reply to known shard locations immediately when waitingForUpdate, #24064

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ShardCoordinator.scala

@@ -478,34 +478,23 @@ abstract class ShardCoordinator(typeName: String, settings: ClusterShardingSetti
       }
 
     case GetShardHome(shard) ⇒
-      if (rebalanceInProgress.contains(shard)) {
-        log.debug("GetShardHome [{}] request ignored, because rebalance is in progress for this shard.", shard)
-      } else if (!hasAllRegionsRegistered()) {
-        log.debug("GetShardHome [{}] request ignored, because not all regions have registered yet.", shard)
-      } else {
-        state.shards.get(shard) match {
-          case Some(ref) ⇒
-            if (regionTerminationInProgress(ref))
-              log.debug("GetShardHome [{}] request ignored, due to region [{}] termination in progress.", shard, ref)
-            else
-              sender() ! ShardHome(shard, ref)
-          case None ⇒
-            val activeRegions = state.regions -- gracefulShutdownInProgress
-            if (activeRegions.nonEmpty) {
-              val getShardHomeSender = sender()
-              val regionFuture = allocationStrategy.allocateShard(getShardHomeSender, shard, activeRegions)
-              regionFuture.value match {
-                case Some(Success(region)) ⇒
-                  continueGetShardHome(shard, region, getShardHomeSender)
-                case _ ⇒
-                  // continue when future is completed
-                  regionFuture.map { region ⇒
-                    AllocateShardResult(shard, Some(region), getShardHomeSender)
-                  }.recover {
-                    case _ ⇒ AllocateShardResult(shard, None, getShardHomeSender)
-                  }.pipeTo(self)
-              }
-            }
+      if (!handleGetShardHome(shard)) {
+        // location not know, yet
+        val activeRegions = state.regions -- gracefulShutdownInProgress
+        if (activeRegions.nonEmpty) {
+          val getShardHomeSender = sender()
+          val regionFuture = allocationStrategy.allocateShard(getShardHomeSender, shard, activeRegions)
+          regionFuture.value match {
+            case Some(Success(region)) ⇒
+              continueGetShardHome(shard, region, getShardHomeSender)
+            case _ ⇒
+              // continue when future is completed
+              regionFuture.map { region ⇒
+                AllocateShardResult(shard, Some(region), getShardHomeSender)
+              }.recover {
+                case _ ⇒ AllocateShardResult(shard, None, getShardHomeSender)
+              }.pipeTo(self)
+          }
         }
       }
 
@@ -610,6 +599,31 @@ abstract class ShardCoordinator(typeName: String, settings: ClusterShardingSetti
 
   }: Receive).orElse[Any, Unit](receiveTerminated)
 
+  /**
+   * @return `true` if the message could be handled without state update, i.e.
+   *         the shard location was known or the request was ignored
+   */
+  def handleGetShardHome(shard: String): Boolean = {
+    if (rebalanceInProgress.contains(shard)) {
+      log.debug("GetShardHome [{}] request ignored, because rebalance is in progress for this shard.", shard)
+      true
+    } else if (!hasAllRegionsRegistered()) {
+      log.debug("GetShardHome [{}] request ignored, because not all regions have registered yet.", shard)
+      true
+    } else {
+      state.shards.get(shard) match {
+        case Some(ref) ⇒
+          if (regionTerminationInProgress(ref))
+            log.debug("GetShardHome [{}] request ignored, due to region [{}] termination in progress.", shard, ref)
+          else
+            sender() ! ShardHome(shard, ref)
+          true
+        case None ⇒
+          false // location not known, yet, caller will handle allocation
+      }
+    }
+  }
+
   def receiveTerminated: Receive = {
     case t @ Terminated(ref) ⇒
       if (state.regions.contains(ref)) {
@@ -1010,6 +1024,10 @@ class DDataShardCoordinator(typeName: String, settings: ClusterShardingSettings,
         key, error, evt)
       throw cause
 
+    case GetShardHome(shard) ⇒
+      if (!handleGetShardHome(shard))
+        stash() // must wait for update that is in progress
+
     case _ ⇒ stash()
   }
 

akka-cluster-sharding/src/multi-jvm/scala/akka/cluster/sharding/ClusterShardingSingleShardPerEntitySpec.scala

