src/Pure/Admin/isabelle_cronjob.scala

   val main_dir = Path.explode("~/cronjob")
   val run_dir = main_dir + Path.explode("run")
   val log_dir = main_dir + Path.explode("log")
 
   val main_state_file = run_dir + Path.explode("main.state")
-  val main_log = log_dir + Path.explode("main.log")  // owned by logger
-
-
-  /* managed repository clones */
+  val main_log = log_dir + Path.explode("main.log")  // owned by log service
+
+
+  /* task logging */
+
+  sealed case class Logger_Task(name: String, body: Logger => Unit)
+
+  class Log_Service private[Isabelle_Cronjob](progress: Progress)
+  {
+    private val thread: Consumer_Thread[String] =
+      Consumer_Thread.fork("cronjob: logger", daemon = true)(
+        consume = (text: String) =>
+          {
+            File.append(main_log, text + "\n")   // critical
+            progress.echo(text)
+            true
+          })
+
+    def shutdown() { thread.shutdown() }
+
+    val hostname = Isabelle_System.hostname()
+
+    def log(date: Date, task_name: String, msg: String): Unit =
+      thread.send(
+        "[" + Build_Log.print_date(date) + ", " + hostname + ", " + task_name + "]: " + msg)
+
+    def start_logger(start_date: Date, task_name: String): Logger =
+      new Logger(this, start_date, task_name)
+
+    def run_task(start_date: Date, task: Logger_Task)
+    {
+      val logger = start_logger(start_date, task.name)
+      val res = Exn.capture { task.body(logger) }
+      val end_date = Date.now()
+      val err =
+        res match {
+          case Exn.Res(_) => None
+          case Exn.Exn(exn) => Some(Exn.message(exn))
+        }
+      logger.log_end(end_date, err)
+    }
+
+    def fork_task(start_date: Date, task: Logger_Task): Task =
+      new Task(task.name, run_task(start_date, task))
+  }
+
+  class Logger private[Isabelle_Cronjob](
+    val log_service: Log_Service, val start_date: Date, val task_name: String)
+  {
+    def log(date: Date, msg: String): Unit = log_service.log(date, task_name, msg)
+
+    def log_end(end_date: Date, err: Option[String])
+    {
+      val elapsed_time = end_date.time - start_date.time
+      val msg =
+        (if (err.isEmpty) "finished" else "ERROR " + err.get) +
+        (if (elapsed_time.seconds < 3.0) "" else ", elapsed time " + elapsed_time.message_hms)
+      log(end_date, msg)
+    }
+
+    log(start_date, "started")
+  }
+
+  class Task private[Isabelle_Cronjob](name: String, body: => Unit)
+  {
+    private val future: Future[Unit] = Future.thread("cronjob: " + name) { body }
+    def is_finished: Boolean = future.is_finished
+  }
+
+
+
+  /** particular tasks **/
+
+  /* identify repository snapshots */
 
   val isabelle_repos = main_dir + Path.explode("isabelle-build_history")
   val afp_repos = main_dir + Path.explode("AFP-build_history")
 
-  def pull_repos(root: Path): String =
-  {
-    val hg = Mercurial.repository(root)
-    hg.pull(options = "-q")
-    hg.identify("tip", options = "-i")
-  }
-
-
-
-  /** particular tasks **/
-
-  /* identify repository snapshots */
-
-  def isabelle_identify(start_date: Date)
-  {
-    val isabelle_id = pull_repos(isabelle_repos)
-    val afp_id = pull_repos(afp_repos)
-
-    val log_path = log_dir + Build_Log.log_path("isabelle_identify", start_date)
-    Isabelle_System.mkdirs(log_path.dir)
-    File.write(log_path,
-      Library.terminate_lines(
-        List("isabelle_identify: " + Build_Log.print_date(start_date),
-          "",
-          "Isabelle version: " + isabelle_id,
-          "AFP version: " + afp_id)))
-  }
+  val isabelle_identify =
+    Logger_Task("isabelle_identify", logger =>
+      {
+        def pull_repos(root: Path): String =
+        {
+          val hg = Mercurial.repository(root)
+          hg.pull(options = "-q")
+          hg.identify("tip", options = "-i")
+        }
+
+        val isabelle_id = pull_repos(isabelle_repos)
+        val afp_id = pull_repos(afp_repos)
+
+        val log_path = log_dir + Build_Log.log_path("isabelle_identify", logger.start_date)
+        Isabelle_System.mkdirs(log_path.dir)
+        File.write(log_path,
+          Library.terminate_lines(
+            List("isabelle_identify: " + Build_Log.print_date(logger.start_date),
+              "",
+              "Isabelle version: " + isabelle_id,
+              "AFP version: " + afp_id)))
+      })
 
