!str #15026 change thunk publisher api to () => Option[T]

akka-stream/src/main/scala/akka/stream/impl/ActorPublisher.scala

@@ -4,11 +4,9 @@
 package akka.stream.impl
 
 import java.util.concurrent.atomic.AtomicReference
-
 import akka.actor.{ Actor, ActorLogging, ActorRef, Props, Terminated }
-import akka.stream.{ MaterializerSettings, Stop }
+import akka.stream.{ MaterializerSettings }
 import org.reactivestreams.{ Publisher, Subscriber }
-
 import scala.annotation.tailrec
 import scala.collection.immutable
 import scala.concurrent.duration.Duration

akka-stream/src/main/scala/akka/stream/impl/IteratorPublisher.scala

@@ -5,7 +5,6 @@ package akka.stream.impl
 
 import akka.actor.Props
 import akka.stream.MaterializerSettings
-import akka.stream.Stop
 
 /**
  * INTERNAL API

akka-stream/src/main/scala/akka/stream/impl/Stop.scala

@@ -1,18 +1,15 @@
 /**
  * Copyright (C) 2014 Typesafe Inc. <http://www.typesafe.com>
  */
-package akka.stream
+package akka.stream.impl
 
-import scala.util.control.NoStackTrace
+import scala.util.control.ControlThrowable
 
 /**
+ * INTERNAL API
+ *
  * This exception must be thrown from a callback-based stream publisher to
  * signal the end of stream (if the produced stream is not infinite). This is used for example in
  * [[akka.stream.scaladsl.Flow#apply]] (the variant which takes a closure).
  */
-case object Stop extends RuntimeException("Stop this flow") with NoStackTrace {
-  /**
-   * Java API: get the singleton instance
-   */
-  def getInstance = this
-}
+private[akka] case object Stop extends ControlThrowable

akka-stream/src/main/scala/akka/stream/javadsl/Flow.scala

@@ -10,7 +10,12 @@ import scala.concurrent.Future
 import scala.util.Failure
 import scala.util.Success
 import org.reactivestreams.{ Publisher, Subscriber }
-import akka.japi._
+import akka.japi.Creator
+import akka.japi.Function
+import akka.japi.Function2
+import akka.japi.Pair
+import akka.japi.Predicate
+import akka.japi.Procedure
 import akka.japi.Util.immutableSeq
 import akka.stream._
 import akka.stream.scaladsl.{ Flow ⇒ SFlow }
@@ -55,11 +60,10 @@ object Flow {
 
   /**
    * Define the sequence of elements to be produced by the given Callable.
-   * The stream ends normally when evaluation of the Callable results in
-   * a [[akka.stream.Stop]] exception being thrown; it ends exceptionally
-   * when any other exception is thrown.
+   * The stream ends normally when evaluation of the `Callable` returns a `null`.
+   * The stream ends exceptionally when an exception is thrown from the `Callable`.
    */
-  def create[T](block: Callable[T]): Flow[T] = new FlowAdapter(SFlow.apply(() ⇒ block.call()))
+  def create[T](block: Callable[T]): Flow[T] = new FlowAdapter(SFlow.apply(() ⇒ Option(block.call())))
 
   /**
    * Elements are produced from the tick `Callable` periodically with the specified interval.

akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala

@@ -14,6 +14,7 @@ import akka.stream.impl.FlowImpl
 import akka.stream.impl.Ast.TickPublisherNode
 import scala.concurrent.duration.FiniteDuration
 import scala.concurrent.duration.FiniteDuration
+import akka.stream.impl.Stop
 
 /**
  * Scala API
@@ -46,11 +47,11 @@ object Flow {
 
   /**
    * Define the sequence of elements to be produced by the given closure.
-   * The stream ends normally when evaluation of the closure results in
-   * a [[akka.stream.Stop]] exception being thrown; it ends exceptionally
-   * when any other exception is thrown.
+   * The stream ends normally when evaluation of the `Callable` returns a `None`.
+   * The stream ends exceptionally when an exception is thrown from the `Callable`.
    */
-  def apply[T](f: () ⇒ T): Flow[T] = FlowImpl(ThunkPublisherNode(f), Nil)
+  def apply[T](f: () ⇒ Option[T]): Flow[T] =
+    FlowImpl(ThunkPublisherNode(() ⇒ f().getOrElse(throw Stop)), Nil)
 
   /**
    * Start a new `Flow` from the given `Future`. The stream will consist of

akka-stream/src/test/java/akka/stream/javadsl/FlowTest.java

@@ -333,7 +333,7 @@ public class FlowTest {
       @Override
       public Integer call() {
         if (countdown == 0)
-          throw akka.stream.Stop.getInstance();
+          return null;
         else {
           countdown -= 1;
           return countdown;
@@ -490,7 +490,8 @@ public class FlowTest {
         return "tick-" + (count++);
       }
     };
-      Flow.create(FiniteDuration.create(1, TimeUnit.SECONDS), FiniteDuration.create(500, TimeUnit.MILLISECONDS), tick).foreach(new Procedure<String>() {
+    Flow.create(FiniteDuration.create(1, TimeUnit.SECONDS), FiniteDuration.create(500, TimeUnit.MILLISECONDS), tick)
+        .foreach(new Procedure<String>() {
           public void apply(String elem) {
             probe.getRef().tell(elem, ActorRef.noSender());
           }

akka-stream/src/test/scala/akka/stream/FlowSpec.scala

@@ -320,11 +320,11 @@ class FlowSpec extends AkkaSpec(ConfigFactory.parseString("akka.actor.debug.rece
     "if an internal error occurs future subscribers' onError should be called instead of onSubscribed" in pending
 
     "be covariant" in {
-      val f1: Flow[Fruit] = Flow(() ⇒ new Apple)
-      val p1: Publisher[Fruit] = Flow(() ⇒ new Apple).toPublisher()
-      val f2: Flow[Publisher[Fruit]] = Flow(() ⇒ new Apple).splitWhen(_ ⇒ true)
-      val f3: Flow[(Boolean, Publisher[Fruit])] = Flow(() ⇒ new Apple).groupBy(_ ⇒ true)
-      val f4: Flow[(immutable.Seq[Apple], Publisher[Fruit])] = Flow(() ⇒ new Apple).prefixAndTail(1)
+      val f1: Flow[Fruit] = Flow(() ⇒ Some(new Apple))
+      val p1: Publisher[Fruit] = Flow(() ⇒ Some(new Apple)).toPublisher()
+      val f2: Flow[Publisher[Fruit]] = Flow(() ⇒ Some(new Apple)).splitWhen(_ ⇒ true)
+      val f3: Flow[(Boolean, Publisher[Fruit])] = Flow(() ⇒ Some(new Apple)).groupBy(_ ⇒ true)
+      val f4: Flow[(immutable.Seq[Apple], Publisher[Fruit])] = Flow(() ⇒ Some(new Apple)).prefixAndTail(1)
     }
 
   }