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use crate::{FutureObj, LocalFutureObj};
use core::fmt;
/// The `Spawn` trait allows for pushing futures onto an executor that will
/// run them to completion.
pub trait Spawn {
/// Spawns a future that will be run to completion.
///
/// # Errors
///
/// The executor may be unable to spawn tasks. Spawn errors should
/// represent relatively rare scenarios, such as the executor
/// having been shut down so that it is no longer able to accept
/// tasks.
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError>;
/// Determines whether the executor is able to spawn new tasks.
///
/// This method will return `Ok` when 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<(), SpawnError> {
Ok(())
}
}
/// The `LocalSpawn` is similar to [`Spawn`], but allows spawning futures
/// that don't implement `Send`.
pub trait LocalSpawn {
/// Spawns a future that will be run to completion.
///
/// # Errors
///
/// The executor may be unable to spawn tasks. Spawn errors should
/// represent relatively rare scenarios, such as the executor
/// having been shut down so that it is no longer able to accept
/// tasks.
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError>;
/// Determines whether the executor is able to spawn new tasks.
///
/// This method will return `Ok` when 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_local(&self) -> Result<(), SpawnError> {
Ok(())
}
}
/// An error that occurred during spawning.
pub struct SpawnError {
_priv: (),
}
impl fmt::Debug for SpawnError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("SpawnError").field(&"shutdown").finish()
}
}
impl fmt::Display for SpawnError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Executor is shutdown")
}
}
#[cfg(feature = "std")]
impl std::error::Error for SpawnError {}
impl SpawnError {
/// Spawning failed because the executor has been shut down.
pub fn shutdown() -> Self {
Self { _priv: () }
}
/// Check whether spawning failed to the executor being shut down.
pub fn is_shutdown(&self) -> bool {
true
}
}
impl<Sp: ?Sized + Spawn> Spawn for &Sp {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
Sp::spawn_obj(self, future)
}
fn status(&self) -> Result<(), SpawnError> {
Sp::status(self)
}
}
impl<Sp: ?Sized + Spawn> Spawn for &mut Sp {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
Sp::spawn_obj(self, future)
}
fn status(&self) -> Result<(), SpawnError> {
Sp::status(self)
}
}
impl<Sp: ?Sized + LocalSpawn> LocalSpawn for &Sp {
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
Sp::spawn_local_obj(self, future)
}
fn status_local(&self) -> Result<(), SpawnError> {
Sp::status_local(self)
}
}
impl<Sp: ?Sized + LocalSpawn> LocalSpawn for &mut Sp {
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
Sp::spawn_local_obj(self, future)
}
fn status_local(&self) -> Result<(), SpawnError> {
Sp::status_local(self)
}
}
#[cfg(feature = "alloc")]
mod if_alloc {
use super::*;
use alloc::{boxed::Box, rc::Rc};
impl<Sp: ?Sized + Spawn> Spawn for Box<Sp> {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_obj(future)
}
fn status(&self) -> Result<(), SpawnError> {
(**self).status()
}
}
impl<Sp: ?Sized + LocalSpawn> LocalSpawn for Box<Sp> {
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_local_obj(future)
}
fn status_local(&self) -> Result<(), SpawnError> {
(**self).status_local()
}
}
impl<Sp: ?Sized + Spawn> Spawn for Rc<Sp> {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_obj(future)
}
fn status(&self) -> Result<(), SpawnError> {
(**self).status()
}
}
impl<Sp: ?Sized + LocalSpawn> LocalSpawn for Rc<Sp> {
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_local_obj(future)
}
fn status_local(&self) -> Result<(), SpawnError> {
(**self).status_local()
}
}
#[cfg(not(futures_no_atomic_cas))]
impl<Sp: ?Sized + Spawn> Spawn for alloc::sync::Arc<Sp> {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_obj(future)
}
fn status(&self) -> Result<(), SpawnError> {
(**self).status()
}
}
#[cfg(not(futures_no_atomic_cas))]
impl<Sp: ?Sized + LocalSpawn> LocalSpawn for alloc::sync::Arc<Sp> {
fn spawn_local_obj(&self, future: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
(**self).spawn_local_obj(future)
}
fn status_local(&self) -> Result<(), SpawnError> {
(**self).status_local()
}
}
}