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  • row number over text column sort

    - by Marty Trenouth
    I'm having problems with dynamic sorting using ROW Number in SQL Server. I have it working but it's throwing errors on non numeric fields. What do I need to change to get sorts with Alpha Working??? ID Description 5 Test 6 Desert 3 A evil Ive got a Sql Prodcedure CREATE PROCEDURE [CRUDS].[MyTable_Search] -- Add the parameters for the stored procedure here -- Full Parameter List @ID int = NULL, @Description nvarchar(256) = NULL, @StartIndex int = 0, @Count int = null, @Order varchar(128) = 'ID asc' AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; -- Insert statements for procedure here Select * from ( Select ROW_NUMBER() OVER (Order By case when @Order = 'ID asc' then [TableName].ID when @Order = 'Description asc' then [TableName].Description end asc, case when @Order = 'ID desc' then [TableName].ID when @Order = 'Description desc' then [TableName].Description end desc ) as row, [TableName].* from [TableName] where (@ID IS NULL OR [TableName].ID = @ID) AND (@Description IS NULL OR [TableName].Description = @Description) ) as a where row > @StartIndex and (@Count is null or row <= @StartIndex + @Count) order by case when @Order = 'ID asc' then a.ID when @Order = 'Description asc' then a.Description end asc, case when @Order = 'ID desc' then a.ID when @Order = 'Description desc' then a.Description end desc END

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  • Practical non-image based CAPTCHA approaches?

    - by Jeff Atwood
    It looks like we'll be adding CAPTCHA support to Stack Overflow. This is necessary to prevent bots, spammers, and other malicious scripted activity. We only want human beings to post or edit things here! We'll be using a JavaScript (jQuery) CAPTCHA as a first line of defense: http://docs.jquery.com/Tutorials:Safer_Contact_Forms_Without_CAPTCHAs The advantage of this approach is that, for most people, the CAPTCHA won't ever be visible! However, for people with JavaScript disabled, we still need a fallback and this is where it gets tricky. I have written a traditional CAPTCHA control for ASP.NET which we can re-use. However, I'd prefer to go with something textual to avoid the overhead of creating all these images on the server with each request. I've seen things like.. ASCII text captcha: \/\/(_)\/\/ math puzzles: what is 7 minus 3 times 2? trivia questions: what tastes better, a toad or a popsicle? Maybe I'm just tilting at windmills here, but I'd like to have a less resource intensive, non-image based <noscript> compatible CAPTCHA if possible. Ideas?

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  • jQuery tokeninput plugin + passing id to another tokeninput url

    - by Elson Solano
    I am using a jquery plugin called jQuery Tokeninput http://loopj.com/jquery-tokeninput/ and I am having a logic issue. var country_id = ""; jQuery("#demo-input-prevent-duplicates").tokenInput(host+"/forms/campaign_location.php?action=country", { theme: "facebook", hintText: "Enter a Country...", placeholder: "Enter a Country...", preventDuplicates: true, onAdd: function(item) { country_id = item.id; }, onDelete: function(){ hideElements(); }, tokenDelimiter: "|", }); My question here is how would I pass the value of country_id to the parameter of the below code. I'm not seeing how to do this one on the jquery tokeninput documentation. jQuery("#targ_state").tokenInput(host+"/forms/campaign_location.php?action=stateorprovince&cid="+country_id, { theme: "facebook", preventDuplicates: true, hintText: "Enter a State or Province...", placeholder: "Enter a State or Province..." }); If you'll look on this part of the code, I am passing the country_id that was generated above on the "onAdd". This doesn't work though. jQuery("#targ_state").tokenInput(host+"/forms/campaign_location.php?action=stateorprovince&cid="+country_id .... How would I do that one? Your help would be greatly appreciated and of course, rewarded! Thanks! :-)

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  • webpage scrollbar scrolls to top when typing in input box, how to fix?

