src/Pure/Tools/build_process.scala

clarified modules;

/*  Title:      Pure/Tools/build_process.scala
    Author:     Makarius

Build process for sessions, with build database, optional heap, and
optional presentation.
*/

package isabelle


import scala.collection.immutable.SortedMap
import scala.math.Ordering
import scala.annotation.tailrec


object Build_Process {
  /** static context **/

  object Context {
    def apply(
      store: Sessions.Store,
      build_deps: Sessions.Deps,
      progress: Progress = new Progress,
      hostname: String = Isabelle_System.hostname(),
      numa_shuffling: Boolean = false,
      build_heap: Boolean = false,
      max_jobs: Int = 1,
      fresh_build: Boolean = false,
      no_build: Boolean = false,
      verbose: Boolean = false,
      session_setup: (String, Session) => Unit = (_, _) => (),
      uuid: String = UUID.random().toString
    ): Context = {
      val sessions_structure = build_deps.sessions_structure
      val build_graph = sessions_structure.build_graph

      val sessions =
        Map.from(
          for ((name, (info, _)) <- build_graph.iterator)
          yield {
            val deps = info.parent.toList
            val ancestors = sessions_structure.build_requirements(deps)
            val sources_shasum = build_deps.sources_shasum(name)
            val session_context =
              Build_Job.Session_Context.load(
                uuid, name, deps, ancestors, sources_shasum, info.timeout, store,
                progress = progress)
            name -> session_context
          })

      val sessions_time = {
        val maximals = build_graph.maximals.toSet
        def descendants_time(name: String): Double = {
          if (maximals.contains(name)) sessions(name).old_time.seconds
          else {
            val descendants = build_graph.all_succs(List(name)).toSet
            val g = build_graph.restrict(descendants)
            (0.0 :: g.maximals.flatMap { desc =>
              val ps = g.all_preds(List(desc))
              if (ps.exists(p => !sessions.isDefinedAt(p))) None
              else Some(ps.map(p => sessions(p).old_time.seconds).sum)
            }).max
          }
        }
        Map.from(
          for (name <- sessions.keysIterator)
          yield name -> descendants_time(name)).withDefaultValue(0.0)
      }

      val ordering =
        new Ordering[String] {
          def compare(name1: String, name2: String): Int =
            sessions_time(name2) compare sessions_time(name1) match {
              case 0 =>
                sessions(name2).timeout compare sessions(name1).timeout match {
                  case 0 => name1 compare name2
                  case ord => ord
                }
              case ord => ord
            }
        }

      val numa_nodes = Host.numa_nodes(enabled = numa_shuffling)
      new Context(store, build_deps, sessions, ordering, hostname, numa_nodes,
        build_heap = build_heap, max_jobs = max_jobs, fresh_build = fresh_build,
        no_build = no_build, verbose = verbose, session_setup, uuid = uuid)
    }
  }

  // static context of one particular instance, identified by uuid
  final class Context private(
    val store: Sessions.Store,
    val build_deps: Sessions.Deps,
    val sessions: State.Sessions,
    val ordering: Ordering[String],
    val hostname: String,
    val numa_nodes: List[Int],
    val build_heap: Boolean,
    val max_jobs: Int,
    val fresh_build: Boolean,
    val no_build: Boolean,
    val verbose: Boolean,
    val session_setup: (String, Session) => Unit,
    val uuid: String
  ) {
    def build_options: Options = store.options

    def sessions_structure: Sessions.Structure = build_deps.sessions_structure

    def sources_shasum(name: String): SHA1.Shasum = sessions(name).sources_shasum

    def old_command_timings(name: String): List[Properties.T] =
      sessions.get(name) match {
        case Some(session_context) =>
          Properties.uncompress(session_context.old_command_timings_blob, cache = store.cache)
        case None => Nil
      }

    def store_heap(name: String): Boolean =
      build_heap || Sessions.is_pure(name) ||
      sessions.valuesIterator.exists(_.ancestors.contains(name))
  }



  /** dynamic state **/

  type Progress_Messages = SortedMap[Long, Progress.Message]

  case class Entry(name: String, deps: List[String], info: JSON.Object.T = JSON.Object.empty) {
    def is_ready: Boolean = deps.isEmpty
    def resolve(dep: String): Entry =
      if (deps.contains(dep)) copy(deps = deps.filterNot(_ == dep)) else this
  }

  case class Result(
    process_result: Process_Result,
    output_shasum: SHA1.Shasum,
    node_info: Host.Node_Info,
    current: Boolean
  ) {
    def ok: Boolean = process_result.ok
  }

  object State {
    type Sessions = Map[String, Build_Job.Session_Context]
    type Pending = List[Entry]
    type Running = Map[String, Build_Job]
    type Results = Map[String, Result]
  }

