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• Backbone: Easiest way to maintain reference to 'this' for a Model inside callbacks

  - by Garrett

  var JavascriptHelper = Backbone.Model.extend("JavascriptHelper", {}, // never initialized as an instance { myFn: function() { $('.selector').live('click', function() { this.anotherFn(); // FAIL! }); }, anotherFn: function() { alert('This is never called from myFn()'); } } ); The usual _.bindAll(this, ...) approach won't work here because I am never initializing this model as an instance. Any ideas? Thanks.

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• backbone marionette - displaying a view in a layout region which has already been rendered

  - by Justin Wyllie

  I have something like this: //render the layout Layout.layout = new Layout.Screen(); MyApp.SomeRegion.show(Layout.layout); //render a view into it var mView = new CompositeView({collection: data}); Layout.layout.SomeRegion.show(mView); That all works fine. The layout has 3 regions. The above has rendered a view into one of them. Now, later, I want (in response to some user interaction) to render another view into one of the other regions. So I try: var mView2 = new CompositeView({collection: data}); Layout.layout.SomeOtherRegion.show(mView); But 'SomeOtherRegion' no longer exists on Layout.layout. I looked at this in Firebug. In the first case Layout.layout has my three regions defined on it. In the second case, not. Though they are still there in the regions object. This is the same layout instance. It looks like once a layout has been rendered you cannot render into it again? There must be a way. Nb. I don't want to re-render the layout. I hope that makes sense --Justin Wyllie

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• Functional Methods on Collections

  - by GlenPeterson

  I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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• Creating a custom collections class using System.Collections.CollectionBase

  This article will show you how you can create a class that can behave just like a collection class.

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• loading js files and other dependent js files asynchronously

  - by taber

  I'm looking for a clean way to asynchronously load the following types of javascript files: a "core" js file (hmm, let's just call it, oh i don't know, "jquery!" haha), x number of js files that are dependent on the "core" js file being loaded, and y number of other unrelated js files. I have a couple ideas of how to go about it, but not sure what the best way is. I'd like to avoid loading scripts in the document body. So for example, I want the following 4 javascript files to load asynchronously, appropriately named: /js/my-contact-page-js-functions.js // unrelated/independent script /js/jquery-1.3.2.min.js // the "core" script /js/jquery.color.min.js // dependent on jquery being loaded http://thirdparty.com/js/third-party-tracking-script.js // another unrelated/independent script But this won't work because it's not guaranteed that jQuery is loaded before the color plugin... (function() { a=[ '/js/my-contact-page-functions.js', '/js/jquery-1.4.2.min.js', '/js/jquery.color.js', 'http://cdn.thirdparty.com/third-party-tracking-script.js', ], d=document, h=d.getElementsByTagName('head')[0], s, i, l=a.length; for(i=0;i<l;i++){ s=d.createElement('script'); s.type='text/javascript'; s.async=true; s.src=a[i]; h.appendChild(s); } })(); Is it pretty much not possible to load jquery and the color plugin asynchronously? (Since the color plugin requires that jQuery is loaded first.) The first method I was considering is to just combine the color plugin script with jQuery source into one file. Then another idea I had was loading the color plugin like so: $(window).ready(function() { $.getScript("/js/jquery.color.js"); }); Anyone have any thoughts on how you'd go about this? Thanks!

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• Backbone Model fetched from Lithium controller is not loaded properly in bb Model

  - by Nilesh Kale

  I'm using backbone.js and Lithium. I'm fetching a model from the server by passing in a _id that is received as a hidden parameter on the page. The database MongoDB has stored the data correctly and can be viewed from console as: { "_id" : ObjectId("50bb82694fbe3de417000001"), "holiday_name" : "SHREE15", "description": "", "star_rating" : "3", "holiday_type" : "family", "rooms" : "1", "adults" : "2", "child" :"0", "emails" : "" } The Lithium Model class is so: class Holidays extends \lithium\data\Model { public $validates = array( 'holiday_name' => array( array( 'notEmpty', 'required' => true, 'message' => 'Please key-in a holiday name! (eg. Family trip for summer holidays)' ))); } The backbone Holiday model is so: window.app.IHoliday = Backbone.Model.extend({ urlRoot: HOLIDAY_URL, idAttribute: "_id", id: "_id", // Default attributes for the holiday. defaults: { }, // Ensure that each todo created has `title`. initialize: function(props) { }, The code for backbone/fetch is: var Holiday = new window.app.IHoliday({ _id: holiday_id }); Holiday.fetch( { success: function(){ alert('Holiday fetched:' + JSON.stringify(Holiday)); console.log('HOLIDAY Fetched: \n' + JSON.stringify(Holiday)); console.log('Holiday name:' + Holiday.get('holiday_name')); } } ); Lithium Controller Code is: public function load($holiday_id) { $Holiday = Holidays::find($holiday_id); return compact('Holiday'); } PROBLEM: The output of the backbone model fetched from server is as below and the Holiday model is not correctly 'formed' when data returns into backbone Model: HOLIDAY Fetched: {"_id":"50bb82694fbe3de417000001","Holiday":{"_id":"50bb82694fbe3de417000001","holiday_name":"SHREE15","description":"","star_rating":"3","holiday_type":"family","rooms":"1","adults":"2","child":"0","emails":""}} iplann...view.js (line 68) Holiday name:undefined Clearly there is some issue when the data is passed/translated from Lithium and loaded up as a model into backbone Holiday model. Is there something very obviously wrong in my code?

