Refactor: Move interrupt wakers/operations into separate modules

Pin implements Deref too, so by dereferencing only once we get a `&Box` reference. Since Box also implements Future, the type of `future_ref` was still correct. To avoid this error in the future, we added an assertion to catch duplicate task IDson `pending_tasks.insert()`.

Cargo.lock

@@ -1,5 +1,11 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "autocfg"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8aac770f1885fd7e387acedd76065302551364496e46b3dd00860b2f8359b9d"
+
 [[package]]
 name = "bit_field"
 version = "0.9.0"
@@ -17,6 +23,9 @@ name = "blog_os"
 version = "0.1.0"
 dependencies = [
  "bootloader",
+ "conquer-once",
+ "crossbeam-queue",
+ "futures-util",
  "lazy_static",
  "linked_list_allocator",
  "pc-keyboard",
@@ -33,12 +42,76 @@ version = "0.8.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c3ed4f735c4e455ba86a3d2939b1c0729414153642106c9d035693355630a42c"
 
+[[package]]
+name = "cfg-if"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
+
+[[package]]
+name = "conquer-once"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6f7644600a548ecad74e4a918392af1798f7dd045be610be3203b9e129b4f98f"
+dependencies = [
+ "conquer-util",
+]
+
+[[package]]
+name = "conquer-util"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "654fb2472cc369d311c547103a1fa81d467bef370ae7a0680f65939895b1182a"
+
 [[package]]
 name = "cpuio"
 version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "22b8e308ccfc5acf3b82f79c0eac444cf6114cb2ac67a230ca6c177210068daa"
 
+[[package]]
+name = "crossbeam-queue"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c695eeca1e7173472a32221542ae469b3e9aac3a4fc81f7696bcad82029493db"
+dependencies = [
+ "cfg-if",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3c7c73a2d1e9fc0886a08b93e98eb643461230d5f1925e4036204d5f2e261a8"
+dependencies = [
+ "autocfg",
+ "cfg-if",
+]
+
+[[package]]
+name = "futures-core"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f25592f769825e89b92358db00d26f965761e094951ac44d3663ef25b7ac464a"
+
+[[package]]
+name = "futures-task"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b0a34e53cf6cdcd0178aa573aed466b646eb3db769570841fda0c7ede375a27"
+
+[[package]]
+name = "futures-util"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22766cf25d64306bedf0384da004d05c9974ab104fcc4528f1236181c18004c5"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "pin-utils",
+]
+
 [[package]]
 name = "lazy_static"
 version = "1.4.0"
@@ -81,6 +154,12 @@ dependencies = [
  "cpuio",
 ]
 
+[[package]]
+name = "pin-utils"
+version = "0.1.0-alpha.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5894c618ce612a3fa23881b152b608bafb8c56cfc22f434a3ba3120b40f7b587"
+
 [[package]]
 name = "scopeguard"
 version = "1.1.0"

Cargo.toml

@@ -26,6 +26,19 @@ linked_list_allocator = "0.8.0"
 version = "1.0"
 features = ["spin_no_std"]
 
+[dependencies.crossbeam-queue]
+version = "0.2.1"
+default-features = false
+features = ["alloc"]
+
+[dependencies.futures-util]
+version = "0.3.4"
+default-features = false
+features = ["alloc", "async-await"]
+
+[dependencies.conquer-once]
+version = "0.2.0"
+default-features = false
 
