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  • open/save file in smartGWT

    - by Karthikeyan
    Hi All, I have implemented RPCService, RPCServiceAsync & RPCServieImpl. On clicking a button a service in server side will be called and it will fetch data from DB and file is created. Once the file is created, then i need to open that file in client side and need to prompt a dialog box with open/save options. how can i implement this opening a file part. pls suggest a way to implement t.. Reply pls.. thanks in advance....

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  • How to organize a large number of objects

    - by shane
    We have a large number of documents and metadata (xml files) associated with these documents. What is the best way to organize them? Currently we put them into a series of nested folders: /repository/category/date(when they were loaded into our db)/document_number.pdf and .xml We use the path as a unique identifier for the document in our system. This is more versatile than putting them all in a single flat folder. also it is independent from our database/application, so we can reload them in case of failure. Yet, it introduces some limitations. for example we can't move the files once they've been placed in this structure, also it takes work to put them this way. What is the best practice? How websites such as Scribd deal with this problem?

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  • Is it possible to hide the tabbar when a button is pressed to allow a full screen view of the conten

    - by Jonah
    I have a UITabBar in the detail view of my navigation based application. I am storing text and images in a tableview and would like the user to be able to tap on a cell to hide the navigation controller and the tabbar for full screen viewing of the content. I found this code for hiding the top bars, but it does not seem as easy to hide the tabbar. [[UIApplication sharedApplication] setStatusBarHidden:YES animated:YES]; [self.navigationController setNavigationBarHidden:YES animated:YES]; Does anyone know how to do this? This code does not work to hide the tabBar once the view is already loaded. yourTabViewController.hidesBottomBarWhenPushed = YES;

