Jago

A simplified Java virtual machine written in Go language. This project 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 figure out how we should design one. I ignore some production-level features and make it as simplified as possible so as to demonstrate the idea. For the educational purpose, it is 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.

The Ebook about how it works internally is in progress: https://www.gitbook.com/book/richdyang/go-my-jvm

Roadmap

How to run

build and set gopath

❯ cd ~/jago
❯ export GOPATH=`pwd`
❯ export PATH=$PATH:`pwd`/bin
❯ ./build.sh

jago command help

❯ jago -h
    _                   
   (_) __ _  __ _  ___  
   | |/ _` |/ _` |/ _ \ 
   | | (_| | (_| | (_) |   version 1.0.0
  _/ |\__,_|\__, |\___/    
 |__/       |___/     


Command: 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 protected]>

COMMANDS:
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --classpath value, --cp value  application classpath separated by colon
   --log:thread value          log level of instruction execution, options: info, debug, trace
   --log:classloader value          log level of class loading, options: info, debug, trace
   --help, -h                     show help
   --version, -v                  print the version

Run a calendar program

❯ jago --log:thread info -cp . example/Calendar 8 2017
    _                   
   (_) __ _  __ _  ___  
   | |/ _` |/ _` |/ _ \ 
   | | (_| | (_| | (_) |   version 1.0.0
  _/ |\__,_|\__, |\___/    
 |__/       |___/     


Command: jago --log:thread info -cp . example/Calendar 8 2017 

Add new classpath: .
------------------------------------------------------------

   August 2017
 S  M Tu  W Th  F  S
       1  2  3  4  5 
 6  7  8  9 10 11 12 
13 14 15 16 17 18 19 
20 21 22 23 24 25 26 
27 28 29 30 31

Run a pyramid program

❯ jago --log:thread info -cp . example/Pyramid        
    _                   
   (_) __ _  __ _  ___  
   | |/ _` |/ _` |/ _ \ 
   | | (_| | (_| | (_) |   version 1.0.0
  _/ |\__,_|\__, |\___/    
 |__/       |___/     


Command: jago --log:thread info -cp . example/Pyramid 

Add new classpath: .
------------------------------------------------------------

Pyramid pattern of star in Java : 
     * 
    * * 
   * * * 
  * * * * 
 * * * * * 
Pyramid of numbers in Java : 
     0 
    0 1 
   0 1 2 
  0 1 2 3 
 0 1 2 3 4

run a program traversing a tree in the level order

❯ jago --log:thread info -cp . example/TreeLevelOrderTraverse
    _                   
   (_) __ _  __ _  ___  
   | |/ _` |/ _` |/ _ \ 
   | | (_| | (_| | (_) |   version 1.0.0
  _/ |\__,_|\__, |\___/    
 |__/       |___/     


Command: jago --log:thread info -cp . example/TreeLevelOrderTraverse 

Add a new classpath: .
------------------------------------------------------------


    ___3__
   /      \
   9      20
         /  \
        15   7
[[3], [9, 20], [15, 7]]

    ___1__
   /      \
  _2       3
 /          \
 4           5
[[1], [2, 3], [4, 5]]

                _______________1______________
               /                              \
               2______                  _______3______
                      \                /              \
                       4            ___5__             6  
                                   /      \                
                                  _7       8                
                                 /                           
                                 9                            
[[1], [2, 3], [4, 5, 6], [7, 8], [9]]

Run a program with exception

❯ jago --log:thread info -cp . test/test_athrow
    _                   
   (_) __ _  __ _  ___  
   | |/ _` |/ _` |/ _ \ 
   | | (_| | (_| | (_) |   version 1.0.0
  _/ |\__,_|\__, |\___/    
 |__/       |___/     


Command: jago --log:thread info -cp . test/test_athrow 

Add new classpath: .
------------------------------------------------------------

prepare to go

Exception in thread "main" test/Exception2: this is exception 2
         at test.test_athrow.rest(test_athrow.java:33)
         at test.test_athrow.onRoad(test_athrow.java:25)
         at test.test_athrow.go(test_athrow.java:20)
         at test.test_athrow.main(test_athrow.java:8)

Showcases with example programs

Print pyramid

jago --log:thread debug --log:classloader debug example.Pyramid

Show Calendar

jago --log:thread debug --log:classloader debug example.Calendar 8 2017

Tree Traverse

jago --log:thread debug --log:classloader debug example.TreeInOrderTraverse

jago --log:thread debug --log:classloader debug example.TreeLevelOrderTraverse

Exception handling

jago --log:thread debug --log:classloader debug test.test_athrow

Print system properties

jago --log:thread debug --log:classloader debug test.test_system_properties

Multi-threading

jago --log:thread debug --log:classloader debug test.test_thread

jago --log:thread debug --log:classloader debug example.Multithread

Thread sleep or wait and interrupt

jago --log:thread debug --log:classloader debug example.SleepInterrupt

jago --log:thread debug --log:classloader debug example.WaitInterrupt

Java monitor lock with synchronized

jago --log:thread debug --log:classloader debug example.Counter

Java wait() and notify(), notifyAll()

jago --log:thread debug --log:classloader debug example.ProducerConsumer

trace the execution

log/thread-[name].log

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 symbols 🔹 mean pure Java methods while the yellow ones 🔸 mean native methods which is implemented within Jago internally.

The fire symbols 🔥 mean throwing exception (thrown by athrow bytecode, rethrown if uncaught or thrown by VM internally), the blue water symbols 💧 mean an exception is caught by a method.

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

log/classloader.log

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.

log/threads.log

This log file records thread creation/exit information and object monitor enter/exit, thread sleep(), wait(), notify() etc.

log/misc.log

Other trivial logs

Runtime libraries solution (TBD)

weimingtom / jago Goto Github PK

jago's Introduction