RFR: 8183545: Event tracing, transition hooks

[Erik Gahlin]

Looks good.

Erik

> Hi all,
>
> Please review.
>
> This patch adds a new bit in suspend flag for the tracing backend.
> Thus tracing backend can suspend threads on certain transitions.
>
> (David H and Dan D have looked at this, that's why they are on CC)
>
> I have also put in a oneliner in:
> src/share/vm/classfile/javaClasses.cpp
>
> Which adds Threads_lock->owned_by_self() to the assert.
> Threads_lock->owned_by_self() give the same guarantees as 
> is_Watcher_thread(), e.g. there is no safepoint.
>
> If you really insist I can put the oneliner in a separate issue, but 
> the tracing backend changes depends on both.
>
> Issue: https://bugs.openjdk.java.net/browse/JDK-8183545
> Webrev: http://cr.openjdk.java.net/~rehn/8183545/webrev/index.html
>
> Test: openjdk build on Linux x64
>
> Thanks!
>
> /Robbin