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perf(@angular/build): reduce watcher debounce latency for faster incremental rebuilds #34048

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alan-agius4 merged 2 commits into from
Sep 9, 2026
Merged

perf(@angular/build): reduce watcher debounce latency for faster incremental rebuilds #34048

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50b8f2e
perf(@angular/build): reduce watcher debounce latency for faster incr…
alan-agius4 Sep 8, 2026
92b9a2f
fixup! perf(@angular/build): reduce watcher debounce latency for fast…
alan-agius4 Sep 9, 2026
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29 changes: 27 additions & 2 deletions packages/angular/build/src/tools/esbuild/watcher.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,12 @@ class WatcherQueue {
private currentChangedFiles: ChangedFiles | undefined;
private isClosed = false;
private timeoutId: NodeJS.Timeout | undefined;
private firstChangeTime: number | undefined;

constructor(
private readonly debounceMs = 100,
private readonly maxWaitMs = 500,
) {}

addChange(type: 'added' | 'modified' | 'removed', file: string): void {
if (this.isClosed) {
Expand All @@ -167,16 +173,25 @@ class WatcherQueue {
}

private scheduleFlush(): void {
const now = Date.now();
const firstChangeTime = (this.firstChangeTime ??= now);

if (this.timeoutId) {
clearTimeout(this.timeoutId);
}

const elapsed = now - firstChangeTime;
const remainingMaxWait = Math.max(0, this.maxWaitMs - elapsed);
const delay = Math.min(this.debounceMs, remainingMaxWait);

this.timeoutId = setTimeout(() => {
this.timeoutId = undefined;
this.flush();
}, 250);
}, delay);
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}

private flush(): void {
this.firstChangeTime = undefined;
if (
this.currentChangedFiles &&
this.currentChangedFiles.all.length > 0 &&
Expand Down Expand Up @@ -224,6 +239,7 @@ class WatcherQueue {
clearTimeout(this.timeoutId);
this.timeoutId = undefined;
}
this.firstChangeTime = undefined;

this.isClosed = true;
this.currentChangedFiles = undefined;
Expand Down Expand Up @@ -511,7 +527,16 @@ async function createChokidarWatcher(
): Promise<BuildWatcher> {
const chokidar = chokidarModule ?? (await import('chokidar'));
const watchedFiles = new Set<string>();
const queue = new WatcherQueue();

let queue: WatcherQueue;
if (options?.polling) {
const pollingInterval = options.interval ?? 100;
const debounceMs = Math.min(250, Math.max(100, Math.ceil(pollingInterval * 1.5)));
const maxWaitMs = Math.max(500, debounceMs * 3);
queue = new WatcherQueue(debounceMs, maxWaitMs);
} else {
queue = new WatcherQueue();
}

const rootDir = options?.cwd ?? process.cwd();
const isCaseSensitive = isFileSystemCaseSensitive(rootDir);
Expand Down
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