RFR: JDK-8222373 Improve CDS performance for custom class loaders

[yumin qi]

HI, Jiangli

  Thanks for your comments.
  Yes, the implementation may land on adding a public API.
  Are the custom loaded classes treated well enough now with dynamic
dump/share? I haven't checked that recently.

Thanks
Yumin

On Thu, Jun 20, 2019 at 8:08 AM Jiangli Zhou <jianglizhou at google.com> wrote:

> Hi Yumin,
>
> Moving away from re-reading class byte stream and re-computing CRC at
> runtime is definitely in the right direction. That will make CDS user
> defined class loader support become beneficial.
>
> To make the user defined class loader support usable, the following
> two areas need to be redesigned:
>
> 1) Class Loader API, I see Alan also brought that up in his reply
>     A new archive-aware class loader should be introduced to assist
> CDS. That will help design a cleaner set of APIs. It will also make
> CDS implementation cleaner in this area.
>
> 2) Dumping process
>     This is for both the static dumping process and dynamic dumping
> process. For the static dumping process, a complete new design is
> needed in order to make the support adoptable.
>
> Best regards,
>
> Jiangli
>
> On Wed, Jun 19, 2019 at 6:37 PM yumin qi <yumin.qi at gmail.com> wrote:
> >
> > Hi, Please review:
> > bug: https://bugs.openjdk.java.net/browse/JDK-8222373
> > webrev: http://cr.openjdk.java.net/~minqi/8222373/01/
> >
> > To load shared class from CDS, first class file stream is read from jar
> > file, then load the class with the stream. In vm, the stream is used to
> > calculate file size and crc32 which are used to compare with the counter
> > parts stored in CDS.
> >
> > In fact, when CDS mapped, every SharedClassPathEntry is checked for
> > validation, if there is mismatch JVM will exit. That is, if user updated
> > jars and did not recreated CDS archive, it would fail. This can make us
> > load the class from CDS directly (if it is in CDS) without checking class
> > file length and crc32, so skip getting byte stream from source to save
> time.
> >
> > Tests: submit passed
> > local on linux-x86_64: jtreg/runtime
> >
> >
> > Thanks
> > Yumin
>