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  • File Watcher Task

    The task will detect changes to existing files as well as new files, both actions will cause the file to be found when available. A file is available when the task can open it exclusively. This is important for files that take a long time to be written, such as large files, or those that are just written slowly or delivered via a slow network link. It can also be set to look for existing files first (1.2.4.55). The full path of the found file is returned in up to three ways: The ExecValueVariable of the task. This can be set to any String variable. The OutputVariableName when specified. This can be set to any String variable. The FullPath variable within OnFileFoundEvent. This is a File Watcher Task specific event.   Advanced warning of a file having been detected, but not yet available is returned through the OnFileWatcherEvent. This event does not always coincide with the completion of the task, as completion and the OnFileFoundEvent is delayed until the file is ready for use. This event indicates that a file has been detected, and that file will now be monitored until it becomes available. The task will only detect and report on the first file that is created or changes, any subsequent changes will be ignored. Task properties and there usages are documented below: Property Data Type Description Filter String Default filter *.* will watch all files. Standard windows wildcards and patterns can be used to restrict the files monitored. FindExistingFiles Boolean Indicates whether the task should check for any existing files that match the path and filter criteria, before starting the file watcher. IncludeSubdirectories Boolean Indicates whether changes in subdirectories are accepted or ignored. OutputVariableName String The name of the variable into which the full file path found will be written on completion of the task. The variable specified should be of type string. Path String Path to watch for new files or changes to existing files. The path is a directory, not a full filename. For a specific file, enter the file name in the Filter property and the directory in the Path property. PathInputType FileWatcherTask.InputType Three input types are supported for the path: Connection - File connection manager, of type existing folder. Direct Input - Type the path directly into the UI or set on the property as a literal string. Variable – The name of the variable which contains the path. Timeout Integer Time in minutes to wait for a file. If no files are detected within the timeout period the task will fail. The default value of 0 means infinite, and will not expire. TimeoutAsWarning Boolean The default behaviour is to raise an error and fail the task on timeout. This property allows you to suppress the error on timeout, a warning event is raised instead, and the task succeeds. The default value is false.   Installation The task is provided as an MSI file which you can download and run to install it. This simply places the files on disk in the correct locations and also installs the assemblies in the Global Assembly Cache as per Microsoft’s recommendations. You may need to restart the SQL Server Integration Services service, as this caches information about what components are installed, as well as restarting any open instances of Business Intelligence Development Studio (BIDS) / Visual Studio that you may be using to build your SSIS packages. For 2005/2008 Only - Finally you will have to add the task to the Visual Studio toolbox manually. Right-click the toolbox, and select Choose Items.... Select the SSIS Control Flow Items tab, and then check the File Watcher Task in the Choose Toolbox Items window. This process has been described in detail in the related FAQ entry for How do I install a task or transform component? We recommend you follow best practice and apply the current Microsoft SQL Server Service pack to your SQL Server servers and workstations. Downloads The File Watcher Task  is available for SQL Server 2005, SQL Server 2008 (includes R2) and SQL Server 2012. Please choose the version to match your SQL Server version, or you can install multiple versions and use them side by side if you have more than one version of SQL Server installed. File Watcher Task for SQL Server 2005 File Watcher Task for SQL Server 2008 File Watcher Task for SQL Server 2012 Version History SQL Server 2012 Version 3.0.0.16 - SQL Server 2012 release. Includes upgrade support for both 2005 and 2008 packages to 2012. (5 Jun 2012) SQL Server 2008 Version 2.0.0.14 - Fixed user interface bug. A migration problem caused the UI type editors to reference an old SQL 2005 assembly. (17 Nov 2008) Version 2.0.0.7 - SQL Server 2008 release. (20 Oct 2008) SQL Server 2005 Version 1.2.6.100 - Fixed UI bug with TimeoutAsWarning property not saving correctly. Improved expression support in UI. File availability detection changed to use read-only lock, allowing reduced permissions to be used. Corrected installed issue which prevented installation on 64-bit machines with SSIS runtime only components. (18 Mar 2007) Version 1.2.5.73 - Added TimeoutAsWarning property. Gives the ability to suppress the error on timeout, a warning event is raised instead, and the task succeeds. (Task Version 3) (27 Sep 2006) Version 1.2.4.61 - Fixed a bug which could cause a loop condition with an unexpected exception such as incorrect file permissions. (20 Sep 2006) Version 1.2.4.55 - Added FindExistingFiles property. When true the task will check for an existing file before the file watcher itself actually starts. (Task Version 2) (8 Sep 2006) Version 1.2.3.39 - SQL Server 2005 RTM Refresh. SP1 Compatibility Testing. Property type validation improved. (12 Jun 2006) Version 1.2.1.0 - SQL Server 2005 IDW 16 Sept CTP. Futher UI enhancements, including expression indicator. Fixed bug caused by execution within loop Subsequent iterations detected