Java scriptcore brief introduction
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The document provides a comprehensive overview of JavaScript core concepts, detailing its execution environment, memory management, and compilation techniques. It discusses the JavaScript virtual machine, just-in-time (JIT) compilation, data flow graph JITs, garbage collection methods, and the role of inline caching. Additionally, the document highlights various aspects of JavaScript bindings, OOP features, and optimizations for improved performance.
![id win = [webView windowScriptObject];
id location = [win valueForKey:@"location"];
NSString *href = [location valueForKey:@"href"];
JavaScript in Objective-C](https://image.slidesharecdn.com/javascriptcore-130613234141-phpapp01/85/Java-scriptcore-brief-introduction-7-320.jpg)
![VM
• Register-Based
[ 0] enter
[ 1] mov r0, Cell: 0133FC40(@k0)
[ 4] put_by_id r0, a(@id0), Int32:
100(@k1)
[ 13] mov r0, Cell: 0133FC40(@k0)
[ 16] put_by_id r0, b(@id1), Int32:
200(@k2)
[ 25] mov r0, Cell: 0133FC40(@k0)
[ 28] put_by_id r0, c(@id2), Int32:
300(@k3)
[ 37] resolve_global r0, a(@id0)
[ 43] resolve_global r1, b(@id1)
[ 49] add r0, r0, r1
[ 54] resolve_global r1, c(@id2)
[ 60] mul r0, r0, r1
[ 65] ret r0](https://image.slidesharecdn.com/javascriptcore-130613234141-phpapp01/85/Java-scriptcore-brief-introduction-42-320.jpg)
![function sub(a,b)
{
return a-b;
}
function add(a,b)
{
return a+b;
}
i=0;
while(i<3000)
{
value = add(i,i+2);
i=i+1;
}
value = value + 1;
[ 0] enter
[ 1] mov r0, Undefined(@k0)
[ 4] resolve_base r1, i(@id0), 20975696, 20978944
[ 11] mov r0, Int32: 0(@k1)
[ 14] put_to_base r1, i(@id0), r0, 20978944
[ 19] resolve r1, i(@id0), 20975712
[ 24] jnless r1, Int32: 3000(@k2), 78(->102)
[ 28] loop_hint
[ 0] enter
[ 1] add r0, r-8, r-9
[ 6] ret r0](https://image.slidesharecdn.com/javascriptcore-130613234141-phpapp01/85/Java-scriptcore-brief-introduction-44-320.jpg)
![Bytecode
[ 32] put_to_base r1, s(@id0), r0, 35719584
[ 37] resolve_base r1, i(@id2), 35719328, 35719616
[ 44] mov r0, Int32: 0(@k3)
[ 47] put_to_base r1, i(@id2), r0, 35719616
[ 52] resolve r1, i(@id2), 35719344
[ 57] jnless r1, Int32: 3000(@k4), 78(->135)
[ 61] loop_hint
[ 62] resolve_base r1, value(@id3), 35719360, 35719648
[ 69] resolve_with_this r5, r2, add(@id4), 35719376
[ 75] resolve r4, i(@id2), 35719344
[ 80] resolve r6, i(@id2), 35719344
[ 0] enter
[ 1] sub r0, r-8, r-9
[ 6] ret r0](https://image.slidesharecdn.com/javascriptcore-130613234141-phpapp01/85/Java-scriptcore-brief-introduction-47-320.jpg)
Java scriptcore brief introduction
- 2. Agenda • JavaScript • JavaScript Core & WebCore • JavaScript VM • JavaScript Compiler • JavaScript JIT • And ……
- 3. JavaScript
- 4. JavaScript • Garbage collection • Dynamic typing • No classes, prototypes allow OOP • eval, call, apply, inner functions, closures
- 6. JavaScript – Closure & Scope Chain
- 7. id win = [webView windowScriptObject]; id location = [win valueForKey:@"location"]; NSString *href = [location valueForKey:@"href"]; JavaScript in Objective-C
- 8. JavaScript Core and WebCore
- 9. 模块
- 11. JavaScript – Running Environment • VM • Global Object • Execution Context – Exec State
- 13. Property Access
- 14. Execution Context .Global Code .Function Code .Eval Code
- 16. JS Binding • W3C Web IDL
- 17. JS Binding
- 18. JS Binding
- 19. Console
- 23. Script Element
- 24. HTML Parser
- 26. JS blocked by CSS
- 27. JavaScript Execution - async
- 28. JavaScript Execution - defer
- 29. W3C Standard • Running a script – <LINK>
- 30. Inside of JSC
- 31. Running in JSC
- 33. 前端功能组 后端功能组
- 35. Parser
- 36. Lexer & Parser i=3; Variable Equal Constant End To assign 3 to variable i.
