RFR: JDK-8134030: test/serviceability/dcmd/gc/HeapDumpTest fails to verify the dump

[David Holmes]

Hi Andreas,

On 31/10/2015 12:03 AM, Andreas Eriksson wrote:
> Hi,
>
> Please review this change to heap dump logic.
> Including runtime list, since this is related to class loading.
>
> Bug:
> JDK-8134030: test/serviceability/dcmd/gc/HeapDumpTest fails to verify
> the dump
> https://bugs.openjdk.java.net/browse/JDK-8134030
>
> Webrev: http://cr.openjdk.java.net/~aeriksso/8134030/webrev.00/
>
> A heap dump can occur at a point where an InstanceKlass doesn't have a
> Java class mirror yet.
> To avoid a crash because of this JDK-8131600 [1] excluded classes that
> are not linked yet from the dump.
>
> The problem here is that since a class that has been loaded is already
> exposed to the Java side, another class can have a reference to the
> excluded class.
> So, if it has been *loaded* but not *linked* it will be excluded, but
> can still be referenced by other classes in the dump.

I'm having trouble seeing exactly when the class is marked as "loaded" 
but it certainly seems to be after the mirror has been set. However 
linking happens even later than that - so if you still see a crash 
excluding linked classes then I fear you will also see problems 
excluding loaded classes!

David
-----


> This gives the following warning in HeapDumpTest:
> WARNING: Failed to resolve object id 0x6c003d348 [...].
>
> This fix changes heapDumper.cpp to only exclude classes that are not yet
> loaded instead.
>
> I'd like confirmation on this from someone who knows more about loaded
> vs linked, but I think that this is correct:
> When a class has been loaded, we are guaranteed that a Java class mirror
> is setup, so the crash seen in JDK-8131600 still cannot happen.
> This seems to be confirmed by the manual reproducer from JDK-8131600,
> which still succeeds with this fix.
>
> Also in this change is the re-addition of the actual heap dump
> verification call in HeapDumpTest, which was accidentally removed when
> the test was re-factored.
>
> Regards,
> Andreas
>
> [1]: https://bugs.openjdk.java.net/browse/JDK-8131600