Method updateTask

src/master/master.cpp:11103–11250

void Master::updateTask(Task* task, const StatusUpdate& update)
{
  CHECK_NOTNULL(task);

  // Get the unacknowledged status.
  const TaskStatus& status = update.status();

  // NOTE: Refer to comments on `StatusUpdate` message in messages.proto for
  // the difference between `update.latest_state()` and `status.state()`.

  // Updates from the slave have 'latest_state' set.
  Option<TaskState> latestState;
  if (update.has_latest_state()) {
    latestState = update.latest_state();
  }

  const TaskState updateState = latestState.getOrElse(status.state());

  // Determine whether the task transitioned to terminal or
  // unreachable prior to changing the task state.
  auto isTerminalOrUnreachableState = [](const TaskState& state) {
    return protobuf::isTerminalState(state) || state == TASK_UNREACHABLE;
  };

  bool transitionedToTerminalOrUnreachable =
    !isTerminalOrUnreachableState(task->state()) &&
    isTerminalOrUnreachableState(updateState);

  // Indicates whether we should send a notification to subscribers,
  // set if the task transitioned to a new state.
  bool sendSubscribersUpdate = false;

  Framework* framework = getFramework(task->framework_id());

  // If the task has already transitioned to a terminal state,
  // do not update its state. Note that we are being defensive
  // here because this should not happen unless there is a bug
  // in the master code.
  //
  // TODO(bmahler): Check that we're not transitioning from
  // TASK_UNREACHABLE to another state.
  if (!protobuf::isTerminalState(task->state())) {
    if (task->state() != updateState && framework != nullptr) {
      // When we observe a transition away from a non-terminal state,
      // decrement the relevant metric.
      framework->metrics.decrementActiveTaskState(task->state());

      framework->metrics.incrementTaskState(updateState);
    }

    task->set_state(updateState);
  }

  // If this is a (health) check status update, always forward it to
  // subscribers.
  if (status.reason() == TaskStatus::REASON_TASK_CHECK_STATUS_UPDATED ||
      status.reason() == TaskStatus::REASON_TASK_HEALTH_CHECK_STATUS_UPDATED) {
    sendSubscribersUpdate = true;