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fix(grid): every result grid leaks (extension-method listener on PiiMaskingController is never removed); ~5 MB per run

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評価

難易度
3/5
見積もり時間
1〜2日
初心者へのやさしさ
55/100
issue の種類
バグ
明瞭さ
明確に書かれている
活発さ
活発
技術スタック
dart, flutter
領域
desktop, performance

調査の方向性

Start with the listener registration and disposal in lib/features/workspace/result_grid_view.dart, then read the extension handlers in lib/features/workspace/grid/grid_pii_masking.dart and inspect the horizontal scroll listener pair. Add a guard under test/guards/ and a widget test that disposes VirtualResultGrid and checks PiiMaskingController.instance.hasListeners; run those tests. Done means listeners are removed and the guard catches extension method tear-offs used in listener pairs.

索引モデルが issue の本文から書いたものです。

説明

bug data-grid P1 performance stability
Problem

Every result grid that is ever shown is kept in memory for the rest of the session, together with its whole result set and its widget / render / semantics tree. Each query run and each closed tab leaks one grid.

Cause: _VirtualResultGridState registers _onPiiMaskingChanged as a listener on the app-wide singleton PiiMaskingController.instance (lib/features/workspace/result_grid_view.dart:167) and removes it in dispose() (:392), but _onPiiMaskingChanged is declared in an extension _GridPiiMasking on _VirtualResultGridState (lib/features/workspace/grid/grid_pii_masking.dart:34). In Dart, tearing off an extension method creates a new closure each time and two such closures are not equal, so removeListener(_onPiiMaskingChanged) does not find the one that addListener(_onPiiMaskingChanged) stored. The listener stays in the singleton's list and keeps the state alive forever: state -> widget -> CompactResultDataset / rows -> element tree -> render objects -> semantics.

Minimal reproduction of the language behavior:

class Owner { void inClass() {} void reg(Notifier n){ n.add(inClass); n.add(ext);} void unreg(Notifier n){ n.remove(inClass); n.remove(ext);} }
extension E on Owner { void ext() {} }
// after reg + unreg: 1 listener is left (the extension tear-off); `o.inClass == o.inClass` is true, `o.ext == o.ext` is false
Measurements

Profile build of dev 0.4.22+5, app benchmark harness, Dart heap after a forced full GC (getAllocationProfile(gc: true)), heavySql = 5000 rows x 20 columns, retaining paths from the VM service:

Re-running a query 6 more times in the same tab

live _VirtualResultGridState live CompactResultDataset Dart heap
after 1 result 1 1 62 MB
after 6 re-runs 6 6 92.5 MB (+5 MB per run)

Opening a tab, running the query, closing the tab (confirming "Discard & Close"), 4 times

baseline after 4 cycles
mounted QueryEditorTab / ResultsTab 1 1
live QueryEditorTab instances 2 6
live ResultsTab 2 6
live VirtualResultGrid / _VirtualResultGridState 1 5
live CompactResultDataset 1 5
live FocusNode 105 235
live AnimationController 147 323
Dart heap 58 MB 87-90 MB

Retaining path of every leaked grid state (identical for all, 6 elements):

_VirtualResultGridState <- Context.0[] <- _Closure <- _List.N[] <- PiiMaskingController._listeners <- (static field PiiMaskingController.instance)

and of the leaked CompactResultDataset: _LazyDatasetRowList.dataset <- ResultsTab.rows <- _ResultsTabState._widget ... <- _VirtualResultGridState._focusNode ... <- PiiMaskingController._listeners.

A session of 100 queries on a 5000 x 20 result leaks on the order of 500 MB of Dart heap, more for larger results and a lot more for a result with a raised row cap.

Solution
  • Declare _onPiiMaskingChanged (and _onHorizontalScroll, which has the same shape) inside the State class instead of an extension, or keep the listener in a field: late final VoidCallback _piiListener = _onPiiMaskingChanged; and use that field for both addListener and removeListener.
  • A scan of lib/ found exactly these two addListener / removeListener pairs whose handler is an extension method; _onHorizontalScroll is attached to a controller that dispose() discards, so it is harmless in practice, but should be fixed the same way.
  • Add a guard test in test/guards/ that fails when the argument of addListener( / removeListener( is a method declared in an extension (the regex scan used for this report is enough).
Acceptance
  • PiiMaskingController.instance has no listeners after a VirtualResultGrid is disposed (widget test: pump the grid, remove it, assert hasListeners == false).
  • 6 re-runs of the same query in one tab leave 1 live _VirtualResultGridState (check with a leak test or leak_tracker).
  • Closing a tab releases QueryEditorTab, ResultsTab, the grid and its dataset.
  • Heap after N re-runs is flat in the app benchmark (add a leak_rerun scenario that prints live-instance counts after GC).

Related: #1549, #1552 (memory of the result path).

主要言語
Dart
スター
23
フォーク
1
平均マージ
31分
マージ済み PR（30日）
570

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