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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_target_has_atomic! {
            use alloc::{ sync::Arc };

            impl<Sp: ?Sized + Spawn> Spawn for Arc<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 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()
                }
            }
        }
    }