[concurrency-interest] ConcurrentHashMap bulk parallel operations

Rémi Forax forax at univ-mlv.fr
Tue Aug 14 10:42:55 EDT 2012


On 08/14/2012 04:11 PM, Doug Lea wrote:
> On 08/14/12 09:59, Tim Peierls wrote:
>> On Tue, Aug 14, 2012 at 9:44 AM, Doug Lea <dl at cs.oswego.edu
>> <mailto:dl at cs.oswego.edu>> wrote:
>>
>>     * While preliminary performance checks are promising, beware that
>>     the very first parallel task execution time can be terrible.
>>     Really terrible. A lot of code needs compiling, threads
>>     need to  be constructed, memory needs to be reserved, etc,
>>     to get going. Hopefully some of this will improve.
>>
>>
>> First for the JVM? for the CHM classloader? for the CHM instance?
>>
>
> The worst case is for "All of the above". Others generally less so.
> Here's an example run of an in-progress test program that just
> computes sums in different ways in a CHM with about 10M elements:
>
> Sequential:
>   time:    1.331
> First parallel run:
>   time:    8.189
> Next few runs:
>   time:    0.064
>   time:    0.064
>   time:    0.047
>   time:    0.044
> ...
> (stays around the same time from there)
> Now switch to a different (more expensive) sum function:
>   time:    1.214
>   time:    0.080
>   time:    0.075
> ...

Doug, can you do the same test but instead of switching to a more 
expensive sum function,
just switch to the same function but declared in an other inner class, 
and then switch again
to the same function declared in a third inner class.

>
>
> -Doug

Rémi



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