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<!DOCTYPE html>

<html>

<head>

<title>Writing node.js extensions with C++ and V8</title>

</head>

<h2 class="title">Konstantin <strong>Käfer</strong></h2>

<div class="topright" style="background:url(github-twitter.png) no-repeat; padding:16px 16px 16px 138px;">kkaefer</div>

<h1 class="title"><strong>node.js</strong> extensions<br>with <strong>C++</strong> and V8</h1>

</section>

</section>

</section>

<div>

<h3>C++ is faster than JavaScript.

</div>

</section>

<h3>

If possible, write it in JavaScript.<br>

<small class="slide" id="slow-js-cpp-boundary">JS ⟷ C++ boundary is slow to cross</small>

</h3>

<pre class="slide" id="benchmark-function">function() { return Math.floor(133.7 / Math.PI); }</pre>

<td width="20%">native JS</td>

<td><span class="bar" style="width:100%"> ~83,333,333 calls/s</span></td>

</tr>

<td>V8 return</td>

<td><span class="bar" style="width:18%"></span> ~13,333,333 calls/s</td>

</tr>

<td>V8 async</td>

<td><span class="bar" style="width:2%"></span> ~1,745,200 calls/s</td>

</tr>

<td>thread pool</td>

<td><span class="bar" style="width:1px"></span> ~83,682 calls/s (0.1%)</td>

</tr>

</table>

</section>

<div>

<li class="slide" id="why-cpp-v8">V8 is written in C++</li>

<li class="slide" id="why-cpp-existing">Wrapping existing C/C++ libraries</li>

<li class="slide" id="why-cpp-threads">Use more threads</li>

</ul>

</div>

</section>

<h2>The bare minimum</h2>

<div class="filename">modulename.cpp</div>

#include <node/v8.h>

#include <node/node.h>

void RegisterModule(v8::Handle<v8::Object> target) {

// Add properties to target

}

// Register the module with node.

NODE_MODULE(modulename, RegisterModule);</textarea>

</section>

<h2>The bare minimum</h2>

<div class="filename">wscript</div>

#!/usr/bin/env python

def set_options(ctx):

ctx.tool_options('compiler_cxx')

def configure(ctx):

ctx.check_tool('compiler_cxx')

ctx.check_tool('node_addon')

def build(ctx):

t = ctx.new_task_gen('cxx', 'shlib', 'node_addon')

t.source = ['modulename.cpp']

# Must be same as first parameter in NODE_MODULE.

t.target = 'modulename'</textarea>

</section>

<h3 class="callout"><a href="https://github.com/kkaefer/node-cpp-modules"><span style="color:#999">https://github.com/</span><br>kkaefer/node-cpp-modules</a></h1>

</section>

<h2>Compiling</h2>

<pre>

<span class="black">$ <span class="cursor"> </span><span class="slide" id="configure-1"><strong>node-waf configure</strong><span class="cursor"> </span></span></span><span class="slide" id="configure-2">

Setting srcdir to : <span class="green">/.../minimum</span>

Setting blddir to : <span class="green">/.../minimum/build</span>

Checking for program g++ or c++ : <span class="green">/usr/bin/g++</span>

Checking for program cpp : <span class="green">/usr/bin/cpp</span>

Checking for program ar : <span class="green">/usr/bin/ar</span>

Checking for program ranlib : <span class="green">/usr/bin/ranlib</span>

Checking for g++ : <span class="green">ok</span>

Checking for node path : <span class="yellow">not found</span>

Checking for node prefix : <span class="green">ok /usr/local</span>

<span class="green">'configure' finished successfully (0.057s)</span>

<span class="black">$ </span><span class="cursor"> </span></span><span class="slide black" id="configure-3"><strong>node-waf build</strong><span class="cursor"> </span></span>

<span class="slide" id="configure-4"><span class="green">Waf: Entering directory `/.../minimum/build'</span>

[1/2] <span class="green">cxx: modulename.cpp -> build/Release/modulename_1.o</span>

[2/2] <span class="yellow">cxx_link: build/Release/modulename_1.o ->

build/Release/modulename.node</span>

<span class="green">Waf: Leaving directory `/.../minimum/build'</span>

<span class="green">'build' finished successfully (0.539s)</span>

</pre>

</section>

<h2>Requiring from JavaScript</h2>

<pre>

> <span class="cursor"> </span><span class="slide" id="requiring-execute">require('./build/Release/modulename.node');<span class="cursor"> </span></span><span class="slide" id="empty-object">