- 42. VM • Register-Based [ 0] enter [ 1] mov r0, Cell: 0133FC40(@k0) [ 4] put_by_id r0, a(@id0), Int32: 100(@k1) [ 13] mov r0, Cell: 0133FC40(@k0) [ 16] put_by_id r0, b(@id1), Int32: 200(@k2) [ 25] mov r0, Cell: 0133FC40(@k0) [ 28] put_by_id r0, c(@id2), Int32: 300(@k3) [ 37] resolve_global r0, a(@id0) [ 43] resolve_global r1, b(@id1) [ 49] add r0, r0, r1 [ 54] resolve_global r1, c(@id2) [ 60] mul r0, r0, r1 [ 65] ret r0
- 43. VM • Stack Based 0： bipush 100 2: istore_1 3: sipush 200 6: istore_2 7: sipush 300 10: istore_3 11: iload_1 12: iload_2 13: iadd 14: iload_3 15: imul 16: ireturn
- 44. function sub(a,b) { return a-b; } function add(a,b) { return a+b; } i=0; while(i<3000) { value = add(i,i+2); i=i+1; } value = value + 1; [ 0] enter [ 1] mov r0, Undefined(@k0) [ 4] resolve_base r1, i(@id0), 20975696, 20978944 [ 11] mov r0, Int32: 0(@k1) [ 14] put_to_base r1, i(@id0), r0, 20978944 [ 19] resolve r1, i(@id0), 20975712 [ 24] jnless r1, Int32: 3000(@k2), 78(->102) [ 28] loop_hint [ 0] enter [ 1] add r0, r-8, r-9 [ 6] ret r0
- 45. Low Level Interpreter • 执行ByteCode • Offlineasm
- 47. Bytecode [ 32] put_to_base r1, s(@id0), r0, 35719584 [ 37] resolve_base r1, i(@id2), 35719328, 35719616 [ 44] mov r0, Int32: 0(@k3) [ 47] put_to_base r1, i(@id2), r0, 35719616 [ 52] resolve r1, i(@id2), 35719344 [ 57] jnless r1, Int32: 3000(@k4), 78(->135) [ 61] loop_hint [ 62] resolve_base r1, value(@id3), 35719360, 35719648 [ 69] resolve_with_this r5, r2, add(@id4), 35719376 [ 75] resolve r4, i(@id2), 35719344 [ 80] resolve r6, i(@id2), 35719344 [ 0] enter [ 1] sub r0, r-8, r-9 [ 6] ret r0
- 49. JIT – Just in time • 编译为本地代码 • 占用执行时间
- 50. JIT - Interpreter • Classic Interpreter – Implementation • while(1) { switch(…) …} – Easy implementation – Performance limitation • Obsoleted in WebKit.
- 51. JIT • ◮ Compiler generates machine code from bytecode (jit/*) • ◮ Big switch with emit-calls • ◮ Uses target specific macro assembler and assembler classes • ◮ Target specific assember constructs instruction words • ◮ Register allocation
- 52. Baseline JIT • 与Interpreter相似, 执行ByteCode • 转为机器码执行
- 53. DFG JIT • Data Flow Graph JIT • 推测优化、局部寄存器分配 • 基于数据流图的类型推测 – SSA
- 54. Traced JIT
- 55. Execution – Dynamic Compiler
- 57. Type Inference o.x * o.x + o.y * o.y 1. Type Prediction 2. Type Checks
- 58. Garbage Collection • Mark – Sweep – Reference Counting – Bitmap
- 59. Forward …
- 60. Compiler
- 63. Trampolines
- 64. Inline Cache
- 65. Inline Cache • Polymorphic Inline Cache – Source Code:PolymorphicPutByIdList.h/.cpp
- 66. Common Sub-expression Elimination • Value numbering • CSE
- 67. Register Allocation • Linear Scan • Register Allocation RegisterID *BytecodeGenerator::newRegister()
- 68. Generational GC • Card marking Write Barriers Tracer: Marks and traces Java Mutator: Modifies Blue and Green objects Write barrier on objects Tracer: Traces rest of graph Tracer: Clean blue object
- 69. Any more…
- 70. • LLVM IR to JavaScript (Emscripten) – Python,Ruby,Lua for WebBrowser – C++ to JavaScript • JavaScript on LLVM – Farbic Engine VM/JIT
- 72. Garbage Collection • Pause time • Pause predictability • CPU usage • Memory footprint • Virtual memory interaction • Cache interaction • Effects on program locality • Compiler and runtime impact
- 73. • ECMA Harmony – 6th version
- 74. Key Reference • Virtual Machine & JavaScript Engine – <LINK>