vmTestbase/nsk/jvmti/GarbageCollectionStart/gcstart001/ is failing in the loom repo. The test generates a lot (1000+) of gc's, which results in a bunch of of GarbageCollectionStart + GarbageCollectionFinish events. It expects that when a start event arrives, the count of the number of finish events is one less than the number of starts events so far, including the current start event. Likewise when a finish event arrives the number of start events and finish events should be equal. Basically it's checking that it receives start/finish events in ordered pairs.

However, sometimes during a test run it looks like a finish event gets delayed, resulting in the next start event being received before the previous finish event is received. This causes a test error to be reported at the time this is detected, although the test will still continue to run to completion after reporting this error, and will report more errors if this happens again (it's very common to see this happen twice in a test run).

Based on the output you can see that the finish even is delayed, not lost. Otherwise you would see a bunch of errors after the first one, and at the end it would not be reporting that the same number of start and finish events were received.

This is only happening in the loom repo. Here's one test with two reported failures. There were about 200 GCs in this test run:

The following fake exception stacktrace is for failure analysis.
nsk.share.Fake_Exception_for_RULE_Creation: (gcstart001.cpp:58) TEST FAILED: GarbageCollectionStart event has no a matched pair GarbageCollectionFinish:
at nsk_lvcomplain(nsk_tools.cpp:172)
# ERROR: gcstart001.cpp, 58: TEST FAILED: GarbageCollectionStart event has no a matched pair GarbageCollectionFinish:
42 GarbageCollectionStart events 40 GarbageCollectionFinish events
# ERROR: gcstart001.cpp, 75: TEST FAILED: GarbageCollectionFinish event has no a matched pair GarbageCollectionStart:
42 GarbageCollectionStart events 41 GarbageCollectionFinish events
# ERROR: gcstart001.cpp, 58: TEST FAILED: GarbageCollectionStart event has no a matched pair GarbageCollectionFinish:
401 GarbageCollectionStart events 399 GarbageCollectionFinish events
# ERROR: gcstart001.cpp, 75: TEST FAILED: GarbageCollectionFinish event has no a matched pair GarbageCollectionStart:
401 GarbageCollectionStart events 400 GarbageCollectionFinish events