git_features/
threading.rs

1//! Type definitions for putting shared ownership and synchronized mutation behind the `threading` feature toggle.
2//!
3//! That way, single-threaded applications will not have to use thread-safe primitives, and simply do not specify the 'threading' feature.
4
5#[cfg(feature = "parallel")]
6mod _impl {
7    use std::sync::Arc;
8
9    /// A thread-safe cell which can be written to only once.
10    #[cfg(feature = "once_cell")]
11    pub type OnceCell<T> = once_cell::sync::OnceCell<T>;
12    /// A reference counted pointer type for shared ownership.
13    pub type OwnShared<T> = Arc<T>;
14    /// A synchronization primitive which can start read-only and transition to support mutation.
15    pub type MutableOnDemand<T> = parking_lot::RwLock<T>;
16    /// A synchronization primitive which provides read-write access right away.
17    pub type Mutable<T> = parking_lot::Mutex<T>;
18    /// A guarded reference suitable for safekeeping in a struct.
19    pub type RefGuard<'a, T> = parking_lot::RwLockReadGuard<'a, T>;
20    /// A mapped reference created from a RefGuard
21    pub type MappedRefGuard<'a, U> = parking_lot::MappedRwLockReadGuard<'a, U>;
22
23    /// Get a shared reference through a [`MutableOnDemand`] for read-only access.
24    pub fn get_ref<T>(v: &MutableOnDemand<T>) -> RefGuard<'_, T> {
25        v.read()
26    }
27
28    /// Get a mutable reference through a [`MutableOnDemand`] for read-write access.
29    pub fn get_mut<T>(v: &MutableOnDemand<T>) -> parking_lot::RwLockWriteGuard<'_, T> {
30        v.write()
31    }
32
33    /// Get a mutable reference through a [`Mutable`] for read-write access.
34    pub fn lock<T>(v: &Mutable<T>) -> parking_lot::MutexGuard<'_, T> {
35        v.lock()
36    }
37
38    /// Downgrade a handle previously obtained with [`get_mut()`] to drop mutation support.
39    pub fn downgrade_mut_to_ref<'a, T>(
40        v: parking_lot::RwLockWriteGuard<'a, T>,
41        _orig: &'a MutableOnDemand<T>,
42    ) -> RefGuard<'a, T> {
43        parking_lot::RwLockWriteGuard::downgrade(v)
44    }
45
46    /// Map a read guard into a sub-type it contains.
47    pub fn map_ref<T, U: ?Sized>(v: RefGuard<'_, T>, f: impl FnOnce(&T) -> &U) -> MappedRefGuard<'_, U> {
48        parking_lot::RwLockReadGuard::map(v, f)
49    }
50}
51
52#[cfg(not(feature = "parallel"))]
53mod _impl {
54    use std::{
55        cell::{Ref, RefCell, RefMut},
56        rc::Rc,
57    };
58
59    /// A thread-safe cell which can be written to only once.
60    #[cfg(feature = "once_cell")]
61    pub type OnceCell<T> = once_cell::unsync::OnceCell<T>;
62    /// A reference counted pointer type for shared ownership.
63    pub type OwnShared<T> = Rc<T>;
64    /// A synchronization primitive which can start read-only and transition to support mutation.
65    pub type MutableOnDemand<T> = RefCell<T>;
66    /// A synchronization primitive which provides read-write access right away.
67    pub type Mutable<T> = RefCell<T>;
68    /// A guarded reference suitable for safekeeping in a struct.
69    pub type RefGuard<'a, T> = Ref<'a, T>;
70    /// A mapped reference created from a RefGuard
71    pub type MappedRefGuard<'a, U> = Ref<'a, U>;
72
73    /// Get a shared reference through a [`MutableOnDemand`] for read-only access.
74    pub fn get_mut<T>(v: &RefCell<T>) -> RefMut<'_, T> {
75        v.borrow_mut()
76    }
77
78    /// Get a mutable reference through a [`Mutable`] for read-write access.
79    pub fn lock<T>(v: &Mutable<T>) -> RefMut<'_, T> {
80        v.borrow_mut()
81    }
82
83    /// Get a mutable reference through a [`MutableOnDemand`] for read-write access.
84    pub fn get_ref<T>(v: &RefCell<T>) -> RefGuard<'_, T> {
85        v.borrow()
86    }
87
88    /// Downgrade a handle previously obtained with [`upgrade_ref_to_mut()`] to drop mutation support.
89    pub fn downgrade_mut_to_ref<'a, T>(v: RefMut<'a, T>, orig: &'a RefCell<T>) -> RefGuard<'a, T> {
90        drop(v);
91        orig.borrow()
92    }
93
94    /// Map a read guard into a sub-type it contains.
95    pub fn map_ref<T, U: ?Sized>(v: RefGuard<'_, T>, f: impl FnOnce(&T) -> &U) -> MappedRefGuard<'_, U> {
96        Ref::map(v, f)
97    }
98}
99
100pub use _impl::*;
git_features/threading.rs

git_features/
threading.rs
