1 files changed, 551 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/lock/mutex.rs b/third_party/rust/futures-util/src/lock/mutex.rs
new file mode 100644
index 0000000000..335ad14273
--- /dev/null
+++ b/third_party/rust/futures-util/src/lock/mutex.rs
@@ -0,0 +1,551 @@
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::pin::Pin;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex as StdMutex};
+use std::{fmt, mem};
+
+use slab::Slab;
+
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll, Waker};
+
+/// A futures-aware mutex.
+///
+/// # Fairness
+///
+/// This mutex provides no fairness guarantees. Tasks may not acquire the mutex
+/// in the order that they requested the lock, and it's possible for a single task
+/// which repeatedly takes the lock to starve other tasks, which may be left waiting
+/// indefinitely.
+pub struct Mutex<T: ?Sized> {
+    state: AtomicUsize,
+    waiters: StdMutex<Slab<Waiter>>,
+    value: UnsafeCell<T>,
+}
+
+impl<T: ?Sized> fmt::Debug for Mutex<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let state = self.state.load(Ordering::SeqCst);
+        f.debug_struct("Mutex")
+            .field("is_locked", &((state & IS_LOCKED) != 0))
+            .field("has_waiters", &((state & HAS_WAITERS) != 0))
+            .finish()
+    }
+}
+
+impl<T> From<T> for Mutex<T> {
+    fn from(t: T) -> Self {
+        Self::new(t)
+    }
+}
+
+impl<T: Default> Default for Mutex<T> {
+    fn default() -> Self {
+        Self::new(Default::default())
+    }
+}
+
+enum Waiter {
+    Waiting(Waker),
+    Woken,
+}
+
+impl Waiter {
+    fn register(&mut self, waker: &Waker) {
+        match self {
+            Self::Waiting(w) if waker.will_wake(w) => {}
+            _ => *self = Self::Waiting(waker.clone()),
+        }
+    }
+
+    fn wake(&mut self) {
+        match mem::replace(self, Self::Woken) {
+            Self::Waiting(waker) => waker.wake(),
+            Self::Woken => {}
+        }
+    }
+}
+
+const IS_LOCKED: usize = 1 << 0;
+const HAS_WAITERS: usize = 1 << 1;
+
+impl<T> Mutex<T> {
+    /// Creates a new futures-aware mutex.
+    pub fn new(t: T) -> Self {
+        Self {
+            state: AtomicUsize::new(0),
+            waiters: StdMutex::new(Slab::new()),
+            value: UnsafeCell::new(t),
+        }
+    }
+
+    /// Consumes this mutex, returning the underlying data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::lock::Mutex;
+    ///
+    /// let mutex = Mutex::new(0);
+    /// assert_eq!(mutex.into_inner(), 0);
+    /// ```
+    pub fn into_inner(self) -> T {
+        self.value.into_inner()
+    }
+}
+
+impl<T: ?Sized> Mutex<T> {
+    /// Attempt to acquire the lock immediately.
+    ///
+    /// If the lock is currently held, this will return `None`.
+    pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        let old_state = self.state.fetch_or(IS_LOCKED, Ordering::Acquire);
+        if (old_state & IS_LOCKED) == 0 {
+            Some(MutexGuard { mutex: self })
+        } else {
+            None
+        }
+    }
+
+    /// Attempt to acquire the lock immediately.
+    ///
+    /// If the lock is currently held, this will return `None`.
+    pub fn try_lock_owned(self: &Arc<Self>) -> Option<OwnedMutexGuard<T>> {
+        let old_state = self.state.fetch_or(IS_LOCKED, Ordering::Acquire);
+        if (old_state & IS_LOCKED) == 0 {
+            Some(OwnedMutexGuard { mutex: self.clone() })
+        } else {
+            None
+        }
+    }
+
+    /// Acquire the lock asynchronously.
+    ///
+    /// This method returns a future that will resolve once the lock has been
+    /// successfully acquired.
+    pub fn lock(&self) -> MutexLockFuture<'_, T> {
+        MutexLockFuture { mutex: Some(self), wait_key: WAIT_KEY_NONE }
+    }
+
+    /// Acquire the lock asynchronously.