    - by derei
    I have a HTML table that is scrollable and I'm forcing the scroll bar at the bottom. But every time I type something in a input box situated inside <thead> it scrolls back to top. I have no idea how to stop it to do that... I'm sorry for not explaining it better, if anybody wants to help, I could provide a link. I cannot place it public because is a private project. Thanks, let me know. EDIT -added jsfiddle example (below is the link) click here for jsfiddle example EDIT2 the issue seem to be present only in Chrome, but that it's more than enough (the app is intended to be used in chrome) EDIT3 I found a similar issue here: on webkit browsers typing into edit box causes scrolling , so the problem seem explained: the parent element gets focus on the side where the input-box is. I verified this on a mockup-template and it acts accordingly. *The question is:*how to prevent this to happen? I am forced by situation to have the input-box as child for the scrollable div, but I don't want that scroll to move (somehow to not give focus to the parent element, when I type in the input-box). Any idea?

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  • iPhone Custom CA certificate for an application which uses NSURLConnection?

    - by jr
    I have an application which is communicating with many different sites and each site has its own SSL certificate signed by our own internal CA. Doing this prevents us the need from purchasing SSL certificates for each site (hundreds or thousands) and is more secure then using a wildcard certificate with a shared key on each of those sites. So, basically using a CA certificate is the only way. Right now, I have a mobileprovision file which will install the CA certificate as a profile on the phone. When our iPhone application launches if it gets an SSL Certificate error it redirects to a this mobile provision file via Safari and the user will be prompted to install the CA. The problem is that I am concerned that the Apple AppStore might deny my app for doing this (Just some feedback from other developers at this point), and I wanted to research other ways to accomplish this. Basically what I need to accomplish is allow an SSL connection which will verify against a custom CA certificate which will be embedded in my application. This will make the CA certificate active for only the calls I make. I am using the standard NSURLConnection methods in order to communicate with the service. Is this possible? Can someone show me how to load the CA (what form PEM?) and add it to the list of trusted CA certificates for my application? If that is not possible what other options do I have? Just trusting all certificates isn't really any option, we want to prevent man in the middle attacks and only trust our CA issued certificates. Thanks!

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  • NSApp Sheets question in cocoa

    - by califguy
    Hi, Here's what I am trying to do. I need to prompt the user for a password prompt and until he enters the password and hits, say the Enter button on the sheet, I want to prevent the code being parsed in the background. Here's the code to run the sheet and when the user enters the password and hits Enter, endSpeedSheet is run. I am calling all of this from my Main() function. What I am noticing is that the when the main function runs, the sheet shows up, the user is prompted for a password. But in the background, I already see " Code gets here" has been run. This means the code has already run in the background. What I need is the code to wait at the password prompt and then use this password after the Sheet has been dismissed. Any idea's on what I am missing here ? - (IBAction) showSpeedSheet:(id)sender { [NSApp beginSheet:speedSheet modalForWindow:(NSWindow *)window modalDelegate:nil didEndSelector:nil contextInfo:nil]; } -(IBAction)endSpeedSheet:(id)sender { joinPassword = [joinPasswordLabel stringValue]; [NSApp endSheet:speedSheet]; [speedSheet orderOut:sender]; } -(IBAction)main:(id)sender { [self showSpeedSheet:(id)sender]; // More Code here NSLog(@" Code gets here"); }

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  • Is this a safe way to release resources in Java?

    - by palto
    Usually when code needs some resource that needs to be released I see it done like this: InputStream in = null; try{ in = new FileInputStream("myfile.txt"); doSomethingWithStream(in); }finally{ if(in != null){ in.close(); } } What I don't like is that you have to initialize the variable to null and after that set it to another value and in the finally block check if the resource was initialized by checking if it is null. If it is not null, it needs to be released. I know I'm nitpicking, but I feel like this could be done cleaner. What I would like to do is this: InputStream in = new FileInputStream("myfile.txt"); try{ doSomethingWithStream(in); }finally{ in.close(); } To my eyes this looks almost as safe as the previous one. If resource initialization fails and it throws an exception, there's nothing to be done(since I didn't get the resource) so it doesn't have to be inside the try block. The only thing I'm worried is if there is some way(I'm not Java certified) that an exception or error can be thrown between operations? Even simpler example: Inputstream in = new FileInputStream("myfile.txt"); in.close(); Is there any way the stream would be left open that a try-finally block would prevent?

