RFR: 8278123: serviceability/dcmd/vm/ClassLoaderStatsTest.java failing with java.lang.AssertionError: Should have a hidden class

[Leonid Mesnik]

On Thu, 28 Apr 2022 00:44:18 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> The test failed if GC happens somewhere between
>> Class<?> c = Class.forName("TestClass", true, dummyloader);
>> and
>> OutputAnalyzer output = executor.execute("VM.classloader_stats");
>> 
>> The fix is to make hc static as Chris proposed. 
>> 
>> To verfiy fix I add System.gc() before executor.execute("VM.classloader_stats");
>
> test/hotspot/jtreg/serviceability/dcmd/vm/ClassLoaderStatsTest.java line 178:
> 
>> 176:     static {
>> 177:         try {
>> 178:             // Create a hidden class, keep reference in the case if GC happens
> 
> "Create a hidden class. Keep a reference in case a GC happens."
> 
> I hadn't noticed the original comment when first suggesting making the Class reference static. I wonder what was meant by "non-strong class".

This line added by  8238358: Implementation of JEP 371: Hidden Classes which has many co-authors. Hope someone could provide an explanation during this review.

It might be possible that the goal was to verify that  VM.classloader_stats provide might provide info for non-reachable clasees. However it makes test to fragile, since can't block class unloading now.

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PR: https://git.openjdk.java.net/jdk/pull/8438