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

[Magnus Ihse Bursie]

On 2017-10-05 11:07, Claes Redestad wrote:
>
>
> On 2017-10-05 10:59, Magnus Ihse Bursie wrote:
>>> How often is -Xbootclasspath/p used?
>>>
>>> Why not use "-XX:-VerifySharedSpaces -XX:SharedArchiveFile=local.jsa 
>>> -Xshare:auto"? That way you will have the start-up benefit if possible.
>>
>> My worry here is that -Xshare:auto will not work correctly if 
>> -Xbootclasspath/p is used. Maybe someone can guarantee that this will 
>> work and convince me that it will never fail, but I don't think this 
>> risk is worth the marginal gain.
>
> 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has been superseded using -Xbootclasspath/p?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. :-(

/Magnus
>
> /Claes