fix(plugins): cap the per-plugin state transition history - #501
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ChuckBuilds merged 2 commits intoAug 25, 2026
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PluginStateManager recorded every state transition in a per-plugin list
and never trimmed it. The only code that removed entries was
clear_state(), called solely from PluginManager.unload_plugin(), so a
plugin that stays loaded -- normal operation -- never released one.
The list is written on the hot scheduling path. Every update cycle
appends twice: _reserve_for_update() sets RUNNING and _finish() sets
ENABLED back again. At the default 60s update interval that is 2,880
entries per plugin per day, and nothing reads them -- get_state_info()
only takes their len(). Pure dead weight.
Measured against the unpatched class, ten plugins on a 60s interval:
sim uptime history entries heap growth
1 day 28,810 7.7 MB
7 days 201,610 53.9 MB
30 days 864,010 230.9 MB (still climbing)
With the cap it is flat at 2,000 entries / 0.5 MB from day one.
On a 1 GB board 231 MB of garbage is fatal on its own, and the failure
is not a clean OOM: once MemAvailable falls far enough fork() starts
returning ENOMEM, so sshd accepts connections and closes them before its
banner while the kernel still answers pings. The board looks like a
hardware fault and needs a power cycle. Same family as the ceilings
added in ChuckBuilds#464.
Retain the most recent 200 transitions per plugin in a deque and let the
rest age out. state_history_count is surfaced through the web API, so
the lifetime total is tracked separately rather than plateauing at the
cap. get_state_history() now returns a copy under the lock; it was
handing out the manager's own list, which a caller could mutate.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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📝 WalkthroughWalkthrough
ChangesPlugin state history
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The change caps retained plugin history and preserves lifetime counts, but transition records remain partially mutable and plugin unloading can race with updates, leaving stale history or counts. The PR is mergeable with explicit owner awareness and follow-up on these bounded correctness issues. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@src/plugin_system/plugin_state.py`:
- Around line 159-174: Update get_state_history in the plugin state manager to
return a new dictionary for each transition, preserving the existing
oldest-first ordering and defensive-copy contract. Add a regression assertion
that mutating a returned entry does not alter the manager-owned history.
- Around line 292-296: Update unload_plugin() to serialize plugin unloading with
active update workers, ensuring no worker can call set_state() between
clear_state() and worker shutdown. Hold the per-plugin lock across worker
stopping/joining and the clear_state() cleanup, or otherwise stop and join all
active workers before clearing state, preserving complete removal of the
plugin’s state, history, and transition count.
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src/plugin_system/plugin_state.pytest/test_plugin_state_history_cap.py
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Review follow-ups on the transition history. get_state_history() copied only the outer list, so a caller holding a returned transition could rewrite the manager's record of what happened -- which contradicted the defensive-copy guarantee in its own docstring. Copy each entry too. Every value in a transition is immutable, so a shallow copy per entry is enough. test_get_state_history_entries_are_copies pins it; without the change it fails with 'tampered' == 'enabled'. clear_state() mutated five shared dicts without holding _lock, while every other mutator takes it. A concurrent set_state() could interleave and leave a plugin with history but no state. Drop the five as one unit. This does not close the wider unload-vs-worker race, which lives in PluginManager.unload_plugin() and predates this change: an update worker still in flight can call set_state() after clear_state() returns and recreate the entry. Serialising that needs the per-plugin lock held across worker join in unload_plugin(), which is a separate change. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Summary
PluginStateManagerrecords every state transition in a per-plugin list andnever trims it. The only code that removes entries is
clear_state(), calledsolely from
PluginManager.unload_plugin()— so a plugin that stays loaded,i.e. normal operation, never releases a single entry.
The list is written on the hot scheduling path. Every update cycle appends
twice:
At the default 60s update interval that is 2,880 entries per plugin per day,
and nothing ever reads them —
get_state_info()only takes theirlen(). It ispure dead weight.
Measurement
Driving the real scheduling path against the unpatched class, ten plugins on a
60s interval:
With the cap it is flat at 2,000 entries / 0.5 MB from day one.
Growth scales with plugin count and inversely with update interval: 5 plugins at
60s is ~4 MB/day, 20 plugins ~16 MB/day.
Why this matters on a small board
231 MB of garbage is fatal on its own on a 1 GB Pi, and the failure is not a
clean OOM. Once
MemAvailablefalls far enough,fork()starts returningENOMEM — so
sshdaccepts the TCP connection and closes it before sending itsbanner, systemd cannot respawn the display, and the panel goes dark while the
kernel keeps answering pings at 0% loss. It reads as a hardware fault and needs
a power cycle.
Same family as the ceilings added in #464, and it is invisible in a short RSS
sample: at ~8 MB/day the slope does not show up in the five-minute profile that
concluded "arena bloat, not leaked objects" in the
MALLOC_ARENA_MAXnote. Italso affects every install that has at least one plugin with an
update()method — no particular plugin required.
Changes
MAX_STATE_HISTORY_PER_PLUGIN = 200transitions perplugin in a
deque(maxlen=…); older ones age out. Both append sites(
set_stateandset_state_with_error) go through one_record_transition()helper.
state_history_countis surfaced through/api/v3, so the lifetime totalis tracked separately rather than plateauing at the cap — the number the API
reports is unchanged in meaning.
get_state_history()returns a copy under the lock. It was handing out themanager's own list, which a caller could mutate; the new test pins that.
The 200 entries are kept because a rolling tail of recent transitions is what
makes the history useful for debugging a flapping plugin — the bug is retaining
all of them, not retaining any.
Testing
test/test_plugin_state_history_cap.py— 7 tests. Verified as a real regressiontest; against the unpatched class (constant added, capping not yet applied):
All 7 pass with the fix. Full suite: 3735 passed, same 10 pre-existing failures
as
upstream/mainon this machine (macOS-specific:findmnt, systemd unitdrift, pixlet download, plus the known web/vegas bound assertions) — verified by
running the identical suite on an untouched
upstream/maincheckout, whichgives 3728 passed and those same 10.
Summary by CodeRabbit
New Features
Bug Fixes