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  • NewBie Question, jQuery: How can we implement if...else logic and call function

    - by Rachel
    I am new to jQuery and so don't mind this question if it sounds stupid but here is something that I am trying to do : I have 3 functions like: AddToCart Function which adds item to the shopping cart: //offer_id is the offer which we are trying to add to cart. addToCart: function(offer_id) { this.submit({action: 'add', 'offer_id': offer_id}, {'app_server_url': this.app_server_url}); }, RemoveFromCart which removes data from the cart //target is link clicked and event is the click event. removeFromCart: function(target, event) { this.uniqueElmt('cart_table').find('.sb_item_remove').unbind('click'); var offer_id = $(target).parent().find('.offer_id').html(); this.submit({action: 'remove', 'offer_id': offer_id, 'next_action': this.config.current_action}, {'app_server_url': this.app_server_url}); }, Get the current state of the cart //return string which represents current state of cart. getCartItems: function() { return this.contents; } Now I am trying to do 3 things: if there is no content in cart and addToCart is called than some action, so basically here we need to check the current state of cart and that is obtained by calling getCartItems and if it is Null and than if addToCart is called than we perform some action if there is content in the cart and addToCart is called than some action,so basically here we need to check the current state of cart and that is obtained by calling getCartItems and check if it is Null or not and than if addToCart is called than we perform some action if we had some content in the cart. if there is content in the cart and removeFromCart is called some action, so basically here we need to check the current state of cart and that is obtained by calling getCartItems and if it is not Null and if removeFromCart is called than we perform some action Pseudocode of what I am trying to do: if there is no content in cart and addToCart is called than $(document).track( { 'module' : 'Omniture', 'event' : 'instant', 'args' : { 'linkTrackVars' : 'products,events', 'linkTrackEvents' : 'scAdd,scOpen', 'linkType' : 'o', 'linkName' : 'Cart : First Product Added' // could be blank, but can include event name as added feature 'svalues' : { 'products' : ';OFFERID1[,;OFFERID2]', 'events' : 'scAdd,scOpen', }, } 'defer' : '0' } ); if there is content in the cart and addToCart is called than $(document).track( { 'module' : 'Omniture', 'event' : 'instant', 'args' : { 'linkTrackVars' : 'products,events', 'linkTrackEvents' : 'scAdd', 'linkType' : 'o', 'linkName' : 'Cart : Product Added' // could be blank, but can include event name as added feature 'svalues' : { 'products' : ';OFFERID1[,;OFFERID2]', 'events' : 'scAdd', }, }, 'defer' : '0' } ); if there is content in the cart and removeFromCart is called $(document).track( { 'module' : 'Omniture', 'event' : 'instant', 'args' : { 'linkTrackVars' : 'products,events', 'linkTrackEvents' : 'scRemove', 'linkType' : 'o', 'linkName' : 'Cart : Product Removed' // could be blank, but can include event name as added feature 'svalues' : { 'products' : ';OFFERID1[,;OFFERID2]', 'events' : 'scRemove', }, } 'defer' : '0' } ); My basic concern is that am complete newbie to jQuery and JavaScript and so am not sure how can I implement if...else logic and how can I call a funtion using jQuery/JavaScript.

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  • iPhone: Tracking/Identifying individual touches

