RFR: 8241456: ThreadRunner shouldn't use Wicket for threads starting synchronization

[Leonid Mesnik]

On 3/26/20 4:06 PM, David Holmes wrote:
> Hi Leonid,
>
> On 27/03/2020 7:39 am, Leonid Mesnik wrote:
>> Replying with correct summary.
>>
>> Leonid
>>
>> On 3/23/20 8:55 PM, Leonid Mesnik wrote:
>>> Hi
>>>
>>> Could you please review following fix which update ThreadsRunner to 
>>> use AtomicInteger/spinOnWait instead of Wicket to synchronize 
>>> starting of stress test threads.
>>>
>>> Failing tests allocated all memory by earlier started threads before 
>>> Lock.unlock is called in the latest threads. So thread might get an 
>>> OOME exception while trying to release lock and/or get into 
>>> inconsistent state.
>
> You have a bug in Wicket:
>
> +        try {
> +            lock.lock();
> ...
> +        } finally {
> +            lock.unlock();
>
> The lock() has to go outside the try block. That is why you were 
> getting IllegalMonitorStateExceptions when the lock() threw OOME.
Thanks for explanation. But anyway, as I understand locks use memory and 
might be inconsistent if OOME happened.
>
> But the OOME itself is still a problem as it means you can't use any 
> proper synchronizer. I don't like seeing the spin-loops but in this 
> code you may have no choice if memory may already be exhausted.

It should be really short spin-loop, test only start thread during this 
loop and don't do anything more. Also, it is done only once for all 
stress test. The goal is to start thread completely before heap is 
exhausted.

Leonid

>
> David
> -----
>
>
>>>
>>> The bug was introduced by 
>>> https://bugs.openjdk.java.net/browse/JDK-8241123 
>>> <https://bugs.openjdk.java.net/browse/JDK-8241123>
>>> The Atomic works fine for stress test finishing sync. I just didn't 
>>> expect that tests might OOME while releasing start lock.
>>> Verified that tests now don't fail with -Xcomp -server 
>>> -XX:-TieredCompilation -XX:-UseCompressedOops.
>>>
>>> webrev: http://cr.openjdk.java.net/~lmesnik/8241456/webrev.00/ 
>>> <http://cr.openjdk.java.net/~lmesnik/8241456/webrev.00/>
>>> bug: https://bugs.openjdk.java.net/browse/JDK-8241456 
>>> <https://bugs.openjdk.java.net/browse/JDK-8241456>
>>>
>>> Leonid