src/Pure/PIDE/headless.scala

--- a/src/Pure/PIDE/headless.scala	Fri Mar 27 12:15:26 2020 +0100
+++ b/src/Pure/PIDE/headless.scala	Fri Mar 27 12:28:55 2020 +0100
@@ -585,7 +585,7 @@
       session.phase_changed += session_phase
 
       progress.echo("Starting session " + session_base_info.session + " ...")
-      Isabelle_Process.start(session, options, session_base_info.sessions_structure,
+      Isabelle_Process(session, options, session_base_info.sessions_structure,
         logic = session_base_info.session, modes = print_mode)
 
       session_error.join match {