    - by FlorianZ
    I have a quick question regarding tracking touches on the iPhone and I seem to not be able to come to a conclusion on this, so any suggestions / ideas are greatly appreciated: I want to be able to track and identify touches on the iphone, ie. basically every touch has a starting position and a current/moved position. Touches are stored in a std::vector and they shall be removed from the container, once they ended. Their position shall be updated once they move, but I still want to keep track of where they initially started (gesture recognition). I am getting the touches from [event allTouches], thing is, the NSSet is unsorted and I seem not to be able to identify the touches that are already stored in the std::vector and refer to the touches in the NSSet (so I know which ones ended and shall be removed, or have been moved, etc.) Here is my code, which works perfectly with only one finger on the touch screen, of course, but with more than one, I do get unpredictable results... - (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event { [self handleTouches:[event allTouches]]; } - (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event { [self handleTouches:[event allTouches]]; } - (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event { [self handleTouches:[event allTouches]]; } - (void) touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event { [self handleTouches:[event allTouches]]; } - (void) handleTouches:(NSSet*)allTouches { for(int i = 0; i < (int)[allTouches count]; ++i) { UITouch* touch = [[allTouches allObjects] objectAtIndex:i]; NSTimeInterval timestamp = [touch timestamp]; CGPoint currentLocation = [touch locationInView:self]; CGPoint previousLocation = [touch previousLocationInView:self]; if([touch phase] == UITouchPhaseBegan) { Finger finger; finger.start.x = currentLocation.x; finger.start.y = currentLocation.y; finger.end = finger.start; finger.hasMoved = false; finger.hasEnded = false; touchScreen->AddFinger(finger); } else if([touch phase] == UITouchPhaseEnded || [touch phase] == UITouchPhaseCancelled) { Finger& finger = touchScreen->GetFingerHandle(i); finger.hasEnded = true; } else if([touch phase] == UITouchPhaseMoved) { Finger& finger = touchScreen->GetFingerHandle(i); finger.end.x = currentLocation.x; finger.end.y = currentLocation.y; finger.hasMoved = true; } } touchScreen->RemoveEnded(); } Thanks!

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  • Django Initial for a ManyToMany Field

    - by gramware
    I have a form that edits an instance of my model. I would like to use the form to pass all the values as hidden with an inital values of username defaulting to the logged in user so that it becomes a subscribe form. The problem is that the normal initial={'field':value} doesn't seem to work for manytomany fields. how do i go about it? my views.py @login_required def event_view(request,eventID): user = UserProfile.objects.get(pk=request.session['_auth_user_id']) event = events.objects.get(eventID = eventID) if request.method == 'POST': form = eventsSusbcribeForm( request.POST,instance=event) if form.is_valid(): form.save() return HttpResponseRedirect('/events/') else: form = eventsSusbcribeForm(instance=event) return render_to_response('event_view.html', {'user':user,'event':event, 'form':form},context_instance = RequestContext( request )) my forms.py class eventsSusbcribeForm(forms.ModelForm): eventposter = forms.ModelChoiceField(queryset=UserProfile.objects.all(), widget=forms.HiddenInput()) details = forms.CharField(widget=forms.Textarea(attrs={'cols':'50', 'rows':'5'}),label='Enter Event Description here') date = forms.DateField(widget=SelectDateWidget()) class Meta: model = events exclude = ('deleted') def __init__(self, *args, **kwargs): super(eventsSusbcribeForm, self).__init__(*args, **kwargs) self.fields['username'].initial = (user.id for user in UserProfile.objects.filter())

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  • How can I set Invitee in Google Calendar through Python?

    - by Dhaval dave
    I am Setting Google Calendar via python command like this def _InsertQuickAddEvent(self, content="Tennis with dddddd on 5/19/2010 4am-5:30am"): """Creates an event with the quick_add property set to true so the content is processed as quick add content instead of as an event description.""" event = gdata.calendar.CalendarEventEntry() who = whois("[email protected]") event.content = atom.Content(text=content) event.quick_add = gdata.calendar.QuickAdd(value='true'); new_event = self.cal_client.InsertEvent(event, '/calendar/feeds/default/private/full') return new_event this code is given by Google API Can any one suggest what to do to add invitee in this? Important links for that http://code.google.com/apis/calendar/data/1.0/developers_guide_python.html

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  • How to impose maxlength on textArea in HTML , Javascript

    - by Rakesh Juyal
    I would like to have some functionality by which if i write <textarea maxlength="50"></textarea> <textarea maxlength="150"></textarea> <textarea maxlength="250"></textarea> it will automatically impose the maxlength on the textArea. If possible please donot provide the solution in JQuery. Note: This can be done if i do something like this: <textarea onkeypress="return imposeMaxLength(event, this, 110);" rows="4" cols="50"> function imposeMaxLength(Event, Object, MaxLen) { return (Object.value.length <= MaxLen)||(Event.keyCode == 8 ||Event.keyCode==46||(Event.keyCode>=35&&Event.keyCode<=40)) } copied from another thread But the point is I don't want to write onKeyPress and onKeyUp every time i declare a textArea.

