From 5b74dc8acca8b915af29d12ae0a43bde15c5df97 Mon Sep 17 00:00:00 2001
From: John Nunley <dev@notgull.net>
Date: Thu, 25 Apr 2024 22:53:55 -0700
Subject: [PATCH] Merge fetch_and andthe prev_value check
cc https://github.com/smol-rs/concurrent-queue/pull/58#discussion_r1574686897
Signed-off-by: John Nunley <dev@notgull.net>
---
src/single.rs | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)
diff --git a/src/single.rs b/src/single.rs
index 048f486..f88c478 100644
--- a/src/single.rs
+++ b/src/single.rs
@@ -65,23 +65,27 @@ impl<T> Single<T> {
}
if prev == state {
- // Swap out the value.
- // SAFETY: We have locked the state.
- let prev_value = unsafe {
- self.slot
- .with_mut(move |slot| ptr::replace(slot, MaybeUninit::new(value)))
- };
-
- // We can unlock the slot now.
- self.state.fetch_and(!LOCKED, Ordering::Release);
-
- // If the value was pushed, initialize it and return it.
+ // If the value was pushed, swap out the value.
let prev_value = if prev & PUSHED == 0 {
+ // SAFETY: write is safe because we have locked the state.
+ self.slot.with_mut(|slot| unsafe {
+ slot.write(MaybeUninit::new(value));
+ });
None
} else {
- Some(unsafe { prev_value.assume_init() })
+ // SAFETY: replace is safe because we have locked the state, and
+ // assume_init is safe because we have checked that the value was pushed.
+ let prev_value = unsafe {
+ self.slot.with_mut(move |slot| {
+ ptr::replace(slot, MaybeUninit::new(value)).assume_init()
+ })
+ };
+ Some(prev_value)
};
+ // We can unlock the slot now.
+ self.state.fetch_and(!LOCKED, Ordering::Release);
+
// Return the old value.
return Ok(prev_value);
}