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• Inside the Concurrent Collections: ConcurrentBag

  - by Simon Cooper

  Unlike the other concurrent collections, ConcurrentBag does not really have a non-concurrent analogy. As stated in the MSDN documentation, ConcurrentBag is optimised for the situation where the same thread is both producing and consuming items from the collection. We'll see how this is the case as we take a closer look. Again, I recommend you have ConcurrentBag open in a decompiler for reference. Thread Statics ConcurrentBag makes heavy use of thread statics - static variables marked with ThreadStaticAttribute. This is a special attribute that instructs the CLR to scope any values assigned to or read from the variable to the executing thread, not globally within the AppDomain. This means that if two different threads assign two different values to the same thread static variable, one value will not overwrite the other, and each thread will see the value they assigned to the variable, separately to any other thread. This is a very useful function that allows for ConcurrentBag's concurrency properties. You can think of a thread static variable: [ThreadStatic] private static int m_Value; as doing the same as: private static Dictionary<Thread, int> m_Values; where the executing thread's identity is used to automatically set and retrieve the corresponding value in the dictionary. In .NET 4, this usage of ThreadStaticAttribute is encapsulated in the ThreadLocal class. Lists of lists ConcurrentBag, at its core, operates as a linked list of linked lists: Each outer list node is an instance of ThreadLocalList, and each inner list node is an instance of Node. Each outer ThreadLocalList is owned by a particular thread, accessible through the thread local m_locals variable: private ThreadLocal<ThreadLocalList<T>> m_locals It is important to note that, although the m_locals variable is thread-local, that only applies to accesses through that variable. The objects referenced by the thread (each instance of the ThreadLocalList object) are normal heap objects that are not specific to any thread. Thinking back to the Dictionary analogy above, if each value stored in the dictionary could be accessed by other means, then any thread could access the value belonging to other threads using that mechanism. Only reads and writes to the variable defined as thread-local are re-routed by the CLR according to the executing thread's identity. So, although m_locals is defined as thread-local, the m_headList, m_nextList and m_tailList variables aren't. This means that any thread can access all the thread local lists in the collection by doing a linear search through the outer linked list defined by these variables. Adding items So, onto the collection operations. First, adding items. This one's pretty simple. If the current thread doesn't already own an instance of ThreadLocalList, then one is created (or, if there are lists owned by threads that have stopped, it takes control of one of those). Then the item is added to the head of that thread's list. That's it. Don't worry, it'll get more complicated when we account for the other operations on the list! Taking & Peeking items This is where it gets tricky. If the current thread's list has items in it, then it peeks or removes the head item (not the tail item) from the local list and returns that. However, if the local list is empty, it has to go and steal another item from another list, belonging to a different thread. It iterates through all the thread local lists in the collection using the m_headList and m_nextList variables until it finds one that has items in it, and it steals one item from that list. Up to this point, the two threads had been operating completely independently. To steal an item from another thread's list, the stealing thread has to do it in such a way as to not step on the owning thread's toes. Recall how adding and removing items both operate on the head of the thread's linked list? That gives us an easy way out - a thread trying to steal items from another thread can pop in round the back of another thread's list using the m_tail variable, and steal an item from the back without the owning thread knowing anything about it. The owning thread can carry on completely independently, unaware that one of its items has been nicked. However, this only works when there are at least 3 items in the list, as that guarantees there will be at least one node between the owning thread performing operations on the list head and the thread stealing items from the tail - there's no chance of the two threads operating on the same node at the same time and causing a race condition. If there's less than three items in the list, then there does need to be some synchronization between the two threads. In this case, the lock on the ThreadLocalList object is used to mediate access to a thread's list when there's the possibility of contention. Thread synchronization In ConcurrentBag, this is done using several mechanisms: Operations performed by the owner thread only take out the lock when there are less than three items in the collection. With three or greater items, there won't be any conflict with a stealing thread operating on the tail of the list. If a lock isn't taken out, the owning thread sets the list's m_currentOp variable to a non-zero value for the duration of the operation. This indicates to all other threads that there is a non-locked operation currently occuring on that list. The stealing thread always takes out the lock, to prevent two threads trying to steal from the same list at the same time. After taking out the lock, the stealing thread spinwaits until m_currentOp has been set to zero before actually performing the steal. This ensures there won't be a conflict with the owning thread when the number of items in the list is on the 2-3 item borderline. If any add or remove operations are started in the meantime, and the list is below 3 items, those operations try to take out the list's lock and are blocked until the stealing thread has finished. This allows a thread to steal an item from another thread's list without corrupting it. What about synchronization in the collection as a whole? Collection synchronization Any thread that operates on the collection's global structure (accessing anything outside the thread local lists) has to take out the collection's global lock - m_globalListsLock. This single lock is sufficient when adding a new thread local list, as the items inside each thread's list are unaffected. However, what about operations (such as Count or ToArray) that need to access every item in the collection? In order to ensure a consistent view, all operations on the collection are stopped while the count or ToArray is performed. This is done by freezing the bag at the start, performing the global operation, and unfreezing at the end: The global lock is taken out, to prevent structural alterations to the collection. m_needSync is set to true. This notifies all the threads that they need to take out their list's lock irregardless of what operation they're doing. All the list locks are taken out in order. This blocks all locking operations on the lists. The freezing thread waits for all current lockless operations to finish by spinwaiting on each m_currentOp field. The global operation can then be performed while the bag is frozen, but no other operations can take place at the same time, as all other threads are blocked on a list's lock. Then, once the global operation has finished, the locks are released, m_needSync is unset, and normal concurrent operation resumes. Concurrent principles That's the essence of how ConcurrentBag operates. Each thread operates independently on its own local list, except when they have to steal items from another list. When stealing, only the stealing thread is forced to take out the lock; the owning thread only has to when there is the possibility of contention. And a global lock controls accesses to the structure of the collection outside the thread lists. Operations affecting the entire collection take out all locks in the collection to freeze the contents at a single point in time. So, what principles can we extract here? Threads operate independently Thread-static variables and ThreadLocal makes this easy. Threads operate entirely concurrently on their own structures; only when they need to grab data from another thread is there any thread contention. Minimised lock-taking Even when two threads need to operate on the same data structures (one thread stealing from another), they do so in such a way such that the probability of actually blocking on a lock is minimised; the owning thread always operates on the head of the list, and the stealing thread always operates on the tail. Management of lockless operations Any operations that don't take out a lock still have a 'hook' to force them to lock when necessary. This allows all operations on the collection to be stopped temporarily while a global snapshot is taken. Hopefully, such operations will be short-lived and infrequent. That's all the concurrent collections covered. I hope you've found it as informative and interesting as I have. Next, I'll be taking a closer look at ThreadLocal, which I came across while analyzing ConcurrentBag. As you'll see, the operation of this class deserves a much closer look.