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  • JavaScript addEvent function

    - by Yalmaz Khalil
    I have an addEvent function: function addEvent(elem, event, func ) { if (typeof (window.event) != 'undefined') elem.attachEvent('on' + event, func); else elem.addEventListener(event, func, false); } <a href="#" id="link">link</a> and I'm trying to add the following to window.onload: addEvent(window, 'load', function (){ // add another event var link= document.getElementById('link'); addEvent(link, 'click', function () {alert('Hi'); }); }); My question is: why does the link event not work?

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  • Routing redirection decision

    - by programming late night
    I have really no idea why I'm asking this as this a really completely irrelevant question for which I should have figured out an answer within milliseconds, yet I'm doing it. So in my project I have a Router class which splits up the request and selects the right page to be loaded. Fine so far. Now I have a page displayed when the user requests a page that doesn't exist, you know, 404. So theoretically, if the user entered mydomain.com/404 (I use mod_rewrite with a requests collector via index.php?req=*) the 404 error would be shown to him, but in fact there was no error - the 404 page would be displayed as a perfectly normal page. So if someone would try out requesting the 404 page via /404, he would be shown the page but he can't tell if the 404 page he requested doesn't exist and he is actually getting a, you guessed it, 404 error or if he actually found some flaw in the system that makes him able to see an error page when there is no error. I don't know how dumb this whole thing here is but I'm sure some of you have in fact ran into this problem already. Short version: If the user enters mydomain.com/404 the 404 page is shown even though there is no 404 error. I know this is a completely irrelevant question, please don't tell me, but I just spontaneously wanted to hear your thoughts on it. Strange eh? Should I redirect direct access to my 404-page to the home page? Should I do nothing? Should I just go to bed and stop asking irrelevant stuff?

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  • In China. Want to set up my own private proxy. Already have website/webhosting. Help please! n00b with respect to coding/programming, go easy on me [closed]

    - by user1725461
    I am in China and have used freegate in the past -- http://en.wikipedia.org/wiki/Freegate Recently I've been having too many problems with that and some other web-based proxies I usually use. I have a website that is hosted in the US which I can access from China. Is there an easy way for me to setup my own secure private proxy? I'm sick of all my internet problems and looking for a new workable solution. Thank you! PS: and I really hope this is the right place for such a question...

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  • Iphone memory leak with malloc

    - by Icky
    Hello. I have memory leak, found by instruments and it is supposed to be in this line of code: indices = malloc( sizeof(indices[0]) * totalQuads * 6); This is actually a code snippet from a tutorial, something which i think is leak-free so to say. Now I reckon, the error is somewhere else, but I do not know, where. These are the last trackbacks: 5 ColorRun -[EAGLView initWithCoder:] /Users/thomaskopinski/programming/colorrun_3.26/Classes/EAGLView.m:98 4 ColorRun -[EAGLView initGame] /Users/thomaskopinski/programming/colorrun_3.26/Classes/EAGLView.m:201 3 ColorRun -[SpriteSheet initWithImageNamed:spriteWidth:spriteHeight:spacing:imageScale:] /Users/thomaskopinski/programming/colorrun_3.26/SpriteSheet.m:68 2 ColorRun -[Image initWithImage:scale:] /Users/thomaskopinski/programming/colorrun_3.26/Image.m:122 1 ColorRun -[Image initImpl] /Users/thomaskopinski/programming/colorrun_3.26/Image.m:158 0 libSystem.B.dylib malloc Does anyone know how to approach this?

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  • What is the benefits and drawbacks of using header files?

    - by vodkhang
    I had some experience on programming languages like Java, C#, Scala as well as some lower level programming language like C, C++, Objective - C. My observation is that low level languages separate out header files and implementation files while other higher level programming language never separate it out. They use some identifiers like public, private, protected to do the jobs of header files. I saw one benefit of using header file (in some book like Code Complete), they talk about that using header files, people can never look at our implementation file and it helps with encapsulation. A drawback is that it creates too many files for me. Sometimes, it looks like verbose. It is just my thought and I don't know if there are any other benefits and drawbacks that people ever see and work with header file This question may not relate directly to programming but I think that if I can understand better about programming to interface, design software.

