pekko/akka-persistence/src/main/scala/akka/persistence/journal/AsyncWriteJournal.scala

/**
 * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
 * Copyright (C) 2012-2013 Eligotech BV.
 */

package akka.persistence.journal

import scala.collection.immutable
import scala.concurrent.Future
import scala.util._

import akka.actor._
import akka.pattern.{ pipe, PromiseActorRef }
import akka.persistence._
import akka.persistence.JournalProtocol._

/**
 * Abstract journal, optimized for asynchronous, non-blocking writes.
 */
trait AsyncWriteJournal extends Actor with AsyncReplay {
  import AsyncWriteJournal._
  import context.dispatcher

  private val extension = Persistence(context.system)

  private val resequencer = context.actorOf(Props[Resequencer])
  private var resequencerCounter = 1L

  def receive = {
    case WriteBatch(persistentBatch, processor) ⇒
      val cctr = resequencerCounter
      def resequence(f: PersistentRepr ⇒ Any) = persistentBatch.zipWithIndex.foreach {
        case (p, i) ⇒ resequencer ! Desequenced(f(p), cctr + i + 1, processor, p.sender)
      }
      writeAsync(persistentBatch.map(_.prepareWrite())) onComplete {
        case Success(_) ⇒
          resequencer ! Desequenced(WriteBatchSuccess, cctr, processor, self)
          resequence(WriteSuccess(_))
        case Failure(e) ⇒
          resequencer ! Desequenced(WriteBatchFailure(e), cctr, processor, self)
          resequence(WriteFailure(_, e))
      }
      resequencerCounter += persistentBatch.length + 1
    case Replay(fromSequenceNr, toSequenceNr, processorId, processor) ⇒
      // Send replayed messages and replay result to processor directly. No need
      // to resequence replayed messages relative to written and looped messages.
      replayAsync(processorId, fromSequenceNr, toSequenceNr) { p ⇒
        if (!p.deleted) processor.tell(Replayed(p), p.sender)
      } map {
        maxSnr ⇒ ReplaySuccess(maxSnr)
      } recover {
        case e ⇒ ReplayFailure(e)
      } pipeTo (processor)
    case c @ Confirm(processorId, sequenceNr, channelId) ⇒
      confirmAsync(processorId, sequenceNr, channelId) onComplete {
        case Success(_) ⇒ if (extension.publishPluginCommands) context.system.eventStream.publish(c)
        case Failure(e) ⇒ // TODO: publish failure to event stream
          context.system.eventStream.publish(c)
      }
    case d @ Delete(processorId, fromSequenceNr, toSequenceNr, permanent) ⇒
      deleteAsync(processorId, fromSequenceNr, toSequenceNr, permanent) onComplete {
        case Success(_) ⇒ if (extension.publishPluginCommands) context.system.eventStream.publish(d)
        case Failure(e) ⇒ // TODO: publish failure to event stream
      }
    case Loop(message, processor) ⇒
      resequencer ! Desequenced(LoopSuccess(message), resequencerCounter, processor, sender)
      resequencerCounter += 1
  }

  //#journal-plugin-api
  /**
   * Plugin API: asynchronously writes a batch of persistent messages to the journal.
   * The batch write must be atomic i.e. either all persistent messages in the batch
   * are written or none.
   */
  def writeAsync(persistentBatch: immutable.Seq[PersistentRepr]): Future[Unit]

  /**
   * Plugin API: asynchronously deletes all persistent messages within the range from
   * `fromSequenceNr` to `toSequenceNr` (both inclusive). If `permanent` is set to
   * `false`, the persistent messages are marked as deleted, otherwise they are
   * permanently deleted.
   *
   * @see [[AsyncReplay]]
   */
  def deleteAsync(processorId: String, fromSequenceNr: Long, toSequenceNr: Long, permanent: Boolean): Future[Unit]

  /**
   * Plugin API: asynchronously writes a delivery confirmation to the journal.
   */
  def confirmAsync(processorId: String, sequenceNr: Long, channelId: String): Future[Unit]
  //#journal-plugin-api
}

/**
 * INTERNAL API.
 */
private[persistence] object AsyncWriteJournal {
  case class Desequenced(msg: Any, snr: Long, target: ActorRef, sender: ActorRef)

  class Resequencer extends Actor {
    import scala.collection.mutable.Map

    private val delayed = Map.empty[Long, Desequenced]
    private var delivered = 0L

    def receive = {
      case d: Desequenced ⇒ resequence(d)
    }

    @scala.annotation.tailrec
    private def resequence(d: Desequenced) {
      if (d.snr == delivered + 1) {
        delivered = d.snr
        d.target tell (d.msg, d.sender)
      } else {
        delayed += (d.snr -> d)
      }
      val ro = delayed.remove(delivered + 1)
      if (ro.isDefined) resequence(ro.get)
    }
  }
}