chrome-devtools-frontend/front_end/entrypoints/heap_snapshot_worker/HeapSnapshot.ts

Chrome DevTools UI

/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* eslint-disable rulesdir/prefer-private-class-members */

import * as i18n from '../../core/i18n/i18n.js';
import * as Platform from '../../core/platform/platform.js';
import * as HeapSnapshotModel from '../../models/heap_snapshot_model/heap_snapshot_model.js';

import {AllocationProfile} from './AllocationProfile.js';
import type {HeapSnapshotWorkerDispatcher} from './HeapSnapshotWorkerDispatcher.js';

export interface HeapSnapshotItem {
  itemIndex(): number;

  serialize(): Object;
}

export class HeapSnapshotEdge implements HeapSnapshotItem {
  snapshot: HeapSnapshot;
  protected readonly edges: Platform.TypedArrayUtilities.BigUint32Array;
  edgeIndex: number;
  constructor(snapshot: HeapSnapshot, edgeIndex?: number) {
    this.snapshot = snapshot;
    this.edges = snapshot.containmentEdges;
    this.edgeIndex = edgeIndex || 0;
  }

  clone(): HeapSnapshotEdge {
    return new HeapSnapshotEdge(this.snapshot, this.edgeIndex);
  }

  hasStringName(): boolean {
    throw new Error('Not implemented');
  }

  name(): string {
    throw new Error('Not implemented');
  }

  node(): HeapSnapshotNode {
    return this.snapshot.createNode(this.nodeIndex());
  }

  nodeIndex(): number {
    if (typeof this.snapshot.edgeToNodeOffset === 'undefined') {
      throw new Error('edgeToNodeOffset is undefined');
    }

    return this.edges.getValue(this.edgeIndex + this.snapshot.edgeToNodeOffset);
  }

  toString(): string {
    return 'HeapSnapshotEdge: ' + this.name();
  }

  type(): string {
    return this.snapshot.edgeTypes[this.rawType()];
  }

  itemIndex(): number {
    return this.edgeIndex;
  }

  serialize(): HeapSnapshotModel.HeapSnapshotModel.Edge {
    return new HeapSnapshotModel.HeapSnapshotModel.Edge(
        this.name(), this.node().serialize(), this.type(), this.edgeIndex);
  }

  rawType(): number {
    if (typeof this.snapshot.edgeTypeOffset === 'undefined') {
      throw new Error('edgeTypeOffset is undefined');
    }

    return this.edges.getValue(this.edgeIndex + this.snapshot.edgeTypeOffset);
  }

  isInternal(): boolean {
    throw new Error('Not implemented');
  }

  isInvisible(): boolean {
    throw new Error('Not implemented');
  }

  isWeak(): boolean {
    throw new Error('Not implemented');
  }

  getValueForSorting(_fieldName: string): number {
    throw new Error('Not implemented');
  }

  nameIndex(): number {
    throw new Error('Not implemented');
  }
}

export interface HeapSnapshotItemIterator {
  hasNext(): boolean;

  item(): HeapSnapshotItem;

  next(): void;
}

export interface HeapSnapshotItemIndexProvider {
  itemForIndex(newIndex: number): HeapSnapshotItem;
}

export class HeapSnapshotNodeIndexProvider implements HeapSnapshotItemIndexProvider {
  #node: HeapSnapshotNode;
  constructor(snapshot: HeapSnapshot) {
    this.#node = snapshot.createNode();
  }

  itemForIndex(index: number): HeapSnapshotNode {
    this.#node.nodeIndex = index;
    return this.#node;
  }
}

export class HeapSnapshotEdgeIndexProvider implements HeapSnapshotItemIndexProvider {
  #edge: JSHeapSnapshotEdge;
  constructor(snapshot: HeapSnapshot) {
    this.#edge = snapshot.createEdge(0);
  }

  itemForIndex(index: number): HeapSnapshotEdge {
    this.#edge.edgeIndex = index;
    return this.#edge;
  }
}

export class HeapSnapshotRetainerEdgeIndexProvider implements HeapSnapshotItemIndexProvider {
  readonly #retainerEdge: JSHeapSnapshotRetainerEdge;
  constructor(snapshot: HeapSnapshot) {
    this.#retainerEdge = snapshot.createRetainingEdge(0);
  }

  itemForIndex(index: number): HeapSnapshotRetainerEdge {
    this.#retainerEdge.setRetainerIndex(index);
    return this.#retainerEdge;
  }
}

export class HeapSnapshotEdgeIterator implements HeapSnapshotItemIterator {
  readonly #sourceNode: HeapSnapshotNode;
  edge: JSHeapSnapshotEdge;
  constructor(node: HeapSnapshotNode) {
    this.#sourceNode = node;
    this.edge = node.snapshot.createEdge(node.edgeIndexesStart());
  }

  hasNext(): boolean {
    return this.edge.edgeIndex < this.#sourceNode.edgeIndexesEnd();
  }

  item(): HeapSnapshotEdge {
    return this.edge;
  }

  next(): void {
    if (typeof this.edge.snapshot.edgeFieldsCount === 'undefined') {
      throw new Error('edgeFieldsCount is undefined');
    }
    this.edge.edgeIndex += this.edge.snapshot.edgeFieldsCount;
  }
}

export class HeapSnapshotRetainerEdge implements HeapSnapshotItem {
  protected snapshot: HeapSnapshot;
  #retainerIndexInternal!: number;
  #globalEdgeIndex!: number;
  #retainingNodeIndex?: number;
  #edgeInstance?: JSHeapSnapshotEdge|null;
  #nodeInstance?: HeapSnapshotNode|null;
  constructor(snapshot: HeapSnapshot, retainerIndex: number) {
    this.snapshot = snapshot;
    this.setRetainerIndex(retainerIndex);
  }

  clone(): HeapSnapshotRetainerEdge {
    return new HeapSnapshotRetainerEdge(this.snapshot, this.retainerIndex());
  }

  hasStringName(): boolean {
    return this.edge().hasStringName();
  }

  name(): string {
    return this.edge().name();
  }

  nameIndex(): number {
    return this.edge().nameIndex();
  }

  node(): HeapSnapshotNode {
    return this.nodeInternal();
  }

  nodeIndex(): number {
    if (typeof this.#retainingNodeIndex === 'undefined') {
      throw new Error('retainingNodeIndex is undefined');
    }

    return this.#retainingNodeIndex;
  }

  retainerIndex(): number {
    return this.#retainerIndexInternal;
  }

  setRetainerIndex(retainerIndex: number): void {
    if (retainerIndex === this.#retainerIndexInternal) {
      return;
    }

    if (!this.snapshot.retainingEdges || !this.snapshot.retainingNodes) {
      throw new Error('Snapshot does not contain retaining edges or retaining nodes');
    }

