Apple

>
> I have a long running process that periodically (once every half hour) uses
> FSEvents API to find list of modified files in a particular folder. I am
> seeing following problem with the APIs:

Any particular reason you're not just leaving an FSEventStream open while
your long-running process runs? It takes more work to dig through historical
events because they need to be read out of on-disk logs.

I use the set of changes in one go every half hour (or more - the duration is configurable and could be very long). If I keep the stream open, then I will have to persist the events till I use them (to avoid losing them on app crash or reboot). Since FSEvents already persists the events, it makes sense to not duplicate the effort and read them when needed.

> If fseventsd daemon is stopped and started (using launchctl or killing the
> process), then further calls to FSEvents API fails. FSEventsStreamStart()
> always fails after fseventsd is restarted. APIs like
> FSEventsGetCurrentEventId() starts returning 0 and
> FSEventsCopyUUIDForDevice() returns NULL UUID, both of which are wrong.
>
> Please let me know what is required to successfully call FSEvents API after
> restart of fseventd daemon. I want to take care of this issue so that my
> application starts using FSEvents even when fseventsd is restarted.

You should never need or want to stop/restart fseventsd.
fseventsd should always be running... otherwise events will be dropped.

My app never stops/starts fseventsd. However, I want to make sure that the app does not miss any file change in any scenario - be it someone killing fseventsd or restarting it using the supported launchctl command. If the daemon is restarted, I detect that using changed UUID (and use alternative methods to detect changes).

However, I expect that in the next cycle (second after the restart) I should be able to use FSEvents again - but this is the case where the API is not working.

If fseventsd isn't working properly, please file a bug with Apple.
If the FSEvents API isn't working properly, please file a bug with Apple.

If the FSEvents API isn't working properly BECAUSE fseventsd is being
manipulated in unusual/unsupported ways, you can file a bug with Apple
but it probably won't be assigned a very high priority.

Thanks for the inputs. But being new to Mac development, I want to know if my understanding about the API and Carbon framework is correct and I am not missing something which can fix the problem. To explain the case, consider a small C code:

#import <CoreServices/CoreServices.h>

int main()

{

while (1)

{

printf("Current Event ID = %d\n", FSEventsGetCurrentEventId());

// any initialization/cleanup needed here to handle restart case ??

sleep(5);

}

Until fseventsd is stopped, everything works fine and the program print correct event ID values. However, when stopped, the program starts printing 0, and it keeps printing 0 forever - even long after the daemon comes up. My query is - is there some initialization/cleanup API that can be called to make the next call work correctly. If not, then I will open a bug with Apple.

Thanks,

Ashish

THanks
--macko