Performance: Optimize AudioEngine subscriber unsubscriptions using Sets

[ysdede]

What changed

Refactored subscriber lists in src/lib/audio/AudioEngine.ts (segmentCallbacks, windowCallbacks, audioChunkCallbacks, and visualizationCallbacks) from Array to Set.
Modified subscription add and delete methods accordingly, taking advantage of Set's built-in .add() and .delete() APIs instead of Array.filter().

Why it was needed

Using Array.filter() to remove subscribers created a new Array object each time, causing O(N) array reallocation and Garbage Collection (GC) churn. Given these events can be bound or unbound during specific lifecycle methods in a performance-critical audio recording path, reducing unnecessary allocations aids frame rate stability and lessens main thread pauses due to GC. Using Set ensures O(1) unsubscription and mutation in-place.

Impact

Significantly lowers memory allocation pressure and prevents Array reallocations. O(N) time complexity to remove elements was reduced to O(1). This change eliminates Array.filter() allocations within hot execution paths. Set.prototype.forEach still preserves insertion order so execution sequences remain entirely unaltered.

How to verify

1. Run npm run test and verify that all 219 tests pass.
2. The core audio streaming logic inside AudioEngine functions as before.

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PR created automatically by Jules for task 10374202247365408348 started by @ysdede

Summary by Sourcery

Enhancements:

• Replace array-backed callback lists with Set-based collections for segment, window, audio chunk, and visualization subscribers to enable O(1) add/remove operations without array reallocations.

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📥 Commits

Reviewing files that changed from the base of the PR and between 474dbe6 and b054a87.

📒 Files selected for processing (1)

• src/lib/audio/AudioEngine.ts

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• Create PR with unit tests
• Commit unit tests in branch performance/optimize-audio-engine-callbacks-10374202247365408348

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[qodo-code-review]

Review Summary by Qodo

Optimize AudioEngine callbacks using Sets for O(1) unsubscription

✨ Enhancement

Walkthroughs

Description

• Refactored subscriber callback lists from Arrays to Sets
• Reduced unsubscription complexity from O(N) to O(1)
• Eliminates Array.filter() allocations in hot audio paths
• Preserves callback execution order via Set.forEach semantics

Diagram

flowchart LR
  A["Array-based callbacks<br/>with filter()"] -- "Refactor to Set" --> B["Set-based callbacks<br/>with delete()"]
  A -- "O(N) complexity<br/>GC churn" --> C["Performance issue"]
  B -- "O(1) complexity<br/>In-place mutation" --> D["Optimized performance"]

Loading

File Changes

1. src/lib/audio/AudioEngine.ts ✨ Enhancement +13/-13

Convert callback subscriber lists to Sets

• Changed segmentCallbacks, windowCallbacks, audioChunkCallbacks, and visualizationCallbacks
 from Array to Set type declarations
• Updated subscription methods to use Set.add() instead of Array.push()
• Replaced Array.filter() unsubscription logic with Set.delete() for O(1) removal
• Maintained callback execution order through Set.forEach iteration semantics

src/lib/audio/AudioEngine.ts

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[qodo-code-review]

Code Review by Qodo

🐞 Bugs (1)   📘 Rule violations (0)   📎 Requirement gaps (0)

🐞\ ≡ Correctness (1)

1. Set mutation changes dispatch 🐞 ≡

Description

Callback lists now use Set with in-place delete, so modifications during notification can change
which callbacks run within the same notification cycle (e.g., unsubscribing another listener can
cause it to be skipped, and newly-added listeners may run immediately). This is a behavioral change
from the previous Array+filter approach, which effectively provided a snapshot for in-flight
iterations by rebinding to a new Array.

Code

src/lib/audio/AudioEngine.ts[R478-482]

    onAudioChunk(callback: (chunk: Float32Array) => void): () => void {
-        this.audioChunkCallbacks.push(callback);
+        this.audioChunkCallbacks.add(callback);
        return () => {
-            this.audioChunkCallbacks = this.audioChunkCallbacks.filter((cb) => cb !== callback);
+            this.audioChunkCallbacks.delete(callback);
        };

Evidence

Subscriptions/unsubscriptions now mutate Sets in place (add/delete), while notifications iterate
directly over those same Sets. With the prior Array implementation, unsubscription used filter() and
reassigned a new array, so an in-flight iterator would continue over the old array object,
preserving a stable listener list for that dispatch; the new Set approach makes the iteration
observe live mutations.

src/lib/audio/AudioEngine.ts[39-52]
src/lib/audio/AudioEngine.ts[78-78]
src/lib/audio/AudioEngine.ts[442-447]
src/lib/audio/AudioEngine.ts[478-483]
src/lib/audio/AudioEngine.ts[935-940]
src/lib/audio/AudioEngine.ts[687-695]
src/lib/audio/AudioEngine.ts[764-778]
src/lib/audio/AudioEngine.ts[729-762]
src/lib/audio/AudioEngine.ts[946-967]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The subscriber collections were changed to `Set` and are mutated in-place via `.delete()`. Notification loops iterate directly over those Sets, so if any callback subscribes/unsubscribes during dispatch, the set's iteration can skip not-yet-called listeners or include newly added ones in the same cycle, which differs from the prior Array+filter rebinding behavior.

## Issue Context
This affects all four callback collections (`segmentCallbacks`, `windowCallbacks`, `audioChunkCallbacks`, `visualizationCallbacks`). The previous `Array.filter()` pattern reassigned a new array, effectively making in-flight dispatch iterate over a stable snapshot.

## Fix Focus Areas
Consider snapshotting the current subscribers before iterating (or maintaining a stable iteration snapshot updated only on subscribe/unsubscribe) to preserve dispatch semantics:
- src/lib/audio/AudioEngine.ts[687-695]
- src/lib/audio/AudioEngine.ts[729-762]
- src/lib/audio/AudioEngine.ts[764-778]
- src/lib/audio/AudioEngine.ts[946-967]
- src/lib/audio/AudioEngine.ts[442-483]
- src/lib/audio/AudioEngine.ts[935-940]ेय

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[sourcery-ai]

Hey - I've left some high level feedback:

• Now that the callback collections are Sets instead of Arrays, scan remaining usages of segmentCallbacks, windowCallbacks, audioChunkCallbacks, and visualizationCallbacks in this file for any array-specific operations (e.g. .length, indexing, .map, .filter, .slice) and update them to Set-appropriate patterns (e.g. .size, for..of, forEach).

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Now that the callback collections are Sets instead of Arrays, scan remaining usages of `segmentCallbacks`, `windowCallbacks`, `audioChunkCallbacks`, and `visualizationCallbacks` in this file for any array-specific operations (e.g. `.length`, indexing, `.map`, `.filter`, `.slice`) and update them to Set-appropriate patterns (e.g. `.size`, `for..of`, `forEach`).

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[gemini-code-assist]

Code Review

This pull request refactors the AudioEngine class to use Set instead of Array for managing various callback collections, including speech segments, windowed audio, audio chunks, and visualization updates. This change simplifies the subscription and unsubscription logic by utilizing the native add and delete methods of the Set object. I have no feedback to provide.