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  • how to add an ajax jQuery code, that return a row from php file [DB] and then change the value of input text?

    - by Nisreen KH
    //this is a code in php which is fetch a record from database <?php include("dbconn.inc"); $data=mysql_query("SELECT `subtitle`, `mian-title`, `page_num`, `note_path`, `flash_path` FROM `main-page` WHERE `page_num` =".$r." LIMIT 1"); echo $data; if (mysql_num_rows($data) == 0) { echo "No rows found, nothing to print so am exiting"; exit; } while ($row = mysql_fetch_assoc($data)) { echo $row['page_num']; } include("close.php"); ?> //and this is a code in html <form method="post" action="data.php"> <input name="Button1" type="submit" value="&lt;&lt;" /> <input name="test" style="width: 31px; height: 23px" type="text" /> // this is a value of page_num in DB. <input name="Button2" type="submit" value="&gt;&gt;" > </form> //i want to add an ajax code to retrieve the record from php code, and then change the input values depends on returned data ,and also to prevent refreshing the page always!!

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  • Why does mobile first responsive design tend to not use max-width queries alongside the min-width queries?

    - by Sam
    First off, I understand the basic principles behind mobile first responsive web design, and totally agree with them. But one thing I don't understand: In my experience, not all styles for small screens can be used for the larger version of a website. For example, usually smaller versions tend to have larger clickable areas, hamburger navigation, etc. So I sometimes have to override these specific styles, aside from just progressively enhancing the base styles. So I was wondering: why is max-width rarely mentioned (or used) in the context of mobile-first responsive web design? Because it looks like it could be used to isolate styles for smaller screens that are not useful for larger screens, and would thus prevent unnecessary duplication of code. A quote which mentions min-width as typically mobile-first, but not max-width: Mobile first, from a coding perspective, means that your base style is typically a single-column, fully-fluid layout. You use @media (min-width: whatever) to add a grid-based layout on top of that. from: http://gomakethings.com/mobile-first-and-internet-explorer/ EDIT: So to be more specific: I was wondering if there is a reason to exclude max-width from a mobile-first responsive design (as it seems like it can be useful for writing your css as DRY as possible, as some styles for small screens will not be used for bigger screens).

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  • Phonegap Android application exiting - but not really - when home button is pressed

    - by Lucas T
    I have created an Phonegap 1.5/Android application. My client reports that, when he leaves the app using the Home button, and then relaunches it using the app icon, the app relaunches from the start instead of resuming. However, when he holds the home button, the app appears in the running apps, and when he accesses the app through this menu, the app resumes in the expected way. I thought this could be linked to the app being automatically closed by the OS due to a lack of memory, but if that was the case the app shouldn't appear in the running apps. I could not reproduce the bug on my Sony Ericsson XPERIA with Android 2.3.4, the client has experienced this behaviour on a Motorola Defy and on another phone (i'll add the reference of the other phone and the OS versions as soon as I get them). The initialization process of the app is declared this way : window.addEventListener('load', function(){ document.addEventListener('deviceready', _onDeviceReady, false); }, false); Could this be fixed by attaching the processes to other events (although I doubt it, the app really seems to be relaunched from the start) ? Is there a declaration to make in the Android Manifest to prevent this behavior ? Is that a known bug in some Android phones/versions ?

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  • validation controls are not validating on enabling on client side using java script, plz guide

    - by haansi
    Hi, As per requirement I disabled all validation controls in page on PageLoad event in server side. On clicking submit button I want to activate them and validate the page and if the page is ok submit other wise not. I am able to enable all validaters but one thing that I am unable to understand is that they do not validate the page. I set alerts and check they are being enabled but they do not validate the page and let the page submit. I am sorry I couldn't get where I am wrong, may be there need to call some validation method as well or I should prevent default behavior of button. please guide me. Below is my script: <script type="text/javascript"> function NextClicked() { var _ddlStatus = document.getElementById("<%=ddlEmpStatus.ClientID%>"); var _selectedIndex = _ddlStatus.selectedIndex; if (_selectedIndex == 0) { alert("Nothing selected"); }<br/> else<br/> if (_selectedIndex == 1) { for (i = 0; i < Page_Validators.length; i++) { Page_Validators[i].Enabled = true; } } } </script> thanks in anticipation.