{}

> <span class="cursor"> </span></span>

</pre>

</section>

<h3>

Develop with<br>

<code>$ <em class="slide" id="developing-cpp-clang" style="visibility:visible">CXX=clang</em> node-waf configure</code><br>

</h3>

</section>

<h2>Defining functions</h2>

<div class="filename">modulename.cpp</div>

using namespace v8;

Handle<Value> TheAnswer(const Arguments& args) {

HandleScope scope;

// Do stuff here.

return scope.Close(Integer::New(42));

}</textarea>

<ul>

<li class="slide" id="handlescope"><code>HandleScope</code> cleans up handles created in this function</li>

<li class="slide" id="scope-close">Preserve returned value with <code>scope.Close()</code></li>

</ul>

</section>

<h2>Exporting functions</h2>

<div class="filename">modulename.cpp</div>

Handle<Value> TheAnswer(const Arguments& args) { ... }

void RegisterModule(Handle<Object> target) {

NODE_SET_METHOD(target, "theAnswer", TheAnswer);

}

NODE_MODULE(modulename, RegisterModule);</textarea>

<ul>

<li class="slide" id="exports"><code>target</code> is what node.js calls <code>exports</code></li>

</ul>

> <span class="cursor"> </span><span class="slide" id="exports-load-1">var mod = require('./build/Release/modulename.node');<span class="cursor"> </span></span>

<span class="slide" id="exports-load-2">{ theAnswer: <span class="green">[Function]</span> }

> <span class="cursor"> </span></span><span class="slide" id="exports-load-3">mod.theAnswer();<span class="cursor"> </span></span>

> <span class="cursor"> </span></span>

</pre>

</section>

<h2>Function arguments</h2>

<div class="filename">modulename.cpp</div>

Handle<Value> Fibonacci(const Arguments& args) {

HandleScope scope;

if (args.Length() < 1) {

return ThrowException(Exception::TypeError(

String::New("First argument must be a number")));

}

Local<Integer> integer = args[0]->ToInteger();

int32_t seq = integer->Value();

// ...

}</textarea>

<ul>

<li class="slide" id="args-value"><code>args</code> contains elements of type <code>Value</code></li>

<li class="slide" id="cast">Cast to specific type with <code>To*</code> functions</li>

</ul>

</section>

</section>

<h2>Callback functions</h2>

<div class="filename">modulename.cpp</div>

Handle<Value> CallbackFunction(const Arguments& args) {

HandleScope scope;

if (!args[0]->IsFunction()) {

return ThrowException(Exception::TypeError(String::New(

"First argument must be a callback function")));

}

Local<Function> callback = Local<Function>::Cast(args[1]);

// ...

if (error) {

Local<Value> err = Exception::Error(

String::New("Something went wrong!"));

Local<Value> argv[] = { err };

callback->Call(Context::GetCurrent()->Global(), 1, argv);

} else {

Local<Value> argv[] = {

Local<Value>::New(Null()),

Local<Value>::New(Integer::New(42))

};

callback->Call(Context::GetCurrent()->Global(), 2, argv);

}

return Undefined();

}</textarea>

<ul>

<li class="slide" id="calling-retains"><code>Call</code> automatically retains arguments</li>

<li class="slide" id="dont-forget-handlescope">Don’t forget <code>HandleScope scope</code> at the top</li>

</ul>

</section>

<h2>The thread pool</h2>

<li class="slide" id="single-threaded">JavaScript is single-threaded</li>

<li class="slide" id="io-cpu-in-threadpool">I/O and CPU in thread pool</li>

<li class="slide" id="no-v8-access">No V8 access from worker!</li>

</ul>

</section>

<h2>Passing data to the thread pool</h2>

struct Baton {

uv_work_t request;

Persistent<Function> callback;

int error_code;

std::string error_message;

// Custom data

int32_t result;

};</textarea>

<ul>

<li class="slide" id="baton-not-required">Not required, just a convention</li>

<li class="slide" id="persistent-handles"><code>Persistent</code> is a <code>Handle</code> that stays around until diposed of</li>

</ul>

</section>

<h2>Calling asynchronously</h2>

Handle<Value> Async(const Arguments& args) {

HandleScope scope;

if (!args[0]->IsFunction()) {

return ThrowException(Exception::TypeError(

String::New("Callback function required")));

}

Local<Function> callback = Local<Function>::Cast(args[0]);

Baton* baton = new Baton();

baton->request.data = baton;

baton->callback = Persistent<Function>::New(callback);

uv_queue_work(uv_default_loop(), &baton->request,

AsyncWork, AsyncAfter);

return Undefined();

}</textarea>

</section>

<h2>Worker function</h2>

void AsyncWork(uv_work_t* req) {

// No HandleScope!