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• Backbone.js Adding Model to Collection Issue

  - by jtmgdevelopment

  I am building a test application in Backbone.js (my first app using Backbone). The app goes like this: Load Data from server "Plans" Build list of plans and show to screen There is a button to add a new plan Once new plan is added, add to collection ( do not save to server as of now ) redirect to index page and show the new collection ( includes the plan you just added) My issue is with item 5. When I save a plan, I add the model to the collection then redirect to the initial view. At this point, I fetch data from the server. When I fetch data from the server, this overwrites my collection and my added model is gone. How can I prevent this from happening? I have found a way to do this but it is definitely not the correct way at all. Below you will find my code examples for this. Thanks for the help. PlansListView View: var PlansListView = Backbone.View.extend({ tagName : 'ul', initialize : function() { _.bindAll( this, 'render', 'close' ); //reset the view if the collection is reset this.collection.bind( 'reset', this.render , this ); }, render : function() { _.each( this.collection.models, function( plan ){ $( this.el ).append( new PlansListItemView({ model: plan }).render().el ); }, this ); return this; }, close : function() { $( this.el ).unbind(); $( this.el ).remove(); } });//end NewPlanView Save Method var NewPlanView = Backbone.View.extend({ tagName : 'section', template : _.template( $( '#plan-form-template' ).html() ), events : { 'click button.save' : 'savePlan', 'click button.cancel' : 'cancel' }, intialize: function() { _.bindAll( this, 'render', 'save', 'cancel' ); }, render : function() { $( '#container' ).append( $( this.el ).html(this.template( this.model.toJSON() )) ); return this; }, savePlan : function( event ) { this.model.set({ name : 'bad plan', date : 'friday', desc : 'blah', id : Math.floor(Math.random()*11), total_stops : '2' }); this.collection.add( this.model ); app.navigate('', true ); event.preventDefault(); }, cancel : function(){} }); Router (default method): index : function() { this.container.empty(); var self = this; //This is a hack to get this to work //on default page load fetch all plans from the server //if the page has loaded ( this.plans is defined) set the updated plans collection to the view //There has to be a better way!! if( ! this.plans ) { this.plans = new Plans(); this.plans.fetch({ success: function() { self.plansListView = new PlansListView({ collection : self.plans }); $( '#container' ).append( self.plansListView.render().el ); if( self.requestedID ) self.planDetails( self.requestedID ); } }); } else { this.plansListView = new PlansListView({ collection : this.plans }); $( '#container' ).append( self.plansListView.render().el ); if( this.requestedID ) self.planDetails( this.requestedID ); } }, New Plan Route: newPlan : function() { var plan = new Plan({name: 'Cool Plan', date: 'Monday', desc: 'This is a great app'}); this.newPlan = new NewPlanView({ model : plan, collection: this.plans }); this.newPlan.render(); } FULL CODE ( function( $ ){ var Plan = Backbone.Model.extend({ defaults: { name : '', date : '', desc : '' } }); var Plans = Backbone.Collection.extend({ model : Plan, url : '/data/' }); $( document ).ready(function( e ){ var PlansListView = Backbone.View.extend({ tagName : 'ul', initialize : function() { _.bindAll( this, 'render', 'close' ); //reset the view if the collection is reset this.collection.bind( 'reset', this.render , this ); }, render : function() { _.each( this.collection.models, function( plan ){ $( this.el ).append( new PlansListItemView({ model: plan }).render().el ); }, this ); return this; }, close : function() { $( this.el ).unbind(); $( this.el ).remove(); } });//end var PlansListItemView = Backbone.View.extend({ tagName : 'li', template : _.template( $( '#list-item-template' ).html() ), events :{ 'click a' : 'listInfo' }, render : function() { $( this.el ).html( this.template( this.model.toJSON() ) ); return this; }, listInfo : function( event ) { } });//end var PlanView = Backbone.View.extend({ tagName : 'section', events : { 'click button.add-plan' : 'newPlan' }, template: _.template( $( '#plan-template' ).html() ), initialize: function() { _.bindAll( this, 'render', 'close', 'newPlan' ); }, render : function() { $( '#container' ).append( $( this.el ).html( this.template( this.model.toJSON() ) ) ); return this; }, newPlan : function( event ) { app.navigate( 'newplan', true ); }, close : function() { $( this.el ).unbind(); $( this.el ).remove(); } });//end var NewPlanView = Backbone.View.extend({ tagName : 'section', template : _.template( $( '#plan-form-template' ).html() ), events : { 'click button.save' : 'savePlan', 'click button.cancel' : 'cancel' }, intialize: function() { _.bindAll( this, 'render', 'save', 'cancel' ); }, render : function() { $( '#container' ).append( $( this.el ).html(this.template( this.model.toJSON() )) ); return this; }, savePlan : function( event ) { this.model.set({ name : 'bad plan', date : 'friday', desc : 'blah', id : Math.floor(Math.random()*11), total_stops : '2' }); this.collection.add( this.model ); app.navigate('', true ); event.preventDefault(); }, cancel : function(){} }); var AppRouter = Backbone.Router.extend({ container : $( '#container' ), routes : { '' : 'index', 'viewplan/:id' : 'planDetails', 'newplan' : 'newPlan' }, initialize: function(){ }, index : function() { this.container.empty(); var self = this; //This is a hack to get this to work //on default page load fetch all plans from the server //if the page has loaded ( this.plans is defined) set the updated plans collection to the view //There has to be a better way!! if( ! this.plans ) { this.plans = new Plans(); this.plans.fetch({ success: function() { self.plansListView = new PlansListView({ collection : self.plans }); $( '#container' ).append( self.plansListView.render().el ); if( self.requestedID ) self.planDetails( self.requestedID ); } }); } else { this.plansListView = new PlansListView({ collection : this.plans }); $( '#container' ).append( self.plansListView.render().el ); if( this.requestedID ) self.planDetails( this.requestedID ); } }, planDetails : function( id ) { if( this.plans ) { this.plansListView.close(); this.plan = this.plans.get( id ); if( this.planView ) this.planView.close(); this.planView = new PlanView({ model : this.plan }); this.planView.render(); } else{ this.requestedID = id; this.index(); } if( ! this.plans ) this.index(); }, newPlan : function() { var plan = new Plan({name: 'Cool Plan', date: 'Monday', desc: 'This is a great app'}); this.newPlan = new NewPlanView({ model : plan, collection: this.plans }); this.newPlan.render(); } }); var app = new AppRouter(); Backbone.history.start(); }); })( jQuery );

