On Fri, 25 Oct 2024 06:49:48 GMT, Stefan Karlsson <stef...@openjdk.org> wrote:
>> When testing Lilliput we found a failure in >> `serviceability/sa/ClhsdbJstackWithConcurrentLock.java` test when running >> with C1-only. >> >> The test uses the SA's thread printing feature to print the threads *and* >> the "concurrent locks" / AbstractOwnableSynchronizers. It then verifies that >> the expected lock is listed in the section for "Locked ownable >> synchronizers". >> >> When we turned on Lilliput's -XX:+UseCompactObjectHeaders this stopped >> working, and we got nothing reported in that section: >> >> >> "Thread-0" #31 prio=5 tid=0x00007a708c259ad0 nid=1480533 waiting on >> condition [0x00007a706fefe000] >> java.lang.Thread.State: TIMED_WAITING (sleeping) >> JavaThread state: _thread_blocked >> - java.lang.Thread.sleepNanos0(long) @bci=0 (Interpreted frame) >> - java.lang.Thread.sleepNanos(long) @bci=33, line=497 (Interpreted frame) >> - java.lang.Thread.sleep(long) @bci=25, line=528 (Interpreted frame) >> - LingeredAppWithConcurrentLock.lockMethod(java.util.concurrent.locks.Lock) >> @bci=13, line=38 (Interpreted frame) >> - locked <0x00000000ffd32d88> (a >> java.util.concurrent.locks.ReentrantLock) >> - LingeredAppWithConcurrentLock.lambda$main$0() @bci=3, line=46 >> (Interpreted frame) >> - LingeredAppWithConcurrentLock$$Lambda+0x00007a7023001000.run() @bci=0 >> (Interpreted frame) >> - java.lang.Thread.runWith(java.lang.Object, java.lang.Runnable) @bci=5, >> line=1589 (Interpreted frame) >> - java.lang.Thread.run() @bci=19, line=1576 (Interpreted frame) >> >> Locked ownable synchronizers: >> - None >> >> >> It should be saying: >> >> Locked ownable synchronizers: >> - <0x00000000ffd32d88>, (a >> java/util/concurrent/locks/ReentrantLock$NonfairSync) >> >> >> The problem lies within the code that searches for objects in the heap. It >> collects a bunch of regions and searches them for objects. However, the code >> that describes the TLAB regions are stale and doesn't match the C++ >> implementation in the JVM. When Lilliput shrinks the headers the SA code is >> broken enough to cause the TLAB regions to be reported as overlapping. This >> has ripple effects that the object iterators stop working. >> >> I can get this test to pass, with and without compact object headers, by >> fixing the code in `ThreadLocalAllocBuffer::hard_end()`. >> >> This is a reproducer of the problem: >> >> make -C ../build/fastdebug test >> TEST=serviceability/sa/ClhsdbJstackWithConcurrentLock.java >> JTREG="JAVA_OPTIONS=-XX:TieredStopAtLevel=2 -XX:+UnlockExperimentalVMOptions >> -XX:+UseCompactObjectHeaders" >> >> >> I've test... > > Stefan Karlsson has updated the pull request incrementally with one > additional commit since the last revision: > > Copyright Marked as reviewed by cjplummer (Reviewer). ------------- PR Review: https://git.openjdk.org/jdk/pull/21662#pullrequestreview-2394351437