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  • Is it possible to make JQuery keydown respond faster?

    - by Drew Paul
    I am writing a simple page with JQuery and HTML5 canvas tags where I move a shape on the canvas by pressing 'w' for up, 's' for down, 'a' for left, and 'd' for right. I have it all working, but I would like the shape to start moving at a constant speed upon striking a key. Right now there is some kind of hold period and then the movement starts. How can I get the movement to occur immediately? Here the important part of my code: Your browser does not support the HTML5 canvas tag. start navigating coords should pop up here key should pop up here var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); //keypress movements var xtriggered = 0; var keys = {}; var north = -10; var east = 10; var flipednorth = 0; $(document).ready(function(e){ $("input").keydown(function(){ keys[event.which] = true; if (event.which == 13) { event.preventDefault(); } //press w for north if (event.which == 87) { north++; flipednorth--; } //press s for south if (event.which == 83) { north--; flipednorth++; } //press d for east if (event.which == 68) { east++; } //press a for west if (event.which == 65) { east--; } var msg = 'x: ' + flipednorth*5 + ' y: ' + east*5; ctx.beginPath(); ctx.arc(east*6,flipednorth*6,40,0,2*Math.PI); ctx.stroke(); $('#soul2').html(msg); $('#soul3').html(event.which ); $("input").css("background-color","#FFFFCC"); }); $("input").keyup(function(){ delete keys[event.which]; $("input").css("background-color","#D6D6FF"); }); }); </script> please let me know if I shouldn't be posting code this lengthy.

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  • LINQ to SQL - database relationships won't update after submit

    - by Quantic Programming
    I have a Database with the tables Users and Uploads. The important columns are: Users -> UserID Uploads -> UploadID, UserID The primary key in the relationship is Users -> UserID and the foreign key is Uploads -> UserID. In LINQ to SQL, I do the following operations: Retrieve files var upload = new Upload(); upload.UserID = user.UserID; upload.UploadID = XXX; db.Uploads.InsertOnSubmit(upload) db.SubmitChanges(); If I do that and rerun the application (and the db object is re-built, of course) - if do something like this: foreach(var upload in user.Uploads) I get all the uploads with that user's ID. (like added in the previous example) The problem is, that my application, after adding an upload an submitting changes, doesn't update the user.Uploads collection. i.e - I don't get the newly added uploads. The user object is stored in the Session object. At first, I though that the LINQ to SQL Framework doesn't update the reference of the object, therefore I should simply "reset" the user object from a new SQL request. I mean this: Session["user"] = db.Users.Where(u => u.UserID == user.UserID).SingleOrDefault(); (Where user is the previous user) But it didn't help. Please note: After rerunning the application, user.Uploads does have the new upload! Did anyone experience this type of problem, or is it normal behavior? I am a newbie to this framework. I would gladly take any advice. Thank you!

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  • Flex: Problem with CollectionEvent on ArrayCollection

    - by dasnervtdoch
    Hi there, got a reference to an arrayCollection and add event listener like this: collection.addEventListener(CollectionEvent.COLLECTION_CHANGE, onCollectionChange); that´s fine. Now some other component does have the same reference and is adding items to and removing items from that collection. Each time the handler is called: private function onProjectPersonsChange(event:Event):void { if (event.kind == CollectionEventKind.ADD) { //do something } else if (event.kind == CollectionEventKind.REMOVE) { //do something //here is the problem: event.items.length = 0 } else { trace('CollectionEvent: kind not handled!'); } } Does somebody know why the removed item is not in 'items'? Thanks in advance!

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  • Which is the best and appropriate way to write the code in Winforms ?

