more uniform group for map_future, which is relevant for cancel in worker_task vs. future_job -- prefer peer group despite 81d03a29980c;
--- a/src/Pure/Concurrent/future.ML Thu Oct 18 13:26:49 2012 +0200
+++ b/src/Pure/Concurrent/future.ML Thu Oct 18 13:53:02 2012 +0200
@@ -563,7 +563,7 @@
fun map_future f x =
let
val task = task_of x;
- val group = new_group (SOME (Task_Queue.group_of_task task));
+ val group = Task_Queue.group_of_task task;
val (result, job) = future_job group true (fn () => f (join x));
val extended = SYNCHRONIZED "extend" (fn () =>