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

@@ -33,14 +33,14 @@ dependencies = [
  "spin",
  "uart_16550",
  "volatile",
- "x86_64 0.11.1",
+ "x86_64",
 ]
 
 [[package]]
 name = "bootloader"
-version = "0.9.3"
+version = "0.8.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "44ac0bdf4930c3c4d7f0d04eb6f15d7dcb9d5972b1ff9cd2bee0128112260fc7"
+checksum = "c3ed4f735c4e455ba86a3d2939b1c0729414153642106c9d035693355630a42c"
 
 [[package]]
 name = "cfg-if"
@@ -65,9 +65,9 @@ checksum = "654fb2472cc369d311c547103a1fa81d467bef370ae7a0680f65939895b1182a"
 
 [[package]]
 name = "cpuio"
-version = "0.3.0"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d531514efb06912141fa65967447de805691b685a7565c87d1765afe34a98aa7"
+checksum = "22b8e308ccfc5acf3b82f79c0eac444cf6114cb2ac67a230ca6c177210068daa"
 
 [[package]]
 name = "crossbeam-queue"
@@ -147,9 +147,9 @@ checksum = "c48392db76c4e9a69e0b3be356c5f97ebb7b14413c5e4fd0af4755dbf86e2fce"
 
 [[package]]
 name = "pic8259_simple"
-version = "0.2.0"
+version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af2a5497fb8e59bf8015f67b7dff238d75ef445e03f23edac24ac3a8f09be952"
+checksum = "dc64b2fd10828da8521b6cdabe0679385d7d2a3a6d4c336b819d1fa31ba35c72"
 dependencies = [
  "cpuio",
 ]
@@ -160,24 +160,6 @@ version = "0.1.0-alpha.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5894c618ce612a3fa23881b152b608bafb8c56cfc22f434a3ba3120b40f7b587"
 
-[[package]]
-name = "proc-macro2"
-version = "1.0.18"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "beae6331a816b1f65d04c45b078fd8e6c93e8071771f41b8163255bbd8d7c8fa"
-dependencies = [
- "unicode-xid",
-]
-
-[[package]]
-name = "quote"
-version = "1.0.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
-dependencies = [
- "proc-macro2",
-]
-
 [[package]]
 name = "scopeguard"
 version = "1.1.0"
@@ -199,33 +181,16 @@ dependencies = [
  "lock_api",
 ]
 
-[[package]]
-name = "syn"
-version = "1.0.33"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e8d5d96e8cbb005d6959f119f773bfaebb5684296108fb32600c00cde305b2cd"
-dependencies = [
- "proc-macro2",
- "quote",
- "unicode-xid",
-]
-
 [[package]]
 name = "uart_16550"
-version = "0.2.7"
+version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e58fc40dc1712664fc9b0a7bd8ca2f21ab49960924fb245a80a05e1e92f3dfe9"
+checksum = "d44b0f30cb82b0fbc15b78ade1064226529ad52028bc8cb8accb98ff6f3d7131"
 dependencies = [
  "bitflags",
- "x86_64 0.11.0",
+ "x86_64",
 ]
 
-[[package]]
-name = "unicode-xid"
-version = "0.2.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
-
 [[package]]
 name = "volatile"
 version = "0.2.6"
@@ -234,28 +199,10 @@ checksum = "6af0edf5b4faacc31fc51159244d78d65ec580f021afcef7bd53c04aeabc7f29"
 
 [[package]]
 name = "x86_64"
-version = "0.11.0"
+version = "0.9.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "365de37eb7c6da582cbb510dd0f3f1235d24ff6309a8a96e8a9909cc9bfd608f"
+checksum = "4206b60c9f99766329b66962aa8ddc01df6c7edd02edc046b7a69d5df9fcdbcf"
 dependencies = [
  "bit_field",
  "bitflags",
 ]
-
-[[package]]
-name = "x86_64"
-version = "0.11.1"
-dependencies = [
- "bit_field",
- "bitflags",
- "x86_64-idt-general-handler",
-]
-
-[[package]]
-name = "x86_64-idt-general-handler"
-version = "0.1.0"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn",
-]

