Merge pull request #4608 from diondokter/upstream-drs-2

[embassy-executor]: Upstream "Earliest Deadline First" Scheduler (version 2)

1 files changed, 0 insertions, 88 deletions

diff --git a/embassy-executor/src/raw/run_queue_atomics.rs b/embassy-executor/src/raw/run_queue_atomics.rs
deleted file mode 100644
index ce511d79a..000000000
--- a/embassy-executor/src/raw/run_queue_atomics.rs
+++ /dev/null
@@ -1,88 +0,0 @@
-use core::ptr;
-use core::ptr::NonNull;
-use core::sync::atomic::{AtomicPtr, Ordering};
-
-use super::{TaskHeader, TaskRef};
-use crate::raw::util::SyncUnsafeCell;
-
-pub(crate) struct RunQueueItem {
-    next: SyncUnsafeCell<Option<TaskRef>>,
-}
-
-impl RunQueueItem {
-    pub const fn new() -> Self {
-        Self {
-            next: SyncUnsafeCell::new(None),
-        }
-    }
-}
-
-/// Atomic task queue using a very, very simple lock-free linked-list queue:
-///
-/// To enqueue a task, task.next is set to the old head, and head is atomically set to task.
-///
-/// Dequeuing is done in batches: the queue is emptied by atomically replacing head with
-/// null. Then the batch is iterated following the next pointers until null is reached.
-///
-/// Note that batches will be iterated in the reverse order as they were enqueued. This is OK
-/// for our purposes: it can't create fairness problems since the next batch won't run until the
-/// current batch is completely processed, so even if a task enqueues itself instantly (for example
-/// by waking its own waker) can't prevent other tasks from running.
-pub(crate) struct RunQueue {
-    head: AtomicPtr<TaskHeader>,
-}
-
-impl RunQueue {
-    pub const fn new() -> Self {
-        Self {
-            head: AtomicPtr::new(ptr::null_mut()),
-        }
-    }
-
-    /// Enqueues an item. Returns true if the queue was empty.
-    ///
-    /// # Safety
-    ///
-    /// `item` must NOT be already enqueued in any queue.
-    #[inline(always)]
-    pub(crate) unsafe fn enqueue(&self, task: TaskRef, _: super::state::Token) -> bool {
-        let mut was_empty = false;
-
-        self.head
-            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |prev| {
-                was_empty = prev.is_null();
-                unsafe {
-                    // safety: the pointer is either null or valid
-                    let prev = NonNull::new(prev).map(|ptr| TaskRef::from_ptr(ptr.as_ptr()));
-                    // safety: there are no concurrent accesses to `next`
-                    task.header().run_queue_item.next.set(prev);
-                }
-                Some(task.as_ptr() as *mut _)
-            })
-            .ok();
-
-        was_empty
-    }
-
-    /// Empty the queue, then call `on_task` for each task that was in the queue.
-    /// NOTE: It is OK for `on_task` to enqueue more tasks. In this case they're left in the queue
-    /// and will be processed by the *next* call to `dequeue_all`, *not* the current one.
-    pub(crate) fn dequeue_all(&self, on_task: impl Fn(TaskRef)) {
-        // Atomically empty the queue.
-        let ptr = self.head.swap(ptr::null_mut(), Ordering::AcqRel);
-
-        // safety: the pointer is either null or valid
-        let mut next = unsafe { NonNull::new(ptr).map(|ptr| TaskRef::from_ptr(ptr.as_ptr())) };
-
-        // Iterate the linked list of tasks that were previously in the queue.
-        while let Some(task) = next {
-            // If the task re-enqueues itself, the `next` pointer will get overwritten.
-            // Therefore, first read the next pointer, and only then process the task.
-            // safety: there are no concurrent accesses to `next`
-            next = unsafe { task.header().run_queue_item.next.get() };
-
-            task.header().state.run_dequeue();
-            on_task(task);
-        }
-    }
-}