UseCaseScheduler.kt

interface UseCaseScheduler {

    fun execute(runnable: Runnable)

    fun <V : UseCase.ResponseValue> notifyResponse(response: V,
                                                   useCaseCallback: UseCase.UseCaseCallback<V>)

    fun <V : UseCase.ResponseValue> onError(
            useCaseCallback: UseCase.UseCaseCallback<V>, t: Throwable)
}

UseCaseThreadPoolScheduler.kt

import android.os.Handler
import java.util.concurrent.ArrayBlockingQueue
import java.util.concurrent.ThreadPoolExecutor
import java.util.concurrent.TimeUnit

class UseCaseThreadPoolScheduler : UseCaseScheduler {

    val POOL_SIZE = 2

    val MAX_POOL_SIZE = 4

    val TIMEOUT = 30

    private val mHandler = Handler()

    internal var mThreadPoolExecutor: ThreadPoolExecutor

    init {
        mThreadPoolExecutor = ThreadPoolExecutor(POOL_SIZE, MAX_POOL_SIZE, TIMEOUT.toLong(),
                TimeUnit.SECONDS, ArrayBlockingQueue(POOL_SIZE))
    }

    override fun execute(runnable: Runnable) {
        mThreadPoolExecutor.execute(runnable)
    }

    override fun <V : UseCase.ResponseValue> notifyResponse(response: V,
                                                   useCaseCallback: UseCase.UseCaseCallback<V>) {
        mHandler.post { useCaseCallback.onSuccess(response) }
    }

    override fun <V : UseCase.ResponseValue> onError(
            useCaseCallback: UseCase.UseCaseCallback<V>, t: Throwable) {
        mHandler.post { useCaseCallback.onError(t) }
    }

}