    this.#retainerIndexInternal = retainerIndex;
    this.#globalEdgeIndex = this.snapshot.retainingEdges[retainerIndex];
    this.#retainingNodeIndex = this.snapshot.retainingNodes[retainerIndex];
    this.#edgeInstance = null;
    this.#nodeInstance = null;
  }

  set edgeIndex(edgeIndex: number) {
    this.setRetainerIndex(edgeIndex);
  }

  private nodeInternal(): HeapSnapshotNode {
    if (!this.#nodeInstance) {
      this.#nodeInstance = this.snapshot.createNode(this.#retainingNodeIndex);
    }
    return this.#nodeInstance;
  }

  protected edge(): JSHeapSnapshotEdge {
    if (!this.#edgeInstance) {
      this.#edgeInstance = this.snapshot.createEdge(this.#globalEdgeIndex);
    }
    return this.#edgeInstance;
  }

  toString(): string {
    return this.edge().toString();
  }

  itemIndex(): number {
    return this.#retainerIndexInternal;
  }

  serialize(): HeapSnapshotModel.HeapSnapshotModel.Edge {
    const node = this.node();
    const serializedNode = node.serialize();
    serializedNode.distance = this.#distance();
    serializedNode.ignored = this.snapshot.isNodeIgnoredInRetainersView(node.nodeIndex);

    return new HeapSnapshotModel.HeapSnapshotModel.Edge(
        this.name(), serializedNode, this.type(), this.#globalEdgeIndex);
  }

  type(): string {
    return this.edge().type();
  }

  isInternal(): boolean {
    return this.edge().isInternal();
  }

  getValueForSorting(fieldName: string): number {
    if (fieldName === '!edgeDistance') {
      return this.#distance();
    }
    throw new Error('Invalid field name');
  }

  #distance(): number {
    if (this.snapshot.isEdgeIgnoredInRetainersView(this.#globalEdgeIndex)) {
      return HeapSnapshotModel.HeapSnapshotModel.baseUnreachableDistance;
    }
    return this.node().distanceForRetainersView();
  }
}

export class HeapSnapshotRetainerEdgeIterator implements HeapSnapshotItemIterator {
  readonly #retainersEnd: number;
  retainer: JSHeapSnapshotRetainerEdge;
  constructor(retainedNode: HeapSnapshotNode) {
    const snapshot = retainedNode.snapshot;
    const retainedNodeOrdinal = retainedNode.ordinal();
    if (!snapshot.firstRetainerIndex) {
      throw new Error('Snapshot does not contain firstRetainerIndex');
    }
    const retainerIndex = snapshot.firstRetainerIndex[retainedNodeOrdinal];
    this.#retainersEnd = snapshot.firstRetainerIndex[retainedNodeOrdinal + 1];
    this.retainer = snapshot.createRetainingEdge(retainerIndex);
  }

  hasNext(): boolean {
    return this.retainer.retainerIndex() < this.#retainersEnd;
  }

  item(): HeapSnapshotRetainerEdge {
    return this.retainer;
  }

  next(): void {
    this.retainer.setRetainerIndex(this.retainer.retainerIndex() + 1);
  }
}

export class HeapSnapshotNode implements HeapSnapshotItem {
  snapshot: HeapSnapshot;
  nodeIndex: number;
  constructor(snapshot: HeapSnapshot, nodeIndex?: number) {
    this.snapshot = snapshot;
    this.nodeIndex = nodeIndex || 0;
  }

  distance(): number {
    return this.snapshot.nodeDistances[this.nodeIndex / this.snapshot.nodeFieldCount];
  }

  distanceForRetainersView(): number {
    return this.snapshot.getDistanceForRetainersView(this.nodeIndex);
  }

  className(): string {
    return this.snapshot.strings[this.classIndex()];
  }

  classIndex(): number {
    return this.#detachednessAndClassIndex() >>> SHIFT_FOR_CLASS_INDEX;
  }

  // Returns a key which can uniquely describe both the class name for this node
  // and its Location, if relevant. These keys are meant to be cheap to produce,
  // so that building aggregates is fast. These keys are NOT the same as the
  // keys exposed to the frontend by functions such as aggregatesWithFilter and
  // aggregatesForDiff.
  classKeyInternal(): string|number {
    // It is common for multiple JavaScript constructors to have the same
    // name, so the class key includes the location if available for nodes of
    // type 'object'.
    //
    // JavaScript Functions (node type 'closure') also have locations, but it
    // would not be helpful to split them into categories by location because
    // many of those categories would have only one instance.
    if (this.rawType() !== this.snapshot.nodeObjectType) {
      return this.classIndex();
    }
    const location = this.snapshot.getLocation(this.nodeIndex);
    return location ? `${location.scriptId},${location.lineNumber},${location.columnNumber},${this.className()}` :
                      this.classIndex();
  }

  setClassIndex(index: number): void {
    let value = this.#detachednessAndClassIndex();
    value &= BITMASK_FOR_DOM_LINK_STATE;        // Clear previous class index.
    value |= (index << SHIFT_FOR_CLASS_INDEX);  // Set new class index.
    this.#setDetachednessAndClassIndex(value);
    if (this.classIndex() !== index) {
      throw new Error('String index overflow');
    }
  }

  dominatorIndex(): number {
    const nodeFieldCount = this.snapshot.nodeFieldCount;
    return this.snapshot.dominatorsTree[this.nodeIndex / this.snapshot.nodeFieldCount] * nodeFieldCount;
  }

  edges(): HeapSnapshotEdgeIterator {
    return new HeapSnapshotEdgeIterator(this);
  }

  edgesCount(): number {
    return (this.edgeIndexesEnd() - this.edgeIndexesStart()) / this.snapshot.edgeFieldsCount;
  }

  id(): number {
    throw new Error('Not implemented');
  }

  rawName(): string {
    return this.snapshot.strings[this.rawNameIndex()];
  }

  isRoot(): boolean {
    return this.nodeIndex === this.snapshot.rootNodeIndex;
  }

  isUserRoot(): boolean {
    throw new Error('Not implemented');
  }

  isHidden(): boolean {
    throw new Error('Not implemented');
  }

  isArray(): boolean {
    throw new Error('Not implemented');
  }

  isSynthetic(): boolean {
    throw new Error('Not implemented');
  }

  isDocumentDOMTreesRoot(): boolean {
    throw new Error('Not implemented');
  }

  name(): string {
    return this.rawName();
  }

  retainedSize(): number {
    return this.snapshot.retainedSizes[this.ordinal()];
  }

  retainers(): HeapSnapshotRetainerEdgeIterator {
    return new HeapSnapshotRetainerEdgeIterator(this);
  }

  retainersCount(): number {
    const snapshot = this.snapshot;
    const ordinal = this.ordinal();
    return snapshot.firstRetainerIndex[ordinal + 1] - snapshot.firstRetainerIndex[ordinal];
  }

