RFR (XXXS) 8173693 disable post_class_unload() for non JavaThread initiators

[Gerald Thornbrugh]

Hi Dan,

Your changes look good.

Thanks,

Jerry
> On Jan 31, 2017, at 10:18 AM, Daniel D. Daugherty <daniel.daugherty at oracle.com> wrote:
> 
> Greetings,
> 
> I have a very small work around for a JVM/TI event posting bug:
> 
>    JDK-8173693 disable post_class_unload() for non JavaThread initiators
>    https://bugs.openjdk.java.net/browse/JDK-8173693
> 
> This work around disables the JVM/TI post_class_unload() function
> when the thread requesting the event is not a JavaThread. See:
> 
>    JDK-8173658 JvmtiExport::post_class_unload() is broken for non-JavaThread initiators
>    https://bugs.openjdk.java.net/browse/JDK-8173658
> 
> for the gory details of what can (and has) gone wrong.
> 
> Fixing JDK-8173658 is non-trivial so this work around is proposed
> to avoid allowing a Class Unload event to crash the VM or silently
> corrupt the non JavaThread that tried to post the event.
> 
> Webrev URL: http://cr.openjdk.java.net/~dcubed/8173693-webrev/0-jdk9-hs/
> 
> Testing: Oracle internal VM/NSK JVM/TI test suite
>         JPRT testing (in progress)
> 
> 
> Thanks, in advance, for any comments, questions or suggestions.
> 
> Dan