Expand Down Expand Up @@ -669,8 +671,8 @@ impl<'a, R: RawMutex + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display for Mutex
unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> StableAddress for MutexGuard<'a, R, T> {}

/// An RAII mutex guard returned by the `Arc` locking operations on `Mutex`.
///
/// This is similar to the `MutexGuard` struct, except instead of using a reference to unlock the `Mutex` it
///
/// This is similar to the `MutexGuard` struct, except instead of using a reference to unlock the `Mutex` it
/// uses an `Arc<Mutex>`. This has several advantages, most notably that it has an `'static` lifetime.
#[cfg(feature = "arc_lock")]
#[must_use = "if unused the Mutex will immediately unlock"]
Expand Down Expand Up @@ -719,7 +721,7 @@ impl<R: RawMutexFair, T: ?Sized> ArcMutexGuard<R, T> {

// SAFETY: make sure the Arc gets it reference decremented
let mut s = ManuallyDrop::new(s);
unsafe { ptr::drop_in_place(&mut s.mutex) };
unsafe { ptr::drop_in_place(&mut s.mutex) };
}

/// Temporarily unlocks the mutex to execute the given function.
Expand Down Expand Up @@ -781,93 +783,99 @@ impl<R: RawMutex, T: ?Sized> Drop for ArcMutexGuard<R, T> {
/// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
/// subfield of the protected data.
///
/// The main difference between `OwnedMappedMutexGuard` and `MutexGuard` is that the
/// The main difference between `MappedMutexGuard` and `MutexGuard` is that the
/// former doesn't support temporarily unlocking and re-locking, since that
/// could introduce soundness issues if the locked object is modified by another
/// thread.
#[must_use = "if unused the Mutex will immediately unlock"]
pub struct OwnedMappedMutexGuard<'a, R: RawMutex, T: 'a> {
pub struct MappedMutexGuard<'a, R: RawMutex, T: ?Sized + 'a> {
raw: &'a R,
// We use `&'a mut` to make this type invariant over `'a`
marker: PhantomData<&'a mut ()>,
// `data` at the end so we can cast `MappedMutexGuard<'_, _, [T; N]>` to `MappedMutexGuard<'_, _, [T]>`.
data: T,
}

/// An `OwnedMappedMutexGuard` that contains a mutable pointer (for backwards compatibility)
pub type MappedMutexGuard<'a, R, T> = OwnedMappedMutexGuard<'a, R, &'a mut T>;

unsafe impl<'a, R: RawMutex + Sync + 'a, T: Sync + 'a> Sync for OwnedMappedMutexGuard<'a, R, T> {}
unsafe impl<'a, R: RawMutex + 'a, T: Send + 'a> Send for OwnedMappedMutexGuard<'a, R, T> where
unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync
for MappedMutexGuard<'a, R, T>
{
}
unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + Send + 'a> Send for MappedMutexGuard<'a, R, T> where
R::GuardMarker: Send
{
}

impl<'a, R: RawMutex + 'a, T: 'a> OwnedMappedMutexGuard<'a, R, T> {
/// Makes a new `OwnedMappedMutexGuard` for a component of the locked data.
impl<'a, R: RawMutex + 'a, T: 'a> MappedMutexGuard<'a, R, T> {
/// Makes a new `MappedMutexGuard` for a component of the locked data.
///
/// This operation cannot fail as the `OwnedMappedMutexGuard` passed
/// This operation cannot fail as the `MappedMutexGuard` passed
/// in already locked the mutex.
///
/// This is an associated function that needs to be
/// used as `OwnedMappedMutexGuard::map(...)`. A method would interfere with methods of
/// used as `MappedMutexGuard::map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn map<U: 'a, F>(s: Self, f: F) -> OwnedMappedMutexGuard<'a, R, U>
pub fn map<U, F>(mut s: Self, f: F) -> MappedMutexGuard<'a, R, U>
where
F: FnOnce(T) -> U,
{
use core::ptr;

let mut s = mem::ManuallyDrop::new(s);

let raw = s.raw;

let data = unsafe { ptr::read(&mut s.data) };

let data = f(data);
OwnedMappedMutexGuard {

mem::forget(s);

