RFR(L): 8195098: Low latency hashtable for read-mostly scenarios

[Robbin Ehn]

Thanks Gerard, Robbin

On 05/14/2018 06:58 PM, Gerard Ziemski wrote:
> Thank you Robbin for addressing all my concerns and answering all my questions. I will probably have more later, but we can handle that then.
> 
> Very impressive hashtable.
> 
> 
> cheers
> 
> 
>> On May 11, 2018, at 2:54 PM, Robbin Ehn <robbin.ehn at oracle.com> wrote:
>>
>> Hi Gerard,
>>
>> On 2018-05-10 19:55, Gerard Ziemski wrote:
>>> hi Robbin,
>>> There are 2 minor issues that caught my eye, anything else we can fix in followup issues:
>>> #1
>>>   // This method looks on the _invisible_epoch field and
>>>   // does a write_synchronize if needed.
>>>   void write_synchonize_on_visible_epoch(Thread* thread);
>>> a) I think in the word “looks” in the comment should be “locks”
>>
>> I don't like lock, sine it implies mutual exclusiveness. I added an explanation, hopefully you like it.
>>
>>> b) Why is the method name using word “visible” when it locks on an “invisible” epoch?
>>
>> The method only does write_synchronize if the the 'epoch'/generation was seen by another thread. Hence write_synchonize_on_visible_epoch, e.g. it only does
>> wite_synchronize if hashtable state was publish to another thread. Hopefully my
>> explanation added above makes it much clearer.
>>
>>> #2 ScopedCS and MultiGetHandle look identical?
>>
>> ScopedCS is an internal class only and MultiGetHandle an interface class.
>> But since they provide same type scoped with identical code I let
>> MultiGetHandle inherit from ScopedCS instead and removed the code duplication, thanks!
>>
>> Please see incremental:
>> http://cr.openjdk.java.net/~rehn/8195098/v3/inc/
>>
>> For reference full:
>> http://cr.openjdk.java.net/~rehn/8195098/v3/full/webrev/
>>
>> Thanks, Robbin
>>
>>> // ScopedCS
>>> template <typename VALUE, typename CONFIG, MEMFLAGS F>
>>> inline ConcurrentHashTable<VALUE, CONFIG, F>::
>>>   ScopedCS::ScopedCS(Thread* thread, ConcurrentHashTable<VALUE, CONFIG, F>* cht)
>>>     : _thread(thread), _cht(cht)
>>> {
>>>   GlobalCounter::critical_section_begin(_thread);
>>>   // This version is published now.
>>>   if (OrderAccess::load_acquire(&_cht->_invisible_epoch) != NULL) {
>>>     OrderAccess::release_store_fence(&_cht->_invisible_epoch, (Thread*)NULL);
>>>   }
>>> }
>>> template <typename VALUE, typename CONFIG, MEMFLAGS F>
>>> inline ConcurrentHashTable<VALUE, CONFIG, F>::
>>>   ScopedCS::~ScopedCS()
>>> {
>>>   GlobalCounter::critical_section_end(_thread);
>>> }
>>> // MultiGetHandle
>>> template <typename VALUE, typename CONFIG, MEMFLAGS F>
>>> inline ConcurrentHashTable<VALUE, CONFIG, F>::
>>>   MultiGetHandle::MultiGetHandle(Thread* thread,
>>>                                  ConcurrentHashTable<VALUE, CONFIG, F>* cht)
>>>     : _thread(thread), _cht(cht)
>>> {
>>>   GlobalCounter::critical_section_begin(_thread);
>>>   // This version is published now.
>>>   if (OrderAccess::load_acquire(&_cht->_invisible_epoch) != NULL) {
>>>     OrderAccess::release_store_fence(&_cht->_invisible_epoch, (Thread*)NULL);
>>>   }
>>> }
>>> template <typename VALUE, typename CONFIG, MEMFLAGS F>
>>> inline ConcurrentHashTable<VALUE, CONFIG, F>::
>>>   MultiGetHandle::~MultiGetHandle()
>>> {
>>>   GlobalCounter::critical_section_end(_thread);
>>> }
>>> cheers
>>>> On May 2, 2018, at 4:03 AM, Robbin Ehn <robbin.ehn at oracle.com> wrote:
>>>>
>>>> Hi all,
>>>>
>>>> Here is an update with Gerard's and Coleen's input.
>>>>
>>>> Inc:
>>>> http://cr.openjdk.java.net/~rehn/8195098/v1/inc/webrev/
>>>> Full:
>>>> http://cr.openjdk.java.net/~rehn/8195098/v1/full/webrev/
>>>>
>>>> Thanks, Robbin
>