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• Node.js/ v8: How to make my own snapshot to accelerate startup

  - by Anand

  I have a node.js (v0.6.12) application that starts by evaluating a Javascript file, startup.js. It takes a long time to evaluate startup.js, and I'd like to 'bake it in' to a custom build of Node if possible. The v8 source directory distributed with Node, node/deps/v8/src, contains a SconScript that can almost be used to do this. On line 302, we have LIBRARY_FILES = ''' runtime.js v8natives.js array.js string.js uri.js math.js messages.js apinatives.js date.js regexp.js json.js liveedit-debugger.js mirror-debugger.js debug-debugger.js '''.split() Those javascript files are present in the same directory. Something in the build process apparently evaluates them, takes a snapshot of state, and saves it as a byte string in node/out/Release/obj/release/snapshot.cc (on Mac OS). Some customization of the startup snapshot is possible by altering the SconScript. For example, I can change the definition of the builtin Date.toString by altering date.js. I can even add new global variables by adding startup.js to the list of library files, with contents global.test = 1. However, I can't put just any javascript code in startup.js. If it contains Date.toString = 1;, an error results even though the code is valid at the node repl: Build failed: -> task failed (err #2): {task: libv8.a SConstruct -> libv8.a} make: *** [program] Error 1 And it obviously can't make use of code that depends on libraries Node adds to v8. global.underscore = require('underscore'); causes the same error. I'd ideally like a tool, customSnapshot, where customSnapshot startup.js evaluates startup.js with node and then dumps a snapshot to a file, snapshot.cc, which I can put into the node source directory. I can then build node and tell it not to rebuild the snapshot.

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• Namespaced Backbone.js Views not firing events

  - by Stasio

  I'm currently getting started with Backbone.js. I've wrote some examples with Backbone and they are working fine. But now I need to use Backbone.js with Rails 3.1 and CoffeeScript. I took my well-working examples and rewrote on CoffeeScript using backbone-rails gem. And got the following problem. I've simplyfied code, but the problem is still remaining I've got the following files: Here I'm starting my Backbone app at main.js.coffee file according to my main_controller in rails app: $ = jQuery $-> CsfTaskManager.init() Here is backbone app description: #= require_self #= require_tree ./templates #= require_tree ./models #= require_tree ./views #= require_tree ./routers window.CsfTaskManager = Models: {} Collections: {} Routers: {} Views: {} init: -> new CsfTaskManager.Routers.AppRouter() Backbone.history.start() This is my apps' router: class CsfTaskManager.Routers.AppRouter extends Backbone.Router initialize: (options) -> goalsBlock = new CsfTaskManager.Views.goalsView() routes: "!/": "root", some other routes... And finally view: class CsfTaskManager.Views.goalsView extends Backbone.View initialize: -> this.goals = new CsfTaskManager.Collections.GoalsCollection() el: $('div#app'), events: "click .add-btn": "addGoal" addGoal: -> alert('ji') HTML page has such code: <div id="app"> <div class="app-screen hidden" id="goal-form" style="display: block; "> <button class="btn" id="load"> Load </button> <h3> New Goal </h3> <div class="form-stacked"> <form accept-charset="UTF-8" action="/goals" class="new_goal" id="new_goal" method="post"><div style="margin:0;padding:0;display:inline"><input name="utf8" type="hidden" value="?"><input name="authenticity_token" type="hidden" value="Pnt+V/tS1/b079M/1ZIRdw2ss1D6bvJKVh868DXRjUg="></div> <label for="goal_title">Title</label> <p></p> <input class="goal-title" id="goal_title" name="goal[title]" size="30" type="text"> <p></p> <label for="goal_note">Note</label> <p></p> <input class="goal-note" id="goal_note" name="goal[note]" size="30" type="text"> </form> </div> <p> <button class="add-btn btn"> Add </button> </p> <ul id="goals-list"></ul> </div> <table class="app-screen bordered-table" id="calendar-grid" style="display: none; "> <tbody><tr> <td colspan="2"> week </td> </tr> <tr> <td> day </td> <td> <div id="calendar"></div> </td> </tr> </tbody></table> <div class="app-screen hidden" id="role-form" style="display: none; "> <h3> New User Role </h3> <div class="form-stacked"> <form accept-charset="UTF-8" action="/roles" class="new_role" id="new_role" method="post"><div style="margin:0;padding:0;display:inline"><input name="utf8" type="hidden" value="?"><input name="authenticity_token" type="hidden" value="Pnt+V/tS1/b079M/1ZIRdw2ss1D6bvJKVh868DXRjUg="></div> <label for="role_title">Title</label> <p></p> <input class="role-title" id="role_name" name="role[name]" size="30" type="text"> <p></p> <label for="role_note">Note</label> <p></p> <input class="role-note" id="role_description" name="role[description]" size="30" type="text"> </form> </div> <p> <button class="add-btn btn"> Add </button> </p> </div> </div> So .add-btn element is nested in #app, but click on this button doesn't fire event. Where can be a trouble? Before, when I had the same app in one .js file, without of coffeescript, namespacing and backbone-rails gem, everything was allright. Bytheway, appRouter works fine, goalsView object is created successfully too, but events don't fire for some reasons. Please give me some hint, because I'm really got stuck...

