Split libcore/task.rs into submodules

7 files changed, 676 insertions, 0 deletions

diff --git a/src/libcore/task/context.rs b/src/libcore/task/context.rs
new file mode 100644
index 00000000000..c69d45248a5
--- /dev/null
+++ b/src/libcore/task/context.rs
@@ -0,0 +1,92 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+use fmt;
+use super::{Executor, Waker, LocalWaker};
+
+/// Information about the currently-running task.
+///
+/// Contexts are always tied to the stack, since they are set up specifically
+/// when performing a single `poll` step on a task.
+pub struct Context<'a> {
+    local_waker: &'a LocalWaker,
+    executor: &'a mut Executor,
+}
+
+impl<'a> fmt::Debug for Context<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Context")
+            .finish()
+    }
+}
+
+impl<'a> Context<'a> {
+    /// Create a new task `Context` with the provided `local_waker`, `waker`, and `executor`.
+    #[inline]
+    pub fn new(local_waker: &'a LocalWaker, executor: &'a mut Executor) -> Context<'a> {
+        Context {
+            local_waker,
+            executor,
+        }
+    }
+
+    /// Get the `LocalWaker` associated with the current task.
+    #[inline]
+    pub fn local_waker(&self) -> &'a LocalWaker {
+        self.local_waker
+    }
+
+    /// Get the `Waker` associated with the current task.
+    #[inline]
+    pub fn waker(&self) -> &'a Waker {
+        unsafe { &*(self.local_waker as *const LocalWaker as *const Waker) }
+    }
+
+    /// Get the default executor associated with this task.
+    ///
+    /// This method is useful primarily if you want to explicitly handle
+    /// spawn failures.
+    #[inline]
+    pub fn executor(&mut self) -> &mut Executor {
+        self.executor
+    }
+
+    /// Produce a context like the current one, but using the given waker instead.
+    ///
+    /// This advanced method is primarily used when building "internal
+    /// schedulers" within a task, where you want to provide some customized
+    /// wakeup logic.
+    #[inline]
+    pub fn with_waker<'b>(&'b mut self, local_waker: &'b LocalWaker) -> Context<'b> {
+        Context {
+            local_waker,
+            executor: self.executor,
+        }
+    }
+
+    /// Produce a context like the current one, but using the given executor
+    /// instead.
+    ///
+    /// This advanced method is primarily used when building "internal
+    /// schedulers" within a task.
+    #[inline]
+    pub fn with_executor<'b, E>(&'b mut self, executor: &'b mut E) -> Context<'b>
+        where E: Executor
+    {
+        Context {
+            local_waker: self.local_waker,
+            executor: executor,
+        }
+    }
+}
diff --git a/src/libcore/task/executor.rs b/src/libcore/task/executor.rs
new file mode 100644
index 00000000000..fcef6d5ffc8
--- /dev/null
+++ b/src/libcore/task/executor.rs
@@ -0,0 +1,44 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+use super::{TaskObj, SpawnObjError, SpawnErrorKind};
+
+/// A task executor.
+///
+/// A *task* is a `()`-producing async value that runs at the top level, and will
+/// be `poll`ed until completion. It's also the unit at which wake-up
+/// notifications occur. Executors, such as thread pools, allow tasks to be
+/// spawned and are responsible for putting tasks onto ready queues when
+/// they are woken up, and polling them when they are ready.
+pub trait Executor {
+    /// Spawn the given task, polling it until completion.
+    ///
+    /// # Errors
+    ///
+    /// The executor may be unable to spawn tasks, either because it has
+    /// been shut down or is resource-constrained.
+    fn spawn_obj(&mut self, task: TaskObj) -> Result<(), SpawnObjError>;
+
+    /// Determine whether the executor is able to spawn new tasks.
+    ///
+    /// # Returns
+    ///
+    /// An `Ok` return means the executor is *likely* (but not guaranteed)
+    /// to accept a subsequent spawn attempt. Likewise, an `Err` return
+    /// means that `spawn` is likely, but not guaranteed, to yield an error.
