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// 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 marker::Unpin; 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<dyn UnsafeWake>, } impl Unpin for Waker {} 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<dyn UnsafeWake>) -> Self { Waker { 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 } /// Returns whether or not this `Waker` and `other` `LocalWaker` 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_local(&self, other: &LocalWaker) -> bool { self.will_wake(&other.0) } } 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)] #[derive(Clone)] pub struct LocalWaker(Waker); impl Unpin for LocalWaker {} 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 `local_waker_from_nonlocal` or `local_waker` to convert a `Waker` /// into a `LocalWaker`. /// /// 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<dyn UnsafeWake>) -> Self { LocalWaker(Waker::new(inner)) } /// Borrows this `LocalWaker` as a `Waker`. /// /// `Waker` is nearly identical to `LocalWaker`, but is threadsafe /// (implements `Send` and `Sync`). #[inline] pub fn as_waker(&self) -> &Waker { &self.0 } /// Converts this `LocalWaker` into a `Waker`. /// /// `Waker` is nearly identical to `LocalWaker`, but is threadsafe /// (implements `Send` and `Sync`). #[inline] pub fn into_waker(self) -> Waker { self.0 } /// Wake up the task associated with this `LocalWaker`. #[inline] pub fn wake(&self) { unsafe { self.0.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.0.will_wake(&other.0) } /// 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.0.will_wake(other) } } impl From<LocalWaker> for Waker { /// Converts a `LocalWaker` into a `Waker`. /// /// This conversion turns a `!Sync` `LocalWaker` into a `Sync` `Waker`, allowing a wakeup /// object to be sent to another thread, but giving up its ability to do specialized /// thread-local wakeup behavior. #[inline] fn from(local_waker: LocalWaker) -> Self { local_waker.0 } } impl fmt::Debug for LocalWaker { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("LocalWaker") .finish() } } /// 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`. 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() } }