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  • What's so bad about building XML with string concatenation?

    - by wsanville
    In the thread What’s your favorite “programmer ignorance” pet peeve?, the following answer appears, with a large amount of upvotes: Programmers who build XML using string concatenation. My question is, why is building XML via string concatenation (such as a StringBuilder in C#) bad? I've done this several times in the past, as it's sometimes the quickest way for me to get from point A to point B when to comes to the data structures/objects I'm working with. So far, I have come up with a few reasons why this isn't the greatest approach, but is there something I'm overlooking? Why should this be avoided? Probably the biggest reason I can think of is you need to escape your strings manually, and most programmers will forget this. It will work great for them when they test it, but then "randomly" their apps will fail when someone throws an & symbol in their input somewhere. Ok, I'll buy this, but it's really easy to prevent the problem (SecurityElement.Escape to name one). When I do this, I usually omit the XML declaration (i.e. <?xml version="1.0"?>). Is this harmful? Performance penalties? If you stick with proper string concatenation (i.e. StringBuilder), is this anything to be concerned about? Presumably, a class like XmlWriter will also need to do a bit of string manipulation... There are more elegant ways of generating XML, such as using XmlSerializer to automatically serialize/deserialize your classes. Ok sure, I agree. C# has a ton of useful classes for this, but sometimes I don't want to make a class for something really quick, like writing out a log file or something. Is this just me being lazy? If I am doing something "real" this is my preferred approach for dealing w/ XML.

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  • Image creation performance / image caching

    - by Kilnr
    Hello, I'm writing an application that has a scrollable image (used to display a map). The map background consists of several tiles (premade from a big JPG file), that I draw on a Graphics object. I also use a cache (Hashtable), to prevent from having to create every image when I need it. I don't keep everything in memory, because that would be too much. The problem is that when I'm scrolling through the map, and I need an image that wasn't cached, it takes about 60-80 ms to create it. Depending on screen resolution, tile size and scroll direction, this can occur multiple times in one scroll operation (for different tiles). In my case, it often happens that this needs to be done 4 times, which introduces a delay of more than 300 ms, which is extremely noticeable. The easiest thing for me would be that there's some way to speed up the creation of Images, but I guess that's just wishful thinking... Besides that, I suppose the most obvious thing to do is to load the tiles predictively (e.g. when scrolling to the right, precache the tiles to the right), but then I'm faced with the rather difficult task of thinking up a halfway decent algorithm for this. My actual question then is: how can I best do this predictive loading? Maybe I could offload the creation of images to a separate thread? Other things to consider? Thanks in advance.

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  • What's an effective way to move data from one open browser tab to another?

    - by slk
    I am looking for a quick way to grab some data off of one Web page and throw it into another. I don't have access to the query string in the URL of the second page, so passing the data that way is not an option. Right now, I am using a Greasemonkey user script in tandem with a JS bookmarklet trigger: javascript:doIt(); // ==UserScript== // @include public_site // @include internal_site // ==/UserScript== if (document.location.host.match(internal_site)) { var datum1 = GM_getValue("d1"); var datum2 = GM_getValue("d2"); } unsafeWindow.doIt = function() { if(document.location.host.match(public_site)) { var d1 = innerHTML of page element 1; var d2 = innerHTML of page element 2; //Next two lines use setTimeout to bypass GM_setValue restriction window.setTimeout(function() {GM_setValue("d1", d1);}, 0); window.setTimeout(function() {GM_setValue("d2", d2);}, 0); } else if(document.location.host.match(internal_site)) { document.getElementById("field1").value = datum1; document.getElementById("field2").value = datum2; } } While I am open to another method, I would prefer to stay with this basic model if possible, as this is just a small fraction of the code in doIt() which is used on several other pages, mostly to automate date-based form fills; people really like their "magic button." The above code works, but there's an interruption to the workflow: In order for the user to know which page on the public site to grab data from, the internal page has to be opened first. Then, once the GM cookie is set from the public page, the internal page has to be reloaded to get the proper information into the internal page variables. I'm wondering if there's any way to GM_getValue() at bookmarklet-clicktime to prevent the need for a refresh. Thanks!

