RFR (S) : JDK-8245043 : Simplified contention benchmark

[Daniel D. Daugherty]

> Hard to understand the logic unless you already know JMH (which I don't). 

Same here. I read thru the test, but that didn't help me understand
what it is testing or measuring or even what the output (if any)
means. Kinda lost in the woods here...

Dan


On 5/18/20 7:35 PM, David Holmes wrote:
> On 19/05/2020 8:38 am, Sergey Kuksenko wrote:
>> 2. Does "volatile Table[] sharedLocks" need to be volatile?
>
> I think the intent is that the array needs to be published safely - 
> though without knowing full details of JMH it is impossible to see how 
> the array creation and filling relates to threads being started (ie 
> does setup() happen-before any threads are started? If so then 
> publication is already safe.) But if the intent is to do safe 
> publication then refreshArray is wrong:
>
>   85     void refreshArray() {
>   86         sharedLocks = new Table[locksSize];
>   87         for (int i = 0; i < locksSize; i++) {
>   88             sharedLocks[i] = new Table(i);
>   89         }
>   90     }
>
> you would need to create a tmp array and fill it, then assign to 
> sharedLocks with the volatile write that publishes the array.
>
>> On 5/18/20 1:33 PM, eric.caspole at oracle.com wrote:
>>> Hi everyone,
>>> Could you review this new JMH for lock contention and wait which 
>>> started from trying to simplify what happens in Dacapo H2, but also 
>>> I added more parameters to vary the size of time spent in locked and 
>>> unlocked regions to cover more scenarios. Some combos of parameters 
>>> here do track what we have observed in H2 in builds across 15. This 
>>> should be easier to analyze going forward.
>
> Hard to understand the logic unless you already know JMH (which I don't).
>
>>>
>>> JBS:
>>> https://bugs.openjdk.java.net/browse/JDK-8245043
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~ecaspole/JDK-8245043/01/webrev/
>
>  135             Object waiter = null;
>  136             while (waiter == null) {
>  137                 waiter = sharedLocks[state.sharedLockIndex];
>  138             }
>
> why is the while loop needed? The array entry can't be null (if the 
> array is safely published).
>
> Cheers,
> David
> -----
>
>>>
>>> Thanks,
>>> Eric