Currently, Parapin only supports a single parallel port at a time. It is not possible to have a single instance of the library manage multiple instances of a parallel port. This may be a problem for software that is simultaneously trying to control multiple parallel ports. Someday, I may fix this, but it will make the interface messier (a port handle will have to be passed to every function along with pin specifiers).
The C-library version of Parapin should probably do better probing of the parallel port, but my desire to do this was limited because it replicates what is already done by the Linux kernel (and I usually use the kernel version of Parapin these days anyway).
If you have bug reports, patches, suggestions, or any other comments, please feel free to contact me at firstname.lastname@example.org. I love getting feedback.