code: func NewFilePool(N int64, dir string) Pool {
  	return &filePool{N: N, Directory: dir}
  }
docs: // NewFilePool returns a Pool, Get() returns a file-based buffer of max size N.
  // Put() closes and deletes the underlying file for the buffer.
  // Get() may return an error if it fails to create a file for the buffer.
  // Put() may return an error if it fails to delete the file.