 [package.metadata.bootimage]
 test-args = [

src/driver/keyboard.rs

@@ -0,0 +1,75 @@
+use crate::{print, println, task::interrupt_wake};
+use conquer_once::spin::OnceCell;
+use core::future::Future;
+use core::{
+    pin::Pin,
+    task::{Context, Poll},
+};
+use crossbeam_queue::ArrayQueue;
+use futures_util::task::AtomicWaker;
+use pc_keyboard::{layouts, DecodedKey, HandleControl, Keyboard, ScancodeSet1};
+
+static WAKER: AtomicWaker = AtomicWaker::new();
+static SCANCODE_QUEUE: OnceCell<ArrayQueue<u8>> = OnceCell::uninit();
+
+pub fn init() {
+    SCANCODE_QUEUE
+        .try_init_once(|| ArrayQueue::new(10))
+        .expect("failed to init scancode queue");
+}
+
+/// Called by the keyboard interrupt handler
+///
+/// Must not block (including spinlocks).
+pub(crate) fn keyboard_scancode(scancode: u8) {
+    let scancode_queue = SCANCODE_QUEUE
+        .try_get()
+        .expect("scancode queue not initialized");
+    if let Err(_) = scancode_queue.push(scancode) {
+        println!("WARNING: dropping keyboard input");
+    }
+    if let Some(waker) = WAKER.take() {
+        interrupt_wake(waker);
+    }
+}
+
+fn next_scancode() -> impl Future<Output = u8> {
+    NextScancode
+}
+
+struct NextScancode;
+
+impl Future for NextScancode {
+    type Output = u8;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<u8> {
+        let scancodes = SCANCODE_QUEUE
+            .try_get()
+            .expect("scancode queue not initialized");
+        // fast path
+        if let Ok(scancode) = scancodes.pop() {
+            return Poll::Ready(scancode);
+        }
+
+        WAKER.register(&cx.waker());
+        match scancodes.pop() {
+            Ok(scancode) => Poll::Ready(scancode),
+            Err(crossbeam_queue::PopError) => Poll::Pending,
+        }
+    }
+}
+
+pub async fn keyboard_task() {
+    let mut keyboard = Keyboard::new(layouts::Us104Key, ScancodeSet1, HandleControl::Ignore);
+
+    loop {
+        if let Ok(Some(key_event)) = keyboard.add_byte(next_scancode().await) {
+            if let Some(key) = keyboard.process_keyevent(key_event) {
+                match key {
+                    DecodedKey::Unicode(character) => print!("{}", character),
+                    DecodedKey::RawKey(key) => print!("{:?}", key),
+                }
+            }
+        }
+    }
+}

src/driver/mod.rs

@@ -0,0 +1,6 @@
+pub mod keyboard;
+pub mod timer;
+
+pub fn init() {
+    keyboard::init();
+}

src/driver/timer.rs

@@ -0,0 +1,55 @@
+use crate::{print, task::interrupt_wake};
+use core::future::Future;
+use core::{
+    pin::Pin,
+    sync::atomic::{AtomicU64, Ordering},
+    task::{Context, Poll},
+};
+use futures_util::task::AtomicWaker;
+
+static TICKS: AtomicU64 = AtomicU64::new(0);
+static WAKER: AtomicWaker = AtomicWaker::new();
+
+/// Called by the timer interrupt handler
+///
+/// Must not block (including spinlocks).
+pub(crate) fn tick() {
+    TICKS.fetch_add(1, Ordering::Release);
+    if let Some(waker) = WAKER.take() {
+        interrupt_wake(waker);
+    }
+}
+
+fn next_tick() -> impl Future<Output = u64> {
+    static NEXT_TICK: AtomicU64 = AtomicU64::new(1);
+
+    NextTick {
+        ticks: NEXT_TICK.fetch_add(1, Ordering::Release),
+    }
+}
+
+struct NextTick {
+    ticks: u64,
+}
+
+impl Future for NextTick {
+    type Output = u64;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<u64> {
+        WAKER.register(&cx.waker());
+        let current_ticks = TICKS.load(Ordering::Acquire);
+        if self.ticks < current_ticks {
+            self.ticks += 1;
+            Poll::Ready(self.ticks)
+        } else {
+            Poll::Pending
+        }
+    }
+}
+
+pub async fn timer_task() {
+    loop {
+        next_tick().await;
+        print!(".");
+    }
+}

src/interrupts.rs

@@ -1,4 +1,4 @@
-use crate::{gdt, hlt_loop, print, println};
+use crate::{gdt, hlt_loop, println};
 use lazy_static::lazy_static;
 use pic8259_simple::ChainedPics;
 use spin;
@@ -72,7 +72,8 @@ extern "x86-interrupt" fn double_fault_handler(
 }
 
 extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
-    print!(".");
+    crate::driver::timer::tick();
+
     unsafe {
         PICS.lock()
             .notify_end_of_interrupt(InterruptIndex::Timer.as_u8());
@@ -80,28 +81,11 @@ extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptSt
 }
 
 extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
-    use pc_keyboard::{layouts, DecodedKey, HandleControl, Keyboard, ScancodeSet1};
-    use spin::Mutex;
     use x86_64::instructions::port::Port;
-
-    lazy_static! {
-        static ref KEYBOARD: Mutex<Keyboard<layouts::Us104Key, ScancodeSet1>> = Mutex::new(
-            Keyboard::new(layouts::Us104Key, ScancodeSet1, HandleControl::Ignore)
-        );
-    }
-
-    let mut keyboard = KEYBOARD.lock();
     let mut port = Port::new(0x60);
-
     let scancode: u8 = unsafe { port.read() };
-    if let Ok(Some(key_event)) = keyboard.add_byte(scancode) {
-        if let Some(key) = keyboard.process_keyevent(key_event) {
-            match key {
-                DecodedKey::Unicode(character) => print!("{}", character),
-                DecodedKey::RawKey(key) => print!("{:?}", key),
-            }
-        }
-    }
+
+    crate::driver::keyboard::keyboard_scancode(scancode);
 
     unsafe {
         PICS.lock()

src/lib.rs

@@ -5,7 +5,10 @@
 #![feature(alloc_error_handler)]
 #![feature(const_fn)]
 #![feature(alloc_layout_extra)]
+#![feature(wake_trait)]
 #![feature(const_in_array_repeat_expressions)]
+#![feature(type_alias_impl_trait)]
+#![feature(asm)]
 #![test_runner(crate::test_runner)]
 #![reexport_test_harness_main = "test_main"]
 
@@ -14,17 +17,23 @@ extern crate alloc;
 use core::panic::PanicInfo;
 
 pub mod allocator;
+pub mod driver;
 pub mod gdt;
 pub mod interrupts;
 pub mod memory;
 pub mod serial;
+pub mod task;
 pub mod vga_buffer;
 
 pub fn init() {
     gdt::init();
     interrupts::init_idt();
     unsafe { interrupts::PICS.lock().initialize() };
-    x86_64::instructions::interrupts::enable();
+}
+
+pub fn init_heap_structures() {
+    task::init();
+    driver::init();
 }
 
 pub fn test_runner(tests: &[&dyn Fn()]) {

src/main.rs

@@ -26,6 +26,7 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
     let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
 
     allocator::init_heap(&mut mapper, &mut frame_allocator).expect("heap initialization failed");
+    blog_os::init_heap_structures();
 
     // allocate a number on the heap
     let heap_value = Box::new(41);
@@ -51,11 +52,24 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
         Rc::strong_count(&cloned_reference)
     );
 
+    use blog_os::task::executor::Executor;
+
+    let mut executor = Executor::new();
+    executor.spawn(bar());
+
+    executor.spawn(async {
         #[cfg(test)]
         test_main();
+    });
 
+    executor.spawn(async {
         println!("It did not crash!");
-    blog_os::hlt_loop();
+    });
+
+    executor.spawn(blog_os::driver::timer::timer_task());
+    executor.spawn(blog_os::driver::keyboard::keyboard_task());
+
+    executor.run();
 }
 
 /// This function is called on panic.
@@ -71,3 +85,15 @@ fn panic(info: &PanicInfo) -> ! {
 fn panic(info: &PanicInfo) -> ! {
     blog_os::test_panic_handler(info)
 }
+
+async fn test() -> u32 {
+    42
+}
+
+async fn foo() -> u32 {
+    test().await * 2
+}
+
+async fn bar() {
+    println!("foo result: {}", foo().await);
+}