Cargo.toml

@@ -13,12 +13,12 @@ name = "stack_overflow"
 harness = false
 
 [dependencies]
-bootloader = { version = "0.9.3", features = ["map_physical_memory"]}
+bootloader = { version = "0.8.0", features = ["map_physical_memory"]}
 volatile = "0.2.6"
 spin = "0.5.2"
-x86_64 = { path = "../../x86_64" }
+x86_64 = "0.9.6"
 uart_16550 = "0.2.0"
-pic8259_simple = "0.2.0"
+pic8259_simple = "0.1.1"
 pc-keyboard = "0.5.0"
 linked_list_allocator = "0.8.0"
 
@@ -31,14 +31,14 @@ version = "0.2.1"
 default-features = false
 features = ["alloc"]
 
-[dependencies.conquer-once]
-version = "0.2.0"
-default-features = false
-
 [dependencies.futures-util]
 version = "0.3.4"
 default-features = false
-features = ["alloc"]
+features = ["alloc", "async-await"]
+
+[dependencies.conquer-once]
+version = "0.2.0"
+default-features = false
 
 [package.metadata.bootimage]
 test-args = [

README.md

@@ -1,10 +1,10 @@
-# Blog OS (Async/Await)
+# Blog OS (Heap Allocation)
 
-[![Build Status](https://github.com/phil-opp/blog_os/workflows/Build%20Code/badge.svg?branch=post-12)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Build+Code%22+branch%3Apost-12)
+[![Build Status](https://github.com/phil-opp/blog_os/workflows/Build%20Code/badge.svg?branch=post-10)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Build+Code%22+branch%3Apost-10)
 
-This repository contains the source code for the [Async/Await][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.
+This repository contains the source code for the [Heap Allocation][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.
 
-[post]: https://os.phil-opp.com/async-await/
+[post]: https://os.phil-opp.com/heap-allocation/
 
 **Check out the [master branch](https://github.com/phil-opp/blog_os) for more information.**
 

src/allocator.rs

@@ -35,7 +35,7 @@ pub fn init_heap(
             .allocate_frame()
             .ok_or(MapToError::FrameAllocationFailed)?;
         let flags = PageTableFlags::PRESENT | PageTableFlags::WRITABLE;
-        unsafe { mapper.map_to(page, frame, flags, frame_allocator)?.flush() };
+        mapper.map_to(page, frame, flags, frame_allocator)?.flush();
     }
 
     unsafe {

src/allocator/linked_list.rs

@@ -45,7 +45,7 @@ impl LinkedListAllocator {
     /// Adds the given memory region to the front of the list.
     unsafe fn add_free_region(&mut self, addr: usize, size: usize) {
         // ensure that the freed region is capable of holding ListNode
-        assert_eq!(align_up(addr, mem::align_of::<ListNode>()), addr);
+        assert!(align_up(addr, mem::align_of::<ListNode>()) == addr);
         assert!(size >= mem::size_of::<ListNode>());
 
         // create a new list node and append it at the start of the list

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

@@ -1,10 +1,8 @@
-use crate::{gdt, hlt_loop, print, println};
+use crate::{gdt, hlt_loop, println};
 use lazy_static::lazy_static;
 use pic8259_simple::ChainedPics;
 use spin;
-use x86_64::structures::idt::{
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame, PageFaultErrorCode};
-    self, InterruptDescriptorTable, InterruptStackFrame, PageFaultErrorCode,
-};
 
 pub const PIC_1_OFFSET: u8 = 32;
 pub const PIC_2_OFFSET: u8 = PIC_1_OFFSET + 8;
@@ -32,8 +30,6 @@ pub static PICS: spin::Mutex<ChainedPics> =
 lazy_static! {
     static ref IDT: InterruptDescriptorTable = {
         let mut idt = InterruptDescriptorTable::new();
-
-        idt::set_general_handler!(&mut idt, default_handler);
         idt.breakpoint.set_handler_fn(breakpoint_handler);
         idt.page_fault.set_handler_fn(page_fault_handler);
         unsafe {
@@ -41,6 +37,8 @@ lazy_static! {
                 .set_handler_fn(double_fault_handler)
                 .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
         }
+        idt[InterruptIndex::Timer.as_usize()].set_handler_fn(timer_interrupt_handler);
+        idt[InterruptIndex::Keyboard.as_usize()].set_handler_fn(keyboard_interrupt_handler);
         idt
     };
 }
@@ -49,18 +47,6 @@ pub fn init_idt() {
     IDT.load();
 }
 
