From d5f81e19d1417fa00921a838968d76beb85334a3 Mon Sep 17 00:00:00 2001
From: Alexander Golubev <alexander.golubev@gmail.com>
Date: Sat, 16 Jan 2016 12:17:19 -0500
Subject: [PATCH] =str #18890 Polish Source.queue

---
 .../engine/client/PoolInterfaceActor.scala    |   2 +-
 .../scaladsl/AcknowledgeSourceSpec.scala      |  96 --------
 .../akka/stream/scaladsl/FlowBufferSpec.scala |   3 +-
 .../akka/stream/scaladsl/FlowDelaySpec.scala  |   4 +-
 .../akka/stream/scaladsl/QueueSinkSpec.scala  |  17 +-
 .../stream/scaladsl/QueueSourceSpec.scala     | 228 ++++++++++++++++++
 .../scala/akka/stream/OverflowStrategy.scala  |  48 ++--
 .../src/main/scala/akka/stream/Queue.scala    |  46 +++-
 .../stream/impl/AcknowledgePublisher.scala    |  92 -------
 .../stream/impl/ActorRefSourceActor.scala     |   9 +-
 .../main/scala/akka/stream/impl/Modules.scala |  36 +--
 .../main/scala/akka/stream/impl/Sinks.scala   |  27 +--
 .../main/scala/akka/stream/impl/Sources.scala | 127 ++++++++++
 .../main/scala/akka/stream/impl/Stages.scala  |   2 +-
 .../scala/akka/stream/impl/fusing/Ops.scala   |  30 ++-
 .../scala/akka/stream/javadsl/Source.scala    |  34 +--
 .../scala/akka/stream/scaladsl/Flow.scala     |   4 +-
 .../scala/akka/stream/scaladsl/Source.scala   |  34 +--
 .../scala/akka/stream/stage/GraphStage.scala  |  58 ++++-
 19 files changed, 565 insertions(+), 332 deletions(-)
 delete mode 100644 akka-stream-tests/src/test/scala/akka/stream/scaladsl/AcknowledgeSourceSpec.scala
 create mode 100644 akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSourceSpec.scala
 delete mode 100644 akka-stream/src/main/scala/akka/stream/impl/AcknowledgePublisher.scala
 create mode 100644 akka-stream/src/main/scala/akka/stream/impl/Sources.scala

diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/client/PoolInterfaceActor.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/client/PoolInterfaceActor.scala
index 51317681f8..a89c87ceef 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/client/PoolInterfaceActor.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/client/PoolInterfaceActor.scala
@@ -6,7 +6,7 @@ package akka.http.impl.engine.client
 
 import java.net.InetSocketAddress
 
-import akka.stream.OverflowStrategy.Fail.BufferOverflowException
+import akka.stream.BufferOverflowException
 
 import scala.annotation.tailrec
 import scala.concurrent.Promise
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/AcknowledgeSourceSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/AcknowledgeSourceSpec.scala
deleted file mode 100644
index 8c394c9b5c..0000000000
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/AcknowledgeSourceSpec.scala
+++ /dev/null
@@ -1,96 +0,0 @@
-/**
- * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
- */
-package akka.stream.scaladsl
-
-import akka.stream.testkit.Utils._
-import akka.stream.testkit.{ AkkaSpec, TestSubscriber }
-import akka.stream.{ ActorMaterializer, OverflowStrategy }
-import scala.concurrent.Future
-import scala.concurrent.duration._
-import scala.concurrent._
-import akka.pattern.pipe
-
-class AcknowledgeSourceSpec extends AkkaSpec {
-  implicit val materializer = ActorMaterializer()
-  implicit val ec = system.dispatcher
-
-  def assertSuccess(b: Boolean, fb: Future[Boolean]): Unit =
-    Await.result(fb, 1.second) should be(b)
-
-  "A AcknowledgeSource" must {
-
-    "emit received messages to the stream" in {
-      val s = TestSubscriber.manualProbe[Int]()
-      val queue = Source.queue(10, OverflowStrategy.fail).to(Sink.fromSubscriber(s)).run()
-      val sub = s.expectSubscription
-      sub.request(2)
-      assertSuccess(true, queue.offer(1))
-      s.expectNext(1)
-      assertSuccess(true, queue.offer(2))
-      s.expectNext(2)
-      assertSuccess(true, queue.offer(3))
-      sub.cancel()
-    }
-
-    "buffer when needed" in {
-      val s = TestSubscriber.manualProbe[Int]()
-      val queue = Source.queue(100, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
-      val sub = s.expectSubscription
-      for (n ← 1 to 20) assertSuccess(true, queue.offer(n))
-      sub.request(10)
-      for (n ← 1 to 10) assertSuccess(true, queue.offer(n))
-      sub.request(10)
-      for (n ← 11 to 20) assertSuccess(true, queue.offer(n))
-
-      for (n ← 200 to 399) assertSuccess(true, queue.offer(n))
-      sub.request(100)
-      for (n ← 300 to 399) assertSuccess(true, queue.offer(n))
-      sub.cancel()
-    }
-
-    "not fail when 0 buffer space and demand is signalled" in assertAllStagesStopped {
-      val s = TestSubscriber.manualProbe[Int]()
-      val queue = Source.queue(0, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
-      val sub = s.expectSubscription
-      sub.request(1)
-      assertSuccess(true, queue.offer(1))
-      s.expectNext(1)
-      sub.cancel()
-    }
-
-    "return false when can reject element to buffer" in assertAllStagesStopped {
-      val s = TestSubscriber.manualProbe[Int]()
-      val queue = Source.queue(1, OverflowStrategy.dropNew).to(Sink.fromSubscriber(s)).run()
-      val sub = s.expectSubscription
-      assertSuccess(true, queue.offer(1))
-      assertSuccess(false, queue.offer(2))
-      sub.request(1)
-      s.expectNext(1)
-      sub.cancel()
-    }
-
-    "wait when buffer is full and backpressure is on" in assertAllStagesStopped {
-      val s = TestSubscriber.manualProbe[Int]()
-      val queue = Source.queue(2, OverflowStrategy.backpressure).to(Sink.fromSubscriber(s)).run()
-      val sub = s.expectSubscription
-      assertSuccess(true, queue.offer(1))
-
-      val addedSecond = queue.offer(2)
-
-      addedSecond.pipeTo(testActor)
-      expectNoMsg(300.millis)
-
-      sub.request(1)
-      s.expectNext(1)
-      assertSuccess(true, addedSecond)
-
-      sub.request(1)
-      s.expectNext(2)
-
-      sub.cancel()
-    }
-
-  }
-
-}
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowBufferSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowBufferSpec.scala
index 283a907360..a3222867c3 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowBufferSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowBufferSpec.scala
@@ -6,8 +6,7 @@ package akka.stream.scaladsl
 import scala.concurrent.Await
 import scala.concurrent.Future
 import scala.concurrent.duration._
-import akka.stream.{ ActorMaterializer, ActorMaterializerSettings, OverflowStrategy }
-import akka.stream.OverflowStrategy.Fail.BufferOverflowException
+import akka.stream.{ BufferOverflowException, ActorMaterializer, ActorMaterializerSettings, OverflowStrategy }
 import akka.stream.testkit._
 import akka.stream.testkit.scaladsl._
 import akka.stream.testkit.Utils._
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowDelaySpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowDelaySpec.scala
index 0cb262bbd9..8c0dc7b7b5 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowDelaySpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowDelaySpec.scala
@@ -7,7 +7,7 @@ import akka.stream.Attributes._
 import akka.stream.testkit.Utils._
 import akka.stream.testkit.scaladsl.TestSink
 import akka.stream.testkit.{ AkkaSpec, TestPublisher, TestSubscriber }
-import akka.stream.{ DelayOverflowStrategy, ActorMaterializer }
+import akka.stream.{ BufferOverflowException, DelayOverflowStrategy, ActorMaterializer }
 