+    #[inline]
+    fn status(&self) -> Result<(), SpawnErrorKind> {
+        Ok(())
+    }
+}
diff --git a/src/libcore/task/mod.rs b/src/libcore/task/mod.rs
new file mode 100644
index 00000000000..66ab21d177d
--- /dev/null
+++ b/src/libcore/task/mod.rs
@@ -0,0 +1,33 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+//! Types and Traits for working with asynchronous tasks.
+
+mod context;
+pub use self::context::Context;
+
+mod executor;
+pub use self::executor::Executor;
+
+mod poll;
+pub use self::poll::Poll;
+
+mod spawn_error;
+pub use self::spawn_error::{SpawnErrorKind, SpawnObjError};
+
+mod task;
+pub use self::task::{TaskObj, UnsafeTask};
+
+mod wake;
+pub use self::wake::{Waker, LocalWaker, UnsafeWake};
diff --git a/src/libcore/task/poll.rs b/src/libcore/task/poll.rs
new file mode 100644
index 00000000000..10c954f0e80
--- /dev/null
+++ b/src/libcore/task/poll.rs
@@ -0,0 +1,83 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+/// Indicates whether a value is available or if the current task has been
+/// scheduled to receive a wakeup instead.
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum Poll<T> {
+    /// Represents that a value is immediately ready.
+    Ready(T),
+
+    /// Represents that a value is not ready yet.
+    ///
+    /// When a function returns `Pending`, the function *must* also
+    /// ensure that the current task is scheduled to be awoken when
+    /// progress can be made.
+    Pending,
+}
+
+impl<T> Poll<T> {
+    /// Change the ready value of this `Poll` with the closure provided
+    pub fn map<U, F>(self, f: F) -> Poll<U>
+        where F: FnOnce(T) -> U
+    {
+        match self {
+            Poll::Ready(t) => Poll::Ready(f(t)),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    /// Returns whether this is `Poll::Ready`
+    pub fn is_ready(&self) -> bool {
+        match *self {
+            Poll::Ready(_) => true,
+            Poll::Pending => false,
+        }
+    }
+
+    /// Returns whether this is `Poll::Pending`
+    pub fn is_pending(&self) -> bool {
+        !self.is_ready()
+    }
+}
+
+impl<T, E> Poll<Result<T, E>> {
+    /// Change the success value of this `Poll` with the closure provided
+    pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
+        where F: FnOnce(T) -> U
+    {
+        match self {
+            Poll::Ready(Ok(t)) => Poll::Ready(Ok(f(t))),
+            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    /// Change the error value of this `Poll` with the closure provided
+    pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
+        where F: FnOnce(E) -> U
+    {
+        match self {
+            Poll::Ready(Ok(t)) => Poll::Ready(Ok(t)),
+            Poll::Ready(Err(e)) => Poll::Ready(Err(f(e))),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+impl<T> From<T> for Poll<T> {
+    fn from(t: T) -> Poll<T> {
+        Poll::Ready(t)
+    }
+}
diff --git a/src/libcore/task/spawn_error.rs b/src/libcore/task/spawn_error.rs
new file mode 100644
index 00000000000..5dd9c5be689
--- /dev/null
+++ b/src/libcore/task/spawn_error.rs
@@ -0,0 +1,51 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+use fmt;
+use super::TaskObj;
+
+/// Provides the reason that an executor was unable to spawn.
+pub struct SpawnErrorKind {
+    _hidden: (),
+}
+
+impl fmt::Debug for SpawnErrorKind {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("SpawnErrorKind")
+            .field(&"shutdown")
+            .finish()
+    }
+}
+
+impl SpawnErrorKind {
+    /// Spawning is failing because the executor has been shut down.
+    pub fn shutdown() -> SpawnErrorKind {
+        SpawnErrorKind { _hidden: () }
+    }
+
+    /// Check whether this error is the `shutdown` error.
