I now have an answer directly from Apple.
The scenario was wrong to begin with. When saving the last event id treated, you must also save with it the UUID of the event stream. An event id is valid only for a given event stream, which is identified by its UUID (see FSEventsCopyUUIDForDevice()
).
Whenever the event id counter wraps around, a new event stream UUID is generated. So if you relaunch the app after the event id counter wrapped around, your stored last event id won’t be valid anymore, and you’ll know it as the event stream UUID won’t be the same.
If you encounter the kFSEventStreamEventFlagEventIdsWrapped
flag, it means the counter wrapped around while your app was open. However, there’s nothing particular to be done. You should just be sure to get the new event stream UUID if you want to save the last event id.