kevent behavior

[Ivan Radovanovic]

On 03/19/15 11:01, Konstantin Belousov napisa:
> On Thu, Mar 19, 2015 at 07:33:06AM +0100, Ivan Radovanovic wrote:
>> Hi guys,
>>
>> Is there defined (and guaranteed) behavior of kevent if kqueue FD is
>> being closed while blocking kevent call is in progress?
>>
>> Possible scenario would be like this:
>>
>> Thread 1:
>> ...
>> kfd = kqueue();
>> ...
>> // create second thread afterwords
>> // and do blocking wait for events
>> result = kevent(kfd, changelist, nchanges, eventlist, nevents, NULL);
>> if (result == -1)
>> 	// check if there was request to stop listening for events
>>
>>
>> Thread 2:
>> // do something
>> // then close kqueue's fd
>> close(kfd);
>>
>>
>> I am asking this because file watcher implementation for mono is
>> implemented that way (which I find nicer than using timeout), but this
>> is apparently based on expected kevent behavior under Darwin, and I
>> can't find any mention that in FreeBSD kevent is going to behave the
>> same way (at least not on kqueue(2) manual page)
>
> The only special action taken by kqueue subsystem when a file descriptor
> becomes invalid due to close, is the removal of all registered events
> which reference the closing file descriptor. And, to prevent kqueue
> code from stepping on its own toes, the close() call is put into
> uninterruptible sleep with the "kqclose" wait channel until all
> currently active kevent(2) calls release the references.
>

So if I understand you correctly close(kfd) would simply block because 
kevent on same kqueue descriptor is in progress?