netstack3_base/
resource_references.rs

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
130
131
132
// Copyright 2024 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Helper types, traits, and aliases for dealing with resource references.

use core::convert::Infallible as Never;

use crate::sync::{DynDebugReferences, MapRcNotifier, PrimaryRc, RcNotifier};

/// A context trait determining the types to be used for reference
/// notifications.
pub trait ReferenceNotifiers {
    /// The receiver for shared reference destruction notifications.
    type ReferenceReceiver<T: 'static>: 'static;
    /// The notifier for shared reference destruction notifications.
    type ReferenceNotifier<T: Send + 'static>: RcNotifier<T> + 'static;

    /// Creates a new Notifier/Receiver pair for `T`.
    ///
    /// `debug_references` is given to provide information on outstanding
    /// references that caused the notifier to be requested.
    fn new_reference_notifier<T: Send + 'static>(
        debug_references: DynDebugReferences,
    ) -> (Self::ReferenceNotifier<T>, Self::ReferenceReceiver<T>);
}

/// A context trait that allows core to defer observing proper resource cleanup
/// to bindings.
///
/// This trait exists as a debug utility to expose resources that are not
/// removed from the system as expected.
pub trait DeferredResourceRemovalContext: ReferenceNotifiers {
    /// Defers the removal of some resource `T` to bindings.
    ///
    /// Bindings can watch `receiver` and notify when resource removal is not
    /// completing in a timely manner.
    fn defer_removal<T: Send + 'static>(&mut self, receiver: Self::ReferenceReceiver<T>);

    /// A shorthand for [`defer_removal`] that takes a `ReferenceReceiver` from
    /// the `Deferred` variant of a [`RemoveResourceResult`].
    ///
    /// The default implementation is `track_caller` when the `instrumented`
    /// feature is available so implementers can track the caller location when
    /// needed.
    #[cfg_attr(feature = "instrumented", track_caller)]
    fn defer_removal_result<T: Send + 'static>(
        &mut self,
        result: RemoveResourceResultWithContext<T, Self>,
    ) {
        match result {
            // We don't need to do anything for synchronously removed resources.
            RemoveResourceResult::Removed(_) => (),
            RemoveResourceResult::Deferred(d) => self.defer_removal(d),
        }
    }
}

/// The result of removing some reference-counted resource from core.
#[derive(Debug)]
pub enum RemoveResourceResult<R, D> {
    /// The resource was synchronously removed and no more references to it
    /// exist.
    Removed(R),
    /// The resource was marked for destruction but there are still references
    /// to it in existence. The provided receiver can be polled on to observe
    /// resource destruction completion.
    Deferred(D),
}

impl<R, D> RemoveResourceResult<R, D> {
    /// Maps the `Removed` variant to a different type.
    pub fn map_removed<N, F: FnOnce(R) -> N>(self, f: F) -> RemoveResourceResult<N, D> {
        match self {
            Self::Removed(r) => RemoveResourceResult::Removed(f(r)),
            Self::Deferred(d) => RemoveResourceResult::Deferred(d),
        }
    }

    /// Maps the `Deferred` variant to a different type.
    pub fn map_deferred<N, F: FnOnce(D) -> N>(self, f: F) -> RemoveResourceResult<R, N> {
        match self {
            Self::Removed(r) => RemoveResourceResult::Removed(r),
            Self::Deferred(d) => RemoveResourceResult::Deferred(f(d)),
        }
    }
}

impl<R> RemoveResourceResult<R, Never> {
    /// A helper function to unwrap a [`RemoveResourceResult`] that can never be
    /// [`RemoveResourceResult::Deferred`].
    pub fn into_removed(self) -> R {
        match self {
            Self::Removed(r) => r,
        }
    }
}

/// An alias for [`RemoveResourceResult`] that extracts the receiver type from
/// the bindings context.
pub type RemoveResourceResultWithContext<S, BT> =
    RemoveResourceResult<S, <BT as ReferenceNotifiers>::ReferenceReceiver<S>>;

/// An extension of [`ReferenceNotifiers`] providing extra functionality.
pub trait ReferenceNotifiersExt: ReferenceNotifiers {
    /// Unwraps a [`PrimaryRc`] if it has no pending references, otherwise
    /// notifying with [`Self::ReferenceNotifier`].
    ///
    /// S: Is the state held behind the [`PrimaryRc`].
    /// O: Is the desired output state, once references have been destructed.
    /// F: Is a function that converts S to O.
    fn unwrap_or_notify_with_new_reference_notifier<
        S: Send + Sync + 'static,
        O: Send,
        F: Send + Copy + 'static + FnOnce(S) -> O,
    >(
        primary: PrimaryRc<S>,
        map: F,
    ) -> RemoveResourceResultWithContext<O, Self> {
        let debug_references = PrimaryRc::debug_references(&primary).into_dyn();
        match PrimaryRc::unwrap_or_notify_with(primary, || {
            let (notifier, receiver) = Self::new_reference_notifier::<O>(debug_references);
            let notifier = MapRcNotifier::new(notifier, map);
            (notifier, receiver)
        }) {
            Ok(state) => RemoveResourceResult::Removed(map(state)),
            Err(receiver) => RemoveResourceResult::Deferred(receiver),
        }
    }
}

impl<N: ReferenceNotifiers> ReferenceNotifiersExt for N {}