+    ///
+    /// This method returns a future that will resolve once the lock has been
+    /// successfully acquired.
+    pub fn lock_owned(self: Arc<Self>) -> OwnedMutexLockFuture<T> {
+        OwnedMutexLockFuture { mutex: Some(self), wait_key: WAIT_KEY_NONE }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::Mutex;
+    ///
+    /// let mut mutex = Mutex::new(0);
+    /// *mutex.get_mut() = 10;
+    /// assert_eq!(*mutex.lock().await, 10);
+    /// # });
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        // We know statically that there are no other references to `self`, so
+        // there's no need to lock the inner mutex.
+        unsafe { &mut *self.value.get() }
+    }
+
+    fn remove_waker(&self, wait_key: usize, wake_another: bool) {
+        if wait_key != WAIT_KEY_NONE {
+            let mut waiters = self.waiters.lock().unwrap();
+            match waiters.remove(wait_key) {
+                Waiter::Waiting(_) => {}
+                Waiter::Woken => {
+                    // We were awoken, but then dropped before we could
+                    // wake up to acquire the lock. Wake up another
+                    // waiter.
+                    if wake_another {
+                        if let Some((_i, waiter)) = waiters.iter_mut().next() {
+                            waiter.wake();
+                        }
+                    }
+                }
+            }
+            if waiters.is_empty() {
+                self.state.fetch_and(!HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+            }
+        }
+    }
+
+    // Unlocks the mutex. Called by MutexGuard and MappedMutexGuard when they are
+    // dropped.
+    fn unlock(&self) {
+        let old_state = self.state.fetch_and(!IS_LOCKED, Ordering::AcqRel);
+        if (old_state & HAS_WAITERS) != 0 {
+            let mut waiters = self.waiters.lock().unwrap();
+            if let Some((_i, waiter)) = waiters.iter_mut().next() {
+                waiter.wake();
+            }
+        }
+    }
+}
+
+// Sentinel for when no slot in the `Slab` has been dedicated to this object.
+const WAIT_KEY_NONE: usize = usize::MAX;
+
+/// A future which resolves when the target mutex has been successfully acquired, owned version.
+pub struct OwnedMutexLockFuture<T: ?Sized> {
+    // `None` indicates that the mutex was successfully acquired.
+    mutex: Option<Arc<Mutex<T>>>,
+    wait_key: usize,
+}
+
+impl<T: ?Sized> fmt::Debug for OwnedMutexLockFuture<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OwnedMutexLockFuture")
+            .field("was_acquired", &self.mutex.is_none())
+            .field("mutex", &self.mutex)
+            .field(
+                "wait_key",
+                &(if self.wait_key == WAIT_KEY_NONE { None } else { Some(self.wait_key) }),
+            )
+            .finish()
+    }
+}
+
+impl<T: ?Sized> FusedFuture for OwnedMutexLockFuture<T> {
+    fn is_terminated(&self) -> bool {
+        self.mutex.is_none()
+    }
+}
+
+impl<T: ?Sized> Future for OwnedMutexLockFuture<T> {
+    type Output = OwnedMutexGuard<T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+
+        let mutex = this.mutex.as_ref().expect("polled OwnedMutexLockFuture after completion");
+
+        if let Some(lock) = mutex.try_lock_owned() {
+            mutex.remove_waker(this.wait_key, false);
+            this.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        {
+            let mut waiters = mutex.waiters.lock().unwrap();
+            if this.wait_key == WAIT_KEY_NONE {
+                this.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
+                if waiters.len() == 1 {
+                    mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+                }
+            } else {
+                waiters[this.wait_key].register(cx.waker());
+            }
+        }
+
+        // Ensure that we haven't raced `MutexGuard::drop`'s unlock path by
+        // attempting to acquire the lock again.
+        if let Some(lock) = mutex.try_lock_owned() {
+            mutex.remove_waker(this.wait_key, false);
+            this.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        Poll::Pending
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedMutexLockFuture<T> {
+    fn drop(&mut self) {
+        if let Some(mutex) = self.mutex.as_ref() {
+            // This future was dropped before it acquired the mutex.
