I want my code to be notified when any file under (either directly or indirectly) a given directory is modified. By "modified", I mead I want my code to be notified whenever a file's contents are altered, it's renamed, or it's deleted; or if a new file is added. For my application, there can be thousands of files.

I looked as FSEvents, but its Technology Overview says, in part:

The important point to take away is that the granularity of notifications is at a directory level. It tells you only that something in the directory has changed, but does not tell you what changed.

It also says:

The file system events API is also not designed for finding out when a particular file changes. For such purposes, the kqueues mechanism is more appropriate.

However, in order to use kqueue on a given file, one has to open the file to obtain a file descriptor. It's impractical to manage thousands of file descriptors (and would probably exceed the maximum allowable number of open file descriptors anyway).

Curiously, under Windows, I can use the ReadDirectoryChangesW() function and it does precisely what I want.

So how can one do what I want under Mac OS X? Or, asked another way: how would one go about writing the equivalent of ReadDirectoryChangesW() for Mac OS X in user-space (and do so very efficiently)?