[concurrency-interest] ConcurrentHashMap bulk parallel operations

Doug Lea dl at cs.oswego.edu
Tue Aug 14 10:11:26 EDT 2012

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:

   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


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