  selfSize(): number {
    const snapshot = this.snapshot;
    return snapshot.nodes.getValue(this.nodeIndex + snapshot.nodeSelfSizeOffset);
  }

  type(): string {
    return this.snapshot.nodeTypes[this.rawType()];
  }

  traceNodeId(): number {
    const snapshot = this.snapshot;
    return snapshot.nodes.getValue(this.nodeIndex + snapshot.nodeTraceNodeIdOffset);
  }

  itemIndex(): number {
    return this.nodeIndex;
  }

  serialize(): HeapSnapshotModel.HeapSnapshotModel.Node {
    return new HeapSnapshotModel.HeapSnapshotModel.Node(
        this.id(), this.name(), this.distance(), this.nodeIndex, this.retainedSize(), this.selfSize(), this.type());
  }

  rawNameIndex(): number {
    const snapshot = this.snapshot;
    return snapshot.nodes.getValue(this.nodeIndex + snapshot.nodeNameOffset);
  }

  edgeIndexesStart(): number {
    return this.snapshot.firstEdgeIndexes[this.ordinal()];
  }

  edgeIndexesEnd(): number {
    return this.snapshot.firstEdgeIndexes[this.ordinal() + 1];
  }

  ordinal(): number {
    return this.nodeIndex / this.snapshot.nodeFieldCount;
  }

  nextNodeIndex(): number {
    return this.nodeIndex + this.snapshot.nodeFieldCount;
  }

  rawType(): number {
    const snapshot = this.snapshot;
    return snapshot.nodes.getValue(this.nodeIndex + snapshot.nodeTypeOffset);
  }

  isFlatConsString(): boolean {
    if (this.rawType() !== this.snapshot.nodeConsStringType) {
      return false;
    }
    for (let iter = this.edges(); iter.hasNext(); iter.next()) {
      const edge = iter.edge;
      if (!edge.isInternal()) {
        continue;
      }
      const edgeName = edge.name();
      if ((edgeName === 'first' || edgeName === 'second') && edge.node().name() === '') {
        return true;
      }
    }
    return false;
  }

  #detachednessAndClassIndex(): number {
    const {snapshot, nodeIndex} = this;
    const nodeDetachednessAndClassIndexOffset = snapshot.nodeDetachednessAndClassIndexOffset;
    return nodeDetachednessAndClassIndexOffset !== -1 ?
        snapshot.nodes.getValue(nodeIndex + nodeDetachednessAndClassIndexOffset) :
        (snapshot.detachednessAndClassIndexArray as Uint32Array)[nodeIndex / snapshot.nodeFieldCount];
  }

  #setDetachednessAndClassIndex(value: number): void {
    const {snapshot, nodeIndex} = this;
    const nodeDetachednessAndClassIndexOffset = snapshot.nodeDetachednessAndClassIndexOffset;
    if (nodeDetachednessAndClassIndexOffset !== -1) {
      snapshot.nodes.setValue(nodeIndex + nodeDetachednessAndClassIndexOffset, value);
    } else {
      (snapshot.detachednessAndClassIndexArray as Uint32Array)[nodeIndex / snapshot.nodeFieldCount] = value;
    }
  }

  detachedness(): DOMLinkState {
    return this.#detachednessAndClassIndex() & BITMASK_FOR_DOM_LINK_STATE;
  }

  setDetachedness(detachedness: DOMLinkState): void {
    let value = this.#detachednessAndClassIndex();
    value &= ~BITMASK_FOR_DOM_LINK_STATE;  // Clear the old bits.
    value |= detachedness;                 // Set the new bits.
    this.#setDetachednessAndClassIndex(value);
  }
}

export class HeapSnapshotNodeIterator implements HeapSnapshotItemIterator {
  node: HeapSnapshotNode;
  readonly #nodesLength: number;
  constructor(node: HeapSnapshotNode) {
    this.node = node;
    this.#nodesLength = node.snapshot.nodes.length;
  }

  hasNext(): boolean {
    return this.node.nodeIndex < this.#nodesLength;
  }

  item(): HeapSnapshotNode {
    return this.node;
  }

  next(): void {
    this.node.nodeIndex = this.node.nextNodeIndex();
  }
}

export class HeapSnapshotIndexRangeIterator implements HeapSnapshotItemIterator {
  readonly #itemProvider: HeapSnapshotItemIndexProvider;
  readonly #indexes: number[]|Uint32Array;
  #position: number;
  constructor(itemProvider: HeapSnapshotItemIndexProvider, indexes: number[]|Uint32Array) {
    this.#itemProvider = itemProvider;
    this.#indexes = indexes;
    this.#position = 0;
  }

  hasNext(): boolean {
    return this.#position < this.#indexes.length;
  }

  item(): HeapSnapshotItem {
    const index = this.#indexes[this.#position];
    return this.#itemProvider.itemForIndex(index);
  }

  next(): void {
    ++this.#position;
  }
}

export class HeapSnapshotFilteredIterator implements HeapSnapshotItemIterator {
  #iterator: HeapSnapshotItemIterator;
  #filter: ((arg0: HeapSnapshotItem) => boolean)|undefined;
  constructor(iterator: HeapSnapshotItemIterator, filter?: ((arg0: HeapSnapshotItem) => boolean)) {
    this.#iterator = iterator;
    this.#filter = filter;
    this.skipFilteredItems();
  }

  hasNext(): boolean {
    return this.#iterator.hasNext();
  }

  item(): HeapSnapshotItem {
    return this.#iterator.item();
  }

  next(): void {
    this.#iterator.next();
    this.skipFilteredItems();
  }

  private skipFilteredItems(): void {
    while (this.#iterator.hasNext() && this.#filter && !this.#filter(this.#iterator.item())) {
      this.#iterator.next();
    }
  }
}

export class HeapSnapshotProgress {
  readonly #dispatcher: HeapSnapshotWorkerDispatcher|undefined;
  constructor(dispatcher?: HeapSnapshotWorkerDispatcher) {
    this.#dispatcher = dispatcher;
  }

  updateStatus(status: string): void {
    this.sendUpdateEvent(i18n.i18n.serializeUIString(status));
  }

  updateProgress(title: string, value: number, total: number): void {
    const percentValue = ((total ? (value / total) : 0) * 100).toFixed(0);
    this.sendUpdateEvent(i18n.i18n.serializeUIString(title, {PH1: percentValue}));
  }

  reportProblem(error: string): void {
    // May be undefined in tests.
    if (this.#dispatcher) {
      this.#dispatcher.sendEvent(HeapSnapshotModel.HeapSnapshotModel.HeapSnapshotProgressEvent.BrokenSnapshot, error);
    }
  }

  private sendUpdateEvent(serializedText: string): void {
    // May be undefined in tests.
    if (this.#dispatcher) {
      this.#dispatcher.sendEvent(HeapSnapshotModel.HeapSnapshotModel.HeapSnapshotProgressEvent.Update, serializedText);
    }
  }
}

