Access the messages of actor mailbox - akka

Question

I want to read the messages in ShardRegions mailbox. In previous akka version, we could use the following code to get only the size of mailbox:
getContext().getMailboxSize();
Is there any way to fetch the type of messages in the mailbox?

Answer 1

Here is the solution
Define a wrapper mailbox for shard region like this:
class UnboundedMailboxWrapper extends MailboxType with ProducesMessageQueue[UnboundedMailboxWrapper.MessageQueue] {
def this(settings: ActorSystem.Settings, config: Config) = this()
final override def create(owner: Option[ActorRef], system: Option[ActorSystem]): MessageQueue =
new UnboundedMailboxWrapper.MessageQueue
}
object UnboundedMailboxWrapper {
class MessageQueue extends ConcurrentLinkedQueue[Envelope] with UnboundedQueueBasedMessageQueue {
val runtime = RuntimeManager.runtime
final def queue: Queue[Envelope] = this
override def enqueue(receiver: ActorRef, handle: Envelope): Unit = {
runtime.queue.add(handle)
queue add handle
}
override def dequeue(): Envelope = {
if (!runtime.queue.isEmpty) runtime.mailbox.queue.poll()
queue.poll()
}
}
}
in this mailbox we duplicate the element which added, to another queue, so when calculate size and other operation on it, there is no any impact on performance of mailbox queue
In duplicated queue we can calculate the number of messages and sort them:
def getElemets(): String = {
runtime.queue.asScala.toList.groupBy(_.message.getClass.getName)
.map(e ⇒ (e._1, e._2.length)).toSeq
.sortBy(_._2).foldLeft("") { (a, b) ⇒
b._1 + ":" + b._2 + "\n" + a
}
}
and with JMX or any other way we can call this method in runtime
and finlally assign this mailbox to ShardRegion dispatcher:
monit-dispatcher {
mailbox-type = "im.actor.server.cluster.UnboundedMailboxWrapper"
}
akka.cluster.sharding {
use-dispatcher = "monit-dispatcher"
}