diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index 87d4a25afd5..1aeb30c667e 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -71,6 +71,12 @@ pub fn vtable(&self) -> &'static RawWakerVTable {
/// pointer of a properly constructed [`RawWaker`] object from inside the
/// [`RawWaker`] implementation. Calling one of the contained functions using
/// any other `data` pointer will cause undefined behavior.
+///
+/// These functions must all be thread-safe (even though [`RawWaker`] is
+/// \![Send] + \![Sync]
)
+/// because [`Waker`] is [Send] + [Sync]
, and thus wakers may be moved to
+/// arbitrary threads or invoked by `&` reference. For example, this means that if the
+/// `clone` and `drop` functions manage a reference count, they must do so atomically.
#[stable(feature = "futures_api", since = "1.36.0")]
#[derive(PartialEq, Copy, Clone, Debug)]
pub struct RawWakerVTable {
@@ -110,6 +116,12 @@ impl RawWakerVTable {
/// Creates a new `RawWakerVTable` from the provided `clone`, `wake`,
/// `wake_by_ref`, and `drop` functions.
///
+ /// These functions must all be thread-safe (even though [`RawWaker`] is
+ /// \![Send] + \![Sync]
)
+ /// because [`Waker`] is [Send] + [Sync]
, and thus wakers may be moved to
+ /// arbitrary threads or invoked by `&` reference. For example, this means that if the
+ /// `clone` and `drop` functions manage a reference count, they must do so atomically.
+ ///
/// # `clone`
///
/// This function will be called when the [`RawWaker`] gets cloned, e.g. when
@@ -157,9 +169,9 @@ pub const fn new(
}
}
-/// The `Context` of an asynchronous task.
+/// The context of an asynchronous task.
///
-/// Currently, `Context` only serves to provide access to a `&Waker`
+/// Currently, `Context` only serves to provide access to a [`&Waker`](Waker)
/// which can be used to wake the current task.
#[stable(feature = "futures_api", since = "1.36.0")]
pub struct Context<'a> {
@@ -172,7 +184,7 @@ pub struct Context<'a> {
}
impl<'a> Context<'a> {
- /// Create a new `Context` from a `&Waker`.
+ /// Create a new [`Context`] from a [`&Waker`](Waker).
#[stable(feature = "futures_api", since = "1.36.0")]
#[must_use]
#[inline]
@@ -180,7 +192,7 @@ pub fn from_waker(waker: &'a Waker) -> Self {
Context { waker, _marker: PhantomData }
}
- /// Returns a reference to the `Waker` for the current task.
+ /// Returns a reference to the [`Waker`] for the current task.
#[stable(feature = "futures_api", since = "1.36.0")]
#[must_use]
#[inline]
@@ -202,7 +214,18 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// This handle encapsulates a [`RawWaker`] instance, which defines the
/// executor-specific wakeup behavior.
///
-/// Implements [`Clone`], [`Send`], and [`Sync`].
+/// The typical life of a [`Waker`] is that it is constructed by an executor, wrapped in a
+/// [`Context`], then passed to [`Future::poll()`]. Then, if the future chooses to return
+/// [`Poll::Pending`], it must also store the waker somehow and call [`Waker::wake()`] when
+/// the future should be polled again.
+///
+/// Implements [`Clone`], [`Send`], and [`Sync`]; therefore, a waker may be invoked
+/// from any thread, including ones not in any way managed by the executor. For example,
+/// this might be done to wake a future when a blocking function call completes on another
+/// thread.
+///
+/// [`Future::poll()`]: core::future::Future::poll
+/// [`Poll::Pending`]: core::task::Poll::Pending
#[repr(transparent)]
#[stable(feature = "futures_api", since = "1.36.0")]
pub struct Waker {
@@ -219,18 +242,21 @@ unsafe impl Sync for Waker {}
impl Waker {
/// Wake up the task associated with this `Waker`.
///
- /// As long as the runtime keeps running and the task is not finished, it is
- /// guaranteed that each invocation of `wake` (or `wake_by_ref`) will be followed
- /// by at least one `poll` of the task to which this `Waker` belongs. This makes
+ /// As long as the executor keeps running and the task is not finished, it is
+ /// guaranteed that each invocation of [`wake()`](Self::wake) (or
+ /// [`wake_by_ref()`](Self::wake_by_ref)) will be followed by at least one
+ /// [`poll()`] of the task to which this [`Waker`] belongs. This makes
/// it possible to temporarily yield to other tasks while running potentially
/// unbounded processing loops.
///
/// Note that the above implies that multiple wake-ups may be coalesced into a
- /// single `poll` invocation by the runtime.
+ /// single [`poll()`] invocation by the runtime.
///
/// Also note that yielding to competing tasks is not guaranteed: it is the
/// executor’s choice which task to run and the executor may choose to run the
/// current task again.
+ ///
+ /// [`poll()`]: crate::future::Future::poll
#[inline]
#[stable(feature = "futures_api", since = "1.36.0")]
pub fn wake(self) {
@@ -250,8 +276,8 @@ pub fn wake(self) {
/// Wake up the task associated with this `Waker` without consuming the `Waker`.
///
- /// This is similar to `wake`, but may be slightly less efficient in the case
- /// where an owned `Waker` is available. This method should be preferred to
+ /// This is similar to [`wake()`](Self::wake), but may be slightly less efficient in
+ /// the case where an owned `Waker` is available. This method should be preferred to
/// calling `waker.clone().wake()`.
#[inline]
#[stable(feature = "futures_api", since = "1.36.0")]
@@ -263,7 +289,7 @@ pub fn wake_by_ref(&self) {
unsafe { (self.waker.vtable.wake_by_ref)(self.waker.data) }
}
- /// Returns `true` if this `Waker` and another `Waker` have awoken the same task.
+ /// Returns `true` if this `Waker` and another [`Waker`] would awake 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