V8: An Open-Source, High-Performance JavaScript Engine

DownloadV8: An Open-Source, High-Performance JavaScript Engine

Download Presentation
(129) |   (0) |   (0)
Views: 557 | Added: 24-05-2012
Rate Presentation: 0 0
. Who Am I?. Kasper Lund, virtual machine addict2000-2002: CLDC HI (Sun Microsystems)2002-2006: Resilient (OOVM)2006-2008: V8 (Google)Primary areas of interests:Dynamic programming languagesInterpretation and dynamic code generationMethod dispatching. 3. . Challenges in Implementing JavaScr
V8: An Open-Source, High-Performance JavaScript Engine

An Image/Link below is provided (as is) to

Download Policy: Content on the Website is provided to you AS IS for your information and personal use only and may not be sold or licensed nor shared on other sites. SlideServe reserves the right to change this policy at anytime. While downloading, If for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

1. V8: An Open-Source, High-Performance JavaScript Engine Kasper Lund October 4, 2008

2. Who Am I? Kasper Lund, virtual machine addict 2000-2002: CLDC HI (Sun Microsystems) 2002-2006: Resilient (OOVM) 2006-2008: V8 (Google) Primary areas of interests: Dynamic programming languages Interpretation and dynamic code generation Method dispatching

3. 3 Challenges in Implementing JavaScript A very dynamic programming language Objects contain properties (ie, fields or methods)? Properties can be added or removed on the fly Objects with completely different sets of properties can appear at the same property access site Properties can be found in an object's prototype chain Functions can be moved from one object to another

4. 4 Motivation for a New JavaScript Engine When starting the project: Browsers had slow JavaScript implementations They did not scale to large applications with many objects They even had memory leaks when running web apps The solution seemed simple: Build a completely new engine from the ground up Find a way to categorize objects into classes Bring to bear techniques from static class-based languages

5. 5 V8: A Scalable High-performance JS Engine The goal was to raise the performance bar for JavaScript execution Key design ideas in V8: Hidden classes and hidden class transitions Inline caching Compilation to native code Efficient memory-management system

6. 6 Hidden Classes In a static object-oriented language, a particular property is always found at a known offset in instances of a particular class This is fast to access In JavaScript, there are no classes Objects appearing at a property access site may have a given property or not, found at various places in the object This is slow - we need to speed it up Hidden classes encode object layout and shared structure Introduced behind-the-scenes Enable class-based optimizations

7. 7 Hidden Classes Example: function Point(x, y) { this.x = x; this.y = y; } var p = new Point(1, 2); var q = new Point(3, 4);

8. 8 How Dynamic is JavaScript at Runtime? Introducing hidden classes allows us to measure how many different classes are seen at a site in the code Roughly 90% of all access sites see objects with the same hidden class Conclusion: JavaScript is not as dynamic at runtime as you might think We can use class-based object-oriented optimization techniques

9. 9 Inline Caching Each property access and function call is governed by an inline cache stub Stubs are in one of three states: Uninitialized: not executed yet Monomorphic: only one class of objects seen Megamorphic: more than one class of objects seen

10. 10 Monomorphic Stub for Loading a Property 0xf7c0d32d: [Code] Instructions (size = 37) 0xf7c0d344 0 8b442404 mov eax,[esp+0x4] 0xf7c0d348 4 a801 test al,0x1 0xf7c0d34a 6 0f8414000000 jz 32 0xf7c0d350 12 8178ff81ab8ff7 cmp [eax+0xff],0xf78fab81 0xf7c0d357 19 0f8507000000 jnz 32 0xf7c0d35d 25 8b5803 mov ebx,[eax+0x3] 0xf7c0d360 28 8b4307 mov eax,[ebx+0x7] 0xf7c0d363 31 c3 ret 0xf7c0d364 32 e993daffff jmp LoadIC_Miss

11. Megamorphic State Lookup monomorphic stub in global lookup table Hashed lookup based on address of class and hash code of the property name Verify that the stub is suitable Check that the stub type matches (load, store, call) Check that the property name matches Call the monomorphic stub Class check automatically handled by the stub Access is reasonably fast if all checks pass

12. Does It Really Matter? Property load timings: Monomorphic: 0.000249 usec Megamorphic: 0.001390 usec (x5.5) No inline caching: 0.008665 usec (x34.8) Overall: Inline caching speeds up benchmarks with a factor of ~11 Faster property access is important to real apps too

13. 13 Native-code Compiler JavaScript source code is translated directly into machine code There is no intermediate bytecode, because there is no interpreter Functions are compiled JIT-style Source code is parsed into syntax trees A simple one-pass code generator is used Only a few optimizations are applied Code generators are implemented for x86 and ARM

14. 14 Efficient Memory Management Design goals: Fast object allocation Scalable object heap Small garbage collection pause times V8 uses a generational garbage collector

15. 15 Object Heap Organization Young Generation New space: newly allocated objects, collected frequently Old Generation Code space: executable code objects Old data space: objects with no pointers to the young gen. Large object space: to avoid moving objects > 8KB Hidden class space: requires special GC processing Old pointer space: the rest of the old objects

16. 16 Types of Garbage Collection Scavenge collections are most frequent Copying collector operating on the young generation Allows single-pointer allocation Pause times bounded by live data in young gen Typical pause times: 1-2 ms Mark-sweep collections for most full collections Processes all spaces Uses single-pointer and free-list allocation Pause times bound by size of heap Typical pause times: 30-50 ms Mark-sweep-compact to eliminate fragmentation Typical pause times: 50-150 ms

17. 17 Where is the JavaScript Library? All library functions are implemented in JavaScript Examples: Array.prototype.join, String.prototype.replace The benefits of not implementing it inside the engine: Keeps the core engine cleaner Easier to change and extend Capitalizes on the performance of the JavaScript compiler One drawback is startup time ~30 ms ... ... but there is a solution

18. 18 Snapshotting of the Object Heap V8 allows saving the initial heap in a snapshot Serialized form is very fast to read Includes pre-compiled code for JavaScript builtins Integrated in the build system and embedded directly in V8 With snapshots, the startup time is reduced to 4-8 ms

19. Open-Source Open-source code and developed in the open Permissive standard three clause BSD license Developed in the open, all code reviews are public See http://code.google.com/p/v8 Interesting projects already using V8: Chromium V8R: Extensible JavaScript scripting shell PyV8: Python running on top of V8

20. Benchmarks Benchmarking a new scripting engine is tricky V8 is optimized for property accesses and function calls No existing benchmark suites really exercise that But it?s important to a lot of real world web apps The industry needs realistic and well-written benchmarks No single existing benchmark suite covers all of JavaScript How do we go about measuring performance today?

21. 21 http://code.google.com/apis/v8/run.html Richards OS kernel simulation benchmark, originally written in BCPL by Martin Richards (539 lines)? DeltaBlue One-way constraint solver, originally written in Smalltalk by John Maloney and Mario Wolczko (880 lines)? Crypto Encryption and decryption benchmark based on code by Tom Wu (1689 lines)? RayTrace Ray tracer benchmark based on code by Adam Burmister (3418 lines)? EarleyBoyer Classic Scheme benchmarks, translated to JavaScript by Florian Loitsch's Scheme2Js compiler (4682 lines)?

22. Summary V8 is a high-performance JavaScript engine Runs well-structured applications really fast Raises the performance bar for scripting languages Scales to larger applications V8 is open-source and developed in the open Embed it in your own projects Use it for scripting on your computer Incorporate the best ideas into your own scripting engine

Other Related Presentations

Copyright © 2014 SlideServe. All rights reserved | Powered By DigitalOfficePro