sel4_async_single_threaded_executor/
enter.rs

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1//
2// Copyright 2023, Colias Group, LLC
3// Copyright (c) 2017 The Tokio Authors
4// Copyright (c) 2016 Alex Crichton
5//
6// SPDX-License-Identifier: MIT OR Apache-2.0
7//
8
9use core::cell::Cell;
10use core::fmt;
11
12#[thread_local]
13static ENTERED: Cell<bool> = Cell::new(false);
14
15/// Represents an executor context.
16///
17/// For more details, see [`enter` documentation](enter()).
18pub struct Enter {
19    _priv: (),
20}
21
22/// An error returned by `enter` if an execution scope has already been
23/// entered.
24pub struct EnterError {
25    _priv: (),
26}
27
28impl fmt::Debug for EnterError {
29    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
30        f.debug_struct("EnterError").finish()
31    }
32}
33
34impl fmt::Display for EnterError {
35    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
36        write!(f, "an execution scope has already been entered")
37    }
38}
39
40/// Marks the current thread as being within the dynamic extent of an
41/// executor.
42///
43/// Executor implementations should call this function before beginning to
44/// execute a task, and drop the returned [`Enter`](Enter) value after
45/// completing task execution:
46///
47/// ```
48/// use futures::executor::enter;
49///
50/// let enter = enter().expect("...");
51/// /* run task */
52/// drop(enter);
53/// ```
54///
55/// Doing so ensures that executors aren't
56/// accidentally invoked in a nested fashion.
57///
58/// # Error
59///
60/// Returns an error if the current thread is already marked, in which case the
61/// caller should panic with a tailored error message.
62pub fn enter() -> Result<Enter, EnterError> {
63    if ENTERED.get() {
64        Err(EnterError { _priv: () })
65    } else {
66        ENTERED.set(true);
67        Ok(Enter { _priv: () })
68    }
69}
70
71impl fmt::Debug for Enter {
72    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
73        f.debug_struct("Enter").finish()
74    }
75}
76
77impl Drop for Enter {
78    fn drop(&mut self) {
79        assert!(ENTERED.get());
80        ENTERED.set(false);
81    }
82}
sel4_async_single_threaded_executor/enter.rs

sel4_async_single_threaded_executor/
enter.rs
