1 use std::cell::UnsafeCell;
2 use std::fmt;
3 use std::ops;
4 use std::panic;
5 
6 /// `AtomicUsize` providing an additional `unsync_load` function.
7 pub(crate) struct AtomicUsize {
8     inner: UnsafeCell<std::sync::atomic::AtomicUsize>,
9 }
10 
11 unsafe impl Send for AtomicUsize {}
12 unsafe impl Sync for AtomicUsize {}
13 impl panic::RefUnwindSafe for AtomicUsize {}
14 impl panic::UnwindSafe for AtomicUsize {}
15 
16 impl AtomicUsize {
new(val: usize) -> AtomicUsize17     pub(crate) const fn new(val: usize) -> AtomicUsize {
18         let inner = UnsafeCell::new(std::sync::atomic::AtomicUsize::new(val));
19         AtomicUsize { inner }
20     }
21 
22     /// Performs an unsynchronized load.
23     ///
24     /// # Safety
25     ///
26     /// All mutations must have happened before the unsynchronized load.
27     /// Additionally, there must be no concurrent mutations.
unsync_load(&self) -> usize28     pub(crate) unsafe fn unsync_load(&self) -> usize {
29         // See <https://github.com/tokio-rs/tokio/issues/6155>
30         self.load(std::sync::atomic::Ordering::Relaxed)
31     }
32 
with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R33     pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {
34         // safety: we have mutable access
35         f(unsafe { (*self.inner.get()).get_mut() })
36     }
37 }
38 
39 impl ops::Deref for AtomicUsize {
40     type Target = std::sync::atomic::AtomicUsize;
41 
deref(&self) -> &Self::Target42     fn deref(&self) -> &Self::Target {
43         // safety: it is always safe to access `&self` fns on the inner value as
44         // we never perform unsafe mutations.
45         unsafe { &*self.inner.get() }
46     }
47 }
48 
49 impl ops::DerefMut for AtomicUsize {
deref_mut(&mut self) -> &mut Self::Target50     fn deref_mut(&mut self) -> &mut Self::Target {
51         // safety: we hold `&mut self`
52         unsafe { &mut *self.inner.get() }
53     }
54 }
55 
56 impl fmt::Debug for AtomicUsize {
fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result57     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
58         (**self).fmt(fmt)
59     }
60 }
61