refactor mega-commit.

- reorganised the entire project so that the entire kernel is a single codebase rather than a kernel and a libk.

kernel/src/arch/x86_64/processing/async_io/task.rs

@@ -0,0 +1,148 @@
+//! Allows creation of asynchronous IO bound tasks.
+//!
+//! Written by @zxq5 for the most part with code from
+//! [here](https://github.com/phil-opp/blog_os/).
+//!
+
+use alloc::boxed::Box;
+use alloc::collections::BTreeMap;
+use alloc::sync::Arc;
+use alloc::task::Wake;
+use core::{
+    future::Future,
+    pin::Pin,
+    sync::atomic::AtomicU64,
+    task::{Context, Poll, Waker},
+};
+use crossbeam::queue::ArrayQueue;
+use x86_64::instructions::interrupts::{self, enable_and_hlt};
+
+pub struct Task {
+    id: TaskId,
+    future: Pin<Box<dyn Future<Output = ()>>>,
+}
+
+impl Task {
+    pub fn new(future: impl Future<Output = ()> + 'static) -> Self {
+        Self {
+            id: TaskId::new(),
+            future: Box::pin(future),
+        }
+    }
+
+    fn poll(&mut self, context: &mut Context) -> Poll<()> {
+        self.future.as_mut().poll(context)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+struct TaskId(u64);
+
+impl TaskId {
+    fn new() -> Self {
+        static NEXT: AtomicU64 = AtomicU64::new(0);
+        Self(NEXT.fetch_add(1, core::sync::atomic::Ordering::Relaxed))
+    }
+}
+
+pub struct Executor {
+    tasks: BTreeMap<TaskId, Task>,
+    task_queue: Arc<ArrayQueue<TaskId>>,
+    waker_cache: BTreeMap<TaskId, Waker>,
+}
+
+impl Executor {
+    pub fn new() -> Self {
+        Self {
+            tasks: BTreeMap::new(),
+            task_queue: Arc::new(ArrayQueue::new(100)),
+            waker_cache: BTreeMap::new(),
+        }
+    }
+
+    pub fn spawn(&mut self, task: Task) {
+        let task_id = task.id;
+        if self.tasks.insert(task.id, task).is_some() {
+            panic!("task with same id already in tasks");
+        }
+        self.task_queue.push(task_id).expect("queue full");
+    }
+
+    fn run_ready_tasks(&mut self) {
+        // destructure `self` to avoid borrow checker errors
+        let Self {
+            tasks,
+            task_queue,
+            waker_cache,
+        } = self;
+
+        while let Some(task_id) = task_queue.pop() {
+            let task = match tasks.get_mut(&task_id) {
+                Some(task) => task,
+                None => continue, // task no longer exists
+            };
+            let waker = waker_cache
+                .entry(task_id)
+                .or_insert_with(|| TaskWaker::new_waker(task_id, task_queue.clone()));
+            let mut context = Context::from_waker(waker);
+            match task.poll(&mut context) {
+                Poll::Ready(()) => {
+                    // task done -> remove it and its cached waker
+                    tasks.remove(&task_id);
+                    waker_cache.remove(&task_id);
+                }
+                Poll::Pending => {}
+            }
+        }
+    }
+
+    pub fn run(&mut self) -> ! {
+        loop {
+            self.run_ready_tasks();
+            self.sleep_if_idle();
+        }
+    }
+
+    fn sleep_if_idle(&self) {
+        interrupts::disable();
+        if self.task_queue.is_empty() {
+            enable_and_hlt();
+        } else {
+            interrupts::enable();
+        }
+    }
+}
+
+impl Default for Executor {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+struct TaskWaker {
+    task_id: TaskId,
+    task_queue: Arc<ArrayQueue<TaskId>>,
+}
+
+impl TaskWaker {
+    fn wake_task(&self) {
+        self.task_queue.push(self.task_id).expect("task_queue full");
+    }
+
+    fn new_waker(task_id: TaskId, task_queue: Arc<ArrayQueue<TaskId>>) -> Waker {
+        Waker::from(Arc::new(Self {
+            task_id,
+            task_queue,
+        }))
+    }
+}
+
+impl Wake for TaskWaker {
+    fn wake(self: Arc<Self>) {
+        self.wake_task();
+    }
+
+    fn wake_by_ref(self: &Arc<Self>) {
+        self.wake_task();
+    }
+}