diff -r ed4b47b8c7dc -r 420f55912b3e src/Pure/System/invoke_scala.scala
--- a/src/Pure/System/invoke_scala.scala	Tue Mar 14 00:09:15 2017 +0100
+++ b/src/Pure/System/invoke_scala.scala	Tue Mar 14 00:13:38 2017 +0100
@@ -77,6 +77,12 @@
   override def init(init_session: Session): Unit =
     synchronized { session = init_session }
 
+  override def exit(): Unit = synchronized
+  {
+    for ((id, future) <- futures) cancel(id, future)
+    futures = Map.empty
+  }
+
   private def fulfill(id: String, tag: Invoke_Scala.Tag.Value, res: String): Unit =
     synchronized
     {
@@ -119,12 +125,6 @@
     }
   }
 
-  override def exit(): Unit = synchronized
-  {
-    for ((id, future) <- futures) cancel(id, future)
-    futures = Map.empty
-  }
-
   val functions =
     List(
       Markup.INVOKE_SCALA -> invoke_scala _,