From c79dcf8c5c162168562d491c520bee585c1bdf01 Mon Sep 17 00:00:00 2001
From: Johannes Rieken <johannes.rieken@gmail.com>
Date: Wed, 12 Jan 2022 17:23:46 +0100
Subject: [PATCH] use "sliding window" average for language feature delays,
 https://github.com/microsoft/vscode/issues/140557

---
 src/vs/base/common/numbers.ts                 | 34 +++++++++++++++++++
 .../languages/languageFeatureRegistry.ts      |  6 ++--
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/src/vs/base/common/numbers.ts b/src/vs/base/common/numbers.ts
index 9edfddfe5338a..3b06c0d26b9e8 100644
--- a/src/vs/base/common/numbers.ts
+++ b/src/vs/base/common/numbers.ts
@@ -34,3 +34,37 @@ export class MovingAverage {
 		return this._val;
 	}
 }
+
+export class SlidingWindowAverage {
+
+	private _n: number = 0;
+	private _val = 0;
+
+	private readonly _values: number[] = [];
+	private _index: number = 0;
+	private _sum = 0;
+
+	constructor(size: number) {
+		this._values = new Array(size);
+		this._values.fill(0, 0, size);
+	}
+
+	update(value: number) {
+		const oldValue = this._values[this._index];
+		this._values[this._index] = value;
+		this._index = (this._index + 1) % this._values.length;
+
+		this._sum -= oldValue;
+		this._sum += value;
+
+		if (this._n < this._values.length) {
+			this._n += 1;
+		}
+
+		this._val = this._sum / this._n;
+	}
+
+	get value(): number {
+		return this._val;
+	}
+}
diff --git a/src/vs/editor/common/languages/languageFeatureRegistry.ts b/src/vs/editor/common/languages/languageFeatureRegistry.ts
index 80fde38e2aa42..e1de00b5e6e49 100644
--- a/src/vs/editor/common/languages/languageFeatureRegistry.ts
+++ b/src/vs/editor/common/languages/languageFeatureRegistry.ts
@@ -7,7 +7,7 @@ import { Emitter, Event } from 'vs/base/common/event';
 import { doHash } from 'vs/base/common/hash';
 import { IDisposable, toDisposable } from 'vs/base/common/lifecycle';
 import { LRUCache } from 'vs/base/common/map';
-import { MovingAverage } from 'vs/base/common/numbers';
+import { SlidingWindowAverage } from 'vs/base/common/numbers';
 import { ITextModel } from 'vs/editor/common/model';
 import { LanguageFilter, LanguageSelector, score } from 'vs/editor/common/languages/languageSelector';
 import { shouldSynchronizeModel } from 'vs/editor/common/services/model';
@@ -197,7 +197,7 @@ function weakHash(obj: object): number {
  */
 export class LanguageFeatureRequestDelays {
 
-	private readonly _cache = new LRUCache<string, MovingAverage>(50, 0.7);
+	private readonly _cache = new LRUCache<string, SlidingWindowAverage>(50, 0.7);
 
 
 	constructor(
@@ -228,7 +228,7 @@ export class LanguageFeatureRequestDelays {
 		const key = this._key(model);
 		let avg = this._cache.get(key);
 		if (!avg) {
-			avg = new MovingAverage();
+			avg = new SlidingWindowAverage(12);
 			this._cache.set(key, avg);
 		}
 		avg.update(value);