RFR(M): 8199852: Print more information about class loaders in LinkageErrors.

[Lindenmaier, Goetz]

Hi Lois, 

The intention to normalize the output makes completely sense.
It starts with using external_name everywhere ��.

But you need a method that reports about a classloader that does
not belong to a class. There are places where I want to report three 
class loaders, but only one class name.

For example: "classloader A can not load class B because ..."

Also, as I understand, the class loader can be in a different module
than the loaded class. So you might want to report both. (Well, 
this could be handled by the enum you describe).

I'll read the docu you mention.  I already had a look at the test
you mention, but it seemed not to fit for the messages here.
If the tests pass, I will post another change for IllegalAccessError
that uses the same method. I wanted to hold that back until 
this one is finished, but maybe it makes sense to look at all the
messages at a time.

Please also have a look at the wording of the new messages in the
bug description.
https://bugs.openjdk.java.net/browse/JDK-8199852
https://bugs.openjdk.java.net/browse/JDK-8199940

Best regards,
  Goetz.


> -----Original Message-----
> From: Lois Foltan [mailto:lois.foltan at oracle.com]
> Sent: Wednesday, March 21, 2018 8:27 PM
> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
> dev at openjdk.java.net
> Subject: Re: RFR(M): 8199852: Print more information about class loaders in
> LinkageErrors.
> 
> On 3/21/2018 3:06 PM, Lois Foltan wrote:
> 
> > On 3/21/2018 9:03 AM, Lindenmaier, Goetz wrote:
> >
> >> Hi Lois,
> >>
> >> Thanks for looking at this!
> >>
> >> I had a look at Klass::class_loader_and_module_name(), but there are
> >> places
> >> where you only want to report the class loader information, therefore I
> >> decided to do it this way. (If you like this, I have more of these in
> >> work :)).
> >> For example see expectedErrorMessageDuplicate1 in the test.
> >> Also, there might just be a classloader at hand, not a class as needed
> >> for that method.
> >>
> >> But maybe it would make sense to call describe_external() in
> >> class_loader_and_module_name() to get more information about
> >> the classloader?
> >
> > Hi Goetz,
> >
> > In the JDK 9 time frame we strove to construct the string representing
> > the class loader, module name & module version in a defined,
> > structured manner.  This allows for consistency across error messages,
> > stack dumps, etc.  Use of Klass::class_loader_and_name() gives us this
> > consistency and you can see some examples of its use in
> > ClassCastException messages. See,
> > https://bugs.openjdk.java.net/browse/JDK-8165550 and the test,
> > test/hotspot/jtreg/runtime/modules/CCE_module_message.java. I
> strongly
> > encourage you to use Klass::class_loader_and_name() and not add
> > describe_external().  Klass::class_loader_and_name() could be enhanced
> > to take an enum parameter that allows for tailoring of the message
> > itself, for example including/not including the module name when
> > available, including the parent loader, etc.  It could be pulled out
> > of Klass for use to obtain a class loader's name when a Klass is not
> > available, although Coleen just recently moved it to Klass.  I would
> > support this type of change.
> See the javadoc for java.lang.StackTraceElement,
> https://docs.oracle.com/javase/9/docs/api/java/lang/StackTraceElement.ht
> ml.
> Specifically the API Note in the StackTraceElement.toString()
> description which documents the format and contains examples.
> Lois
> 
> >
> > Thanks,
> > Lois
> >
> >>
> >> Best regards,
> >>    Goetz.
> >>
> >>
> >>
> >>> -----Original Message-----
> >>> From: Lois Foltan [mailto:lois.foltan at oracle.com]
> >>> Sent: Mittwoch, 21. März 2018 13:22
> >>> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-
> runtime-
> >>> dev at openjdk.java.net
> >>> Subject: Re: RFR(M): 8199852: Print more information about class
> >>> loaders in
> >>> LinkageErrors.
> >>>
> >>> On 3/21/2018 7:55 AM, Lindenmaier, Goetz wrote:
> >>>
> >>>> Hi,
> >>>>
> >>>> ClassLoaders have a field containing a name since Java 9.
> >>>>
> >>>> This change improves some of the messages of LinkageErrors to
> >>>> print the name of the loader involved, as well as the parent of the
> >>>> loader.
> >>>> This simplifies tracking down the component causing an error in large
> >>>> Java systems.
> >>>>
> >>>> Please review:
> >>>> http://cr.openjdk.java.net/~goetz/wr18/8199852-
> >>> exMsg_Linkage/01/index.html
> >>>> I ran this through all our tests (jck, jtreg, spec etc).  I will
> >>>> run it through
> >>> submit-hs
> >>>> (or jdk/submit) once it's reviewed.
> >>>>
> >>>> Best regards,
> >>>>     Goetz.
> >>>>
> >>>>
> >>>>
> >>>>
> >>> Hi Goetz,
> >>>
> >>> This looks promising and something that we started to do in the JDK 9
> >>> time frame.  Instead of adding the new method
> >>> java_lang_ClassLoader::describe_external() can you possible
> use/improve
> >>> upon Klass::class_loader_and_module_name() in order to avoid
> duplicate
> >>> code?
> >>>
> >>> Thanks,
> >>> Lois
> >