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fix: settle WebSocket event waiters in linear time #2389

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Merged
HAYDEN-OAI merged 1 commit into from
Aug 18, 2026
Merged

fix: settle WebSocket event waiters in linear time #2389

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98 changes: 91 additions & 7 deletions src/core/EventEmitter.ts
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@ type EventListener<Events, EventType extends keyof Events> = Events[EventType];
type EventListeners<Events, EventType extends keyof Events> = {
listener: EventListener<Events, EventType>;
once?: boolean;
removed?: boolean;
detached?: boolean;
}[];

/** Extracts the ordered listener-argument tuple for one named event. */
Expand All @@ -17,6 +19,12 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
#listeners: {
[Event in keyof EventTypes]?: EventListeners<EventTypes, Event>;
} = Object.create(null);
#emittedListenerRegistrations = new WeakMap<
object,
{ event: PropertyKey; registration: { removed?: boolean; detached?: boolean } }
>();
#pendingListenerCleanup = new Set<PropertyKey>();
#listenerDispatchDepth = 0;

/**
* Adds the listener function to the end of the listeners array for the event.
Expand All @@ -43,7 +51,22 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
if (!listeners) {
return this;
}
const index = listeners.findIndex((l) => l.listener === listener);

const emittedRegistration = this.#emittedListenerRegistrations.get(listener as object);
if (
emittedRegistration?.event === event &&
!emittedRegistration.registration.removed &&
!emittedRegistration.registration.detached
) {
this.#removeEmittedListener(
event,
emittedRegistration.registration as EventListeners<EventTypes, Event>[number],
);
return this;
}
const index = listeners.findIndex(
(registration) => !registration.removed && registration.listener === listener,
);
if (index !== -1) {
listeners.splice(index, 1);
}
Expand All @@ -61,6 +84,52 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
return this;
}

#onceForEmitted<Event extends keyof EventTypes>(
event: Event,
listener: EventListener<EventTypes, Event>,
): void {
const previousListeners = this.#listeners[event];
const previousLength = previousListeners?.length ?? 0;
this.once(event, listener);
const listeners = this.#listeners[event];
const [registration] = listeners?.slice(-1) ?? [];
if (
(previousListeners === undefined || listeners === previousListeners) &&
listeners?.length === previousLength + 1 &&
registration?.listener === listener &&
registration.once
) {
this.#emittedListenerRegistrations.set(listener as object, { event, registration });
}
}

#removeEmittedListener<Event extends keyof EventTypes>(
event: Event,
registration: EventListeners<EventTypes, Event>[number],
): void {
if (registration.removed) {
return;
}

registration.removed = true;
this.#emittedListenerRegistrations.delete(registration.listener as object);
this.#pendingListenerCleanup.add(event);
if (this.#listenerDispatchDepth === 0) {
this.#cleanupEmittedListeners();
}
}

#cleanupEmittedListeners(): void {
for (const event of this.#pendingListenerCleanup) {
const eventType = event as keyof EventTypes;
const listeners = this.#listeners[eventType];
if (listeners) {
this.#listeners[eventType] = listeners.filter((listener) => !listener.removed) as any;
}
}
this.#pendingListenerCleanup.clear();
}

/**
* This is similar to `.once()`, but returns a Promise that resolves the next time
* the event is triggered, instead of calling a listener callback.
Expand Down Expand Up @@ -98,9 +167,9 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
};

if (event !== 'error') {
this.once('error', listeners.onError as any);
this.#onceForEmitted('error', listeners.onError as any);
}
this.once(event, listeners.onEvent as any);
this.#onceForEmitted(event, listeners.onEvent as any);
});
}

Expand All @@ -111,16 +180,31 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
) {
const listeners: EventListeners<EventTypes, Event> | undefined = this.#listeners[event];
if (listeners) {
this.#listeners[event] = listeners.filter((l) => !l.once) as any;
for (const { listener } of listeners as any) {
listener(...(args as any));
this.#listeners[event] = listeners.filter((listener) => {
if (listener.once) {
listener.detached = true;
}
return !listener.once && !listener.removed;
}) as any;
this.#listenerDispatchDepth += 1;
try {
for (const registration of listeners as any) {
if (!registration.removed) {
registration.listener(...(args as any));
}
}
} finally {
this.#listenerDispatchDepth -= 1;
if (this.#listenerDispatchDepth === 0) {
this.#cleanupEmittedListeners();
}
}
}
}

protected _hasListener(event: keyof EventTypes): boolean {
const listeners = this.#listeners[event];
return listeners && listeners.length > 0;
return listeners && listeners.some((listener) => !listener.removed);
}
}