 import scala.concurrent.Await
 import scala.concurrent.duration._
@@ -103,7 +103,7 @@ class FlowDelaySpec extends AkkaSpec {
         .withAttributes(inputBuffer(16, 16))
         .runWith(TestSink.probe[Int])
         .request(100)
-        .expectError(new DelayOverflowStrategy.Fail.BufferOverflowException("Buffer overflow for delay combinator (max capacity was: 16)!"))
+        .expectError(new BufferOverflowException("Buffer overflow for delay combinator (max capacity was: 16)!"))
 
     }
 
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSinkSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSinkSpec.scala
index 2249f82c13..2c6b927e11 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSinkSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSinkSpec.scala
@@ -5,7 +5,7 @@ package akka.stream.scaladsl
 
 import akka.actor.Status
 import akka.pattern.pipe
-import akka.stream.ActorMaterializer
+import akka.stream.{ OverflowStrategy, ActorMaterializer }
 import akka.stream.testkit.Utils._
 import akka.stream.testkit.{ AkkaSpec, _ }
 
@@ -97,5 +97,20 @@ class QueueSinkSpec extends AkkaSpec {
       queue.pull()
     }
 
+    "fail pull future when stream is completed" in assertAllStagesStopped {
+      val probe = TestPublisher.manualProbe[Int]()
+      val queue = Source.fromPublisher(probe).runWith(Sink.queue())
+      val sub = probe.expectSubscription()
+
+      queue.pull().pipeTo(testActor)
+      sub.sendNext(1)
+      expectMsg(Some(1))
+
+      sub.sendComplete()
+      Await.result(queue.pull(), noMsgTimeout) should be(None)
+
+      queue.pull().onFailure { case e ⇒ e.isInstanceOf[IllegalStateException] should ===(true) }
+    }
+
   }
 }
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSourceSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSourceSpec.scala
new file mode 100644
index 0000000000..be9605a319
--- /dev/null
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/QueueSourceSpec.scala
@@ -0,0 +1,228 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.stream.scaladsl
+
+import akka.actor.{ NoSerializationVerificationNeeded, Status }
+import akka.pattern.pipe
+import akka.stream._
+import akka.stream.impl.QueueSource
+import akka.stream.stage.OutHandler
+import akka.stream.testkit.Utils._
+import akka.stream.testkit.{ AkkaSpec, TestSubscriber }
+import akka.testkit.TestProbe
+
+import scala.concurrent.duration._
+import scala.concurrent.{ Future, _ }
+
+class QueueSourceSpec extends AkkaSpec {
+  implicit val materializer = ActorMaterializer()
+  implicit val ec = system.dispatcher
+  val pause = 300.millis
+
+  def assertSuccess(f: Future[QueueOfferResult]): Unit = {
+    f pipeTo testActor
+    expectMsg(QueueOfferResult.Enqueued)
+  }
+
+  object SourceTestMessages {
+    case object Pull extends NoSerializationVerificationNeeded
+    case object Finish extends NoSerializationVerificationNeeded
+  }
+
+  def testSource(maxBuffer: Int, overflowStrategy: OverflowStrategy, probe: TestProbe): Source[Int, SourceQueue[Int]] = {
+    class QueueSourceTestStage(maxBuffer: Int, overflowStrategy: OverflowStrategy)
+      extends QueueSource[Int](maxBuffer, overflowStrategy) {
+
+      override def createLogicAndMaterializedValue(inheritedAttributes: Attributes) = {
+        val (logic, inputStream) = super.createLogicAndMaterializedValue(inheritedAttributes)
+        val outHandler = logic.handlers(out.id).asInstanceOf[OutHandler]
+        logic.handlers(out.id) = new OutHandler {
+          override def onPull(): Unit = {
+            probe.ref ! SourceTestMessages.Pull
+            outHandler.onPull()
+          }
+          override def onDownstreamFinish(): Unit = {
+            probe.ref ! SourceTestMessages.Finish
+            outHandler.onDownstreamFinish()
+          }
+
+        }
+        (logic, inputStream)
+      }
+    }
+    Source.fromGraph(new QueueSourceTestStage(maxBuffer, overflowStrategy))
+  }
+
+  "A QueueSourceSpec" must {
+
+    "emit received messages to the stream" in {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(10, OverflowStrategy.fail).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      for (i ← 1 to 3) {
+        sub.request(1)
+        assertSuccess(queue.offer(i))
+        s.expectNext(i)
+      }
+
+      queue.watchCompletion().pipeTo(testActor)
+      expectNoMsg(pause)
+
+      sub.cancel()
+      expectMsg(())
+    }
+
+    "buffer when needed" in {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(100, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      for (n ← 1 to 20) assertSuccess(queue.offer(n))
+      sub.request(10)
+      for (n ← 1 to 10) assertSuccess(queue.offer(n))
+      sub.request(10)
+      for (n ← 11 to 20) assertSuccess(queue.offer(n))
+
+      for (n ← 200 to 399) assertSuccess(queue.offer(n))
+      sub.request(100)
+      for (n ← 300 to 399) assertSuccess(queue.offer(n))
+      sub.cancel()
+    }
+
+    "not fail when 0 buffer space and demand is signalled" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(0, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      sub.request(1)
+
+      assertSuccess(queue.offer(1))
+
+      sub.cancel()
+    }
+
+    "wait for demand when buffer is 0" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(0, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      queue.offer(1).pipeTo(testActor)
+      expectNoMsg(pause)
+      sub.request(1)
+      expectMsg(QueueOfferResult.Enqueued)
+      s.expectNext(1)
+      sub.cancel()
+    }
+
+    "finish offer and complete futures when stream completed" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(0, OverflowStrategy.dropHead).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+
+      queue.watchCompletion.pipeTo(testActor)
+      queue.offer(1) pipeTo testActor
+      expectNoMsg(pause)
+
+      sub.cancel()
+
+      expectMsgAllOf(QueueOfferResult.QueueClosed, ())
+    }
+
+    "fail stream on buffer overflow in fail mode" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(1, OverflowStrategy.fail).to(Sink.fromSubscriber(s)).run()
+      s.expectSubscription
+
+      queue.offer(1)
+      queue.offer(2)
+      s.expectError()
+    }
+
+    "remember pull from downstream to send offered element immediately" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val probe = TestProbe()
+      val queue = testSource(1, OverflowStrategy.dropHead, probe).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+
+      sub.request(1)
+      probe.expectMsg(SourceTestMessages.Pull)
+      assertSuccess(queue.offer(1))
+      s.expectNext(1)
+      sub.cancel()
+    }
+
+    "fail offer future if user does not wait in backpressure mode" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(5, OverflowStrategy.backpressure).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+
+      for (i ← 1 to 5) assertSuccess(queue.offer(i))
+
+      queue.offer(6).pipeTo(testActor)
+      expectNoMsg(pause)
+
+      val future = queue.offer(7)
+      future.onFailure { case e ⇒ e.isInstanceOf[IllegalStateException] should ===(true) }
+      future.onSuccess { case _ ⇒ fail() }
+      Await.ready(future, pause)
+
+      sub.request(1)
+      s.expectNext(1)
+      expectMsg(QueueOfferResult.Enqueued)
+      sub.cancel()
+    }
+
+    "complete watching future with failure if stream failed" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(1, OverflowStrategy.fail).to(Sink.fromSubscriber(s)).run()
+      queue.watchCompletion().pipeTo(testActor)
+      queue.offer(1) //need to wait when first offer is done as initialization can be done in this moment
+      queue.offer(2)
+      expectMsgClass(classOf[Status.Failure])
+    }
+
+    "return false when elemen was not added to buffer" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(1, OverflowStrategy.dropNew).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+
+      queue.offer(1)
+      queue.offer(2) pipeTo testActor
+      expectMsg(QueueOfferResult.Dropped)
+
+      sub.request(1)
+      s.expectNext(1)
+      sub.cancel()
+    }
+
+    "wait when buffer is full and backpressure is on" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(1, OverflowStrategy.backpressure).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      assertSuccess(queue.offer(1))
+
+      queue.offer(2) pipeTo testActor
+      expectNoMsg(pause)
+
+      sub.request(1)
+      s.expectNext(1)
+
+      sub.request(1)
+      s.expectNext(2)
+      expectMsg(QueueOfferResult.Enqueued)
+
+      sub.cancel()
+    }
+
+    "fail offer future when stream is completed" in assertAllStagesStopped {
+      val s = TestSubscriber.manualProbe[Int]()
+      val queue = Source.queue(1, OverflowStrategy.dropNew).to(Sink.fromSubscriber(s)).run()
+      val sub = s.expectSubscription
+      queue.watchCompletion().pipeTo(testActor)
+      sub.cancel()
+      expectMsg(())
+
+      queue.offer(1).onFailure { case e ⇒ e.isInstanceOf[IllegalStateException] should ===(true) }
+    }
+
+  }
+
+}
diff --git a/akka-stream/src/main/scala/akka/stream/OverflowStrategy.scala b/akka-stream/src/main/scala/akka/stream/OverflowStrategy.scala
index 25f0fb5c89..e900d46e2f 100644
--- a/akka-stream/src/main/scala/akka/stream/OverflowStrategy.scala
+++ b/akka-stream/src/main/scala/akka/stream/OverflowStrategy.scala
@@ -3,48 +3,53 @@
  */
 package akka.stream
 
