Hermetic Java (static image packaging/formatting) investigation and proposal

Fri Feb 3 01:08:04 UTC 2023

Hi Brian,

Thanks for the response!

On Thu, Feb 2, 2023 at 9:16 AM Brian Goetz <brian.goetz at oracle.com> wrote:

> Thanks for sharing this information!
>
> As far as I understand it, this is a _packaging mechanism_ to take a
> combination of JDK, application classfiles and resources, and native
> libraries, and combine them into a single executable, and the benefits of
> this include "one file to distribute" and "can't run the app on the wrong
> JDK".  Further, the system classloader has been modified to load classes
> out of the image rather than from the file system.
>
> My question is about your relationship to the "closed world" assumption
> (and the optimizations that can derive from it); I am unsure of whether you
> make any closed-world assumptions in your current approach?  Is there any
> reason why classes cannot be loaded dynamically, `invokedynamic` sites
> can't be linked dynamically, etc?  Secondarily, does your current
> implementation perform any optimizations related to faster startup and
> warmup?
>
> My assumption is that the answer is "no restrictions on dynamism, no
> specific optimizations for startup/warmup, it's purely a packaging
> mechanism", combined with a reminder that the sorts of optimizations that
> have been explored elsewhere (Native Image, CraC, SnapStart) could equally
> well be combined with your packaging approach.
>
> Do I have it right?
>

You are right in the above. :-) In our current investigation/work, we don't
apply any restrictions on loading classes and JNI native libraries. When
desired, it can still dynamically load classes and native libraries from
outside the image. With a hermetic Java image, our usages (at least all the
cases that we have experimented with so far) do not require such
flexibility. In those cases, closed world assumptions could be applied. We
haven't done any optimization related work yet, beyond the
packaging/formatting itself. We hope the hermetic Java image solution can
be a vessel to faciality those sorts of optimizations.

Best regards,
Jiangli

>
> Cheers,
> -Brian
>
>
>
> On 2/2/2023 11:13 AM, Jiangli Zhou wrote:
>
> (Resending in plain text formatting)
>
> Hi,
>
> During the last one and a half years, Google has done some extensive
> research on linux-x64 with Java static image, as project Hermetic Java [1].
> We would like to share our experiences/results with the community and
> present our approach for discussion under the Leyden project. We hope to
> contribute the work to OpenJDK through project Leyden, via the JEP [2]
> process as needed.
>
> With Hermetic Java, our main goal is to create a single executable image
> including the Java runtime environment, Java application and the
> dependencies. This addresses some real-world Java deployment issues and
> challenges that we have encountered over the years.  We believe it fits
> very well with the overall goal of project Leyden in the following aspects:
>
>   - Provide a build-time created static image derived from an application
> and JDK; Image executes as a standalone program.
>   - Satisfy closed-world constraints.
>   - Is built on top of OpenJDK and can utilize existing OpenJDK components
> including the Hotspot VM, runtime JIT compiler (C1, C2), CDS, etc.
>
> Our focus has been on the image packaging and formatting part. This works
> roughly as follows:
>
> 1. The executable image (see slide #10 of [1]) consists of three sections:
> the ELF executable section (see slide #14), the JDK runtime section (see
> slide #20, #21) and the JAR section (see slide #22).
>
> The ELF section is at the beginning of the image and contains the Java
> launcher executable, which allows the image to work as a native executable.
> The JDK runtime section contains the JDK lib/modules image starting at a
> page-aligned file offset. This section can include other data that requires
> special alignment, such as the CDS archive. The JAR section holds the Java
> application classes, dependent library classes, and resources. JDK runtime
> resource files, such as java.security and java.policy are also packaged
> within the JAR section.
>
> 2. The Java launcher executable is statically linked with Hotspot/JDK
> natives and application JNI natives (see slide #15 - #18).
>
> For static native library support, we enhance and complete existing
> OpenJDK work [3, 4, 5]. It provides a flexible solution for loading
> built-in (static) native libraries while still allowing dynamically loading
> shared JNI libraries (if desired).
>
> 3. With a single executable image, we define the image file path as the
> java.home (see slide #23). A JavaHome class is used to provide uniform APIs
> for accessing JDK resources in traditional and Hermetic Java (single image)
> execution modes.
>
> Hermetic Java is an accumulation of wisdom that Google obtained from
> real-world production deployments over many years (years before the current
> project research/experiments). We would love to gather feedback from
> community members. Any input and feedback are welcome and appreciated!
>
> We are happy to provide additional information and answer questions (open
> to discussions in any form).
>
> [1] http://cr.openjdk.java.net/~jiangli/hermetic_java.pdf
>
> [2] http://cr.openjdk.java.net/~mr/jep/jep-2.0-02.html
>
> [3] https://bugs.openjdk.org/browse/JDK-8005716
>
> [4] https://bugs.openjdk.org/browse/JDK-8136556
>
> [5] https://bugs.openjdk.org/browse/JDK-8232748
>
> Best regards,
>
> Jiangli
>
>
>
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