=str #19585 fix long initialization for InputStreamSinkSpec

akka-stream/src/main/scala/akka/stream/impl/io/InputStreamSinkStage.scala

@@ -22,6 +22,7 @@ private[akka] object InputStreamSinkStage {
   sealed trait StreamToAdapterMessage
   case class Data(data: ByteString) extends StreamToAdapterMessage
   case object Finished extends StreamToAdapterMessage
+  case object Initialized extends StreamToAdapterMessage
   case class Failed(cause: Throwable) extends StreamToAdapterMessage
 
   sealed trait StageWithCallback {
@@ -42,7 +43,7 @@ private[akka] class InputStreamSinkStage(readTimeout: FiniteDuration) extends Gr
   require(maxBuffer > 0, "Buffer size must be greater than 0")
 
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, InputStream) = {
-    val dataQueue = new LinkedBlockingDeque[StreamToAdapterMessage](maxBuffer + 1)
+    val dataQueue = new LinkedBlockingDeque[StreamToAdapterMessage](maxBuffer + 2)
 
     val logic = new GraphStageLogic(shape) with StageWithCallback {
       var pullRequestIsSent = true
@@ -61,7 +62,10 @@ private[akka] class InputStreamSinkStage(readTimeout: FiniteDuration) extends Gr
           pull(in)
         }
 
-      override def preStart() = pull(in)
+      override def preStart() = {
+        dataQueue.add(Initialized)
+        pull(in)
+      }
 
       setHandler(in, new InHandler {
         override def onPush(): Unit = {
@@ -94,6 +98,7 @@ private[akka] class InputStreamAdapter(sharedBuffer: BlockingQueue[StreamToAdapt
                                        readTimeout: FiniteDuration)
   extends InputStream {
 
+  var isInitialized = false
   var isActive = true
   var isStageAlive = true
   val subscriberClosedException = new IOException("Reactive stream is terminated, no reads are possible")
@@ -101,8 +106,10 @@ private[akka] class InputStreamAdapter(sharedBuffer: BlockingQueue[StreamToAdapt
 
   @scala.throws(classOf[IOException])
   private[this] def executeIfNotClosed[T](f: () ⇒ T): T =
-    if (isActive) f()
-    else throw subscriberClosedException
+    if (isActive) {
+      waitIfNotInitialized()
+      f()
+    } else throw subscriberClosedException
 
   @scala.throws(classOf[IOException])
   override def read(): Int = {
@@ -186,6 +193,15 @@ private[akka] class InputStreamAdapter(sharedBuffer: BlockingQueue[StreamToAdapt
     }
   }
 
+  private[this] def waitIfNotInitialized(): Unit = {
+    if (!isInitialized) {
+      sharedBuffer.poll(readTimeout.toMillis, TimeUnit.MILLISECONDS) match {
+        case Initialized ⇒ isInitialized = true
+        case _           ⇒ require(false, "First message must be Initialized notification")
+      }
+    }
+  }
+
   private[this] def grabDataChunk(): Option[ByteString] = {
     detachedChunk match {
       case None ⇒