src/Pure/Tools/isabelle_process.scala

     this(new IsabelleSystem, new EventBus[IsabelleProcess.Result] + Console.println, args: _*)
 
 
   /* process information */
 
-  private var proc: Process = null
-  private var closing = false
-  private var pid: String = null
-  private var the_session: String = null
+  @volatile private var proc: Process = null
+  @volatile private var closing = false
+  @volatile private var pid: String = null
+  @volatile private var the_session: String = null
   def session = the_session
 
 
   /* results */