+    pub fn is_shutdown(&self) -> bool {
+        true
+    }
+}
+
+/// The result of a failed spawn
+#[derive(Debug)]
+pub struct SpawnObjError {
+    /// The kind of error
+    pub kind: SpawnErrorKind,
+
+    /// The task for which spawning was attempted
+    pub task: TaskObj,
+}
diff --git a/src/libcore/task/task.rs b/src/libcore/task/task.rs
new file mode 100644
index 00000000000..dc4ff314e5b
--- /dev/null
+++ b/src/libcore/task/task.rs
@@ -0,0 +1,98 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+use fmt;
+use future::Future;
+use mem::PinMut;
+use super::{Context, Poll};
+
+/// A custom trait object for polling tasks, roughly akin to
+/// `Box<Future<Output = ()> + Send>`.
+pub struct TaskObj {
+    ptr: *mut (),
+    poll_fn: unsafe fn(*mut (), &mut Context) -> Poll<()>,
+    drop_fn: unsafe fn(*mut ()),
+}
+
+unsafe impl Send for TaskObj {}
+
+impl TaskObj {
+    /// Create a `TaskObj` from a custom trait object representation.
+    #[inline]
+    pub fn new<T: UnsafeTask>(t: T) -> TaskObj {
+        TaskObj {
+            ptr: t.into_raw(),
+            poll_fn: T::poll,
+            drop_fn: T::drop,
+        }
+    }
+}
+
+impl fmt::Debug for TaskObj {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("TaskObj")
+            .finish()
+    }
+}
+
+impl Future for TaskObj {
+    type Output = ();
+
+    #[inline]
+    fn poll(self: PinMut<Self>, cx: &mut Context) -> Poll<()> {
+        unsafe {
+            (self.poll_fn)(self.ptr, cx)
+        }
+    }
+}
+
+impl Drop for TaskObj {
+    fn drop(&mut self) {
+        unsafe {
+            (self.drop_fn)(self.ptr)
+        }
+    }
+}
+
+/// A custom implementation of a task trait object for `TaskObj`, providing
+/// a hand-rolled vtable.
+///
+/// This custom representation is typically used only in `no_std` contexts,
+/// where the default `Box`-based implementation is not available.
+///
+/// The implementor must guarantee that it is safe to call `poll` repeatedly (in
+/// a non-concurrent fashion) with the result of `into_raw` until `drop` is
+/// called.
+pub unsafe trait UnsafeTask: Send + 'static {
+    /// Convert a owned instance into a (conceptually owned) void pointer.
+    fn into_raw(self) -> *mut ();
+
+    /// Poll the task represented by the given void pointer.
+    ///
+    /// # Safety
+    ///
+    /// The trait implementor must guarantee that it is safe to repeatedly call
+    /// `poll` with the result of `into_raw` until `drop` is called; such calls
+    /// are not, however, allowed to race with each other or with calls to `drop`.
+    unsafe fn poll(task: *mut (), cx: &mut Context) -> Poll<()>;
+
+    /// Drops the task represented by the given void pointer.
+    ///
+    /// # Safety
+    ///
+    /// The trait implementor must guarantee that it is safe to call this
+    /// function once per `into_raw` invocation; that call cannot race with
+    /// other calls to `drop` or `poll`.
+    unsafe fn drop(task: *mut ());
+}
diff --git a/src/libcore/task/wake.rs b/src/libcore/task/wake.rs
new file mode 100644
index 00000000000..4fd45be56fb
--- /dev/null
+++ b/src/libcore/task/wake.rs
@@ -0,0 +1,275 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![unstable(feature = "futures_api",
+            reason = "futures in libcore are unstable",
+            issue = "50547")]
+
+use fmt;
+use ptr::NonNull;
+
+/// A `Waker` is a handle for waking up a task by notifying its executor that it
+/// is ready to be run.
+///
+/// This handle contains a trait object pointing to an instance of the `UnsafeWake`
+/// trait, allowing notifications to get routed through it.
+#[repr(transparent)]
+pub struct Waker {
+    inner: NonNull<UnsafeWake>,
+}
+
+unsafe impl Send for Waker {}
+unsafe impl Sync for Waker {}
+
+impl Waker {
+    /// Constructs a new `Waker` directly.
+    ///
+    /// Note that most code will not need to call this. Implementers of the
+    /// `UnsafeWake` trait will typically provide a wrapper that calls this
+    /// but you otherwise shouldn't call it directly.
