add user/src/bin/stackless_coutine.rs

user/src/bin/stackful_coroutine.rs

@@ -7,13 +7,12 @@
 #![feature(naked_functions)]
 #![feature(asm)]
 
+extern crate alloc;
 #[macro_use]
 extern crate user_lib;
 
-#[macro_use]
-extern crate alloc;
-
 use core::arch::asm;
+
 #[macro_use]
 use alloc::vec;
 use alloc::vec::Vec;

user/src/bin/stackless_coroutine.rs

@@ -0,0 +1,127 @@
+#![no_std]
+#![no_main]
+
+use core::future::Future;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use core::task::{RawWaker, RawWakerVTable, Waker};
+
+extern crate alloc;
+use alloc::collections::VecDeque;
+
+use alloc::boxed::Box;
+
+#[macro_use]
+extern crate user_lib;
+
+enum State {
+    Halted,
+    Running,
+}
+
+struct Task {
+    state: State,
+}
+
+impl Task {
+    fn waiter<'a>(&'a mut self) -> Waiter<'a> {
+        Waiter { task: self }
+    }
+}
+
+struct Waiter<'a> {
+    task: &'a mut Task,
+}
+
+impl<'a> Future for Waiter<'a> {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context) -> Poll<Self::Output> {
+        match self.task.state {
+            State::Halted => {
+                self.task.state = State::Running;
+                Poll::Ready(())
+            }
+            State::Running => {
+                self.task.state = State::Halted;
+                Poll::Pending
+            }
+        }
+    }
+}
+
+struct Executor {
+    tasks: VecDeque<Pin<Box<dyn Future<Output = ()>>>>,
+}
+
+impl Executor {
+    fn new() -> Self {
+        Executor {
+            tasks: VecDeque::new(),
+        }
+    }
+
+    fn push<C, F>(&mut self, closure: C)
+    where
+        F: Future<Output = ()> + 'static,
+        C: FnOnce(Task) -> F,
+    {
+        let task = Task {
+            state: State::Running,
+        };
+        self.tasks.push_back(Box::pin(closure(task)));
+    }
+
+    fn run(&mut self) {
+        let waker = create_waker();
+        let mut context = Context::from_waker(&waker);
+
+        while let Some(mut task) = self.tasks.pop_front() {
+            match task.as_mut().poll(&mut context) {
+                Poll::Pending => {
+                    self.tasks.push_back(task);
+                }
+                Poll::Ready(()) => {}
+            }
+        }
+    }
+}
+
+pub fn create_waker() -> Waker {
+    // Safety: The waker points to a vtable with functions that do nothing. Doing
+    // nothing is memory-safe.
+    unsafe { Waker::from_raw(RAW_WAKER) }
+}
+
+const RAW_WAKER: RawWaker = RawWaker::new(core::ptr::null(), &VTABLE);
+const VTABLE: RawWakerVTable = RawWakerVTable::new(clone, wake, wake_by_ref, drop);
+
+unsafe fn clone(_: *const ()) -> RawWaker {
+    RAW_WAKER
+}
+unsafe fn wake(_: *const ()) {}
+unsafe fn wake_by_ref(_: *const ()) {}
+unsafe fn drop(_: *const ()) {}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    println!("stackless coroutine Begin..");
+    let mut exec = Executor::new();
+    println!(" Create futures");
+    for instance in 1..=3 {
+        exec.push(move |mut task| async move {
+            println!("   Task {}: begin state", instance);
+            task.waiter().await;
+            println!("   Task {}: next state", instance);
+            task.waiter().await;
+            println!("   Task {}: end state", instance);
+        });
+    }
+
+    println!(" Running");
+    exec.run();
+    println!(" Done");
+    println!("stackless coroutine PASSED");
+
+    0
+}