FTD JVM Internals

Transcript

1. JVM Internals FTD Group
2. acknowledgment • God • iMasters • FTD Group
3. who we are? FTD Group http://friendstechday.wordpress.com/about/
4. JVM? WORA? What?
5. Java Virtual Machine • The Java Virtual Machine Specification • Written in C/C++ • Stack based VM • Different implementations • Symbolic reference • Garbage Collected • Java Bytecode • JIT (Just-In-Time)
7. Stack based VM
8. 1 + 2 = ?
9. (+ 1 2) Lisp? RPN?
10. operand stack PUSH 1 1 1 PUSH 2 2 ADD 3
11. operand stack - bytecode iconst_1 1 1 iconst_2 2 iadd 3
12. Java bytecode is the instruction set of the Java virtual machine opcode = 1 or 2 bytes 256 possible opcodes 198 are currently in use 51 are reserved for future use 3 are set aside as permanently unimplemented list of all opcodes: http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html
13. variable declaration int i; 0: iconst_0 // push 0 to top of the operand stack 1: istore_1 // Pop value from top of operand stack and store as local variable 1
14. object instantiation Object ftd = new Object(); 0: new #2 // Class java/lang/Object 1: dup // duplicate the value on top of the stack 2: invokespecial #3 // Method java/lang/Object “<init>()V”
15. #1, #4, #100? #Wat?
16. Runtime Constant Pool The constant pool contains the following types: • Integer, Long, Float, Double • String, Uft8 • Class • NameAndType • Fieldref, Methodref, InterfaceMethodref
17. Java Bytecode Type Description B byte signed byte C char Unicode character D double double-precision floating-point value F float single-precision floating-point value I int integer J long long integer L<classname> reference an instance of class <classname> S short signed short Z boolean true or false [ reference one array dimension
18. Java Code Java Bytecode Expression double d[][][]; [[[D Object mymethod(int I, double d, Thread t) (IDLjava/lang/Thread;)Ljava/lang/Object;
19. javap -v SimpleClass
20. Not only Java Stack lives, but also Heap.
21. Java Heap memory
22. Code Cache used for compilation and storage of methods that have been compiled to native code by the JIT compiler
23. if >= java1.8 no PermGen yes Metaspace
24. everything is wonderful in Java?.... it depends bro!
25. which the size of a Java String with "Java" content? String java = “Java”;
26. answer: 64 bytes Ahh… how.. WATTT???
27. Java memory consumption 8 bytes Object Header 8 bytes Object reference (x86 may use XX:+UseCompressedOops) 8 bytes alignment (WAT?)
28. data alignment 8 bytes alignment 5 bytes used 3 bytes paddind
29. String explanation Field Type Size (bytes) HEADER 16 value “Java” char[] (16 + 8) + (4 * 2) = 32 offset int 4 count int 4 hash int 4 PADDING = 60 + 4 TOTAL 64 bytes
30. which the size of a java. lang.Boolean? Boolean b = false;
31. answer: 24 bytes Ahh… how.. WATTT???
32. Ok .. But what about classes? OOP?
33. Class File Format ClassFile { u4 magic; u2 minor_version; u2 major_version; u2 constant_pool_count; cp_info contant_pool[constant_pool_count – 1]; u2 access_flags; u2 this_class; u2 super_class; u2 interfaces_count; u2 interfaces[interfaces_count]; u2 fields_count; field_info fields[fields_count]; u2 methods_count; method_info methods[methods_count]; u2 attributes_count; attribute_info attributes[attributes_count]; }
34. javap -v SimpleClass
35. And what about the Classloader?
36. 1. Create a initial class using Bootstrap classloader; 2. links the initial class; 3. initializes it; 4. and invokes the public class method void main(String[]) JVM initialization order
37. find, check headers class file, super loading, binary created 3 steps, verifying and preparing the type and its direct supers structurally correct, and obeys the semantic requirements allocation of memory foe data structures executing initialization method <clinit> (optional) checking corrected symbolic references
39. Java debug without ide? Is it possible?
40. jdb (included in the JDK 1.2 package)
41. FTD Group THANK YOU! JOIN US! “And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what {is} that good, and acceptable, and perfect, will of God.” (Romans 12:2)