A simplified Java virtual machine written in Go language. One aim is to learn JVM specification in depth and try to understand the behind-the-scene behaviour when a Java program runs.
I only refer to "Java Virtual Machine Specification" and then look into how we should design one. Some production-level features are intentionally ignored and it is supposed to make it as simplified as possible so as to demonstrate the general idea. For the educational purpose, it is more than enough.
If you have no time to read OpenJDK source code or always guess the JVM behaviour when you need to tune your program, then your right here to be the lord of your universe.
Any thought is welcome and I am happy to be wrong.
- Java class file reader
- Interpreter engine
- Class loader delegation
- multi-threading support
- JDK native methods
How to run
build and install
❯ cd ~/jago ❯ ./build.sh
By default, jago will be installed to
/usr/local/jago ├── bin │ └── jago ├── jdk │ └── classes │ ├── META-INF │ ├── apple │ ├── com │ ├── java │ ├── javax │ ├── jdk │ ├── org │ └── sun └── log ├── classloader.log ├── io.log ├── misc.log ├── thread-bootstrap.log ├── thread-main.log └── threads.log
❯ jago -h NAME: Jago - A simplified Java Virtual Machine for the educational purpose USAGE: jago [-options] class [args...] VERSION: 1.0.0 DESCRIPTION: A Java Virtual Machine demonstrating the basic features of execution engine, class loading, type/value system, exception handling, native methods etc. AUTHOR: Chao Yang <email@example.com> COMMANDS: help, h Shows a list of commands or help for one command GLOBAL OPTIONS: --classpath value, --cp value application classpath separated by colon --noLogo, --nl don't show logo --debug, -d debug mode --trace, -t trace mode --log:thread value log level of instruction execution in a thread context, options: info, debug, trace --log:classloader value log level of class loading, options: info, debug, trace --profile, -p profile jago --help, -h show help --version, -v print the version
Run a calendar program
❯ jago --log:thread info -cp . Calendar 8 2018
Run a pyramid program
❯ jago --log:thread info -cp . Pyramid
run a program traversing a tree in the level order
❯ jago --log:thread info -cp . TreeLevelOrderTraverse
Run a program into exception
❯ jago --log:thread info -cp . test/test_athrow
More examples to demonstrate features
- Print system properties
jago -d test.test_system_properties
jago -d test.test_thread
jago -d Multithread
- Thread sleep or
jago -d SleepInterrupt
jago -d WaitInterrupt
- Java monitor lock with
jago -d Counter
- Java wait() and
jago -d ProducerConsumer
trace the execution
This log file records the each instruction execution and method call hierarchy within a thread context. Set the log level to info to view call hierarchy more clearly.
The blue diamond symbol
The fire symbol
athrow bytecode, rethrown if uncaught or thrown by VM internally), while the blue water symbol
- TRACE: log all low level bytecode instructions, method call and exception thrown/caught
- DEBUG: only method call and exception thrown/caught
- INFO: only exception thrown/caught info
This log file records the class loading process, including what triggers a class loading and when its class initialization method <clinit> is invoked. The trigger reason can be viewed after a class name.
This log file records thread creation/exit information and object monitor enter/exit, thread sleep(), wait(), notify() etc.
This log file records I/O details around system interactions.
Other trivial logs
- run jago with
go tool pprof --pdf /usr/local/bin/jago /var/../cpu.pprof > cpu.pdf
Really sorry, I have no time to write documentation but it is in my plan. The Ebook about how it works internally is in progress: https://www.gitbook.com/book/richdyang/go-my-jvm