[9] RFR(S): 8054402: "klass->is_loader_alive(_is_alive)) failed: must be alive" for anonymous classes

[Tobias Hartmann]

Hi,

please review the following patch that fixes JDK-8054402.

Bug: https://bugs.openjdk.java.net/browse/JDK-8054402
Webrev: http://cr.openjdk.java.net/~thartmann/8054402/webrev.00/

== Problem ==
The test [1] rarely fails with the assert 
'klass->is_loader_alive(_is_alive)) failed: must be alive' in 
'CheckClass::check_class' (nmethod.cpp) because a IC in a compiled 
method [2] references an unloaded anonymous Klass* [3] (i.e., the Klass 
has an unloaded mirror class [4]). Usually, ICs are cleaned in 
'nmethod::do_unloading' by 'clean_ic_if_metadata_is_dead' if they 
reference stale metadata. In this case, the check for stale metadata is 
not performed because 'unloading_occurred' is set to false and therefore 
no class unloading should have happened.
The error is in 'SystemDictionary::do_unloading'. First, 
'ClassLoaderDataGraph::do_unloading ' is invoked to remove the class 
loader data of unloaded classes. Next, 'Dictionary::do_unloading' is 
called to remove the system dictionary entries of dead classes. 
'unloading_occurred' is only set to true if dead class loaders were 
found _and_ entries were removed from the system dictionary. The problem 
is that anonymous classes are not in the system dictionary. In the rare 
case where only anonymous classes were unloaded, 'unloading_occurred' is 
set to false even if (anonymous) class unloading occurred.

== Solution ==
The variable 'unloading_occurred' is always set to true if dead class 
loaders were found.
I was able to write a jtreg test that deterministically triggers the bug.

== Testing ==
- New jtreg test
- Failing test [1]
- JPRT

Thanks,
Tobias


[1] 
java/util/stream/test/org/openjdk/tests/java/util/stream/InfiniteStreamWithLimitOpTest.java
[2] java.util.stream.Streams$RangeIntSpliterator::forEachRemaining
[3] 
java.util.stream.StreamSpliterators$IntWrappingSpliterator$$Lambda$170/25231275
[4] java/util/stream/StreamSpliterators$IntWrappingSpliterator$$Lambda$170