RFR 8243572: Multiple tests fail with assert(cld->klasses() != 0LL) failed: unexpected NULL for cld->klasses()

[David Holmes]

Hi Harold,

Not a review ...

On 29/04/2020 3:27 am, Harold Seigel wrote:
> Hi,
> 
> Please review this fix for JDK-8243572 and JDK-8243336.  Both failures 
> were caused by calling function ClassLoaderData::klasses() and expecting 
> a non-null return value. However, when the CLD had no classes then NULL 
> was returned causing the assertion failure in one case and SIGSEGV in 
> the other.
> 
> Function klasses() was called in these places to determine if the 
> ClassLoaderData was for a hidden class or an unsafe anonymous class. 
> This was done during CLD statistics collection and for JFR events 
> involving CLD's.
> 
> Since the JDK has replaced uses of unsafe anonymous classes with hidden 
> classes, there should be very few unsafe anonymous classes.  So, it was 
> decided (with mgronlun and mchung) that the VM and JFR need no longer 
> distinguish between hidden and unsafe anonymous classes when gathering 
> CLD statistics and when CLD's are displayed in JFR events.  Instead, 
> unsafe anonymous classes will be counted as hidden classes for CLD 
> statistics, and JFR will show CLD's for both hidden and unsafe anonymous 
> classes as hidden.

Okay, but putting aside the decision to no longer distinguish between 
old VM unsafe anonymous classes and new hidden classes, what was the 
actual source of the failure here? The CLD has no classes, but what code 
was expecting to find classes and why? Was it just an oversight with the 
new hidden classes code?

Thanks,
David

> Open Webrev: 
> http://cr.openjdk.java.net/~hseigel/bug_8243572/webrev/index.html
> 
> JBS Bugs: https://bugs.openjdk.java.net/browse/JDK-8243572 and 
> https://bugs.openjdk.java.net/browse/JDK-8243336
> 
> The fix was regression tested by running Mach5 tiers 1 and 2 tests and 
> builds on Linux-x64, Solaris, Windows, and Mac OS X, by running Mach5 
> tiers 3-5 tests on Linux-x64, and running tier 7 tests multiple times on 
> Windows and also on Mac OS X.  Tier 7 testing on Linux-X64 is in progress.
> 
> Thanks, Harold
>