TemplateRateLimiter

Rate limiter for Android Auto template invalidation calls.

Android Auto has recommended update frequency limits to prevent UI lag and ANRs. This class provides throttling with trailing edge guarantee - ensuring the final state is always rendered even if intermediate updates are skipped.

Problem Solved

During active navigation, guidance state updates can occur multiple times per second (maneuver changes, distance updates, ETA updates). Calling invalidate() for each update overwhelms the Android Auto host and can cause:

• UI lag and stuttering

• ANRs (Application Not Responding)

• Excessive template rebuilds

Solution: Throttle with Trailing Edge

This limiter uses a "throttle with trailing edge" pattern:

1. Immediate execution: First call executes immediately

2. Throttling: Subsequent calls within the cooldown period are skipped

3. Trailing edge: If calls were skipped, one final call executes after cooldown

This ensures:

• Responsive initial updates (no delay on first call)

• Limited update frequency (respects host capabilities)

• Final state consistency (trailing edge guarantees last state is rendered)

Usage

class MyScreen : Screen(carContext) {
    private val rateLimiter = TemplateRateLimiter(
        scope = screenScope,
        minIntervalMs = 100L,
        tag = "MyScreen"
    )

    fun onStateChanged() {
        rateLimiter.requestInvalidate { invalidate() }
    }

    override fun onDestroy(owner: LifecycleOwner) {
        rateLimiter.cancel()
    }
}

Thread Safety

This class uses AtomicLong for timestamp tracking and coroutine-based scheduling, making it safe for concurrent access from multiple threads.

Parameters

See also