+import OverflowStrategies._
+
 /**
- * Represents a strategy that decides how to deal with a buffer that is full but is about to receive a new element.
+ * Represents a strategy that decides how to deal with a buffer of time based stage
+ * that is full but is about to receive a new element.
  */
-sealed abstract class OverflowStrategy extends Serializable
-sealed trait DelayOverflowStrategy extends Serializable
+sealed abstract class DelayOverflowStrategy extends Serializable
 
-private[akka] trait BaseOverflowStrategy {
+final case class BufferOverflowException(msg: String) extends RuntimeException(msg)
+/**
+ * Represents a strategy that decides how to deal with a buffer that is full but is
+ * about to receive a new element.
+ */
+sealed abstract class OverflowStrategy extends DelayOverflowStrategy
 
+private[akka] object OverflowStrategies {
   /**
    * INTERNAL API
    */
-  private[akka] case object DropHead extends OverflowStrategy with DelayOverflowStrategy
-
+  private[akka] case object DropHead extends OverflowStrategy
   /**
    * INTERNAL API
    */
-  private[akka] case object DropTail extends OverflowStrategy with DelayOverflowStrategy
-
+  private[akka] case object DropTail extends OverflowStrategy
   /**
    * INTERNAL API
    */
-  private[akka] case object DropBuffer extends OverflowStrategy with DelayOverflowStrategy
-
+  private[akka] case object DropBuffer extends OverflowStrategy
   /**
    * INTERNAL API
    */
-  private[akka] case object DropNew extends OverflowStrategy with DelayOverflowStrategy
-
+  private[akka] case object DropNew extends OverflowStrategy
   /**
    * INTERNAL API
    */
-  private[akka] case object Backpressure extends OverflowStrategy with DelayOverflowStrategy
-
+  private[akka] case object Backpressure extends OverflowStrategy
   /**
    * INTERNAL API
    */
-  private[akka] case object Fail extends OverflowStrategy with DelayOverflowStrategy {
-    final case class BufferOverflowException(msg: String) extends RuntimeException(msg)
-  }
+  private[akka] case object Fail extends OverflowStrategy
+  /**
+   * INTERNAL API
+   */
+  private[akka] case object EmitEarly extends DelayOverflowStrategy
 }
 
-object OverflowStrategy extends BaseOverflowStrategy {
+object OverflowStrategy {
   /**
    * If the buffer is full when a new element arrives, drops the oldest element from the buffer to make space for
    * the new element.
@@ -79,12 +84,7 @@ object OverflowStrategy extends BaseOverflowStrategy {
   def fail: OverflowStrategy = Fail
 }
 
-object DelayOverflowStrategy extends BaseOverflowStrategy {
-  /**
-   * INTERNAL API
-   */
-  private[akka] case object EmitEarly extends DelayOverflowStrategy
-
+object DelayOverflowStrategy {
   /**
    * If the buffer is full when a new element is available this strategy send next element downstream without waiting
    */
diff --git a/akka-stream/src/main/scala/akka/stream/Queue.scala b/akka-stream/src/main/scala/akka/stream/Queue.scala
index 919edba4f3..ddd9eed8d5 100644
--- a/akka-stream/src/main/scala/akka/stream/Queue.scala
+++ b/akka-stream/src/main/scala/akka/stream/Queue.scala
@@ -12,13 +12,21 @@ trait SourceQueue[T] {
 
   /**
    * Method offers next element to a stream and returns future that:
-   * - competes with true if element is consumed by a stream
-   * - competes with false when stream dropped offered element
-   * - fails if stream is completed or cancelled.
+   * - completes with `Enqueued` if element is consumed by a stream
+   * - completes with `Dropped` when stream dropped offered element
+   * - completes with `QueueClosed` when stream is completed during future is active
+   * - completes with `Failure(f)` when failure to enqueue element from upstream
+   * - fails when stream is completed or you cannot call offer in this moment because of implementation rules
+   * (like for backpressure mode and full buffer you need to wait for last offer call Future completion)
    *
    * @param elem element to send to a stream
    */
-  def offer(elem: T): Future[Boolean]
+  def offer(elem: T): Future[QueueOfferResult]
+
+  /**
+   * Method returns future that completes when stream is completed and fails when stream failed
+   */
+  def watchCompletion(): Future[Unit]
 }
 
