What do you mean near-zero? You said that inotify doesn't work (and ned14 offers his comments about it). If you are using polling, I do not understand how your approach could be using non-zero amount of resources. Let's say you are monitoring a directory with 1 million files, how can you store the state in less than 20MB of memory (which is about the most optimistic lower bound that I can think of)? What is your secret sauce? Do you mean there is no overhead beyond the baseline watcher? But what about the overhead of the baseline watcher itself?

For what it's worth, in spite of ned14's comments, I have never seen inotify fail in practice (except for if it hits the os file descriptor limits in which case it does fail noisily). The tool I wrote uses inotify for linux. It is used by thousands of developers every day as part of an editor integration and there are no open issues about dropped file events.

Your time frame is probably about right. It took me about a year to work through all the edge cases.