DesktopFile

It is allowed to call this method even if there is an ongoing previous closure process. In such case the future of the ongoing closure is returned.

When a file is opened, this reports true. As soon as close is called, this method reports false, even if the asynchronous closure is still going on. At this point no further reads or writes should be made.

Advances the position by len bytes. Note that negative numbers are allowed, essentially moving the position backwards.