Native Image Committer and Community Meeting 2023-10-19

[christianwimmer]

List of all past and upcoming meetings: #3933

New and Noteworthy

• Mirroring of PRs and the graal repository is broken right now, we are working on a fix.

• Renaming of compiler packages to jdk.compiler.graal: No renaming of native-image packages, i.e., no renaming of anything that starts with com.oracle.svm
  [GR-48318] Move compiler packages and module to jdk.compiler.graal namespace. #7621

• More cleanup of pre-JDK21 code:
  [GR-48504] [GR-48899] [GR-47055] Clean up virtual threads code. #7608

• Unconditionally enable ParseOnce and InlineBeforeAnalysis: Quarkus confirmed it is OK, Spring does not wok at all when those options are disabled, still waiting for confirmation from Micronaut. After this initial PR, we can delete a lot of code.
  [GR-48579] Always use ParseOnce and InlineBeforeAnalysis. #7573

• The new class initialization strategy is now enabled hopefully forever:
  [GR-48612] Enable --strict-image-heap by default. #7474

• Proper implementation of module detection in the driver. Removing the build option from the native-image-agent ended up in this PR too.
  [GR-48354] Consolidate application module name detection. #7454
  [GR-48144] Fix native-image build with --no-jlinking #7205

• Ensure that machine code does not need relocations after linking, because some systems (including but not limited to GraalOS) do not like executable code that is modified by the loader.
  [GR-47886] Directly patch LoadMethod Constants. #7566

• Better tracking of SubstrateVM code that is ported over from C++ code of HotSpot:
  [GR-48704] Introduce @BasedOnJDKClass Annotation #7561

• Cgroup detection code from JDK now also works with OpenJDK:
  [GR-49300] Break the initialization cycle in NIO/cgroups code. #7553

• OpenJDK Project Panama support: Since this is a preview feature on JDK 21, we will only support JDK 22 going forward.
  [GR-46740] Fix native downcalls on JDK 22 #7554

• Monitoring / tools:
  [GR-48869] [GR-48569] Improve crash log output. #7619
  [GR-49221] Add support for --enable-monitoring=threaddump. #7612
  Omit internal jdk.JavaMonitorWait JFR events #7518
  [GR-47507] [GR-48180] Reduce logging overhead in debug info generator. #7568 In general, we need to be careful with logging/error reporting statements that unconditionally construct expensive messages that are only used when logging is enabled / when there is an actual error.

Deep Dive: Layered Native Images

Planned implementation tasks for #7626

Programming model

• Remove reachability handler for reflection (and resource, proxy, ...) configuration. Reachability information is no longer available to the user.
• (Good to have) Initialize more of the JDK at run time
• Implement filtering of reflection, resources, ... at image run time so that over-registration in the base image (to increase sharing) is not visible to the extension image.

Static analysis and shadow heap

• Change the static analysis for the base image to include everything, i.e., pre-saturate all type flows.
• Persist the information necessary to be consumed by the static analysis for the extension. The information has to include the types / signatures available. It also needs to include the calls to interface methods or virtual methods that could be overwritten by the extension (which needs to treat any such method as an entry point). Load the information when building an extension image.
• Persist the shadow heap, and load it again when building an extension image.
• (for Performance) Persist the parsed GraalIR graphs, and load them on demand when there is need to inline them in extension images.
• When loading a shadow heap, re-connect certain hosted objects (like for enum instances and singleton) with already existing shadow heap objects. Identify JDK objects that must be unique, and JDK tables that need to be extended (like list of packages, list of modules, list of method handle shapes, ...)

Runtime system

• Implement an open-world strategy for type checks (instanceof, Class.isAssignableFrom).
• Implement an open-world strategy for interface calls (not all classes that implement the interface are known, so cannot use current simple vtable calls).
• (not needed for first prototype) Support a code base register that is used for all indirect calls.
• Support an image heap that comes from multiple layered images.
• Support code info and frame info metadata that comes from multiple layered images.

Loader (not needed for first prototype)

• Put the image code into a separate section, i.e., hide it from the linker.
• C code that assembles the various image code sections, i.e., code that runs before the first call to Java code is possible.