+            //
+            // Remove ourselves from the map, waking up another waiter if we
+            // had been awoken to acquire the lock.
+            mutex.remove_waker(self.wait_key, true);
+        }
+    }
+}
+
+/// An RAII guard returned by the `lock_owned` and `try_lock_owned` methods.
+/// When this structure is dropped (falls out of scope), the lock will be
+/// unlocked.
+pub struct OwnedMutexGuard<T: ?Sized> {
+    mutex: Arc<Mutex<T>>,
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for OwnedMutexGuard<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OwnedMutexGuard")
+            .field("value", &&**self)
+            .field("mutex", &self.mutex)
+            .finish()
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedMutexGuard<T> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized> Deref for OwnedMutexGuard<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.mutex.value.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for OwnedMutexGuard<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.mutex.value.get() }
+    }
+}
+
+/// A future which resolves when the target mutex has been successfully acquired.
+pub struct MutexLockFuture<'a, T: ?Sized> {
+    // `None` indicates that the mutex was successfully acquired.
+    mutex: Option<&'a Mutex<T>>,
+    wait_key: usize,
+}
+
+impl<T: ?Sized> fmt::Debug for MutexLockFuture<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MutexLockFuture")
+            .field("was_acquired", &self.mutex.is_none())
+            .field("mutex", &self.mutex)
+            .field(
+                "wait_key",
+                &(if self.wait_key == WAIT_KEY_NONE { None } else { Some(self.wait_key) }),
+            )
+            .finish()
+    }
+}
+
+impl<T: ?Sized> FusedFuture for MutexLockFuture<'_, T> {
+    fn is_terminated(&self) -> bool {
+        self.mutex.is_none()
+    }
+}
+
+impl<'a, T: ?Sized> Future for MutexLockFuture<'a, T> {
+    type Output = MutexGuard<'a, T>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mutex = self.mutex.expect("polled MutexLockFuture after completion");
+
+        if let Some(lock) = mutex.try_lock() {
+            mutex.remove_waker(self.wait_key, false);
+            self.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        {
+            let mut waiters = mutex.waiters.lock().unwrap();
+            if self.wait_key == WAIT_KEY_NONE {
+                self.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
+                if waiters.len() == 1 {
+                    mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+                }
+            } else {
+                waiters[self.wait_key].register(cx.waker());
+            }
+        }
+
+        // Ensure that we haven't raced `MutexGuard::drop`'s unlock path by
+        // attempting to acquire the lock again.
+        if let Some(lock) = mutex.try_lock() {
+            mutex.remove_waker(self.wait_key, false);
+            self.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        Poll::Pending
+    }
+}
+
+impl<T: ?Sized> Drop for MutexLockFuture<'_, T> {
+    fn drop(&mut self) {
+        if let Some(mutex) = self.mutex {
+            // This future was dropped before it acquired the mutex.
+            //
+            // Remove ourselves from the map, waking up another waiter if we
+            // had been awoken to acquire the lock.
+            mutex.remove_waker(self.wait_key, true);
+        }
+    }
+}
+
+/// An RAII guard returned by the `lock` and `try_lock` methods.
+/// When this structure is dropped (falls out of scope), the lock will be
+/// unlocked.
+pub struct MutexGuard<'a, T: ?Sized> {
+    mutex: &'a Mutex<T>,
+}
+
+impl<'a, T: ?Sized> MutexGuard<'a, T> {
+    /// Returns a locked view over a portion of the locked data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::{Mutex, MutexGuard};
+    ///
+    /// let data = Mutex::new(Some("value".to_string()));
+    /// {
+    ///     let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
+    ///     assert_eq!(&*locked_str, "value");
+    /// }
+    /// # });
+    /// ```
+    #[inline]
+    pub fn map<U: ?Sized, F>(this: Self, f: F) -> MappedMutexGuard<'a, T, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let mutex = this.mutex;
+        let value = f(unsafe { &mut *this.mutex.value.get() });
+        // Don't run the `drop` method for MutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard { mutex, value, _marker: PhantomData }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MutexGuard").field("value", &&**self).field("mutex", &self.mutex).finish()
+    }
+}
+
+impl<T: ?Sized> Drop for MutexGuard<'_, T> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized> Deref for MutexGuard<'_, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.mutex.value.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.mutex.value.get() }
+    }
+}
+
+/// An RAII guard returned by the `MutexGuard::map` and `MappedMutexGuard::map` methods.