-fn default_handler(stack_frame: &mut InterruptStackFrame, index: u8, error_code: Option<u64>) {
-    if index == 32 {
-        print!("{} ", index);
-    } else {
-        println!("INTERRUPT {}: \n{:#?}", index, stack_frame);
-    }
-
-    unsafe {
-        PICS.lock().notify_end_of_interrupt(index);
-    }
-}
-
 extern "x86-interrupt" fn breakpoint_handler(stack_frame: &mut InterruptStackFrame) {
     println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
 }
@@ -86,7 +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());
@@ -95,10 +82,10 @@ extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptSt
 
 extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
     use x86_64::instructions::port::Port;
-
     let mut port = Port::new(0x60);
     let scancode: u8 = unsafe { port.read() };
-    crate::task::keyboard::add_scancode(scancode);
+
+    crate::driver::keyboard::keyboard_scancode(scancode);
 
     unsafe {
         PICS.lock()
@@ -106,8 +93,13 @@ extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: &mut Interrup
     }
 }
 
+#[cfg(test)]
+use crate::{serial_print, serial_println};
+
 #[test_case]
 fn test_breakpoint_exception() {
+    serial_print!("test_breakpoint_exception...");
     // invoke a breakpoint exception
     x86_64::instructions::interrupts::int3();
+    serial_println!("[ok]");
 }

src/lib.rs

@@ -4,8 +4,11 @@
 #![feature(abi_x86_interrupt)]
 #![feature(alloc_error_handler)]
 #![feature(const_fn)]
-#![feature(const_in_array_repeat_expressions)]
+#![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"]
 
@@ -14,6 +17,7 @@ extern crate alloc;
 use core::panic::PanicInfo;
 
 pub mod allocator;
+pub mod driver;
 pub mod gdt;
 pub mod interrupts;
 pub mod memory;
@@ -25,27 +29,17 @@ pub fn init() {
     gdt::init();
     interrupts::init_idt();
     unsafe { interrupts::PICS.lock().initialize() };
-    x86_64::instructions::interrupts::enable();
-}
-pub trait Testable {
-    fn run(&self) -> ();
 }
 
-impl<T> Testable for T
+pub fn init_heap_structures() {
-where
+    task::init();
-    T: Fn(),
+    driver::init();
-{
-    fn run(&self) {
-        serial_print!("{}...\t", core::any::type_name::<T>());
-        self();
-        serial_println!("[ok]");
-    }
 }
 
-pub fn test_runner(tests: &[&dyn Testable]) {
+pub fn test_runner(tests: &[&dyn Fn()]) {
     serial_println!("Running {} tests", tests.len());
     for test in tests {
-        test.run();
+        test();
     }
     exit_qemu(QemuExitCode::Success);
 }

src/main.rs

@@ -6,8 +6,8 @@
 
 extern crate alloc;
 
+use alloc::{boxed::Box, rc::Rc, vec, vec::Vec};
 use blog_os::println;
-use blog_os::task::{executor::Executor, keyboard, Task};
 use bootloader::{entry_point, BootInfo};
 use core::panic::PanicInfo;
 
@@ -26,13 +26,49 @@ 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();
 
-    #[cfg(test)]
+    // allocate a number on the heap
-    test_main();
+    let heap_value = Box::new(41);
+    println!("heap_value at {:p}", heap_value);
+
+    // create a dynamically sized vector
+    let mut vec = Vec::new();
+    for i in 0..500 {
+        vec.push(i);
+    }
+    println!("vec at {:p}", vec.as_slice());
+
+    // create a reference counted vector -> will be freed when count reaches 0
+    let reference_counted = Rc::new(vec![1, 2, 3]);
+    let cloned_reference = reference_counted.clone();
+    println!(
+        "current reference count is {}",
+        Rc::strong_count(&cloned_reference)
+    );
+    core::mem::drop(reference_counted);
+    println!(
+        "reference count is {} now",
+        Rc::strong_count(&cloned_reference)
+    );
+
+    use blog_os::task::executor::Executor;
 
     let mut executor = Executor::new();
-    executor.spawn(Task::new(example_task()));
+    executor.spawn(bar());
-    executor.spawn(Task::new(keyboard::print_keypresses()));
+
+    executor.spawn(async {
+        #[cfg(test)]
+        test_main();
+    });
+
+    executor.spawn(async {
+        println!("It did not crash!");
+    });
+
+    executor.spawn(blog_os::driver::timer::timer_task());
+    executor.spawn(blog_os::driver::keyboard::keyboard_task());
+
     executor.run();
 }
 
