JVM Internals (2015)
•
8 likes•8,198 views
A brief explanation on how the JVM loads and execute its code is done here. Register and stack based execution are explained, and different garbage collection algorithms are shown using graphs to make it easy to understand what happens under the hood. This talk uses the Java Virtual Machine as a main example, but most of the concepts extends to any modern virtual machine available today.
Recommended
More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (20)
Similar to JVM Internals (2015)
Similar to JVM Internals (2015) (20)
Recently uploaded
Recently uploaded (20)
JVM Internals (2015)
- 1. JVM INTERNALS Introduction toVirtual Machines and the JVM 1 LuizTeston www.fracta.cc
- 2. This presentation is available online at fracta.cc/presentations/jvm 2
- 4. Mimics a Real Machine 4
- 5. Loads and execute code 5
- 7. Java classes are loaded on demand 7
- 8. How they are loaded is up to the classloader 8
- 9. 9
- 10. 10
- 12. 12
- 13. 13
- 15. boor jars LibraryA.jar LibraryB.jar Load class “Main” 15
- 16. boor jars LibraryA.jar LibraryB.jar Load class “Main” Not Here 16
- 17. boor jars LibraryA.jar LibraryB.jar Load class “Main” Not Here Not Here 17
- 18. boor jars LibraryA.jar LibraryB.jar Load class “Main” Not Here Not Here Wait… 18
- 19. boor jars LibraryA.jar LibraryB.jar Load class “Main” Not Here Not Here Not Here run time generated code 19
- 20. boor jars LibraryA.jar LibraryB.jar Load class “Main” Not Here Not Here Not Here run time generated code Here! 20
- 22. INTERPRETING 22
- 23. Line of text AST 23
- 24. Simple example: sum of two numbers 24
- 25. 25
- 27. int variable: jint variable: i 27
- 28. int variable: jint variable: i sum 28
- 29. int variable: jint variable: i sum return 29
- 30. Errors usually are caught at runtime 30
- 31. COMPILING 31
- 32. Code compiled to binary prior to the execution. 32
- 33. Some errors can be caught at compile time 33
- 34. Binary can be: native code,VM bytecode and so on… 34
- 35. Bytecode: Byte sized OPCODE 35
- 37. Works like your processor 37
- 38. Simple example: summing two numbers 38
- 39. R1 R2 RN… 39
- 40. R1 R2 RN… 1 40
- 42. R1 R2 RN… 3 42
- 43. STACK BASEDVM 43
- 44. Works like you HP48G calculator 44
- 45. 45
- 46. 1 46
- 47. 1 2 47
- 48. 1 2 + 48
- 49. 3 49
- 50. JVM IS STACK BASED 50
- 51. Eventually byte code is compiled to native code on the fly 51
- 53. C/C++ Approach: memory as a big array 53
- 55. index size variable 1 1 i 55
- 56. index size variable 1 1 i 2 2 l 56
- 57. index size variable 1 1 i 2 2 l 3 4 c 57
- 58. index size variable 1 1 i 3 4 c 58
- 59. Few caveats for this approach 59
- 61. Possible memory fragmentation 4 sized var doesn’t fit 61
- 63. Possible memory leak used vars unused vars 63
- 65. Possible invalid pointer variable pointing here 65
- 66. JVM based approach: Garbage Collector 66
- 70. Eden Survivor 1 Survivor 2 off you goGC 70
- 72. Eden Survivor 1 Survivor 2 GC t ? 72
- 73. Eden Survivor 1 Survivor 2 GC t ? Wait… 73
- 74. Eden Survivor 1 Survivor 2 GC ? t Wait… 74
- 75. Eden Survivor 1 Survivor 2 GC ? t off you go 75
- 76. Eden Survivor 1 Survivor 2 GC ? t t2 76
- 77. Eden Survivor 1 Survivor 2 GC ? t t2 t is still used within t2 77
- 78. Eden Survivor 1 Survivor 2 GC ? t t2 ? is not used… 78
- 79. Eden Survivor 1 Survivor 2 GC ? t t2 Whatever, I have plenty of memory 79
- 80. Few caveats for this approach 80
- 81. GC Wait… GC needs to be properly configured 81
- 82. GC … GC can be unpredictable 82
- 83. GC No control over memory layout 83
- 84. GC No control over memory layout Let me do this job! 84
- 86. GC Having a GC doing the hard work is good. 86
- 87. HANDS ON 87
- 88. • Create a .java file • Compile it into a .class file • Analyse its binary content
- 89. 89
- 90. 90
- 91. 91
- 92. 92 magic number
- 93. 93 Source code info (can be removed by compilation args)
- 95. 95 Yes, we appended to a string, but strings are immutable in Java.
- 97. Time to take a look on the JVM Assembly code 97
- 98. 98
- 99. 99
- 100. 100 main method
- 101. 101 arg to int into a variable
- 104. 104
- 105. 105 Constructor
- 106. 106 can you see the loop?
- 107. 107 can you see the loop?
- 108. 108 add method changing a field
- 109. Going further, let’s look the native assembly code 109
- 110. • Google for java dissablembler plugin. Install it (hdis-i386 or hdis-amd64) • See the native assembly output • Enjoy analysing it
- 112. large iteration count, so it can be JIT compiled
- 114. native code for java.lang.Object constructor
- 116. native code for addTimes
- 117. related to the loop within addTimes
- 118. native assembly
- 119. related bytecode
- 121. native code for add method
- 122. bytecode for add method
- 123. QUESTIONS?
- 124. WHO AM I Luiz Teston Principle Engineer, CTO at FRACTA • 15 years on the field, working on non trivial projects using Java, C++ and functional programming • lteston@fracta.cc • http://fracta.cc • http://linkedin.com/in/teston • http://twitter.com/FeuTeston
- 125. KEEP INTOUCH Feedback about the presentation appreciated. lteston@fracta.cc www.fracta.cc
- 126. REFERENCES • Garbage Collection:Algorithms for Automatic Dynamic Memory Management, by Richard Jones and Rafael Lins. • Virtual Machines:Versatile Platforms for Systems and Processes, by Jim Smith and Ravi Nair. • https://docs.oracle.com/javase/7/docs/api/java/lang/ClassLoader.html • http://www.ibm.com/developerworks/ibm/library/it-haggar_bytecode/ • http://docs.oracle.com/javase/specs/jvms/se8/html/index.html • http://mechanical-sympathy.blogspot.ie/2013/06/printing-generated-assembly-code- from.html • http://www.slideshare.net/CharlesNutter/redev-2011-jvm-jit-for-dummies-what-the-jvm- does-with-your-bytecode-when-youre-not-looking 126