Problems persist in KQueueSelectorProvider (Mac) in 7u6 ea

[Jason T. Greene]

I have been pretty short on time with paternity leave, but I was able to 
debug this a little bit further. One of the main issues is that interest 
ops is zero on keys that kqueue is returning, hence the tight loop.

There appears to be thread safety issues with EV_ADD/EV_DELETE from 
multiple threads. Synchronizing KQueueArrayWrapper.setInterest(int,int) 
seems to resolve both issues, at least so far.

I do wonder if an alternative approach using EV_ENABLE/EV_DISABLE might 
eliminate the need for extra locking.


On 8/10/12 6:36 PM, David M. Lloyd wrote:
> We're consistently seeing issues under load on Mac with
> KQueueSelectorProvider.
>
> There are two possibly related symptoms: the KQueueSelectorImpl is going
> into a mode where select() does not block, despite the continued
> emptiness of the selected key set; and FileDispatcherImpl#preClose0 is
> hanging, presumably in dup2(), trying to close a socket.
>
> My current hypothesis that some evil race condition exists and is being
> tripped between kqueue and dup2 (a relatively rare way to close a
> socket, at least until NIO came along I guess).  My thought though is
> that sockets should not be preclosed this way: instead it would be
> better to use shutdown(fd, SHUT_RDWR), which would effectively preclose
> the socket and hopefully dodge this issue.
>
> I'm hopefully going to have time to try out a patch which does this, but
> I'm taking a couple weeks off starting tonight so I may not have time,
> so we shall see.


-- 
Jason T. Greene
JBoss AS Lead / EAP Platform Architect
JBoss, a division of Red Hat