feat(executor): added async task

[sususu5]

No description provided.

[Copilot]

Pull request overview

This PR introduces an async task executor to the axtask module, enabling asynchronous task execution alongside the existing synchronous task system. The implementation adds a global ready queue for async tasks with spawn, polling, and execution control functions.

Key changes:

• New async executor module with task spawning and execution control (run_once, run_for, run_until_idle)
• Integration with existing block_on to drive executor tasks during synchronous future polling
• Comprehensive test coverage for executor fairness, self-wake, and execution control

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
modules/axtask/src/executor.rs	New async executor implementation with ready queue, AsyncTask wrapper, and execution control functions
modules/axtask/src/lib.rs	Adds executor module to the crate's public API
modules/axtask/src/api.rs	Initializes executor during scheduler initialization
modules/axtask/src/task.rs	Changes TaskId::new() visibility from private to pub(crate) for executor use
modules/axtask/src/future/mod.rs	Integrates executor into block_on by polling up to 3 async tasks per iteration
modules/axtask/src/tests.rs	Adds comprehensive test suite for executor functionality including completion, self-wake, fairness, and run_for tests

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[AsakuraMizu]

Good job 👍

[sususu5]

Good job 👍

What should be the focus of the next optimization? Scaling the async task queue to per-CPU, or optimizing the Waker implementation?

[Copilot]

Pull request overview

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The magic number 3 for max async tasks to run is unexplained. Consider extracting this as a named constant (e.g., MAX_ASYNC_TASKS_PER_POLL) to clarify why this specific value was chosen and make it easier to tune if needed.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 7 changed files in this pull request and generated 3 comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

This new find_area method is identical to the existing find_area_mut method on line 113 (which also calls self.areas.find(vaddr)). The only difference is that find_area_mut returns a mutable reference. This creates duplicate logic. Consider whether this new method is necessary, or if callers should use find_area_mut and simply not mutate the result.

[Copilot]

The magic number 64 for SPIN_LIMIT lacks explanation. Consider adding a comment explaining why this specific value was chosen and what trade-offs it represents between spinning and yielding.

Suggested change

	pub fn run_until_idle() {
	pub fn run_until_idle() {
	// Number of consecutive spin iterations before yielding the CPU.
	// 64 is a small power-of-two chosen as a compromise: it allows short-lived
	// bursts of wakeups to be handled without an expensive scheduler yield,
	// while still bounding the time spent busy-waiting when the system is idle.

[sususu5]

Per-CPU Async Architecture

• Implemented AxExecutor with per-CPU ready queues: Localizes task scheduling to reduce lock contention and improve cache locality on multi-core systems.

Optimized block_on Logic

• Refactored block_on: Efficiently drives async tasks while waiting for a future. The new flow ensures the current thread blocks (parks) only when:
  1. The main future is still Pending.
  2. The local run queue is fully drained.
  3. No new wakeups occurred during the drain phase (preventing lost wakeups).

Tests

• Added unit tests covering the executor's lifecycle, queue operations, and per-CPU scheduling behavior to ensure correctness.