RFR: 8268902: Testing for threadObj != NULL is unnecessary in handshake

[Coleen Phillimore]

On Wed, 16 Jun 2021 16:03:04 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> The handshake code tests if the JavaThread->is_exiting or that the threadObj() is null. Ever since JDK-8244997, once the JavaThread is running, the _threadObj won't be null until JavaThread is destroyed. So testing is_exiting is all you need to do.
> In gtest, the test JavaThread doesn't create a _threadObj JDK-8215948 so removing this unnecessary test allows writing gtests for handshakes.
> 
> Tested with tier1-6.

I am looking at all the threads we create in the vm like the ServiceThread (look for Threads::add()), but not attach_current_thread in jni.  You're right, we have to make this thread safepoint here.
I wonder why some threads we create call ThreadGroup.add and some don't.  There's lots of duplicate code that's slightly different for each.
Unfortunately now I need a fix for JDK-8215948, hopefully without another duplicate copy of this thread creation code so I can write my handshake test.

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PR: https://git.openjdk.java.net/jdk/pull/4512