+str #18798: Fuzzing mode for the interpreter

*PHEAR ME*

akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala

@@ -10,6 +10,7 @@ import akka.stream.stage._
 import scala.annotation.tailrec
 import scala.collection.immutable
 import akka.stream._
+import scala.concurrent.forkjoin.ThreadLocalRandom
 import scala.util.control.NonFatal
 
 /**
@@ -332,7 +333,8 @@ private[stream] final class GraphInterpreter(
   val inHandlers: Array[InHandler], // Lookup table for the InHandler of a connection
   val outHandlers: Array[OutHandler], // Lookup table for the outHandler of the connection
   val logics: Array[GraphStageLogic], // Array of stage logics
-  val onAsyncInput: (GraphStageLogic, Any, (Any) ⇒ Unit) ⇒ Unit) {
+  val onAsyncInput: (GraphStageLogic, Any, (Any) ⇒ Unit) ⇒ Unit,
+  val fuzzingMode: Boolean) {
   import GraphInterpreter._
 
   // Maintains additional information for events, basically elements in-flight, or failure.
@@ -579,14 +581,17 @@ private[stream] final class GraphInterpreter(
   }
 
   private def dequeue(): Int = {
-    if (queueHead == queueTail) NoEvent
-    else {
-      val idx = queueHead & mask
-      val elem = eventQueue(idx)
-      eventQueue(idx) = NoEvent
-      queueHead += 1
-      elem
+    val idx = queueHead & mask
+    if (fuzzingMode) {
+      val swapWith = (ThreadLocalRandom.current.nextInt(queueTail - queueHead) + queueHead) & mask
+      val ev = eventQueue(swapWith)
+      eventQueue(swapWith) = eventQueue(idx)
+      eventQueue(idx) = ev
     }
+    val elem = eventQueue(idx)
+    eventQueue(idx) = NoEvent
+    queueHead += 1
+    elem
   }
 
   private def enqueue(connection: Int): Unit = {
@@ -624,8 +629,9 @@ private[stream] final class GraphInterpreter(
   }
 
   private[stream] def push(connection: Int, elem: Any): Unit = {
-    if ((portStates(connection) & InClosed) == 0) {
-      portStates(connection) ^= PushStartFlip
+    val currentState = portStates(connection)
+    portStates(connection) = currentState ^ PushStartFlip
+    if ((currentState & InClosed) == 0) {
       connectionSlots(connection) = elem
       enqueue(connection)
     }
@@ -633,8 +639,8 @@ private[stream] final class GraphInterpreter(
 
   private[stream] def pull(connection: Int): Unit = {
     val currentState = portStates(connection)
+    portStates(connection) = currentState ^ PullStartFlip
     if ((currentState & OutClosed) == 0) {
-      portStates(connection) = currentState ^ PullStartFlip
       enqueue(connection)
     }
   }