RFR: JDK-8232773: ClassLoading Debug Output for Specific Classes

[Ioi Lam]

Hi Adam,

The HotSpot logging option:

       -Xlog:class+load=debug

will show the class loader, super class, interfaces, size of the 
classfile, etc.

A related option:

       -Xlog:class+resolve=debug

shows all the class resolution done by the Java code during execution.

You're right that these logs happen only when the class is successfully 
loaded/resolved. If we add similar logs for failures, will that address 
your needs? The syntax would be something like

       -Xlog:class+load+failure=debug

BTW, the bug report mention "What each ClassLoaders' classpath was", but 
custom class loader doesn't necessarily have the notion of "a class path".


Thanks.
- Ioi

On 10/22/19 8:42 AM, Adam Farley8 wrote:
> Hi David,
>
> I didn't, no. Thanks for pointing it out. :)
>
> I see this tells us where the class comes from, much like
> "-verbose:class".
>
> So it's useful when a class can be successfully loaded, but
> doesn't tell us which classloaders tried to load the class,
> nor where they looked, etc.
>
> Something I could have done a better job conveying was that
> the core question this debugging is meant to answer is:
>
> "Why didn't OpenJDK load the class I wanted it to?"
>
> "-Xlog:class+load" seems very useful for finding where a
> class came from, which answers the "loading the wrong version
> of a class" problem, but does not seem to give us
> information in the case of class loading failure.
>
> Also, thanks for moving the bug to the correct component. :)
>
> Best Regards
>
> Adam Farley
> IBM Runtimes
>
>
> David Holmes <david.holmes at oracle.com> wrote on 22/10/2019 14:12:55:
>
>> From: David Holmes <david.holmes at oracle.com>
>> To: Adam Farley8 <adam.farley at uk.ibm.com>, Java Core Libs <core-
>> libs-dev at openjdk.java.net>
>> Date: 22/10/2019 14:14
>> Subject: [EXTERNAL] Re: RFR: JDK-8232773: ClassLoading Debug Output
>> for Specific Classes
>>
>> Hi Adam,
>>
>> Did you look at the logging available from the VM: -Xlog:class+load?
>>
>> BTW I moved the bug you filed to the correct component.
>>
>> Cheers,
>> David
>>
>> On 22/10/2019 8:40 pm, Adam Farley8 wrote:
>>> Hey All,
>>>
>>> This one goes out to anyone who's struggled to figure out
>>> why OpenJDK isn't loading their class.
>>>
>>> The requirement is for OpenJDK to give more detailed
>>> information while loading user-specified classes (e.g. the
>>> one OpenJDK is failing to load). Some debug information is
>>> available while the loading is in-progress, and more is
>>> available after the fact, but it seems there is not a way
>>> to monitor what the ClassLoaders are actually doing without
>>> the use of debugging tools.
>>>
>>> For your approval: a formal write-up of the problem (as
>>> I understand it), and a draft webrev containing the
>>> proposed solution.
>>>
>>> Tests will be developed and added if/when the issue is
>>> accepted as a problem, and a solution has been selected.
>>>
>>> Please review and opine.
>>>
>>> Bug: https://urldefense.proofpoint.com/v2/url?
> u=https-3A__bugs.openjdk.java.net_browse_JDK-2D8232773&d=DwICaQ&c=jf_iaSHvJObTbx-
>> siA1ZOg&r=P5m8KWUXJf-
>>
> CeVJc0hDGD9AQ2LkcXDC0PMV9ntVw5Ho&m=evj-5Q-0QflLNXj0WL5j9WrCHzNRovUvazY9IH_qNkI&s=WEfc_wG4s2o_lhOKcZOykIG0RNybBiMMVbKIzmrlY3k&e=
>>> Webrev: https://urldefense.proofpoint.com/v2/url?
> u=http-3A__cr.openjdk.java.net_-7Eafarley_8232773_webrev_&d=DwICaQ&c=jf_iaSHvJObTbx-
>> siA1ZOg&r=P5m8KWUXJf-
>>
> CeVJc0hDGD9AQ2LkcXDC0PMV9ntVw5Ho&m=evj-5Q-0QflLNXj0WL5j9WrCHzNRovUvazY9IH_qNkI&s=jDSMDaCpBBZcYMU-
>> IUqDh8PoCyl1Jk1G-QGIPKGjgeY&e=
>>> Thanks for your time. :)
>>>
>>> Best Regards
>>>
>>> Adam Farley
>>> IBM Runtimes
>>>
>>>
>>> Unless stated otherwise above:
>>> IBM United Kingdom Limited - Registered in England and Wales with
> number
>>> 741598.
>>> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
> 3AU
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>