  // dynamic state of various instances, distinguished by uuid
  sealed case class State(
    serial: Long = 0,
    progress_seen: Long = 0,
    numa_index: Int = 0,
    sessions: State.Sessions = Map.empty,   // static build targets
    pending: State.Pending = Nil,           // dynamic build "queue"
    running: State.Running = Map.empty,     // presently running jobs
    results: State.Results = Map.empty      // finished results
  ) {
    def echo(progress: Progress, message_serial: Long, message: Progress.Message): State =
      if (message_serial > progress_seen) {
        progress.output(message)
        copy(progress_seen = message_serial)
      }
      else {
        error("Bad serial " + message_serial + " (already seen) for progress message:\n" + message)
      }

    def numa_next(numa_nodes: List[Int]): (Option[Int], State) =
      if (numa_nodes.isEmpty) (None, this)
      else {
        val available = numa_nodes.zipWithIndex
        val used =
          Set.from(for (job <- running.valuesIterator; i <- job.node_info.numa_node) yield i)
        val candidates = available.drop(numa_index) ::: available.take(numa_index)
        val (n, i) =
          candidates.find({ case (n, i) => i == numa_index && !used(n) }) orElse
          candidates.find({ case (n, _) => !used(n) }) getOrElse candidates.head
        (Some(n), copy(numa_index = (i + 1) % available.length))
      }

    def finished: Boolean = pending.isEmpty

    def remove_pending(name: String): State =
      copy(pending = pending.flatMap(
        entry => if (entry.name == name) None else Some(entry.resolve(name))))

    def is_running(name: String): Boolean = running.isDefinedAt(name)

    def stop_running(): Unit = running.valuesIterator.foreach(_.cancel())

    def finished_running(): List[Build_Job] =
      List.from(running.valuesIterator.filter(_.is_finished))

    def add_running(name: String, job: Build_Job): State =
      copy(running = running + (name -> job))

    def remove_running(name: String): State =
      copy(running = running - name)

    def make_result(
      name: String,
      process_result: Process_Result,
      output_shasum: SHA1.Shasum,
      node_info: Host.Node_Info = Host.Node_Info.none,
      current: Boolean = false
    ): State = {
      val entry = name -> Build_Process.Result(process_result, output_shasum, node_info, current)
      copy(results = results + entry)
    }
  }



  /** SQL data model **/

  object Data {
    val database = Path.explode("$ISABELLE_HOME_USER/build.db")

    def make_table(name: String, columns: List[SQL.Column], body: String = ""): SQL.Table =
      SQL.Table("isabelle_build" + if_proper(name, "_" + name), columns, body = body)

    object Generic {
      val uuid = SQL.Column.string("uuid")
      val name = SQL.Column.string("name")

      def sql_equal(uuid: String = "", name: String = ""): SQL.Source =
        SQL.and(
          if_proper(uuid, Generic.uuid.equal(uuid)),
          if_proper(name, Generic.name.equal(name)))

      def sql_member(uuid: String = "", names: Iterable[String] = Nil): SQL.Source =
        SQL.and(
          if_proper(uuid, Generic.uuid.equal(uuid)),
          if_proper(names, Generic.name.member(names)))
    }

    object Base {
      val uuid = Generic.uuid.make_primary_key
      val ml_platform = SQL.Column.string("ml_platform")
      val options = SQL.Column.string("options")

      val table = make_table("", List(uuid, ml_platform, options))
    }

    object Serial {
      val serial = SQL.Column.long("serial")

      val table = make_table("serial", List(serial))
    }

    object Progress {
      val serial = SQL.Column.long("serial").make_primary_key
      val kind = SQL.Column.int("kind")
      val text = SQL.Column.string("text")
      val verbose = SQL.Column.bool("verbose")
      val uuid = Generic.uuid

      val table = make_table("progress", List(serial, kind, text, verbose, uuid))
    }

