1 use std::cell::UnsafeCell; 2 use std::fmt; 3 use std::ops; 4 5 /// `AtomicUsize` providing an additional `load_unsync` function. 6 pub(crate) struct AtomicUsize { 7 inner: UnsafeCell<std::sync::atomic::AtomicUsize>, 8 } 9 10 unsafe impl Send for AtomicUsize {} 11 unsafe impl Sync for AtomicUsize {} 12 13 impl AtomicUsize { new(val: usize) -> AtomicUsize14 pub(crate) const fn new(val: usize) -> AtomicUsize { 15 let inner = UnsafeCell::new(std::sync::atomic::AtomicUsize::new(val)); 16 AtomicUsize { inner } 17 } 18 19 /// Performs an unsynchronized load. 20 /// 21 /// # Safety 22 /// 23 /// All mutations must have happened before the unsynchronized load. 24 /// Additionally, there must be no concurrent mutations. unsync_load(&self) -> usize25 pub(crate) unsafe fn unsync_load(&self) -> usize { 26 *(*self.inner.get()).get_mut() 27 } 28 with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R29 pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R { 30 // safety: we have mutable access 31 f(unsafe { (*self.inner.get()).get_mut() }) 32 } 33 } 34 35 impl ops::Deref for AtomicUsize { 36 type Target = std::sync::atomic::AtomicUsize; 37 deref(&self) -> &Self::Target38 fn deref(&self) -> &Self::Target { 39 // safety: it is always safe to access `&self` fns on the inner value as 40 // we never perform unsafe mutations. 41 unsafe { &*self.inner.get() } 42 } 43 } 44 45 impl ops::DerefMut for AtomicUsize { deref_mut(&mut self) -> &mut Self::Target46 fn deref_mut(&mut self) -> &mut Self::Target { 47 // safety: we hold `&mut self` 48 unsafe { &mut *self.inner.get() } 49 } 50 } 51 52 impl fmt::Debug for AtomicUsize { fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result53 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { 54 (**self).fmt(fmt) 55 } 56 } 57