Optimize (Linked-)HashMap lookup when backing array is null

[Christoph Dreis]

Hi Roger,

> How does the performance degrade when the computation of the hash
> is non-trivial. For example, with an array as a key or an object with 
> fields that are objects?
> The original code made a point of computing the hash only once.

HashMap.get() and HashMap.containsKey() etc. would still calculate it only once.
Only computeIfPresent would degrade. Did you mean that?

Cheers,
Christoph

On 5/19/20 3:21 PM, Claes Redestad wrote:
>> Thanks for producing the simpler variant and getting some comparative
>> runs done.
>>
>> On 2020-05-19 19:50, Christoph Dreis wrote:
>>> I would probably go for the first version although it is a bit more 
>>> complicated and has the computeIfPresent caveat, because it doesn't 
>>> slow down the common Map.get() case when the map is actually filled.
>>
>> It is a bit of step up in complexity, but getting the win without adding
>> a branch to Map.get() _is_ a nice property.
>>
>>>
>>> Let me know what you think.
>>
>> If core libs maintainers are fine with the added complexity of your
>> original patch, I think it looks ok.
>>
>> /Claes