JVM Internals Demystified

Confoo 2015

Transcript

1. ༼ つ ◕_◕ ༽つ JVM Internals ༼ つ ◕_◕ ༽つ Demystified! ( ͡° ͜ ʖ ͡°) ༼ つ ◕_◕ ༽つ ༼ つ ◕_◕ ༽つ
2. What we will NOT see here • Pure JVM boring theory • Assembly fear stuff • 0xFF • 0100111
3. What we will see here • Why internals? • Method Area • Heap • Threads • Further reading • Funny Gifs and images!
4. Bonjour
5. Hi! I’m Hanneli São Paulo, Brazil
6. Hi! I’m Hanneli Meanwhile here in Canada
8. No advanced stuff Simplified way
9. If you understand computer architecture classes You understand JVM
10. Why do I Need to Understand Internals?
11. We live in a simplified era
12. All externalised
13. All externalised (Almost)Normal dressed developers (external)
14. Do I need internal details?
15. Developer showing internal details
16. Memory analyse • Help! Perm gem problems! • Search for memory leaks • Memory analyser tools • Understand how JVM works
17. What’s the relation between: JVM Memory Bytecode Assembly Low Level OpCode Operator Operation Java
19. How do I get started? • http://www.artima.com/insidejvm/ed2/jvmP.html
20. How do I get started?
21. JVM - Low level Assembly
22. I know how to write Java code
23. ༼ つ ◕_◕ ༽つ classes ༼ つ ◕_◕ ༽つ
24. What happens when I invoke a method in Java
25. WAIT How many kinds of methods do you know?
26. 2 types of methods Clazz.method(); object.method(); static instance
27. From Assembly classes: op code + operand operation + operand
28. operation + operand add r1, r2 public int add(int r1, int r2) operation operators == parameters
29. Method calls in JVM static instance operation + operand operation + operand invokevirtual invokestatic
30. Where are the Operands? Special place
31. Where are the Operands? Real place
32. Symbolic place called pool
33. JVM keeps this fake references It’s a strategy to deal with dynamic linking
34. While JVM does need the content of this fake box (pool), it remais unresolved
35. Each fake reference for each method is unique
36. Each fake reference for each method is unique So JVM can replace the fake calls with true invokes.
37. Back to methods Clazz.method(int a); object.method(parameter); class Lol { public int myMethod(int a){ // } } Class stuff
38. Method Area JVM Class stuff Class stuff Class stuff Non-Heap Code Cache Permanent Generation
39. Done? object
40. ༼ つ ◕_◕ ༽つ object ༼ つ ◕_◕ ༽つ
41. Method Area JVM Class stuff Class stuff Class stuff Non-Heap Permanent Generation HEAP Permanent Generation object object object
42. Young gen JVM - The Heap HEAP Lol lol = new LOL(); lol object object object
43. JVM - The Heap HEAP Permanent Generation object object object object object object object object object object object object object object object object Hey, Im’m heavy
44. JVM - The Heap HEAP Permanent Generation object object object object object object object object object object object object object object object object Checks all the objects on the heap Garbage collector
45. Old gen Young generation JVM - The Heap HEAP object object Eden lol Survivor object Will be taken for GC
46. Last step Where does my application run?
47. Last step public static void main(String[] args){ …}
48. ༼ つ ◕_◕ ༽つ thread ༼ つ ◕_◕ ༽つ
49. JVM - Thread Thread Heap Non-Heap
50. JVM - Thread Thread Program Counter Stack Frame Frame Frame Frame Frame Local variables [] Return Value Pointer to Method Area Pointer to Heap Area Operand Operand Operand Operand Stack
51. JVM - Sum up Program Counter Stack Frame Frame Frame Frame Heap Non-Heap Object instances Class Stuff/ Method Area Similar to Computer Architecture
52. ༼ つ ◕_◕ ༽つ JVM ༼ つ ◕_◕ ༽つ
53. ( ͡° ͜ ʖ ͡°) JVM ( ͡° ͜ ʖ ͡°)
54. Thanks!! Questions? @hannelita hannelita@gmail.com
55. References • http://www.artima.com/insidejvm/ed2/jvmP.html • http://www.cubrid.org/blog/dev-platform/understanding-jvm-internals/ • http://architects.dzone.com/articles/understanding-jvm-internals • http://www.ourdailycodes.com/2013/09/inside-java-jvm-memory- structure-2.html • http://javarevisited.blogspot.ca/2011/04/garbage-collection-in-java.html • http://www.slideshare.net/BalamuruganSoundararajan/invoke-dynamics • http://www.javaworld.com/article/2076949/learn-java/how-the-java-virtual- machine-handles-method-invocation-and-return.html • http://blog.jamesdbloom.com/JVMInternals.html#threads