 /**
@@ -35,3 +43,33 @@ trait SinkQueue[T] {
    */
   def pull(): Future[Option[T]]
 }
+
+sealed abstract class QueueOfferResult
+
+/**
+ * Contains types that is used as return types for async callbacks to streams
+ */
+object QueueOfferResult {
+
+  /**
+   * Type is used to indicate that stream is successfully enqueued an element
+   */
+  final case object Enqueued extends QueueOfferResult
+
+  /**
+   * Type is used to indicate that stream is dropped an element
+   */
+  final case object Dropped extends QueueOfferResult
+
+  /**
+   * Type is used to indicate that stream is failed before or during call to the stream
+   * @param cause - exception that stream failed with
+   */
+  final case class Failure(cause: Throwable) extends QueueOfferResult
+
+  /**
+   * Type is used to indicate that stream is completed before call
+   */
+  case object QueueClosed extends QueueOfferResult
+}
+
diff --git a/akka-stream/src/main/scala/akka/stream/impl/AcknowledgePublisher.scala b/akka-stream/src/main/scala/akka/stream/impl/AcknowledgePublisher.scala
deleted file mode 100644
index 1f7ed0e1e1..0000000000
--- a/akka-stream/src/main/scala/akka/stream/impl/AcknowledgePublisher.scala
+++ /dev/null
@@ -1,92 +0,0 @@
-/**
- * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
- */
-package akka.stream.impl
-
-import akka.actor.{ ActorRef, Props }
-import akka.stream.OverflowStrategy
-import akka.stream.OverflowStrategy._
-import akka.stream.actor.ActorPublisherMessage.Request
-import akka.stream.impl.AcknowledgePublisher.{ Rejected, Ok }
-
-/**
- * INTERNAL API
- */
-private[akka] object AcknowledgePublisher {
-  def props(bufferSize: Int, overflowStrategy: OverflowStrategy) =
-    Props(new AcknowledgePublisher(bufferSize, overflowStrategy))
-
-  case class Ok()
-  case class Rejected()
-}
-
-/**
- * INTERNAL API
- */
-private[akka] class AcknowledgePublisher(bufferSize: Int, overflowStrategy: OverflowStrategy)
-  extends ActorRefSourceActor(bufferSize, overflowStrategy) {
-
-  var backpressedElem: Option[ActorRef] = None
-
-  override def requestElem: Receive = {
-    case _: Request ⇒
-      // totalDemand is tracked by super
-      if (bufferSize != 0)
-        while (totalDemand > 0L && !buffer.isEmpty) {
-          //if buffer is full - sent ack message to sender in case of Backpressure mode
-          if (buffer.isFull) backpressedElem match {
-            case Some(ref) ⇒
-              ref ! Ok(); backpressedElem = None
-            case None ⇒ //do nothing
-          }
-          onNext(buffer.dequeue())
-        }
-  }
-
-  override def receiveElem: Receive = {
-    case elem if isActive ⇒
-      if (totalDemand > 0L) {
-        onNext(elem)
-        sendAck(true)
-      } else if (bufferSize == 0) {
-        log.debug("Dropping element because there is no downstream demand: [{}]", elem)
-        sendAck(false)
-      } else if (!buffer.isFull)
-        enqueueAndSendAck(elem)
-      else (overflowStrategy: @unchecked) match {
-        case DropHead ⇒
-          log.debug("Dropping the head element because buffer is full and overflowStrategy is: [DropHead]")
-          buffer.dropHead()
-          enqueueAndSendAck(elem)
-        case DropTail ⇒
-          log.debug("Dropping the tail element because buffer is full and overflowStrategy is: [DropTail]")
-          buffer.dropTail()
-          enqueueAndSendAck(elem)
-        case DropBuffer ⇒
-          log.debug("Dropping all the buffered elements because buffer is full and overflowStrategy is: [DropBuffer]")
-          buffer.clear()
-          enqueueAndSendAck(elem)
-        case DropNew ⇒
-          log.debug("Dropping the new element because buffer is full and overflowStrategy is: [DropNew]")
-          sendAck(false)
-        case Fail ⇒
-          log.error("Failing because buffer is full and overflowStrategy is: [Fail]")
-          onErrorThenStop(new Fail.BufferOverflowException(s"Buffer overflow (max capacity was: $bufferSize)!"))
-        case Backpressure ⇒
-          log.debug("Backpressuring because buffer is full and overflowStrategy is: [Backpressure]")
-          sendAck(false) //does not allow to send more than buffer size
-      }
-  }
-
-  def enqueueAndSendAck(elem: Any): Unit = {
-    buffer.enqueue(elem)
-    if (buffer.isFull && overflowStrategy == Backpressure) backpressedElem = Some(sender)
-    else sendAck(true)
-  }
-
-  def sendAck(isOk: Boolean): Unit = {
-    val msg = if (isOk) Ok() else Rejected()
-    context.sender() ! msg
-  }
-
-}
diff --git a/akka-stream/src/main/scala/akka/stream/impl/ActorRefSourceActor.scala b/akka-stream/src/main/scala/akka/stream/impl/ActorRefSourceActor.scala
index 1e9c35ed4e..32dabdbe10 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/ActorRefSourceActor.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/ActorRefSourceActor.scala
@@ -6,14 +6,15 @@ package akka.stream.impl
 import akka.actor.ActorLogging
 import akka.actor.Props
 import akka.actor.Status
-import akka.stream.OverflowStrategy
+import akka.stream.OverflowStrategies._
+import akka.stream.{ BufferOverflowException, OverflowStrategy, OverflowStrategies }
 
 /**
  * INTERNAL API
  */
 private[akka] object ActorRefSourceActor {
   def props(bufferSize: Int, overflowStrategy: OverflowStrategy) = {
-    require(overflowStrategy != OverflowStrategy.Backpressure, "Backpressure overflowStrategy not supported")
+    require(overflowStrategy != OverflowStrategies.Backpressure, "Backpressure overflowStrategy not supported")
     Props(new ActorRefSourceActor(bufferSize, overflowStrategy))
   }
 }
@@ -58,7 +59,7 @@ private[akka] class ActorRefSourceActor(bufferSize: Int, overflowStrategy: Overf
         log.debug("Dropping element because there is no downstream demand: [{}]", elem)
       else if (!buffer.isFull)
         buffer.enqueue(elem)
-      else (overflowStrategy: @unchecked) match {
+      else overflowStrategy match {
         case DropHead ⇒
           log.debug("Dropping the head element because buffer is full and overflowStrategy is: [DropHead]")
           buffer.dropHead()
@@ -76,7 +77,7 @@ private[akka] class ActorRefSourceActor(bufferSize: Int, overflowStrategy: Overf
           log.debug("Dropping the new element because buffer is full and overflowStrategy is: [DropNew]")
         case Fail ⇒
           log.error("Failing because buffer is full and overflowStrategy is: [Fail]")
-          onErrorThenStop(new Fail.BufferOverflowException(s"Buffer overflow (max capacity was: $bufferSize)!"))
+          onErrorThenStop(new BufferOverflowException(s"Buffer overflow (max capacity was: $bufferSize)!"))
         case Backpressure ⇒
           // there is a precondition check in Source.actorRefSource factory method
           log.debug("Backpressuring because buffer is full and overflowStrategy is: [Backpressure]")
diff --git a/akka-stream/src/main/scala/akka/stream/impl/Modules.scala b/akka-stream/src/main/scala/akka/stream/impl/Modules.scala
index 1f5a737656..90455ebf6e 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/Modules.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/Modules.scala
@@ -3,19 +3,14 @@
  */
 package akka.stream.impl
 
