[14] RFR 8235829: graal crashes with Zombie.java test

[David Holmes]

Hi Coleen,

On 16/12/2019 9:41 pm, coleen.phillimore at oracle.com wrote:
> Summary: Start ServiceThread before compiler threads, and run nmethod 
> barriers for zgc before adding to the service thread queue, or posting 
> the events on the java thread queue.

I can't comment on most of this but the earlier starting of the service 
thread has some concerns:

- there is a lot of JDK level initialization which now will not have 
happened before the service thread is started and it is far from obvious 
that all possible initialization dependencies will be satisfied

- current starting of the service thread in Management::initialize is 
guarded by "#if INCLUDE_MANAGEMENT", but now you are starting the 
service thread unconditionally for all builds. Hmm just saw your latest 
comment to the bug report - so the service thread is now (for quite some 
time?) being used for other than management tasks and so should always 
be present even if INCLUDE_MANAGEMENT is not enabled. Is that sufficient 
or are there likely to be other changes needed to actually ensure that 
all works correctly  e.g. any code the service thread executes that is 
only defined for INCLUDE_MANAGEMENT will need to be compiled out explicitly.

- the service thread and the notification thread are (were?) closely 
related but now started at completely different times

The bug report states the problem as:

"The graal crash is because compiled_method_load events are added to the 
ServiceThread's deferred event queue before the ServiceThread is created 
so are not walked to keep them from being zombied."

so why isn't the solution to ensure the deferred event queue is walked? 
I'm not clear how starting the service thread relates to walking the queue.

Thanks,
David

> See bug for description of the problems found with the new Zombie.java 
> test.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/2019/8235829.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8235829
> 
> Ran tier1 all platforms, and tier2-8 testing, as well as rerunning 
> original test failure from bug 
> https://bugs.openjdk.java.net/browse/JDK-8173361.
> 
> Thanks,
> Coleen