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• Use-cases for node.js and c#

  - by Chase Florell

  I do quite a bit of ASP.NET work (C#, MVC), but most of it is typical web development. I do Restful architecture using CRUD repositories. Most of my clients don't have a lot of advanced requirements within their applications. I'm now looking at node.js and it's performance implications (I'm addicted to speed), but I haven't delved into it all that much. I'm wondering if node.js can realistically replace my typical web development in C# and ASP.NET MVC (not rewriting existing apps, but when working on new ones) node.js can complement an ASP.NET MVC app by adding some async goodness to the existing architecture. Are there use-cases for/against C# and node.js? Edit I love ASP.NET MVC and am super excited with where it's going. Just trying to see if there are special use cases that would favor node.js

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• Node.js Or servlets?

  - by Nilesh

  I have heard a lot and read about the Javascript server side language i.e Node.js, and saw many comparisons in favor of Node. I don't understand what makes it better or faster, or how it even relates to something as mature as Java Servlets. But Servlets are built on top of a multithreaded programming language as opposed to Node.js. Then how can node.js be faster? If suppose 1000K users query for a database records, then shouldn't Node.js be slower than Servlets. Also Don't servlets have better security compared to Node.js?

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• proper way to dynamically assign backbone.js view el

  - by kikuchiyo

  I would like to create two ( or more ) view instances, each with different el attributes, and have events bound to them via backbone.js view's events hash ( not through jQuery ). Getting events to trigger when all instantiations have the same el is easy: someView = Backbone.View.extend({ el: '#someDiv', events: { 'click': 'someFunction' }, someFunction: function(){ //Do something here } }); So far, if I assign el in the initialize function, and set events normally as follows, events do not trigger: someView = Backbone.View.extend({ events: { 'click': 'someFunction' }, initialize: function( options ){ this.el = options.el }, someFunction: function(){ //Do something here } }); My first instinct was to have el be a function that returns the string representation of the dom element of interest: someView = Backbone.View.extend({ el: function(){ return '#someDiv-' + this.someNumber }, events: { 'click': 'someFunction' }, initialize: function( options ){ this.someNumber = options.someNumber }, someFunction: function(){ //Do something here } }); However, this triggers someFunction x times if I have x instantiations of someView. Next I tried setting both the el and events attributes in initialize: someView = Backbone.View.extend({ initialize: function( options ){ this.el = options.el this.events = { 'click': 'someFunction' } }, someFunction: function(){ //Do something here } }); but this does not trigger events. At this point I'm pretty much fishing. Does anyone know how instantiate a backbone.js view with an el specific to that instance that has events that only trigger for that instance, and not other instances of the View?

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• Problem Render backbone collection using Mustache template

  - by RameshVel

  I am quite new to backbone js and Mustache. I am trying to load the backbone collection (Object array) on page load from rails json object to save the extra call . I am having troubles rendering the backbone collection using mustache template. My model & collection are var Item = Backbone.Model.extend({ }); App.Collections.Items= Backbone.Collection.extend({ model: Item, url: '/items' }); and view App.Views.Index = Backbone.View.extend({ el : '#itemList', initialize: function() { this.render(); }, render: function() { $(this.el).html(Mustache.to_html(JST.item_template(),this.collection )); //var test = {name:"test",price:100}; //$(this.el).html(Mustache.to_html(JST.item_template(),test )); } }); In the above view render, i can able to render the single model (commented test obeject), but not the collections. I am totally struck here, i have tried with both underscore templating & mustache but no luck. And this is the Template <li> <div> <div style="float: left; width: 70px"> <a href="#"> <img class="thumbnail" src="http://placehold.it/60x60" alt=""> </a> </div> <div style="float: right; width: 292px"> <h4> {{name}} <span class="price">Rs {{price}}</span></h4> </div> </div> </li> and my object array kind of looks like this

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• How does Backbone.js connect View to Model

  - by William Sham

  I am trying to learn backbone.js through the following example. Then I got stuck at the point ItemView = Backbone.View.extend why you can use this.model.get? I thought this is referring to the instance of ItemView that would be created. Then why would ItemView has a model property at all?!! (function($){ var Item = Backbone.Model.extend({ defaults: { part1: 'hello', part2: 'world' } }); var List = Backbone.Collection.extend({ model: Item }); var ItemView = Backbone.View.extend({ tagName: 'li', initialize: function(){ _.bindAll(this, 'render'); }, render: function(){ $(this.el).html('<span>'+this.model.get('part1')+' '+this.model.get('part2')+'</span>'); return this; } }); var ListView = Backbone.View.extend({ el: $('body'), events: { 'click button#add': 'addItem' }, initialize: function(){ _.bindAll(this, 'render', 'addItem', 'appendItem'); this.collection = new List(); this.collection.bind('add', this.appendItem); this.counter = 0; this.render(); }, render: function(){ $(this.el).append("<button id='add'>Add list item</button>"); $(this.el).append("<ul></ul>"); _(this.collection.models).each(function(item){ appendItem(item); }, this); }, addItem: function(){ this.counter++; var item = new Item(); item.set({ part2: item.get('part2') + this.counter }); this.collection.add(item); }, appendItem: function(item){ var itemView = new ItemView({ model: item }); $('ul', this.el).append(itemView.render().el); } }); var listView = new ListView(); })(jQuery);

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• Understanding node.js: some real-life examples

  - by steweb

  Hi all! As a curious web developer I've been hearing about node.js for several months and (just) now I'd like to learn it and, most of all, understand its "engine". So, as a real newbie about node.js I'm going to follow some tutorials. And as every new technology over the internet, find a very good and exhaustive tutorial is like looking for a needle in a haystack :) My "big question" can be split into this 3 sub-questions: I know node.js can be very useful to build web-chats. But, apart from this example (and from helloworld one :D), how could I use it? Which are the real-life examples that let me think i.e. "oh, it's fantastic, I could really integrate it for my daily projects"? I also know it implements some JS specifications. It is required to deeply know other programming languages apart from JS? Where can I find a good reference (basically, I don't want to search "node.js reference" on google hoping to be lucky enough to get some good websites)? Thanks everyone!