@@ -50,16 +86,14 @@ fn panic(info: &PanicInfo) -> ! {
     blog_os::test_panic_handler(info)
 }
 
-async fn async_number() -> u32 {
+async fn test() -> u32 {
     42
 }
 
-async fn example_task() {
+async fn foo() -> u32 {
-    let number = async_number().await;
+    test().await * 2
-    println!("async number: {}", number);
 }
 
-#[test_case]
+async fn bar() {
-fn trivial_assertion() {
+    println!("foo result: {}", foo().await);
-    assert_eq!(1, 1);
 }

src/memory.rs

@@ -2,6 +2,7 @@ use bootloader::bootinfo::{MemoryMap, MemoryRegionType};
 use x86_64::{
     structures::paging::{
         FrameAllocator, Mapper, OffsetPageTable, Page, PageTable, PhysFrame, Size4KiB,
+        UnusedPhysFrame,
     },
     PhysAddr, VirtAddr,
 };
@@ -44,12 +45,11 @@ pub fn create_example_mapping(
     use x86_64::structures::paging::PageTableFlags as Flags;
 
     let frame = PhysFrame::containing_address(PhysAddr::new(0xb8000));
+    // FIXME: ONLY FOR TEMPORARY TESTING
+    let unused_frame = unsafe { UnusedPhysFrame::new(frame) };
     let flags = Flags::PRESENT | Flags::WRITABLE;
 
-    let map_to_result = unsafe {
+    let map_to_result = mapper.map_to(page, unused_frame, flags, frame_allocator);
-        // FIXME: this is not safe, we do it only for testing
-        mapper.map_to(page, frame, flags, frame_allocator)
-    };
     map_to_result.expect("map_to failed").flush();
 }
 
@@ -57,7 +57,7 @@ pub fn create_example_mapping(
 pub struct EmptyFrameAllocator;
 
 unsafe impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
-    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+    fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
         None
     }
 }
@@ -82,7 +82,7 @@ impl BootInfoFrameAllocator {
     }
 
     /// Returns an iterator over the usable frames specified in the memory map.
-    fn usable_frames(&self) -> impl Iterator<Item = PhysFrame> {
+    fn usable_frames(&self) -> impl Iterator<Item = UnusedPhysFrame> {
         // get usable regions from memory map
         let regions = self.memory_map.iter();
         let usable_regions = regions.filter(|r| r.region_type == MemoryRegionType::Usable);
@@ -91,12 +91,14 @@ impl BootInfoFrameAllocator {
         // transform to an iterator of frame start addresses
         let frame_addresses = addr_ranges.flat_map(|r| r.step_by(4096));
         // create `PhysFrame` types from the start addresses
-        frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)))
+        let frames = frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)));
+        // we know that the frames are really unused
+        frames.map(|f| unsafe { UnusedPhysFrame::new(f) })
     }
 }
 
 unsafe impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
-    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+    fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
         let frame = self.usable_frames().nth(self.next);
         self.next += 1;
         frame

src/task/executor.rs

@@ -1,102 +1,127 @@
-use super::{Task, TaskId};
+use super::interrupt_wakeups::interrupt_wakeups;
-use alloc::{collections::BTreeMap, sync::Arc, task::Wake};
+use crate::println;
-use core::task::{Context, Poll, Waker};
+use alloc::{
-use crossbeam_queue::ArrayQueue;
+    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 {
-    tasks: BTreeMap<TaskId, Task>,
+    task_queue: VecDeque<Task>,
-    task_queue: Arc<ArrayQueue<TaskId>>,
+    wake_queue: Arc<SegQueue<TaskId>>,
-    waker_cache: BTreeMap<TaskId, Waker>,
+    pending_tasks: BTreeMap<TaskId, Task>,
 }
 
 impl Executor {
     pub fn new() -> Self {
         Executor {
-            tasks: BTreeMap::new(),
+            task_queue: VecDeque::new(),
-            task_queue: Arc::new(ArrayQueue::new(100)),
+            wake_queue: Arc::new(SegQueue::new()),
-            waker_cache: BTreeMap::new(),
+            pending_tasks: BTreeMap::new(),
         }
     }
 