+/// When this structure is dropped (falls out of scope), the lock will be unlocked.
+pub struct MappedMutexGuard<'a, T: ?Sized, U: ?Sized> {
+    mutex: &'a Mutex<T>,
+    value: *mut U,
+    _marker: PhantomData<&'a mut U>,
+}
+
+impl<'a, T: ?Sized, U: ?Sized> MappedMutexGuard<'a, T, U> {
+    /// Returns a locked view over a portion of the locked data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::{MappedMutexGuard, Mutex, MutexGuard};
+    ///
+    /// let data = Mutex::new(Some("value".to_string()));
+    /// {
+    ///     let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
+    ///     let locked_char = MappedMutexGuard::map(locked_str, |s| s.get_mut(0..1).unwrap());
+    ///     assert_eq!(&*locked_char, "v");
+    /// }
+    /// # });
+    /// ```
+    #[inline]
+    pub fn map<V: ?Sized, F>(this: Self, f: F) -> MappedMutexGuard<'a, T, V>
+    where
+        F: FnOnce(&mut U) -> &mut V,
+    {
+        let mutex = this.mutex;
+        let value = f(unsafe { &mut *this.value });
+        // Don't run the `drop` method for MappedMutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard { mutex, value, _marker: PhantomData }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized + fmt::Debug> fmt::Debug for MappedMutexGuard<'_, T, U> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MappedMutexGuard")
+            .field("value", &&**self)
+            .field("mutex", &self.mutex)
+            .finish()
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Drop for MappedMutexGuard<'_, T, U> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Deref for MappedMutexGuard<'_, T, U> {
+    type Target = U;
+    fn deref(&self) -> &U {
+        unsafe { &*self.value }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> DerefMut for MappedMutexGuard<'_, T, U> {
+    fn deref_mut(&mut self) -> &mut U {
+        unsafe { &mut *self.value }
+    }
+}
+
+// Mutexes can be moved freely between threads and acquired on any thread so long
+// as the inner value can be safely sent between threads.
+unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
+unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
+
+// It's safe to switch which thread the acquire is being attempted on so long as
+// `T` can be accessed on that thread.
+unsafe impl<T: ?Sized + Send> Send for MutexLockFuture<'_, T> {}
+
+// doesn't have any interesting `&self` methods (only Debug)
+unsafe impl<T: ?Sized> Sync for MutexLockFuture<'_, T> {}
+
+// It's safe to switch which thread the acquire is being attempted on so long as
+// `T` can be accessed on that thread.
+unsafe impl<T: ?Sized + Send> Send for OwnedMutexLockFuture<T> {}
+
+// doesn't have any interesting `&self` methods (only Debug)
+unsafe impl<T: ?Sized> Sync for OwnedMutexLockFuture<T> {}
+
+// Safe to send since we don't track any thread-specific details-- the inner
+// lock is essentially spinlock-equivalent (attempt to flip an atomic bool)
+unsafe impl<T: ?Sized + Send> Send for MutexGuard<'_, T> {}
+unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
+
+unsafe impl<T: ?Sized + Send> Send for OwnedMutexGuard<T> {}
+unsafe impl<T: ?Sized + Sync> Sync for OwnedMutexGuard<T> {}
+
+unsafe impl<T: ?Sized + Send, U: ?Sized + Send> Send for MappedMutexGuard<'_, T, U> {}
+unsafe impl<T: ?Sized + Sync, U: ?Sized + Sync> Sync for MappedMutexGuard<'_, T, U> {}
+
+#[test]
+fn test_mutex_guard_debug_not_recurse() {
+    let mutex = Mutex::new(42);
+    let guard = mutex.try_lock().unwrap();
+    let _ = format!("{:?}", guard);
+    let guard = MutexGuard::map(guard, |n| n);
+    let _ = format!("{:?}", guard);
+}