Baton* baton = static_cast<Baton*>(req->data);

// Do work in threadpool here.

// Set baton->error_code/message on failures.

}</textarea>

<ul>

<li class="slide" id="asyncwork-blocking">Function <code>AsyncWork</code> is blocking</li>

<li class="slide" id="dont-do-v8-in-threadpool">Do <em class="red">not</em> use any V8 code, not even variable reads</li>

<li class="slide" id="convert-to-pod">Convert values to POD or C++ types and store them in the baton</li>

</ul>

</section>

<h2>After function</h2>

void AsyncAfter(uv_work_t* req) {

HandleScope scope;

Baton* baton = static_cast<Baton*>(req->data);

if (baton->error) {

// Call baton->callback with error object.

} else {

// Call baton->callback with results.

}

baton->callback.Dispose();

delete baton;

}</textarea>

<ul>

<li class="slide" id="dispose-of-permanent-handles"><code>callback</code> function is Permanent, need to delete manually</li>

</ul>

</section>

<h2>Wrap callbacks in TryCatch</h2>

if (baton->error) {

Local<Value> err = Exception::Error(

String::New(baton->error_message.c_str()));

Local<Value> argv[] = { err };

TryCatch try_catch;

baton->callback->Call(

Context::GetCurrent()->Global(), 1, argv);

if (try_catch.HasCaught()) {

node::FatalException(try_catch);

}

} else {

// ...

}</textarea>

<ul>

<li class="slide" id="node-fatalexception"><code>node::FatalException</code> throws at the top of the event loop</li>

<li class="slide" id="catch-fatalexception">Catchable with <code>process.on('uncaughtException', ...)</code></li>

</ul>

</section>

<div>

<h2>API design</h2>

<li class="slide" id="api-how-sync-async">Challenge: Synchronous ➞ Asynchronous</li>

<li class="slide" id="api-how-eventemitter">Use <code>EventEmitter</code></li>

<li class="slide" id="api-how-chainable">Chainable calls</li>

<li class="slide" id="api-how-instances">Instantiating objects vs. functions</li>

<li class="slide" id="api-how-hard-to-misuse">Make it hard to misuse</li>

<li class="slide" id="api-how-javascripty">Make it feel as “JavaScripty” as possible</li>

</ul>

</div>

</section>

<h2><code>node-sqlite3</code> API</h2>

var db = new sqlite3.Database('file.db');

db.run('CREATE TABLE baz (bar)');

db.get('SELECT foo from bar', function(err, result) {

});

</textarea>

<ul>

<li class="slide" id="node-sqlite3-no-open">No <code>open()</code> function, <code>new</code> implicitly opens</li>

<li class="slide" id="node-sqlite3-autoexec">Statements are executed as soon as database is open</li>

<li class="slide" id="node-sqlite3-no-close">No need to “close” the database</li>

<li class="slide" id="node-sqlite3-events">No callback? <code>'error'</code> event on the <code>Database</code> object</li>

</section>

<h2><code>node-blend</code> API</h2>

<ul>

<li>Blends two images of the same size</li>

</ul>

var blend = require('blend');

var image1 = <Buffer>;

var image2 = <Buffer>;

blend([ image1, image2 ], function(err, image) {

// image is a Buffer of blended pixels.

});

</textarea>

<ul>

<li class="slide" id="node-blend-no-obj">No need to create objects with <code>new</code> if you don’t require state</li>

</ul>

</section>

<h2>More documentation</h2>

<div class="topright" style="background:url(github-twitter.png) no-repeat; padding:16px 16px 16px 138px;">kkaefer</div>

<ul>

<li><a href="https://github.com/kkaefer/node-cpp-modules">https://github.com/kkaefer/node-cpp-modules</a></li>

<li><a href="https://github.com/joyent/libuv/blob/master/include/uv.h">https://github.com/joyent/libuv/blob/master/include/uv.h</a></li>

<li><a href="http://create.tpsitulsa.com/wiki/V8_Cookbook">http://create.tpsitulsa.com/wiki/V8_Cookbook</a></li>

</ul>

<ul>

<li>Thanks to <a href="https://twitter.com/mraleph">@mraleph</a> for answering lots of questions<br> and <a href="https://twitter.com/izs">@izs</a>, <a href="https://twitter.com/orlandov">@orlandov</a>, and all other extension authors!</li>

</ul>

</section>

$(function() {

$.extend(true, $.deck.defaults, {

codemirror: {

theme: 'kkaefer'

}

});

$.deck('.slide');

});

</script>

</body>

</html>

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