-    pub fn spawn(&mut self, task: Task) {
+    pub fn spawn(&mut self, task: impl Future<Output = ()> + 'static) {
-        let task_id = task.id;
+        self.task_queue.push_back(Box::pin(task))
-        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");
     }
 
     pub fn run(&mut self) -> ! {
         loop {
             self.run_ready_tasks();
-            self.sleep_if_idle();
+            self.apply_interrupt_wakeups();
+            self.wake_waiting_tasks();
+            self.hlt_if_idle();
         }
     }
 
     fn run_ready_tasks(&mut self) {
-        // destructure `self` to avoid borrow checker errors
+        while let Some(mut task) = self.task_queue.pop_front() {
-        let Self {
+            let waker = self.create_waker(&task).into();
-            tasks,
+            let mut context = Context::from_waker(&waker);
-            task_queue,
+            match task.as_mut().poll(&mut context) {
-            waker_cache,
+                Poll::Ready(()) => {} // task done
-        } = self;
+                Poll::Pending => {
-
+                    // add task to pending_tasks and wait for wakeup
-        while let Ok(task_id) = task_queue.pop() {
+                    let task_id = Self::task_id(&task);
-            let task = match tasks.get_mut(&task_id) {
+                    if self.pending_tasks.insert(task_id, task).is_some() {
-                Some(task) => task,
+                        panic!("Task with same ID already in pending_tasks");
-                None => continue, // task no longer exists
+                    }
-            };
-            let waker = waker_cache
-                .entry(task_id)
-                .or_insert_with(|| TaskWaker::new(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 => {}
             }
         }
     }
 
-    fn sleep_if_idle(&self) {
+    /// Invoke wakers for tasks woken by interrupts
-        use x86_64::instructions::interrupts::{self, enable_interrupts_and_hlt};
+    ///
+    /// 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();
+        }
+    }
 
-        interrupts::disable();
+    fn wake_waiting_tasks(&mut self) {
-        if self.task_queue.is_empty() {
+        while let Ok(task_id) = self.wake_queue.pop() {
-            enable_interrupts_and_hlt();
+            if let Some(task) = self.pending_tasks.remove(&task_id) {
+                self.task_queue.push_back(task);
             } else {
-            interrupts::enable();
+                println!("WARNING: woken task not found in pending_tasks");
             }
         }
     }
 
-struct TaskWaker {
+    /// 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,
-    task_queue: Arc<ArrayQueue<TaskId>>,
 }
 
-impl TaskWaker {
+impl Wake for Waker {
-    fn new(task_id: TaskId, task_queue: Arc<ArrayQueue<TaskId>>) -> Waker {
-        Waker::from(Arc::new(TaskWaker {
-            task_id,
-            task_queue,
-        }))
-    }
-
-    fn wake_task(&self) {
-        self.task_queue.push(self.task_id).expect("task_queue full");
-    }
-}
-
-impl Wake for TaskWaker {
     fn wake(self: Arc<Self>) {
-        self.wake_task();
+        self.wake_by_ref();
     }
 
     fn wake_by_ref(self: &Arc<Self>) {
-        self.wake_task();
+        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/keyboard.rs