    - by Harikrishna
    What is the best way to write the code ? (1) Like directly writing the code in the button_click() event. or (2) Make the function of that code which I write in button_click() event and write this function in one class and then that function I should call in the button_Click() event.Like is it called three-tired approach to write the code ? Like in button_Click() event I write the code to save the records in csv file from datatable.So I should write that code in button_Click() event or I should make one new function and one new class and write that code in that function which is the new class and calling that function in button_Click() event. This is only one example but I am talking about all the code written in my application that which is the appropriate and best way to write the code and what are the benefits ? Note that I write the code in Winforms with c#.

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  • AS3 get closest date to today

    - by fana
    Hi, I have a XML file with a few concert dates. In my flash/AS3 file, I would like to show only the up coming event, relative to current date. Like this: Event 01: 30-05-2010 Event 02: 02-06-2010 Event 03: 05-06-2010 Today is 28-05-2010, so I need to list Event 01. On 01-06-2010 I need to list Event 02. I have the basic AS3 code for listing the XML working, but I'm having trouble filtering the result. Any ideas? Thanks.

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  • Question about custom events

    - by Malfist
    I'm making custom events for C# and sometimes it isn't working. This is how I'm making the event happen: private bool isDoorOpen; public bool IsDoorOpen { get { return isDoorOpen;} private set { isDoorOpen = value; DoorsChangeState(this, null);} } And these are the event declarations: //events public delegate void ChangedEventHandler(Elevator sender, EventArgs e); public event ChangedEventHandler PositionChanged; public event ChangedEventHandler DirectionChanged; public event ChangedEventHandler BreaksChangeState; public event ChangedEventHandler DoorsChangeState; This works as long as there are methods attached to the events, but if there isn't, it throws a null ref exception. What am I doing wrong?

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  • Does a Required Restart for Windows Update log an event? If so what is the source/id?

    - by Beuy
    Hi there, Does anyone happen to know if a required restart in order to apply Windows Updates creates a entry in the event log? If so which log is it under, and what is the source/id? I have a legacy system that needs to an account, constantly logged into console for applications to function as required (Some old PROCOMS modem software for customers without Internet access but a telephone (Dial-up? Separate issue, don't get me started -.-)). When an update is applied to this machine that requires a restart (Server 2003) I would like an e-mail alert to be sent.

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  • OSX Lion - Stuck in Drag mode and mouse click events are not going through. Can I manually generate a mouseup event?

    - by Yuji Tomita
    My mouse is stuck in "drag" mode. This generally happens in Photoshop, but happens dragging files and such as well. Clicking rapidly here and there generally solves the problem. Sometimes though, it won't go away until a restart. Unplugging devices, etc., doesn't do anything. For example, right now, my mouse moves but can not click anything so I am using the keyboard to navigate this site. Is there a way to "reset" however the OS stores mouse states? Can I manually fire off a MouseUp event? It's strange that even when human input devices are unplugged, the files are still in drag state.

