Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 293 insertions, 0 deletions

diff --git a/third_party/rust/futures-util/src/lock/bilock.rs b/third_party/rust/futures-util/src/lock/bilock.rs
new file mode 100644
index 0000000000..7ddc66ad2c
--- /dev/null
+++ b/third_party/rust/futures-util/src/lock/bilock.rs
@@ -0,0 +1,293 @@
+//! Futures-powered synchronization primitives.
+
+use alloc::boxed::Box;
+use alloc::sync::Arc;
+use core::cell::UnsafeCell;
+use core::ops::{Deref, DerefMut};
+use core::pin::Pin;
+use core::sync::atomic::AtomicPtr;
+use core::sync::atomic::Ordering::SeqCst;
+use core::{fmt, ptr};
+#[cfg(feature = "bilock")]
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll, Waker};
+
+/// A type of futures-powered synchronization primitive which is a mutex between
+/// two possible owners.
+///
+/// This primitive is not as generic as a full-blown mutex but is sufficient for
+/// many use cases where there are only two possible owners of a resource. The
+/// implementation of `BiLock` can be more optimized for just the two possible
+/// owners.
+///
+/// Note that it's possible to use this lock through a poll-style interface with
+/// the `poll_lock` method but you can also use it as a future with the `lock`
+/// method that consumes a `BiLock` and returns a future that will resolve when
+/// it's locked.
+///
+/// A `BiLock` is typically used for "split" operations where data which serves
+/// two purposes wants to be split into two to be worked with separately. For
+/// example a TCP stream could be both a reader and a writer or a framing layer
+/// could be both a stream and a sink for messages. A `BiLock` enables splitting
+/// these two and then using each independently in a futures-powered fashion.
+///
+/// This type is only available when the `bilock` feature of this
+/// library is activated.
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct BiLock<T> {
+    arc: Arc<Inner<T>>,
+}
+
+#[derive(Debug)]
+struct Inner<T> {
+    state: AtomicPtr<Waker>,
+    value: Option<UnsafeCell<T>>,
+}
+
+unsafe impl<T: Send> Send for Inner<T> {}
+unsafe impl<T: Send> Sync for Inner<T> {}
+
+impl<T> BiLock<T> {
+    /// Creates a new `BiLock` protecting the provided data.
+    ///
+    /// Two handles to the lock are returned, and these are the only two handles
+    /// that will ever be available to the lock. These can then be sent to separate
+    /// tasks to be managed there.
+    ///
+    /// The data behind the bilock is considered to be pinned, which allows `Pin`
+    /// references to locked data. However, this means that the locked value
+    /// will only be available through `Pin<&mut T>` (not `&mut T`) unless `T` is `Unpin`.
+    /// Similarly, reuniting the lock and extracting the inner value is only
+    /// possible when `T` is `Unpin`.
+    pub fn new(t: T) -> (Self, Self) {
+        let arc = Arc::new(Inner {
+            state: AtomicPtr::new(ptr::null_mut()),
+            value: Some(UnsafeCell::new(t)),
+        });
+
+        (Self { arc: arc.clone() }, Self { arc })
+    }
+
+    /// Attempt to acquire this lock, returning `Pending` if it can't be
+    /// acquired.
+    ///
+    /// This function will acquire the lock in a nonblocking fashion, returning
+    /// immediately if the lock is already held. If the lock is successfully
+    /// acquired then `Poll::Ready` is returned with a value that represents
+    /// the locked value (and can be used to access the protected data). The
+    /// lock is unlocked when the returned `BiLockGuard` is dropped.
+    ///
+    /// If the lock is already held then this function will return
+    /// `Poll::Pending`. In this case the current task will also be scheduled
+    /// to receive a notification when the lock would otherwise become
+    /// available.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if called outside the context of a future's
+    /// task.
+    pub fn poll_lock(&self, cx: &mut Context<'_>) -> Poll<BiLockGuard<'_, T>> {
+        let mut waker = None;
+        loop {
+            let n = self.arc.state.swap(invalid_ptr(1), SeqCst);
+            match n as usize {
+                // Woohoo, we grabbed the lock!
+                0 => return Poll::Ready(BiLockGuard { bilock: self }),
+
+                // Oops, someone else has locked the lock
+                1 => {}
+
+                // A task was previously blocked on this lock, likely our task,
+                // so we need to update that task.
+                _ => unsafe {
+                    let mut prev = Box::from_raw(n);
+                    *prev = cx.waker().clone();
+                    waker = Some(prev);
+                },
+            }
+
+            // type ascription for safety's sake!
+            let me: Box<Waker> = waker.take().unwrap_or_else(|| Box::new(cx.waker().clone()));
+            let me = Box::into_raw(me);
+
+            match self.arc.state.compare_exchange(invalid_ptr(1), me, SeqCst, SeqCst) {
+                // The lock is still locked, but we've now parked ourselves, so
+                // just report that we're scheduled to receive a notification.
+                Ok(_) => return Poll::Pending,
+
+                // Oops, looks like the lock was unlocked after our swap above
+                // and before the compare_exchange. Deallocate what we just
+                // allocated and go through the loop again.
+                Err(n) if n.is_null() => unsafe {
+                    waker = Some(Box::from_raw(me));
+                },
+
+                // The top of this loop set the previous state to 1, so if we
+                // failed the CAS above then it's because the previous value was
+                // *not* zero or one. This indicates that a task was blocked,
+                // but we're trying to acquire the lock and there's only one
+                // other reference of the lock, so it should be impossible for
+                // that task to ever block itself.
