RFR: 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes

[Daniel D.Daugherty]

On Thu, 29 Jul 2021 20:29:27 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

> A trivial follow-up to:
> 
> JDK-8271251 JavaThread::java_suspend() fails with "fatal error: Illegal threadstate encountered: 6"
> 
> that adds a stronger sanity check of thread state when polling for safepoint/handshakes.
> 
> This fix was used to test @pchilano's fix for JDK-8271251 in my JDK17 Mach5
> Tier[1-8] runs for JDK-8271251. It has also been tested with Mach5 Tier[1-3]
> for jdk/jdk (JDK18).

Just to be clear: While I tested this fix with JDK17 bits, this fix is
targeted to jdk/jdk (JDK18).

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PR: https://git.openjdk.java.net/jdk/pull/4936