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  • GPGPU

    WhatGPU obviously stands for Graphics Processing Unit (the silicon powering the display you are using to read this blog post). The extra GP in front of that stands for General Purpose computing.So, altogether GPGPU refers to computing we can perform on GPU for purposes beyond just drawing on the screen. In effect, we can use a GPGPU a bit like we already use a CPU: to perform some calculation (that doesn’t have to have any visual element to it). The attraction is that a GPGPU can be orders of magnitude faster than a CPU.WhyWhen I was at the SuperComputing conference in Portland last November, GPGPUs were all the rage. A quick online search reveals many articles introducing the GPGPU topic. I'll just share 3 here: pcper (ignoring all pages except the first, it is a good consumer perspective), gizmodo (nice take using mostly layman terms) and vizworld (answering the question on "what's the big deal").The GPGPU programming paradigm (from a high level) is simple: in your CPU program you define functions (aka kernels) that take some input, can perform the costly operation and return the output. The kernels are the things that execute on the GPGPU leveraging its power (and hence execute faster than what they could on the CPU) while the host CPU program waits for the results or asynchronously performs other tasks.However, GPGPUs have different characteristics to CPUs which means they are suitable only for certain classes of problem (i.e. data parallel algorithms) and not for others (e.g. algorithms with branching or recursion or other complex flow control). You also pay a high cost for transferring the input data from the CPU to the GPU (and vice versa the results back to the CPU), so the computation itself has to be long enough to justify the overhead transfer costs. If your problem space fits the criteria then you probably want to check out this technology.HowSo where can you get a graphics card to start playing with all this? At the time of writing, the two main vendors ATI (owned by AMD) and NVIDIA are the obvious players in this industry. You can read about GPGPU on this AMD page and also on this NVIDIA page. NVIDIA's website also has a free chapter on the topic from the "GPU Gems" book: A Toolkit for Computation on GPUs.If you followed the links above, then you've already come across some of the choices of programming models that are available today. Essentially, AMD is offering their ATI Stream technology accessible via a language they call Brook+; NVIDIA offers their CUDA platform which is accessible from CUDA C. Choosing either of those locks you into the GPU vendor and hence your code cannot run on systems with cards from the other vendor (e.g. imagine if your CPU code would run on Intel chips but not AMD chips). Having said that, both vendors plan to support a new emerging standard called OpenCL, which theoretically means your kernels can execute on any GPU that supports it. To learn more about all of these there is a website: gpgpu.org. The caveat about that site is that (currently) it completely ignores the Microsoft approach, which I touch on next.On Windows, there is already a cross-GPU-vendor way of programming GPUs and that is the DirectX API. Specifically, on Windows Vista and Windows 7, the DirectX 11 API offers a dedicated subset of the API for GPGPU programming: DirectCompute. You use this API on the CPU side, to set up and execute the kernels that run on the GPU. The kernels are written in a language called HLSL (High Level Shader Language). You can use DirectCompute with HLSL to write a "compute shader", which is the term DirectX uses for what I've been referring to in this post as a "kernel". For a comprehensive collection of links about this (including tutorials, videos and samples) please see my blog post: DirectCompute.Note that there are many efforts to build even higher level languages on top of DirectX that aim to expose GPGPU programming to a wider audience by making it as easy as today's mainstream programming models. I'll mention here just two of those efforts: Accelerator from MSR and Brahma by Ananth. Comments about this post welcome at the original blog.

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  • The long road to bug-free software

    - by Tony Davis
    The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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  • The long road to bug-free software

    - by Tony Davis
    The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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  • A more elegant way to start a multithread alarm in Rebol VID ? (What's the equivalent of load event?

    - by Rebol Tutorial
    I want to trigger an alarm when the GUI starts. I can't see what's the equivalent of load event of other language in Rebol VID, so I put it in the periodic handler which is quite circumvoluted. So how to do this more cleanly ? alarm-data: none set-alarm: func [ "Set alarm for future time." seconds "Seconds from now to ring alarm." message [string! unset!] "Message to print on alarm." ] [ alarm-data: reduce [now/time + seconds message] ] ring: func [ "Action for when alarm comes due." message [string! unset!] ] [ set-face monitor either message [message]["RIIIING!"] ; Your sound playing can also go here (my computer doesn't have speakers). ] periodic: func [ "Called every second, checks alarms." fact action event ] [ either alarm-data [ ; Update alarm countdown. set-face monitor rejoin [ "Alarm will ring in " to integer! alarm-data/1 - now/time " seconds." ] ; Check alarm. if now/time > alarm-data/1 [ ring alarm-data/2 ;alarm-data: none ; Reset once fired. ] ][ either value? 'message [ set-alarm seconds message ][ set-alarm seconds "Alarm triggered!" ] ] ] alarm: func[seconds message [string! unset!]][ system/words/seconds: seconds if value? 'message [ system/words/message: message ] view layout [ monitor: text 256 "" rate 1 feel [engage: :periodic] button 256 "re/start countdown" [ either value? 'message [ set-alarm seconds message ][ set-alarm seconds "Alarm triggered!" ] set-face monitor "Alarm set." ] ] ]

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  • C# .Net 3.5 Asynchronous Socket Server Performance Problem