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• Rails/Node.js interaction

  - by lpvn

  I and my co-worker are developing a web application with rails and node.js and we can't reach a consensus regarding a particular architectural decision. Our setup is basically a rails server working with node.js and redis, when a client makes a http request to our rails API in some cases our rails application posts the response to a redis database and then node.js transmits the response via websocket. Our disagreement occurs in the following point: my co-worker thinks that using node.js to send data to clients is somewhat business logic and should be inside the model, so in the first code he wrote he used commands of broadcast in callbacks and other places of the model, he's convinced that the models are the best place for the interaction between rails and node. I on the other hand think that using node.js belongs to the runtime realm, my take is that the broadcast commands and other node.js interactions should be in the controller and should only be used in a model if passed through a well defined interface, just like the situation when a model needs to access the current user of a session. At this point we're tired of arguing over this same thing and our discussion consists in us repeating to ourselves our same opinions over and over. Could anyone, preferably with experience in the same setup, give us an unambiguous response saying which solution is more adequate and why it is?

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• Backbone.js (model instanceof Model) via Chrome Extension

  - by Leoncelot

  Hey guys, This is my first time ever posting on this site and the problem I'm about to pose is difficult to articulate due to the set of variables required to arrive at it. Let me just quickly explain the framework I'm working with. I'm building a Chrome Extension using jQuery, jQuery-ui, and Backbone The entire JS suite for the extension is written in CoffeeScript and I'm utilizing Rails and the asset pipeline to manage it all. This means that when I want to deploy my extension code I run rake assets:precompile and copy the resulting compressed JS to my extensions Directory. The nice thing about this approach is that I can actually run the extension js from inside my Rails app by including the library. This is basically the same as my extensions background.js file which injects the js as a content script. Anyway, the problem I've recently encountered was when I tried testing my extension on my buddy's site, whiskeynotes.com. What I was noticing is that my backbone models were being mangled upon adding them to their respective collections. So something like this.collection.add(new SomeModel) created some nonsense version of my model. This code eventually runs into Backbone's prepareModel code _prepareModel: function(model, options) { options || (options = {}); if (!(model instanceof Model)) { var attrs = model; options.collection = this; model = new this.model(attrs, options); if (!model._validate(model.attributes, options)) model = false; } else if (!model.collection) { model.collection = this; } return model; }, Now, in most of the sites on which I've tested the extension, the result is normal, however on my buddy's site the !(model instance Model) evaluates to true even though it is actually an instance of the correct class. The consequence is a super messed up version of the model where the model's attributes is a reference to the models collection (strange right?). Needless to say, all kinds of crazy things were happening afterward. Why this is occurring is beyond me. However changing this line (!(model instanceof Model)) to (!(model instanceof Backbone.Model)) seems to fix the problem. I thought maybe it had something to do with the Flot library (jQuery graph library) creating their own version of 'Model' but looking through the source yielded no instances of it. I'm just curious as to why this would happen. And does it make sense to add this little change to the Backbone source? Update: I just realized that the "fix" doesn't actually work. I can also add that my backbone Models are namespaced in a wrapping object so that declaration looks something like class SomeNamespace.SomeModel extends Backbone.Model

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• Backbone events not firing (this.el undefined) & general feedback on use of the framework