the same file as the first iteration. Added IncludeSubdirectories property. Fixed bug when changes made in subdirectories, and folder change was detected, causing task failure. (Task Version 1) (6 Oct 2005) Version 1.2.0.0 - SQL Server 2005 IDW 15 June CTP. Changes made include an enhanced UI, the PathInputType property for greater flexibility with path input, the OutputVariableName property, and the new OnFileFoundEvent event. (7 Sep 2005) Version 1.1.2 - Public Release (16 Nov 2004) Screenshots   Troubleshooting Make sure you have downloaded the version that matches your version of SQL Server. We offer separate downloads for SQL Server 2005 and SQL Server 2008. If you an error when you try and use the task along the lines of The task with the name "File Watcher Task" and the creation name ... is not registered for use on this computer, this usually indicates that the internal cache of SSIS components needs to be updated. This cache is held by the SSIS service, so you need restart the the SQL Server Integration Services service. You can do this from the Services applet in Control Panel or Administrative Tools in Windows. You can also restart the computer if you prefer. You may also need to restart any current instances of Business Intelligence Development Studio (BIDS) / Visual Studio that you may be using to build your SSIS packages. The full error message is shown below for reference: TITLE: Microsoft Visual Studio ------------------------------ The task with the name "File Watcher Task" and the creation name "Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTask, Konesans.Dts.Tasks.FileWatcherTask, Version=1.2.0.0, Culture=neutral, PublicKeyToken=b2ab4a111192992b" is not registered for use on this computer. Contact Information: File Watcher Task A similar error message can be shown when trying to edit the task if the Microsoft Exception Message Box is not installed. This useful component is installed as part of the SQL Server Management Studio tools but occasionally due to the custom options chosen during SQL Server 2005 setup it may be absent. If you get an error like Could not load file or assembly 'Microsoft.ExceptionMessageBox.. you can manually download and install the missing component. It is available as part of the Feature Pack for SQL Server 2005 release. The feature packs are occasionally updated by Microsoft so you may like to check for a more recent edition, but you can find the Microsoft Exception Message Box download links here - Feature Pack for Microsoft SQL Server 2005 - April 2006 If you encounter this problem on SQL Server 2008, please check that you have installed the SQL Server client components. The component is no longer available as a separate download for SQL Server 2008  as noted in the Microsoft documentation for Deploying an Exception Message Box Application The full error message is shown below for reference, although note that the Version will change between SQL Server 2005 and SQL Server 2008: TITLE: Microsoft Visual Studio ------------------------------ Cannot show the editor for this task. ------------------------------ ADDITIONAL INFORMATION: Could not load file or assembly 'Microsoft.ExceptionMessageBox, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified. (Konesans.Dts.Tasks.FileWatcherTask) Once installation is complete you need to manually add the task to the toolbox before you will see it and to be able add it to packages - How do I install a task or transform component? If you are still having issues then contact us, but please provide as much detail as possible about error, as well as which version of the the task you are using and details of the SSIS tools installed. Sample Code If you wanted to use the task programmatically then here is some sample code for creating a basic package and configuring the task. It uses a variable to supply the path to watch, and also sets a variable for the OutputVariableName. Once execution is complete it writes out the file found to the console. /// <summary> /// Create a package with an File Watcher Task /// </summary> public void FileWatcherTaskBasic() { // Create the package Package package = new Package(); package.Name = "FileWatcherTaskBasic"; // Add variable for input path, the folder to look in package.Variables.Add("InputPath", false, "User", @"C:\Temp\"); // Add variable for the file found, to be used on OutputVariableName property package.Variables.Add("FileFound", false, "User", "EMPTY"); // Add the Task package.Executables.Add("Konesans.Dts.Tasks.FileWatcherTask.FileWatcherTask, " + "Konesans.Dts.Tasks.FileWatcherTask, Version=1.2.0.0, Culture=neutral, PublicKeyToken=b2ab4a111192992b"); // Get the task host wrapper TaskHost taskHost = package.Executables[0] as TaskHost; // Set basic properties taskHost.Properties["PathInputType"].SetValue(taskHost, 1); // InputType.Variable taskHost.Properties["Path"].SetValue(taskHost, "User::InputPath"); taskHost.Properties["OutputVariableName"].SetValue(taskHost, "User::FileFound"); #if DEBUG // Save package to disk, DEBUG only new Application().SaveToXml(String.Format(@"C:\Temp\{0}.dtsx", package.Name), package, null); #endif // Display variable value before execution to check EMPTY Console.WriteLine("Result Variable: {0}", package.Variables["User::FileFound"].Value); // Execute package package.Execute(); // Display variable value after execution, e.g. C:\Temp\File.txt Console.WriteLine("Result Variable: {0}", package.Variables["User::FileFound"].Value); // Perform simple check for execution errors if (package.Errors.Count > 0) foreach (DtsError error in package.Errors) { Console.WriteLine("ErrorCode : {0}", error.ErrorCode); Console.WriteLine(" SubComponent : {0}", error.SubComponent); Console.WriteLine(" Description : {0}", error.Description); } else Console.WriteLine("Success - {0}", package.Name); // Clean-up package.Dispose(); } (Updated installation and troubleshooting sections, and added sample code July 2009)