MappedMutexGuard {
raw,
data,
marker: PhantomData,
}
}

/// Attempts to make a new `OwnedMappedMutexGuard` for a component of the
/// Attempts to make a new `MappedMutexGuard` for a component of the
/// locked data. The original guard is returned if the closure returns `None`.
///
/// This operation cannot fail as the `OwnedMappedMutexGuard` passed
/// This operation cannot fail as the `MappedMutexGuard` passed
/// in already locked the mutex.
///
/// This is an associated function that needs to be
/// used as `OwnedMappedMutexGuard::try_map(...)`. A method would interfere with methods of
/// used as `MappedMutexGuard::try_map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn try_map<U: 'a, F>(s: Self, f: F) -> Result<OwnedMappedMutexGuard<'a, R, U>, Self>
pub fn try_map<U, F>(mut s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
where
F: FnOnce(T) -> Result<U, T>,
{
use core::ptr;

let mut s = mem::ManuallyDrop::new(s);

let raw = s.raw;
let data = unsafe { ptr::read(&mut s.data) };

f(data)
.map(|data| OwnedMappedMutexGuard {
// This relies on the fact that `Result::map` and `Result::map_err` will never panic (so long
// as the closures passed to them do not panic). If these closures are replaced with ones
// that may panic, this could lead to the mutex being unlocked twice.
let out = f(data)
.map(|data| MappedMutexGuard {
raw,
data,
marker: PhantomData,
})
.map_err(|data| OwnedMappedMutexGuard {
.map_err(|data| MappedMutexGuard {
raw,
data,
marker: PhantomData,
})
});

mem::forget(s);

out
}
}

impl<'a, R: RawMutexFair + 'a, T: 'a> OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutexFair + 'a, T: 'a> MappedMutexGuard<'a, R, T> {
/// Unlocks the mutex using a fair unlock protocol.
///
/// By default, mutexes are unfair and allow the current thread to re-lock
Expand All @@ -890,7 +898,7 @@ impl<'a, R: RawMutexFair + 'a, T: 'a> OwnedMappedMutexGuard<'a, R, T> {
}
}

impl<'a, R: RawMutex + 'a, T: 'a> Deref for OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Deref for MappedMutexGuard<'a, R, T> {
type Target = T;

#[inline]
Expand All @@ -899,30 +907,30 @@ impl<'a, R: RawMutex + 'a, T: 'a> Deref for OwnedMappedMutexGuard<'a, R, T> {
}
}

impl<'a, R: RawMutex + 'a, T: 'a> DerefMut for OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> DerefMut for MappedMutexGuard<'a, R, T> {
#[inline]
fn deref_mut(&mut self) -> &mut T {
&mut self.data
}
}

impl<'a, R: RawMutex + 'a, T: 'a> Drop for OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Drop for MappedMutexGuard<'a, R, T> {
#[inline]
fn drop(&mut self) {
// Safety: A OwnedMappedMutexGuard always holds the lock.
// Safety: A MappedMutexGuard always holds the lock.
unsafe {
self.raw.unlock();
}
}
}

impl<'a, R: RawMutex + 'a, T: fmt::Debug + 'a> fmt::Debug for OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutex + 'a, T: fmt::Debug + 'a> fmt::Debug for MappedMutexGuard<'a, R, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}

impl<'a, R: RawMutex + 'a, T: fmt::Display + 'a> fmt::Display for OwnedMappedMutexGuard<'a, R, T> {
impl<'a, R: RawMutex + 'a, T: fmt::Display + 'a> fmt::Display for MappedMutexGuard<'a, R, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(**self).fmt(f)
}
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