Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 275 insertions, 0 deletions

diff --git a/third_party/rust/try-lock/src/lib.rs b/third_party/rust/try-lock/src/lib.rs
new file mode 100644
index 0000000000..80a240efe1
--- /dev/null
+++ b/third_party/rust/try-lock/src/lib.rs
@@ -0,0 +1,275 @@
+#![doc(html_root_url = "https://docs.rs/try-lock/0.2.3")]
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+#![deny(warnings)]
+#![cfg_attr(not(test), no_std)]
+
+//! A light-weight lock guarded by an atomic boolean.
+//!
+//! Most efficient when contention is low, acquiring the lock is a single
+//! atomic swap, and releasing it just 1 more atomic swap.
+//!
+//! # Example
+//!
+//! ```
+//! use std::sync::Arc;
+//! use try_lock::TryLock;
+//!
+//! // a thing we want to share
+//! struct Widget {
+//!     name: String,
+//! }
+//!
+//! // lock it up!
+//! let widget1 = Arc::new(TryLock::new(Widget {
+//!     name: "Spanner".into(),
+//! }));
+//!
+//! let widget2 = widget1.clone();
+//!
+//!
+//! // mutate the widget
+//! let mut locked = widget1.try_lock().expect("example isn't locked yet");
+//! locked.name.push_str(" Bundle");
+//!
+//! // hands off, buddy
+//! let not_locked = widget2.try_lock();
+//! assert!(not_locked.is_none(), "widget1 has the lock");
+//!
+//! // ok, you can have it
+//! drop(locked);
+//!
+//! let locked2 = widget2.try_lock().expect("widget1 lock is released");
+//!
+//! assert_eq!(locked2.name, "Spanner Bundle");
+//! ```
+
+#[cfg(test)]
+extern crate core;
+
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+use core::sync::atomic::{AtomicBool, Ordering};
+use core::marker::PhantomData;
+
+/// A light-weight lock guarded by an atomic boolean.
+///
+/// Most efficient when contention is low, acquiring the lock is a single
+/// atomic swap, and releasing it just 1 more atomic swap.
+///
+/// It is only possible to try to acquire the lock, it is not possible to
+/// wait for the lock to become ready, like with a `Mutex`.
+#[derive(Default)]
+pub struct TryLock<T> {
+    is_locked: AtomicBool,
+    value: UnsafeCell<T>,
+}
+
+impl<T> TryLock<T> {
+    /// Create a `TryLock` around the value.
+    #[inline]
+    pub fn new(val: T) -> TryLock<T> {
+        TryLock {
+            is_locked: AtomicBool::new(false),
+            value: UnsafeCell::new(val),
+        }
+    }
+
+    /// Try to acquire the lock of this value.
+    ///
+    /// If the lock is already acquired by someone else, this returns
+    /// `None`. You can try to acquire again whenever you want, perhaps
+    /// by spinning a few times, or by using some other means of
+    /// notification.
+    ///
+    /// # Note
+    ///
+    /// The default memory ordering is to use `Acquire` to lock, and `Release`
+    /// to unlock. If different ordering is required, use
+    /// [`try_lock_explicit`](TryLock::try_lock_explicit) or
+    /// [`try_lock_explicit_unchecked`](TryLock::try_lock_explicit_unchecked).
+    #[inline]
+    pub fn try_lock(&self) -> Option<Locked<T>> {
+        unsafe {
+            self.try_lock_explicit_unchecked(Ordering::Acquire, Ordering::Release)
+        }
+    }
+
+    /// Try to acquire the lock of this value using the lock and unlock orderings.
+    ///
+    /// If the lock is already acquired by someone else, this returns
+    /// `None`. You can try to acquire again whenever you want, perhaps
+    /// by spinning a few times, or by using some other means of
+    /// notification.
+    #[inline]
+    #[deprecated(
+        since = "0.2.3",
+        note = "This method is actually unsafe because it unsafely allows \
+        the use of weaker memory ordering. Please use try_lock_explicit instead"
+    )]
+    pub fn try_lock_order(&self, lock_order: Ordering, unlock_order: Ordering) -> Option<Locked<T>> {
+        unsafe {
+            self.try_lock_explicit_unchecked(lock_order, unlock_order)
+        }
+    }
+
+    /// Try to acquire the lock of this value using the specified lock and
+    /// unlock orderings.
+    ///
+    /// If the lock is already acquired by someone else, this returns
+    /// `None`. You can try to acquire again whenever you want, perhaps
+    /// by spinning a few times, or by using some other means of
+    /// notification.
