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derived.ts
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derived.ts
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/*---------------------------------------------------------------------------------------------
* Copyright (c) Microsoft Corporation. All rights reserved.
* Licensed under the MIT License. See License.txt in the project root for license information.
*--------------------------------------------------------------------------------------------*/
import { assertFn } from 'vs/base/common/assert';
import { strictEquals, EqualityComparer } from 'vs/base/common/equals';
import { DisposableStore, IDisposable } from 'vs/base/common/lifecycle';
import { BaseObservable, IChangeContext, IObservable, IObserver, IReader, _setDerivedOpts, } from 'vs/base/common/observableInternal/base';
import { DebugNameData, IDebugNameData, Owner } from 'vs/base/common/observableInternal/debugName';
import { getLogger } from 'vs/base/common/observableInternal/logging';
/**
* Creates an observable that is derived from other observables.
* The value is only recomputed when absolutely needed.
*
* {@link computeFn} should start with a JS Doc using `@description` to name the derived.
*/
export function derived<T>(computeFn: (reader: IReader) => T): IObservable<T>;
export function derived<T>(owner: Owner, computeFn: (reader: IReader) => T): IObservable<T>;
export function derived<T>(computeFnOrOwner: ((reader: IReader) => T) | Owner, computeFn?: ((reader: IReader) => T) | undefined): IObservable<T> {
if (computeFn !== undefined) {
return new Derived(
new DebugNameData(computeFnOrOwner, undefined, computeFn),
computeFn,
undefined,
undefined,
undefined,
strictEquals
);
}
return new Derived(
new DebugNameData(undefined, undefined, computeFnOrOwner as any),
computeFnOrOwner as any,
undefined,
undefined,
undefined,
strictEquals
);
}
export function derivedOpts<T>(
options: IDebugNameData & {
equalsFn?: EqualityComparer<T>;
onLastObserverRemoved?: (() => void);
},
computeFn: (reader: IReader) => T
): IObservable<T> {
return new Derived(
new DebugNameData(options.owner, options.debugName, options.debugReferenceFn),
computeFn,
undefined,
undefined,
options.onLastObserverRemoved,
options.equalsFn ?? strictEquals
);
}
_setDerivedOpts(derivedOpts);
/**
* Represents an observable that is derived from other observables.
* The value is only recomputed when absolutely needed.
*
* {@link computeFn} should start with a JS Doc using `@description` to name the derived.
*
* Use `createEmptyChangeSummary` to create a "change summary" that can collect the changes.
* Use `handleChange` to add a reported change to the change summary.
* The compute function is given the last change summary.
* The change summary is discarded after the compute function was called.
*
* @see derived
*/
export function derivedHandleChanges<T, TChangeSummary>(
options: IDebugNameData & {
createEmptyChangeSummary: () => TChangeSummary;
handleChange: (context: IChangeContext, changeSummary: TChangeSummary) => boolean;
equalityComparer?: EqualityComparer<T>;
},
computeFn: (reader: IReader, changeSummary: TChangeSummary) => T
): IObservable<T> {
return new Derived(
new DebugNameData(options.owner, options.debugName, undefined),
computeFn,
options.createEmptyChangeSummary,
options.handleChange,
undefined,
options.equalityComparer ?? strictEquals
);
}
export function derivedWithStore<T>(computeFn: (reader: IReader, store: DisposableStore) => T): IObservable<T>;
export function derivedWithStore<T>(owner: object, computeFn: (reader: IReader, store: DisposableStore) => T): IObservable<T>;
export function derivedWithStore<T>(computeFnOrOwner: ((reader: IReader, store: DisposableStore) => T) | object, computeFnOrUndefined?: ((reader: IReader, store: DisposableStore) => T)): IObservable<T> {
let computeFn: (reader: IReader, store: DisposableStore) => T;
let owner: Owner;
if (computeFnOrUndefined === undefined) {
computeFn = computeFnOrOwner as any;
owner = undefined;
} else {
owner = computeFnOrOwner;
computeFn = computeFnOrUndefined as any;
}
const store = new DisposableStore();
return new Derived(
new DebugNameData(owner, undefined, computeFn),
r => {
store.clear();
return computeFn(r, store);
}, undefined,
undefined,
() => store.dispose(),
strictEquals
);
}
export function derivedDisposable<T extends IDisposable | undefined>(computeFn: (reader: IReader) => T): IObservable<T>;
export function derivedDisposable<T extends IDisposable | undefined>(owner: Owner, computeFn: (reader: IReader) => T): IObservable<T>;
export function derivedDisposable<T extends IDisposable | undefined>(computeFnOrOwner: ((reader: IReader) => T) | Owner, computeFnOrUndefined?: ((reader: IReader) => T)): IObservable<T> {
let computeFn: (reader: IReader) => T;
let owner: Owner;
if (computeFnOrUndefined === undefined) {
computeFn = computeFnOrOwner as any;
owner = undefined;
} else {
owner = computeFnOrOwner;
computeFn = computeFnOrUndefined as any;
}
const store = new DisposableStore();
return new Derived(
new DebugNameData(owner, undefined, computeFn),
r => {
store.clear();
const result = computeFn(r);
if (result) {
store.add(result);
}
return result;
}, undefined,
undefined,
() => store.dispose(),
strictEquals
);
}
const enum DerivedState {
/** Initial state, no previous value, recomputation needed */
initial = 0,
/**
* A dependency could have changed.
