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<!--
Google IO 2012/2013 HTML5 Slide Template
Authors: Eric Bidelman <ebidel@gmail.com>
Luke Mahé <lukem@google.com>
URL: https://code.google.com/p/io-2012-slides
-->
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="chrome=1">
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<link rel="stylesheet" media="all" href="theme/css/default.css">
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<base target="_blank"> <!-- This amazingness opens all links in a new tab. -->
<script data-main="js/slides" src="js/require-1.0.8.min.js"></script>
</head>
<body style="opacity: 0">
<slides class="layout-widescreen">
<!-- <slide class="logoslide nobackground">
<article class="flexbox vcenter">
<span><img src="images/angularjs.png"></span>
</article>
</slide>
-->
<slide class="title-slide segue nobackground fill" style="background-image: url(images/promises.jpg)">
<!-- <aside class="gdbar"><img src="images/angularjs.png"></aside> -->
<!-- The content of this hgroup is replaced programmatically through the slide_config.json. -->
<hgroup class="auto-fadein">
<h1 class="yellow" data-config-title><!-- populated from slide_config.json --></h1>
<h2 data-config-subtitle><!-- populated from slide_config.json --></h2>
<p class="yellow2" data-config-presenter><!-- populated from slide_config.json --></p>
</hgroup>
</slide>
<slide class="segue dark nobackground">
<!-- <aside class="gdbar"><img src="images/google_developers_icon_128.png"></aside> -->
<hgroup>
<h2 class="yellow">Why Promises ?</h2>
<h3 class="yellow">Let's step back to the basics</h3>
</hgroup>
</slide>
<slide>
<hgroup class="centered">
<h3>Single thread synchronous model aka. blocking</h3>
</hgroup>
<br><br>
<article style="float: left">
<br>
<br>
<br>
<br>
<ul>
<li>Suppose a program consisting of 3 distinct tasks</li>
<li>Tasks are performed one at a time</li>
<li>Always in a defined order</li>
<li>Simplest style of programming</li>
</ul>
</article>
<article class="centered">
<img src="images/sync.png" class="auto-fade-in" alt="Description" title="Description">
<footer class="source">source: <a href="http://krondo.com/?p=1209">krondo.com</a></footer>
</article>
</slide>
<slide>
<hgroup class="centered">
<h3>Multi threaded model</h3>
</hgroup>
<br><br>
<article style="float: left; width: 60%">
<br>
<br>
<br>
<br>
<ul>
<li>Tasks run in separate threads</li>
<li>Threads are handled by the OS</li>
<li>Threads can run concurrently</li>
<li>They often <b>end up just waiting</b></li>
<li>Or interleaved together in single CPU</li>
<li>Tasks might get suspended arbitrarily by OS</li>
<li>Thread communication and synchronisation is a diffcult topic</li>
</ul>
</article>
<article class="centered">
<br>
<br>
<br>
<br>
<br>
<img src="images/threaded.png" class="auto-fade-in" alt="Description" title="Description">
<footer class="source">source: <a href="http://krondo.com/?p=1209">krondo.com</a></footer>
</article>
</slide>
<slide class="fill nobackground" style="background-image: url(images/ihavenoidea.jpg)">
<!-- <hgroup>
<h2 class="white">Full Image (with Optional Header)</h2>
</hgroup>
--> <!-- <footer class="source white">www.flickr.com/photos/25797459@N06/5438799763/</footer> -->
</slide>
<slide>
<hgroup class="centered">
<h3>Single thread asynchronous model = <b>Javascript</b></h3>
</hgroup>
<br><br>
<article style="float: left">
<br>
<br>
<br>
<br>
<ul>
<li>Tasks interleaved inside the same Thread</li>
<li>Goodness of synchronous + multithreaded </li>
<li>Programmer in control, not the OS</li>
<li>Tasks are not suspended arbitrarily</li>
</ul>
</article>
<article class="centered">
<img src="images/async.png" class="auto-fade-in" alt="Description" title="Description">
<footer class="source">source: <a href="http://krondo.com/?p=1209">krondo.com</a></footer>
</article>
</slide>
<slide>
<hgroup class="centered">
<h3>Single thread asynchronous model = <b>Javascript</b></h3>
</hgroup>
<br><br>
<article style="float: left">
<br>
<h4>The <b class="blue">event loop</b> handles task scheduling</h4>
<br><br>
<pre class="prettyprint" data-lang="javascript" >
// Event loop pseudo code
for(;;) {
if (endOfProgram)
quit();
<b>if(eventToHandle) { // task waiting, task finished ...
