https://github.com/platypusguy/jacobin

A more than minimal JVM written in Go and capable of running Java 17 classes.
https://github.com/platypusguy/jacobin

golang golang-application java jvm

Last synced: about 2 months ago
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A more than minimal JVM written in Go and capable of running Java 17 classes.

• Host: GitHub
• URL: https://github.com/platypusguy/jacobin
• Owner: platypusguy
• License: mpl-2.0
• Created: 2021-07-21T20:47:57.000Z (about 3 years ago)
• Default Branch: main
• Last Pushed: 2024-04-13T03:26:37.000Z (5 months ago)
• Last Synced: 2024-04-14T02:52:48.212Z (5 months ago)
• Topics: golang, golang-application, java, jvm
• Language: Go
• Homepage: http://www.jacobin.org
• Size: 2.78 MB
• Stars: 664
• Watchers: 9
• Forks: 25
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE
  • Authors: AUTHORS.txt

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• my-awesome - platypusguy/jacobin - application,java,jvm pushed_at:2024-09 star:0.7k fork:0.0k A more than minimal JVM written in Go and capable of running Java 17 classes. (Go)

README

        
![Go version](https://img.shields.io/github/go-mod/go-version/platypusguy/jacobin?filename=src%2Fgo.mod)

![Workflow](https://github.com/platypusguy/jacobin/actions/workflows/go.yml/badge.svg)



# jacobin

A more-than-minimal JVM written in Go. 



# Status

## Intended feature set:

* Java 17 functionality, but...

* No JNI (Oracle intends to replace it; see [JEP 389](https://openjdk.java.net/jeps/389))

* No security manager (Oracle intends to remove it; see [JEP 411](https://openjdk.java.net/jeps/411))

* No JIT

* Somewhat less stringent bytecode verification

* Does not enforce Java 17's sealed classes

## What we've done so far and what we need to do:

### Command-line parsing

* Gets options from the three environment variables. [Details here](https://github.com/platypusguy/jacobin/wiki/Command-line-Processing)

* Parses the command line; identify JVM options and application options

* Responds to most options listed in the `java -help` output

**To do**:

 * Handling @files (which contain command-line options)

 * Parsing complex classpaths

### Class loading

* Correctly reads and parses most classes

* Extracts bytecode and parameters needed for execution

* Automated pre-loading of core Java classes (`Object`, etc.)

* `java.*`, `javax.*`, `jdk.*`, `sun.*` classes are loaded from the `JAVA_HOME` directory (i.e., from JDK binaries)

* Handles JAR files

  

**To do**:

* Handle more-complex classes

* Handle interfaces

* Handle inner classes

### Verification, Linking, Preparation, Initialization

* Performs [format check](https://docs.oracle.com/javase/specs/jvms/se11/html/jvms-4.html#jvms-4.8) of class file.

* Linking, preparation, and initialization -- minimally and only as needed at execution time

**To do:**

* Verification

* Robust preparation and initialization

### Execution

* Execution of bytecodes :pencil2: The primary focus of current coding work


  198 bytecodes fully operational, including one- and multi-dimensional arrays

* Static initialization blocks

* Throwing exceptions

* Running native functions (written in go). [Details here.](https://github.com/platypusguy/jacobin/wiki/Native-golang-functions-methods )

  

**To do:**

* invokedynamic

* Calls to superclasses

* Inner and nested classes

* Exception-tree walking

* Annotations

### Instrumentation

* Instruction-level tracing (use `-trace:inst` to enable this feature)

* Extensive logging data (use `-verbose:finest` to enable. Caveat: this produces *a lot* of data)

**To do:**

* Emit instrumented data to a port, for reading/display by a separate program.

## Garbage Collection

GC is handled by the golang runtime, which has its own GC

## Understanding the Code

A detailed roadmap to the code base can be found [in the wiki](https://github.com/platypusguy/jacobin/wiki/Roadmap-to-Jacobin-source-code).

# If you want to test Jacobin

At present, we're not looking for testers because we know the missing features and we're working on them. Testing, at this point, will likely result in frustration. However, if for your own enjoyment, you still want to try it out, see directions and cautions on our [Release Page](https://github.com/platypusguy/jacobin/releases). (If you want some fun, run your program on Jacobin with the `-trace:inst` option and watch the executing Java bytecodes whiz by along with the changing contents of the op stack.) 

We expect/hope/trust that in 2024, we'll be ready to ask interested users to test Jacobin on real programs and share their feedback with us. 

# Thanks

The project's [home page](https://jacobin.org/) carries a lengthy note at the bottom that expresses our thanks to vendors and programmers who have made the Jacobin project possible. They are many and we are deeply grateful to them.