// An "interface" to be used when classifying plain JS objects in the snapshot.
// An object matches the interface if it contains every listed property (even
// if it also contains extra properties).
interface InterfaceDefinition {
  name: string;
  properties: string[];
}

export class HeapSnapshotProblemReport {
  readonly #errors: string[];
  constructor(title: string) {
    this.#errors = [title];
  }

  addError(error: string): void {
    if (this.#errors.length > 100) {
      return;
    }
    this.#errors.push(error);
  }

  toString(): string {
    return this.#errors.join('\n  ');
  }
}
export interface Profile {
  /* eslint-disable @typescript-eslint/naming-convention */
  root_index: number;
  nodes: Platform.TypedArrayUtilities.BigUint32Array;
  edges: Platform.TypedArrayUtilities.BigUint32Array;
  snapshot: HeapSnapshotHeader;
  samples: number[];
  strings: string[];
  locations: number[];
  trace_function_infos: Uint32Array;
  trace_tree: Object;
  /* eslint-enable @typescript-eslint/naming-convention */
}

export interface LiveObjects {
  [x: number]: {count: number, size: number, ids: number[]};
}

/**
 * DOM node link state.
 */
const enum DOMLinkState {
  UNKNOWN = 0,
  ATTACHED = 1,
  DETACHED = 2,
}
const BITMASK_FOR_DOM_LINK_STATE = 3;

// The class index is stored in the upper 30 bits of the detachedness field.
const SHIFT_FOR_CLASS_INDEX = 2;

// After this many properties, inferInterfaceDefinitions can stop adding more
// properties to an interface definition if the name is getting too long.
const MIN_INTERFACE_PROPERTY_COUNT = 1;

// The maximum length of an interface name produced by inferInterfaceDefinitions.
// This limit can be exceeded if the first MIN_INTERFACE_PROPERTY_COUNT property
// names are long.
const MAX_INTERFACE_NAME_LENGTH = 120;

// Each interface definition produced by inferInterfaceDefinitions will match at
// least this many objects. There's no point in defining interfaces which match
// only a single object.
const MIN_OBJECT_COUNT_PER_INTERFACE = 2;

// Each interface definition produced by inferInterfaceDefinitions should
// match at least 1 out of 1000 Objects in the heap. Otherwise, we end up with a
// long tail of unpopular interfaces that don't help analysis.
const MIN_OBJECT_PROPORTION_PER_INTERFACE = 1000;

export abstract class HeapSnapshot {
  nodes: Platform.TypedArrayUtilities.BigUint32Array;
  containmentEdges: Platform.TypedArrayUtilities.BigUint32Array;
  readonly #metaNode: HeapSnapshotMetaInfo;
  readonly #rawSamples: number[];
  #samples: HeapSnapshotModel.HeapSnapshotModel.Samples|null;
  strings: string[];
  readonly #locations: number[];
  readonly #progress: HeapSnapshotProgress;
  readonly #noDistance: number;
  rootNodeIndexInternal: number;
  #snapshotDiffs: {
    [x: string]: {
      [x: string]: HeapSnapshotModel.HeapSnapshotModel.Diff,
    },
  };
  #aggregatesForDiffInternal?: {
    interfaceDefinitions: string,
    aggregates: {
      [x: string]: HeapSnapshotModel.HeapSnapshotModel.AggregateForDiff,
    },
  };
  #aggregates: {
    [x: string]: {
      [x: string]: AggregatedInfo,
    },
  };
  #aggregatesSortedFlags: {
    [x: string]: boolean,
  };
  profile: Profile;
  nodeTypeOffset!: number;
  nodeNameOffset!: number;
  nodeIdOffset!: number;
  nodeSelfSizeOffset!: number;
  #nodeEdgeCountOffset!: number;
  nodeTraceNodeIdOffset!: number;
  nodeFieldCount!: number;
  nodeTypes!: string[];
  nodeArrayType!: number;
  nodeHiddenType!: number;
  nodeObjectType!: number;
  nodeNativeType!: number;
  nodeStringType!: number;
  nodeConsStringType!: number;
  nodeSlicedStringType!: number;
  nodeCodeType!: number;
  nodeSyntheticType!: number;
  nodeClosureType!: number;
  nodeRegExpType!: number;
  edgeFieldsCount!: number;
  edgeTypeOffset!: number;
  edgeNameOffset!: number;
  edgeToNodeOffset!: number;
  edgeTypes!: string[];
  edgeElementType!: number;
  edgeHiddenType!: number;
  edgeInternalType!: number;
  edgeShortcutType!: number;
  edgeWeakType!: number;
  edgeInvisibleType!: number;
  edgePropertyType!: number;
  #locationIndexOffset!: number;
  #locationScriptIdOffset!: number;
  #locationLineOffset!: number;
  #locationColumnOffset!: number;
  #locationFieldCount!: number;
  nodeCount!: number;
  #edgeCount!: number;
  retainedSizes!: Float64Array;
  firstEdgeIndexes!: Uint32Array;
  retainingNodes!: Uint32Array;
  retainingEdges!: Uint32Array;
  firstRetainerIndex!: Uint32Array;
  nodeDistances!: Int32Array;
  firstDominatedNodeIndex!: Uint32Array;
  dominatedNodes!: Uint32Array;
  dominatorsTree!: Uint32Array;
  #allocationProfile!: AllocationProfile;
  nodeDetachednessAndClassIndexOffset!: number;
  #locationMap!: Map<number, HeapSnapshotModel.HeapSnapshotModel.Location>;
  #ignoredNodesInRetainersView: Set<number>;
  #ignoredEdgesInRetainersView: Set<number>;
  #nodeDistancesForRetainersView: Int32Array|undefined;
  #edgeNamesThatAreNotWeakMaps: Platform.TypedArrayUtilities.BitVector;
  detachednessAndClassIndexArray?: Uint32Array;
  #essentialEdges?: Platform.TypedArrayUtilities.BitVector;
  #interfaceNames: Map<string, number>;
  #interfaceDefinitions?: InterfaceDefinition[];

  constructor(profile: Profile, progress: HeapSnapshotProgress) {
    this.nodes = profile.nodes;
    this.containmentEdges = profile.edges;
    this.#metaNode = profile.snapshot.meta;
    this.#rawSamples = profile.samples;
    this.#samples = null;
    this.strings = profile.strings;
    this.#locations = profile.locations;
    this.#progress = progress;

    this.#noDistance = -5;
    this.rootNodeIndexInternal = 0;
    if (profile.snapshot.root_index) {
      this.rootNodeIndexInternal = profile.snapshot.root_index;
    }