+    ///
+    /// If you're working with the standard library then it's recommended to
+    /// use the `Waker::from` function instead which works with the safe
+    /// `Arc` type and the safe `Wake` trait.
+    #[inline]
+    pub unsafe fn new(inner: NonNull<UnsafeWake>) -> Self {
+        Waker { inner: inner }
+    }
+
+    /// Wake up the task associated with this `Waker`.
+    #[inline]
+    pub fn wake(&self) {
+        unsafe { self.inner.as_ref().wake() }
+    }
+
+    /// Returns whether or not this `Waker` and `other` awaken the same task.
+    ///
+    /// This function works on a best-effort basis, and may return false even
+    /// when the `Waker`s would awaken the same task. However, if this function
+    /// returns true, it is guaranteed that the `Waker`s will awaken the same
+    /// task.
+    ///
+    /// This function is primarily used for optimization purposes.
+    #[inline]
+    pub fn will_wake(&self, other: &Waker) -> bool {
+        self.inner == other.inner
+    }
+}
+
+impl Clone for Waker {
+    #[inline]
+    fn clone(&self) -> Self {
+        unsafe {
+            self.inner.as_ref().clone_raw()
+        }
+    }
+}
+
+impl fmt::Debug for Waker {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Waker")
+            .finish()
+    }
+}
+
+impl Drop for Waker {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            self.inner.as_ref().drop_raw()
+        }
+    }
+}
+
+/// A `LocalWaker` is a handle for waking up a task by notifying its executor that it
+/// is ready to be run.
+///
+/// This is similar to the `Waker` type, but cannot be sent across threads.
+/// Task executors can use this type to implement more optimized singlethreaded wakeup
+/// behavior.
+#[repr(transparent)]
+pub struct LocalWaker {
+    inner: NonNull<UnsafeWake>,
+}
+
+impl !Send for LocalWaker {}
+impl !Sync for LocalWaker {}
+
+impl LocalWaker {
+    /// Constructs a new `LocalWaker` directly.
+    ///
+    /// Note that most code will not need to call this. Implementers of the
+    /// `UnsafeWake` trait will typically provide a wrapper that calls this
+    /// but you otherwise shouldn't call it directly.
+    ///
+    /// If you're working with the standard library then it's recommended to
+    /// use the `LocalWaker::from` function instead which works with the safe
+    /// `Rc` type and the safe `LocalWake` trait.
+    ///
+    /// For this function to be used safely, it must be sound to call `inner.wake_local()`
+    /// on the current thread.
+    #[inline]
+    pub unsafe fn new(inner: NonNull<UnsafeWake>) -> Self {
+        LocalWaker { inner: inner }
+    }
+
+    /// Wake up the task associated with this `LocalWaker`.
+    #[inline]
+    pub fn wake(&self) {
+        unsafe { self.inner.as_ref().wake_local() }
+    }
+
+    /// Returns whether or not this `LocalWaker` and `other` `LocalWaker` awaken the same task.
+    ///
+    /// This function works on a best-effort basis, and may return false even
+    /// when the `LocalWaker`s would awaken the same task. However, if this function
+    /// returns true, it is guaranteed that the `LocalWaker`s will awaken the same
+    /// task.
+    ///
+    /// This function is primarily used for optimization purposes.
+    #[inline]
+    pub fn will_wake(&self, other: &LocalWaker) -> bool {
+        self.inner == other.inner
+    }
+
+    /// Returns whether or not this `LocalWaker` and `other` `Waker` awaken the same task.
+    ///
+    /// This function works on a best-effort basis, and may return false even
+    /// when the `Waker`s would awaken the same task. However, if this function
+    /// returns true, it is guaranteed that the `LocalWaker`s will awaken the same
+    /// task.
+    ///
+    /// This function is primarily used for optimization purposes.