-import java.util.concurrent.atomic.AtomicInteger
-
 import akka.NotUsed
 import akka.actor._
 import akka.stream._
-import akka.stream.impl.AcknowledgePublisher.{ Ok, Rejected }
 import akka.stream.impl.StreamLayout.Module
-import akka.util.Timeout
 import org.reactivestreams._
 
 import scala.annotation.unchecked.uncheckedVariance
-import scala.concurrent.duration.{ FiniteDuration, _ }
-import scala.concurrent.{ Future, Promise }
+import scala.concurrent.Promise
 import scala.language.postfixOps
 
 /**
@@ -122,32 +117,3 @@ private[akka] final class ActorRefSource[Out](
   override def withAttributes(attr: Attributes): Module =
     new ActorRefSource(bufferSize, overflowStrategy, attr, amendShape(attr))
 }
-
-/**
- * INTERNAL API
- */
-private[akka] final class AcknowledgeSource[Out](bufferSize: Int, overflowStrategy: OverflowStrategy,
-                                                 val attributes: Attributes, shape: SourceShape[Out],
-                                                 timeout: FiniteDuration = 5 seconds)
-  extends SourceModule[Out, SourceQueue[Out]](shape) {
-
-  override def create(context: MaterializationContext) = {
-    import akka.pattern.ask
-    val ref = ActorMaterializer.downcast(context.materializer).actorOf(context,
-      AcknowledgePublisher.props(bufferSize, overflowStrategy))
-    implicit val t = Timeout(timeout)
-
-    (akka.stream.actor.ActorPublisher[Out](ref), new SourceQueue[Out] {
-      implicit val ctx = context.materializer.executionContext
-      override def offer(out: Out): Future[Boolean] = (ref ? out).map {
-        case Ok()       ⇒ true
-        case Rejected() ⇒ false
-      }
-    })
-  }
-
-  override protected def newInstance(shape: SourceShape[Out]): SourceModule[Out, SourceQueue[Out]] =
-    new AcknowledgeSource[Out](bufferSize, overflowStrategy, attributes, shape, timeout)
-  override def withAttributes(attr: Attributes): Module =
-    new AcknowledgeSource(bufferSize, overflowStrategy, attr, amendShape(attr), timeout)
-}
diff --git a/akka-stream/src/main/scala/akka/stream/impl/Sinks.scala b/akka-stream/src/main/scala/akka/stream/impl/Sinks.scala
index 70ff5b0008..739df1def1 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/Sinks.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/Sinks.scala
@@ -10,7 +10,7 @@ import akka.actor.{ ActorRef, Props }
 import akka.stream.Attributes.InputBuffer
 import akka.stream._
 import akka.stream.impl.StreamLayout.Module
-import akka.stream.stage.{ AsyncCallback, GraphStageLogic, GraphStageWithMaterializedValue, InHandler }
+import akka.stream.stage._
 import org.reactivestreams.{ Publisher, Subscriber }
 
 import scala.annotation.unchecked.uncheckedVariance
@@ -243,11 +243,7 @@ private[akka] final class HeadOptionStage[T] extends GraphStageWithMaterializedV
  * INTERNAL API
  */
 private[akka] class QueueSink[T]() extends GraphStageWithMaterializedValue[SinkShape[T], SinkQueue[T]] {
-  trait RequestElementCallback[E] {
-    val requestElement = new AtomicReference[AnyRef](Nil)
-  }
-
-  type Requested[E] = Promise[Option[T]]
+  type Requested[E] = Promise[Option[E]]
 
   val in = Inlet[T]("queueSink.in")
   override val shape: SinkShape[T] = SinkShape.of(in)
@@ -261,15 +257,17 @@ private[akka] class QueueSink[T]() extends GraphStageWithMaterializedValue[SinkS
     val buffer = FixedSizeBuffer[Received[T]](maxBuffer + 1)
     var currentRequest: Option[Requested[T]] = None
 
-    val stageLogic = new GraphStageLogic(shape) with RequestElementCallback[Requested[T]] {
+    val stageLogic = new GraphStageLogic(shape) with CallbackWrapper[Requested[T]] {
 
       override def preStart(): Unit = {
         setKeepGoing(true)
-        val list = requestElement.getAndSet(callback.invoke _).asInstanceOf[List[Requested[T]]]
-        list.reverse.foreach(callback.invoke)
+        initCallback(callback.invoke)
         pull(in)
       }
 
+      override def postStop(): Unit = stopCallback(promise ⇒
+        promise.failure(new IllegalStateException("Stream is terminated. QueueSink is detached")))
+
       private val callback: AsyncCallback[Requested[T]] =
         getAsyncCallback(promise ⇒ currentRequest match {
           case Some(_) ⇒
@@ -311,17 +309,8 @@ private[akka] class QueueSink[T]() extends GraphStageWithMaterializedValue[SinkS
 