    - by iBrAaAa
    I'm developing an Asynchronous Game Server using .Net Socket Asynchronous Model( BeginAccept/EndAccept...etc.) The problem I'm facing is described like that: When I have only one client connected, the server response time is very fast but once a second client connects, the server response time increases too much. I've measured the time from a client sends a message to the server until it gets the reply in both cases. I found that the average time in case of one client is about 17ms and in case of 2 clients about 280ms!!! What I really see is that: When 2 clients are connected and only one of them is moving(i.e. requesting service from the server) it is equivalently equal to the case when only one client is connected(i.e. fast response). However, when the 2 clients move at the same time(i.e. requests service from the server at the same time) their motion becomes very slow (as if the server replies each one of them in order i.e. not simultaneously). Basically, what I am doing is that: When a client requests a permission for motion from the server and the server grants him the request, the server then broadcasts the new position of the client to all the players. So if two clients are moving in the same time, the server is eventually trying to broadcast to both clients the new position of each of them at the same time. EX: Client1 asks to go to position (2,2) Client2 asks to go to position (5,5) Server sends to each of Client1 & Client2 the same two messages: message1: "Client1 at (2,2)" message2: "Client2 at (5,5)" I believe that the problem comes from the fact that Socket class is thread safe according MSDN documentation http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.aspx. (NOT SURE THAT IT IS THE PROBLEM) Below is the code for the server: /// /// This class is responsible for handling packet receiving and sending /// public class NetworkManager { /// /// An integer to hold the server port number to be used for the connections. Its default value is 5000. /// private readonly int port = 5000; /// /// hashtable contain all the clients connected to the server. /// key: player Id /// value: socket /// private readonly Hashtable connectedClients = new Hashtable(); /// /// An event to hold the thread to wait for a new client /// private readonly ManualResetEvent resetEvent = new ManualResetEvent(false); /// /// keeps track of the number of the connected clients /// private int clientCount; /// /// The socket of the server at which the clients connect /// private readonly Socket mainSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); /// /// The socket exception that informs that a client is disconnected /// private const int ClientDisconnectedErrorCode = 10054; /// /// The only instance of this class. /// private static readonly NetworkManager networkManagerInstance = new NetworkManager(); /// /// A delegate for the new client connected event. /// /// the sender object /// the event args public delegate void NewClientConnected(Object sender, SystemEventArgs e); /// /// A delegate for the position update message reception. /// /// the sender object /// the event args public delegate void PositionUpdateMessageRecieved(Object sender, PositionUpdateEventArgs e); /// /// The event which fires when a client sends a position message /// public PositionUpdateMessageRecieved PositionUpdateMessageEvent { get; set; } /// /// keeps track of the number of the connected clients /// public int ClientCount { get { return clientCount; } } /// /// A getter for this class instance. /// /// only instance. public static NetworkManager NetworkManagerInstance { get { return networkManagerInstance; } } private NetworkManager() {} /// Starts the game server and holds this thread alive /// public void StartServer() { //Bind the mainSocket to the server IP address and port mainSocket.Bind(new IPEndPoint(IPAddress.Any, port)); //The server starts to listen on the binded socket with max connection queue //1024 mainSocket.Listen(1024); //Start accepting clients asynchronously mainSocket.BeginAccept(OnClientConnected, null); //Wait until there is a client wants to connect resetEvent.WaitOne(); } /// /// Receives connections of new clients and fire the NewClientConnected event /// private void OnClientConnected(IAsyncResult asyncResult) { Interlocked.Increment(ref clientCount); ClientInfo newClient = new ClientInfo { WorkerSocket = mainSocket.EndAccept(asyncResult), PlayerId = clientCount }; //Add the new client to the hashtable and