Status of AppCDS

[August Nagro]

> you have to create the shared archive if not using a JRE installer.

I've tried `java -Xshare:dump` on a Windows and Mac machine with JRE 9
installed with the oracle installer. In both cases I had to run the
following to generate the archive:

```
sudo touch /lib/[arch]/server/classes.jsa
sudo chmod 777 /lib/[arch]/server/classes.jsa
java -Xshare:dump
```

> Not sure it is still considered "experimental" but it is still evolving.
It is a commercial feature in Java 9 but will not be in the future:

That's great; I was just going off the docs for `-XX:+UseAppCDS` on the man
page for java.

> *CDS has been constantly improved over the last few releases andcontinues
to be improved for the next versions of the platform.

Good to here!

- August

On Mon, Oct 2, 2017 at 9:30 PM David Holmes <david.holmes at oracle.com> wrote:

> Moving to hotspot-runtime-dev and bcc'ing the discuss list.
>
> Hello Augusto,
>
> On 3/10/2017 7:25 AM, August Nagro wrote:
> > Hello,
> >
> > Both Class Data Sharing (CDS) [1] and AppCDS [2] are very interesting but
> > seemingly neglected features of the Java Platform, offering the ability
> to
> > reduce startup time.
>
> AppCDS is under continual development and is not "neglected" at all.
>
> > Class Data Sharing is the global cache stored in
> > /lib/[arch]/server/classes.jsa, and circumvents long class-loading times
> by
> > caching the JVM’s internal representation of system jars and
> memory-mapping
> > them in during startup. The feature's documentation [1] has been updated
> > for Java 9, but I have yet to see a JDK or JRE installation that can use
> it
> > without manually generating the archive. In every case I've encountered,
> > the file needs to first be created (and given appropriate access
> > permissions) with admin access, and then generated by `java
> -Xshare:dump`.
>
> Yes you have to create the shared archive if not using a JRE installer.
> But that can be done by whomever deploys the JRE in your environment. My
> understanding is that, due to the format of the archive, a given archive
> is only guaranteed to beusable on the machine on which it was created.
>
> > AppCDS extends the same feature to user libraries. It works well, but has
> > been experimental since (before?) JDK 8 and is commercial.
>
> Not sure it is still considered "experimental" but it is still evolving.
> It is a commercial feature in Java 9 but will not be in the future:
>
> http://mail.openjdk.java.net/pipermail/discuss/2017-September/004281.html
>
> >
> > Java has been criticized for its slow startup times. Improvements would
> > enable command line utilities, the realistic use of JShell .jsh scripts
> > (currently takes >4 seconds for hello world on my Mac [3]), and other
> > applications. I'm not sure how *CDS concerts with other OpenJDK efforts
> > like AOT compilation, but it offers the advantage of architecture
> > independency and the ability to be shared across multiple JVMs.
>
> An archive can be shared across multiple JVMs on the same machine.
>
> > Is *CDS doomed for deprecation, or will it be improved? Without work to
> CDS
> > or changes to AppCDS, the current state is not very usable.
>
> *CDS has been constantly improved over the last few releases and
> continues to be improved for the next versions of the platform.
>
> Regards,
> David Holmes
>
> > Regards,
> >
> > August Nagro
> >
> > [1]: https://docs.oracle.com/javase/9/vm/class-data-sharing.htm
> > [2]:
> >
> http://docs.oracle.com/javase/9/tools/java.htm#JSWOR-GUID-31503FCE-93D0-4175-9B4F-F6A738B2F4C4
> >
> > [3]:
> > Executing command `jshell helloworld.jsh`, with file containing
> > ```
> > System.out.println("hello world");
> > /exit
> > ```
> >
>