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  • Prepping a conference

    - by Laurent Bugnion
    I have had the chance to talk at many conferences these past few years, and came up with a way to prepare them which works really well for me. Most importantly, it would make it quite easy to overcome an emergency (for example if my laptop would suddenly lose data). The whole code as well as the slides and other documents are in the cloud. I also use source control for my demos, so that I always have the latest and the greatest, but also a history of changes I made to my demos. Finally I have a system of code snippets which works great, and I often had very positive remarks from the audience regarding that. Putting everything in the cloud The one thing I used to be the most scared of was a sudden crash of my laptop, and being unable to restore in time for a conference. Most conferences ask speakers to send slides a few days (or weeks…) in advance, but let's face it, we all have last minute changes to our talks and I always come in the conference with updated slides that I pass to the management team. The answer to that dilemma used to be working off memory sticks, and that worked not bad. However last year I started putting all the documents relating to a conference in a DropBox folder, and that works great too. Obviously DropBox works only if you have connectivity, so if I for instance update slides while on an international flight, I cannot save to the cloud. The obvious answer to that is to backup everything on a memory stick… but I have to admit, I have been trusting my luck and working off my laptop HD and then synching everything to the cloud after landing. Of course on some US national flights you get WiFi on board, so in that case it is even simpler :) Usually after the conference is done, I remove the files from DropBox and copy them to their "final destination". They are backed up from there to BackBlaze, the great online backup service I am using routinely (I currently have about 90GB of data in BackBlaze). Outlining the presentations I like to have a written outline of my presentations written somewhere. I keep it simple, just write the various sections of the presentation with timing. I guess it is a remnant of the time when I was a private pilot, and using checklists for flight preparation. For example: Demo about designability 15' (0:37) Switch to Blend Open MainPage.xaml Create a DataTemplate ... Here I can immediately see during the presentation if I am taking too much time for my demo (0:37 is where I need to be when I am done with this section of the presentation, and 15' is the time that this particular section takes). I keep these sections reasonable, I don't detail every step of the preparation. Typically I have one such section for every 10-15 minutes of my talks. Yes, I am timing my presentations. I keep adjusting these numbers when I rehearse, and this really helps to feel more confident during the presentations. This is especially important for presentations that are long, like my MIX11 demo which clocked at 57 minutes (I had a lot of stuff to show…). Such presentations are risky, because if anything goes wrong, you will have to cut stuff, so the answer to that is: Rehearse, rehearse and when you're done rehearsing, rehearse a little more. I also have a "Preparation" section where I outline what I need to do before a presentation. For instance: Preparation Reboot in VHD Make sure MSN and Twitter are not running. Open VS10 and load demo Open Blend and load demo Run the WP7 emulator ... I typically start preparing my laptop an hour before the talk, starting everything I need to start and then putting my laptop to sleep. Saving and printing the outline, Timing Printing is a real problem because it is really hard to find a printer at most conference venues, and also quite hard in hotels. To solve that, I simply write everything in OneNote (synched to the cloud, now you start to know what I like ;) and then I print it to a PDF (I use CutePDFWriter) that I save to my Kindle. During the presentation, I read the outline off the Kindle (I mostly just need a quick check to see how I am timing). For timing during the presentation, I use the free tool ChronoGPS on my Windows Phone 7, but of course any phone these days has a clock/chrono application. In some conferences, they even have timers that the presenters can see, but they tend to count down and I prefer to count up… so I just use my own :) Source control for demos For demos, I create a separate folder and use Mercurial as source control. Mercurial has the huge advantage (over SVN or TFS) to work offline too, so I can commit while on a plane, and all the history is saved. Then when I have connectivity I push everything to the cloud (I am using the fantastic Trunksapp.com for my private repositories). Here too the obvious downside is the risk of losing my last changes if my laptop crashes before I can push to the cloud, and here too the obvious answer would be to work from a memory stick… though I have to admit I didn't do that lately (except when I was writing Silverlight 4 Unleashed, where I was really paranoid…) And code snippets? I am one of these presenters who hates to type in front of an audience. I can type really fast (writing two books has this advantage, it really teaches you to touch type and be fast at it) but in the context of an audience, on a stage where it is often damn cold (an issue I had a lot in past conferences, air conditioning can freeze your fingers and make it really hard to type), it doesn't work as well. I don't know for you, but I really dislike seeing a presentation where the speaker uses the backspace key more often than others ;) To solve that, I like to have my code ready in snippets, and drag them to the screen. Then I can spend time explaining each code snippet, while highlighting portions of the code (always highlight what you talk about, the audience often doesn't even see the cursor and doesn't know where you are on the screen!) Over the years I have used various solutions for code snippets, and now I have one which works really well… if you take a few precautions! I use the Visual Studio Toolbox. Preparing the code snippets You can store code snippets in the Toolbox for anything, XAML, C# etc. I arrange the snippets in the order in which I need them, which is a great way to remember what comes next in the presentation. I also separate them by topic, to make it easier to find them, for example when I switch to the slides and then back to the code. Remember that no matter how experienced you are, you will feel more nervous on stage than while you are preparing, so any way to make it easier for you is going to be beneficial to the audience. To store a code snippet, I do the following: Open the final demo that you want to show to the audience in Visual Studio. In your code, select a snippet of code that you want to explain in particular. Make sure that the Visual Studio Toolbox is open (menu View, Toolbox or Ctrl-Alt-X). Drag the selected snippet from the code window to the toolbox. (if needed) drag the snippet to the correct location (for example between two other code snippets so that you can access it as you speak through the demo). Right click on the snippet and select Rename Item from the context menu. Select a meaningful name. For me I use the following conventions: If it is a method, I use the method's name. If it is not a whole method, I use a descriptive name. If it is the content of a method (i.e. the body only, without the method's signature), I use "-> MethodName". This reminds me during the presentation that this is only the body, and that I need to insert that into an existing signature. This is the case, for instance, when I use Visual Studio to automatically generate the members of an interface’s implementation; then I only need to insert my snippet inside the generated method body. Saving the snippets This is the most important!! It happened to me a few times that VS10 lost its settings. When that happens, the snippets are lost too! Yeah that really sucks, especially (as it happened once) when this is the case about an hour before a talk… Stress and sweat follows, not good conditions to start a talk in front of an audience believe me. Thankfully, saving snippets is really easy with the following steps: Select the menu Tools, Import and Export Settings. Select Export selected environment settings and press Next. Uncheck All Settings. Then expand General Settings and select Toolbox (only!). Press Next. Select your source control folder and save under a meaningful name (for instance Snippets.vssettings). Commit to source control and push to the cloud. By the way, this also has the advantage of applying source control to the snippets file (which is an XML file), so you get history for free on that file! Reimporting the snippets If VS loses its settings and you need to reimport the snippets, this can be done super easily and very fast. Make sure that the Toolbox is empty. When you import snippets, they are merged with existing ones, they do not replace the content of the Toolbox. Unless merging is really what you want, make sure that your Toolbox is clean before you import, it is really easier. Select the menu Tools, Import and Export Settings. Select Import selected environment settings and press Next. Select No, just import new settings and press Next. Press Browse and select the Snippets.vssettings file. Press Finish. Et voila, all your snippets appear again in the Toolbox. Whew, the worst was averted and you can start your demo without sweating! (I had to do that once literally 5 minutes before the start of a demo, while my laptop was already hooked to the projector, and it went just fine). What about special tools? When using special tools (for example beta versions of tools you have an early access to), or a special configuration of your laptop, things can get tricky because you cannot really be sure that you will get a laptop with the same tools and the same configuration at the conference. To solve that, I use the following precautions: I make my demos from a Virtual Hard Disk. The great John Papa made a very easy-to-follow web page where he explains how to create a VHD and install Win7 to it. This gives you the full power of your laptop (as fast as booting from the metal). For me, I have a basic configuration that I saved on a USB harddrive (Win7 plus drivers, basic settings for desktop, folder options, taskbar etc) and Visual Studio 2010 SP1 on it. When preparing, I start by copying this "basis VHD" to my laptop. I install additional tools and configurations. I save the VHD back to the USB harddrive in a different folder. This would allow me to reinstall my demo environment quite fast, for example in case of harddrive failure. Replace the harddrive, copy the VHD to it, configure the BCD and you can start. Unfortunately this only works if the laptop itself still works. In the worst case of total failure, my security is to back all the installers up: The installers I use are synched on all my laptops and backed up to BackBlaze. If the worst happens and my laptop is absolutely broken, I can download the installer from BackBlaze and install on another laptop. This of course takes some time, and if that happens 5 minutes before a presentation, well… I don't have an answer to that, except of course crossing my fingers. Still, all that gives me additional security. Conclusion Remember folks, talking to an audience, large or small, will make you nervous. Just ask Scott Hanselman :) The goal here is to create the best possible conditions for you, and to create an environment where everything is saved and easy to restore, where everything is well known and provides you with additional confidence. The cooler you feel before the presentation (and during ;)), the better your presentation will be. Here too, the goal is to provide the best user experience you can have, which in turn will make it more enjoyable for your audience! Happy presenting :) Laurent   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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  • C# GridView dynamically built columns with textboxes ontextchanged

