Building Workers With Coroutines

TaskEngineWorker.kt

typealias TaskEngineMessageToProcess = MessageToProcess<TaskEngineMessage>

fun CoroutineScope.startPulsarTaskEngineWorker(
    taskEngineConsumer: Consumer<TaskEngineEnvelope>,
    taskEngine: TaskEngine,
    logChannel: SendChannel<TaskEngineMessageToProcess>?,
    enginesNumber: Int
) = launch(Dispatchers.IO) {

    val taskInputChannel = Channel<TaskEngineMessageToProcess>()
    val taskResultsChannel = Channel<TaskEngineMessageToProcess>()

    // coroutine dedicated to pulsar message pulling
    launch(CoroutineName("task-engine-message-puller")) {
        while (isActive) {
            val message: Message<TaskEngineEnvelope> = taskEngineConsumer.receiveAsync().await()

            try {
                val envelope = readBinary(message.data, TaskEngineEnvelope.serializer())
                taskInputChannel.send(MessageToProcess(envelope.message(), message.messageId))
            } catch (e: Exception) {
                taskEngineConsumer.negativeAcknowledge(message.messageId)
                throw e
            }
        }
    }

    // coroutines dedicated to Task Engine
    repeat(enginesNumber) {
        launch(CoroutineName("task-engine-$it")) {
            for (messageToProcess in taskInputChannel) {
                try {
                    messageToProcess.output = taskEngine.handle(messageToProcess.message)
                } catch (e: Exception) {
                    messageToProcess.exception = e
                }
                taskResultsChannel.send(messageToProcess)
            }
        }
    }

    // coroutine dedicated to pulsar message acknowledging
    launch(CoroutineName("task-engine-message-acknowledger")) {
        for (messageToProcess in taskResultsChannel) {
            if (messageToProcess.exception == null) {
                taskEngineConsumer.acknowledgeAsync(messageToProcess.messageId).await()
            } else {
                taskEngineConsumer.negativeAcknowledge(messageToProcess.messageId)
            }
            logChannel?.send(messageToProcess)
        }
    }
}

data class MessageToProcess<T> (
    val message: T,
    val messageId: MessageId,
    var exception: Exception? = null,
    var output: Any? = null
)