code: private long getBytesWritten() {
      long bytesWritten = 0;
      for (Optional<Fork> fork : this.forks.keySet()) {
        bytesWritten += fork.get().getBytesWritten();
      }
      return bytesWritten;
    }
docs: Get the total number of bytes written by every {@link Fork}s of this {@link Task}.
  
  @return the number of bytes written by every {@link Fork}s of this {@link Task}