    object Sessions {
      val name = Generic.name.make_primary_key
      val deps = SQL.Column.string("deps")
      val ancestors = SQL.Column.string("ancestors")
      val sources = SQL.Column.string("sources")
      val timeout = SQL.Column.long("timeout")
      val old_time = SQL.Column.long("old_time")
      val old_command_timings = SQL.Column.bytes("old_command_timings")
      val uuid = Generic.uuid

      val table = make_table("sessions",
        List(name, deps, ancestors, sources, timeout, old_time, old_command_timings, uuid))
    }

    object Pending {
      val name = Generic.name.make_primary_key
      val deps = SQL.Column.string("deps")
      val info = SQL.Column.string("info")

      val table = make_table("pending", List(name, deps, info))
    }

    object Running {
      val name = Generic.name.make_primary_key
      val hostname = SQL.Column.string("hostname")
      val numa_node = SQL.Column.int("numa_node")

      val table = make_table("running", List(name, hostname, numa_node))
    }

    object Results {
      val name = Generic.name.make_primary_key
      val hostname = SQL.Column.string("hostname")
      val numa_node = SQL.Column.string("numa_node")
      val rc = SQL.Column.int("rc")
      val out = SQL.Column.string("out")
      val err = SQL.Column.string("err")
      val timing_elapsed = SQL.Column.long("timing_elapsed")
      val timing_cpu = SQL.Column.long("timing_cpu")
      val timing_gc = SQL.Column.long("timing_gc")

      val table =
        make_table("results",
          List(name, hostname, numa_node, rc, out, err, timing_elapsed, timing_cpu, timing_gc))
    }

    def get_serial(db: SQL.Database): Long =
      db.using_statement(Serial.table.select())(stmt =>
        stmt.execute_query().iterator(_.long(Serial.serial)).nextOption.getOrElse(0L))

    def set_serial(db: SQL.Database, serial: Long): Unit =
      if (get_serial(db) != serial) {
        db.using_statement(Serial.table.delete())(_.execute())
        db.using_statement(Serial.table.insert()) { stmt =>
          stmt.long(1) = serial
          stmt.execute()
        }
      }

    def read_progress(db: SQL.Database, seen: Long = 0, uuid: String = ""): Progress_Messages =
      db.using_statement(
        Progress.table.select(
          sql =
            SQL.where(
              SQL.and(
                if (seen <= 0) "" else Progress.serial.ident + " > " + seen,
                Generic.sql_equal(uuid = uuid))))
      ) { stmt =>
          SortedMap.from(stmt.execute_query().iterator { res =>
            val serial = res.long(Progress.serial)
            val kind = isabelle.Progress.Kind(res.int(Progress.kind))
            val text = res.string(Progress.text)
            val verbose = res.bool(Progress.verbose)
            serial -> isabelle.Progress.Message(kind, text, verbose = verbose)
          })
        }

    def write_progress(
      db: SQL.Database,
      message_serial: Long,
      message: isabelle.Progress.Message,
      uuid: String
    ): Unit = {
      db.using_statement(Progress.table.insert()) { stmt =>
        stmt.long(1) = message_serial
        stmt.int(2) = message.kind.id
        stmt.string(3) = message.text
        stmt.bool(4) = message.verbose
        stmt.string(5) = uuid
        stmt.execute()
      }
    }

    def read_sessions_domain(db: SQL.Database): Set[String] =
      db.using_statement(Sessions.table.select(List(Sessions.name)))(stmt =>
        Set.from(stmt.execute_query().iterator(_.string(Sessions.name))))

    def read_sessions(db: SQL.Database, names: Iterable[String] = Nil): State.Sessions =
      db.using_statement(
        Sessions.table.select(sql = if_proper(names, Sessions.name.where_member(names)))
      ) { stmt =>
          Map.from(stmt.execute_query().iterator { res =>
            val name = res.string(Sessions.name)
            val deps = split_lines(res.string(Sessions.deps))
            val ancestors = split_lines(res.string(Sessions.ancestors))
            val sources_shasum = SHA1.fake_shasum(res.string(Sessions.sources))
            val timeout = Time.ms(res.long(Sessions.timeout))
            val old_time = Time.ms(res.long(Sessions.old_time))
            val old_command_timings_blob = res.bytes(Sessions.old_command_timings)
            val uuid = res.string(Sessions.uuid)
            name -> Build_Job.Session_Context(name, deps, ancestors, sources_shasum,
              timeout, old_time, old_command_timings_blob, uuid)
          })
        }

