[wildfly-dev] issues with IBM JVM on Linux

[Alexey Loubyansky]

I've been trying to narrow down sporadic failures in the wfcore patching 
tests on the IBM JVM on Linux (version info below) for the last few 
days. I wanted to share this because what I see doesn't make sense to 
me. And I am not sure whether other modules have similar issues.

So, in patching tests the (sporadic) problem appears when parsing XML 
attributes. E.g. if there is an element with attributes 'name' and 
'add-on', sometimes the value of name will end up containing the value 
of add-on attribute. Here is the actual code for this (Attribute is an 
enum) from org.jboss.as.patching.metadata.PatchXmlUtils:

String name = null;
boolean isAddOn = false;
final int count = reader.getAttributeCount();
for (int i = 0; i < count; i++) {
     final String value = reader.getAttributeValue(i);
     final Attribute attribute = 
Attribute.forName(reader.getAttributeLocalName(i));
     if(Attribute.NAME == attribute) {
         name = value;
     } else if (Attribute.ADD_ON == attribute) {
         isAddOn = Boolean.valueOf(value);
     } else {
         throw unexpectedAttribute(reader, i);
     }
}

So, sometimes the tests fail because the value of name is 'true', 
apparently. This is just one example. It affects parsing attributes in 
general in this class.

I noticed that if I do anything with variable 'value' in the loop (or 
pass it as an argument to some method and actually do something with it 
in that method), e.g. System.err.println("value=" + value); the problem 
goes away.

Another workaround I've found is to inline the variable, i.e. use 
reader.getAttributeValue(i) directly instead of using a variable.

By the "problem goes away" I mean that I haven't seen these kind of 
failures anymore with the changes I mentioned. To give some statistics, 
with the original code the tests would fail from 2 to 5 times out of 10 
runs.
With the inlined variable value they pass 100%. I've be running them for 
3 days now.

Here is the JVM info.

java version "1.8.0"
Java(TM) SE Runtime Environment (build pxi3280-20150129_02)
IBM J9 VM (build 2.8, JRE 1.8.0 Linux x86-32 20150116_231420 (JIT 
enabled, AOT enabled)
J9VM - R28_Java8_GA_20150116_2030_B231420
JIT  - tr.r14.java_20150109_82886.02
GC   - R28_Java8_GA_20150116_2030_B231420
J9CL - 20150116_231420)
JCL - 20150123_01 based on Oracle jdk8u31-b12


Any ideas or suggestions?


Thanks,
Alexey