uexec 0.1.4

Simple work-stealing global and local executor
Documentation 
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_holder::FutureHolder, local_future::LocalRes, main_task::MainTaskContext,
    receiver::Receiver, state::State, threads::Threads, JoinHandle, LocalFuture, LocalJoinHandle,
};

use std::{
    future::Future,
    sync::{
        atomic::{AtomicBool, AtomicU64, Ordering},
        Arc,
    },
};

use crossbeam_utils::sync::Parker;

/* The actual executor */
#[derive(Default)]
pub(crate) struct Executor {
    /* Generate a new id for each task */
    task_id: AtomicU64,
    threads: Threads,
    state: State,
}

enum SetupResult<R> {
    Ok(R),
    Pending {
        receiver: Receiver<LocalRes<R>>,
        main_task_exited: Arc<AtomicBool>,
    },
}

impl Executor {
    pub(crate) fn local() -> Self {
        crate::PARKER.with(|parker| Self {
            task_id: AtomicU64::new(1),
            threads: Threads::default().with_current(parker.unparker().clone()),
            state: Default::default(),
        })
    }

    fn next_task_id(&self) -> u64 {
        self.task_id.fetch_add(1, Ordering::Relaxed)
    }

    fn next(&self) -> Option<FutureHolder> {
        self.state.next().or_else(|| crate::EXECUTOR.next())
    }

    pub(crate) fn block_on<R: 'static, F: Future<Output = R> + 'static>(&self, future: F) -> R {
        crate::PARKER.with(|parker| match self.setup(future, parker) {
            SetupResult::Ok(res) => res,
            SetupResult::Pending {
                receiver,
                main_task_exited,
            } => self.run(receiver, main_task_exited, parker),
        })
    }

    fn setup<R: 'static, F: Future<Output = R> + 'static>(
        &self,
        future: F,
        parker: &Parker,
    ) -> SetupResult<R> {
        crate::EXECUTOR.register_current_thread(parker.unparker().clone());
        let main_task = MainTaskContext::new(parker.unparker().clone());
        let main_task_exited = main_task.exited();
        let handle = self._spawn(LocalFuture(future), Some(main_task));
        let mut receiver = Receiver::new(handle, parker.unparker().clone());
        if let Some(res) = crate::EXECUTOR.poll_receiver(&mut receiver) {
            SetupResult::Ok(res.0)
        } else {
            SetupResult::Pending {
                receiver,
                main_task_exited,
            }
        }
    }

    fn run<R: 'static>(
        &self,
        mut receiver: Receiver<LocalRes<R>>,
        main_task_exited: Arc<AtomicBool>,
        parker: &Parker,
    ) -> R {
        loop {
            while let Some(future) = self.next() {
                future.run();
            }
            if main_task_exited.load(Ordering::Acquire) {
                if let Some(res) = crate::EXECUTOR.poll_receiver(&mut receiver) {
                    return res.0;
                }
            }
            if !self.state.has_pollable_tasks() && !crate::EXECUTOR.has_pollable_tasks() {
                parker.park();
            }
        }
    }

    pub(crate) fn spawn<R: 'static, F: Future<Output = R> + 'static>(
        &self,
        future: F,
    ) -> LocalJoinHandle<R> {
        self._spawn(future, None)
    }

    fn _spawn<R: 'static, F: Future<Output = R> + 'static>(
        &self,
        future: F,
        main_task: Option<MainTaskContext>,
    ) -> LocalJoinHandle<R> {
        let future = LocalFuture(future);
        let id = self.next_task_id();
        let (sender, receiver) = flume::bounded(1);
        FutureHolder::new(
            id,
            async move {
                let res = future.await;
                drop(sender.send_async(res).await);
            },
            self.threads.clone(),
            self.state.clone(),
            main_task,
        )
        .run();
        LocalJoinHandle(JoinHandle::new(id, receiver, self.state.clone()))
    }
}