RFR: 8193513: add support for printing a stack trace on class loading [v2]

[Ioi Lam]

On Fri, 30 Jun 2023 17:23:18 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> if (log_is_enabled(Info, class, load, cause)) {
>>   doStuff();
>> }
>> 
>> HTH
>
> Are you saying `log_is_enabled(Info, class, load, cause)` implies `log_is_enabled(Info, class, load)`?
> Or do I need:
> 
>   if (!log_is_enabled(Info, class, load) && !log_is_enabled(Info, class, load, cause)) {
>     return;
>   }
> 
> to extend the check on [line 3793](https://github.com/openjdk/jdk/blob/e8ff74c7e84ec2440a51fee1b4c45e87332807a0/src/hotspot/share/oops/instanceKlass.cpp#L3793)?
> 
> I don't understand the relationship between `class+load+cause` and `class+load` and the comment on `log_is_enabled` doesn't help much.

Usually, the user would need to specify both. Otherwise just having the cause without the `class+load` would be rather useless


java -Xlog:class+load  -Xlog:class+load+cause 


Which can be combined like:


java -Xlog:class+load,class+load+cause 


or 


java -Xlog:class+load*=info


(To see usages of `-Xlog`, you can grep for `[-]Xlog:` in the *.java files under test/hotspot/jtreg)


In terms of implementing this PR, I would suggest handling the class+load and class+load+cause indecently. Something like



void InstanceKlass::print_class_load_logging(ClassLoaderData* loader_data,
                                             const ModuleEntry* module_entry,
                                             const ClassFileStream* cfs) const {
  if (ClassListWriter::is_enabled()) {
    ClassListWriter::write(this, cfs);
  }

  log_class_load(...);  // handle -Xlog:class+load 
                        // (the rest of the old print_class_load_logging() function)
  log_class_load_cause(...);  // handle -Xlog:class+load
}


The output would be something like


[0.014s][info][class,load] java.lang.Thread$State source: shared objects file
[0.014s][info][class,load,cause] 	at jdk.internal.misc.VM.toThreadState(java.base/VM.java:336)
[0.014s][info][class,load,cause] 	at java.lang.Thread.threadState(java.base/Thread.java:2731)
[0.014s][info][class,load,cause] 	at java.lang.Thread.isTerminated(java.base/Thread.java:2738)
[0.014s][info][class,load,cause]	at java.lang.Thread.getThreadGroup(java.base/Thread.java:1957)
...


This way, you don't need to repeat the class name, which is already printed by `-Xlog:class+load`

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14553#discussion_r1248225100