    - by tnriverfish
    My page is a bulk order form that has many products and various size options. I've got a gridview that has a 3 static columns with labels. There are then some dynamically built columns. Each of the dynamically built columns have a textbox in them. The textbox is for quantity. Trying to either update the server with the quantity entered each time a textbox is changed (possibly ontextchanged event) or loop though each of the rows column by column and gather all the items that have a quantity and process those items and their quantities all at once (via button onclick). If I put the process that builds the GridView behind a if(!Page.IsPostBack) then the when a textchanged event fires the gridview only gets the static fields and the dynamic ones are gone. If I remove the if(!Page.IsPostBack) the process to gather and build the page is too heavy on processing and takes too long to render the page again. Some advice would be appreciated. Thanks

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  • When is calculating or variable-reading faster?

    - by Andreas Hornig
    hi, to be honest, I don't really know what the "small green men" in my cpu and compiler do, so I sometimes would like to know :). Currently I would like to know what's faster, so that I can design my code in a more efficient way. So for example I want to calclate something at different points in my sourcecode, when will it be faster to calculate it once and store it in a variable that's read and used for the next points it's needed and when is it faster to calculate it everytime? I think it's depending on how "complex" and "long" the calculation is and how fast then cache is, where variables are stored, but I don't have any clue what's faster :). Thanks for any reply to my tiny but important question! Andreas PS: perhaps it's important to know that I code in JAVA, but it's more a genral question.

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  • Change Sprite Anchorpoint without moving it?

    - by Oscar Gomez
    I am trying to change my Sprite anchor point so that I can rotate over a 0.0f,0.0f anchorpoint. At first my object is rotation at the default anchor point (0.5f,0.5f). However later on I need it to rotate over a 0.0,0.0 AnchorPoint. The problem is I cannot change the anchor point and change the position accordingly, so it stays on the same position, without the object appearing to quickly move and reposition to its original point. Is there a way I can set the anchor point and the position of my Sprite at once, without it moving at all?. Thank you. -Oscar

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  • jQuery closing pop-up after successful form submit

    - by RyanP13
    Hi, I have a pop up form that i wish to close on successfull submit of the form. Currently we are only validating on the server side which will create an unordered list of validation errors with the class .error_message. Once the form has been successfully submitted i want to close the window. Currently the jQuery i am using for this is as follows but does not work because the first time the form has been submitted the number of error messages will always be zero. $(document).ready(function() { $('form#emailQuote').submit(function() { var $emailErrors = $('form#emailQuote ul.error_message').length; alert($emailErrors); if ($emailErrors == 0) { //window.close(); alert('no errors'); } else { //alert('errors'); alert('errors'); } }); });

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  • Problems with matching emails with regex

    - by Gandalf StormCrow
    Hello, I'm trying to match an email address here is what I've come up with so far : String text = "[email protected]"; String regex = "(\\w+)@{1}(\\w+){2,}\\.{1}\\w{2,4}"; This however works with following cases : [email protected] [email protected] [email protected] So it matches any alphanumeric character repeated once or more that comes before one @ followed by any alphanumeric character repeated at least two times(which is minimal characters for any domain name) followed by one .(dot) and followed by any alphanumeric character repeated at least 2 times and at most 4 times(because there are domains such as .us or .mobi). This expression however does not work with emails such as : [email protected] [email protected] [email protected] [email protected] etc as many subdomains or [email protected] [email protected] [email protected] [email protected] I've just started to learn regex and I found interesting to try to solve problems such as these by using regex .. not partially but for each case, any help would be much appriciated. Thank you

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  • WPF Binding issues

    - by Nitin Chaudhari
    I have WPF window which binds a local Dependency property to a property of my usercontrol. So now I see the value which the window gave me in my usercontrol. I achieve this by setting DataContext of window to the window itself Now once the window is loaded i set the DataContext of usercontrol to a ViewModel class, and at some point of time(based on user action) the control changes values in the control. All fine so far. But now the changed value is not reflected in Windows dependency property. How I can resolve this issue?

