1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![unstable(feature = "futures_api",
12 reason = "futures in libcore are unstable",
19 /// A `Waker` is a handle for waking up a task by notifying its executor that it
20 /// is ready to be run.
22 /// This handle contains a trait object pointing to an instance of the `UnsafeWake`
23 /// trait, allowing notifications to get routed through it.
26 inner: NonNull<dyn UnsafeWake>,
29 impl Unpin for Waker {}
30 unsafe impl Send for Waker {}
31 unsafe impl Sync for Waker {}
34 /// Constructs a new `Waker` directly.
36 /// Note that most code will not need to call this. Implementers of the
37 /// `UnsafeWake` trait will typically provide a wrapper that calls this
38 /// but you otherwise shouldn't call it directly.
40 /// If you're working with the standard library then it's recommended to
41 /// use the `Waker::from` function instead which works with the safe
42 /// `Arc` type and the safe `Wake` trait.
44 pub unsafe fn new(inner: NonNull<dyn UnsafeWake>) -> Self {
48 /// Wake up the task associated with this `Waker`.
51 unsafe { self.inner.as_ref().wake() }
54 /// Returns whether or not this `Waker` and `other` awaken the same task.
56 /// This function works on a best-effort basis, and may return false even
57 /// when the `Waker`s would awaken the same task. However, if this function
58 /// returns true, it is guaranteed that the `Waker`s will awaken the same
61 /// This function is primarily used for optimization purposes.
63 pub fn will_wake(&self, other: &Waker) -> bool {
64 self.inner == other.inner
68 impl Clone for Waker {
70 fn clone(&self) -> Self {
72 self.inner.as_ref().clone_raw()
77 impl fmt::Debug for Waker {
78 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
79 f.debug_struct("Waker")
88 self.inner.as_ref().drop_raw()
93 /// A `LocalWaker` is a handle for waking up a task by notifying its executor that it
94 /// is ready to be run.
96 /// This is similar to the `Waker` type, but cannot be sent across threads.
97 /// Task executors can use this type to implement more optimized singlethreaded wakeup
100 pub struct LocalWaker {
101 inner: NonNull<dyn UnsafeWake>,
104 impl Unpin for LocalWaker {}
105 impl !Send for LocalWaker {}
106 impl !Sync for LocalWaker {}
109 /// Constructs a new `LocalWaker` directly.
111 /// Note that most code will not need to call this. Implementers of the
112 /// `UnsafeWake` trait will typically provide a wrapper that calls this
113 /// but you otherwise shouldn't call it directly.
115 /// If you're working with the standard library then it's recommended to
116 /// use the `local_waker_from_nonlocal` or `local_waker` to convert a `Waker`
117 /// into a `LocalWaker`.
119 /// For this function to be used safely, it must be sound to call `inner.wake_local()`
120 /// on the current thread.
122 pub unsafe fn new(inner: NonNull<dyn UnsafeWake>) -> Self {
126 /// Wake up the task associated with this `LocalWaker`.
129 unsafe { self.inner.as_ref().wake_local() }
132 /// Returns whether or not this `LocalWaker` and `other` `LocalWaker` awaken the same task.
134 /// This function works on a best-effort basis, and may return false even
135 /// when the `LocalWaker`s would awaken the same task. However, if this function
136 /// returns true, it is guaranteed that the `LocalWaker`s will awaken the same
139 /// This function is primarily used for optimization purposes.
141 pub fn will_wake(&self, other: &LocalWaker) -> bool {
142 self.inner == other.inner
145 /// Returns whether or not this `LocalWaker` and `other` `Waker` awaken the same task.
147 /// This function works on a best-effort basis, and may return false even
148 /// when the `Waker`s would awaken the same task. However, if this function
149 /// returns true, it is guaranteed that the `LocalWaker`s will awaken the same
152 /// This function is primarily used for optimization purposes.
154 pub fn will_wake_nonlocal(&self, other: &Waker) -> bool {
155 self.inner == other.inner
159 impl From<LocalWaker> for Waker {
161 fn from(local_waker: LocalWaker) -> Self {
162 let inner = local_waker.inner;
163 mem::forget(local_waker);
168 impl Clone for LocalWaker {
170 fn clone(&self) -> Self {
171 let waker = unsafe { self.inner.as_ref().clone_raw() };
172 let inner = waker.inner;
178 impl fmt::Debug for LocalWaker {
179 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
180 f.debug_struct("Waker")
185 impl Drop for LocalWaker {
189 self.inner.as_ref().drop_raw()
194 /// An unsafe trait for implementing custom memory management for a `Waker` or `LocalWaker`.
196 /// A `Waker` conceptually is a cloneable trait object for `Wake`, and is
197 /// most often essentially just `Arc<dyn Wake>`. However, in some contexts
198 /// (particularly `no_std`), it's desirable to avoid `Arc` in favor of some
199 /// custom memory management strategy. This trait is designed to allow for such
202 /// When using `std`, a default implementation of the `UnsafeWake` trait is provided for
203 /// `Arc<T>` where `T: Wake`.
204 pub unsafe trait UnsafeWake: Send + Sync {
205 /// Creates a clone of this `UnsafeWake` and stores it behind a `Waker`.
207 /// This function will create a new uniquely owned handle that under the
208 /// hood references the same notification instance. In other words calls
209 /// to `wake` on the returned handle should be equivalent to calls to
210 /// `wake` on this handle.
214 /// This function is unsafe to call because it's asserting the `UnsafeWake`
215 /// value is in a consistent state, i.e. hasn't been dropped.
216 unsafe fn clone_raw(&self) -> Waker;
218 /// Drops this instance of `UnsafeWake`, deallocating resources
219 /// associated with it.
222 /// This method is intended to have a signature such as:
224 /// ```ignore (not-a-doctest)
225 /// fn drop_raw(self: *mut Self);
228 /// Unfortunately in Rust today that signature is not object safe.
229 /// Nevertheless it's recommended to implement this function *as if* that
230 /// were its signature. As such it is not safe to call on an invalid
231 /// pointer, nor is the validity of the pointer guaranteed after this
232 /// function returns.
236 /// This function is unsafe to call because it's asserting the `UnsafeWake`
237 /// value is in a consistent state, i.e. hasn't been dropped.
238 unsafe fn drop_raw(&self);
240 /// Indicates that the associated task is ready to make progress and should
243 /// Executors generally maintain a queue of "ready" tasks; `wake` should place
244 /// the associated task onto this queue.
248 /// Implementations should avoid panicking, but clients should also be prepared
253 /// This function is unsafe to call because it's asserting the `UnsafeWake`
254 /// value is in a consistent state, i.e. hasn't been dropped.
255 unsafe fn wake(&self);
257 /// Indicates that the associated task is ready to make progress and should
258 /// be `poll`ed. This function is the same as `wake`, but can only be called
259 /// from the thread that this `UnsafeWake` is "local" to. This allows for
260 /// implementors to provide specialized wakeup behavior specific to the current
261 /// thread. This function is called by `LocalWaker::wake`.
263 /// Executors generally maintain a queue of "ready" tasks; `wake_local` should place
264 /// the associated task onto this queue.
268 /// Implementations should avoid panicking, but clients should also be prepared
273 /// This function is unsafe to call because it's asserting the `UnsafeWake`
274 /// value is in a consistent state, i.e. hasn't been dropped, and that the
275 /// `UnsafeWake` hasn't moved from the thread on which it was created.
276 unsafe fn wake_local(&self) {