A journey through the wonderful world of Node.js C++ addons. This talk was given at the September 8, 2015 NodeMN meetup. Code: https://github.com/cb1kenobi/nodemn

1. Node.js/io.js
Native C++ Addons
Chris Barber
NodeMN Sept 8, 2015

2. About Me
• Lead Software Engineer at
Appcelerator
• JavaScript hacker since 2000
• Open source
o Titanium
o Dojo Toolkit
• @cb1kenobi
o https://github.com/cb1kenobi
o https://twitter.com/cb1kenobi

3. My Projects
• node-ios-device
o https://www.npmjs.com/package/node-ios-device
o Talks to Apple’s MobileDevice framework to query iOS devices, install
apps, and tail syslog
• lcdstats
o https://www.npmjs.com/package/lcdstats
o Prints system info to LCD screen using USB

4. What is a C++ Addon?

5. What is a C++ Addon?
• Dynamically linked shared object (.so, .dll)
• Direct access to V8 APIs
• Expose C++ functions to JavaScript

6. Getting Started
• Python 2.7
o Python 3 won't work
o Needed by GYP
• C++ toolchain
o g++, make
o Xcode + CLI tools
o Visual Studio

7. Example Addon

8. Example Addon
• example.cpp
o Your C++ file
• binding.gyp
o GYP file that says what and how your C++ should be compiled
• package.json
o “gypfile”: true
o Tells NPM to run node-gyp

9. example.cpp
#include <node.h>
using namespace v8;
void helloMethod(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Handle<Object> exports) {
NODE_SET_METHOD(exports, "hello", helloMethod);
}
NODE_MODULE(example, init)

10. binding.gyp
{
"targets": [
{
"target_name": "example",
"sources": [ "example.cpp" ]
}
]
}

11. package.json
{
"name": "example",
"version": "1.0.0",
"description": "C++ addon example",
"gypfile": true
}

12. Build & Run
$npm build .
> example@1.0.0 install /Users/chris/projects/nodemn/example
> node-gyp rebuild
CXX(target) Release/obj.target/example/example.o
SOLINK_MODULE(target) Release/example.node
$node
>var example = require('./build/Release/example.node')
undefined
>example.hello()
'world'
$ node –v
v0.12.7

13. Build System

14. GYP
• Generate Your Projects
• https://code.google.com/p/gyp/
• Written in Python (requires 2.7)
• Generates projects:
o Makefiles, Xcode, Visual Studio, etc
• .gyp file
o JSON + comments + double or single quotes + trailing commas
• Features:
o Variables, includes, defaults, targets, dependencies, conditions, actions
• Use to be used for V8 and Chrome
o Now replaced by gn
o V8 still ships a GYP file

15. node-gyp
• https://github.com/nodejs/node-gyp
• Node.js-based CLI tool that wraps GYP and builds
your C++ addons
• Bundled with NPM

16. Building addons
• NPM way:
$ npm build .
• node-gyp way:
$ sudo npm install -g node-gyp
$ node-gyp configure
$ node-gyp build

17. node-gyp configure
• Downloads Node dev files
o Stored in ~/.node-gyp
• Invokes GYP
o Creates build project files

18. Node.js Versions

19. Module API Versions
Node.js API Version
0.8.x 1
0.9.0 - 0.9.8 10
0.9.9 11
0.10.x 11
0.11.0 - 0.11.7 12
0.11.8 - 0.11.10 13
0.11.11 - 0.11.16 14
0.12.0 - 0.12.7 14
4.0.0 46
io.js API Version
1.0.x 42
1.1.0 – 1.8.4 43
2.x 44
3.x 45

