From 42251fafe727a5aa63d8e555963122fd94d9a629 Mon Sep 17 00:00:00 2001
From: Carl Lerche <me@carllerche.com>
Date: Wed, 17 May 2023 10:56:29 -0700
Subject: [PATCH] remove atomic-ness

---
 .../runtime/scheduler/multi_thread/worker.rs  | 52 +++++--------------
 tokio/src/runtime/task/atomic_cell.rs         | 22 ++++++--
 2 files changed, 32 insertions(+), 42 deletions(-)

diff --git a/tokio/src/runtime/scheduler/multi_thread/worker.rs b/tokio/src/runtime/scheduler/multi_thread/worker.rs
index 93f4dc99e..75d701b0f 100644
--- a/tokio/src/runtime/scheduler/multi_thread/worker.rs
+++ b/tokio/src/runtime/scheduler/multi_thread/worker.rs
@@ -626,53 +626,29 @@ impl Core {
             .or_else(|| self.run_queue.pop())
     }
 
-    /// Function responsible for stealing tasks from another worker
-    ///
-    /// Note: Only if less than half the workers are searching for tasks to steal
-    /// a new worker will actually try to steal. The idea is to make sure not all
-    /// workers will be trying to steal at the same time.
     fn steal_work(&mut self, worker: &Worker) -> Option<Notified> {
-        const ATTEMPTS: usize = 4;
-
         if !self.transition_to_searching(worker) {
             return None;
         }
 
-        // Number of remotes
         let num = worker.handle.shared.remotes.len();
+        // Start from a random worker
+        let start = self.rand.fastrand_n(num as u32) as usize;
 
-        // Run this a few times
-        for i in 0..ATTEMPTS {
-            // Only try stealing the LIFO slot
-            let steal_lifo = i == ATTEMPTS - 1;
+        for i in 0..num {
+            let i = (start + i) % num;
 
-            // Start from a random worker
-            let start = self.rand.fastrand_n(num as u32) as usize;
+            // Don't steal from ourself! We know we don't have work.
+            if i == worker.index {
+                continue;
+            }
 
-            for i in 0..num {
-                let i = (start + i) % num;
-
-                // Don't steal from ourself! We know we don't have work.
-                if i == worker.index {
-                    continue;
-                }
-
-                let target = &worker.handle.shared.remotes[i];
-                if let Some(task) = target
-                    .steal
-                    .steal_into(&mut self.run_queue, &mut self.metrics)
-                {
-                    return Some(task);
-                }
-
-                if steal_lifo {
-                    // Try stealing from the LIFO slot
-                    if let Some(task) = target.lifo_slot.take_remote() {
-                        self.metrics.incr_steal_count(1);
-                        self.metrics.incr_steal_operations();
-                        return Some(task);
-                    }
-                }
+            let target = &worker.handle.shared.remotes[i];
+            if let Some(task) = target
+                .steal
+                .steal_into(&mut self.run_queue, &mut self.metrics)
+            {
+                return Some(task);
             }
         }
 
diff --git a/tokio/src/runtime/task/atomic_cell.rs b/tokio/src/runtime/task/atomic_cell.rs
index 54b00d868..57e421ce9 100644
--- a/tokio/src/runtime/task/atomic_cell.rs
+++ b/tokio/src/runtime/task/atomic_cell.rs
@@ -5,25 +5,33 @@ use crate::runtime::task::{Header, Notified};
 use std::marker::PhantomData;
 use std::ptr::{self, NonNull};
 
-pub(crate) struct AtomicCell<S> {
-    task: AtomicPtr<Header>,
+pub(crate) struct AtomicCell<S: 'static> {
+    // task: AtomicPtr<Header>,
+    task: std::cell::UnsafeCell<Option<Notified<S>>>,
     _p: PhantomData<S>,
 }
 
+unsafe impl<S: 'static> Send for AtomicCell<S> {}
+unsafe impl<S: 'static> Sync for AtomicCell<S> {}
+
 impl<S> AtomicCell<S> {
     pub(crate) fn new() -> AtomicCell<S> {
         AtomicCell {
-            task: AtomicPtr::default(),
+            // task: AtomicPtr::default(),
+            task: Default::default(),
             _p: PhantomData,
         }
     }
 
     /// Should be called from a local context
     pub(crate) fn is_some(&self) -> bool {
-        !self.task.load(Acquire).is_null()
+        // !self.task.load(Acquire).is_null()
+        unsafe { (*self.task.get()).is_some() }
     }
 
     pub(crate) fn take_local(&self) -> Option<Notified<S>> {
+        unsafe { (*self.task.get()).take() }
+        /*
         let ptr = self.task.load(Acquire);
 
         if ptr.is_null() {
@@ -39,9 +47,12 @@ impl<S> AtomicCell<S> {
         }
 
         NonNull::new(ptr).map(|ptr| unsafe { Notified::from_raw(ptr) })
+        */
     }
 
     pub(crate) fn swap_local(&self, task: Notified<S>) -> Option<Notified<S>> {
+        std::mem::replace(unsafe { &mut (*self.task.get()) }, Some(task))
+        /*
         let next = task.into_raw().as_ptr();
         let prev = self.task.load(Acquire);
 
@@ -66,8 +77,10 @@ impl<S> AtomicCell<S> {
         // 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);
 
@@ -87,4 +100,5 @@ impl<S> AtomicCell<S> {
 
         return None;
     }
+    */
 }