handleEvent(eventToHandle); // Callback </b>
}
}
</pre>
</article>
<article class="centered">
<img src="images/eventloop.png" class="auto-fade-in" alt="Description" title="Description" style="height:350px">
<footer class="source">source: <a href="http://krondo.com/?p=1209">krondo.com</a></footer>
</article>
</slide>
<slide>
<hgroup class="centered">
<h3>Single thread asynchronous model = <b>Javascript</b></h3>
</hgroup>
<br><br>
<article style="float: left">
<br>
<h3 class="red">Therefore</h3>
<br><br>
<ul>
<li>Each task must be <b>non blocking</b></li>
<li>Otherwise you get freezes and lags</li>
</ul>
</article>
<article class="centered">
<img src="images/async.png" class="auto-fade-in" alt="Description" title="Description">
<footer class="source">source: <a href="http://krondo.com/?p=1209">krondo.com</a></footer>
</article>
</slide>
<slide>
<hgroup>
<h2>Stupid Asynchronous API: <b>Callbacks</b></h2>
<h3>Asynchronous = Non Blocking</h3>
</hgroup>
<article class="">
<h3 class="centered"> <b>Callbacks</b> are a way to make tasks non blocking</h3>
<br>
<pre class="prettyprint" data-lang="javascript" >
task1(function task2(task1Result) {
// do something with task 1 result
})
var task1 = function(callback) {
result = longRunningTask(); // Blocking call
callback(result); // Calling a passed callback
}
</pre>
</article>
</slide>
<slide>
<hgroup>
<h2>Stupid Asynchronous API: <b>Callbacks</b></h2>
<h3>Asynchronous = Non Blocking</h3>
</hgroup>
<article class="">
<h3 class="centered"> <b>Callbacks</b> are messy </h3>
<br>
<pre class="prettyprint" data-lang="javascript" >
$('#button').click(function () {
askForTwitterHandle(function(twitterHandle) {
twitterHandle.getTweets(function (tweets) {
processTweets(function (processedTweets) {
ui.show(processedTweets);
});
});
});
});
</pre>
</article>
</slide>
<slide>
<article class="smaller">
<h3 class="centered"> <b>Callbacks</b> error handling is worse, no exception propagation </h3>
<pre class="prettyprint" data-lang="javascript" >
$('#button').click(function () {
askForTwitterHandle(function(twitterHandle) {
twitterHandle.getTweets(function (tweets) {
...
});
}, function onFailure(error) {
handleError(error);
});
});
</pre>
<h3 class="centered">In the synchronous model we have <b>try/catch</b></h3>
<pre class="prettyprint" data-lang="javascript" >
try {
handle = askForTwitterHandle();
tweets = handle.getTweets();
...
} catch (errorMessage) {
console.log('I messed up');
}
</pre>
</article>
</slide>
<slide class="fill nobackground" style="background-image: url(images/callbacks-hack.jpg); background-position: center; background-size: auto 100%;">
<!-- <hgroup>
<h2 class="white">Full Image (with Optional Header)</h2>
</hgroup>
--> <!-- <footer class="source white">www.flickr.com/photos/25797459@N06/5438799763/</footer> -->
</slide>
<slide>
<hgroup>
<h2>Promises are the right abstraction</h2>
</hgroup>
<article>
</pre>
<h4 class="centered">Instead of calling a passed callback, we return a promise</h4>
<br><br>
<pre class="prettyprint" data-lang="javascript" >
ajax('template.html', function(err, template) {
if (err)
handleError();
render(template);
})
// Becomes
<b>var promiseForTemplate = $http.get('template.html');
promiseForTemplate.then(render, handleError)</b>
</pre>
</article>
</slide>
<slide>
<hgroup>
<h2>Promises guarantees</h2>
</hgroup>
<article>
</pre>
<pre class="prettyprint" data-lang="javascript" >
promiseForTemplate.then(onFulfilled, onFailed);
</pre>
<br><br>
<ul>
<li>Only one of <b>onFulfilled</b> or <b>onFailed</b> will be called</li>
<li><b>onFulfilled</b> will be called with a single value (return value)</li>
<li><b>onFailed</b> will be called with a single rejection reason (thrown exception) </li>
<li>If the promise if already settled, the handlers are guaranteed to be called anyway</li>
<li>The handlers will always be called asynchronousy</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Promises can be chained</h2>
</hgroup>
<article>
</pre>
<pre class="prettyprint" data-lang="javascript" >
//
var transformedPromise = promiseForTemplate.then(onFulfilled, onFailed);
</pre>
<br><br>
<ul>
<li>If <b>onFulfilled</b> returns a value</li>
<ul>
<li><b>transformedPromise</b> is <u>resolved</u> with that value</li>
</ul>
<li>If <b>onFulfilled</b> returns a promise</li>
<ul>
<li><b>transformedPromise</b> will adapt it's state</li>
</ul>
<li>If <b>onFailed</b> throws an exception</li>
<ul>
<li><b>transformedPromise</b> will be rejected with that exception</li>
</ul>
</ul>
</article>
</slide>
<slide>
<article class="">
<hgroup>
<h2>Example</h2>
</hgroup>
<br><br>
<h3>Sync</h3>
<pre class="prettyprint" data-lang="javascript" >
var user = getUser(); // blocking, ie, prompt for password
var username = user.name;
</pre>
<br><br>
