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#![unstable(feature = "futures_api", reason = "futures in libcore are unstable", issue = "50547")] use fmt; use marker::Unpin; /// A `RawWaker` allows the implementor of a task executor to create a [`Waker`] /// which provides customized wakeup behavior. /// /// [vtable]: https://en.wikipedia.org/wiki/Virtual_method_table /// /// It consists of a data pointer and a [virtual function pointer table (vtable)][vtable] that /// customizes the behavior of the `RawWaker`. #[derive(PartialEq, Debug)] pub struct RawWaker { /// A data pointer, which can be used to store arbitrary data as required /// by the executor. This could be e.g. a type-erased pointer to an `Arc` /// that is associated with the task. /// The value of this field gets passed to all functions that are part of /// the vtable as the first parameter. data: *const (), /// Virtual function pointer table that customizes the behavior of this waker. vtable: &'static RawWakerVTable, } impl RawWaker { /// Creates a new `RawWaker` from the provided `data` pointer and `vtable`. /// /// The `data` pointer can be used to store arbitrary data as required /// by the executor. This could be e.g. a type-erased pointer to an `Arc` /// that is associated with the task. /// The value of this poiner will get passed to all functions that are part /// of the `vtable` as the first parameter. /// /// The `vtable` customizes the behavior of a `Waker` which gets created /// from a `RawWaker`. For each operation on the `Waker`, the associated /// function in the `vtable` of the underlying `RawWaker` will be called. pub const fn new(data: *const (), vtable: &'static RawWakerVTable) -> RawWaker { RawWaker { data, vtable, } } } /// A virtual function pointer table (vtable) that specifies the behavior /// of a [`RawWaker`]. /// /// The pointer passed to all functions inside the vtable is the `data` pointer /// from the enclosing [`RawWaker`] object. /// /// The functions inside this struct are only intended be called on the `data` /// 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. #[derive(PartialEq, Copy, Clone, Debug)] pub struct RawWakerVTable { /// This function will be called when the [`RawWaker`] gets cloned, e.g. when /// the [`Waker`] in which the [`RawWaker`] is stored gets cloned. /// /// The implementation of this function must retain all resources that are /// required for this additional instance of a [`RawWaker`] and associated /// task. Calling `wake` on the resulting [`RawWaker`] should result in a wakeup /// of the same task that would have been awoken by the original [`RawWaker`]. pub clone: unsafe fn(*const ()) -> RawWaker, /// This function will be called when `wake` is called on the [`Waker`]. /// It must wake up the task associated with this [`RawWaker`]. /// /// The implemention of this function must not consume the provided data /// pointer. pub wake: unsafe fn(*const ()), /// This function gets called when a [`RawWaker`] gets dropped. /// /// The implementation of this function must make sure to release any /// resources that are associated with this instance of a [`RawWaker`] and /// associated task. pub drop: unsafe fn(*const ()), } /// A `Waker` is a handle for waking up a task by notifying its executor that it /// is ready to be run. /// /// This handle encapsulates a [`RawWaker`] instance, which defines the /// executor-specific wakeup behavior. /// /// Implements [`Clone`], [`Send`], and [`Sync`]. #[repr(transparent)] pub struct Waker { waker: RawWaker, } impl Unpin for Waker {} unsafe impl Send for Waker {} unsafe impl Sync for Waker {} impl Waker { /// Wake up the task associated with this `Waker`. pub fn wake(&self) { // The actual wakeup call is delegated through a virtual function call // to the implementation which is defined by the executor. // SAFETY: This is safe because `Waker::new_unchecked` is the only way // to initialize `wake` and `data` requiring the user to acknowledge // that the contract of `RawWaker` is upheld. unsafe { (self.waker.vtable.wake)(self.waker.data) } } /// Returns whether or not this `Waker` and other `Waker` have 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. pub fn will_wake(&self, other: &Waker) -> bool { self.waker == other.waker } /// Creates a new `Waker` from [`RawWaker`]. /// /// The behavior of the returned `Waker` is undefined if the contract defined /// in [`RawWaker`]'s and [`RawWakerVTable`]'s documentation is not upheld. /// Therefore this method is unsafe. pub unsafe fn new_unchecked(waker: RawWaker) -> Waker { Waker { waker, } } } impl Clone for Waker { fn clone(&self) -> Self { Waker { // SAFETY: This is safe because `Waker::new_unchecked` is the only way // to initialize `clone` and `data` requiring the user to acknowledge // that the contract of [`RawWaker`] is upheld. waker: unsafe { (self.waker.vtable.clone)(self.waker.data) }, } } } impl Drop for Waker { fn drop(&mut self) { // SAFETY: This is safe because `Waker::new_unchecked` is the only way // to initialize `drop` and `data` requiring the user to acknowledge // that the contract of `RawWaker` is upheld. unsafe { (self.waker.vtable.drop)(self.waker.data) } } } impl fmt::Debug for Waker { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let vtable_ptr = self.waker.vtable as *const RawWakerVTable; f.debug_struct("Waker") .field("data", &self.waker.data) .field("vtable", &vtable_ptr) .finish() } }