libasync: clean up executor

libasync/src/executor.rs

@@ -1,13 +1,12 @@
+use alloc::{boxed::Box, vec::Vec};
 use core::{
-    cell::{RefCell, UnsafeCell},
+    cell::UnsafeCell,
     future::Future,
     mem::MaybeUninit,
     pin::Pin,
     sync::atomic::{AtomicBool, Ordering},
     task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
 };
-use alloc::{boxed::Box, vec::Vec};
-//use futures::future::FutureExt;
 use pin_utils::pin_mut;
 
 // NOTE `*const ()` is &AtomicBool
@@ -39,35 +38,32 @@ fn wrap_waker(ready: &AtomicBool) -> Waker {
 /// This is a singleton
 pub struct Executor {
     // Entered block_on() already?
-    in_block_on: RefCell<bool>,
+    in_block_on: bool,
 
     /// Tasks reside on the heap, so that we just queue pointers. They
     /// must also be pinned in memory because our RawWaker is a pointer
     /// to their `ready` field.
-    tasks: RefCell<Vec<Pin<Box<Task>>>>,
+    tasks: Vec<Pin<Box<Task>>>,
 }
 
 impl Executor {
     /// Creates a new instance of the executor
     pub fn new() -> Self {
         Self {
-            in_block_on: RefCell::new(false),
+            in_block_on: false,
-            tasks: RefCell::new(Vec::new()),
+            tasks: Vec::new(),
         }
     }
 
-    pub fn block_on<T>(&self, f: impl Future<Output = T>) -> T {
+    pub fn block_on<T>(&mut self, f: impl Future<Output = T>) -> T {
         // we want to avoid reentering `block_on` because then all the code
         // below has to become more complex. It's also likely that the
         // application will only call `block_on` once on an infinite task
         // (`Future<Output = !>`)
-        {
+        if self.in_block_on {
-            let mut in_block_on = self.in_block_on.borrow_mut();
+            panic!("nested `block_on`");
-            if *in_block_on {
-                panic!("nested `block_on`");
-            }
-            *in_block_on = true;
         }
+        self.in_block_on = true;
 
         pin_mut!(f);
         let ready = AtomicBool::new(true);
@@ -77,17 +73,14 @@ impl Executor {
             // advance the main task
             if ready.load(Ordering::Relaxed) {
                 ready.store(false, Ordering::Relaxed);
-
-                // println!("run block_on");
                 let mut cx = Context::from_waker(&waker);
                 if let Poll::Ready(val) = f.as_mut().poll(&mut cx) {
                     break val;
                 }
-                // println!("ran block_on");
             }
 
             // advance all tasks
-            core::mem::swap(&mut *self.tasks.borrow_mut(), &mut backup);
+            core::mem::swap(&mut self.tasks, &mut backup);
             for mut task in backup.drain(..) {
                 // NOTE we don't need a CAS operation here because `wake` invocations that come from
                 // interrupt handlers (the only source of 'race conditions' (!= data races)) are
@@ -106,20 +99,16 @@ impl Executor {
                     }
                 }
                 // Requeue
-                self.tasks.borrow_mut().push(task);
+                self.tasks.push(task);
             }
-
-            // // try to sleep; this will be a no-op if any of the previous tasks generated a SEV or an
-            // // interrupt ran (regardless of whether it generated a wake-up or not)
-            // asm::wfe();
         };
-        self.in_block_on.replace(false);
+        self.in_block_on = false;
         val
     }
 
-    pub fn spawn(&self, f: impl Future + 'static) {
+    pub fn spawn(&mut self, f: impl Future<Output = ()> + 'static) {
         let task = Box::pin(Task::new(f));
-        self.tasks.borrow_mut().push(task);
+        self.tasks.push(task);
     }
 }
 
@@ -129,10 +118,10 @@ pub struct Task {
 }
 
 impl Task {
-    fn new(f: impl Future + 'static) -> Self {
+    fn new(f: impl Future<Output = ()> + 'static) -> Self {
         Task {
             ready: AtomicBool::new(true),
-            f: Box::pin(async { f.await; }),
+            f: Box::pin(f),
         }
     }
 }
@@ -140,18 +129,17 @@ impl Task {
 /// Returns a handle to the executor singleton
 ///
 /// This lazily initializes the executor and allocator when first called
-pub(crate) fn current() -> &'static Executor {
+pub(crate) fn current() -> &'static mut Executor {
     static INIT: AtomicBool = AtomicBool::new(false);
     static mut EXECUTOR: UnsafeCell<MaybeUninit<Executor>> = UnsafeCell::new(MaybeUninit::uninit());
 
     if INIT.load(Ordering::Relaxed) {
-        unsafe { &*(EXECUTOR.get() as *const Executor) }
+        unsafe { EXECUTOR.get_mut().assume_init_mut() }
     } else {
         unsafe {
-            let executorp = EXECUTOR.get() as *mut Executor;
+            let executor = EXECUTOR.get_mut().write(Executor::new());
-            executorp.write(Executor::new());
             INIT.store(true, Ordering::Relaxed);
-            &*executorp
+            executor
         }
     }
 }

libasync/src/task.rs

@@ -17,7 +17,7 @@ pub fn block_on<T>(f: impl Future<Output = T>) -> T {
 /// Spawns a task onto the executor
 ///
 /// The spawned task will not make any progress until `block_on` is called.
-pub fn spawn(f: impl Future + 'static) {
+pub fn spawn(f: impl Future<Output = ()> + 'static) {
     executor::current().spawn(f)
 }