code: public Job fork() {
      init();
      H2OCountedCompleter task = new H2OCountedCompleter() {
        @Override public void compute2() {
          try {
            try {
              // Exec always waits till the end of computation
              Job.this.exec();
              Job.this.remove();
            } catch (Throwable t) {
              if(!(t instanceof ExpectedExceptionForDebug))
                Log.err(t);
              Job.this.cancel(t);
            }
          } finally {
              tryComplete();
          }
        }
      };
      start(task);
      H2O.submitTask(task);
      return this;
    }
docs: Forks computation of this job.
  
  <p>The call does not block.</p>
  @return always returns this job.