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  • SO_LINGER and closing sockets(WINSOCK)

    - by Johnny Walked
    hey. im writing a multithreaded winsock application and im having some issues with closing the sockets. first of all, is there a limit for a number of simultaneously open sockets? lets say like 32 sockets all in once. i establish a connection on one of the sockets, and passing information and it all goes right. problem is when i disconnect the socket and then reconnect to the same destination, i get a RST from the server after my SYN. i dont have the code for the server app so i cant debug it. when i used SO_LINGER and it sent a RST flag at the end of each session - it worked. but i dont want to end my connections this way. when not using SO_LINGER a FIN flag was sent but it seems the connection was not really closed. any help? thanks

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  • Unique identifier for an email

    - by Skywalker
    I am writing a C# application which allows users to store emails in a MS SQL Server database. Many times, multiple users will be copied on an email from a customer. If they all try to add the same email to the database, I want to make sure that the email is only added once. MD5 springs to mind as a way to do this. I don't need to worry about malicious tampering, only to make sure that the same email will map to the same hash and that no two emails with different content will map to the same hash. My question really boils down to how one would combine multiple fields into one MD5 (or other) hash value. Some of these fields will have a single value per email (e.g. subject, body, sender email address) while others will have multiple values (varying numbers of attachments, recipients). I want to develop a way of uniquely identifying an email that will be platform and language independent (not based on serialization). Any advice?

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  • How to Use Steam In-Home Streaming

    - by Chris Hoffman
    Steam’s In-Home Streaming is now available to everyone, allowing you to stream PC games from one PC to another PC on the same local network. Use your gaming PC to power your laptops and home theater system. This feature doesn’t allow you to stream games over the Internet, only the same local network. Even if you tricked Steam, you probably wouldn’t get good streaming performance over the Internet. Why Stream? When you use Steam In-Home streaming, one PC sends its video and audio to another PC. The other PC views the video and audio like it’s watching a movie, sending back mouse, keyboard, and controller input to the other PC. This allows you to have a fast gaming PC power your gaming experience on slower PCs. For example, you could play graphically demanding games on a laptop in another room of your house, even if that laptop has slower integrated graphics. You could connect a slower PC to your television and use your gaming PC without hauling it into a different room in your house. Streaming also enables cross-platform compatibility. You could have a Windows gaming PC and stream games to a Mac or Linux system. This will be Valve’s official solution for compatibility with old Windows-only games on the Linux (Steam OS) Steam Machines arriving later this year. NVIDIA offers their own game streaming solution, but it requires certain NVIDIA graphics hardware and can only stream to an NVIDIA Shield device. How to Get Started In-Home Streaming is simple to use and doesn’t require any complex configuration — or any configuration, really. First, log into the Steam program on a Windows PC. This should ideally be a powerful gaming PC with a powerful CPU and fast graphics hardware. Install the games you want to stream if you haven’t already — you’ll be streaming from your PC, not from Valve’s servers. (Valve will eventually allow you to stream games from Mac OS X, Linux, and Steam OS systems, but that feature isn’t yet available. You can still stream games to these other operating systems.) Next, log into Steam on another computer on the same network with the same Steam username. Both computers have to be on the same subnet of the same local network. You’ll see the games installed on your other PC in the Steam client’s library. Click the Stream button to start streaming a game from your other PC. The game will launch on your host PC, and it will send its audio and video to the PC in front of you. Your input on the client will be sent back to the server. Be sure to update Steam on both computers if you don’t see this feature. Use the Steam > Check for Updates option within Steam and install the latest update. Updating to the latest graphics drivers for your computer’s hardware is always a good idea, too. Improving Performance Here’s what Valve recommends for good streaming performance: Host PC: A quad-core CPU for the computer running the game, minimum. The computer needs enough processor power to run the game, compress the video and audio, and send it over the network with low latency. Streaming Client: A GPU that supports hardware-accelerated H.264 decoding on the client PC. This hardware is included on all recent laptops and PCs. Ifyou have an older PC or netbook, it may not be able to decode the video stream quickly enough. Network Hardware: A wired network connection is ideal. You may have success with wireless N or AC networks with good signals, but this isn’t guaranteed. Game Settings: While streaming a game, visit the game’s setting screen and lower the resolution or turn off VSync to speed things up. In-Home Steaming Settings: On the host PC, click Steam > Settings and select In-Home Streaming to view the In-Home Streaming settings. You can modify your streaming settings to improve performance and reduce latency. Feel free to experiment with the options here and see how they affect performance — they should be self-explanatory. Check Valve’s In-Home Streaming documentation for troubleshooting information. You can also try streaming non-Steam games. Click Games > Add a Non-Steam Game to My Library on your host PC and add a PC game you have installed elsewhere on your system. You can then try streaming it from your client PC. Valve says this “may work but is not officially supported.” Image Credit: Robert Couse-Baker on Flickr, Milestoned on Flickr

