m: Remove the thread-local executor optimization

This was added in #37 as an optimization, but has since lead to many bugs. See
the issues #53, #57 and #60 for more information. I do not have the bandwidth
to address all of these bugs, so I'm taking the path of least resistance by
just removing the problematic code.

CLoses #53, #57 and #60

Signed-off-by: John Nunley <dev@notgull.net>

Author: notgull

Diff for: src/lib.rs

@@ -26,7 +26,6 @@
     html_logo_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
 )]
 
-use std::cell::RefCell;
 use std::fmt;
 use std::future::Future;
 use std::marker::PhantomData;
@@ -236,56 +235,29 @@ impl<'a> Executor<'a> {
         let runner = Runner::new(self.state());
         let mut rng = fastrand::Rng::new();
 
-        // Set the local queue while we're running.
-        LocalQueue::set(self.state(), &runner.local, {
-            let runner = &runner;
-            async move {
-                // A future that runs tasks forever.
-                let run_forever = async {
-                    loop {
-                        for _ in 0..200 {
-                            let runnable = runner.runnable(&mut rng).await;
-                            runnable.run();
-                        }
-                        future::yield_now().await;
-                    }
-                };
-
-                // Run `future` and `run_forever` concurrently until `future` completes.
-                future.or(run_forever).await
+        // A future that runs tasks forever.
+        let run_forever = async {
+            loop {
+                for _ in 0..200 {
+                    let runnable = runner.runnable(&mut rng).await;
+                    runnable.run();
+                }
+                future::yield_now().await;
             }
-        })
-        .await
+        };
+
+        // Run `future` and `run_forever` concurrently until `future` completes.
+        future.or(run_forever).await
     }
 
     /// Returns a function that schedules a runnable task when it gets woken up.
     fn schedule(&self) -> impl Fn(Runnable) + Send + Sync + 'static {
         let state = self.state().clone();
 
-        // If possible, push into the current local queue and notify the ticker.
+        // TODO: If possible, push into the current local queue and notify the ticker.
         move |runnable| {
-            let mut runnable = Some(runnable);
-
-            // Try to push into the local queue.
-            LocalQueue::with(|local_queue| {
-                // Make sure that we don't accidentally push to an executor that isn't ours.
-                if local_queue.state != &*state as *const State as usize {
-                    return;
-                }
-
-                if let Err(e) = local_queue.queue.push(runnable.take().unwrap()) {
-                    runnable = Some(e.into_inner());
-                    return;
-                }
-
-                local_queue.waker.wake_by_ref();
-            });
-
-            // If the local queue push failed, just push to the global queue.
-            if let Some(runnable) = runnable {
-                state.queue.push(runnable).unwrap();
-                state.notify();
-            }
+            state.queue.push(runnable).unwrap();
+            state.notify();
         }
     }
 
@@ -853,106 +825,6 @@ impl Drop for Runner<'_> {
     }
 }
 
-/// The state of the currently running local queue.
-struct LocalQueue {
-    /// The pointer to the state of the executor.
-    ///
-    /// Used to make sure we don't push runnables to the wrong executor.
-    state: usize,
-
-    /// The concurrent queue.
-    queue: Arc<ConcurrentQueue<Runnable>>,
-
-    /// The waker for the runnable.
-    waker: Waker,
-}
-
-impl LocalQueue {
-    /// Run a function with the current local queue.
-    fn with<R>(f: impl FnOnce(&LocalQueue) -> R) -> Option<R> {
-        std::thread_local! {
-            /// The current local queue.
-            static LOCAL_QUEUE: RefCell<Option<LocalQueue>> = RefCell::new(None);
-        }
-
-        impl LocalQueue {
-            /// Run a function with a set local queue.
-            async fn set<F>(
-                state: &State,
-                queue: &Arc<ConcurrentQueue<Runnable>>,
-                fut: F,
-            ) -> F::Output
-            where
-                F: Future,
-            {
-                // Make the `LocalQueue` structure.
-                let make_local_queue = |waker: &Waker| LocalQueue {
-                    state: state as *const State as usize,
-                    queue: queue.clone(),
-                    waker: waker.clone(),
-                };
-
-                // Store the local queue and the current waker.
-                let mut old = with_waker(|waker| {
-                    LOCAL_QUEUE.with(move |slot| slot.borrow_mut().replace(make_local_queue(waker)))
-                })
-                .await;
-
-                // Restore the old local queue on drop.
-                let _guard = CallOnDrop(move || {
-                    let old = old.take();
-                    let _ = LOCAL_QUEUE.try_with(move |slot| {
-                        *slot.borrow_mut() = old;
-                    });
-                });
-
-                // Pin the future.
-                futures_lite::pin!(fut);
-
-                // Run it such that the waker is updated every time it's polled.
-                future::poll_fn(move |cx| {
-                    LOCAL_QUEUE
-                        .try_with({
-                            let waker = cx.waker();
-                            move |slot| {
-                                let mut slot = slot.borrow_mut();
-                                let qaw = match slot.as_mut() {
-                                    None => {
-                                        // Another local queue dropped itself and replaced with None,
-                                        // we can take its place!
-                                        *slot = Some(make_local_queue(waker));
-                                        return;
-                                    }
-                                    Some(qaw) => qaw,
-                                };
-
-                                // If we've been replaced, just ignore the slot.
-                                if !Arc::ptr_eq(&qaw.queue, queue) {
-                                    return;
-                                }
-
-                                // Update the waker, if it has changed.
-                                if !qaw.waker.will_wake(waker) {
-                                    qaw.waker = waker.clone();
-                                }
-                            }
-                        })
-                        .ok();
-
-                    // Poll the future.
-                    fut.as_mut().poll(cx)
-                })
-                .await
-            }
-        }
-
-        LOCAL_QUEUE
-            .try_with(|local_queue| local_queue.borrow().as_ref().map(f))
-            .ok()
-            .flatten()
-    }
-}
-
 /// Steals some items from one queue into another.
 fn steal<T>(src: &ConcurrentQueue<T>, dest: &ConcurrentQueue<T>) {
     // Half of `src`'s length rounded up.
@@ -1053,15 +925,6 @@ impl<F: FnMut()> Drop for CallOnDrop<F> {
     }
 }
 
-/// Run a closure with the current waker.
-fn with_waker<F: FnOnce(&Waker) -> R, R>(f: F) -> impl Future<Output = R> {
-    let mut f = Some(f);
-    future::poll_fn(move |cx| {
-        let f = f.take().unwrap();
-        Poll::Ready(f(cx.waker()))
-    })
-}
-
 fn _ensure_send_and_sync() {
     use futures_lite::future::pending;