RFR: JDK-8188312 Use CDS if present when running the Boot JDK during build

[Claes Redestad]

On 2017-10-05 11:35, Magnus Ihse Bursie wrote:
>> Using -Xshare:auto should mean any case where a CDS archive can't be 
>> used (for whatever reason) should be silently ignored.  I'd be more
>> worried if -Xshare:on didn't fail in this case!
>
> But we're actively disabling verification of the CDS archive! How is 
> then CDS supposed to know that it contains code for core classes that 
> has been superseded using -Xbootclasspath/p?
>>
>>>
>>> This was supposed to be a quick and simple patch to get a small, but 
>>> useful improvement. It's not worth a lot of investigation or fixes, 
>>> imho.
>>
>> Repeating my suggestion I put as a comment in the RFE: add 
>> -Xshare:auto but leave out the code to dump an archive in the build 
>> (for now),
>> so that those of us who prepare our boot JDK to have CDS archive 
>> generated can get the benefit from it.
> Well then, can you then guarantee that this will not break when 
> replacing stuff using -Xbootclasspath/p? Because I don't want to be 
> debugging things when a slightly different version of the class was 
> *not* used as it should since an old cached version in CDS was picked 
> up instead. :-(

I was not suggesting adding -XX:-VerifySharedSpaces - Ioi can probably 
tell if disabling this verification could lead to a corrupt heap state 
in presence of -Xbootclasspath/p.

I think -Xshare:auto alone is safe no matter what.

/Claes