From 6366f2494190dd9d9dced9a0af9bab8ffe8edcad Mon Sep 17 00:00:00 2001
From: Carl Lerche <me@carllerche.com>
Date: Mon, 26 Jun 2023 17:36:43 +0000
Subject: [PATCH] wip

---
 .../runtime/scheduler/multi_thread/worker.rs  |  3 -
 tokio/src/runtime/task/atomic_cell.rs         | 99 -------------------
 tokio/src/runtime/task/mod.rs                 |  3 -
 3 files changed, 105 deletions(-)
 delete mode 100644 tokio/src/runtime/task/atomic_cell.rs

diff --git a/tokio/src/runtime/scheduler/multi_thread/worker.rs b/tokio/src/runtime/scheduler/multi_thread/worker.rs
index ba35ac5b3..cca3a19df 100644
--- a/tokio/src/runtime/scheduler/multi_thread/worker.rs
+++ b/tokio/src/runtime/scheduler/multi_thread/worker.rs
@@ -257,9 +257,6 @@ type Task = task::Task<Arc<Handle>>;
 /// A notified task handle
 type Notified = task::Notified<Arc<Handle>>;
 
-/// Stealable LIFO slot
-type Lifo = task::AtomicCell<Arc<Handle>>;
-
 /// Value picked out of thin-air. Running the LIFO slot a handful of times
 /// seemms sufficient to benefit from locality. More than 3 times probably is
 /// overweighing. The value can be tuned in the future with data that shows
diff --git a/tokio/src/runtime/task/atomic_cell.rs b/tokio/src/runtime/task/atomic_cell.rs
deleted file mode 100644
index 4ecfe108a..000000000
--- a/tokio/src/runtime/task/atomic_cell.rs
+++ /dev/null
@@ -1,99 +0,0 @@
-use crate::loom::sync::atomic::AtomicPtr;
-use crate::loom::sync::atomic::Ordering::{AcqRel, Acquire, Release};
-use crate::runtime::task::{Header, Notified, RawTask};
-
-use std::marker::PhantomData;
-use std::ptr::{self, NonNull};
-
-pub(crate) struct AtomicCell<S> {
-    task: AtomicPtr<Header>,
-    _p: PhantomData<S>,
-}
-
-impl<S> AtomicCell<S> {
-    pub(crate) fn new() -> AtomicCell<S> {
-        AtomicCell {
-            task: AtomicPtr::default(),
-            _p: PhantomData,
-        }
-    }
-
-    /// Should be called from a local context
-    pub(crate) fn is_some(&self) -> bool {
-        !self.is_none()
-    }
-
-    pub(crate) fn is_none(&self) -> bool {
-        self.task.load(Acquire).is_null()
-    }
-
-    pub(crate) fn take_local(&self) -> Option<Notified<S>> {
-        let ptr = self.task.load(Acquire);
-
-        if ptr.is_null() {
-            return None;
-        }
-
-        if self
-            .task
-            .compare_exchange(ptr, ptr::null_mut(), AcqRel, Acquire)
-            .is_err()
-        {
-            return None;
-        }
-
-        NonNull::new(ptr).map(|ptr| unsafe { Notified::from_raw(RawTask::from_raw(ptr)) })
-    }
-
-    pub(crate) fn swap_local(&self, task: Notified<S>) -> Option<Notified<S>> {
-        let next = task.into_raw().header_ptr().as_ptr();
-        let prev = self.task.load(Acquire);
-
-        if prev.is_null() {
-            // Since this method is only called from the only thread that can
-            // set the value to !null, it is safe to use a store here.
-            self.task.store(next, Release);
-            return None;
-        }
-
-        if self
-            .task
-            .compare_exchange(prev, next, AcqRel, Acquire)
-            .is_ok()
-        {
-            // Safety: we already checked !null above
-            let prev =
-                unsafe { Notified::from_raw(RawTask::from_raw(NonNull::new_unchecked(prev))) };
-            return Some(prev);
-        }
-
-        // The compare-exchanged failed, but there is no need to try again since
-        // this is the only thread that could set the cell to !null.
-        self.task.store(next, Release);
-        None
-    }
-
-    pub(crate) fn take_remote(&self) -> Option<Notified<S>> {
-        let task = self.task.load(Acquire);
-
-        if task.is_null() {
-            return None;
-        }
-
-        // std::thread::sleep(std::time::Duration::from_micros(3));
-
-        // Try to take it once
-        if self
-            .task
-            .compare_exchange(task, ptr::null_mut(), Acquire, Acquire)
-            .is_ok()
-        {
-            // safety: we checked for null above
-            return Some(unsafe {
-                Notified::from_raw(RawTask::from_raw(NonNull::new_unchecked(task)))
-            });
-        }
-
-        None
-    }
-}
diff --git a/tokio/src/runtime/task/mod.rs b/tokio/src/runtime/task/mod.rs
index e9fec729a..932552fb9 100644
--- a/tokio/src/runtime/task/mod.rs
+++ b/tokio/src/runtime/task/mod.rs
@@ -168,9 +168,6 @@
 // unstable. This should be removed once `JoinSet` is stabilized.
 #![cfg_attr(not(tokio_unstable), allow(dead_code))]
 
-mod atomic_cell;
-pub(crate) use atomic_cell::AtomicCell;
-
 mod core;
 use self::core::Cell;
 use self::core::Header;