     (stageLogic, new SinkQueue[T] {
       override def pull(): Future[Option[T]] = {
-        val ref = stageLogic.requestElement
         val p = Promise[Option[T]]
-        ref.get() match {
-          case l: List[_] ⇒
-            if (!ref.compareAndSet(l, p :: l))
-              ref.get() match {
-                case _: List[_]         ⇒ throw new IllegalStateException("Concurrent call of SinkQueue.pull() is detected")
-                case f: Function1[_, _] ⇒ f.asInstanceOf[Requested[T] ⇒ Unit](p)
-              }
-          case f: Function1[_, _] ⇒ f.asInstanceOf[Requested[T] ⇒ Unit](p)
-        }
+        stageLogic.invoke(p)
         p.future
       }
     })
diff --git a/akka-stream/src/main/scala/akka/stream/impl/Sources.scala b/akka-stream/src/main/scala/akka/stream/impl/Sources.scala
new file mode 100644
index 0000000000..e3eda50bca
--- /dev/null
+++ b/akka-stream/src/main/scala/akka/stream/impl/Sources.scala
@@ -0,0 +1,127 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.stream.impl
+
+import akka.stream.OverflowStrategies._
+import akka.stream._
+import akka.stream.stage._
+import scala.concurrent.{ Future, Promise }
+
+/**
+ * INTERNAL API
+ */
+private[akka] class QueueSource[T](maxBuffer: Int, overflowStrategy: OverflowStrategy) extends GraphStageWithMaterializedValue[SourceShape[T], SourceQueue[T]] {
+  type Offered = Promise[QueueOfferResult]
+
+  val out = Outlet[T]("queueSource.out")
+  override val shape: SourceShape[T] = SourceShape.of(out)
+  val completion = Promise[Unit]
+
+  override def createLogicAndMaterializedValue(inheritedAttributes: Attributes) = {
+    val stageLogic = new GraphStageLogic(shape) with CallbackWrapper[(T, Offered)] {
+      val buffer = if (maxBuffer == 0) null else FixedSizeBuffer[T](maxBuffer)
+      var pendingOffer: Option[(T, Offered)] = None
+      var pulled = false
+
+      override def preStart(): Unit = initCallback(callback.invoke)
+      override def postStop(): Unit = stopCallback {
+        case (elem, promise) ⇒ promise.failure(new IllegalStateException("Stream is terminated. SourceQueue is detached"))
+      }
+
+      private def enqueueAndSuccess(elem: T, promise: Offered): Unit = {
+        buffer.enqueue(elem)
+        promise.success(QueueOfferResult.Enqueued)
+      }
+
+      private def bufferElem(elem: T, promise: Offered): Unit = {
+        if (!buffer.isFull) {
+          enqueueAndSuccess(elem, promise)
+        } else overflowStrategy match {
+          case DropHead ⇒
+            buffer.dropHead()
+            enqueueAndSuccess(elem, promise)
+          case DropTail ⇒
+            buffer.dropTail()
+            enqueueAndSuccess(elem, promise)
+          case DropBuffer ⇒
+            buffer.clear()
+            enqueueAndSuccess(elem, promise)
+          case DropNew ⇒
+            promise.success(QueueOfferResult.Dropped)
+          case Fail ⇒
+            val bufferOverflowException = new BufferOverflowException(s"Buffer overflow (max capacity was: $maxBuffer)!")
+            promise.success(QueueOfferResult.Failure(bufferOverflowException))
+            completion.failure(bufferOverflowException)
+            failStage(bufferOverflowException)
+          case Backpressure ⇒
+            pendingOffer match {
+              case Some(_) ⇒
+                promise.failure(new IllegalStateException("You have to wait for previous offer to be resolved to send another request"))
+              case None ⇒
+                pendingOffer = Some((elem, promise))
+            }
+        }
+      }
+
+      private val callback: AsyncCallback[(T, Offered)] = getAsyncCallback(tuple ⇒ {
+        val (elem, promise) = tuple
+
+        if (maxBuffer != 0) {
+          bufferElem(elem, promise)
+          if (pulled) {
+            push(out, buffer.dequeue())
+            pulled = false
+          }
+        } else if (pulled) {
+          push(out, elem)
+          pulled = false
+          promise.success(QueueOfferResult.Enqueued)
+        } else pendingOffer = Some(tuple)
+      })
+
+      setHandler(out, new OutHandler {
+        override def onDownstreamFinish(): Unit = {
+          pendingOffer match {
+            case Some((elem, promise)) ⇒
+              promise.success(QueueOfferResult.QueueClosed)
+              pendingOffer = None
+            case None ⇒ // do nothing
+          }
+          completion.success(())
+          completeStage()
+        }
+
+        override def onPull(): Unit = {
+          if (maxBuffer == 0)
+            pendingOffer match {
+              case Some((elem, promise)) ⇒
+                push(out, elem)
+                promise.success(QueueOfferResult.Enqueued)
+                pendingOffer = None
+              case None ⇒ pulled = true
+            }
+          else if (!buffer.isEmpty) {
+            push(out, buffer.dequeue())
+            pendingOffer match {
+              case Some((elem, promise)) ⇒
+                enqueueAndSuccess(elem, promise)
+                pendingOffer = None
+              case None ⇒ //do nothing
+            }
+          } else pulled = true
+        }
+      })
+    }
+
+    (stageLogic, new SourceQueue[T] {
+      override def watchCompletion() = completion.future
+      override def offer(element: T): Future[QueueOfferResult] = {
+        val p = Promise[QueueOfferResult]()
+        stageLogic.invoke((element, p))
+        p.future
+      }
+    })
+  }
+}
+
diff --git a/akka-stream/src/main/scala/akka/stream/impl/Stages.scala b/akka-stream/src/main/scala/akka/stream/impl/Stages.scala
index e33ee8481c..bfc73d3a78 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/Stages.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/Stages.scala
@@ -87,7 +87,7 @@ private[stream] object Stages {
     val subscriberSource = name("subscriberSource")
     val actorPublisherSource = name("actorPublisherSource")
     val actorRefSource = name("actorRefSource")
-    val acknowledgeSource = name("acknowledgeSource")
+    val queueSource = name("queueSource")
     val inputStreamSource = name("inputStreamSource") and IODispatcher
     val outputStreamSource = name("outputStreamSource") and IODispatcher
     val fileSource = name("fileSource") and IODispatcher
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
index c1074b6c45..5a659d64b9 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
@@ -6,8 +6,8 @@ package akka.stream.impl.fusing
 import akka.event.Logging.LogLevel
 import akka.event.{ LogSource, Logging, LoggingAdapter }
 import akka.stream.Attributes.{ InputBuffer, LogLevels }
-import akka.stream.DelayOverflowStrategy.EmitEarly
 import akka.stream.impl.Stages.DefaultAttributes
+import akka.stream.OverflowStrategies._
 import akka.stream.impl.fusing.GraphStages.SimpleLinearGraphStage
 import akka.stream.impl.{ FixedSizeBuffer, BoundedBuffer, ReactiveStreamsCompliance }
 import akka.stream.stage._
@@ -372,8 +372,6 @@ private[akka] final case class Sliding[T](n: Int, step: Int) extends PushPullSta
  */
 private[akka] final case class Buffer[T](size: Int, overflowStrategy: OverflowStrategy) extends DetachedStage[T, T] {
 
-  import OverflowStrategy._
-
   private val buffer = FixedSizeBuffer[T](size)
 
   override def onPush(elem: T, ctx: DetachedContext[T]): UpstreamDirective =
@@ -394,8 +392,8 @@ private[akka] final case class Buffer[T](size: Int, overflowStrategy: OverflowSt
     if (buffer.isEmpty) ctx.finish()
     else ctx.absorbTermination()
 
-  val enqueueAction: (DetachedContext[T], T) ⇒ UpstreamDirective = {
-    (overflowStrategy: @unchecked) match {
+  val enqueueAction: (DetachedContext[T], T) ⇒ UpstreamDirective =
+    overflowStrategy match {
       case DropHead ⇒ (ctx, elem) ⇒
         if (buffer.isFull) buffer.dropHead()
         buffer.enqueue(elem)
@@ -416,13 +414,13 @@ private[akka] final case class Buffer[T](size: Int, overflowStrategy: OverflowSt
         if (buffer.isFull) ctx.holdUpstream()
         else ctx.pull()
         case Fail ⇒ (ctx, elem) ⇒
-        if (buffer.isFull) ctx.fail(new Fail.BufferOverflowException(s"Buffer overflow (max capacity was: $size)!"))
+        if (buffer.isFull) ctx.fail(new BufferOverflowException(s"Buffer overflow (max capacity was: $size)!"))
         else {
           buffer.enqueue(elem)
           ctx.pull()
         }
     }
-  }
+
 }
 
