FrameThrottle class

A single-slot gate for camera-frame processing that drops frames arriving while a previous frame is still being processed.

Live camera streams deliver frames faster than on-device inference can keep up. Running every frame would queue work and add latency without improving the result, so the usual pattern is to process a frame only once the previous one has finished and drop the rest. FrameThrottle captures that pattern so callers do not have to hand-roll a mutable "busy" flag and the try/finally that must always clear it (forgetting the finally wedges the gate closed forever).

The busy check and set happen synchronously before the first await, so on Dart's single-threaded event loop there is no race between overlapping stream callbacks.

Usage inside a camera image-stream callback:

final _throttle = FrameThrottle();

void _onCameraImage(CameraImage image) {
  _throttle.run(() async {
    final results = await detector.detectFromCameraImage(image);
    if (mounted) setState(() => _results = results);
  });
}