added exponential delay for poisoned message handlers

[Peppi-Ressler]

Added optional exponential delay for republishing messages.

[jendakol]

Suggested change

	class ExponentialDelay(initialDelay: Duration, period: Duration, factor: Double, maxLength: Duration) {
	private val maxMillis = maxLength.toMillis
	def getExponentialDelay(attempts: Int): FiniteDuration = {
	if (attempts == 0) FiniteDuration(initialDelay._1, initialDelay._2)
	else {
	val millis = math.min(
	maxMillis,
	(period.toMillis * math.pow(factor, attempts - 1)).toLong
	)
	FiniteDuration(millis, TimeUnit.MILLISECONDS)
	}
	}
	}
	class ExponentialDelay(initialDelay: Duration, period: Duration, factor: Double, maxLength: Duration) {
	private val maxMillis = maxLength.toMillis
	def getExponentialDelay(attempt: Int): FiniteDuration = {
	if (attempt == 0) FiniteDuration(initialDelay._1, initialDelay._2)
	else {
	val millis = math.min(
	maxMillis,
	(period.toMillis * math.pow(factor, attempt - 1)).toLong
	)
	FiniteDuration(millis, TimeUnit.MILLISECONDS)
	}
	}
	}

[jendakol]

In overall, it looks good.
I have only two problems:

1. Default republish delays - 5 seconds is a weird value :-D But this is not a blocker, if you insist. I'd use just 2 seconds instead ;-)
2. The functionality is not tested. I believe it should be a part of some test case in PoisonedMessageHandlerTest.

[jendakol]

Nice job!