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

[David Holmes]

On Wed, 21 Jun 2023 06:56:13 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> src/hotspot/share/oops/instanceKlass.cpp line 3747:
>> 
>>> 3745:     stringStream st;
>>> 3746:     st.print_cr("Loading %s", external_name());
>>> 3747:     JavaThread::current()->print_stack_on(&st);
>> 
>> If this is called for a class loaded very early in VM initialization you may not yet have a current thread.
>
> When I use `-XX:TraceClassLoadingCause=*`, it all works which suggests there's always a current thread by the time class loading occurs. That said, I will add a null check just to be sure.

Sorry my mistake, yes we have JavaThread::current() before loading any Java classes - but it won't have an associated threadObj().

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PR Review Comment: https://git.openjdk.org/jdk/pull/14553#discussion_r1236943707