<h3>Async with Promise</h3>
<pre class="prettyprint" data-lang="javascript" >
var userNamePromise = getUser().then(function (user){
return user.name;
})</pre>
</article>
</slide>
<slide>
<article class="">
<hgroup>
<h2>Example: throwing an exception</h2>
</hgroup>
<br><br>
<h3>Sync</h3>
<pre class="prettyprint" data-lang="javascript" >
var user = getUser(); // blocking, ie, prompt for password
if (user === null)
throw new Error('null user');
</pre>
<br><br>
<h3>Async with Promise</h3>
<pre class="prettyprint" data-lang="javascript" >
var userPromise = getUser().then(function (user){
if (user === null)
throw new Error('null user');
return user;
})
</pre>
</article>
</slide>
<slide>
<article class="">
<hgroup>
<h2>Example: handling an exception</h2>
</hgroup>
<br><br>
<h3>Sync</h3>
<pre class="prettyprint" data-lang="javascript" >
try {
updateUser(data);
} <b>catch (exp) {
console.log('There was an error', exp);
}</b></pre>
<br>
<h3>Async with Promise: exception propagation</h3>
<pre class="prettyprint" data-lang="javascript" >
var updateUserPromise = updateUser(data).then(undefined, <b>function(exp) {
console.log('There was an error', exp);
}</b>)
</pre>
</article>
</slide>
<slide>
<article class="">
<hgroup>
<h2>Example: exception propagation</h2>
</hgroup>
<h3>Callbacks</h3>
<pre class="prettyprint" data-lang="javascript" >
getUser('spike', function(err, user){
<b>if(err) {
ui.error(err);
}</b> else {
getBestFriend(user, function(err, friend){
<b>if (err) {
ui.error(err);
}</b> else {
ui.showBestFriend(friend, function(err, friend){
<b>if (err) {
ui.error(err);
}</b>
})
}
})
}
})</pre>
<br>
</article>
</slide>
<slide>
<article class="">
<hgroup>
<h2>Example: exception propagation</h2>
</hgroup>
<br>
<br>
<br>
<h3>Promises</h3>
<pre class="prettyprint" data-lang="javascript" >
getUser()
.then(getBestFriend)
.then(ui.showBestFriend)
<b>.then(undefined, ui.error)</b>
</pre>
<br>
</article>
</slide>
<slide>
<hgroup>
<h2>Promises in <span class="red3">Angular</span></h2>
</hgroup>
<article class="">
<ul>
<li>Provided by <b class="blue">$q</b> service</li>
<li>Inspired by the the promise/deferred <code><a href="https://github.com/kriskowal/q">Q library</a></code></li>
<li>Promises are used everywhere Angular needs async</li>
<ul>
<li>$http</li>
<li>$resource</li>
<li>$routeProvider</li>
<li>Controller properties</li>
<li>Response Interceptors</li>
<li>...</li>
</ul>
<li>Is a lightweight implementation of Promises (Q is much more complete)</li>
<li>Optimized for the Angular <b class="blue2">run loop</b></li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Angular Run Loop</h2>
<br><br>
<article class="centered">
<img src="images/runloop.png" alt="" style="height: 455px">
</article>
</hgroup>
</slide>
<slide>
<hgroup>
<h2>How to use Promises in Angular</h2>
</hgroup>
<article>
<pre class="prettyprint" data-lang="javascript" >
.controller('testCtrl', function($scope, $q) { // inject the service
var promiseOfTask = function () {
var deferredTask = $q.defer(); // create a deferred object
var result = blockingTask(); // long running task
deferredTask.<b>resolve(result)</b> // resolve the future promise with the result
return deferredTask.promise // return the promise
}
//using the promise
<b>promiseOfTask().then(function(result){
$scope.updateSomeModel(result);
})</b>
})
</pre>
</article>
</slide>
<slide class="segue dark nobackground">
<aside class="gdbar"><img src="images/angularjs.png"></aside>
<hgroup>
<h2 class="yellow">Demonstration</h2>
<h3 class="yellow">Handling failovers for api calls</h3>
</hgroup>
</slide>
<slide class="dark nobackground">
<!-- <aside class="gdbar"><img src="images/angularjs.png"></aside> -->
<hgroup>
<h2 class="yellow2">Resources: </h2>
</hgroup>
<article>
<ul>
<li class="white">Learn more about promises: <code><a href="http://wiki.commonjs.org/wiki/Promises/A">commonJS Promises/A</a></code></li>
<li class="white">Best tutorial on deferred programming: <code><a href="http://krondo.com/?p=1209">Python Twisted & Deferreds</a></code></li>
<li class="white">Async with coroutines: <code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators?redirectlocale=en-US&redirectslug=JavaScript%2FGuide%2FIterators_and_Generators">Generators in Javascript</a></code></li>
</ul>
<br>
<br>
<br>
<span class="white">Twitter: </span><span class="yellow">@sp4ke</span>
<br><br>
<span class="white">Github: </span><span class="yellow">sp4ke</span>
<br><br>
<span class="white">Demo code: </span><span class="yellow">github.com/sp4ke/angular-promises</span>
<br><br>
<span class="white">Send your love in Bitcoins: </span><span class="yellow">1PPaGXh8wihVPBzyobLq557vHCfsjJdBQk</span>
</article>
</slide>
<slide class="backdrop"></slide>
</slides>
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