Monitoring folders for changes

I'm working on a project that will require an application that watches a list of directories the user specifies f开发者_如何学运维or changes. Also, I'd like to give the users the option of running the application as a service or on an individual basis. Since users can choose to run it on an individual basis I don't think listening for some operating system event triggered by the addition or deletion of files (if such events exist) would be sufficient. I thought about maybe calculating a checksum for the deepest folder and then building up. I could then compare these checksums on subsequent scans to try and pinpoint where the changes have occurred. Would that be an appropriate solution; if not what would be the best way of doing this in an efficient manner?

Also, I'm not quite sure what to tag this as so if you have any recommendations let me know and I'll as them as I see fit.

EDIT: I'll need this method to work on Windows, OS X, and ideally Linux

On Mac OSX, you can use FSEvent, which is similar to inotify interface on Linux.

There exist several methods for tracking changes.

The simplest is to scan the directory on timer and compare timestamps and file sizes. However this is resource-consuming and some changes can be missed (eg. if the file changed twice between checks, first change will be missed).

Next, one can use FindFirstChangeNotification Windows API function (it has it's own limitations, though).

And the most sophisticated and most reliable method is to use a filesystem filter driver. On Windows our CallbackFilter can be used. On MacOS X it's possible to create a filter driver, but I don't know about any ready-to-use product similar to CallbackFilter. On Linux, one can use inotify.

If the filesystems supports CIFS/SMB protcol, you may consider change notification feature in protocol. Refer to http://msdn.microsoft.com/en-us/library/aa302188.aspx for CIFS overview.

man kqueue

(at least, that's how i'd do it on my most oft targeted OS - but you should specify this in your post)