RFR: 8079408: Reimplement TraceClassLoading, TraceClassUnloading, and TraceClassLoaderData with Unified Logging.

[David Holmes]

On 27/01/2016 6:44 AM, Max Ockner wrote:
> David,
> In general, we want to keep logging messages the same as before. This
> fix contains changes to the logging output as well.

Why are we changing the logging output? And why mix the two changes?

Thanks,
David

> Max
> On 1/26/2016 3:33 PM, David Holmes wrote:
>> On 27/01/2016 6:25 AM, Max Ockner wrote:
>>> I am working on changing the affected tests to look for the proper
>>> output.
>>
>> Late to the party but should we not be trying to maintain the existing
>> basic format of the log messages so that anyone who already regularly
>> uses -verbose:class and has scripts etc that check this, will still
>> see basic things like:
>>
>> [Loaded xxx from yyyy]
>>
>> ?
>>
>> David
>>
>>  -Max
>>>
>>> On 1/26/2016 2:23 PM, Coleen Phillimore wrote:
>>>>
>>>> Thanks for recapping the decision.  I didn't remember it from all our
>>>> discussions, etc.
>>>>
>>>> As the one who looks at these logs and is parsing these for CDS, thank
>>>> you for confirming that this is intentional.  Do you really have two
>>>> different output files for info and debug info?
>>>>
>>>> Max/Ioi can you add a comment to the code.  This looks easily like
>>>> someone would "fix" because it looks funny.
>>>>
>>>> Thanks,
>>>> Coleen
>>>>
>>>> On 1/26/16 12:31 AM, Ioi Lam wrote:
>>>>> On 1/25/16 11:58 AM, Coleen Phillimore wrote:
>>>>>>
>>>>>> Hi Max,
>>>>>>
>>>>>> This looks pretty good.  It's a large change!  A couple of comments:
>>>>>>
>>>>>> http://cr.openjdk.java.net/~mockner/classload.03/src/share/vm/classfile/classFileParser.cpp.udiff.html
>>>>>>
>>>>>>
>>>>>>
>>>>>> As Harold pointed out earlier this change should check for 'else'.
>>>>>>
>>>>>> *!if (_log_is_enabled(Info, classload)_) {*
>>>>>> *!_ik->print_loading_log(LogLevel::Info, _loader_data, _stream)_;*
>>>>>> }  else
>>>>>> *+ if (log_is_enabled(Debug, classload)) {*
>>>>>> *+ ik->print_loading_log(LogLevel::Debug, _loader_data, _stream);*
>>>>>> }
>>>>>>
>>>>>
>>>>> Hi Coleen,
>>>>>
>>>>> The case for the 'else' has been discussed before. Please refer to
>>>>>
>>>>> http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-November/016460.html
>>>>>
>>>>>
>>>>> http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-November/016904.html
>>>>>
>>>>>
>>>>>
>>>>> To recap: the reason for NOT having the 'else' is for:
>>>>>
>>>>> java -cp ~/tmp -Xlog:classload=info:file=info.log
>>>>> -Xlog:classload=debug:file=debug.log Foo
>>>>>
>>>>> If you add the 'else' there,  the debug-level output intended for
>>>>> debug.log will be missing.
>>>>>
>>>>> OK, you may say, let's switch the order of the Info and Debug checks.
>>>>> But if you do that, the info.log file will have no content.
>>>>>
>>>>> The 'info' level looks like this
>>>>>
>>>>>   java.lang.Object source: /jdk/lib/modules/bootmodules.jimage
>>>>>
>>>>> The 'debug' level looks like this (in a single line):
>>>>>
>>>>>   java.lang.Object source: /jdk/lib/modules/bootmodules.jimage
>>>>>   klass: 0x00000007c0000fb0 super: 0x0000000000000000
>>>>>   loader: [NULL class_loader] bytes: 1640 checksum: ddb8a6f3
>>>>>
>>>>> Because UL buffers at the line level, I cannot split the output into
>>>>> two parts like this:
>>>>>
>>>>>   [info ][classload] java.lang.Object source: ...
>>>>>   [debug][classload] klass: 0x00000007c0000fb0 super: ...
>>>>>
>>>>> Otherwise some unrelated output may be interleaved between the two
>>>>> lines, making the output impossible to parse. The ability to parse
>>>>> the output is very important to tools that analyze the class loading
>>>>> behavior (e.g., tools related to CDS).
>>>>>
>>>>> Due to this limitation of UL, I think our only choice is to repeat
>>>>> the class name and 'source' in both info and debug levels, hence NO
>>>>> 'else' in the code you quoted:
>>>>>
>>>>>   [info ][classload] java.lang.Object source: ..
>>>>>   [debug][classload] java.lang.Object source: .. klass: .. super: ..
>>>>>
>>>>> Thanks
>>>>> - Ioi
>>>>>
>>>>>
>>>>>
>>>>
>>>
>