91 lines
2.7 KiB
Rust
91 lines
2.7 KiB
Rust
// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![unstable(feature = "futures_api",
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reason = "futures in libcore are unstable",
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issue = "50547")]
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use fmt;
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use super::{FutureObj, LocalFutureObj};
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/// A task executor.
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///
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/// A *task* is a `()`-producing async value that runs at the top level, and will
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/// be `poll`ed until completion. It's also the unit at which wake-up
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/// notifications occur. Executors, such as thread pools, allow tasks to be
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/// spawned and are responsible for putting tasks onto ready queues when
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/// they are woken up, and polling them when they are ready.
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pub trait Executor {
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/// Spawn the given task, polling it until completion.
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///
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/// # Errors
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///
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/// The executor may be unable to spawn tasks, either because it has
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/// been shut down or is resource-constrained.
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fn spawn_obj(&mut self, task: FutureObj<()>) -> Result<(), SpawnObjError>;
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/// Determine whether the executor is able to spawn new tasks.
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///
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/// # Returns
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///
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/// An `Ok` return means the executor is *likely* (but not guaranteed)
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/// to accept a subsequent spawn attempt. Likewise, an `Err` return
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/// means that `spawn` is likely, but not guaranteed, to yield an error.
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#[inline]
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fn status(&self) -> Result<(), SpawnErrorKind> {
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Ok(())
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}
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}
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/// Provides the reason that an executor was unable to spawn.
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pub struct SpawnErrorKind {
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_hidden: (),
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}
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impl fmt::Debug for SpawnErrorKind {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.debug_tuple("SpawnErrorKind")
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.field(&"shutdown")
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.finish()
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}
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}
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impl SpawnErrorKind {
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/// Spawning is failing because the executor has been shut down.
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pub fn shutdown() -> SpawnErrorKind {
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SpawnErrorKind { _hidden: () }
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}
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/// Check whether this error is the `shutdown` error.
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pub fn is_shutdown(&self) -> bool {
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true
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}
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}
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/// The result of a failed spawn
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#[derive(Debug)]
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pub struct SpawnObjError {
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/// The kind of error
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pub kind: SpawnErrorKind,
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/// The task for which spawning was attempted
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pub task: FutureObj<()>,
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}
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/// The result of a failed spawn
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#[derive(Debug)]
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pub struct SpawnLocalObjError {
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/// The kind of error
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pub kind: SpawnErrorKind,
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/// The task for which spawning was attempted
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pub task: LocalFutureObj<()>,
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}
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