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  • Downloading stuff from Oracle: an example

    - by user12587121
    Introduction Oracle has a lot of software on offer.  Components of the stack can evolve at different rates and different versions of the components may be in use at any given time.  All this means that even the process of downloading the bits you need can be somewhat daunting.  Here, by way of example, and hopefully to convince you that there is method in the downloading madness,  we describe how to go about downloading the bits for Oracle Identity Manager  (OIM) 11.1.1.5.Firstly, a couple of preliminary points: Folks with Oracle products already installed and looking for bug fixes, patch bundles or patch sets would go directly to the Oracle support website. This Oracle document is a comprehensive description of the Oracle FMW download process and the licensing that applies to downloaded software.   Downloading Oracle Identity Manager 11.1.1.5     To be sure we download the right versions, first locate the Certification Matrix for OIM 11.1.1.5: first go to the Fusion Certification Page then go to the “System Requirements and Supported Platforms for Oracle Identity and Access Management 11gR1” link. Let’s assume you have a 64 bit Linux Machine and an Oracle database already.  Then our  goal is to end up with a list of files like the following: jdk-6u29-linux-x64.bin                    (Java JDK)V26017-01.zip                             (the Repository Creation Utility to create the DB schemas)wls1035_generic.jar                       (the Weblogic Application Server)ofm_iam_generic_11.1.1.5.0_disk1_1of1.zip (the Identity Managament bits)ofm_soa_generic_11.1.1.5.0_disk1_1of2.zip (the SOA bits)ofm_soa_generic_11.1.1.5.0_disk1_2of2.zip jdevstudio11115install.exe                (optional: JDeveloper IDE)soa-jdev-extension.zip                    (optional: SOA extensions for JDeveloper) Downloading the bits 1.    Download the Java JDK, 64 bit version 1.6.0_24+.2.    Download the RCU: here you will see that the RCU is mentioned on the Identity Management home page but no link is provided.  Do not panic.  Due to the amount and turnover of software available only the latest versions are available for download from the main Oracle site.  Over time software gets moved on to the Oracle edelivery site and it is here that we find the RCU version we require: a.    Go to edelivery: https://edelivery.oracle.com b.    Choose Pack ‘ Oracle Fusion Middleware’ and ‘Linux x86-64’ c.    Click on ‘Oracle Fusion Middleware 11g Media Pack for Linux x86-64’ d.    Download: ‘Oracle Fusion Middleware Repository Creation Utility 11g (11.1.1.5.0) for Linux x86’ (V26017.zip) 3.    Download the Weblogic Application Server: WLS 10.3.54.    Download the Oracle Identity Manager bits: one point to clarify here is that currently  the Identity Management bits come in two trains, essentially one for the Directory Services piece and the other for the Access Management and Identity Management parts.  We need to be careful not to confuse the two, in particular to be clear which of the trains is being referred to by  the documentation: a.   So, with this in mind, go to ‘ Oracle Identity and Access Management (11.1.1.5.0)’ and download Disk1. 5.    Download the SOA bits: a.    Go to the edelivery area as for the RCU and download: i.    Oracle SOA Suite 11g Patch Set 4 (11.1.1.5.0) (Part 1 of 2) ii.    Oracle SOA Suite 11g Patch Set 4 (11.1.1.5.0) (Part 2 of 2) 6.    You will want to download some development tooling (for plugins or BPEL workflow development): a.    Download Jdeveloper 11.1.1.5 (11.1.1.6 may work but best to stick to the versions that correspond to the WLS version we are using) b.    Go to the site for  SOA tools and download the SOA Composite Editor 11.1.1.5 That’s it, you may proceed to the installation. 

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  • Sitemaps on multiple front end servers using a http handler, is that a good idea?

    - by Rihan Meij
    Question 1 We would like to generate a site map for our CMS site We have multiple front end servers with approx a million articles. Environment multiple MS SQL servers multiple front end servers (load balanced) ASP.net - and IIS 6 Windows 2003 To have the site maps (the site map index file, and the site map files) physically on the front end servers will be a operations nightmare and error prone. So we are considering using http handlers instead so that it does not matter what server gets the request, it will be able to serve the correct xml file. Question 2 If we ping Google each time we publish a new article will that effect us negatively if that happens more than once a hour. Thanks!

