Merge remote-tracking branch 'pr/18985' into release-2.3-dev

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

@@ -386,6 +386,34 @@ class SubFlow[-In, +Out, +Mat](delegate: scaladsl.SubFlow[Out, Mat, scaladsl.Flo
   def groupedWithin(n: Int, d: FiniteDuration): SubFlow[In, java.util.List[Out @uncheckedVariance], Mat] =
     new SubFlow(delegate.groupedWithin(n, d).map(_.asJava)) // TODO optimize to one step
 
+  /**
+   * Shifts elements emission in time by a specified amount. It allows to store elements
+   * in internal buffer while waiting for next element to be emitted. Depending on the defined
+   * [[akka.stream.DelayOverflowStrategy]] it might drop elements or backpressure the upstream if
+   * there is no space available in the buffer.
+   *
+   * Delay precision is 10ms to avoid unnecessary timer scheduling cycles
+   *
+   * Internal buffer has default capacity 16. You can set buffer size by calling `withAttributes(inputBuffer)`
+   *
+   * '''Emits when''' there is a pending element in the buffer and configured time for this element elapsed
+   *  * EmitEarly - strategy do not wait to emit element if buffer is full
+   *
+   * '''Backpressures when''' depending on OverflowStrategy
+   *  * Backpressure - backpressures when buffer is full
+   *  * DropHead, DropTail, DropBuffer - never backpressures
+   *  * Fail - fails the stream if buffer gets full
+   *
+   * '''Completes when''' upstream completes and buffered elements has been drained
+   *
+   * '''Cancels when''' downstream cancels
+   *
+   * @param of time to shift all messages
+   * @param strategy Strategy that is used when incoming elements cannot fit inside the buffer
+   */
+  def delay(of: FiniteDuration, strategy: DelayOverflowStrategy): SubFlow[In, Out, Mat] =
+    new SubFlow(delegate.delay(of, strategy))
+
   /**
    * Discard the given number of elements at the beginning of the stream.
    * No elements will be dropped if `n` is zero or negative.