1 files changed, 174 insertions, 0 deletions
diff --git a/src/executor.rs b/src/executor.rs
new file mode 100644
index 0000000..42cd00f
--- /dev/null
+++ b/src/executor.rs
@@ -0,0 +1,174 @@
+use std::{
+    cell::RefCell,
+    collections::VecDeque,
+    marker::PhantomData,
+    mem,
+    rc::Rc,
+    task::{RawWaker, RawWakerVTable, Waker, Context}, pin::Pin,
+};
+
+use futures::{future::LocalBoxFuture, Future, FutureExt};
+
+use crate::reactor::Reactor;
+
+scoped_tls::scoped_thread_local!(pub(crate) static EX: Executor);
+
+pub struct Executor {
+    local_queue: TaskQueue,
+    pub(crate) reactor: Rc<RefCell<Reactor>>,
+
+    /// Make sure the type is `!Send` and `!Sync`.
+    _marker: PhantomData<Rc<()>>,
+}
+
+impl Default for Executor {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+
+impl Executor {
+    pub fn new() -> Self {
+        Self {
+            local_queue: TaskQueue::default(),
+            reactor: Rc::new(RefCell::new(Reactor::default())),
+
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn spawn(fut: impl Future<Output = ()> + 'static) {
+        let t = Rc::new(Task {
+            future: RefCell::new(fut.boxed_local()),
+        });
+        EX.with(|ex| ex.local_queue.push(t));
+    }
+
+    pub fn block_on<F, T, O>(&self, f: F) -> O
+    where
+        F: Fn() -> T,
+        T: Future<Output = O> + 'static,
+    {
+        let _waker = waker_fn::waker_fn(|| {});
+        let cx = &mut Context::from_waker(&_waker);
+
+        EX.set(self, || {
+            let fut = f();
+            pin_utils::pin_mut!(fut);
+            loop {
+                // return if the outer future is ready
+                if let std::task::Poll::Ready(t) = fut.as_mut().poll(cx) {
+                    break t;
+                }
+
+                // consume all tasks
+                while let Some(t) = self.local_queue.pop() {
+                    let future = t.future.borrow_mut();
+                    let w = waker(t.clone());
+                    let mut context = Context::from_waker(&w);
+                    let _ = Pin::new(future).as_mut().poll(&mut context);
+                }
+
+                // no task to execute now, it may ready
+                if let std::task::Poll::Ready(t) = fut.as_mut().poll(cx) {
+                    break t;
+                }
+
+                // block for io
+                self.reactor.borrow_mut().wait();
+            }
+        })
+    }
+}
+
+pub struct TaskQueue {
+    queue: RefCell<VecDeque<Rc<Task>>>,
+}
+
+impl Default for TaskQueue {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl TaskQueue {
+    pub fn new() -> Self {
+        const DEFAULT_TASK_QUEUE_SIZE: usize = 4096;
+        Self::new_with_capacity(DEFAULT_TASK_QUEUE_SIZE)
+    }
+    pub fn new_with_capacity(capacity: usize) -> Self {
+        Self {
+            queue: RefCell::new(VecDeque::with_capacity(capacity)),
+        }
+    }
+
+    pub(crate) fn push(&self, runnable: Rc<Task>) {
+        println!("add task");
+        self.queue.borrow_mut().push_back(runnable);
+    }
+
+    pub(crate) fn pop(&self) -> Option<Rc<Task>> {
+        println!("remove task");
+        self.queue.borrow_mut().pop_front()
+    }
+}
+
+pub struct Task {
+    future: RefCell<LocalBoxFuture<'static, ()>>,
+}
+
+fn waker(wake: Rc<Task>) -> Waker {
+    let ptr = Rc::into_raw(wake) as *const ();
+    let vtable = &Helper::VTABLE;
+    unsafe { Waker::from_raw(RawWaker::new(ptr, vtable)) }
+}
+
+impl Task {
+    fn wake_(self: Rc<Self>) {
+        Self::wake_by_ref_(&self)
+    }
+
+    fn wake_by_ref_(self: &Rc<Self>) {
+        EX.with(|ex| ex.local_queue.push(self.clone()));
+    }
+}
+
+struct Helper;
+
+impl Helper {
+    const VTABLE: RawWakerVTable = RawWakerVTable::new(
+        Self::clone_waker,
+        Self::wake,
+        Self::wake_by_ref,
+        Self::drop_waker,
+    );
+
+    unsafe fn clone_waker(data: *const ()) -> RawWaker {
+        increase_refcount(data);
+        let vtable = &Self::VTABLE;
+        RawWaker::new(data, vtable)
+    }
+
+    unsafe fn wake(ptr: *const ()) {
+        let rc = Rc::from_raw(ptr as *const Task);
+        rc.wake_();
+    }
+
+    unsafe fn wake_by_ref(ptr: *const ()) {
+        let rc = mem::ManuallyDrop::new(Rc::from_raw(ptr as *const Task));
+        rc.wake_by_ref_();
+    }
+
+    unsafe fn drop_waker(ptr: *const ()) {
+        drop(Rc::from_raw(ptr as *const Task));
+    }
+}
+
+#[allow(clippy::redundant_clone)] // The clone here isn't actually redundant.
+unsafe fn increase_refcount(data: *const ()) {
+    // Retain Rc, but don't touch refcount by wrapping in ManuallyDrop
+    let rc = mem::ManuallyDrop::new(Rc::<Task>::from_raw(data as *const Task));
+    // Now increase refcount, but don't drop new refcount either
+    let _rc_clone: mem::ManuallyDrop<_> = rc.clone();
+}