perf: Reduce loops in when clean queue in BroadcastHub

Author: He-Pin

stream/src/main/scala/org/apache/pekko/stream/scaladsl/Hub.scala

@@ -605,10 +605,7 @@ private[pekko] class BroadcastHub[T](startAfterNrOfConsumers: Int, bufferSize: I
             else if (head != finalOffset) {
               // If our final consumer goes away, we roll forward the buffer so a subsequent consumer does not
               // see the already consumed elements. This feature is quite handy.
-              while (head != finalOffset) {
-                queue(head & Mask) = null
-                head += 1
-              }
+              cleanQueueInRange(head, finalOffset)
               head = finalOffset
               tryPull()
             }
@@ -617,6 +614,20 @@ private[pekko] class BroadcastHub[T](startAfterNrOfConsumers: Int, bufferSize: I
       }
     }
 
+    private def cleanQueueInRange(headOffset: Int, upToOffset: Int): Unit = {
+      // we need to clean when head != tail
+      if (headOffset != upToOffset) {
+        val startIdx = headOffset & Mask
+        val endIdx = upToOffset & Mask
+        if (startIdx <= endIdx) {
+          java.util.Arrays.fill(queue, startIdx, endIdx, null)
+        } else {
+          java.util.Arrays.fill(queue, startIdx, queue.length, null)
+          java.util.Arrays.fill(queue, 0, endIdx, null)
+        }
+      }
+    }
+
     // Producer API
     // We are full if the distance between the slowest (known) consumer and the fastest (known) consumer is
     // the buffer size. We must wait until the slowest either advances, or cancels.
@@ -677,11 +688,15 @@ private[pekko] class BroadcastHub[T](startAfterNrOfConsumers: Int, bufferSize: I
       if (offsetOfConsumerRemoved == head) {
         // Try to advance along the wheel. We can skip any wheel slots which have no waiting Consumers, until
         // we either find a nonempty one, or we reached the end of the buffer.
-        while (consumerWheel(head & WheelMask).isEmpty && head != tail) {
-          queue(head & Mask) = null
-          head += 1
+        var upToOffset = head
+        while (consumerWheel(upToOffset & WheelMask).isEmpty) {
+          upToOffset += 1
           unblocked = true
         }
+        if (upToOffset != head) {
+          cleanQueueInRange(head, upToOffset)
+          head = upToOffset
+        }
       }
       unblocked
     }