RFR(S): 8034801: AIX: (ch) Fix synchronization issue in AixPollPort.java

[Volker Simonis]

Hi,

could you please review the following small, AIX-only change:

http://cr.openjdk.java.net/~simonis/webrevs/8034801/
https://bugs.openjdk.java.net/browse/JDK-8034801

On AIX we use the AIXPollPort class to wrap the native pollset functionality.

AIXPollPort is based on the Linux EPollPort class. But on AIX there's
an extra difficulty - we can not modify (with pollset_ctl()) and query
(with pollset_poll()) a pollset concurrently (like this is possible on
Linux with epoll_ctl() and epoll_wait()).

We have therefore synchronized calls to pollset_ctl() and
pollset_poll() by using an extra control queue which handles these
calls sequentially.

This implementation has an error which can lead to a deadlock if we
have a pending pollset_ctl() event in the control queue while the
corresponding pollset is already empty.

This change fixes the problem. It also reduces the number of calls to
pollsetCtl() by checking more exactly which descriptors are removed
from a pollset (thus avoiding calls to pollsetCtl() which just
reinsert a previously deleted descriptor).

This change is for jdk9/hs-comp/jdk (because that’s currently the only
repo with a full AIX-port. But it will be also needed for the downport
to jdk8u, once our port will be integrated there.

Thank you and best regards,
Volker