inotify is a Linux kernel subsystem that acts to extend filesystems to notice changes to the filesystem, and report those changes to applications. It replaces an earlier facility, dnotify, which had similar goals.
One major use is in desktop search utilities like Beagle, where its functionality permits reindexing of changed files without scanning the filesystem for changes every few minutes, which would be very inefficient. By being told that a file has changed directly by the kernel, rather than actively looking, Beagle and such utilities can achieve change-to-reindexing times of only about a second.
Code can be downloaded from : File System Watcher
Note: Windows do have similar API FindFirstChangeNotification , have not tried but details can be found at FindFirstChangeNotification
