Dear Dan, I thought acquire/release semantics mandated that the release should be paired with an acquire. 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.
Otherwise the change looks great. Carsten (not a reviewer). On Mon, Oct 19, 2015 at 8:02 PM, Daniel D. Daugherty < 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/ > > 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 > >