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  • Check a list of packages to install with apt-get

    - by Joel
    I am writing a post-install script for Ubuntu in Perl (same script as seen here). One of the steps is to install a list of packages. The problem is that if apt-get install fails in some of many different ways for any one of the packages the script dies badly. I would like to prevent that from happening. This happens because of the ways that apt-get install fails for packages that it doesn't like. For example when I try to install a nonsense word (i.e. typed in the wrong package name) $ sudo apt-get install oblihbyvl Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package oblihbyvl but if instead the package name has been obsoleted (installing handbrake from ppa) $ sudo apt-get install handbrake Reading package lists... Done Building dependency tree Reading state information... Done Package handbrake is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source E: Package 'handbrake' has no installation candidate $ apt-cache search handbrake handbrake-cli - versatile DVD ripper and video transcoder - command line handbrake-gtk - versatile DVD ripper and video transcoder - GTK GUI I have tried parsing the results of apt-cache and apt-get -s install to try to catch all possibilities before doing the install, but I seem to keep finding new ways to allow failures to continue to the actual install system command. My question is, is there some facility either in Perl (e.g. a module, though I would like to avoid installing modules if possible as this is supposed to be the first thing run after a new install of Ubuntu) or apt-* or dpkg that would let me be sure that the packages are all available to be installed before installing and if not fail gracefully in some way that lets the user decide what to do?

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  • Pass view to viewmodel with datatemplate

    - by jpsstavares
    I have a ParameterView and ParameterViewModel, and I need the ParameterViewModel to have a reference to the Parameter view (more on that later). In the window I have a list of ParameterViewModels and in the ResourceDictionary I add the DataTemplate: <DataTemplate DataType="{x:Type my:ParameterViewModel}" > <my:ParameterView HorizontalAlignment="Left"/> </DataTemplate> I then bind an ItemsControl.ItemSource to the List of ParameterViewModels The problem is: How can I pass the ParameterView to the ParameterViewModel in this scenario? The reason I need the ParameterView in the ParameterViewModel is the following: I have a TextBox whose Text property is binded to the PropertyModelView.Name property. But I want to display a default string when the Name is empty or Null. I've tried to set the property value to the default string I want when that happens but the TextBox.Text is not set in this scenario. I do something like this: private string _name; public string Name { get { return _name; } set { if (value == null || value.Length == 0) Name = _defaultName; else _name = value; } } I've also tried to specifically set the TextBox.Text binding mode to TwoWay without success. I think this is a defense mechanism to prevent an infinite loop from happening but I don't know for sure. Any help on this front would also be highly appreciated. Thanks, José Tavares

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  • Which is the correct design pattern for my PHP application?

    - by user1487141
    I've been struggling to find good way to implement my system which essentially matches the season and episode number of a show from a string, you can see the current working code here: https://github.com/huddy/tvfilename I'm currently rewriting this library and want a nicer way to implement how the the match happens, currently essentially the way it works is: There's a folder with classes in it (called handlers), every handler is a class that implements an interface to ensure a method called match(); exists, this match method uses the regex stored in a property of that handler class (of which there are many) to try and match a season and episode. The class loads all of these handlers by instantiating each one into a array stored in a property, when I want to try and match some strings the method iterates over these objects calling match(); and the first one that returns true is then returned in a result set with the season and episode it matched. I don't really like this way of doing it, it's kind of hacky to me, and I'm hoping a design pattern can help, my ultimate goal is to do this using best practices and I wondered which one I should use? The other problems that exist are: More than one handler could match a string, so they have to be in an order to prevent the more greedy ones matching first, not sure if this is solvable as some of the regex patterns have to be greedy, but possibly a score system, something that shows a percentage of how likely the match is correct, i'd have no idea how to actually implement this though. I'm not if instantiating all those handlers is a good way of doing it, speed is important, but using best practices and sticking to design patterns to create good, extensible and maintainable code is my ultimate priority. It's worth noting the handler classes sometimes do other things than just regex matching, they sometimes prep the string to be matched by removing common words etc. Cheers for any help Billy

