src/Pure/System/isabelle_process.ML

     (case read_command channel of
       [] => (Output.error_msg "Isabelle process: no input"; true)
     | name :: args => (worker_guest (fn () => run_command name args); true))
     handle Runtime.TERMINATE => false
       | exn => (Output.error_msg (ML_Compiler.exn_message exn) handle crash => recover crash; true);
-  in if continue then loop channel else () end;
+  in if continue then loop channel else Future.shutdown () end;
 
 end;
 
 
 (* init *)