+    #[inline]
+    pub fn will_wake_nonlocal(&self, other: &Waker) -> bool {
+        self.inner == other.inner
+    }
+}
+
+impl From<LocalWaker> for Waker {
+    #[inline]
+    fn from(local_waker: LocalWaker) -> Self {
+        Waker { inner: local_waker.inner }
+    }
+}
+
+impl Clone for LocalWaker {
+    #[inline]
+    fn clone(&self) -> Self {
+        unsafe {
+            LocalWaker { inner: self.inner.as_ref().clone_raw().inner }
+        }
+    }
+}
+
+impl fmt::Debug for LocalWaker {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Waker")
+            .finish()
+    }
+}
+
+impl Drop for LocalWaker {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            self.inner.as_ref().drop_raw()
+        }
+    }
+}
+
+/// An unsafe trait for implementing custom memory management for a `Waker` or `LocalWaker`.
+///
+/// A `Waker` conceptually is a cloneable trait object for `Wake`, and is
+/// most often essentially just `Arc<dyn Wake>`. However, in some contexts
+/// (particularly `no_std`), it's desirable to avoid `Arc` in favor of some
+/// custom memory management strategy. This trait is designed to allow for such
+/// customization.
+///
+/// When using `std`, a default implementation of the `UnsafeWake` trait is provided for
+/// `Arc<T>` where `T: Wake` and `Rc<T>` where `T: LocalWake`.
+///
+/// Although the methods on `UnsafeWake` take pointers rather than references,
+pub unsafe trait UnsafeWake: Send + Sync {
+    /// Creates a clone of this `UnsafeWake` and stores it behind a `Waker`.
+    ///
+    /// This function will create a new uniquely owned handle that under the
+    /// hood references the same notification instance. In other words calls
+    /// to `wake` on the returned handle should be equivalent to calls to
+    /// `wake` on this handle.
+    ///
+    /// # Unsafety
+    ///
+    /// This function is unsafe to call because it's asserting the `UnsafeWake`
+    /// value is in a consistent state, i.e. hasn't been dropped.
+    unsafe fn clone_raw(&self) -> Waker;
+
+    /// Drops this instance of `UnsafeWake`, deallocating resources
+    /// associated with it.
+    ///
+    /// FIXME(cramertj)
+    /// This method is intended to have a signature such as:
+    ///
+    /// ```ignore (not-a-doctest)
+    /// fn drop_raw(self: *mut Self);
+    /// ```
+    ///
+    /// Unfortunately in Rust today that signature is not object safe.
+    /// Nevertheless it's recommended to implement this function *as if* that
+    /// were its signature. As such it is not safe to call on an invalid
+    /// pointer, nor is the validity of the pointer guaranteed after this
+    /// function returns.
+    ///
+    /// # Unsafety
+    ///
+    /// This function is unsafe to call because it's asserting the `UnsafeWake`
+    /// value is in a consistent state, i.e. hasn't been dropped.
+    unsafe fn drop_raw(&self);
+
+    /// Indicates that the associated task is ready to make progress and should
+    /// be `poll`ed.
+    ///
+    /// Executors generally maintain a queue of "ready" tasks; `wake` should place
+    /// the associated task onto this queue.
+    ///
+    /// # Panics
+    ///
+    /// Implementations should avoid panicking, but clients should also be prepared
+    /// for panics.
+    ///
+    /// # Unsafety
+    ///
+    /// This function is unsafe to call because it's asserting the `UnsafeWake`
+    /// value is in a consistent state, i.e. hasn't been dropped.
+    unsafe fn wake(&self);
+
+    /// Indicates that the associated task is ready to make progress and should
+    /// be `poll`ed. This function is the same as `wake`, but can only be called
+    /// from the thread that this `UnsafeWake` is "local" to. This allows for
+    /// implementors to provide specialized wakeup behavior specific to the current
+    /// thread. This function is called by `LocalWaker::wake`.
+    ///
+    /// Executors generally maintain a queue of "ready" tasks; `wake_local` should place
+    /// the associated task onto this queue.
+    ///
+    /// # Panics
+    ///
+    /// Implementations should avoid panicking, but clients should also be prepared
+    /// for panics.
+    ///
+    /// # Unsafety
+    ///
+    /// This function is unsafe to call because it's asserting the `UnsafeWake`
+    /// value is in a consistent state, i.e. hasn't been dropped, and that the
+    /// `UnsafeWake` hasn't moved from the thread on which it was created.
+    unsafe fn wake_local(&self) {
+        self.wake()
+    }
+}