Renamed events are not properly combined on macOS 11

[samschott]

On macOS 11 and possibly previous releases, renamed events are not properly combined to a single event but are reported as separate deleted and created events instead.

The FSEventStream on macOS always reports two renamed events: one at the old path and one at the new path. Watchdog tries to combine them intelligently and relies on an undocumented observation that the event IDs of those two events will only differ by one:

watchdog/src/watchdog/observers/fsevents.py

Lines 88 to 96 in d0bb7b8

	# Internal moves appears to always be consecutive in the same
	# buffer and have IDs differ by exactly one (while others
	# don't) making it possible to pair up the two events coming
	# from a singe move operation. (None of this is documented!)
	# Otherwise, guess whether file was moved in or out.
	# TODO: handle id wrapping
	if (i + 1 < len(events) and events[i + 1].is_renamed
	and events[i + 1].event_id == event.event_id + 1):
	cls = DirMovedEvent if event.is_directory else FileMovedEvent

However, macOS 11, the two events will have equal event IDs. This may be the result of changes to APFS and atomic file moves.

[samschott]

Never mind, this issue is bogus. For some reason, the event_id for all events currently is 67584, no matter if they are related or not. I'll look into it.

[samschott]

Those event IDs which Python receives are definitely strange. They are not monotonically increasing and often repeat themselves. Those surely cannot be the event IDs as documented in https://developer.apple.com/documentation/coreservices/fseventstreameventid?language=objc.

@CCP-Aporia, do you have any idea what may be going on here?

[samschott]

Ok, I found the issue. You have been passing event flags instead of IDs:

watchdog/src/watchdog_fsevents.c

Lines 302 to 304 in d0bb7b8

	id = PyLong_FromLongLong(event_flags[i]);
	path = PyUnicode_FromString(event_paths[i]);
	flags = PyLong_FromLong(event_flags[i]);

[HEmile]

I'm having trouble handling EVENT_TYPE_MODIFIED on my macOS 10.15.6. The event doesn't fire, and afterward renaming a file, no other events fire either. Is this related?

[samschott]

No, that is issue #721 which has already been fixed in the master branch.