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  • Client validate in MVC 2

    - by khoailang
    Hello, I'm very new in MVC 2, Let say, I have a page with 1 text box and 2 input typed submit, "back" and "next". I'm using client validation like this: "" type="text/javascript"/" " type="text/javascript"/ " type="text/javascript"/ . . . <% Html.EnableClientValidation(); % . . . . . . and validation rule used for that text box is [StringLength(100, ErrorMessage="This field should be no longer than 100")] My wish is that validation rules will be applied only when I click on Next button. And when I click on Back button, no validation error message will be displayed and form will be posted to server. Is it possible to do that? could you please tell me how? My problem now is that when I click Back, validation rules are applied and prevent me from posting back to server.

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  • Entity Framework 4 Entity with EntityState of Unchanged firing update

    - by Andy
    I am using EF 4, mapping all CUD operations for my entities using sprocs. I have two tables, ADDRESS and PERSON. A PERSON can have multiple ADDRESS associated with them. Here is the code I am running: Person person = (from p in context.People where p.PersonUID == 1 select p).FirstOrDefault(); Address address = (from a in context.Addresses where a.AddressUID == 51 select a).FirstOrDefault(); address.AddressLn2 = "Test"; context.SaveChanges(); The Address being updated is associated with the Person I am retrieveing - although they are not explicitly linked in any way in the code. When the context.SaveChanges() executes not only does the Update sproc for my Address entity get fired (like you would expect), but so does the Update sproc for the Person entity - even though you can see there was no change made to the Person entity. When I check the EntityState of both objects before the context.SaveChanges() call I see that my Address entity has an EntityState of "Modified" and my Person enity has an EntityState of "Unchanged". Why is the Update sproc being called for the Person entity? Is there a setting of some sort that I can set to prevent this from happening?

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  • Locking database edit by key name

    - by Will Glass
    I need to prevent simultaneous edits to a database field. Users are executing a push operation on a structured data field, so I want to sequence the operations, not simply ignore one edit and take the second. Essentially I want to do synchronized(key name) { push value onto the database field } and set up the synchronized item so that only one operation on "key name" will occur at a time. (note: I'm simplifying, it's not always a simple push). A crude way to do this would be a global synchronization, but that bottlenecks the entire app. All I need to do is sequence two simultaneous writes with the same key, which is rare but annoying occurrence. This is a web-based java app, written with Spring (and using JPA/MySQL). The operation is triggered by a user web service call. (the root cause is when a user sends two simultaneous http requests with the same key). I've glanced through the Doug Lea/Josh Bloch/et al Concurrency in Action, but don't see an obvious solution. Still, this seems simple enough I feel there must be an elegant way to do this.

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  • Are background threads a bad idea? Why?

    - by Matt Grande
    So I've been told what I'm doing here is wrong, but I'm not sure why. I have a webpage that imports a CSV file with document numbers to perform an expensive operation on. I've put the expensive operation into a background thread to prevent it from blocking the application. Here's what I have in a nutshell. protected void ButtonUpload_Click(object sender, EventArgs e) { if (FileUploadCSV.HasFile) { string fileText; using (var sr = new StreamReader(FileUploadCSV.FileContent)) { fileText = sr.ReadToEnd(); } var documentNumbers = fileText.Split(new[] {',', '\n', '\r'}, StringSplitOptions.RemoveEmptyEntries); ThreadStart threadStart = () => AnotherClass.ExpensiveOperation(documentNumbers); var thread = new Thread(threadStart) {IsBackground = true}; thread.Start(); } } (obviously with some error checking & messages for users thrown in) So my three-fold question is: a) Is this a bad idea? b) Why is this a bad idea? c) What would you do instead?

