I want my code to be notified when any file under (either directly or indirectly) a given directory is modified. By "modified", I mean 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)?
I haven't tried this myself, but it seems like FSEvents is able to provide file-level notifications as of 10.7 (Lion). From the description of FSEventStreamCreateFlags:
kFSEventStreamCreateFlagFileEventsRequest file-level notifications. Your stream will receive events about individual files in the hierarchy you're watching instead of only receiving directory level notifications. Use this flag with care as it will generate significantly more events than without it.
Available in OS X v10.7 and later.