* We need to explicitly ask them if at least one dependency changed.
*/
dependenciesMightHaveChanged = 1,
/**
* A dependency changed and we need to recompute.
* After recomputation, we need to check the previous value to see if we changed as well.
*/
stale = 2,
/**
* No change reported, our cached value is up to date.
*/
upToDate = 3,
}
export class Derived<T, TChangeSummary = any> extends BaseObservable<T, void> implements IReader, IObserver {
private state = DerivedState.initial;
private value: T | undefined = undefined;
private updateCount = 0;
private dependencies = new Set<IObservable<any>>();
private dependenciesToBeRemoved = new Set<IObservable<any>>();
private changeSummary: TChangeSummary | undefined = undefined;
public override get debugName(): string {
return this._debugNameData.getDebugName(this) ?? '(anonymous)';
}
constructor(
private readonly _debugNameData: DebugNameData,
public readonly _computeFn: (reader: IReader, changeSummary: TChangeSummary) => T,
private readonly createChangeSummary: (() => TChangeSummary) | undefined,
private readonly _handleChange: ((context: IChangeContext, summary: TChangeSummary) => boolean) | undefined,
private readonly _handleLastObserverRemoved: (() => void) | undefined = undefined,
private readonly _equalityComparator: EqualityComparer<T>,
) {
super();
this.changeSummary = this.createChangeSummary?.();
getLogger()?.handleDerivedCreated(this);
}
protected override onLastObserverRemoved(): void {
/**
* We are not tracking changes anymore, thus we have to assume
* that our cache is invalid.
*/
this.state = DerivedState.initial;
this.value = undefined;
for (const d of this.dependencies) {
d.removeObserver(this);
}
this.dependencies.clear();
this._handleLastObserverRemoved?.();
}
public override get(): T {
if (this.observers.size === 0) {
// Without observers, we don't know when to clean up stuff.
// Thus, we don't cache anything to prevent memory leaks.
const result = this._computeFn(this, this.createChangeSummary?.()!);
// Clear new dependencies
this.onLastObserverRemoved();
return result;
} else {
do {
// We might not get a notification for a dependency that changed while it is updating,
// thus we also have to ask all our depedencies if they changed in this case.
if (this.state === DerivedState.dependenciesMightHaveChanged) {
for (const d of this.dependencies) {
/** might call {@link handleChange} indirectly, which could make us stale */
d.reportChanges();
if (this.state as DerivedState === DerivedState.stale) {
// The other dependencies will refresh on demand, so early break
break;
}
}
}
// We called report changes of all dependencies.
// If we are still not stale, we can assume to be up to date again.
if (this.state === DerivedState.dependenciesMightHaveChanged) {
this.state = DerivedState.upToDate;
}
this._recomputeIfNeeded();
// In case recomputation changed one of our dependencies, we need to recompute again.