    this.#snapshotDiffs = {};

    this.#aggregates = {};

    this.#aggregatesSortedFlags = {};
    this.profile = profile;
    this.#ignoredNodesInRetainersView = new Set();
    this.#ignoredEdgesInRetainersView = new Set();
    this.#edgeNamesThatAreNotWeakMaps = Platform.TypedArrayUtilities.createBitVector(this.strings.length);
    this.#interfaceNames = new Map();
  }

  initialize(): void {
    const meta = this.#metaNode;

    this.nodeTypeOffset = meta.node_fields.indexOf('type');
    this.nodeNameOffset = meta.node_fields.indexOf('name');
    this.nodeIdOffset = meta.node_fields.indexOf('id');
    this.nodeSelfSizeOffset = meta.node_fields.indexOf('self_size');
    this.#nodeEdgeCountOffset = meta.node_fields.indexOf('edge_count');
    this.nodeTraceNodeIdOffset = meta.node_fields.indexOf('trace_node_id');
    this.nodeDetachednessAndClassIndexOffset = meta.node_fields.indexOf('detachedness');
    this.nodeFieldCount = meta.node_fields.length;

    this.nodeTypes = meta.node_types[this.nodeTypeOffset];
    this.nodeArrayType = this.nodeTypes.indexOf('array');
    this.nodeHiddenType = this.nodeTypes.indexOf('hidden');
    this.nodeObjectType = this.nodeTypes.indexOf('object');
    this.nodeNativeType = this.nodeTypes.indexOf('native');
    this.nodeStringType = this.nodeTypes.indexOf('string');
    this.nodeConsStringType = this.nodeTypes.indexOf('concatenated string');
    this.nodeSlicedStringType = this.nodeTypes.indexOf('sliced string');
    this.nodeCodeType = this.nodeTypes.indexOf('code');
    this.nodeSyntheticType = this.nodeTypes.indexOf('synthetic');
    this.nodeClosureType = this.nodeTypes.indexOf('closure');
    this.nodeRegExpType = this.nodeTypes.indexOf('regexp');

    this.edgeFieldsCount = meta.edge_fields.length;
    this.edgeTypeOffset = meta.edge_fields.indexOf('type');
    this.edgeNameOffset = meta.edge_fields.indexOf('name_or_index');
    this.edgeToNodeOffset = meta.edge_fields.indexOf('to_node');

    this.edgeTypes = meta.edge_types[this.edgeTypeOffset];
    this.edgeTypes.push('invisible');
    this.edgeElementType = this.edgeTypes.indexOf('element');
    this.edgeHiddenType = this.edgeTypes.indexOf('hidden');
    this.edgeInternalType = this.edgeTypes.indexOf('internal');
    this.edgeShortcutType = this.edgeTypes.indexOf('shortcut');
    this.edgeWeakType = this.edgeTypes.indexOf('weak');
    this.edgeInvisibleType = this.edgeTypes.indexOf('invisible');
    this.edgePropertyType = this.edgeTypes.indexOf('property');

    const locationFields = meta.location_fields || [];

    this.#locationIndexOffset = locationFields.indexOf('object_index');
    this.#locationScriptIdOffset = locationFields.indexOf('script_id');
    this.#locationLineOffset = locationFields.indexOf('line');
    this.#locationColumnOffset = locationFields.indexOf('column');
    this.#locationFieldCount = locationFields.length;

    this.nodeCount = this.nodes.length / this.nodeFieldCount;
    this.#edgeCount = this.containmentEdges.length / this.edgeFieldsCount;

    this.retainedSizes = new Float64Array(this.nodeCount);
    this.firstEdgeIndexes = new Uint32Array(this.nodeCount + 1);
    this.retainingNodes = new Uint32Array(this.#edgeCount);
    this.retainingEdges = new Uint32Array(this.#edgeCount);
    this.firstRetainerIndex = new Uint32Array(this.nodeCount + 1);
    this.nodeDistances = new Int32Array(this.nodeCount);

    this.#progress.updateStatus('Building edge indexes…');
    this.buildEdgeIndexes();
    this.#progress.updateStatus('Building retainers…');
    this.buildRetainers();
    this.#progress.updateStatus('Propagating DOM state…');
    this.propagateDOMState();
    this.#progress.updateStatus('Calculating node flags…');
    this.calculateFlags();
    this.#progress.updateStatus('Calculating distances…');
    this.calculateDistances(/* isForRetainersView=*/ false);
    this.#progress.updateStatus('Calculating shallow sizes…');
    this.calculateShallowSizes();
    this.#progress.updateStatus('Calculating retained sizes…');
    this.buildDominatorTreeAndCalculateRetainedSizes();
    this.#progress.updateStatus('Building dominated nodes…');
    this.firstDominatedNodeIndex = new Uint32Array(this.nodeCount + 1);
    this.dominatedNodes = new Uint32Array(this.nodeCount - 1);
    this.buildDominatedNodes();
    this.#progress.updateStatus('Calculating object names…');
    this.calculateObjectNames();
    this.applyInterfaceDefinitions(this.inferInterfaceDefinitions());
    this.#progress.updateStatus('Calculating statistics…');
    this.calculateStatistics();
    this.#progress.updateStatus('Calculating samples…');
    this.buildSamples();
    this.#progress.updateStatus('Building locations…');
    this.buildLocationMap();
    this.#progress.updateStatus('Finished processing.');

    if (this.profile.snapshot.trace_function_count) {
      this.#progress.updateStatus('Building allocation statistics…');
      const nodes = this.nodes;
      const nodesLength = nodes.length;
      const nodeFieldCount = this.nodeFieldCount;
      const node = this.rootNode();
      const liveObjects: LiveObjects = {};
      for (let nodeIndex = 0; nodeIndex < nodesLength; nodeIndex += nodeFieldCount) {
        node.nodeIndex = nodeIndex;
        const traceNodeId = node.traceNodeId();
        let stats: {
          count: number,
          size: number,
          ids: number[],
        } = liveObjects[traceNodeId];
        if (!stats) {
          liveObjects[traceNodeId] = stats = {count: 0, size: 0, ids: []};
        }
        stats.count++;
        stats.size += node.selfSize();
        stats.ids.push(node.id());
      }
      this.#allocationProfile = new AllocationProfile(this.profile, liveObjects);
      this.#progress.updateStatus('done');
    }
  }