 /**
@@ -961,7 +959,7 @@ private[stream] final class Delay[T](d: FiniteDuration, strategy: DelayOverflowS
     setHandler(in, handler = new InHandler {
       //FIXME rewrite into distinct strategy functions to avoid matching on strategy for every input when full
       override def onPush(): Unit = {
-        if (buffer.isFull) (strategy: @unchecked) match {
+        if (buffer.isFull) strategy match {
           case EmitEarly ⇒
             if (!isTimerActive(timerName))
               push(out, buffer.dequeue()._2)
@@ -969,24 +967,24 @@ private[stream] final class Delay[T](d: FiniteDuration, strategy: DelayOverflowS
               cancelTimer(timerName)
               onTimer(timerName)
             }
-          case DelayOverflowStrategy.DropHead ⇒
+          case DropHead ⇒
             buffer.dropHead()
             grabAndPull(true)
-          case DelayOverflowStrategy.DropTail ⇒
+          case DropTail ⇒
             buffer.dropTail()
             grabAndPull(true)
-          case DelayOverflowStrategy.DropNew ⇒
+          case DropNew ⇒
             grab(in)
             if (!isTimerActive(timerName)) scheduleOnce(timerName, d)
-          case DelayOverflowStrategy.DropBuffer ⇒
+          case DropBuffer ⇒
             buffer.clear()
             grabAndPull(true)
-          case DelayOverflowStrategy.Fail ⇒
-            failStage(new DelayOverflowStrategy.Fail.BufferOverflowException(s"Buffer overflow for delay combinator (max capacity was: $size)!"))
-          case DelayOverflowStrategy.Backpressure ⇒ throw new IllegalStateException("Delay buffer must never overflow in Backpressure mode")
+          case Fail ⇒
+            failStage(new BufferOverflowException(s"Buffer overflow for delay combinator (max capacity was: $size)!"))
+          case Backpressure ⇒ throw new IllegalStateException("Delay buffer must never overflow in Backpressure mode")
         }
         else {
-          grabAndPull(strategy != DelayOverflowStrategy.Backpressure || buffer.size < size - 1)
+          grabAndPull(strategy != Backpressure || buffer.size < size - 1)
           if (!isTimerActive(timerName)) scheduleOnce(timerName, d)
         }
       }
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
index 2aa378591e..8ca7c92d20 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
@@ -272,28 +272,34 @@ object Source {
   /**
    * Creates a `Source` that is materialized as an [[akka.stream.SourceQueue]].
    * You can push elements to the queue and they will be emitted to the stream if there is demand from downstream,
-   * otherwise they will be buffered until request for demand is received.
+   * otherwise they will be buffered until request for demand is received. Elements in the buffer will be discarded
+   * if downstream is terminated.
    *
    * Depending on the defined [[akka.stream.OverflowStrategy]] it might drop elements if
    * there is no space available in the buffer.
    *
    * Acknowledgement mechanism is available.
-   * [[akka.stream.SourceQueue.offer]] returns ``Future[Boolean]`` which completes with true
-   * if element was added to buffer or sent downstream. It completes
-   * with false if element was dropped.
+   * [[akka.stream.SourceQueue.offer]] returns ``Future[StreamCallbackStatus[Boolean]]`` which completes with `Success(true)`
+   * if element was added to buffer or sent downstream. It completes with `Success(false)` if element was dropped. Can also complete
+   * with [[akka.stream.StreamCallbackStatus.Failure]] - when stream failed or [[akka.stream.StreamCallbackStatus.StreamCompleted]]
+   * when downstream is completed.
    *
-   * The strategy [[akka.stream.OverflowStrategy.backpressure]] will not complete `offer():Future` until buffer is full.
+   * The strategy [[akka.stream.OverflowStrategy.backpressure]] will not complete last `offer():Future`
+   * call when buffer is full.
    *
-   * The buffer can be disabled by using `bufferSize` of 0 and then received messages are dropped
-   * if there is no demand from downstream. When `bufferSize` is 0 the `overflowStrategy` does
-   * not matter.
+   * You can watch accessibility of stream with [[akka.stream.SourceQueue.watchCompletion]].
+   * It returns future that completes with success when stream is completed or fail when stream is failed.
    *
-   * @param bufferSize The size of the buffer in element count
+   * The buffer can be disabled by using `bufferSize` of 0 and then received message will wait for downstream demand.
+   * When `bufferSize` is 0 the `overflowStrategy` does not matter.
+   *
+   * SourceQueue that current source is materialized to is for single thread usage only.
+   *
+   * @param bufferSize size of buffer in element count
    * @param overflowStrategy Strategy that is used when incoming elements cannot fit inside the buffer
-   * @param timeout Timeout for ``SourceQueue.offer(T):Future[Boolean]``
    */
-  def queue[T](bufferSize: Int, overflowStrategy: OverflowStrategy, timeout: FiniteDuration): Source[T, SourceQueue[T]] =
-    new Source(scaladsl.Source.queue(bufferSize, overflowStrategy, timeout))
+  def queue[T](bufferSize: Int, overflowStrategy: OverflowStrategy): Source[T, SourceQueue[T]] =
+    new Source(scaladsl.Source.queue(bufferSize, overflowStrategy))
 
 }
 
@@ -1263,7 +1269,7 @@ final class Source[+Out, +Mat](delegate: scaladsl.Source[Out, Mat]) extends Grap
    * @param seed Provides the first state for a batched value using the first unconsumed element as a start
    * @param aggregate Takes the currently batched value and the current pending element to produce a new aggregate
    */
-  def batch[S](max: Long, seed: function.Function[Out, S],aggregate: function.Function2[S, Out, S]): javadsl.Source[S, Mat] =
+  def batch[S](max: Long, seed: function.Function[Out, S], aggregate: function.Function2[S, Out, S]): javadsl.Source[S, Mat] =
     new Source(delegate.batch(max, seed.apply)(aggregate.apply))
 
   /**
@@ -1294,7 +1300,7 @@ final class Source[+Out, +Mat](delegate: scaladsl.Source[Out, Mat]) extends Grap
    * @param seed Provides the first state for a batched value using the first unconsumed element as a start
    * @param aggregate Takes the currently batched value and the current pending element to produce a new batch
    */
-  def batchWeighted[S](max: Long, costFn: function.Function[Out, Long], seed: function.Function[Out, S],aggregate: function.Function2[S, Out, S]): javadsl.Source[S, Mat] =
+  def batchWeighted[S](max: Long, costFn: function.Function[Out, Long], seed: function.Function[Out, S], aggregate: function.Function2[S, Out, S]): javadsl.Source[S, Mat] =
     new Source(delegate.batchWeighted(max, costFn.apply, seed.apply)(aggregate.apply))
 
   /**
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
index 339e9b94ba..06b5e5cd4a 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
@@ -907,8 +907,8 @@ trait FlowOps[+Out, +Mat] {
    * See also [[FlowOps.limit]], [[FlowOps.limitWeighted]] [[FlowOps.batch]] [[FlowOps.batchWeighted]]
    */
   def conflate[S](seed: Out ⇒ S)(aggregate: (S, Out) ⇒ S): Repr[S] = andThen(Conflate(seed, aggregate))
-    //FIXME: conflate can be expressed as a batch
-    //via(Batch(1L, ConstantFun.zeroLong, seed, aggregate).withAttributes(DefaultAttributes.conflate))
+  //FIXME: conflate can be expressed as a batch
+  //via(Batch(1L, ConstantFun.zeroLong, seed, aggregate).withAttributes(DefaultAttributes.conflate))
 
   /**
    * Allows a faster upstream to progress independently of a slower subscriber by aggregating elements into batches
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
index 88e32bd8f6..870774e629 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
@@ -361,7 +361,7 @@ object Source {
    */
   def actorRef[T](bufferSize: Int, overflowStrategy: OverflowStrategy): Source[T, ActorRef] = {
     require(bufferSize >= 0, "bufferSize must be greater than or equal to 0")
-    require(overflowStrategy != OverflowStrategy.Backpressure, "Backpressure overflowStrategy not supported")
+    require(overflowStrategy != OverflowStrategies.Backpressure, "Backpressure overflowStrategy not supported")
     new Source(new ActorRefSource(bufferSize, overflowStrategy, DefaultAttributes.actorRefSource, shape("ActorRefSource")))
   }
 