src/task/executor.rs

@@ -0,0 +1,127 @@
+use super::interrupt_wakeups::interrupt_wakeups;
+use crate::println;
+use alloc::{
+    boxed::Box,
+    collections::{BTreeMap, VecDeque},
+    sync::Arc,
+    task::Wake,
+};
+use core::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+use crossbeam_queue::SegQueue;
+
+pub type Task = Pin<Box<dyn Future<Output = ()>>>;
+type TaskId = usize;
+
+pub struct Executor {
+    task_queue: VecDeque<Task>,
+    wake_queue: Arc<SegQueue<TaskId>>,
+    pending_tasks: BTreeMap<TaskId, Task>,
+}
+
+impl Executor {
+    pub fn new() -> Self {
+        Executor {
+            task_queue: VecDeque::new(),
+            wake_queue: Arc::new(SegQueue::new()),
+            pending_tasks: BTreeMap::new(),
+        }
+    }
+
+    pub fn spawn(&mut self, task: impl Future<Output = ()> + 'static) {
+        self.task_queue.push_back(Box::pin(task))
+    }
+
+    pub fn run(&mut self) -> ! {
+        loop {
+            self.run_ready_tasks();
+            self.apply_interrupt_wakeups();
+            self.wake_waiting_tasks();
+            self.hlt_if_idle();
+        }
+    }
+
+    fn run_ready_tasks(&mut self) {
+        while let Some(mut task) = self.task_queue.pop_front() {
+            let waker = self.create_waker(&task).into();
+            let mut context = Context::from_waker(&waker);
+            match task.as_mut().poll(&mut context) {
+                Poll::Ready(()) => {} // task done
+                Poll::Pending => {
+                    // add task to pending_tasks and wait for wakeup
+                    let task_id = Self::task_id(&task);
+                    if self.pending_tasks.insert(task_id, task).is_some() {
+                        panic!("Task with same ID already in pending_tasks");
+                    }
+                }
+            }
+        }
+    }
+
+    /// Invoke wakers for tasks woken by interrupts
+    ///
+    /// The interrupt handlers can't invoke the waker directly since wakers
+    /// might execute arbitrary code, e.g. allocate, which should not be done
+    /// in interrupt handlers to avoid deadlocks.
+    fn apply_interrupt_wakeups(&mut self) {
+        while let Ok(waker) = interrupt_wakeups().pop() {
+            waker.wake();
+        }
+    }
+
+    fn wake_waiting_tasks(&mut self) {
+        while let Ok(task_id) = self.wake_queue.pop() {
+            if let Some(task) = self.pending_tasks.remove(&task_id) {
+                self.task_queue.push_back(task);
+            } else {
+                println!("WARNING: woken task not found in pending_tasks");
+            }
+        }
+    }
+
+    /// Executes the `hlt` instruction if there are no ready tasks
+    fn hlt_if_idle(&self) {
+        if self.task_queue.is_empty() {
+            // disable interrupts to avoid races
+            x86_64::instructions::interrupts::disable();
+            // check if relevant interrupts occured since the last check
+            if interrupt_wakeups().is_empty() {
+                // no interrupts occured -> hlt to wait for next interrupt
+                x86_64::instructions::interrupts::enable_interrupts_and_hlt();
+            } else {
+                // there were some new wakeups -> continue execution
+                x86_64::instructions::interrupts::enable();
+            }
+        }
+    }
+
+    fn task_id(task: &Task) -> TaskId {
+        let future_ref: &dyn Future<Output = ()> = &**task;
+        future_ref as *const _ as *const () as usize
+    }
+
+    fn create_waker(&self, task: &Task) -> Arc<Waker> {
+        Arc::new(Waker {
+            wake_queue: self.wake_queue.clone(),
+            task_id: Self::task_id(task),
+        })
+    }
+}
+
+pub struct Waker {
+    wake_queue: Arc<SegQueue<TaskId>>,
+    task_id: TaskId,
+}
+
+impl Wake for Waker {
+    fn wake(self: Arc<Self>) {
+        self.wake_by_ref();
+    }
+
+    fn wake_by_ref(self: &Arc<Self>) {
+        self.wake_queue.push(self.task_id);
+    }
+}

src/task/interrupt_wakeups.rs

@@ -0,0 +1,25 @@
+use crate::println;
+use conquer_once::spin::OnceCell;
+use core::task::Waker;
+use crossbeam_queue::ArrayQueue;
+
+static INTERRUPT_WAKEUPS: OnceCell<ArrayQueue<Waker>> = OnceCell::uninit();
+
+pub fn init() {
+    INTERRUPT_WAKEUPS
+        .try_init_once(|| ArrayQueue::new(10))
+        .expect("failed to init interrupt wakeup queue");
+}
+
+/// Queues a waker for waking in an interrupt-safe way
+pub(crate) fn interrupt_wake(waker: Waker) {
+    if let Err(_) = interrupt_wakeups().push(waker) {
+        println!("WARNING: dropping interrupt wakeup");
+    }
+}
+
+pub(super) fn interrupt_wakeups() -> &'static ArrayQueue<Waker> {
+    INTERRUPT_WAKEUPS
+        .try_get()
+        .expect("interrupt wakeup queue not initialized")
+}

src/task/mod.rs

@@ -0,0 +1,8 @@
+pub(crate) use interrupt_wakeups::interrupt_wake;
+
+pub mod executor;
+mod interrupt_wakeups;
+
+pub fn init() {
+    interrupt_wakeups::init();
+}