} while (this.state !== DerivedState.upToDate);
return this.value!;
}
}
private _recomputeIfNeeded() {
if (this.state === DerivedState.upToDate) {
return;
}
const emptySet = this.dependenciesToBeRemoved;
this.dependenciesToBeRemoved = this.dependencies;
this.dependencies = emptySet;
const hadValue = this.state !== DerivedState.initial;
const oldValue = this.value;
this.state = DerivedState.upToDate;
const changeSummary = this.changeSummary!;
this.changeSummary = this.createChangeSummary?.();
try {
/** might call {@link handleChange} indirectly, which could invalidate us */
this.value = this._computeFn(this, changeSummary);
} finally {
// We don't want our observed observables to think that they are (not even temporarily) not being observed.
// Thus, we only unsubscribe from observables that are definitely not read anymore.
for (const o of this.dependenciesToBeRemoved) {
o.removeObserver(this);
}
this.dependenciesToBeRemoved.clear();
}
const didChange = hadValue && !(this._equalityComparator(oldValue!, this.value));
getLogger()?.handleDerivedRecomputed(this, {
oldValue,
newValue: this.value,
change: undefined,
didChange,
hadValue,
});
if (didChange) {
for (const r of this.observers) {
r.handleChange(this, undefined);
}
}
}
public override toString(): string {
return `LazyDerived<${this.debugName}>`;
}
// IObserver Implementation
public beginUpdate<T>(_observable: IObservable<T>): void {
this.updateCount++;
const propagateBeginUpdate = this.updateCount === 1;
if (this.state === DerivedState.upToDate) {
this.state = DerivedState.dependenciesMightHaveChanged;
// If we propagate begin update, that will already signal a possible change.
if (!propagateBeginUpdate) {
for (const r of this.observers) {
r.handlePossibleChange(this);
}
}
}
if (propagateBeginUpdate) {
for (const r of this.observers) {
r.beginUpdate(this); // This signals a possible change
}
}
}
public endUpdate<T>(_observable: IObservable<T>): void {
this.updateCount--;
if (this.updateCount === 0) {
// End update could change the observer list.
const observers = [...this.observers];
for (const r of observers) {
r.endUpdate(this);
}
}
assertFn(() => this.updateCount >= 0);
}
public handlePossibleChange<T>(observable: IObservable<T, unknown>): void {
// In all other states, observers already know that we might have changed.
if (this.state === DerivedState.upToDate && this.dependencies.has(observable) && !this.dependenciesToBeRemoved.has(observable)) {
this.state = DerivedState.dependenciesMightHaveChanged;
for (const r of this.observers) {
r.handlePossibleChange(this);
}
}
}
public handleChange<T, TChange>(observable: IObservable<T, TChange>, change: TChange): void {
if (this.dependencies.has(observable) && !this.dependenciesToBeRemoved.has(observable)) {
const shouldReact = this._handleChange ? this._handleChange({
changedObservable: observable,
change,
didChange: o => o === observable as any,
}, this.changeSummary!) : true;
const wasUpToDate = this.state === DerivedState.upToDate;
if (shouldReact && (this.state === DerivedState.dependenciesMightHaveChanged || wasUpToDate)) {
this.state = DerivedState.stale;
if (wasUpToDate) {
for (const r of this.observers) {
r.handlePossibleChange(this);
}
}
}
}
}
// IReader Implementation
public readObservable<T>(observable: IObservable<T>): T {
// Subscribe before getting the value to enable caching
observable.addObserver(this);
/** This might call {@link handleChange} indirectly, which could invalidate us */
const value = observable.get();
// Which is why we only add the observable to the dependencies now.
this.dependencies.add(observable);
this.dependenciesToBeRemoved.delete(observable);
return value;
}
public override addObserver(observer: IObserver): void {
const shouldCallBeginUpdate = !this.observers.has(observer) && this.updateCount > 0;
super.addObserver(observer);
if (shouldCallBeginUpdate) {
observer.beginUpdate(this);
}
}
public override removeObserver(observer: IObserver): void {
const shouldCallEndUpdate = this.observers.has(observer) && this.updateCount > 0;
super.removeObserver(observer);
if (shouldCallEndUpdate) {
// Calling end update after removing the observer makes sure endUpdate cannot be called twice here.
observer.endUpdate(this);
}
}
}