Expand Down
98 changes: 91 additions & 7 deletions src/lib/EventEmitter.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@ type EventListener<Events, EventType extends keyof Events> = Events[EventType];
type EventListeners<Events, EventType extends keyof Events> = {
listener: EventListener<Events, EventType>;
once?: boolean;
removed?: boolean;
detached?: boolean;
}[];

/** The positional listener arguments associated with a named event. */
Expand All @@ -17,6 +19,12 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
#listeners: {
[Event in keyof EventTypes]?: EventListeners<EventTypes, Event>;
} = Object.create(null);
#emittedListenerRegistrations = new WeakMap<
object,
{ event: PropertyKey; registration: { removed?: boolean; detached?: boolean } }
>();
#pendingListenerCleanup = new Set<PropertyKey>();
#listenerDispatchDepth = 0;

/**
* Adds the listener function to the end of the listeners array for the event.
Expand All @@ -43,7 +51,22 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
if (!listeners) {
return this;
}
const index = listeners.findIndex((l) => l.listener === listener);

const emittedRegistration = this.#emittedListenerRegistrations.get(listener as object);
if (
emittedRegistration?.event === event &&
!emittedRegistration.registration.removed &&
!emittedRegistration.registration.detached
) {
this.#removeEmittedListener(
event,
emittedRegistration.registration as EventListeners<EventTypes, Event>[number],
);
return this;
}
const index = listeners.findIndex(
(registration) => !registration.removed && registration.listener === listener,
);
if (index !== -1) {
listeners.splice(index, 1);
}
Expand All @@ -61,6 +84,52 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
return this;
}

#onceForEmitted<Event extends keyof EventTypes>(
event: Event,
listener: EventListener<EventTypes, Event>,
): void {
const previousListeners = this.#listeners[event];
const previousLength = previousListeners?.length ?? 0;
this.once(event, listener);
const listeners = this.#listeners[event];
const [registration] = listeners?.slice(-1) ?? [];
if (
(previousListeners === undefined || listeners === previousListeners) &&
listeners?.length === previousLength + 1 &&
registration?.listener === listener &&
registration.once
) {
this.#emittedListenerRegistrations.set(listener as object, { event, registration });
}
}

#removeEmittedListener<Event extends keyof EventTypes>(
event: Event,
registration: EventListeners<EventTypes, Event>[number],
): void {
if (registration.removed) {
return;
}

registration.removed = true;
this.#emittedListenerRegistrations.delete(registration.listener as object);
this.#pendingListenerCleanup.add(event);
if (this.#listenerDispatchDepth === 0) {
this.#cleanupEmittedListeners();
}
}

#cleanupEmittedListeners(): void {
for (const event of this.#pendingListenerCleanup) {
const eventType = event as keyof EventTypes;
const listeners = this.#listeners[eventType];
if (listeners) {
this.#listeners[eventType] = listeners.filter((listener) => !listener.removed) as any;
}
}
this.#pendingListenerCleanup.clear();
}

/**
* This is similar to `.once()`, but returns a Promise that resolves the next time
* the event is triggered, instead of calling a listener callback.
Expand Down Expand Up @@ -96,9 +165,9 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
};

if (event !== 'error') {
this.once('error', onError as any);
this.#onceForEmitted('error', onError as any);
}
this.once(event, onEvent as any);
this.#onceForEmitted(event, onEvent as any);
});
}

Expand All @@ -109,15 +178,30 @@ export class EventEmitter<EventTypes extends Record<string, (...args: any) => an
) {
const listeners: EventListeners<EventTypes, Event> | undefined = this.#listeners[event];
if (listeners) {
this.#listeners[event] = listeners.filter((l) => !l.once) as any;
for (const { listener } of listeners as any) {
listener(...(args as any));
this.#listeners[event] = listeners.filter((listener) => {
if (listener.once) {
listener.detached = true;
}
return !listener.once && !listener.removed;
}) as any;
this.#listenerDispatchDepth += 1;
try {
for (const registration of listeners as any) {
if (!registration.removed) {
registration.listener(...(args as any));
}
}
} finally {
this.#listenerDispatchDepth -= 1;
if (this.#listenerDispatchDepth === 0) {
this.#cleanupEmittedListeners();
}
}
}
}

protected _hasListener(event: keyof EventTypes): boolean {
const listeners = this.#listeners[event];
return listeners && listeners.length > 0;
return listeners && listeners.some((listener) => !listener.removed);
}
}
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