20. Building$ node –v
v0.10.40
$ npm build .
> example@1.0.0 install /Users/chris/projects/nodemn/example
> node-gyp rebuild
CXX(target) Release/obj.target/example/example.o
../example.cpp:5:24: error: unknown type name 'FunctionCallbackInfo'
void helloMethod(const FunctionCallbackInfo<Value>& args) {
^
../example.cpp:5:44: error: expected ')'
void helloMethod(const FunctionCallbackInfo<Value>& args) {
^
../example.cpp:5:17: note: to match this '('
void helloMethod(const FunctionCallbackInfo<Value>& args) {
^
../example.cpp:7:15: error: no matching constructor for initialization of 'v8::HandleScope'
HandleScope scope(isolate);
^ ~~~~~~~
/Users/chris/.node-gyp/0.10.40/deps/v8/include/v8.h:473:3: note: candidate constructor not viable: no known conversion from 'v8::Isolate *' to 'const
v8::HandleScope' for 1st argument
HandleScope(const HandleScope&);
^
/Users/chris/.node-gyp/0.10.40/deps/v8/include/v8.h:448:3: note: candidate constructor not viable: requires 0 arguments, but 1 was provided
HandleScope();
^
../example.cpp:8:3: error: use of undeclared identifier 'args'
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
^
../example.cpp:8:37: error: no member named 'NewFromUtf8' in 'v8::String'
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
~~~~~~~~^
5 errors generated.
make: *** [Release/obj.target/example/example.o] Error 1

21. What Happened?
• Node.js 0.11 (unstable) introduced V8 3.17.13.0
o FYI: Node.js 4.0.0 uses V8 4.5.103.30
• Major breaking APIs
• Introduced "isolates"
• V8 continues to change API

22. Node.js 0.12 vs 0.10
// Node.js 0.12
#include <node.h>
using namespace v8;
void helloMethod(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = Isolate::GetCurrent();
HandleScope scope(isolate);
args.GetReturnValue().Set(
String::NewFromUtf8(isolate, "world")
);
}
void init(Handle<Object> exports) {
NODE_SET_METHOD(exports, "hello", helloMethod);
}
NODE_MODULE(hello, init)
// Node.js 0.10
#include <node.h>
#include <v8.h>
using namespace v8;
Handle<Value> helloMethod(const Arguments& args) {
HandleScope scope;
return scope.Close(String::New("world"));
}
void init(Handle<Object> exports) {
exports->Set(String::NewSymbol("hello"),
FunctionTemplate::New(helloMethod)->GetFunction());
}
NODE_MODULE(hello, init)

23. nan to the rescue

24. nan
• Native abstractions for Node.js
• Preprocessor macro magic
• https://www.npmjs.com/package/nan

25. Install
$ npm install nan --save

26. example2.cpp
#include <nan.h>
#include <node.h>
using namespace v8;
NAN_METHOD(helloMethod) {
info.GetReturnValue().Set(Nan::New("world").ToLocalChecked());
}
NAN_MODULE_INIT(init) {
Nan::Set(target,
Nan::New("hello").ToLocalChecked(),
Nan::GetFunction(Nan::New<FunctionTemplate>(helloMethod)).ToLocalChecked()
);
}
NODE_MODULE(example2, init)

27. binding.gyp
{
'targets': [
{
'target_name': 'example2',
'include_dirs': [
'<!(node -e "require('nan')")'
],
'sources': [ 'example2.cpp' ]
}
]
}

28. Build & Run
$ node –v
0.10.40
$ npm build .
> example2@1.0.0 install /Users/chris/projects/nodemn/example2
> node-gyp rebuild
CXX(target) Release/obj.target/example2/example2.o
SOLINK_MODULE(target) Release/example2.node
$ node
> var example2 = require('./build/Release/example2.node')
undefined
> example2.hello()
'world'

29. Build & Run
$ node –v
0.12.7
$ node
> var example2 = require('./build/Release/example2.node')
Error: Module did not self-register.
at Error (native)
at Module.load (module.js:355:32)
at Function.Module._load (module.js:310:12)
at Module.require (module.js:365:17)