    def update_sessions(db:SQL.Database, sessions: State.Sessions): Boolean = {
      val old_sessions = read_sessions_domain(db)
      val insert = sessions.iterator.filterNot(p => old_sessions.contains(p._1)).toList

      for ((name, session) <- insert) {
        db.using_statement(Sessions.table.insert()) { stmt =>
          stmt.string(1) = name
          stmt.string(2) = cat_lines(session.deps)
          stmt.string(3) = cat_lines(session.ancestors)
          stmt.string(4) = session.sources_shasum.toString
          stmt.long(5) = session.timeout.ms
          stmt.long(6) = session.old_time.ms
          stmt.bytes(7) = session.old_command_timings_blob
          stmt.string(8) = session.uuid
          stmt.execute()
        }
      }

      insert.nonEmpty
    }

    def read_pending(db: SQL.Database): List[Entry] =
      db.using_statement(Pending.table.select(sql = SQL.order_by(List(Pending.name)))) { stmt =>
        List.from(
          stmt.execute_query().iterator { res =>
            val name = res.string(Pending.name)
            val deps = res.string(Pending.deps)
            val info = res.string(Pending.info)
            Entry(name, split_lines(deps), info = JSON.Object.parse(info))
          })
      }

    def update_pending(db: SQL.Database, pending: State.Pending): Boolean = {
      val old_pending = read_pending(db)
      val (delete, insert) = Library.symmetric_difference(old_pending, pending)

      if (delete.nonEmpty) {
        db.using_statement(
          Pending.table.delete(
            sql = SQL.where(Generic.sql_member(names = delete.map(_.name)))))(_.execute())
      }

      for (entry <- insert) {
        db.using_statement(Pending.table.insert()) { stmt =>
          stmt.string(1) = entry.name
          stmt.string(2) = cat_lines(entry.deps)
          stmt.string(3) = JSON.Format(entry.info)
          stmt.execute()
        }
      }

      delete.nonEmpty || insert.nonEmpty
    }

    def read_running(db: SQL.Database): List[Build_Job.Abstract] =
      db.using_statement(Running.table.select(sql = SQL.order_by(List(Running.name)))) { stmt =>
        List.from(
          stmt.execute_query().iterator { res =>
            val name = res.string(Running.name)
            val hostname = res.string(Running.hostname)
            val numa_node = res.get_int(Running.numa_node)
            Build_Job.Abstract(name, Host.Node_Info(hostname, numa_node))
          })
      }

    def update_running(db: SQL.Database, running: State.Running): Boolean = {
      val old_running = read_running(db)
      val abs_running = running.valuesIterator.map(_.make_abstract).toList

      val (delete, insert) = Library.symmetric_difference(old_running, abs_running)

      if (delete.nonEmpty) {
        db.using_statement(
          Running.table.delete(
            sql = SQL.where(Generic.sql_member(names = delete.map(_.job_name)))))(_.execute())
      }

      for (job <- insert) {
        db.using_statement(Running.table.insert()) { stmt =>
          stmt.string(1) = job.job_name
          stmt.string(2) = job.node_info.hostname
          stmt.int(3) = job.node_info.numa_node
          stmt.execute()
        }
      }

      delete.nonEmpty || insert.nonEmpty
    }

    def read_results_domain(db: SQL.Database): Set[String] =
      db.using_statement(Results.table.select(List(Results.name)))(stmt =>
        Set.from(stmt.execute_query().iterator(_.string(Results.name))))

    def read_results(db: SQL.Database, names: List[String] = Nil): Map[String, Build_Job.Result] =
      db.using_statement(
        Results.table.select(sql = if_proper(names, Results.name.where_member(names)))
      ) { stmt =>
          Map.from(stmt.execute_query().iterator { res =>
            val name = res.string(Results.name)
            val hostname = res.string(Results.hostname)
            val numa_node = res.get_int(Results.numa_node)
            val rc = res.int(Results.rc)
            val out = res.string(Results.out)
            val err = res.string(Results.err)
            val timing =
              res.timing(
                Results.timing_elapsed,
                Results.timing_cpu,
                Results.timing_gc)
            val node_info = Host.Node_Info(hostname, numa_node)
            val process_result =
              Process_Result(rc,
                out_lines = split_lines(out),
                err_lines = split_lines(err),
                timing = timing)
            name -> Build_Job.Result(node_info, process_result)
          })
        }