increment the number of clients connectedClients.Add(newClient.PlayerId, newClient); //fire the new client event informing that a new client is connected to the server if (NewClientEvent != null) { NewClientEvent(this, System.EventArgs.Empty); } newClient.WorkerSocket.BeginReceive(newClient.Buffer, 0, BasePacket.GetMaxPacketSize(), SocketFlags.None, new AsyncCallback(WaitForData), newClient); //Start accepting clients asynchronously again mainSocket.BeginAccept(OnClientConnected, null); } /// Waits for the upcoming messages from different clients and fires the proper event according to the packet type. /// /// private void WaitForData(IAsyncResult asyncResult) { ClientInfo sendingClient = null; try { //Take the client information from the asynchronous result resulting from the BeginReceive sendingClient = asyncResult.AsyncState as ClientInfo; // If client is disconnected, then throw a socket exception // with the correct error code. if (!IsConnected(sendingClient.WorkerSocket)) { throw new SocketException(ClientDisconnectedErrorCode); } //End the pending receive request sendingClient.WorkerSocket.EndReceive(asyncResult); //Fire the appropriate event FireMessageTypeEvent(sendingClient.ConvertBytesToPacket() as BasePacket); // Begin receiving data from this client sendingClient.WorkerSocket.BeginReceive(sendingClient.Buffer, 0, BasePacket.GetMaxPacketSize(), SocketFlags.None, new AsyncCallback(WaitForData), sendingClient); } catch (SocketException e) { if (e.ErrorCode == ClientDisconnectedErrorCode) { // Close the socket. if (sendingClient.WorkerSocket != null) { sendingClient.WorkerSocket.Close(); sendingClient.WorkerSocket = null; } // Remove it from the hash table. connectedClients.Remove(sendingClient.PlayerId); if (ClientDisconnectedEvent != null) { ClientDisconnectedEvent(this, new ClientDisconnectedEventArgs(sendingClient.PlayerId)); } } } catch (Exception e) { // Begin receiving data from this client sendingClient.WorkerSocket.BeginReceive(sendingClient.Buffer, 0, BasePacket.GetMaxPacketSize(), SocketFlags.None, new AsyncCallback(WaitForData), sendingClient); } } /// /// Broadcasts the input message to all the connected clients /// /// public void BroadcastMessage(BasePacket message) { byte[] bytes = message.ConvertToBytes(); foreach (ClientInfo client in connectedClients.Values) { client.WorkerSocket.BeginSend(bytes, 0, bytes.Length, SocketFlags.None, SendAsync, client); } } /// /// Sends the input message to the client specified by his ID. /// /// /// The message to be sent. /// The id of the client to receive the message. public void SendToClient(BasePacket message, int id) { byte[] bytes = message.ConvertToBytes(); (connectedClients[id] as ClientInfo).WorkerSocket.BeginSend(bytes, 0, bytes.Length, SocketFlags.None, SendAsync, connectedClients[id]); } private void SendAsync(IAsyncResult asyncResult) { ClientInfo currentClient = (ClientInfo)asyncResult.AsyncState; currentClient.WorkerSocket.EndSend(asyncResult); } /// Fires the event depending on the type of received packet /// /// The received packet. void FireMessageTypeEvent(BasePacket packet) { switch (packet.MessageType) { case MessageType.PositionUpdateMessage: if (PositionUpdateMessageEvent != null) { PositionUpdateMessageEvent(this, new PositionUpdateEventArgs(packet as PositionUpdatePacket)); } break; } } } The events fired are handled in a different class, here are the event handling code for the PositionUpdateMessage (Other handlers are irrelevant): private readonly Hashtable onlinePlayers = new Hashtable(); /// /// Constructor that creates a new instance of the GameController class. /// private GameController() { //Start the server server = new Thread(networkManager.StartServer); server.Start(); //Create an event handler for the NewClientEvent of networkManager networkManager.PositionUpdateMessageEvent += OnPositionUpdateMessageReceived; } /// /// this event handler is called when a client asks for movement. /// private void OnPositionUpdateMessageReceived(object sender, PositionUpdateEventArgs e) { Point currentLocation = ((PlayerData)onlinePlayers[e.PositionUpdatePacket.PlayerId]).Position; Point locationRequested = e.PositionUpdatePacket.Position; ((PlayerData)onlinePlayers[e.PositionUpdatePacket.PlayerId]).Position = locationRequested; // Broadcast the new position networkManager.BroadcastMessage(new PositionUpdatePacket { Position = locationRequested, PlayerId = e.PositionUpdatePacket.PlayerId }); }

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