at require (module.js:384:17)
at repl:1:16
at REPLServer.defaultEval (repl.js:132:27)
at bound (domain.js:254:14)
at REPLServer.runBound [as eval] (domain.js:267:12)
at REPLServer.<anonymous> (repl.js:279:12)

30. Why?
• example2.node is compiled for Node.js 0.10.40
o API Version 11
• Node.js 0.12 is API Version 14

31. Addon Compatibility
• API Version
• Node.js version
o 0.11 -> 0.12
• Platform (OS X, Linux, Windows)
• Architecture (32 vs 64-bit)

32. Solutions
• Perfect solution?
o Doesn't exist today
• Pre-build binaries in NPM package
o Pros:
• Users always have a compatible addon ready to go
• Users don't have to have C++ toolchain installed
• Redistributable without needed Internet connection
o Cons:
• Continually larger and larger package file size
• Need to publish new binary for every new Node.js/io.js version
• Need to manage version paths yourself
• node-pre-gyp
o Pros:
• Dynamically downloads binary at runtime; fallback to local build
• Users don't have to have C++ toolchain installed unless required version does
not exist
• Small package size; no binaries in NPM
• Automatically manages version paths
o Cons:
• Need to publish new binary for every new Node.js/io.js version
• Users either need an Internet connection or C++ toolchain

33. Only a partial solution
• New Node.js/io.js releases all the time
• Neglected addons
• Some environments possibly untested
• No way to tell NPM what platforms the addon is
targeting
o NPM just tries to build it

34. State of C++ Addons

35. August 2014
• 90,984 packages
• 66,775 on Github
• 860 are C++ addons
o 1.3% of all NPM packages that are on Github are C++ addons
0.10.30 0.11.13
OS X
Linux
Windows
473 (55%) 126 (14.7%)
417 (48.5%) 129 (15%)
295 (34.3%) 111 (12.9%)

36. September 2015
• 193,225 packages
• 141,953 on Github
• 1,241 are C++ addons
o 0.87% of all NPM packages that are on Github are C++ addons
• ~30% of all NPM packages depend on a C++ addon
o https://medium.com/node-js-javascript/4-0-is-the-new-1-0-386597a3436d
• Note: some C++ addons switched to pure JS impl
0.10.40 0.12.7 4.0.0
OS X
Didn't have time to run tests on Linux & Windows 
729 (58.7%) 513 (41.3%) 237 (19.1%)

37. Addon State Summary
August 2014 September 2015 Growth
# packages 90,984 193,225 2.12x
# on Github 66,775 141,953 2.13x
# C++ addons 860 (1.3%) 1,241 (0.87%) 1.44x
August 2014 September 2015
0.10.30 0.11.13 0.10.40 0.12.7 4.0.0
OS X 473 (55%) 126 (14.7%) 729 (58.7%) 513 (41.3%) 237 (19.1%)
Linux 417 (48.5%) 129 (15%) ? ? ?
Windows 295 (34.3%) 111 (12.9%) ? ? ?

38. Back to some code!

39. ObjectWrap
Expose C++ Object to JS

40. example3.cpp#include <nan.h>
using namespace v8;
class MyObject : public Nan::ObjectWrap {
public:
static NAN_MODULE_INIT(Init) {
Local<FunctionTemplate> tpl = Nan::New<FunctionTemplate>(MyObject::New);
tpl->SetClassName(Nan::New("MyObject").ToLocalChecked());
tpl->InstanceTemplate()->SetInternalFieldCount(1);
SetPrototypeMethod(tpl, "hello", Hello);
Nan::Set(target, Nan::New("MyObject").ToLocalChecked(), tpl->GetFunction());
}
protected:
static NAN_METHOD(New) {
MyObject *obj = new MyObject();
obj->Wrap(info.This());
info.GetReturnValue().Set(info.This());
}
static NAN_METHOD(Hello) {
info.GetReturnValue().Set(Nan::New("world").ToLocalChecked());
}
};
NAN_MODULE_INIT(init) {
MyObject::Init(target);
}
NODE_MODULE(example3, init)

41. Build & Run
$npm build .
> example3@1.0.0 install /Users/chris/projects/nodemn/example3
> node-gyp rebuild
CXX(target) Release/obj.target/example3/example3.o
