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
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129

use crate::future::{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(&mut 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(&mut 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 {
    _hidden: (),
}

impl fmt::Debug for SpawnError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("SpawnError")
            .field(&"shutdown")
            .finish()
    }
}

impl SpawnError {
    /// Spawning failed because the executor has been shut down.
    pub fn shutdown() -> Self {
        Self { _hidden: () }
    }

    /// Check whether spawning failed to the executor being shut down.
    pub fn is_shutdown(&self) -> bool {
        true
    }
}

impl<Sp: ?Sized + Spawn> Spawn for &mut Sp {
    fn spawn_obj(&mut 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 &mut Sp {
    fn spawn_local_obj(&mut 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 alloc::boxed::Box;
    use super::*;

    impl<Sp: ?Sized + Spawn> Spawn for Box<Sp> {
        fn spawn_obj(&mut 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(&mut self, future: LocalFutureObj<'static, ()>)
        -> Result<(), SpawnError> {
            (**self).spawn_local_obj(future)
        }

        fn status_local(&self) -> Result<(), SpawnError> {
            (**self).status_local()
        }
    }
}