AppCDS, DynamicCDS, Leyden and JRuby

[ioi.lam at oracle.com]

On 2/13/25 4:25 PM, Charles Oliver Nutter wrote:
> On Wed, Feb 12, 2025 at 4:22 PM Charles Oliver Nutter 
> <headius at headius.com> wrote:
>
>         Have you tried the -XX:+AutoCreateSharedArchive flag? It
>         should recreate the dynamic archive if you have updated the
>         app's JAR files or updated to a new JDK.
>
>     This is definitely what we want for the JRuby launcher! I've
>     integrated it into the launcher and it seems to work well (my log
>     redirects must still be included to silence CDS warnings, though):
>
>
> I am seeing two peculiar warnings in the log file while using this flag:
>
> [0.001s][info][cds] optimized module handling: disabled due to 
> incompatible property: 
> jdk.module.path=/Users/headius/work/jruby/lib/jruby.jar
>
> This is not a property I'm setting. The full command line for this 
> JRuby execution is here:
>
> /Library/Java/JavaVirtualMachines/zulu-21.jdk/Contents/Home/bin/java 
> @/Users/headius/work/jruby/bin/.jruby.java_opts 
> @/Users/headius/work/jruby/bin/.jruby.module_opts -Xss2048k 
> -XX:+AutoCreateSharedArchive 
> -XX:SharedArchiveFile=/Users/headius/work/jruby/lib/jruby.jsa 
> -Xlog:cds=off -Xlog:cds+dynamic=off 
> -Djffi.boot.library.path=/Users/headius/work/jruby/lib/jni 
> -Djava.security.egd=file:/dev/urandom --module-path 
> /Users/headius/work/jruby/lib/jruby.jar -classpath : 
> -Djruby.home=/Users/headius/work/jruby 
> -Djruby.lib=/Users/headius/work/jruby/lib -Djruby.script=jruby 
> -Djruby.shell=/bin/sh org.jruby.Main -e 1
>
That message is a bit cryptic. Basically "--module-path dir" gets 
translated to "-Djdk.module.path=dir" by the Java launcher. Because of 
that, the archived module graph in the default CDS archive cannot be 
used. This is normal in your use case.


> The java_opts file is empty and the module_opts file just has some 
> add-opens we need.
>
> [0.001s][warning][cds] AutoCreateSharedArchive is ignored because 
> /Users/headius/work/jruby/lib/jruby.jsa is a static archive
>
> I have no idea what this means. Once I get in this state it complains 
> every startup and will also refuse to overwrite the "bad" jsa file. I 
> had thought that it would overwrite the file if it could not use it, 
> so I don't have to manually separate CDS archives from different 
> JDKs... did I misunderstand?


Did you create /Users/headius/work/jruby/lib/jruby.jsa with "java 
-Xshare:dump" or "java -XX:AOTMode=create"? If so, it will be recognized 
as a "static archive".

I created https://bugs.openjdk.org/browse/JDK-8350057 to address this issue.

If you want to work around this bug, you can check the magic number of 
the file:

https://github.com/openjdk/jdk/blob/ff52859d2ad65b97c56dd19323213a0d07be47ae/src/hotspot/share/include/cds.h#L39-L40

#define CDS_ARCHIVE_MAGIC 0xf00baba2
#define CDS_DYNAMIC_ARCHIVE_MAGIC 0xf00baba8

If the magic number is not 0xf00baba8, you can delete the file before 
running with "java -XX:+AutoCreateSharedArchive -XX:SharedArchiveFile=..."

Thanks

- Ioi
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