tuned signature;

--- a/src/Pure/Concurrent/consumer_thread.scala	Tue Sep 07 15:05:57 2021 +0200
+++ b/src/Pure/Concurrent/consumer_thread.scala	Tue Sep 07 15:10:53 2021 +0200
@@ -48,7 +48,7 @@
   private val mailbox = Mailbox[Option[Request]]
 
   private val thread = Isabelle_Thread.fork(name = name, daemon = daemon) { main_loop(Nil) }
-  def is_active: Boolean = active && thread.isAlive
+  def is_active(): Boolean = active && thread.isAlive
   def check_thread: Boolean = Thread.currentThread == thread
 
   private def failure(exn: Throwable): Unit =
@@ -77,7 +77,7 @@
   private def request(req: Request): Unit =
   {
     synchronized {
-      if (is_active) mailbox.send(Some(req))
+      if (is_active()) mailbox.send(Some(req))
       else error("Consumer thread not active: " + quote(thread.getName))
     }
     req.await()
@@ -111,14 +111,14 @@
 
   /* main methods */
 
-  assert(is_active)
+  assert(is_active())
 
   def send(arg: A): Unit = request(new Request(arg))
   def send_wait(arg: A): Unit = request(new Request(arg, acknowledge = true))
 
   def shutdown(): Unit =
   {
-    synchronized { if (is_active) { active = false; mailbox.send(None) } }
+    synchronized { if (is_active()) { active = false; mailbox.send(None) } }
     thread.join()
   }
 }

--- a/src/Pure/PIDE/prover.scala	Tue Sep 07 15:05:57 2021 +0200
+++ b/src/Pure/PIDE/prover.scala	Tue Sep 07 15:10:53 2021 +0200
@@ -302,7 +302,7 @@
 
   def protocol_command_raw(name: String, args: List[Bytes]): Unit =
     command_input match {
-      case Some(thread) if thread.is_active =>
+      case Some(thread) if thread.is_active() =>
         if (trace) {
           val payload = args.foldLeft(0) { case (n, b) => n + b.length }
           Output.writeln(

--- a/src/Pure/PIDE/session.scala	Tue Sep 07 15:05:57 2021 +0200
+++ b/src/Pure/PIDE/session.scala	Tue Sep 07 15:10:53 2021 +0200
@@ -699,7 +699,7 @@
 
   def get_state(): Document.State =
   {
-    if (manager.is_active) {
+    if (manager.is_active()) {
       val promise = Future.promise[Document.State]
       manager.send_wait(Get_State(promise))
       promise.join

--- a/src/Pure/Tools/simplifier_trace.scala	Tue Sep 07 15:05:57 2021 +0200
+++ b/src/Pure/Tools/simplifier_trace.scala	Tue Sep 07 15:10:53 2021 +0200
@@ -287,7 +287,7 @@
 
   def the_manager(session: Session): Consumer_Thread[Any] =
     managers.value.get(session) match {
-      case Some(thread) if thread.is_active => thread
+      case Some(thread) if thread.is_active() => thread
       case _ => error("Bad Simplifier_Trace.manager thread")
     }