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Do not eagerly allocate inherited widget caches when initializing element tree (#95596)
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@ -395,6 +395,53 @@ abstract class Widget extends DiagnosticableTree {
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}
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}
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/// A cache of inherited elements with an optional parent cache.
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///
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/// When looking up an inherited element, this will look through parent
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/// caches until the element is found or the end is reached. When an element
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/// is found, it is cached at the first element where the search began.
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///
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/// The intention of this cache is to speed up the initial build of widget
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/// trees that contain a significant number of inherited widgets by deferring
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/// expensive map allocations until they are needed, and by only allocating
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/// in the "closest" hash map.
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///
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/// This will not cache `null` results if an inherited element is not found.
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@visibleForTesting
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class InheritedTreeCache {
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/// Create a new [InheritedTreeCache] with an optional parent.
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InheritedTreeCache([this._parent]);
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final InheritedTreeCache? _parent;
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final HashMap<Type, InheritedElement> _current = HashMap<Type, InheritedElement>();
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/// Place the [element] in the cache under [type].
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void operator []=(Type type, InheritedElement element) {
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_current[type] = element;
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}
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/// Find the nearest [InheritedElement] of type [type], or `null` if it
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/// cannot be found.
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///
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/// This operation will also cache the inherited element to improve the
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/// speed of future lookups.
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InheritedElement? operator[](Type type) {
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InheritedElement? potential = _current[type];
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if (potential != null) {
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return potential;
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}
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potential = _parent?._lookupWithoutCaching(type);
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if (potential != null) {
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_current[type] = potential;
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}
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return potential;
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}
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InheritedElement? _lookupWithoutCaching(Type type) {
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return _current[type] ?? _parent?._lookupWithoutCaching(type);
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}
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}
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/// A widget that does not require mutable state.
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///
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/// A stateless widget is a widget that describes part of the user interface by
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@ -3937,7 +3984,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
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// implementation to decide whether to rebuild based on whether we had
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// dependencies here.
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}
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_inheritedWidgets = null;
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_inheritedLookup = null;
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_lifecycleState = _ElementLifecycle.inactive;
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}
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@ -4129,7 +4176,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
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return null;
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}
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Map<Type, InheritedElement>? _inheritedWidgets;
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InheritedTreeCache? _inheritedLookup;
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Set<InheritedElement>? _dependencies;
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bool _hadUnsatisfiedDependencies = false;
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@ -4166,7 +4214,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
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@override
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T? dependOnInheritedWidgetOfExactType<T extends InheritedWidget>({Object? aspect}) {
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assert(_debugCheckStateIsActiveForAncestorLookup());
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final InheritedElement? ancestor = _inheritedWidgets == null ? null : _inheritedWidgets![T];
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final InheritedElement? ancestor = _inheritedLookup?[T];
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if (ancestor != null) {
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return dependOnInheritedElement(ancestor, aspect: aspect) as T;
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}
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@ -4177,13 +4225,13 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
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@override
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InheritedElement? getElementForInheritedWidgetOfExactType<T extends InheritedWidget>() {
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assert(_debugCheckStateIsActiveForAncestorLookup());
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final InheritedElement? ancestor = _inheritedWidgets == null ? null : _inheritedWidgets![T];
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final InheritedElement? ancestor = _inheritedLookup?[T];
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return ancestor;
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}
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void _updateInheritance() {
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assert(_lifecycleState == _ElementLifecycle.active);
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_inheritedWidgets = _parent?._inheritedWidgets;
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_inheritedLookup = _parent?._inheritedLookup;
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}
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@override
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@ -5191,12 +5239,8 @@ class InheritedElement extends ProxyElement {
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@override
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void _updateInheritance() {
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assert(_lifecycleState == _ElementLifecycle.active);
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final Map<Type, InheritedElement>? incomingWidgets = _parent?._inheritedWidgets;
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if (incomingWidgets != null)
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_inheritedWidgets = HashMap<Type, InheritedElement>.of(incomingWidgets);
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else
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_inheritedWidgets = HashMap<Type, InheritedElement>();
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_inheritedWidgets![widget.runtimeType] = this;
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_inheritedLookup = InheritedTreeCache(_parent?._inheritedLookup)
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..[widget.runtimeType] = this;
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}
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@override
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79
packages/flutter/test/widgets/inherited_tree_cache_test.dart
Normal file
79
packages/flutter/test/widgets/inherited_tree_cache_test.dart
Normal file
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@ -0,0 +1,79 @@
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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/material.dart';
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import 'package:flutter/src/widgets/framework.dart';
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import 'package:flutter_test/flutter_test.dart';
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void main() {
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testWidgets('InheritedTreeCache returns null if element is not found', (WidgetTester tester) async {
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final InheritedTreeCache parent = InheritedTreeCache();
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expect(parent[InheritedElementA], isNull);
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});
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testWidgets('InheritedTreeCache can look up element from parent', (WidgetTester tester) async {
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final InheritedTreeCache parent = InheritedTreeCache();
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final InheritedTreeCache child = InheritedTreeCache(parent);
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final InheritedElementA elementA = InheritedElementA(const InheritedWidgetA());
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parent[InheritedElementA] = elementA;
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expect(child[InheritedElementA], elementA);
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});
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testWidgets('InheritedTreeCache can look up multiple elements from parent', (WidgetTester tester) async {
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final InheritedTreeCache parent = InheritedTreeCache();
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final InheritedTreeCache child = InheritedTreeCache(parent);
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final InheritedElementA elementA = InheritedElementA(const InheritedWidgetA());
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final InheritedElementA elementB = InheritedElementA(const InheritedWidgetB());
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parent[InheritedElementA] = elementA;
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parent[InheritedElementB] = elementB;
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expect(child[InheritedElementA], elementA);
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expect(child[InheritedElementB], elementB);
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});
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testWidgets('InheritedTreeCache does not cache nulls', (WidgetTester tester) async {
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final InheritedTreeCache parent = InheritedTreeCache();
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final InheritedTreeCache child = InheritedTreeCache(parent);
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final InheritedElementA elementA = InheritedElementA(const InheritedWidgetA());
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// First look up element that has not been cached.
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expect(child[InheritedElementA], null);
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// Then manually add element to parent.
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parent[InheritedElementA] = elementA;
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// Then the child should be able to find it.
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expect(child[InheritedElementA], elementA);
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});
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}
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class InheritedElementA extends InheritedElement {
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InheritedElementA(InheritedWidget widget) : super(widget);
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}
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class InheritedWidgetA extends InheritedWidget {
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const InheritedWidgetA({ Key? key }) : super(child: const SizedBox(), key: key);
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@override
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bool updateShouldNotify(covariant InheritedWidget oldWidget) {
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return true;
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}
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}
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class InheritedElementB extends InheritedElement {
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InheritedElementB(InheritedWidget widget) : super(widget);
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}
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class InheritedWidgetB extends InheritedWidget {
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const InheritedWidgetB({ Key? key }) : super(child: const SizedBox(), key: key);
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@override
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bool updateShouldNotify(covariant InheritedWidget oldWidget) {
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return true;
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}
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}
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