diff -r 85ff8d62c414 -r 6c19c29ddcbe src/Pure/System/program_progress.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/System/program_progress.scala	Tue Mar 12 15:57:25 2024 +0100
@@ -0,0 +1,96 @@
+/*  Title:      Pure/System/program_progress.scala
+    Author:     Makarius
+
+Structured program progress.
+*/
+
+package isabelle
+
+
+object Program_Progress {
+  class Program private[Program_Progress](heading: String, title: String) {
+    private val output_buffer = new StringBuffer(256)  // synchronized
+
+    def output(message: Progress.Message): Unit = synchronized {
+      if (output_buffer.length() > 0) output_buffer.append('\n')
+      output_buffer.append(message.output_text)
+    }
+
+    val start_time: Time = Time.now()
+    private var stop_time: Option[Time] = None
+    def stop_now(): Unit = synchronized { stop_time = Some(Time.now()) }
+
+    def output(): (Command.Results, XML.Body) = synchronized {
+      val output_text = output_buffer.toString
+      val elapsed_time = stop_time.map(t => t - start_time)
+
+      val message_prefix = heading + " "
+      val message_suffix =
+        elapsed_time match {
+          case None => " ..."
+          case Some(t) => " ... (" + t.message + " elapsed time)"
+        }
+
+      val (results, message) =
+        if (output_text.isEmpty) {
+          (Command.Results.empty, XML.string(message_prefix + title + message_suffix))
+        }
+        else {
+          val i = Document_ID.make()
+          val results = Command.Results.make(List(i -> Protocol.writeln_message(output_text)))
+          val message =
+            XML.string(message_prefix) :::
+            List(XML.Elem(Markup(Markup.WRITELN, Markup.Serial(i)), XML.string(title))) :::
+            XML.string(message_suffix)
+          (results, message)
+        }
+
+      (results, List(XML.elem(Markup.TRACING_MESSAGE, message)))
+    }
+  }
+}
+
+abstract class Program_Progress(
+  default_heading: String = "Running",
+  default_title: String = "program",
+  override val verbose: Boolean = false
+) extends Progress {
+  private var _finished_programs: List[Program_Progress.Program] = Nil
+  private var _running_program: Option[Program_Progress.Program] = None
+
+  def output(): (Command.Results, XML.Body) = synchronized {
+    val programs = (_running_program.toList ::: _finished_programs).reverse
+    val programs_output = programs.map(_.output())
+    val results = Command.Results.merge(programs_output.map(_._1))
+    val body = Library.separate(Pretty.Separator, programs_output.map(_._2)).flatten
+    (results, body)
+  }
+
+  private def start_program(heading: String, title: String): Unit = synchronized {
+    _running_program = Some(new Program_Progress.Program(heading, title))
+  }
+
+  def stop_program(): Unit = synchronized {
+    _running_program match {
+      case Some(program) =>
+        program.stop_now()
+        _finished_programs ::= program
+        _running_program = None
+      case None =>
+    }
+  }
+
+  def detect_program(s: String): Option[String]
+
+  override def output(message: Progress.Message): Unit = synchronized {
+    val writeln_msg = if (message.kind == Progress.Kind.writeln) message.text else ""
+    detect_program(writeln_msg).map(Word.explode) match {
+      case Some(a :: bs) =>
+        stop_program()
+        start_program(a, Word.implode(bs))
+      case _ =>
+        if (_running_program.isEmpty) start_program(default_heading, default_title)
+        if (do_output(message)) _running_program.get.output(message)
+    }
+  }
+}