libasync: improve scheduling fairness between block_on and spawned tasks

in the libasync::smoltcp::Sockets::run() case the block_on iface.poll
loop would progress just one task before. now all tasks get to run in
each iteration.

libasync/src/executor.rs

@@ -6,7 +6,7 @@ use core::{
     sync::atomic::{AtomicBool, Ordering},
     task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
 };
-use alloc::{boxed::Box, collections::VecDeque as Deque};
+use alloc::{boxed::Box, vec::Vec};
 //use futures::future::FutureExt;
 use pin_utils::pin_mut;
 
@@ -31,7 +31,7 @@ static VTABLE: RawWakerVTable = {
 /// ready should not move as long as this waker references it. That is
 /// the reason for keeping Tasks in a pinned box.
 fn wrap_waker(ready: &AtomicBool) -> Waker {
-    unsafe { Waker::from_raw(RawWaker::new(ready as *const _ as *const _, &VTABLE)) }
+    unsafe { Waker::from_raw(RawWaker::new(ready as *const _ as *const (), &VTABLE)) }
 }
 
 /// A single-threaded executor
@@ -44,7 +44,7 @@ pub struct Executor {
     /// 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<Deque<Pin<Box<Task>>>>,
+    tasks: RefCell<Vec<Pin<Box<Task>>>>,
 }
 
 impl Executor {
@@ -52,7 +52,7 @@ impl Executor {
     pub fn new() -> Self {
         Self {
             in_block_on: RefCell::new(false),
-            tasks: RefCell::new(Deque::new()),
+            tasks: RefCell::new(Vec::new()),
         }
     }
 
@@ -85,10 +85,9 @@ impl Executor {
                 // println!("ran block_on");
             }
 
-            // println!("tasks: {}", self.tasks.borrow().len());
-            // advance other tasks
-            let next_task = self.tasks.borrow_mut().pop_front();
-            if let Some(mut task) = next_task {
+            // advance all tasks
+            let next_tasks = self.tasks.replace_with(|tasks| Vec::with_capacity(tasks.len()));
+            for mut task in next_tasks.into_iter() {
                 // 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
                 // "oneshot": they'll issue a `wake` and then disable themselves to not run again
@@ -106,7 +105,7 @@ impl Executor {
                     }
                 }
                 // Requeue
-                self.tasks.borrow_mut().push_back(task);
+                self.tasks.borrow_mut().push(task);
             }
 
             // // try to sleep; this will be a no-op if any of the previous tasks generated a SEV or an
@@ -119,7 +118,7 @@ impl Executor {
 
     pub fn spawn(&self, f: impl Future + 'static) {
         let task = Box::pin(Task::new(f));
-        self.tasks.borrow_mut().push_back(task);
+        self.tasks.borrow_mut().push(task);
     }
 }