diff -r 371aacbbd6ef -r c76fd93b3b99 src/Pure/Concurrent/future.ML
--- a/src/Pure/Concurrent/future.ML	Sun Jul 19 17:08:34 2009 +0200
+++ b/src/Pure/Concurrent/future.ML	Sun Jul 19 18:02:40 2009 +0200
@@ -29,7 +29,7 @@
   val enabled: unit -> bool
   type task = Task_Queue.task
   type group = Task_Queue.group
-  val thread_data: unit -> (string * task) option
+  val is_worker: unit -> bool
   type 'a future
   val task_of: 'a future -> task
   val group_of: 'a future -> group
@@ -40,6 +40,7 @@
   val fork_group: group -> (unit -> 'a) -> 'a future
   val fork_deps: 'b future list -> (unit -> 'a) -> 'a future
   val fork_pri: int -> (unit -> 'a) -> 'a future
+  val fork_local: int -> (unit -> 'a) -> 'a future
   val join_results: 'a future list -> 'a Exn.result list
   val join_result: 'a future -> 'a Exn.result
   val join: 'a future -> 'a
@@ -66,11 +67,16 @@
 type task = Task_Queue.task;
 type group = Task_Queue.group;
 
-local val tag = Universal.tag () : (string * task) option Universal.tag in
+local
+  val tag = Universal.tag () : (string * task * group) option Universal.tag;
+in
   fun thread_data () = the_default NONE (Thread.getLocal tag);
-  fun setmp_thread_data data f x = Library.setmp_thread_data tag (thread_data ()) (SOME data) f x;
+  fun setmp_thread_data data f x =
+    Library.setmp_thread_data tag (thread_data ()) (SOME data) f x;
 end;
 
+val is_worker = is_some o thread_data;
+
 
 (* datatype future *)
 
@@ -148,7 +154,7 @@
   let
     val _ = trace_active ();
     val valid = Task_Queue.is_valid group;
-    val ok = setmp_thread_data (name, task) (fn () =>
+    val ok = setmp_thread_data (name, task, group) (fn () =>
       fold (fn job => fn ok => job valid andalso ok) jobs true) ();
     val _ = SYNCHRONIZED "execute" (fn () =>
      (change queue (Task_Queue.finish task);
@@ -277,6 +283,7 @@
 fun fork_group group e = fork_future (SOME group) [] 0 e;
 fun fork_deps deps e = fork_future NONE (map task_of deps) 0 e;
 fun fork_pri pri e = fork_future NONE [] pri e;
+fun fork_local pri e = fork_future (Option.map #3 (thread_data ())) [] pri e;
 
 
 (* join *)
@@ -300,13 +307,13 @@
       val _ = Multithreading.self_critical () andalso
         error "Cannot join future values within critical section";
 
-      val is_worker = is_some (thread_data ());
+      val worker = is_worker ();
       fun join_wait x =
         if SYNCHRONIZED "join_wait" (fn () =>
-          is_finished x orelse (if is_worker then worker_wait () else wait (); false))
+          is_finished x orelse (if worker then worker_wait () else wait (); false))
         then () else join_wait x;
 
-      val _ = if is_worker then join_deps (map task_of xs) else ();
+      val _ = if worker then join_deps (map task_of xs) else ();
       val _ = List.app join_wait xs;
 
     in map get_result xs end) ();
@@ -342,7 +349,7 @@
 fun interruptible_task f x =
   if Multithreading.available then
     Multithreading.with_attributes
-      (if is_some (thread_data ())
+      (if is_worker ()
        then Multithreading.restricted_interrupts
        else Multithreading.regular_interrupts)
       (fn _ => f) x