Watch directory for file changes

Question

I want to monitor a directory (of thousands of files, with about 5 levels of sub directories) for when files are changed. I know I can use the FSEvents API to monitor a directory for when files change inside that directory, but I can't seem to figure out how to determine which file(s) changed. This reference suggests I build a binary tree and traverse the tree each time an event is triggered, is that the best way to determine which files were changed? If not, what are some better alternatives?

Is it better to recursively scan the directory and attach kqueue to every file? I'm not sure how well that would work on thousands of files?

Answer 1

I've used UKKQueue before with mixed results.

I've recently become aware of a better solution, but I haven't tried this. If you only need to target Lion, I think that the new best-practice way to do this is to use an NSFileCoordinator. You implement the methods of NSFilePresenter to indicate which directory you're interested in (the presentedItemURL property) and the system will notify you when a sub item moves/changes/is deleted (via methods like presentedSubitemDidChangeAtURL:)

I'd love to hear how that works out if you do go that route.

Answer 2

If you create your stream using kFSEventStreamCreateFlagFileEvents then you will get events for the changes to each file rather than just a notification of the change to the watched directory. Unfortunately this is only available in OSX 10.7 and later.