2020q3 專題: Java 虛擬機器

目標

1. 理解 Java 虛擬機器運作原理
2. 擴充給定的 Java 虛擬機器，得以執行 Dhrystone 一類的工具
3. 研究其他開放原始碼 JVM 實作

背景知識

• Java Virtual Machine (JVM) & its Architecture
• Learn about JVM internals - what does the JVM do?

Dhrystone for Java

1. 安裝 OpenJDK
   ​​​​$ sudo apt install openjdk-8-jdk
   

2. 取得 Dhrystone for Java 原始程式碼並編譯
   ​​​​$ wget http://www.okayan.jp/DhrystoneApplet/dhry_src.jar
   ​​​​$ unzip dhry_src.jar
   ​​​​$ javac dhry.java
   

3. 執行 Dhrystone for Java，當看到 Please give the number of runs through the benchmark 字樣時，輸入 1000 (或更大的數值)

simple-jvm/dvm

1. 取得原始程式碼並編譯
   ​​​​git clone https://github.com/jserv/simple-dvm
   ​​​​cd simple-dvm/jvm
   ​​​​make
   

2. 測試
   ​​​​./jvm ../tests/Foo1.class
   

3. 預期可見以下輸出

HelloWorld
--------------------
initial value 
random number x : 36
x = 36
y = 6345
c = 0
d = 23456
f = 0
--------------------
c = x + y = 36 + 6345 = 6381
d = d + c = 29837
x = c/2 = 3190
c = x * y = 3190 * 6345 = 20240550
d = d + c = 20270387
x = c/2 = 10120275
c = x - y = 10120275 - 6345 = 10113930
d = d + c = 30384317
x = c/2 = 5056965
c = x / y = 5056965 / 6345 = 797
d = d + c = 30385114
f = 30385114 + 5056965 + 6345 + 797 = 35449221
Foo Test By WJY

threaded interpreter

約可改善 20% 效能

TODO:

1. 描述給定的 Java 虛擬機器 欠缺哪些功能/特徵/元素
   • Constant Pool
     • CONSTANT_Float_info
     • CONSTANT_Long_info
     • CONSTANT_Double_info
     • CONSTANT_String_info
     • CONSTANT_Methodref_info
     • CONSTANT_InterfaceMethodref_info
   • Bytecode
     • object related instruction
       • invoke (e.g. invokevirtual, invokeinterface)
       • field (e.g. getstatic, getfield)
       • create (new)
     • array related instruction (e.g. anewarray, arraylength)
     • stack related instruction (pop, dup, swap)
     • other data type (float, double, long) instruction (e.g. fload, dadd)
     • bitwise instruction (e.g. ior, iand)
     • convert instruction (e.g. i2b, i2d)
     • exception (athrow)
   • Class Loader
     • Bootstrap Class Loader
     • Extension Class Loader
     • System Class Loader
   • Bytecode Verifier
   • JIT Compiler
   • Code Optimizations
   • Garbage Collection
   • Runtime Data Area
     • Native Method Stack
     • Heap
     • Method Area
2. Learn about JVM internals - what does the JVM do? 紀錄不理解的部分
   • 閱讀筆記

關於欠缺的功能/特徵，需要描述更細緻，例如缺少的 Java bytecode, JNI, class field 解析等等。一旦完整列出，才能分別給予不同的優先權，隨後再著手改進。

jserv

Dhrystone: https://en.wikipedia.org/wiki/Dhrystone

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