@@ -387,29 +387,33 @@ object Source {
   /**
    * Creates a `Source` that is materialized as an [[akka.stream.SourceQueue]].
    * You can push elements to the queue and they will be emitted to the stream if there is demand from downstream,
-   * otherwise they will be buffered until request for demand is received.
+   * otherwise they will be buffered until request for demand is received. Elements in the buffer will be discarded
+   * if downstream is terminated.
    *
    * Depending on the defined [[akka.stream.OverflowStrategy]] it might drop elements if
    * there is no space available in the buffer.
    *
    * Acknowledgement mechanism is available.
-   * [[akka.stream.SourceQueue.offer]] returns ``Future[Boolean]`` which completes with true
-   * if element was added to buffer or sent downstream. It completes
-   * with false if element was dropped.
+   * [[akka.stream.SourceQueue.offer]] returns ``Future[StreamCallbackStatus[Boolean]]`` which completes with `Success(true)`
+   * if element was added to buffer or sent downstream. It completes with `Success(false)` if element was dropped. Can also complete
+   * with [[akka.stream.StreamCallbackStatus.Failure]] - when stream failed or [[akka.stream.StreamCallbackStatus.StreamCompleted]]
+   * when downstream is completed.
    *
-   * The strategy [[akka.stream.OverflowStrategy.backpressure]] will not complete `offer():Future` until buffer is full.
+   * The strategy [[akka.stream.OverflowStrategy.backpressure]] will not complete last `offer():Future`
+   * call when buffer is full.
    *
-   * The buffer can be disabled by using `bufferSize` of 0 and then received messages are dropped
-   * if there is no demand from downstream. When `bufferSize` is 0 the `overflowStrategy` does
-   * not matter.
+   * You can watch accessibility of stream with [[akka.stream.SourceQueue.watchCompletion]].
+   * It returns future that completes with success when stream is completed or fail when stream is failed.
    *
-   * @param bufferSize The size of the buffer in element count
+   * The buffer can be disabled by using `bufferSize` of 0 and then received message will wait for downstream demand.
+   * When `bufferSize` is 0 the `overflowStrategy` does not matter.
+   *
+   * SourceQueue that current source is materialized to is for single thread usage only.
+   *
+   * @param bufferSize size of buffer in element count
    * @param overflowStrategy Strategy that is used when incoming elements cannot fit inside the buffer
-   * @param timeout Timeout for ``SourceQueue.offer(T):Future[Boolean]``
    */
-  def queue[T](bufferSize: Int, overflowStrategy: OverflowStrategy, timeout: FiniteDuration = 5.seconds): Source[T, SourceQueue[T]] = {
-    require(bufferSize >= 0, "bufferSize must be greater than or equal to 0")
-    new Source(new AcknowledgeSource(bufferSize, overflowStrategy, DefaultAttributes.acknowledgeSource, shape("AcknowledgeSource")))
-  }
+  def queue[T](bufferSize: Int, overflowStrategy: OverflowStrategy): Source[T, SourceQueue[T]] =
+    Source.fromGraph(new QueueSource(bufferSize, overflowStrategy).withAttributes(DefaultAttributes.queueSource))
 
 }
diff --git a/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala b/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
index 0dddad277b..5e2e3cb55a 100644
--- a/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
+++ b/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
@@ -3,23 +3,21 @@
  */
 package akka.stream.stage
 
-import java.util
 import java.util.concurrent.atomic.{ AtomicReferenceFieldUpdater, AtomicReference }
 import akka.NotUsed
+import java.util.concurrent.locks.ReentrantLock
 import akka.actor._
 import akka.dispatch.sysmsg.{ DeathWatchNotification, SystemMessage, Unwatch, Watch }
 import akka.event.LoggingAdapter
 import akka.japi.function.{ Effect, Procedure }
 import akka.stream._
 import akka.stream.impl.StreamLayout.Module
-import akka.stream.impl.fusing.GraphInterpreter.GraphAssembly
-import akka.stream.impl.fusing.{ GraphInterpreter, GraphModule, GraphStageModule, SubSource, SubSink }
+import akka.stream.impl.fusing.{ GraphInterpreter, GraphStageModule, SubSource, SubSink }
 import akka.stream.impl.{ ReactiveStreamsCompliance, SeqActorName }
 import scala.annotation.tailrec
 import scala.collection.mutable.ArrayBuffer
 import scala.collection.{ immutable, mutable }
 import scala.concurrent.duration.FiniteDuration
-import akka.stream.impl.SubscriptionTimeoutException
 import akka.stream.actor.ActorSubscriberMessage
 import akka.stream.actor.ActorPublisherMessage
 
@@ -1273,3 +1271,55 @@ abstract class AbstractOutHandler extends OutHandler
  * (completing when upstream completes, failing when upstream fails, completing when downstream cancels).
  */
 abstract class AbstractInOutHandler extends InHandler with OutHandler
+
+/**
+ * INTERNAL API
+ * This trait wraps callback for `GraphStage` stage instances and handle gracefully cases when stage is
+ * not yet initialized or already finished.
+ *
+ * While `GraphStage` has not initialized it adds all requests to list.
+ * As soon as `GraphStage` is started it stops collecting requests (pointing to real callback
+ * function) and run all the callbacks from the list
+ *
+ * Supposed to be used by GraphStages that share call back to outer world
+ */
+private[akka] trait CallbackWrapper[T] extends AsyncCallback[T] {
+  private trait CallbackState
+  private case class NotInitialized(list: List[T]) extends CallbackState
+  private case class Initialized(f: T ⇒ Unit) extends CallbackState
+  private case class Stopped(f: T ⇒ Unit) extends CallbackState
+
+  /*
+   * To preserve message order when switching between not initialized / initialized states
+   * lock is used. Case is similar to RepointableActorRef
+   */
+  private[this] final val lock = new ReentrantLock
+
+  private[this] val callbackState = new AtomicReference[CallbackState](NotInitialized(Nil))
+
+  def stopCallback(f: T ⇒ Unit): Unit = locked {
+    callbackState.set(Stopped(f))
+  }
+
+  def initCallback(f: T ⇒ Unit): Unit = locked {
+    val list = (callbackState.getAndSet(Initialized(f)): @unchecked) match {
+      case NotInitialized(l) ⇒ l
+    }
+    list.reverse.foreach(f)
+  }
+
+  override def invoke(arg: T): Unit = locked {
+    callbackState.get() match {
+      case Initialized(cb)          ⇒ cb(arg)
+      case list @ NotInitialized(l) ⇒ callbackState.compareAndSet(list, NotInitialized(arg :: l))
+      case Stopped(cb) ⇒
+        lock.unlock()
+        cb(arg)
+    }
+  }
+
+  private[this] def locked(body: ⇒ Unit): Unit = {
+    lock.lock()
+    try body finally if (lock.isLocked) lock.unlock()
+  }
+}
\ No newline at end of file