O(1) scheduler: Task state transition relative APIs modifications

[vicLin8712]

O(1) scheduler: Task state transition relative APIs modifications

This PR integrates the modified sched_enqueue_task() and sched_dequeue_task() helpers introduced in #36 into the existing task state transition APIs.

This is part 2 of a 3-part stacked PR series, and depends on #36 (Part 1: infrastructure).

Summary

To support a ready-queue-based O(1) scheduler, task state transitions must explicitly maintain the ready queues by invoking the enqueue/dequeue helpers whenever a task moves into or out of the schedulable state set.

This PR updates all relevant task state transition paths to ensure that the ready queue remains consistent with the task’s state.

Detail

The task state transition of the original scheduler is shown below:

Only tasks in TASK_READY or TASK_RUNNING may be selected as the next runnable task.
All other task states are considered non-schedulable and may appear in arbitrary situations.

From this scheduling rule, task states naturally fall into two groups:

• Schedulable: { TASK_RUNNING, TASK_READY }

• Non-schedulable: { all other states }

Therefore, the enqueue/dequeue helper functions must be invoked whenever a task transitions between these two groups.
This ensures that the ready queue accurately reflects the set of tasks eligible for scheduling.

Code changes

This PR is part 2 of the stacked O(1) scheduler series.
Only the commits listed below are unique to this PR:

• Add ready queue dequeue path in mo_task_suspend()
• Add ready queue dequeue path in mo_task_cancel()
• Add sched_enqueue_task() in mo_task_resume()
• Add ready queue enqueue path in mo_task_wakeup()
• Add dequeuing ready queue path in mo_task_delay()
• Add dequeuing ready queue path in _sched_block()

Verification

Linmo still operates under the original linear-search scheduler at this stage.
No scheduling behavior is changed; the ready queue is updated, but not yet used by the dispatch path introduced in later PRs.

All tests/applications in /apps build and run successfully.

Reference

#23 — Prior draft discussion
#36 — Part 1: O(1) scheduler infrastructure (base of this PR)

---

Summary by cubic

Updates task state transitions to keep O(1) ready queues in sync via enqueue/dequeue helpers with embedded rq_node. This is part 2 of the O(1) scheduler; no behavior change and all apps still build and run.

• Refactors

  • Extended KCB with ready_queues[], ready_bitmap, queue_counts[], rr_cursors; added bitmap macros.
  • Added intrusive list helpers list_pushback_node() and list_remove_node(), and rq_node in tcb_t for ready-queue membership.
  • Refactored sched_enqueue_task() and sched_dequeue_task() to update per-priority queues, rr cursors, queue counts, and bitmap.
  • Integrated enqueue/dequeue into mo_task_resume(), mo_task_wakeup(), mo_task_suspend(), mo_task_delay(), mo_task_cancel(), and _sched_block().

• Bug Fixes

  • Removed canceled/suspended/blocked tasks from ready queues to prevent accidental scheduling.
  • Advanced rr_cursors and removed nodes safely to avoid inconsistencies.

^{Written for commit 9ca3f90. Summary will update automatically on new commits.}

[jserv]

Do not include numbers in pull-request titles.

[jserv]

Refine the git commits to ensure each one contains only minimal, functional changes.

[jserv]

The commits below are really annoying:

• Remove attribute((unused) from sched_dequeue_task()
• Add ready queue dequeue path in mo_task_suspend()
• Add ready queue dequeue path in mo_task_cancel()
• Add sched_enqueue_task() in mo_task_resume()
• Add ready queue enqueue path in mo_task_wakeup()
• Add dequeuing ready queue path in mo_task_delay()
• Add dequeuing ready queue path in _sched_block()

Read https://cbea.ms/git-commit/ carefully.