  private buildEdgeIndexes(): void {
    const nodes = this.nodes;
    const nodeCount = this.nodeCount;
    const firstEdgeIndexes = this.firstEdgeIndexes;
    const nodeFieldCount = this.nodeFieldCount;
    const edgeFieldsCount = this.edgeFieldsCount;
    const nodeEdgeCountOffset = this.#nodeEdgeCountOffset;
    firstEdgeIndexes[nodeCount] = this.containmentEdges.length;
    for (let nodeOrdinal = 0, edgeIndex = 0; nodeOrdinal < nodeCount; ++nodeOrdinal) {
      firstEdgeIndexes[nodeOrdinal] = edgeIndex;
      edgeIndex += nodes.getValue(nodeOrdinal * nodeFieldCount + nodeEdgeCountOffset) * edgeFieldsCount;
    }
  }

  private buildRetainers(): void {
    const retainingNodes = this.retainingNodes;
    const retainingEdges = this.retainingEdges;
    // Index of the first retainer in the retainingNodes and retainingEdges
    // arrays. Addressed by retained node index.
    const firstRetainerIndex = this.firstRetainerIndex;

    const containmentEdges = this.containmentEdges;
    const edgeFieldsCount = this.edgeFieldsCount;
    const nodeFieldCount = this.nodeFieldCount;
    const edgeToNodeOffset = this.edgeToNodeOffset;
    const firstEdgeIndexes = this.firstEdgeIndexes;
    const nodeCount = this.nodeCount;

    for (let toNodeFieldIndex = edgeToNodeOffset, l = containmentEdges.length; toNodeFieldIndex < l;
         toNodeFieldIndex += edgeFieldsCount) {
      const toNodeIndex = containmentEdges.getValue(toNodeFieldIndex);
      if (toNodeIndex % nodeFieldCount) {
        throw new Error('Invalid toNodeIndex ' + toNodeIndex);
      }
      ++firstRetainerIndex[toNodeIndex / nodeFieldCount];
    }
    for (let i = 0, firstUnusedRetainerSlot = 0; i < nodeCount; i++) {
      const retainersCount = firstRetainerIndex[i];
      firstRetainerIndex[i] = firstUnusedRetainerSlot;
      retainingNodes[firstUnusedRetainerSlot] = retainersCount;
      firstUnusedRetainerSlot += retainersCount;
    }
    firstRetainerIndex[nodeCount] = retainingNodes.length;

    let nextNodeFirstEdgeIndex: number = firstEdgeIndexes[0];
    for (let srcNodeOrdinal = 0; srcNodeOrdinal < nodeCount; ++srcNodeOrdinal) {
      const firstEdgeIndex = nextNodeFirstEdgeIndex;
      nextNodeFirstEdgeIndex = firstEdgeIndexes[srcNodeOrdinal + 1];
      const srcNodeIndex = srcNodeOrdinal * nodeFieldCount;
      for (let edgeIndex = firstEdgeIndex; edgeIndex < nextNodeFirstEdgeIndex; edgeIndex += edgeFieldsCount) {
        const toNodeIndex = containmentEdges.getValue(edgeIndex + edgeToNodeOffset);
        if (toNodeIndex % nodeFieldCount) {
          throw new Error('Invalid toNodeIndex ' + toNodeIndex);
        }
        const firstRetainerSlotIndex = firstRetainerIndex[toNodeIndex / nodeFieldCount];
        const nextUnusedRetainerSlotIndex = firstRetainerSlotIndex + (--retainingNodes[firstRetainerSlotIndex]);
        retainingNodes[nextUnusedRetainerSlotIndex] = srcNodeIndex;
        retainingEdges[nextUnusedRetainerSlotIndex] = edgeIndex;
      }
    }
  }

  abstract createNode(_nodeIndex?: number): HeapSnapshotNode;
  abstract createEdge(_edgeIndex: number): JSHeapSnapshotEdge;
  abstract createRetainingEdge(_retainerIndex: number): JSHeapSnapshotRetainerEdge;

  private allNodes(): HeapSnapshotNodeIterator {
    return new HeapSnapshotNodeIterator(this.rootNode());
  }

  rootNode(): HeapSnapshotNode {
    return this.createNode(this.rootNodeIndexInternal);
  }

  get rootNodeIndex(): number {
    return this.rootNodeIndexInternal;
  }

  get totalSize(): number {
    return this.rootNode().retainedSize() + (this.profile.snapshot.extra_native_bytes ?? 0);
  }

  private getDominatedIndex(nodeIndex: number): number {
    if (nodeIndex % this.nodeFieldCount) {
      throw new Error('Invalid nodeIndex: ' + nodeIndex);
    }
    return this.firstDominatedNodeIndex[nodeIndex / this.nodeFieldCount];
  }

  private createFilter(nodeFilter: HeapSnapshotModel.HeapSnapshotModel.NodeFilter):
      ((arg0: HeapSnapshotNode) => boolean)|undefined {
    const {minNodeId, maxNodeId, allocationNodeId, filterName} = nodeFilter;
    let filter;
    if (typeof allocationNodeId === 'number') {
      filter = this.createAllocationStackFilter(allocationNodeId);
      if (!filter) {
        throw new Error('Unable to create filter');
      }
      // @ts-ignore key can be added as a static property
      filter.key = 'AllocationNodeId: ' + allocationNodeId;
    } else if (typeof minNodeId === 'number' && typeof maxNodeId === 'number') {
      filter = this.createNodeIdFilter(minNodeId, maxNodeId);
      // @ts-ignore key can be added as a static property
      filter.key = 'NodeIdRange: ' + minNodeId + '..' + maxNodeId;
    } else if (filterName !== undefined) {
      filter = this.createNamedFilter(filterName);
      // @ts-ignore key can be added as a static property
      filter.key = 'NamedFilter: ' + filterName;
    }
    return filter;
  }

  search(
      searchConfig: HeapSnapshotModel.HeapSnapshotModel.SearchConfig,
      nodeFilter: HeapSnapshotModel.HeapSnapshotModel.NodeFilter): number[] {
    const query = searchConfig.query;

    function filterString(matchedStringIndexes: Set<number>, string: string, index: number): Set<number> {
      if (string.indexOf(query) !== -1) {
        matchedStringIndexes.add(index);
      }
      return matchedStringIndexes;
    }

    const regexp =
        searchConfig.isRegex ? new RegExp(query) : Platform.StringUtilities.createPlainTextSearchRegex(query, 'i');

    function filterRegexp(matchedStringIndexes: Set<number>, string: string, index: number): Set<number> {
      if (regexp.test(string)) {
        matchedStringIndexes.add(index);
      }
      return matchedStringIndexes;
    }

    const useRegExp = searchConfig.isRegex || !searchConfig.caseSensitive;
    const stringFilter = useRegExp ? filterRegexp : filterString;
    const stringIndexes = this.strings.reduce(stringFilter, new Set());

    const filter = this.createFilter(nodeFilter);
    const nodeIds = [];
    const nodesLength = this.nodes.length;
    const nodes = this.nodes;
    const nodeNameOffset = this.nodeNameOffset;
    const nodeIdOffset = this.nodeIdOffset;
    const nodeFieldCount = this.nodeFieldCount;
    const node = this.rootNode();

