/** Lock used whenever accessing the state variables (runningTasks, shutdown) of the executor */
  private final Object lock = new Object();

  /*
   * Conceptually, these two variables describe the executor being in
   * one of three states:
   *   - Active: shutdown == false
   *   - Shutdown: runningTasks > 0 and shutdown == true
   *   - Terminated: runningTasks == 0 and shutdown == true
   */
  @GuardedBy("lock")

              runningTask = scheduler().schedule(delegate, executorService, task);
              notifyStarted();
            } catch (Throwable t) {
              restoreInterruptIfIsInterruptedException(t);
              notifyFailed(t);
              if (runningTask != null) {
                // prevent the task from running if possible
                runningTask.cancel(false);
              }

              runningTask = scheduler().schedule(delegate, executorService, task);
              notifyStarted();
            } catch (Throwable t) {
              restoreInterruptIfIsInterruptedException(t);
              notifyFailed(t);
              if (runningTask != null) {
                // prevent the task from running if possible
                runningTask.cancel(false);
              }