Hi Daniil,
On 4/07/2019 1:04 pm, Daniil Titov wrote:
Please review the change the fixes the problem with the debugger not stopping
in the low memory notification code.
The problem here is that the ServiceThread that calls these MXBean listeners is
hidden from the external view that prevents the debugger from stopping in it.
The fix introduces new NotificationThread that is visible to the external view
and offloads the ServiceThread from sending low memory and other notifications
that could result in Java calls ( GC and diagnostic commands notifications) by
moving these activities in this new NotificationThread.
There is a long and unfortunate history with this bug.
The original incarnation of this fix was introducing a new thread at the
Java library level, and I had some concerns about that:
http://mail.openjdk.java.net/pipermail/serviceability-dev/2017-December/022612.html
That effort was resurrected at:
http://mail.openjdk.java.net/pipermail/serviceability-dev/2018-July/024466.html
and
http://mail.openjdk.java.net/pipermail/serviceability-dev/2018-August/024849.html
but was left somewhat in limbo. There was a lot of doubt about the right
way to fix this bug and whether introducing a new thread was too disruptive.
But introducing a new thread in the VM also has the same set of
concerns! This needs consideration by the runtime team before going
ahead. Introducing a new thread likes this needs to be examined in
detail - particularly the synchronization interactions with other
threads. It also introduces another monitor designated safepoint-never
at a time when we are in the process of cleaning up monitors so that
JavaThreads will only use safepoint-check-always monitors.
Unfortunately I'm about to head out for two weeks vacation, and a number
of other key runtime folk are also on vacation. but I'd ask that you
hold off on this until we can look at it in more detail.
Thanks,
David
-----
Testing: Mach5 tier1,tier2 and tier3 tests succeeded.
Webrev: https://cr.openjdk.java.net/~dtitov/8170299/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8170299
Thanks!
--Daniil