    for (let nodeIndex = 0; nodeIndex < nodesLength; nodeIndex += nodeFieldCount) {
      node.nodeIndex = nodeIndex;
      if (filter && !filter(node)) {
        continue;
      }
      if (node.selfSize() === 0) {
        // Nodes with size zero are omitted in the data grid, so avoid returning
        // search results that can't be navigated to.
        continue;
      }
      const name = node.name();
      if (name === node.rawName()) {
        // If the string displayed to the user matches the raw name from the
        // snapshot, then we can use the Set computed above. This avoids
        // repeated work when multiple nodes have the same name.
        if (stringIndexes.has(nodes.getValue(nodeIndex + nodeNameOffset))) {
          nodeIds.push(nodes.getValue(nodeIndex + nodeIdOffset));
        }
      } else {
        // If the node is displaying a customized name, then we must perform the
        // full string search within that name here.
        if (useRegExp ? regexp.test(name) : (name.indexOf(query) !== -1)) {
          nodeIds.push(nodes.getValue(nodeIndex + nodeIdOffset));
        }
      }
    }
    return nodeIds;
  }

  aggregatesWithFilter(nodeFilter: HeapSnapshotModel.HeapSnapshotModel.NodeFilter):
      {[x: string]: HeapSnapshotModel.HeapSnapshotModel.Aggregate} {
    const filter = this.createFilter(nodeFilter);
    // @ts-ignore key is added in createFilter
    const key = filter ? filter.key : 'allObjects';
    return this.getAggregatesByClassKey(false, key, filter);
  }

  private createNodeIdFilter(minNodeId: number, maxNodeId: number): (arg0: HeapSnapshotNode) => boolean {
    function nodeIdFilter(node: HeapSnapshotNode): boolean {
      const id = node.id();
      return id > minNodeId && id <= maxNodeId;
    }
    return nodeIdFilter;
  }

  private createAllocationStackFilter(bottomUpAllocationNodeId: number):
      ((arg0: HeapSnapshotNode) => boolean)|undefined {
    if (!this.#allocationProfile) {
      throw new Error('No Allocation Profile provided');
    }

    const traceIds = this.#allocationProfile.traceIds(bottomUpAllocationNodeId);
    if (!traceIds.length) {
      return undefined;
    }

    const set: {[x: number]: boolean} = {};
    for (let i = 0; i < traceIds.length; i++) {
      set[traceIds[i]] = true;
    }
    function traceIdFilter(node: HeapSnapshotNode): boolean {
      return Boolean(set[node.traceNodeId()]);
    }
    return traceIdFilter;
  }

  private createNamedFilter(filterName: string): (node: HeapSnapshotNode) => boolean {
    // Allocate an array with a single bit per node, which can be used by each
    // specific filter implemented below.
    const bitmap = Platform.TypedArrayUtilities.createBitVector(this.nodeCount);
    const getBit = (node: HeapSnapshotNode): boolean => {
      const ordinal = node.nodeIndex / this.nodeFieldCount;
      return bitmap.getBit(ordinal);
    };

    // Traverses the graph in breadth-first order with the given filter, and
    // sets the bit in `bitmap` for every visited node.
    const traverse = (filter: (node: HeapSnapshotNode, edge: HeapSnapshotEdge) => boolean): void => {
      const distances = new Int32Array(this.nodeCount);
      for (let i = 0; i < this.nodeCount; ++i) {
        distances[i] = this.#noDistance;
      }
      const nodesToVisit = new Uint32Array(this.nodeCount);
      distances[this.rootNode().ordinal()] = 0;
      nodesToVisit[0] = this.rootNode().nodeIndex;
      const nodesToVisitLength = 1;
      this.bfs(nodesToVisit, nodesToVisitLength, distances, filter);
      for (let i = 0; i < this.nodeCount; ++i) {
        if (distances[i] !== this.#noDistance) {
          bitmap.setBit(i);
        }
      }
    };

    const markUnreachableNodes = (): void => {
      for (let i = 0; i < this.nodeCount; ++i) {
        if (this.nodeDistances[i] === this.#noDistance) {
          bitmap.setBit(i);
        }
      }
    };

    switch (filterName) {
      case 'objectsRetainedByDetachedDomNodes':
        // Traverse the graph, avoiding detached nodes.
        traverse((node: HeapSnapshotNode, edge: HeapSnapshotEdge) => {
          return edge.node().detachedness() !== DOMLinkState.DETACHED;
        });
        markUnreachableNodes();
        return (node: HeapSnapshotNode) => !getBit(node);
      case 'objectsRetainedByConsole':
        // Traverse the graph, avoiding edges that represent globals owned by
        // the DevTools console.
        traverse((node: HeapSnapshotNode, edge: HeapSnapshotEdge) => {
          return !(node.isSynthetic() && edge.hasStringName() && edge.name().endsWith(' / DevTools console'));
        });
        markUnreachableNodes();
        return (node: HeapSnapshotNode) => !getBit(node);
      case 'duplicatedStrings': {
        const stringToNodeIndexMap = new Map<string, number>();
        const node = this.createNode(0);
        for (let i = 0; i < this.nodeCount; ++i) {
          node.nodeIndex = i * this.nodeFieldCount;
          const rawType = node.rawType();
          if (rawType === this.nodeStringType || rawType === this.nodeConsStringType) {
            // Check whether the cons string is already "flattened", meaning
            // that one of its two parts is the empty string. If so, we should
            // skip it. We don't help anyone by reporting a flattened cons
            // string as a duplicate with its own content, since V8 controls
            // that behavior internally.
            if (node.isFlatConsString()) {
              continue;
            }
            const name = node.name();
            const alreadyVisitedNodeIndex = stringToNodeIndexMap.get(name);
            if (alreadyVisitedNodeIndex === undefined) {
              stringToNodeIndexMap.set(name, node.nodeIndex);
            } else {
              bitmap.setBit(alreadyVisitedNodeIndex / this.nodeFieldCount);
              bitmap.setBit(node.nodeIndex / this.nodeFieldCount);
            }
          }
        }
        return getBit;
      }
    }
    throw new Error('Invalid filter name');
  }

  getAggregatesByClassKey(sortedIndexes: boolean, key?: string, filter?: ((arg0: HeapSnapshotNode) => boolean)):
      {[x: string]: HeapSnapshotModel.HeapSnapshotModel.Aggregate} {
    let aggregates: {[x: string]: HeapSnapshotModel.HeapSnapshotModel.Aggregate};
    if (key && this.#aggregates[key]) {
      aggregates = this.#aggregates[key];
    } else {
      const aggregatesMap = this.buildAggregates(filter);
      this.calculateClassesRetainedSize(aggregatesMap, filter);

