RX thread switching benchmark

class MainActivity : AppCompatActivity() {

    private var switchFromIoToCompute = 0L
    private var switchFromComputeToIo = 0L
    private var loopCount = 0L
    private var appCreated = 0L

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val publishSubject = PublishSubject.create<Long>()

        var startTime: Long = 0L
        publishSubject.doOnNext {
            startTime = System.nanoTime()
        }
            .observeOn(Schedulers.computation())
            .doOnNext {
                switchFromIoToCompute += System.nanoTime() - startTime
                startTime = System.nanoTime()
            }
            .observeOn(Schedulers.io())
            .doOnNext {
                switchFromComputeToIo += System.nanoTime() - startTime
            }
            .subscribe {
                // Loop
                loopCount++
                publishSubject.onNext(it + 1)
            }

        appCreated = System.nanoTime()
        publishSubject.onNext(0L)

        Observable.interval(0, 1, TimeUnit.SECONDS, AndroidSchedulers.mainThread())
            .subscribe { updateUi() }
    }

    private fun updateUi() {
        val totalSwitching = (switchFromIoToCompute + switchFromComputeToIo) / loopCount
        val appTimeByLoop = (System.nanoTime() - appCreated) / loopCount
        val message = """
            loopCount = $loopCount
            IO -> Compute = ${switchFromIoToCompute / loopCount}
            Compute -> IO = ${switchFromComputeToIo / loopCount}
            Total switching = $totalSwitching
            Total time since activity created / loop count= $appTimeByLoop
            switch time / Percent total time = ${(totalSwitching * 100f) / appTimeByLoop}%
        """.trimIndent()
        text_view.text = message
    }
}