1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96
// 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::{FutureObj, LocalFutureObj}; /// A task executor. /// /// Futures are polled until completion by tasks, a kind of lightweight /// "thread". A *task executor* is responsible for the creation of these tasks /// and the coordination of their execution on real operating system threads. In /// particular, whenever a task signals that it can make further progress via a /// wake-up notification, it is the responsibility of the task executor to put /// the task into a queue to continue executing it, i.e. polling the future in /// it, later. pub trait Executor { /// Spawns a new task with the given future. The future will be polled 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, future: FutureObj<'static, ()>, ) -> Result<(), SpawnObjError>; /// Determines 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(()) } } /// 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 future for which spawning inside a task was attempted pub future: FutureObj<'static, ()>, } /// The result of a failed spawn #[derive(Debug)] pub struct SpawnLocalObjError { /// The kind of error pub kind: SpawnErrorKind, /// The future for which spawning inside a task was attempted pub future: LocalFutureObj<'static, ()>, }