      // In the two previous steps, we used class keys that were simple and
      // could be produced quickly. For many objects, this meant using the index
      // of the string containing its class name. However, string indices are
      // not consistent across snapshots, and this aggregate data might end up
      // being used in a comparison, so here we convert to a more durable format
      // for class keys.
      aggregates = Object.create(null);
      for (const [classKey, aggregate] of aggregatesMap.entries()) {
        const newKey = this.classKeyFromClassKeyInternal(classKey);
        aggregates[newKey] = aggregate;
      }
      if (key) {
        this.#aggregates[key] = aggregates;
      }
    }

    if (sortedIndexes && (!key || !this.#aggregatesSortedFlags[key])) {
      this.sortAggregateIndexes(aggregates);
      if (key) {
        this.#aggregatesSortedFlags[key] = sortedIndexes;
      }
    }

    return aggregates as {
      [x: string]: HeapSnapshotModel.HeapSnapshotModel.Aggregate,
    };
  }

  allocationTracesTops(): HeapSnapshotModel.HeapSnapshotModel.SerializedAllocationNode[] {
    return this.#allocationProfile.serializeTraceTops();
  }

  allocationNodeCallers(nodeId: number): HeapSnapshotModel.HeapSnapshotModel.AllocationNodeCallers {
    return this.#allocationProfile.serializeCallers(nodeId);
  }

  allocationStack(nodeIndex: number): HeapSnapshotModel.HeapSnapshotModel.AllocationStackFrame[]|null {
    const node = this.createNode(nodeIndex);
    const allocationNodeId = node.traceNodeId();
    if (!allocationNodeId) {
      return null;
    }
    return this.#allocationProfile.serializeAllocationStack(allocationNodeId);
  }

  aggregatesForDiff(interfaceDefinitions: string): {[x: string]: HeapSnapshotModel.HeapSnapshotModel.AggregateForDiff} {
    if (this.#aggregatesForDiffInternal?.interfaceDefinitions === interfaceDefinitions) {
      return this.#aggregatesForDiffInternal.aggregates;
    }

    // Temporarily apply the interface definitions from the other snapshot.
    const originalInterfaceDefinitions = this.#interfaceDefinitions;
    this.applyInterfaceDefinitions(JSON.parse(interfaceDefinitions) as InterfaceDefinition[]);
    const aggregates = this.getAggregatesByClassKey(true, 'allObjects');
    this.applyInterfaceDefinitions(originalInterfaceDefinitions ?? []);
    const result: {[x: string]: HeapSnapshotModel.HeapSnapshotModel.AggregateForDiff} = {};

    const node = this.createNode();
    for (const classKey in aggregates) {
      const aggregate = aggregates[classKey];
      const indexes = aggregate.idxs;
      const ids = new Array(indexes.length);
      const selfSizes = new Array(indexes.length);
      for (let i = 0; i < indexes.length; i++) {
        node.nodeIndex = indexes[i];
        ids[i] = node.id();
        selfSizes[i] = node.selfSize();
      }

      result[classKey] = {name: node.className(), indexes, ids, selfSizes};
    }

    this.#aggregatesForDiffInternal = {interfaceDefinitions, aggregates: result};
    return result;
  }

  isUserRoot(_node: HeapSnapshotNode): boolean {
    return true;
  }

  calculateShallowSizes(): void {
  }

  calculateDistances(
      isForRetainersView: boolean, filter?: ((arg0: HeapSnapshotNode, arg1: HeapSnapshotEdge) => boolean)): void {
    const nodeCount = this.nodeCount;

    if (isForRetainersView) {
      const originalFilter = filter;
      filter = (node: HeapSnapshotNode, edge: HeapSnapshotEdge) => {
        return !this.#ignoredNodesInRetainersView.has(edge.nodeIndex()) &&
            (!originalFilter || originalFilter(node, edge));
      };
      if (this.#nodeDistancesForRetainersView === undefined) {
        this.#nodeDistancesForRetainersView = new Int32Array(nodeCount);
      }
    }

    const distances = isForRetainersView ? (this.#nodeDistancesForRetainersView as Int32Array) : this.nodeDistances;
    const noDistance = this.#noDistance;
    for (let i = 0; i < nodeCount; ++i) {
      distances[i] = noDistance;
    }

    const nodesToVisit = new Uint32Array(this.nodeCount);
    let nodesToVisitLength = 0;

    // BFS for user root objects.
    for (let iter = this.rootNode().edges(); iter.hasNext(); iter.next()) {
      const node = iter.edge.node();
      if (this.isUserRoot(node)) {
        distances[node.ordinal()] = 1;
        nodesToVisit[nodesToVisitLength++] = node.nodeIndex;
      }
    }
    this.bfs(nodesToVisit, nodesToVisitLength, distances, filter);

    // BFS for objects not reached from user roots.
    distances[this.rootNode().ordinal()] =
        nodesToVisitLength > 0 ? HeapSnapshotModel.HeapSnapshotModel.baseSystemDistance : 0;
    nodesToVisit[0] = this.rootNode().nodeIndex;
    nodesToVisitLength = 1;
    this.bfs(nodesToVisit, nodesToVisitLength, distances, filter);
  }

  private bfs(
      nodesToVisit: Uint32Array, nodesToVisitLength: number, distances: Int32Array,
      filter?: ((arg0: HeapSnapshotNode, arg1: HeapSnapshotEdge) => boolean)): void {
    // Preload fields into local variables for better performance.
    const edgeFieldsCount = this.edgeFieldsCount;
    const nodeFieldCount = this.nodeFieldCount;
    const containmentEdges = this.containmentEdges;
    const firstEdgeIndexes = this.firstEdgeIndexes;
    const edgeToNodeOffset = this.edgeToNodeOffset;
    const edgeTypeOffset = this.edgeTypeOffset;
    const nodeCount = this.nodeCount;
    const edgeWeakType = this.edgeWeakType;
    const noDistance = this.#noDistance;

    let index = 0;
    const edge = this.createEdge(0);
    const node = this.createNode(0);
    while (index < nodesToVisitLength) {
      const nodeIndex = nodesToVisit[index++];  // shift generates too much garbage.
      const nodeOrdinal = nodeIndex / nodeFieldCount;
      const distance = distances[nodeOrdinal] + 1;
      const firstEdgeIndex = firstEdgeIndexes[nodeOrdinal];
      const edgesEnd = firstEdgeIndexes[nodeOrdinal + 1];
      node.nodeIndex = nodeIndex;
      for (let edgeIndex = firstEdgeIndex; edgeIndex < edgesEnd; edgeIndex += edgeFieldsCount) {
        const edgeType = containmentEdges.getValue(edgeIndex + edgeTypeOffset);
        if (edgeType === edgeWeakType) {
          continue;
        }
        const childNodeIndex = containmentEdges.getValue(edgeI