  - by Leo

  I am very new to backbone.js and I am struggling a little. I figured out a way to get data from the server (in json) onto the screen successfully but am I doing it the right/best way? I know there is something wrong because the only view which contains a valid this.el is the parent view. I suspect that because of this, the events of the view are not firing ()... What is the best way forward? Here is the code: var surveyUrl = "/api/Survey?format=json&callback=?"; $(function () { AnswerOption = Backbone.Model.extend({}); AnswerOptionList = Backbone.Collection.extend({ initialize: function (models, options) { this.bind("add", options.view.render); } }); AnswerOptionView = Backbone.View.extend({ initialize: function () { this.answerOptionList = new AnswerOptionList(null, { view: this }); _.bindAll(this, 'render'); }, events: { "click .answerOptionControl": "updateCheckedState" //does not fire because there is no this.el }, render: function (model) { // Compile the template using underscore var template = _.template($("#questionAnswerOptionTemplate").html(), model.answerOption); $('#answerOptions' + model.answerOption.questionId + '>fieldset').append(template); return this; }, updateCheckedState: function (data) { //never hit... } }); Question = Backbone.Model.extend({}); QuestionList = Backbone.Collection.extend({ initialize: function (models, options) { this.bind("add", options.view.render); } }); QuestionView = Backbone.View.extend({ initialize: function () { this.questionlist = new QuestionList(null, { view: this }); _.bindAll(this, 'render'); }, render: function (model) { // Compile the template using underscore var template = _.template($("#questionTemplate").html(), model.question); $("#questions").append(template); //append answers using AnswerOptionView var view = new AnswerOptionView(); for (var i = 0; i < model.question.answerOptions.length; i++) { var qModel = new AnswerOption(); qModel.answerOption = model.question.answerOptions[i]; qModel.questionChoiceType = ChoiceType(); view.answerOptionList.add(qModel); } $('#questions').trigger('create'); return this; } }); Survey = Backbone.Model.extend({ url: function () { return this.get("id") ? surveyUrl + '/' + this.get("id") : surveyUrl; } }); SurveyList = Backbone.Collection.extend({ model: Survey, url: surveyUrl }); aSurvey = new Survey({ Id: 1 }); SurveyView = Backbone.View.extend({ model: aSurvey, initialize: function () { _.bindAll(this, 'render'); this.model.bind('refresh', this.render); this.model.bind('change', this.render); this.model.view = this; }, // Re-render the contents render: function () { var view = new QuestionView(); //{el:this.el}); for (var i = 0; i < this.model.attributes[0].questions.length; i++) { var qModel = new Question(); qModel.question = this.model.attributes[0].questions[i]; view.questionlist.add(qModel); } } }); window.App = new SurveyView(aSurvey); aSurvey.fetch(); }); -html <body> <div id="questions"></div> <!-- Templates --> <script type="text/template" id="questionAnswerOptionTemplate"> <input name="answerOptionGroup<%= questionId %>" id="answerOptionInput<%= id %>" type="checkbox" class="answerOptionControl"/> <label for="answerOptionInput<%= id %>"><%= text %></label> </script> <script type="text/template" id="questionTemplate"> <div id="question<%=id %>" class="questionWithCurve"> <h1><%= headerText %></h1> <h2><%= subText %></h2> <div data-role="fieldcontain" id="answerOptions<%= id %>" > <fieldset data-role="controlgroup" data-type="vertical"> <legend> </legend> </fieldset> </div> </div> </script> </body> And the JSON from the server: ? ({ "name": "Survey", "questions": [{ "surveyId": 1, "headerText": "Question 1", "subText": "subtext", "type": "Choice", "positionOrder": 1, "answerOptions": [{ "questionId": 1, "text": "Question 1 - Option 1", "positionOrder": 1, "id": 1, "createdOn": "\/Date(1333666034297+0100)\/" }, { "questionId": 1, "text": "Question 1 - Option 2", "positionOrder": 2, "id": 2, "createdOn": "\/Date(1333666034340+0100)\/" }, { "questionId": 1, "text": "Question 1 - Option 3", "positionOrder": 3, "id": 3, "createdOn": "\/Date(1333666034350+0100)\/" }], "questionValidators": [{ "questionId": 1, "value": "3", "type": "MaxAnswers", "id": 1, "createdOn": "\/Date(1333666034267+0100)\/" }, { "questionId": 1, "value": "1", "type": "MinAnswers", "id": 2, "createdOn": "\/Date(1333666034283+0100)\/" }], "id": 1, "createdOn": "\/Date(1333666034257+0100)\/" }, { "surveyId": 1, "headerText": "Question 2", "subText": "subtext", "type": "Choice", "positionOrder": 2, "answerOptions": [{ "questionId": 2, "text": "Question 2 - Option 1", "positionOrder": 1, "id": 4, "createdOn": "\/Date(1333666034427+0100)\/" }, { "questionId": 2, "text": "Question 2 - Option 2", "positionOrder": 2, "id": 5, "createdOn": "\/Date(1333666034440+0100)\/" }, { "questionId": 2, "text": "Question 2 - Option 3", "positionOrder": 3, "id": 6, "createdOn": "\/Date(1333666034447+0100)\/" }], "questionValidators": [{ "questionId": 2, "value": "3", "type": "MaxAnswers", "id": 3, "createdOn": "\/Date(1333666034407+0100)\/" }, { "questionId": 2, "value": "1", "type": "MinAnswers", "id": 4, "createdOn": "\/Date(1333666034417+0100)\/" }], "id": 2, "createdOn": "\/Date(1333666034377+0100)\/" }, { "surveyId": 1, "headerText": "Question 3", "subText": "subtext", "type": "Choice", "positionOrder": 3, "answerOptions": [{ "questionId": 3, "text": "Question 3 - Option 1", "positionOrder": 1, "id": 7, "createdOn": "\/Date(1333666034477+0100)\/" }, { "questionId": 3, "text": "Question 3 - Option 2", "positionOrder": 2, "id": 8, "createdOn": "\/Date(1333666034483+0100)\/" }, { "questionId": 3, "text": "Question 3 - Option 3", "positionOrder": 3, "id": 9, "createdOn": "\/Date(1333666034487+0100)\/" }], "questionValidators": [{ "questionId": 3, "value": "3", "type": "MaxAnswers", "id": 5, "createdOn": "\/Date(1333666034463+0100)\/" }, { "questionId": 3, "value": "1", "type": "MinAnswers", "id": 6, "createdOn": "\/Date(1333666034470+0100)\/" }], "id": 3, "createdOn": "\/Date(1333666034457+0100)\/" }, { "surveyId": 1, "headerText": "Question 4", "subText": "subtext", "type": "Choice", "positionOrder": 4, "answerOptions": [{ "questionId": 4, "text": "Question 4 - Option 1", "positionOrder": 1, "id": 10, "createdOn": "\/Date(1333666034500+0100)\/" }, { "questionId": 4, "text": "Question 4 - Option 2", "positionOrder": 2, "id": 11, "createdOn": "\/Date(1333666034507+0100)\/" }, { "questionId": 4, "text": "Question 4 - Option 3", "positionOrder": 3, "id": 12, "createdOn": "\/Date(1333666034507+0100)\/" }], "questionValidators": [{ "questionId": 4, "value": "3", "type": "MaxAnswers", "id": 7, "createdOn": "\/Date(1333666034493+0100)\/" }, { "questionId": 4, "value": "1", "type": "MinAnswers", "id": 8, "createdOn": "\/Date(1333666034497+0100)\/" }], "id": 4, "createdOn": "\/Date(1333666034490+0100)\/" }], "id": 1, "createdOn": "\/Date(1333666034243+0100)\/" })

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• Sending data through POST request from a node.js server to a node.js server

  - by Masiar

  I'm trying to send data through a POST request from a node.js server to another node.js server. What I do in the "client" node.js is the following: var options = { host: 'my.url', port: 80, path: '/login', method: 'POST' }; var req = http.request(options, function(res){ console.log('status: ' + res.statusCode); console.log('headers: ' + JSON.stringify(res.headers)); res.setEncoding('utf8'); res.on('data', function(chunk){ console.log("body: " + chunk); }); }); req.on('error', function(e) { console.log('problem with request: ' + e.message); }); // write data to request body req.write('data\n'); req.write('data\n'); req.end(); This chunk is taken more or less from the node.js website so it should be correct. The only thing I don't see is how to include username and password in the options variable to actually login. This is how I deal with the data in the server node.js (I use express): app.post('/login', function(req, res){ var user = {}; user.username = req.body.username; user.password = req.body.password; ... }); How can I add those username and password fields to the options variable to have it logged in? Thanks