@@ -1,83 +0,0 @@
-use crate::{print, println};
-use conquer_once::spin::OnceCell;
-use core::{
-    pin::Pin,
-    task::{Context, Poll},
-};
-use crossbeam_queue::ArrayQueue;
-use futures_util::{
-    stream::{Stream, StreamExt},
-    task::AtomicWaker,
-};
-use pc_keyboard::{layouts, DecodedKey, HandleControl, Keyboard, ScancodeSet1};
-
-static SCANCODE_QUEUE: OnceCell<ArrayQueue<u8>> = OnceCell::uninit();
-static WAKER: AtomicWaker = AtomicWaker::new();
-
-/// Called by the keyboard interrupt handler
-///
-/// Must not block or allocate.
-pub(crate) fn add_scancode(scancode: u8) {
-    if let Ok(queue) = SCANCODE_QUEUE.try_get() {
-        if let Err(_) = queue.push(scancode) {
-            println!("WARNING: scancode queue full; dropping keyboard input");
-        } else {
-            WAKER.wake();
-        }
-    } else {
-        println!("WARNING: scancode queue uninitialized");
-    }
-}
-
-pub struct ScancodeStream {
-    _private: (),
-}
-
-impl ScancodeStream {
-    pub fn new() -> Self {
-        SCANCODE_QUEUE
-            .try_init_once(|| ArrayQueue::new(100))
-            .expect("ScancodeStream::new should only be called once");
-        ScancodeStream { _private: () }
-    }
-}
-
-impl Stream for ScancodeStream {
-    type Item = u8;
-
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<u8>> {
-        let queue = SCANCODE_QUEUE
-            .try_get()
-            .expect("scancode queue not initialized");
-
-        // fast path
-        if let Ok(scancode) = queue.pop() {
-            return Poll::Ready(Some(scancode));
-        }
-
-        WAKER.register(&cx.waker());
-        match queue.pop() {
-            Ok(scancode) => {
-                WAKER.take();
-                Poll::Ready(Some(scancode))
-            }
-            Err(crossbeam_queue::PopError) => Poll::Pending,
-        }
-    }
-}
-
-pub async fn print_keypresses() {
-    let mut scancodes = ScancodeStream::new();
-    let mut keyboard = Keyboard::new(layouts::Us104Key, ScancodeSet1, HandleControl::Ignore);
-
-    while let Some(scancode) = scancodes.next().await {
-        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),
-                }
-            }
-        }
-    }
-}

src/task/mod.rs

@@ -1,39 +1,8 @@
-use alloc::boxed::Box;
+pub(crate) use interrupt_wakeups::interrupt_wake;
-use core::{
-    future::Future,
-    pin::Pin,
-    sync::atomic::{AtomicU64, Ordering},
-    task::{Context, Poll},
-};
 
 pub mod executor;
-pub mod keyboard;
+mod interrupt_wakeups;
-pub mod simple_executor;
 
-pub struct Task {
+pub fn init() {
-    id: TaskId,
+    interrupt_wakeups::init();
-    future: Pin<Box<dyn Future<Output = ()>>>,
-}
-
-impl Task {
-    pub fn new(future: impl Future<Output = ()> + 'static) -> Task {
-        Task {
-            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_ID: AtomicU64 = AtomicU64::new(0);
-        TaskId(NEXT_ID.fetch_add(1, Ordering::Relaxed))
-    }
 }

src/task/simple_executor.rs

@@ -1,44 +0,0 @@
-use super::Task;
-use alloc::collections::VecDeque;
-use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
-
-pub struct SimpleExecutor {
-    task_queue: VecDeque<Task>,
-}
-
-impl SimpleExecutor {
-    pub fn new() -> SimpleExecutor {
-        SimpleExecutor {
-            task_queue: VecDeque::new(),
-        }
-    }
-
-    pub fn spawn(&mut self, task: Task) {
-        self.task_queue.push_back(task)
-    }
-
-    pub fn run(&mut self) {
-        while let Some(mut task) = self.task_queue.pop_front() {
-            let waker = dummy_waker();
-            let mut context = Context::from_waker(&waker);
-            match task.poll(&mut context) {
-                Poll::Ready(()) => {} // task done
-                Poll::Pending => self.task_queue.push_back(task),
-            }
-        }
-    }
-}
-
-fn dummy_raw_waker() -> RawWaker {
-    fn no_op(_: *const ()) {}
-    fn clone(_: *const ()) -> RawWaker {
-        dummy_raw_waker()
-    }
-
-    let vtable = &RawWakerVTable::new(clone, no_op, no_op, no_op);
-    RawWaker::new(0 as *const (), vtable)
-}
-
-fn dummy_waker() -> Waker {
-    unsafe { Waker::from_raw(dummy_raw_waker()) }
-}

src/vga_buffer.rs

@@ -3,6 +3,9 @@ use lazy_static::lazy_static;
 use spin::Mutex;
 use volatile::Volatile;
 
+#[cfg(test)]
+use crate::{serial_print, serial_println};
+
 lazy_static! {
     /// A global `Writer` instance that can be used for printing to the VGA text buffer.
     ///
@@ -177,14 +180,18 @@ pub fn _print(args: fmt::Arguments) {
 
