diff -r d682b4000a77 -r f8e52c0152fe src/Pure/Concurrent/consumer_thread.scala
--- a/src/Pure/Concurrent/consumer_thread.scala	Sat Apr 04 21:38:20 2020 +0200
+++ b/src/Pure/Concurrent/consumer_thread.scala	Sun Apr 05 13:05:40 2020 +0200
@@ -47,7 +47,7 @@
   private var active = true
   private val mailbox = Mailbox[Option[Request]]
 
-  private val thread = Standard_Thread.fork(name = name, daemon = daemon) { main_loop(Nil) }
+  private val thread = Isabelle_Thread.fork(name = name, daemon = daemon) { main_loop(Nil) }
   def is_active: Boolean = active && thread.isAlive
   def check_thread: Boolean = Thread.currentThread == thread