RFR: 8241123: Refactor vmTestbase stress framework to use j.u.c and make creation of threads more flexible

[Igor Ignatyev]

> I need more time to get grasp of Wicket and your changes in it; will come back to you after I understand them. 
ok, now when I believe that I have enough understanding of Wicket, I have a few comments:
1.
>   68     private Lock lock = new ReentrantLock();
>   69     private Condition condition = lock.newCondition();
it's better to make these fields final.

2. as all writes and reads of Wicket::count are guarded by lock.lock, there is no need for it to be atomic.
3. adding lock to getWaiters will also remove need for Wicket::waiters to be atomic.

the rest looks good to me.

Thanks,
-- Igor



> On Mar 18, 2020, at 12:48 PM, Igor Ignatyev <igor.ignatyev at oracle.com> wrote:
> 
> Hi Leonid,
> 
> I've started looking at your webrev, and so far have a couple questions:
> 
>> Test vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects003/referringObjects003a.java was updated to don't use Wicket. (The lock has a reference to thread which affects test.)
> can't you use just a volatile boolean field?
> 
>> Wicket "finished" in class ThreadsRunner was changed to atomicInt/sleep to avoid OOME in j.u.c.l.Condition::await() which might happened in stress GC tests.
> won't j.u.c.CountDownLatch be more appropriate and cleaner solution here?
> 
> I need more time to get grasp of Wicket and your changes in it; will come back to you after I understand them. 
> 
> -- Igor
> 
>> On Mar 18, 2020, at 12:37 PM, Leonid Mesnik <leonid.mesnik at oracle.com> wrote:
>> 
>> Hi
>> 
>> Could you please review following fix which slightly refactor vmTestbase stress test harness. This refactoring helps to add virtual threads testing support.
>> 
>> The Wicket uses plain sync/wait/notify mechanism which cause carrier thread starvation and should not be used in virtual threads. The ManagedThread is a subclass of Thread so it couldn't be virtual thread.
>> 
>> 
>> Following fix changes Wicket to use locks/conditions to don't pin vthread to carrier thread while starting testing.
>> 
>> ManagedThread is fixed to keep execution thread as the thread variable and isolate it's creation.
>> 
>> Test vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects003/referringObjects003a.java was updated to don't use Wicket. (The lock has a reference to thread which affects test.)
>> 
>> Wicket "finished" in class ThreadsRunner was changed to atomicInt/sleep to avoid OOME in j.u.c.l.Condition::await() which might happened in stress GC tests.
>> 
>> webrev: http://cr.openjdk.java.net/~lmesnik/8241123/webrev.00/
>> 
>> bug: https://bugs.openjdk.java.net/browse/JDK-8241123
>> 
>> 
>> Leonid
>> 
> 

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