 #[test_case]
 fn test_println_simple() {
+    serial_print!("test_println... ");
     println!("test_println_simple output");
+    serial_println!("[ok]");
 }
 
 #[test_case]
 fn test_println_many() {
+    serial_print!("test_println_many... ");
     for _ in 0..200 {
         println!("test_println_many output");
     }
+    serial_println!("[ok]");
 }
 
 #[test_case]
@@ -192,6 +199,8 @@ fn test_println_output() {
     use core::fmt::Write;
     use x86_64::instructions::interrupts;
 
+    serial_print!("test_println_output... ");
+
     let s = "Some test string that fits on a single line";
     interrupts::without_interrupts(|| {
         let mut writer = WRITER.lock();
@@ -201,4 +210,6 @@ fn test_println_output() {
             assert_eq!(char::from(screen_char.ascii_character), c);
         }
     });
+
+    serial_println!("[ok]");
 }

tests/basic_boot.rs

@@ -4,7 +4,7 @@
 #![test_runner(blog_os::test_runner)]
 #![reexport_test_harness_main = "test_main"]
 
-use blog_os::println;
+use blog_os::{println, serial_print, serial_println};
 use core::panic::PanicInfo;
 
 #[no_mangle] // don't mangle the name of this function
@@ -21,5 +21,7 @@ fn panic(info: &PanicInfo) -> ! {
 
 #[test_case]
 fn test_println() {
+    serial_print!("test_println... ");
     println!("test_println output");
+    serial_println!("[ok]");
 }

tests/heap_allocation.rs

@@ -7,7 +7,7 @@
 extern crate alloc;
 
 use alloc::{boxed::Box, vec::Vec};
-use blog_os::allocator::HEAP_SIZE;
+use blog_os::{allocator::HEAP_SIZE, serial_print, serial_println};
 use bootloader::{entry_point, BootInfo};
 use core::panic::PanicInfo;
 
@@ -30,38 +30,44 @@ fn main(boot_info: &'static BootInfo) -> ! {
 
 #[test_case]
 fn simple_allocation() {
-    let heap_value_1 = Box::new(41);
+    serial_print!("simple_allocation... ");
-    let heap_value_2 = Box::new(13);
+    let heap_value = Box::new(41);
-    assert_eq!(*heap_value_1, 41);
+    assert_eq!(*heap_value, 41);
-    assert_eq!(*heap_value_2, 13);
+    serial_println!("[ok]");
 }
 
 #[test_case]
 fn large_vec() {
+    serial_print!("large_vec... ");
     let n = 1000;
     let mut vec = Vec::new();
     for i in 0..n {
         vec.push(i);
     }
     assert_eq!(vec.iter().sum::<u64>(), (n - 1) * n / 2);
+    serial_println!("[ok]");
 }
 
 #[test_case]
 fn many_boxes() {
+    serial_print!("many_boxes... ");
     for i in 0..HEAP_SIZE {
         let x = Box::new(i);
         assert_eq!(*x, i);
     }
+    serial_println!("[ok]");
 }
 
 #[test_case]
 fn many_boxes_long_lived() {
+    serial_print!("many_boxes_long_lived... ");
     let long_lived = Box::new(1); // new
     for i in 0..HEAP_SIZE {
         let x = Box::new(i);
         assert_eq!(*x, i);
     }
     assert_eq!(*long_lived, 1); // new
+    serial_println!("[ok]");
 }
 
 #[panic_handler]

tests/should_panic.rs

@@ -13,7 +13,7 @@ pub extern "C" fn _start() -> ! {
 }
 
 fn should_fail() {
-    serial_print!("should_panic::should_fail...\t");
+    serial_print!("should_fail... ");
     assert_eq!(0, 1);
 }
 

tests/stack_overflow.rs

@@ -9,7 +9,7 @@ use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
 
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
-    serial_print!("stack_overflow::stack_overflow...\t");
+    serial_print!("stack_overflow... ");
 
     blog_os::gdt::init();
     init_test_idt();
@@ -23,7 +23,6 @@ pub extern "C" fn _start() -> ! {
 #[allow(unconditional_recursion)]
 fn stack_overflow() {
     stack_overflow(); // for each recursion, the return address is pushed
-    volatile::Volatile::new(0).read(); // prevent tail recursion optimizations
 }
 
 lazy_static! {