KDE's kio

The K Desktop Environment [KDE] provides a completely asynchronous virtual file system library called kio.

kio uses the same extended URI syntax that the GNU Midnight Commander uses; but unlike the Midnight Commander, all the file operations are performed through external helper processes ( kioslaves) in an asynchronous fashion. The helper process communicates with the master process using Unix domain sockets and custom protocols; the library performs encoding/decoding of such protocols automatically and notifies the programmer using the Qt [Qt] signal system.

Although this system is closer to the requirements that we have listed at the beginning of this paper, it is still suboptimal, for the following reasons:

• Operations are very simple: the API allows the programmer to download/upload a whole file and perform some simple file operations, but it does not provide all the versatility of the Unix API.
• Each file operation requires an external process: kio does not take advantage of threads.
• There is no API to perform operations in a synchronous fashion, so the programmer needs to spawn a process, request an operation and then wait for the result from it.