Skipped Frames Counter

SkippedFramesCounter.java

import android.view.Choreographer;
import timber.log.Timber;

import java.lang.ref.WeakReference;
import java.lang.reflect.Field;

/**
 * This class is based on a talk by Jason Sendros (Facebook) at Droidcon NYC 2015.
 * This class keeps track of the number of skipped frames and the number of skipped frames
 * caused by GC events.
 */
public class SkippedFramesCounter {

	private static final long NANOS_PER_MILLI = 1000000000;
	private static final int DEFAULT_FRAME_INTERVAL = 16666667;
	private static final int FIRST_FRAME = -1;

	private WeakReference<Object> gcReference;
	private long previousFrame = FIRST_FRAME;
	private long frameInterval;

	// total counts
	private long totalGCSkippedFrames;
	private long totalSkippedFrames;
	private long totalFrames;

	private static final SkippedFramesCounter INSTANCE = new SkippedFramesCounter();

	public static SkippedFramesCounter getInstance() {
		return INSTANCE;
	}

	private SkippedFramesCounter() {
		try {
			Field f = Choreographer.getInstance().getClass().getDeclaredField("mFrameIntervalNanos");
			f.setAccessible(true);
			frameInterval = (Long) f.get(Choreographer.getInstance());
			Timber.i("Frame interval is %d", frameInterval);
		} catch (NoSuchFieldException | IllegalAccessException e) {
			throw new IllegalStateException(e);
		}
		setRef();
	}

	public void start() {
		previousFrame = FIRST_FRAME;
		Choreographer.getInstance().postFrameCallback(callback);
	}

	public void stop() {
		Choreographer.getInstance().removeFrameCallback(callback);
	}

	private final Choreographer.FrameCallback callback = new Choreographer.FrameCallback() {
		@Override
		public void doFrame(long frameTimeNanos) {
			boolean gc = hasGCOccurred();
			if (previousFrame == FIRST_FRAME) {
				Choreographer.getInstance().postFrameCallback(callback);
				previousFrame = frameTimeNanos;
				return;
			}
			long frameTime = frameTimeNanos - previousFrame;
			long skippedFrames = (frameTime / frameInterval) - 1;
			if (skippedFrames > 0) {
				if (gc) {
					totalGCSkippedFrames += skippedFrames;
				}
				totalSkippedFrames += skippedFrames;
				totalFrames += skippedFrames;
			}
			previousFrame = frameTimeNanos;
			Choreographer.getInstance().postFrameCallback(callback);

			totalFrames ++;
		}
	};

	public long getTotalGCSkippedFrames() {
		return totalGCSkippedFrames;
	}

	public long getTotalFrames() {
		return totalFrames;
	}

	public long getTotalSkippedFrames() {
		return totalSkippedFrames;
	}

	public float getPercentSkippedFrames() {
		if (totalFrames == 0) {
			return 0;
		}
		return 1.0f * totalSkippedFrames / totalFrames;
	}

	private boolean hasGCOccurred() {
		if (gcReference.get() == null) {
			setRef();
			return true;
		} else {
			return false;
		}
	}

	private void setRef() {
		gcReference = new WeakReference<>(new Object());
	}

	public void resetCounts() {
		totalFrames = 0;
		totalGCSkippedFrames = 0;
		totalSkippedFrames = 0;
	}
}