diff -r d682b4000a77 -r f8e52c0152fe src/Pure/Concurrent/standard_thread.scala
--- a/src/Pure/Concurrent/standard_thread.scala	Sat Apr 04 21:38:20 2020 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,169 +0,0 @@
-/*  Title:      Pure/Concurrent/standard_thread.scala
-    Author:     Makarius
-
-Standard thread operations.
-*/
-
-package isabelle
-
-
-import java.util.concurrent.{ThreadPoolExecutor, TimeUnit, LinkedBlockingQueue, ThreadFactory}
-
-
-object Standard_Thread
-{
-  /* fork */
-
-  private val counter = Counter.make()
-
-  def make_name(name: String = "", base: String = "thread"): String =
-    proper_string(name).getOrElse(base + counter())
-
-  def current_thread_group: ThreadGroup = Thread.currentThread.getThreadGroup
-
-  def fork(
-    name: String = "",
-    group: ThreadGroup = current_thread_group,
-    pri: Int = Thread.NORM_PRIORITY,
-    daemon: Boolean = false,
-    inherit_locals: Boolean = false,
-    uninterruptible: Boolean = false)(body: => Unit): Standard_Thread =
-  {
-    val main =
-      if (uninterruptible) new Runnable { override def run { Standard_Thread.uninterruptible { body } } }
-      else new Runnable { override def run { body } }
-    val thread =
-      new Standard_Thread(main, name = make_name(name = name), group = group,
-        pri = pri, daemon = daemon, inherit_locals = inherit_locals)
-    thread.start
-    thread
-  }
-
-
-  /* self */
-
-  def self: Standard_Thread =
-    Thread.currentThread match {
-      case thread: Standard_Thread => thread
-      case _ => error("Expected to run on Isabelle/Scala standard thread")
-    }
-
-  def uninterruptible[A](body: => A): A = self.uninterruptible(body)
-
-
-  /* pool */
-
-  lazy val pool: ThreadPoolExecutor =
-    {
-      val m = Value.Int.unapply(System.getProperty("isabelle.threads", "0")) getOrElse 0
-      val n = if (m > 0) m else (Runtime.getRuntime.availableProcessors max 1) min 8
-      val executor =
-        new ThreadPoolExecutor(n, n, 2500L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue[Runnable])
-      executor.setThreadFactory(
-        new Standard_Thread(_, name = make_name(base = "worker"), group = current_thread_group))
-      executor
-    }
-
-
-  /* delayed events */
-
-  final class Delay private[Standard_Thread](
-    first: Boolean, delay: => Time, log: Logger, event: => Unit)
-  {
-    private var running: Option[Event_Timer.Request] = None
-
-    private def run: Unit =
-    {
-      val do_run = synchronized {
-        if (running.isDefined) { running = None; true } else false
-      }
-      if (do_run) {
-        try { event }
-        catch { case exn: Throwable if !Exn.is_interrupt(exn) => log(Exn.message(exn)); throw exn }
-      }
-    }
-
-    def invoke(): Unit = synchronized
-    {
-      val new_run =
-        running match {
-          case Some(request) => if (first) false else { request.cancel; true }
-          case None => true
-        }
-      if (new_run)
-        running = Some(Event_Timer.request(Time.now() + delay)(run))
-    }
-
-    def revoke(): Unit = synchronized
-    {
-      running match {
-        case Some(request) => request.cancel; running = None
-        case None =>
-      }
-    }
-
-    def postpone(alt_delay: Time): Unit = synchronized
-    {
-      running match {
-        case Some(request) =>
-          val alt_time = Time.now() + alt_delay
-          if (request.time < alt_time && request.cancel) {
-            running = Some(Event_Timer.request(alt_time)(run))
-          }
-        case None =>
-      }
-    }
-  }
-
-  // delayed event after first invocation
-  def delay_first(delay: => Time, log: Logger = No_Logger)(event: => Unit): Delay =
-    new Delay(true, delay, log, event)
-
-  // delayed event after last invocation
-  def delay_last(delay: => Time, log: Logger = No_Logger)(event: => Unit): Delay =
-    new Delay(false, delay, log, event)
-}
-
-class Standard_Thread private(
-    main: Runnable,
-    name: String = "",
-    group: ThreadGroup = null,
-    pri: Int = Thread.NORM_PRIORITY,
-    daemon: Boolean = false,
-    inherit_locals: Boolean = false)
-  extends Thread(group, null, name, 0L, inherit_locals)
-{
-  thread =>
-
-  thread.setPriority(pri)
-  thread.setDaemon(daemon)
-
-  override def run { main.run() }
-
-  private var interruptible: Boolean = true
-  private var interrupt_pending: Boolean = false
-
-  override def interrupt: Unit = synchronized
-  {
-    if (interruptible) super.interrupt()
-    else { interrupt_pending = true }
-  }
-
-  def uninterruptible[A](body: => A): A =
-  {
-    require(Thread.currentThread == thread)
-
-    val interruptible0 = synchronized { val b = interruptible; interruptible = false; b }
-    try { body }
-    finally {
-      synchronized {
-        interruptible = interruptible0
-        if (interruptible && interrupt_pending) {
-          interrupt_pending = false
-          super.interrupt()
-        }
-      }
-      Exn.Interrupt.expose()
-    }
-  }
-}