SOLINK_MODULE(target) Release/example3.node
$node
>var example3 = require('./build/Release/example3.node')
undefined
>example3.MyObject
var obj = new example3.MyObject()
undefined
>
[Function: MyObject]
>
obj.hello()
'world'

42. C++ Addon Public API

43. C++ Addon Public API
• Use an index.js to expose a high-level public API
o Things are generally easier in JavaScript
• C++ addon implements low-level API
o Fancy APIs are a lot of work to build in C++

44. libuv

45. • Library for async I/O
• Event loops
• Thread pools
• Thread synchronization
• Async filesystem
• Async networking
• Child processes
• Much more!

46. Case Study: deasync
• https://github.com/abbr/deasync
• Turns async functions into sync
var deasync = require('deasync');
var cp = require('child_process');
var exec = deasync(cp.exec);
console.log(exec('ls -la'));

47. Case Study: deasync
// heavily simplified
// original: https://github.com/abbr/deasync/blob/master/index.js
var binding = require(modPath); // path to deasync.node
function deasync(fn) {
return function() {
var done = false;
fn.apply(this, args);
module.exports.loopWhile(function () { return !done; });
};
}
module.exports.loopWhile = function (pred) {
while (pred()) {
process._tickDomainCallback();
if (pred()) {
binding.run();
}
}
};

48. Case Study: deasync
#include <uv.h>
#include <v8.h>
#include <nan.h>
using namespace v8;
NAN_METHOD(Run) {
Nan::HandleScope scope;
uv_run(uv_default_loop(), UV_RUN_ONCE);
info.GetReturnValue().Set(Nan::Undefined());
}
static NAN_MODULE_INIT(init) {
Nan::Set(target,
Nan::New("run").ToLocalChecked(),
Nan::GetFunction(Nan::New<FunctionTemplate>(Run)).ToLocalChecked()
);
}
NODE_MODULE(deasync, init)

49. Performance

50. Threading
• Node.js is single threaded
• Your C++ code can block your Node app
• Use libuv for async tasks
• uv_queue_work() makes async easy(ier)
• No V8 access from worker threads
• Threads can have their own event loops

51. C++ ⟷ JavaScript Bridge
#include <nan.h>
#include <node.h>
#include <math.h>
using namespace v8;
NAN_METHOD(crunch) {
double n = floor(133.7 / 3.14159265359);
info.GetReturnValue().Set(Nan::New<Number>(n));
}
NAN_MODULE_INIT(init) {
Nan::Set(target,
Nan::New("crunch").ToLocalChecked(),
Nan::GetFunction(Nan::New<FunctionTemplate>(crunch))
.ToLocalChecked()
);
}
NODE_MODULE(example4, init)
function jsCrunch() {
return Math.floor(133.7 / Math.PI);
}
var start = new Date;
for (var i = 0; i < 1e8; i++) {
jsCrunch();
}
var jsDelta = (new Date) - start;
var nativeCrunch = require(
'./build/Release/example4.node').crunch;
start = new Date;
for (var i = 0; i < 1e8; i++) {
nativeCrunch();
}
var nativeDelta = (new Date) - start;
console.log('JS took ' + jsDelta + 'ms');
console.log('Native took ' + nativeDelta + 'ms');
Borrowed from http://kkaefer.github.io/node-cpp-modules

52. C++ ⟷ JavaScript Bridge
$ node index.js
JS took 48ms
Native took 9397ms

53. JavaScript vs C++
• V8 aggressively JITs JavaScript code
o Profiles and compiles it into native instructions
• V8 is really fast
o Object allocation
• Somethings you just can't do in JavaScript
• Really depends on the use case and developer skill
o Leaving it up to you to decide
o Perform your own benchmarks

54. Summary

55. Summary
• Prefer a pure JavaScript solution over a C++ solution
o Unless A) you have to or B) you need performance
• Use nan
• Highly consider using node-pre-gyp + continuous
build server
• Use a JavaScript wrapper to implement public API
• Don't block the main thread
o Use libuv to perform async operations

56. Questions?