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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 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, ()>,
}
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