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

[Lois Foltan]

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.html. 
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
>