Why do we need thumbnailing to be a service?
For user interface applications it makes relatively few sense to run the task of creating a thumbnail in the same context as the mainloop that draws the user interface. On the other hand if each desktop application starts creating either processes or worker threads that will be armed with thumbnailing code, then we will have a lot of threads and processes all running the same code;
Most applications link with a user interface toolkit that will happily deal with the vast majority of pixbuf shaped formats. That doesn’t mean that these toolkits will equally enjoy dealing with PDF, Office and video formats. There’s a lot of code involved here and we should try to avoid requiring everybody to load these complex pieces of code into their processes. I can give a few purely technical reasons like not heaving to map-in code that is not relevant for the application, reducing VmSize (although, admittedly, only things like VmRSS are really important). There are also a few political reasons, like patented formats. In the end I’ll just say it the way it is: it’s a bad architecture;
Application developers are really not very interested in developing LIFO queues and worker threads or processes that will handle the task of creating thumbnails;
Finally, application developers are asking for this (for example F-Spot). Creating thumbnails is not at all an exclusive task for the filemanager.
My proposal
Based on those conclusions I decided to write a DBus specification. I also reimplemented Maemo’s Hildon Thumbnail to be conform this specification. This work has been merged with the TRUNK of the project and will be used on Maemo‘s Fremantle release.
While rewriting Hildon Thumbnail I decided to make sure that the software compiles and runs on any normal desktop. This way the software can serve as a proof of concept and working prototype for the DBus specification. Special care was taken to make sure it feels as desktop neutral as possible.
I opened a bug to officially request a freedesktop.org project for this specification. I hope this organization will offer a platform for further development of this DBus specification. Hildon Thumbnailer can serve as a prototype and will be adapted whenever the specification improves.