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• Three.js Collada import animation not working

  - by Peter Vasilev

  I've been trying to export a Collada animated model to three js. Here is the model: http://bayesianconspiracy.com/files/model.dae It is imported properly(I can see the model) but I can't get it to animate. I've been using the two Collada examples that come with Three js. I've tried just replacing the path with the path to my model but it doesn't work. I've also tried tweaking some stuff but to no avail. When the model is loaded I've checked the 'object.animations' object which seems to be loaded fine(can't tell for sure but there is lots of stuff in it). I've also tried the Three.js editor: http://threejs.org/editor/ which loads the model properly again but I can't play the animation : ( I am using Three JS r62 and Blender 2.68. Any help appreciated!!

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• Windows Azure PowerShell for Node.js

  - by shiju

  The Windows Azure PowerShell for Node.js is a command-line tool that  allows the Node developers to build and deploy Node.js apps in Windows Azure using Windows PowerShell cmdlets. Using Windows Azure PowerShell for Node.js, you can develop, test, deploy and manage Node based hosted service in Windows Azure. For getting the PowerShell for Node.js, click All Programs, Windows Azure SDK Node.js and run  Windows Azure PowerShell for Node.js, as Administrator. The followings are the few PowerShell cmdlets that lets you to work with Node.js apps in Windows Azure Create New Hosted Service New-AzureService <HostedServiceName> The below cmdlet will created a Windows Aazure hosted service named NodeOnAzure in the folder C:\nodejs and this will also create ServiceConfiguration.Cloud.cscfg, ServiceConfiguration.Local.cscfg and ServiceDefinition.csdef and deploymentSettings.json files for the hosted service. PS C:\nodejs> New-AzureService NodeOnAzure The below picture shows the files after creating the hosted service Create Web Role Add-AzureNodeWebRole <RoleName> The following cmdlet will create a hosted service named MyNodeApp along with web.config file. PS C:\nodejs\NodeOnAzure> Add-AzureNodeWebRole MyNodeApp The below picture shows the files after creating the web role app. Install Node Module npm install <NodeModule> The following command will install Node Module Express onto your web role app. PS C:\nodejs\NodeOnAzure\MyNodeApp> npm install Express Run Windows Azure Apps Locally in the Emulator Start-AzureEmulator -launch The following cmdlet will create a local package and run Windows Azure app locally in the emulator PS C:\nodejs\NodeOnAzure\MyNodeApp> Start-AzureEmulator -launch Stop Windows Azure Emulator Stop-AzureEmulator The following cmdlet will stop your Windows Azure in the emulator. PS C:\nodejs\NodeOnAzure\MyNodeApp> Stop-AzureEmulator Download Windows Azure Publishing Settings Get-AzurePublishSettings The following cmdlet will redirect to Windows Azure portal where we can download Windows Azure publish settings PS C:\nodejs\NodeOnAzure\MyNodeApp> Get-AzurePublishSettings Import Windows Azure Publishing Settings Import-AzurePublishSettings <Location of .publishSettings file> The following cmdlet will import the publish settings file from the location c:\nodejs PS C:\nodejs\NodeOnAzure\MyNodeApp>  Import-AzurePublishSettings c:\nodejs\shijuvar.publishSettings Publish Apps to Windows Azure Publish-AzureService –name <Name> –location <Location of Data centre> The following cmdlet will publish the app to Windows Azure with name “NodeOnAzure” in the location Southeast Asia. Please keep in mind that the service name should be unique. PS C:\nodejs\NodeOnAzure\MyNodeApp> Publish-AzureService –name NodeonAzure –location "Southeast Asia” –launch Stop Windows Azure Service Stop-AzureService The following cmdlet will stop your service which you have deployed previously. PS C:\nodejs\NodeOnAzure\MyNodeApp> Stop-AzureService Remove Windows Azure Service Remove-AzureService The following cmdlet will remove your service from Windows Azure. PS C:\nodejs\NodeOnAzure\MyNodeApp> Remove-AzureService Quick Summary for PowerShell cmdlets Create  a new Hosted Service New-AzureService <HostedServiceName> Create a Web Role Add-AzureNodeWebRole <RoleName> Install Node Module npm install <NodeModule> Running Windows Azure Apps Locally in Emulator Start-AzureEmulator -launch Stop Windows Azure Emulator Stop-AzureEmulator Download Windows Azure Publishing Settings Get-AzurePublishSettings Import Windows Azure Publishing Settings Import-AzurePublishSettings <Location of .publishSettings file> Publish Apps to Windows Azure Publish-AzureService –name <Name> –location <Location of Data centre> Stop Windows Azure Service Stop-AzureService Remove Windows Azure Service Remove-AzureService

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• Collision Detection and Resolution in Three.js

  - by androidmaster

  So at the moment am making a simple game using three.js and three.firstpersonControls.js but with the current Three.js r66, they apparently removed checkWallCollision and then in the r67 firstpersonControls removed support for that collision. SO my question is how would i go about checking collision in 3D using three.js and then resolution to that collision. (Pushing player out of the block) Note I used a 2D array to generate the world so it's only cubes that I have to check collision with.... if this is a bad question or am lacking something please tell me before you -rep me, am just not sure how to do this and google doesn't want to help

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• Learning Erlang vs learning node.js

  - by Noli

  I see a lot of crap online about how Erlang kicks node.js' ass in just about every conceivable category. So I'd like to learn Erlang, and give it a shot, but here's the problem. I'm finding that I have a much harder time picking up Erlang than I did picking up node.js. With node.js, I could pick a relatively complex project, and in a day I had something working. With Erlang, I'm running into barriers, and not going nearly as quickly. So.. for those with more experience, is Erlang complicated to learn, or am I just missing something? Node.js might not be perfect, but I seem to be able to get things done with it.

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