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

[Robbin Ehn]

Hi David,

On 12/16/19 12:28 PM, David Holmes wrote:
> 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?

To run VMThread::execute() you must be in _thread_in_vm. (we assert this)
I even think send_thread_stop is less error-prone when 'this' is the same as
Thread::current().

> 
> 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).

We have several test that do:
jvmti->StopThread(thread, exception)
And test like StopAtExit.java which do the java version.

Thanks, Robbin

> 
> Thanks,
> David
> 
>> Passes t1-7.
>>
>> Thanks, Robbin