RFR: 8171373: Reduce copying during initialization of ModuleHashes

[Mandy Chung]

+1

Mandy

> On Dec 16, 2016, at 4:45 PM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Chris, Mandy,
> 
> thanks for reviewing!
> 
> I've made nameToHash final and added a comment, updated in place.
> 
> I'll push this tomorrow unless I hear any objections.
> 
> /Claes
> 
> On 2016-12-16 18:52, Mandy Chung wrote:
>> 
>>> On Dec 16, 2016, at 8:00 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
>>> 
>>> Hi,
>>> 
>>> recent changes to split out ModuleHashes from ModuleDescriptor caused a small/tiny increase in HashMap creation, resize and copying:
>>> 
>>> Webrev: http://cr.openjdk.java.net/~redestad/8171373/webrev.01/
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8171373
>> 
>> I like the optimization for one single module (i.e. java.base) containing the module hashes which is the common case.
>> 
>> Can you add a comment in SystemModuleFinder about the common case and avoid creating a new HashMap unless there is more than one module containing ModuleHashes.
>> 
>> Builder::nameToHash can now be final.
>> 
>> Mandy
>>