RFR(s): 8235913: ThreadStop should be a handshake

[David Holmes]

Hi Robbin,

On 16/12/2019 7:51 pm, Robbin Ehn wrote:
> Hi all, please review:
> 
> Making VM_ThreadStop into a handshake instead.
> 
> Issue:
> https://bugs.openjdk.java.net/browse/JDK-8235913
> 
> Code:
> http://cr.openjdk.java.net/~rehn/8235913/v1/webrev/index.html

It isn't obvious to me that the code in send_thread_stop that was 
previously always executed by the VMThread can be safely executed by the 
target JavaThread itself. In particular when executing 
InlineCacheBuffer::refill_ic_stubs() what state is the JavaThread in?

Do we actually have tests that exercise that particular code path? I'd 
also check that we test JVM TI stopping of the current thread. 
(JVM_ThreadStop is not an issue as it already special cases the current 
thread).

Thanks,
David

> Passes t1-7.
> 
> Thanks, Robbin