Threading & Concurrency Model

Understanding the 4 concurrent threads in Quest 3D WebView that guarantee zero-crash execution.

---

The 4 Operating Threads

Thread	Owner	Responsibilities
Android UI Thread (main)	Android OS	All direct mWebView operations (goBack, loadUrl, evaluateJavascript).
ImageReader Handler Thread	Quest WebView	Asynchronously receives completed frame surfaces from VirtualDisplay.
Unreal Game Thread	Unreal Engine	Executes Blueprint logic, line traces, TickComponent, and reads atomic states.
Unreal Render Thread	Unreal Engine	Executes RHIUpdateTexture2D and NDK memory copy into GPU texture memory.

---

Concurrency Rules & Safety Guarantees

1. All WebView Calls Routed via runOnUiThread:
   • Calling any WebView method from the Unreal Game Thread throws a fatal Android crash. Quest 3D WebView automatically wraps all calls in mActivity.runOnUiThread.
2. Lock-Free State Queries:
   • Navigation state (mCanGoBack, mCanGoForward) and frame flags (mIsFrameDirty) are stored in Java AtomicBoolean and volatile fields, allowing instantaneous lock-free reads from the Game Thread.
3. No Deadlocks:
   • Unreal's Game Thread never blocks waiting for Android's UI thread.