Carsten,
It's been a long time! Thanks for the quick review...
Replies embedded below...
On 10/19/15, 10:09 PM, Carsten Varming wrote:
Dear Dan,
I thought acquire/release semantics mandated that the release should
be paired with an acquire.
Yes, src/share/vm/runtime/orderAccess.hpp is pretty clear about
that. I modeled this fix after some other ObjectMonitor code
that doesn't (yet) follow that mandate.
In this case, the first line in verify_objmon_isinpool should be
changed from "PaddedEnd<ObjectMonitor> * block =
(PaddedEnd<ObjectMonitor> *)gBlockList" to use a load_acquire.
Actually, it seems like there are a lot of reads of gBlockList that
should be replaced with a load_acquire in synchronizer.cpp.
Yes, that would be a good change and cleanup. The really annoying
part is that the current fix seems to have resolved the bug...
Current numbers: 700K iterations of 4 fastdebug instances in parallel
in 4.5 days. I typically saw one failure per day in a three day run...
Otherwise the change looks great.
Thanks!
Dan
Carsten
(not a reviewer).
On Mon, Oct 19, 2015 at 8:02 PM, Daniel D. Daugherty
<daniel.daughe...@oracle.com <mailto:daniel.daughe...@oracle.com>> wrote:
Greetings,
I have a fix for a long standing race between the lock-free
ObjectMonitor
verification code and the normal (locked) ObjectMonitor block
allocation
code path. For this fix, I would like at least a Runtime team reviewer
and a Serviceability team reviewer. Thanks!
JDK-8047212
runtime/ParallelClassLoading/bootstrap/random/inner-complex
assert(ObjectSynchronizer::verify_objmon_isinpool(inf)) failed:
monitor is invalid
https://bugs.openjdk.java.net/browse/JDK-8047212
Webrev URL:
http://cr.openjdk.java.net/~dcubed/8047212-webrev/0-jdk9-hs-rt/
<http://cr.openjdk.java.net/%7Edcubed/8047212-webrev/0-jdk9-hs-rt/>
Testing: Aurora Adhoc RT-SVC nightly batch
4 inner-complex fastdebug parallel runs for 4+ days and
600K iterations without seeing this failure; the experiment
is still running; final results to be reported at the end
of the review cycle
JPRT -testset hotspot
This fix:
- makes ObjectMonitor::gBlockList volatile
- uses "OrderAccess::release_store_ptr(&gBlockList, temp)" to
make sure the new block updates _happen before_ gBlockList is
changed to refer to the new block
- add SA support for a "static pointer volatile" field like:
static ObjectMonitor * volatile gBlockList;
See the following link for a nice description of what "volatile"
means in the different positions on a variable/parameter decl line:
http://www.embedded.com/electronics-blogs/beginner-s-corner/4023801/Introduction-to-the-Volatile-Keyword
Thanks, in advance, for any comments, questions or suggestions.
Dan
