Native Image Committer and Community Meeting 2024-05-30

[christianwimmer]

List of all past and upcoming meetings: #3933

New and Noteworthy

• Layered native images:
  [GR-50176] Implemention of the typeReached conditional for reflection. #8969
  [GR-54198] 'typeReached' for serialization and resources.
  [GR-53670] Layered HelloWorld #8917
  [GR-53552] Remove Future from ImageLayerLoader #8981
  [GR-52945] Label some Layered Image Singletons. #8909
  [GR-54129] [GR-53993] [GR-53995] Introduce image layer object file section. #8972

• Special exceptions for missing configurations:
  [GR-47365] Integrate proxy registration to the reflection config #8822
  [GR-49770] Use Glob Patterns In Resource Config File #8715
  [GR-46386] Throw missing registration errors for JNI calls

• [GR-18214] Compacting garbage collection (non-default). #8870: The mark&compact GC is merged to mainline now, and ready for experiments.

• Usability:
  [GR-43837] Enable --report-unsupported-elements-at-runtime by default and deprecate the option. #8815

• Compatibility
  [GR-51446] Handle unstructured locking to avoid parser bailouts where possible. #8921
  [GR-51479] Implement cgroup support in native code. #8989: Instead of relying on a modified JDK where the cgroup support uses only lower-level functionality (not merged into OpenJDK), use the native implementation from the HotSpot VM also for SubstrateVM.

• Monitoring / tools:
  [GR-47010] Add method modifier and signature to a JfrMethod entry. #8956
  [GR-48384] Update GDB debugging support for Native Image with gdb-debughelpers.py. #8886

Deep Dive: Layered Native Images

First "Hello, World!" is running end-to-end:

[...]
  42.06MB (36.55%) for code area:   100,177 compilation units
  44.73MB (38.86%) for image heap:  587,678 objects and 170 resources
  28.30MB (24.59%) for other data
 115.09MB in total
[...]
Finished generating 'libjavabaselayer' in 1m 21s.


native-image -H:LoadImageLayer=layer-snapshot-libjavabaselayer.json (lots of additional hacks here) HelloWorld
[...]
   5.84kB ( 0.26%) for code area:        32 compilation units
   1.77MB (80.46%) for image heap:   31,854 objects and 51 resources
 434.33kB (19.28%) for other data
   2.20MB in total
[...]
Finished generating 'helloworld' in 13.2s.


[...] ./helloworld
Hello, world!

What is working

• Persisting the static analysis results of the base layer, and loading it when building the application layer
  • Using a simple JSON file, to avoid the overhead of defining an optimized binary format
• When building the base layer, add "everything" from a module as roots and saturate method parameters
• When building the application layer, exclude methods already in the base layer
  • Exclude from static analysis and use persisted analysis information instead
  • Exclude from AOT compilation and invoke via an indirect call to the base layer
• At run time, load the image heap from both layers next to each other
  • Machine code is not sequential, instead the loader handles relocations
  • Base layer library is a proper .so shared object
• Type checks and interface calls use an "open world" strategy
• Linux on AMD64 only

What is still missing

A lot ;-)

Next steps: go through the list of all hacks, prioritize them, and work through the list

• Use build bundle files to persist layer information
• Define a proper concept of "layered image singletons"
  • Some information/objects are defined once in the base layer and never change
  • Some information/objects are available on in the application layer
  • Some information/objects need to be accumulated from all layers
• Accumulate Stack walking / GC metatadata from all layers
  • And eventually reflection metadata too
• Allow method inlining across layers to clean up all the NeverInline directives
  • Persist and reload Graal IR graphs
• Define a proper binary format to avoid eager loading of the whole layer JSON file

Changes to the programming model

• Switch from "type reachable" to "type reached" in the reflection configuration
• Orthogonal to all of the "Hello World" work