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

[eric.caspole at oracle.com]

Thanks Sergey and David, I will clean this up - in the case I have been 
working on I have been using locksSize=1 without further changes and so 
I kind of ignored this part.
Eric


On 5/18/20 7:48 PM, Sergey Kuksenko wrote:
> 
> On 5/18/20 4:35 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.
> 
> JMH does safe publication between @Setup and @Benchmark methods. And 
> yes, I was asking -  because of either volatile is not required or tmp 
> local array reference is required.
> 
>