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feat(scheduler-core): implement builtin_fcfs session and post-allocation hooks (task 2.3)

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Adds begin_session/next_job/end_session/on_dispatch/on_pend, driving a
dual-cursor walk (queue then job) over builtin_fcfs's private ordq_t
state. next_job() returns candidates in (queue priority desc, job
priority desc, queue_time asc) order and NULL once exhausted;
on_dispatch removes permanently, on_pend is a true no-op.

Review flagged an unsynchronized cross-thread access risk between
next_job() (picker thread) and on_dispatch/on_pend (allocator thread)
once wired live in task 2.4 — recorded in tasks.md Implementation Notes
for that task to close before registering builtin_fcfs as the default.

Requirements: 3.2, 3.4, 3.6
This commit is contained in:
Rongsong Shen 2026-08-03 07:18:39 +00:00
parent b7214ebe88
commit fcb32a8b30
5 changed files with 658 additions and 8 deletions
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.kiro/specs/scheduler-core/tasks.md
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@ -41,7 +41,7 @@
- _Requirements: 3.2_
- _Depends: 2.1_
- [ ] 2.3 Implement builtin_fcfs session and post-allocation hooks
- [x] 2.3 Implement builtin_fcfs session and post-allocation hooks
- `begin_session`: reset the iteration cursor to the head of the ordered queue list
- `next_job`: walk queues then jobs in ordering, skipping not-ready queues/jobs, returning the first ready job and advancing the cursor; returns NULL when exhausted
- `end_session`: no-op (iteration state already reset in `begin_session`)
@ -356,3 +356,4 @@
- Background IDE diagnostics ("file not found: rtti.h", "unknown type name" for various xce_* types) have appeared consistently on every scheduler.h/plugin.h/types.h/schedobj.c change so far (tasks 1.1-1.3) and are confirmed stale clangd artifacts each time via independent real `meson compile`/`meson test` runs — not real build failures. Don't let these block a task; verify with the real build instead.
- Meson build dir is `src/xce.build`, not repo-root `xce.build` — build/test commands must run from `src/` (e.g. `cd src && nix develop . --command bash -c "meson test -C xce.build --suite scheduler"`).
- Scheduler testsuite convention: run test binaries directly with `ASAN_OPTIONS=detect_leaks=0` (fixtures aren't torn down, by design — matches existing `meson.build` test registration).
- Task 2.3's review found a real concurrency gap for task 2.4 to close: once builtin_fcfs is wired live, `next_job()` (picker thread) and `on_dispatch`/`on_pend` (allocator thread) can race on the same unsynchronized `fcfs_plugin_data_t` private state — `cbuf_get()` unblocks the picker's next `cbuf_put()` before the allocator finishes processing the dequeued job (jbuf capacity is 1), so the picker can re-enter `next_job()` while the allocator is still mutating `priv->queues` via `on_dispatch`/`on_pend`. Today's production path never hits this because the allocator thread calls a different plugin category (`limit.c`'s resource-limit hook), never `fcfs.c`'s own private state. Task 2.4 must add a mutex guarding `fcfs_plugin_data_t` across all five picker hooks (or an equivalent handoff redesign) before registering builtin_fcfs as the live default.