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  • how can i make sure only a single record is inserted when multiple apache threads are trying to acce

    - by Ed Gl
    I have a web service (xmlrpc service to be exact) that handles among other things writing data into the database. Here's the scenario: I often receive requests to either update or insert a record. What I would do is this: If the record already exists, append to the record, If not, create a new record The issue is that there are certain times I would get a 'burst' of requests, which spawns several apache threads to handle the request. These 'bursts' would come within less than milliseconds of each other. I now have several threads performing #1 and #2. Often two threads would would 'pass' number #1 and actually create two duplicate records (except for the primary key). I'd like to use some locking mechanism to prevent other threads from accessing the table while the other thread finishes its work. I'm just afraid of using it because if something happens I don't want to leave the table locked. Is there a solid way of handling this? I'm open to using locks if I can do it properly. Thanks,

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  • Checking if a function has C-linkage at compile-time

    - by scjohnno
    Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Thanks.

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  • what is the relation between SIGTSTP and SIGCHLD

    - by Rawhi
    I have tow handlers for each one of them (SIGTSTP, SIGCHLD), the thing is that when I pause a process using SIGTSTP the handler function of SIGCHLD run too. what should I do to prevent this . void ExeExternal(char *args[MAX_ARG], char* cmdString, LIST_ELEMENT** pList, int *Susp_Bg_Pid, int *susp) { int pID, status, w; switch (pID = fork()) { case -1: perror("smash error: >"); break; case 0: // Child Process setpgrp(); execv(args[0], args); execvp(args[0], args); perror("error"); exit(EXIT_FAILURE); break; default: if (cmdString[strlen(cmdString) - 1] != '&') { *Susp_Bg_Pid = pID; *susp = 1; while(*susp); } else { InsertElem(pList, args[0], getpid(), pID, 0); } break; } } signal handlers : void signalHandler(int signal) { int pid, cstatus; if (signal == SIGCHLD) { susp = 0; pid = waitpid(-1, &cstatus, WNOHANG); printf("[[child %d terminated]]\n", pid); DelPID(&JobsList, pid); } } void ctrlZsignal(int signal){ kill(Susp_Bg_Pid, SIGTSTP); susp = 0; printf("\nchild %d suspended\n", Susp_Bg_Pid); } Susp_Bg_Pid used to save the paused process id. susp indicates the state of the "smash" the parent process if it is suspended or not .

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  • How to limit TCP writes to particular size and then block untlil the data is read

    - by ustulation
    {Qt 4.7.0 , VS 2010} I have a Server written in Qt and a 3rd party client executable. Qt based server uses QTcpServer and QTcpSocket facilities (non-blocking). Going through the articles on TCP I understand the following: the original implementation of TCP mentioned the negotiable window size to be a 16-bit value, thus maximum being 65535 bytes. But implementations often used the RFC window-scale-extension that allows the sliding window size to be scalable by bit-shifting to yield a maximum of 1 gigabyte. This is implementation defined. This could have resulted in majorly different window sizes on receiver and sender end as the server uses Qt facilities without hardcoding any window size limit. Client 1st asks for all information it can based on the previous messages from the server before handling the new (accumulating) incoming messages. So at some point Server receives a lot of messages each asking for data of several MB's. This the server processes and puts it into the sender buffer. Client however is unable to handle the messages at the same pace and it seems that client’s receiver buffer is far smaller (65535 bytes maybe) than sender’s transmit window size. The messages thus get accumulated at sender’s end until the sender’s buffer is full too after which the TCP writes on sender would block. This however does not happen as sender buffer is much larger. Hence this manifests as increase in memory consumption on the sender’s end. To prevent this from happening, I used Qt’s socket’s waitForBytesWritten() with timeout set to -1 for infinite waiting period. This as I see from the behaviour blocks the thread writing TCP data until the data has actually been sensed by the receiver’s window (which will happen when earlier messages have been processed by the client at application level). This has caused memory consumption at Server end to be almost negligible. is there a better alternative to this (in Qt) if i want to restrict the memory consumption at server end to say x MB's? Also please point out if any of my understandings is incorrect.

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