    def update_results(db: SQL.Database, results: State.Results): Boolean = {
      val old_results = read_results_domain(db)
      val insert = results.iterator.filterNot(p => old_results.contains(p._1)).toList

      for ((name, result) <- insert) {
        val node_info = result.node_info
        val process_result = result.process_result
        db.using_statement(Results.table.insert()) { stmt =>
          stmt.string(1) = name
          stmt.string(2) = node_info.hostname
          stmt.int(3) = node_info.numa_node
          stmt.int(4) = process_result.rc
          stmt.string(5) = cat_lines(process_result.out_lines)
          stmt.string(6) = cat_lines(process_result.err_lines)
          stmt.long(7) = process_result.timing.elapsed.ms
          stmt.long(8) = process_result.timing.cpu.ms
          stmt.long(9) = process_result.timing.gc.ms
          stmt.execute()
        }
      }

      insert.nonEmpty
    }

    def init_database(db: SQL.Database, build_context: Build_Process.Context): Unit = {
      val tables =
        List(
          Base.table,
          Serial.table,
          Progress.table,
          Sessions.table,
          Pending.table,
          Running.table,
          Results.table,
          Host.Data.Node_Info.table)

      for (table <- tables) db.create_table(table)

      val old_pending = Data.read_pending(db)
      if (old_pending.nonEmpty) {
        error("Cannot init build process, because of unfinished " +
          commas_quote(old_pending.map(_.name)))
      }

      for (table <- tables) db.using_statement(table.delete())(_.execute())

      db.using_statement(Base.table.insert()) { stmt =>
        stmt.string(1) = build_context.uuid
        stmt.string(2) = Isabelle_System.getenv("ML_PLATFORM")
        stmt.string(3) = build_context.store.options.make_prefs(Options.init(prefs = ""))
        stmt.execute()
      }
    }

    def update_database(
      db: SQL.Database,
      uuid: String,
      hostname: String,
      state: State
    ): State = {
      val changed =
        List(
          update_sessions(db, state.sessions),
          update_pending(db, state.pending),
          update_running(db, state.running),
          update_results(db, state.results),
          Host.Data.update_numa_index(db, hostname, state.numa_index))

      val serial0 = get_serial(db)
      val serial = if (changed.exists(identity)) serial0 + 1 else serial0

      set_serial(db, serial)
      state.copy(serial = serial)
    }
  }
}



/** main process **/

class Build_Process(
  protected val build_context: Build_Process.Context,
  protected val build_progress: Progress
)
extends AutoCloseable {
  /* context */

  protected val store: Sessions.Store = build_context.store
  protected val build_options: Options = store.options
  protected val build_deps: Sessions.Deps = build_context.build_deps
  protected val verbose: Boolean = build_context.verbose


  /* global state: internal var vs. external database */

  private var _state: Build_Process.State = init_state(Build_Process.State())

  private val _database: Option[SQL.Database] =
    if (!build_options.bool("build_database_test")) None
    else if (store.database_server) Some(store.open_database_server())
    else {
      val db = SQLite.open_database(Build_Process.Data.database)
      try { Isabelle_System.chmod("600", Build_Process.Data.database) }
      catch { case exn: Throwable => db.close(); throw exn }
      Some(db)
    }

  def close(): Unit = synchronized { _database.foreach(_.close()) }

  private def setup_database(): Unit =
    synchronized {
      for (db <- _database) {
        db.transaction { Build_Process.Data.init_database(db, build_context) }
        db.rebuild()
      }
    }

  protected def synchronized_database[A](body: => A): A =
    synchronized {
      _database match {
        case None => body
        case Some(db) => db.transaction { body }
      }
    }

  private def sync_database(): Unit =
    synchronized_database {
      for (db <- _database) {
        _state =
          Build_Process.Data.update_database(
            db, build_context.uuid, build_context.hostname, _state)
      }
    }


  /* progress backed by database */

  object progress extends Progress {
    override def verbose: Boolean = build_progress.verbose

    override def output(message: Progress.Message): Unit =
      synchronized_database {
        val state1 = _state.copy(serial = _state.serial + 1)
        for (db <- _database) {
          Build_Process.Data.write_progress(db, state1.serial, message, build_context.uuid)
          Build_Process.Data.set_serial(db, state1.serial)
        }
        _state =
          if (do_output(message)) state1.echo(build_progress, state1.serial, message)
          else state1
      }

    override def stop(): Unit = build_progress.stop()
    override def stopped: Boolean = build_progress.stopped
  }

  val log: Logger = Logger.make_system_log(progress, build_options)


