nautilus_core/
shared.rs

1// -------------------------------------------------------------------------------------------------
2//  Copyright (C) 2015-2025 Nautech Systems Pty Ltd. All rights reserved.
3//  https://nautechsystems.io
4//
5//  Licensed under the GNU Lesser General Public License Version 3.0 (the "License");
6//  You may not use this file except in compliance with the License.
7//  You may obtain a copy of the License at https://www.gnu.org/licenses/lgpl-3.0.en.html
8//
9//  Unless required by applicable law or agreed to in writing, software
10//  distributed under the License is distributed on an "AS IS" BASIS,
11//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12//  See the License for the specific language governing permissions and
13//  limitations under the License.
14// -------------------------------------------------------------------------------------------------
15
16//! Efficient and ergonomic wrappers around frequently-used `Rc<RefCell<T>>` / `Weak<RefCell<T>>` pairs.
17//!
18//! The NautilusTrader codebase heavily relies on shared, interior-mutable ownership for many
19//! engine components (`Rc<RefCell<T>>`). Repeating that verbose type across many APIs—alongside
20//! its weak counterpart—clutters code and increases the likelihood of accidentally storing a
21//! strong reference where only a weak reference is required (leading to reference cycles).
22//!
23//! `SharedCell<T>` and `WeakCell<T>` are zero-cost new-types that make the intent explicit and
24//! offer convenience helpers (`downgrade`, `upgrade`, `borrow`, `borrow_mut`). Because the
25//! wrappers are `#[repr(transparent)]`, they have the exact same memory layout as the wrapped
26//! `Rc` / `Weak` and introduce no runtime overhead.
27
28//! ## Choosing between `SharedCell` and `WeakCell`
29//!
30//! * Use **`SharedCell<T>`** when the current owner genuinely *owns* (or co-owns) the value –
31//!   just as you would normally store an `Rc<RefCell<T>>`.
32//! * Use **`WeakCell<T>`** for back-references that could otherwise form a reference cycle.
33//!   The back-pointer does **not** keep the value alive, and every access must first
34//!   `upgrade()` to a strong `SharedCell`. This pattern is how we break circular ownership such
35//!   as *Exchange ↔ `ExecutionClient`*: the exchange keeps a `SharedCell` to the client, while the
36//!   client holds only a `WeakCell` back to the exchange.
37
38use std::{
39    cell::{Ref, RefCell, RefMut},
40    rc::{Rc, Weak},
41};
42
43/// Strong, shared ownership of `T` with interior mutability.
44#[repr(transparent)]
45#[derive(Debug)]
46pub struct SharedCell<T>(Rc<RefCell<T>>);
47
48impl<T> Clone for SharedCell<T> {
49    fn clone(&self) -> Self {
50        Self(self.0.clone())
51    }
52}
53
54impl<T> SharedCell<T> {
55    /// Wraps a value inside `Rc<RefCell<..>>`.
56    #[inline]
57    pub fn new(value: T) -> Self {
58        Self(Rc::new(RefCell::new(value)))
59    }
60
61    /// Creates a [`WeakCell`] pointing to the same allocation.
62    #[inline]
63    #[must_use]
64    pub fn downgrade(&self) -> WeakCell<T> {
65        WeakCell(Rc::downgrade(&self.0))
66    }
67
68    /// Immutable borrow of the inner value.
69    #[inline]
70    #[must_use]
71    pub fn borrow(&self) -> Ref<'_, T> {
72        self.0.borrow()
73    }
74
75    /// Mutable borrow of the inner value.
76    #[inline]
77    #[must_use]
78    pub fn borrow_mut(&self) -> RefMut<'_, T> {
79        self.0.borrow_mut()
80    }
81
82    /// Number of active strong references.
83    #[inline]
84    #[must_use]
85    pub fn strong_count(&self) -> usize {
86        Rc::strong_count(&self.0)
87    }
88
89    /// Number of active weak references.
90    #[inline]
91    #[must_use]
92    pub fn weak_count(&self) -> usize {
93        Rc::weak_count(&self.0)
94    }
95}
96
97impl<T> From<Rc<RefCell<T>>> for SharedCell<T> {
98    fn from(inner: Rc<RefCell<T>>) -> Self {
99        Self(inner)
100    }
101}
102
103impl<T> From<SharedCell<T>> for Rc<RefCell<T>> {
104    fn from(shared: SharedCell<T>) -> Self {
105        shared.0
106    }
107}
108
109impl<T> std::ops::Deref for SharedCell<T> {
110    type Target = Rc<RefCell<T>>;
111
112    fn deref(&self) -> &Self::Target {
113        &self.0
114    }
115}
116
117/// Weak counterpart to [`SharedCell`].
118#[repr(transparent)]
119#[derive(Debug)]
120pub struct WeakCell<T>(Weak<RefCell<T>>);
121
122impl<T> Clone for WeakCell<T> {
123    fn clone(&self) -> Self {
124        Self(self.0.clone())
125    }
126}
127
128impl<T> WeakCell<T> {
129    /// Attempts to upgrade the weak reference to a strong [`SharedCell`].
130    #[inline]
131    pub fn upgrade(&self) -> Option<SharedCell<T>> {
132        self.0.upgrade().map(SharedCell)
133    }
134
135    /// Returns `true` if the pointed-to value has been dropped.
136    #[inline]
137    #[must_use]
138    pub fn is_dropped(&self) -> bool {
139        self.0.strong_count() == 0
140    }
141}
142
143impl<T> From<Weak<RefCell<T>>> for WeakCell<T> {
144    fn from(inner: Weak<RefCell<T>>) -> Self {
145        Self(inner)
146    }
147}
148
149impl<T> From<WeakCell<T>> for Weak<RefCell<T>> {
150    fn from(cell: WeakCell<T>) -> Self {
151        cell.0
152    }
153}
nautilus_core/shared.rs

nautilus_core/
shared.rs
