Hi Team, We hit an interesting and exciting intermittent exception in our customer-facing product search instance (all Lucene!) at Amazon:
java.lang.WrongThreadException: Attempted access outside owning thread at java.base/jdk.internal.foreign.MemorySessionImpl.wrongThread(MemorySessionImpl.java:460) at java.base/jdk.internal.misc.ScopedMemoryAccess$ScopedAccessError.newRuntimeException(ScopedMemoryAccess.java:113) at java.base/jdk.internal.misc.ScopedMemoryAccess.getByte(ScopedMemoryAccess.java:518) at java.base/java.lang.invoke.VarHandleSegmentAsBytes.get(VarHandleSegmentAsBytes.java:109) at java.base/java.lang.foreign.MemorySegment.get(MemorySegment.java:1103) at org.apache.lucene.store.MemorySegmentIndexInput$SingleSegmentImpl.readByte(MemorySegmentIndexInput.java:485) at org.apache.lucene.util.fst.ReverseRandomAccessReader.readByte(ReverseRandomAccessReader.java:33) at org.apache.lucene.util.fst.FST.findTargetArc(FST.java:1444) at org.apache.lucene.codecs.lucene90.blocktree.SegmentTermsEnum.seekExact(SegmentTermsEnum.java:511) at org.apache.lucene.index.TermStates.loadTermsEnum(TermStates.java:111) at org.apache.lucene.index.TermStates.build(TermStates.java:96) We are using Corretto Java full version: openjdk full version "19.0.2+9" Looking at how Uwe's magic mrjar code works, it doesn't look like we ever make a thread private MemorySegment? If so, I don't see how this exception could be occurring :) We seem to do this: final MemorySession session = MemorySession.openShared(); Or, maybe we do sometimes make thread private memory segments, and maybe we (Amazon's sources) have a silly thread over-sharing bug, but so far I think that's unlikely -- we are calling TermStates.build from a single thread, which under the hood clones/slices the MMap IndexInputs to seek the terms dictionary on each segment and only that one thread ever interacts with those. It's all just one thread under TermStates.build. This only happened on a few hosts and only for a short period of time, making me suspect some sort of intermittent JVM bug (e.g. HotSpot miscomiplation or so). It is clearly very rare, so we are still using the new MMap (which btw seems to be a big performance gain for our service, which we are still trying to fully understand, more on that later!). Has anyone else seen such errant exceptions with the new Panama based MMap? Are there any known Java issues that smell like this? (A quick search on bugs.openjdk.org ( https://bugs.openjdk.org/browse/JDK-8287809?jql=issuetype%20%3D%20Bug%20AND%20text%20~%20WrongThreadException) did not seem to turn up any obvious candidates). Thanks, Mike McCandless http://blog.mikemccandless.com