+    ///
+    /// # Panic
+    ///
+    /// This method panics if `lock_order` is not any of `Acquire`, `AcqRel`,
+    /// and `SeqCst`, or `unlock_order` is not any of `Release` and `SeqCst`.
+    #[inline]
+    pub fn try_lock_explicit(&self, lock_order: Ordering, unlock_order: Ordering) -> Option<Locked<T>> {
+        match lock_order {
+            Ordering::Acquire |
+            Ordering::AcqRel |
+            Ordering::SeqCst => {}
+            _ => panic!("lock ordering must be `Acquire`, `AcqRel`, or `SeqCst`"),
+        }
+
+        match unlock_order {
+            Ordering::Release |
+            Ordering::SeqCst => {}
+            _ => panic!("unlock ordering must be `Release` or `SeqCst`"),
+        }
+
+        unsafe {
+            self.try_lock_explicit_unchecked(lock_order, unlock_order)
+        }
+    }
+
+    /// Try to acquire the lock of this value using the specified lock and
+    /// unlock orderings without checking that the specified orderings are
+    /// strong enough to be safe.
+    ///
+    /// If the lock is already acquired by someone else, this returns
+    /// `None`. You can try to acquire again whenever you want, perhaps
+    /// by spinning a few times, or by using some other means of
+    /// notification.
+    ///
+    /// # Safety
+    ///
+    /// Unlike [`try_lock_explicit`], this method is unsafe because it does not
+    /// check that the given memory orderings are strong enough to prevent data
+    /// race.
+    ///
+    /// [`try_lock_explicit`]: Self::try_lock_explicit
+    #[inline]
+    pub unsafe fn try_lock_explicit_unchecked(&self, lock_order: Ordering, unlock_order: Ordering) -> Option<Locked<T>> {
+        if !self.is_locked.swap(true, lock_order) {
+            Some(Locked {
+                lock: self,
+                order: unlock_order,
+                _p: PhantomData,
+            })
+        } else {
+            None
+        }
+    }
+
+    /// Take the value back out of the lock when this is the sole owner.
+    #[inline]
+    pub fn into_inner(self) -> T {
+        debug_assert!(!self.is_locked.load(Ordering::Relaxed), "TryLock was mem::forgotten");
+        // Since the compiler can statically determine this is the only owner,
+        // it's safe to take the value out. In fact, in newer versions of Rust,
+        // `UnsafeCell::into_inner` has been marked safe.
+        //
+        // To support older version (1.21), the unsafe block is still here.
+        #[allow(unused_unsafe)]
+        unsafe {
+            self.value.into_inner()
+        }
+    }
+}
+
+unsafe impl<T: Send> Send for TryLock<T> {}
+unsafe impl<T: Send> Sync for TryLock<T> {}
+
+impl<T: fmt::Debug> fmt::Debug for TryLock<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+
+        // Used if the TryLock cannot acquire the lock.
+        struct LockedPlaceholder;
+
+        impl fmt::Debug for LockedPlaceholder {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                f.write_str("<locked>")
+            }
+        }
+
+        let mut builder = f.debug_struct("TryLock");
+        if let Some(locked) = self.try_lock() {
+            builder.field("value", &*locked);
+        } else {
+            builder.field("value", &LockedPlaceholder);
+        }
+        builder.finish()
+    }
+}
+
+/// A locked value acquired from a `TryLock`.
+///
+/// The type represents an exclusive view at the underlying value. The lock is
+/// released when this type is dropped.
+///
+/// This type derefs to the underlying value.
+#[must_use = "TryLock will immediately unlock if not used"]
+pub struct Locked<'a, T: 'a> {
+    lock: &'a TryLock<T>,
+    order: Ordering,
+    /// Suppresses Send and Sync autotraits for `struct Locked`.
+    _p: PhantomData<*mut T>,
+}
+
+impl<'a, T> Deref for Locked<'a, T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &T {
+        unsafe { &*self.lock.value.get() }
+    }
+}
+
+impl<'a, T> DerefMut for Locked<'a, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.lock.value.get() }
+    }
+}
+
+impl<'a, T> Drop for Locked<'a, T> {
+    #[inline]
+    fn drop(&mut self) {
+        self.lock.is_locked.store(false, self.order);
+    }
+}
+
+impl<'a, T: fmt::Debug> fmt::Debug for Locked<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::TryLock;
+
+    #[test]
+    fn fmt_debug() {
+        let lock = TryLock::new(5);
+        assert_eq!(format!("{:?}", lock), "TryLock { value: 5 }");
+
+        let locked = lock.try_lock().unwrap();
+        assert_eq!(format!("{:?}", locked), "5");
+
+        assert_eq!(format!("{:?}", lock), "TryLock { value: <locked> }");
+    }
+}