@@ -0,0 +1,138 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package akka.cluster.sharding
+
+import scala.concurrent.duration._
+
+import akka.actor._
+import akka.cluster.Cluster
+import akka.cluster.MultiNodeClusterSpec
+import akka.remote.testconductor.RoleName
+import akka.remote.testkit.MultiNodeConfig
+import akka.remote.testkit.MultiNodeSpec
+import akka.remote.testkit.STMultiNodeSpec
+import akka.remote.transport.ThrottlerTransportAdapter.Direction
+import akka.testkit._
+import com.typesafe.config.ConfigFactory
+
+/**
+ * one-to-one mapping between shards and entities is not efficient but some use that anyway
+ */
+object ClusterShardingSingleShardPerEntitySpec {
+  class Entity extends Actor {
+    def receive = {
+      case id: Int ⇒ sender() ! id
+    }
+  }
+
+  val extractEntityId: ShardRegion.ExtractEntityId = {
+    case id: Int ⇒ (id.toString, id)
+  }
+
+  val extractShardId: ShardRegion.ExtractShardId = {
+    case id: Int ⇒ id.toString
+  }
+
+}
+
+object ClusterShardingSingleShardPerEntitySpecConfig extends MultiNodeConfig {
+  val first = role("first")
+  val second = role("second")
+  val third = role("third")
+  val fourth = role("fourth")
+  val fifth = role("fifth")
+
+  commonConfig(ConfigFactory.parseString(s"""
+    akka.loglevel = INFO
+    akka.actor.provider = "cluster"
+    akka.cluster.sharding.state-store-mode = ddata
+    akka.cluster.sharding.updating-state-timeout = 1s
+    """).withFallback(MultiNodeClusterSpec.clusterConfig))
+
+  testTransport(on = true)
+}
+
+class ClusterShardingSingleShardPerEntitySpecMultiJvmNode1 extends ClusterShardingSingleShardPerEntitySpec
+class ClusterShardingSingleShardPerEntitySpecMultiJvmNode2 extends ClusterShardingSingleShardPerEntitySpec
+class ClusterShardingSingleShardPerEntitySpecMultiJvmNode3 extends ClusterShardingSingleShardPerEntitySpec
+class ClusterShardingSingleShardPerEntitySpecMultiJvmNode4 extends ClusterShardingSingleShardPerEntitySpec
+class ClusterShardingSingleShardPerEntitySpecMultiJvmNode5 extends ClusterShardingSingleShardPerEntitySpec
+
+abstract class ClusterShardingSingleShardPerEntitySpec extends MultiNodeSpec(ClusterShardingSingleShardPerEntitySpecConfig)
+  with STMultiNodeSpec with ImplicitSender {
+  import ClusterShardingSingleShardPerEntitySpec._
+  import ClusterShardingSingleShardPerEntitySpecConfig._
+
+  override def initialParticipants = roles.size
+
+  def join(from: RoleName, to: RoleName): Unit = {
+    runOn(from) {
+      Cluster(system) join node(to).address
+      startSharding()
+    }
+    enterBarrier(from.name + "-joined")
+  }
+
+  def startSharding(): Unit = {
+    ClusterSharding(system).start(
+      typeName = "Entity",
+      entityProps = Props[Entity],
+      settings = ClusterShardingSettings(system),
+      extractEntityId = extractEntityId,
+      extractShardId = extractShardId)
+  }
+
+  lazy val region = ClusterSharding(system).shardRegion("Entity")
+
+  def joinAndAllocate(node: RoleName, entityId: Int): Unit = {
+    within(10.seconds) {
+      join(node, first)
+      runOn(node) {
+        region ! entityId
+        expectMsg(entityId)
+        lastSender.path should be(region.path / s"$entityId" / s"$entityId")
+      }
+    }
+    enterBarrier(s"started-$entityId")
+  }
+
+  s"Cluster sharding with single shard per entity" must {
+
+    "use specified region" in {
+      joinAndAllocate(first, 1)
+      joinAndAllocate(second, 2)
+      joinAndAllocate(third, 3)
+      joinAndAllocate(fourth, 4)
+      joinAndAllocate(fifth, 5)
+
+      runOn(first) {
+        // coordinator is on 'first', blackhole 3 other means that it can't update with WriteMajority
+        testConductor.blackhole(first, third, Direction.Both).await
+        testConductor.blackhole(first, fourth, Direction.Both).await
+        testConductor.blackhole(first, fifth, Direction.Both).await
+
+        // shard 6 not allocated yet and due to the blackhole it will not be completed
+        region ! 6
+
+        // shard 1 location is know by 'first' region, not involving coordinator
+        region ! 1
+        expectMsg(1)
+
+        // shard 2 location not known at 'first' region yet, but coordinator is on 'first' and should
+        // be able to answer GetShardHome even though previous request for shard 4 has not completed yet
+        region ! 2
+        expectMsg(2)
+        lastSender.path should be(node(second) / "system" / "sharding" / "Entity" / "2" / "2")
+
+        testConductor.passThrough(first, third, Direction.Both).await
+        testConductor.passThrough(first, fourth, Direction.Both).await
+        testConductor.passThrough(first, fifth, Direction.Both).await
+        expectMsg(10.seconds, 6)
+      }
+
+      enterBarrier("after-1")
+    }
+
+  }
+}