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perf - ignore new listeners when leakage threshold is exceeded by far #164885

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merged 1 commit into from
Oct 28, 2022
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perf - ignore new listeners when leakage threshold is exceeded by far #164885

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21 changes: 10 additions & 11 deletions src/vs/base/common/event.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -578,23 +578,17 @@ class LeakageMonitor {
private _warnCountdown: number = 0;

constructor(
readonly customThreshold?: number,
readonly threshold: number,
readonly name: string = Math.random().toString(18).slice(2, 5),
) { }

dispose(): void {
if (this._stacks) {
this._stacks.clear();
}
this._stacks?.clear();
}

check(stack: Stacktrace, listenerCount: number): undefined | (() => void) {

let threshold = _globalLeakWarningThreshold;
if (typeof this.customThreshold === 'number') {
threshold = this.customThreshold;
}

const threshold = this.threshold;
if (threshold <= 0 || listenerCount < threshold) {
return undefined;
}
Expand Down Expand Up @@ -693,7 +687,7 @@ export class Emitter<T> {

constructor(options?: EmitterOptions) {
this._options = options;
this._leakageMon = _globalLeakWarningThreshold > 0 ? new LeakageMonitor(this._options && this._options.leakWarningThreshold) : undefined;
this._leakageMon = _globalLeakWarningThreshold > 0 || this._options?.leakWarningThreshold ? new LeakageMonitor(this._options?.leakWarningThreshold ?? _globalLeakWarningThreshold) : undefined;
this._perfMon = this._options?._profName ? new EventProfiling(this._options._profName) : undefined;
this._deliveryQueue = this._options?.deliveryQueue;
}
Expand Down Expand Up @@ -744,6 +738,11 @@ export class Emitter<T> {
this._listeners = new LinkedList();
}

if (this._leakageMon && this._listeners.size > this._leakageMon.threshold * 3) {
console.warn(`[${this._leakageMon.name}] REFUSES to accept new listeners because it exceeded its threshold by far`);
return Disposable.None;
}

const firstListener = this._listeners.isEmpty();

if (firstListener && this._options?.onFirstListenerAdd) {
Expand All @@ -752,7 +751,7 @@ export class Emitter<T> {

let removeMonitor: Function | undefined;
let stack: Stacktrace | undefined;
if (this._leakageMon && this._listeners.size >= 30) {
if (this._leakageMon && this._listeners.size >= Math.ceil(this._leakageMon.threshold * 0.2)) {
// check and record this emitter for potential leakage
stack = Stacktrace.create();
removeMonitor = this._leakageMon.check(stack, this._listeners.size + 1);
Expand Down