  /* policy operations */

  protected def init_state(state: Build_Process.State): Build_Process.State = {
    val sessions1 =
      build_context.sessions.foldLeft(state.sessions) { case (map, (name, session)) =>
        if (state.sessions.isDefinedAt(name)) map
        else map + (name -> session)
      }

    val old_pending = state.pending.iterator.map(_.name).toSet
    val new_pending =
      List.from(
        for {
          (name, session_context) <- build_context.sessions.iterator
          if !old_pending(name)
        } yield Build_Process.Entry(name, session_context.deps))
    val pending1 = new_pending ::: state.pending

    state.copy(sessions = sessions1, pending = pending1)
  }

  protected def next_job(state: Build_Process.State): Option[String] =
    if (state.running.size < (build_context.max_jobs max 1)) {
      state.pending.filter(entry => entry.is_ready && !state.is_running(entry.name))
        .sortBy(_.name)(build_context.ordering)
        .headOption.map(_.name)
    }
    else None

  protected def start_session(state: Build_Process.State, session_name: String): Build_Process.State = {
    val ancestor_results =
      for (a <- build_context.sessions(session_name).ancestors) yield state.results(a)

    val input_shasum =
      if (ancestor_results.isEmpty) {
        SHA1.shasum_meta_info(SHA1.digest(Path.explode("$POLYML_EXE")))
      }
      else SHA1.flat_shasum(ancestor_results.map(_.output_shasum))

    val store_heap = build_context.store_heap(session_name)

    val (current, output_shasum) =
      store.check_output(session_name,
        sources_shasum = build_context.sources_shasum(session_name),
        input_shasum = input_shasum,
        fresh_build = build_context.fresh_build,
        store_heap = store_heap)

    val all_current = current && ancestor_results.forall(_.current)

    if (all_current) {
      state
        .remove_pending(session_name)
        .make_result(session_name, Process_Result.ok, output_shasum, current = true)
    }
    else if (build_context.no_build) {
      progress.echo_if(verbose, "Skipping " + session_name + " ...")
      state.
        remove_pending(session_name).
        make_result(session_name, Process_Result.error, output_shasum)
    }
    else if (!ancestor_results.forall(_.ok) || progress.stopped) {
      progress.echo(session_name + " CANCELLED")
      state
        .remove_pending(session_name)
        .make_result(session_name, Process_Result.undefined, output_shasum)
    }
    else {
      progress.echo((if (store_heap) "Building " else "Running ") + session_name + " ...")

      store.init_output(session_name)

      val (numa_node, state1) = state.numa_next(build_context.numa_nodes)
      val node_info = Host.Node_Info(build_context.hostname, numa_node)
      val job =
        Build_Job.start_session(build_context, progress, log,
          build_deps.background(session_name), input_shasum, node_info)
      state1.add_running(session_name, job)
    }
  }


  /* run */

  def run(): Map[String, Process_Result] = {
    def finished(): Boolean = synchronized_database { _state.finished }

    def sleep(): Unit =
      Isabelle_Thread.interrupt_handler(_ => progress.stop()) {
        build_options.seconds("editor_input_delay").sleep()
      }

    def start(): Boolean = synchronized_database {
      next_job(_state) match {
        case Some(name) =>
          if (Build_Job.is_session_name(name)) {
            _state = start_session(_state, name)
            true
          }
          else error("Unsupported build job name " + quote(name))
        case None => false
      }
    }

    if (finished()) {
      progress.echo_warning("Nothing to build")
      Map.empty[String, Process_Result]
    }
    else {
      setup_database()
      while (!finished()) {
        if (progress.stopped) synchronized_database { _state.stop_running() }

        for (job <- synchronized_database { _state.finished_running() }) {
          val job_name = job.job_name
          val (process_result, output_shasum) = job.join
          synchronized_database {
            _state = _state.
              remove_pending(job_name).
              remove_running(job_name).
              make_result(job_name, process_result, output_shasum, node_info = job.node_info)
          }
        }

        if (!start()) {
          sync_database()
          sleep()
        }
      }

      synchronized_database {
        for ((name, result) <- _state.results) yield name -> result.process_result
      }
    }
  }
}