The freelist holds the boot-peak count of recycled SchedulerItem*; items_,
to_add_, and defer_queue_ hold the boot-peak vector *capacity* of live
SchedulerItem*. std::vector grows by doubling and retains capacity even when
items drain, so post-boot the vector slack can be larger than the freelist
itself. Swap each with a same-content copy to size them exactly to their
current contents.
Live items are preserved -- the swap-copy idiom builds the new vector from
the existing pointers, then the old (over-capacity) vector is destroyed.
Boot churn (component init, first sensor reads, retries) inflates the freelist
beyond the steady-state high-water mark. Without a one-shot trim that peak
would be retained forever. Adds Scheduler::trim_freelist() and schedules it
from Application::setup() to fire SCHEDULER_FREELIST_TRIM_DELAY_MS (10s) after
setup completes -- well past the bulk of post-setup async work.
Items currently in items_/to_add_/defer_queue_ are untouched; only the
freelist's recycled items are deleted. Post-trim, the freelist regrows to
the new (post-startup) high-water mark.
Adds an assertion that the observed peak pool size exceeds the old
MAX_POOL_SIZE=5 cap. Without this, a silent regression that re-introduced a
small cap could pass the existing pool_full_count == 0 invariant. Phase 5 + 6
of the fixture schedule 8 + 10 same-component timeouts, so the peak should
comfortably exceed 5.
Address Copilot review feedback on PR.
The fixed MAX_POOL_SIZE=5 cap was the source of the heap churn the pool was
meant to prevent: any device with more than 5 concurrent timers (e.g. a board
with 30+ LD2450 sensors) hit a steady-state oscillation of recycle->delete and
acquire->new on every loop iteration.
Replace std::vector<SchedulerItem*> with a singly-linked freelist threaded
through SchedulerItem::next_free, which shares storage with `component` via an
anonymous union (zero per-item overhead -- the component pointer is dead while
pooled). Drop the cap entirely: the freelist quiesces at the application's
natural concurrent-timer high-water mark, which is the working set the device
already needs while those timers are active.
No std::vector means no growth-doubling slack and no realloc copies during
warm-up. Caller of get_item_from_pool_locked_() must overwrite item->component
before unlocking (already true at the sole call site); nullptr remains a valid
live `component` value for SELF_POINTER items, so we cannot pre-clear it.
J. Nick Koston