 
 
   /** cronjob **/
 
-  private class Task(val name: String, body: Date => Unit)
-  {
-    override def toString: String = "cronjob: " + name
-
-    val start_date: Date = Date.now()
-
-    private val future: Future[Unit] = Future.thread(toString) { body(start_date) }
-    def is_finished: Boolean = future.is_finished
-
-    def success: Boolean =
-      future.join_result match {
-        case Exn.Res(_) => true
-        case Exn.Exn(_) => false
-      }
-  }
+  private val all_tasks = List(isabelle_identify)
 
   def cronjob(progress: Progress)
   {
-    /* check */
+    /* soft lock */
 
     val still_running =
       try { Some(File.read(main_state_file)) }
       catch { case ERROR(_) => None }
 

       case None | Some("") =>
       case Some(running) =>
         error("Isabelle cronjob appears to be still running: " + running)
     }
 
-
-    /* logger */
-
-    val hostname = Isabelle_System.hostname()
-
-    val logger: Consumer_Thread[String] =
-      Consumer_Thread.fork("cronjob: logger", daemon = true)(
-        consume = (text: String) =>
-          {
-            File.append(main_log, text + "\n")
-            progress.echo(text)
-            true
-          })
-
-    def log(date: Date, task_name: String, msg: String)
-    {
-      logger.send(
-        "[" + Build_Log.print_date(date) + ", " + hostname + ", " + task_name + "]: " + msg)
-    }
-
-    def log_start(task: Task) { log(task.start_date, task.name, "started") }
-
-    def log_end(end_date: Date, task: Task)
-    {
-      val elapsed_time = end_date.time - task.start_date.time
-      val msg =
-        (if (task.success) "finished" else "FAILED") +
-        (if (elapsed_time.seconds < 3.0) "" else ", elapsed time " + elapsed_time.message_hms)
-      log(end_date, task.name, msg)
-    }
-
-
-    /* manage tasks */
-
-    def manage_tasks(task_specs: List[(String, Date => Unit)])
+    val main_start_date = Date.now()
+    val log_service = new Log_Service(progress)
+
+    File.write(main_state_file, main_start_date + " " + log_service.hostname)
+
+
+    /* parallel tasks */
+
+    def parallel_tasks(tasks: List[Logger_Task])
     {
       @tailrec def await(running: List[Task])
       {
         running.partition(_.is_finished) match {
           case (Nil, Nil) =>
           case (Nil, _ :: _) => Thread.sleep(500); await(running)
-          case (finished, remaining) =>
-            val end_date = Date.now()
-            finished.foreach(log_end(end_date, _))
-            await(remaining)
+          case (_ :: _, remaining) => await(remaining)
         }
       }
-      await(task_specs.map({ case (name, body) => new Task(name, body) }))
+      val start_date = Date.now()
+      await(tasks.map(task => log_service.fork_task(start_date, task)))
     }
 
 
     /* main */
 
-    val main_task = new Task("main", _ => ())
-    File.write(main_state_file, main_task.start_date + " " + hostname)
-    log_start(main_task)
-
-    manage_tasks(List("isabelle_identify" -> isabelle_identify _))
-
-    log_end(Date.now(), main_task)
+    log_service.run_task(main_start_date,
+      Logger_Task("isabelle_cronjob", _ => parallel_tasks(all_tasks)))
+
+    log_service.shutdown()
+
     main_state_file.file.delete
-
-    logger.shutdown()
   }
 
 
 
   /** command line entry point **/