+                Err(n) => panic!("invalid state: {}", n as usize),
+            }
+        }
+    }
+
+    /// Perform a "blocking lock" of this lock, consuming this lock handle and
+    /// returning a future to the acquired lock.
+    ///
+    /// This function consumes the `BiLock<T>` and returns a sentinel future,
+    /// `BiLockAcquire<T>`. The returned future will resolve to
+    /// `BiLockAcquired<T>` which represents a locked lock similarly to
+    /// `BiLockGuard<T>`.
+    ///
+    /// Note that the returned future will never resolve to an error.
+    #[cfg(feature = "bilock")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+    pub fn lock(&self) -> BiLockAcquire<'_, T> {
+        BiLockAcquire { bilock: self }
+    }
+
+    /// Attempts to put the two "halves" of a `BiLock<T>` back together and
+    /// recover the original value. Succeeds only if the two `BiLock<T>`s
+    /// originated from the same call to `BiLock::new`.
+    pub fn reunite(self, other: Self) -> Result<T, ReuniteError<T>>
+    where
+        T: Unpin,
+    {
+        if Arc::ptr_eq(&self.arc, &other.arc) {
+            drop(other);
+            let inner = Arc::try_unwrap(self.arc)
+                .ok()
+                .expect("futures: try_unwrap failed in BiLock<T>::reunite");
+            Ok(unsafe { inner.into_value() })
+        } else {
+            Err(ReuniteError(self, other))
+        }
+    }
+
+    fn unlock(&self) {
+        let n = self.arc.state.swap(ptr::null_mut(), SeqCst);
+        match n as usize {
+            // we've locked the lock, shouldn't be possible for us to see an
+            // unlocked lock.
+            0 => panic!("invalid unlocked state"),
+
+            // Ok, no one else tried to get the lock, we're done.
+            1 => {}
+
+            // Another task has parked themselves on this lock, let's wake them
+            // up as its now their turn.
+            _ => unsafe {
+                Box::from_raw(n).wake();
+            },
+        }
+    }
+}
+
+impl<T: Unpin> Inner<T> {
+    unsafe fn into_value(mut self) -> T {
+        self.value.take().unwrap().into_inner()
+    }
+}
+
+impl<T> Drop for Inner<T> {
+    fn drop(&mut self) {
+        assert!(self.state.load(SeqCst).is_null());
+    }
+}
+
+/// Error indicating two `BiLock<T>`s were not two halves of a whole, and
+/// thus could not be `reunite`d.
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct ReuniteError<T>(pub BiLock<T>, pub BiLock<T>);
+
+impl<T> fmt::Debug for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("ReuniteError").field(&"...").finish()
+    }
+}
+
+impl<T> fmt::Display for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "tried to reunite two BiLocks that don't form a pair")
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: core::any::Any> std::error::Error for ReuniteError<T> {}
+
+/// Returned RAII guard from the `poll_lock` method.
+///
+/// This structure acts as a sentinel to the data in the `BiLock<T>` itself,
+/// implementing `Deref` and `DerefMut` to `T`. When dropped, the lock will be
+/// unlocked.
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct BiLockGuard<'a, T> {
+    bilock: &'a BiLock<T>,
+}
+
+// We allow parallel access to T via Deref, so Sync bound is also needed here.
+unsafe impl<T: Send + Sync> Sync for BiLockGuard<'_, T> {}
+
+impl<T> Deref for BiLockGuard<'_, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.bilock.arc.value.as_ref().unwrap().get() }
+    }
+}
+
+impl<T: Unpin> DerefMut for BiLockGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.bilock.arc.value.as_ref().unwrap().get() }
+    }
+}
+
+impl<T> BiLockGuard<'_, T> {
+    /// Get a mutable pinned reference to the locked value.
+    pub fn as_pin_mut(&mut self) -> Pin<&mut T> {
+        // Safety: we never allow moving a !Unpin value out of a bilock, nor
+        // allow mutable access to it
+        unsafe { Pin::new_unchecked(&mut *self.bilock.arc.value.as_ref().unwrap().get()) }
+    }
+}
+
+impl<T> Drop for BiLockGuard<'_, T> {
+    fn drop(&mut self) {
+        self.bilock.unlock();
+    }
+}
+
+/// Future returned by `BiLock::lock` which will resolve when the lock is
+/// acquired.
+#[cfg(feature = "bilock")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+#[derive(Debug)]
+pub struct BiLockAcquire<'a, T> {
+    bilock: &'a BiLock<T>,
+}
+
+// Pinning is never projected to fields
+#[cfg(feature = "bilock")]
+impl<T> Unpin for BiLockAcquire<'_, T> {}
+
+#[cfg(feature = "bilock")]
+impl<'a, T> Future for BiLockAcquire<'a, T> {
+    type Output = BiLockGuard<'a, T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.bilock.poll_lock(cx)
+    }
+}
+
+// Based on core::ptr::invalid_mut. Equivalent to `addr as *mut T`, but is strict-provenance compatible.
+#[allow(clippy::useless_transmute)]
+#[inline]
+fn invalid_ptr<T>(addr: usize) -> *mut T {
+    // SAFETY: every valid integer is also a valid pointer (as long as you don't dereference that
+    // pointer).
+    unsafe { core::mem::transmute(addr) }
+}