/** @param log Logger. */
    private void execute(GridLogger log) {
      try {
        log.info("Started execute.");

        // Countdown shared job latch so that the main thread know that all jobs are
        // inside the "execute" routine.
        jobLatch.countDown();

        log.info("After job latch.");

        // Await for the main thread to allow jobs to proceed.
        latch.await();

        log.info("After latch.");

        if (awaitMasterLeaveCallback) {
          latch0.await();

          log.info("After latch0.");
        } else log.info("Latch 0 skipped.");
      } catch (InterruptedException e) {
        // We do not expect any interruptions here, hence this statement.
        fail("Unexpected exception: " + e);
      }
    }
    /**
     * @param log Logger.
     * @param job Actual job.
     */
    private void onMasterLeave(GridLogger log, Object job) {
      log.info("Callback executed: " + job);

      latch0.countDown();

      invokeLatch.countDown();
    }