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  • Filtering MySQL query result according to a interval of timestamp

    - by celalo
    Let's say I have a very large MySQL table with a timestamp field. So I want to filter out some of the results not to have too many rows because I am going to print them. Let's say the timestamps are increasing as the number of rows increase and they are like every one minute on average. (Does not necessarily to be exactly once every minute, ex: 2010-06-07 03:55:14, 2010-06-07 03:56:23, 2010-06-07 03:57:01, 2010-06-07 03:57:51, 2010-06-07 03:59:21 ...) As I mentioned earlier I want to filter out some of the records, I do not have specific rule to do that, but I was thinking to filter out the rows according to the timestamp interval. After I achieve filtering I want to have a result set which has a certain amount of minutes between timestamps on average (ex: 2010-06-07 03:20:14, 2010-06-07 03:29:23, 2010-06-07 03:38:01, 2010-06-07 03:49:51, 2010-06-07 03:59:21 ...) Last but not least, the operation should not take incredible amount of time, I need this functionality to be almost fast as a normal select operation. Do you have any suggestions?

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  • Activity tracking usecase for login tracking.

    - by Mdillion
    Creating an activity tracking system for a social site. All user activiti from pooint of login til logoff are to be tracked. This means the first use case is the user's login. Every activity will have the same format so once I figure out how to track one activity then I can create chema for all activities. Currently for login I have steps like: Two solutions I have: Activity 1: User attempts to login Activity 2 A: User has successfully logged in Activity 2 B: User failed to login. Activity 2 B A: User failed to login due to invalid password Activity 2 B B: User failed to login due to locked account. OR Activty 1: User login - with result = Pass or Fail and if Fail reason = flag_id of reason. Accordingly I have to create the schema. For now I have it like this: activity_id object_id (fk) session_id (fk) user_id (fk) flag_id (fk) created_dt friend_id (fk) result (pass/fail) But ofcourse this a work in progress.

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  • How do I automate navigation to a website that requires authentication?

    - by Wiz
    Here's what I'm trying to achieve. I would like to write a script that will navigate to a website that requires me to be authenticated as myself, say Facebook, Live Spaces, Twitter or any other, and then have that script search for certain information on one of the pages of the website. I've done something similar in the past with the Windows.Forms WebBrowser control, which is a full blown implementation of IE that can be controlled through code and will store whatever cookies you get once you're authenticated, but it was very unfriendly to modify and I was hoping to use a scripting language instead, maybe Powershell or something of that sort. Are there maybe some good tutorials about this out there on the web? Thanks!

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  • What useful GDB scripts have you used/written?

    - by nik
    People use gdb on and off for debugging, of course there are lots of other debugging tools across the varied OSes, with and without GUI and, maybe other fancy IDE features. I would like to know what useful gdb scripts you have written and liked. While, I do not mean a dump of commands in a something.gdb file that you source to pull out a bunch of data, if that made your day, go ahead and talk about it. Lets think conditional processing, control loops and functions written for more elegant and refined programming to debug and, maybe even for whitebox testing Things get interesting when you start debugging remote systems (say, over a serial/ethernet interface) And, what if the target is a multi-processor (and, multithreaded) system Let me put a simple case as an example... Say, A script that traversed serially over entries to locate a bad entry in a large hash-table that is implemented on an embedded platform. That helped me debug a broken hash-table once.

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  • Background processing in rails

    - by hashpipe
    Hi, This might seem like a FAQ on stackoverflow, but my requirements are a little different. While I have previously used BackgroundRB and DJ for running background processes in ruby, my requirement this time is to run some heavy analytics and mathematical computations on a huge set of data, and I need to do this only about the first 15 days of the month. Going by this, I am tempted to use cron and run a ruby script to accomplish this goal. What I would like to know / understand is: 1 - Is using cron a good idea (cause I'm not a system admin, and so while I have basic idea of cron, I'm not overly confident of doing it perfectly) 2 - Can we somehow modify DJ to run only on the first 15 days of the month (with / without using cron), and then just stop and exit once all the jobs in the queue for the day are over (don't want it to ping the DB every time for a new job...whatever the jobs will be in the queue when DJ starts, that will be all). I'm not sure if I have put the question in the right manner, but any help in this direction will be much appreciated. Thanks

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  • Style: Dot notation vs. message notation in Objective-C 2.0

    - by groundhog
    In Objective-C 2.0 we got the "dot" notation for properties. I've seen various back and forths about the merits of dot notation vs. message notation. To keep the responses untainted I'm not going to respond either way in the question. What is your thought about dot notation vs. message notation for property accessing? Please try to keep it focused on Objective-C - my one bias I'll put forth is that Objective-C is Objective-C, so your preference that it be like Java or JavaScript aren't valid. Valid commentary is to do with technical issues (operation ordering, cast precedence, performance, etc), clarity (structure vs. object nature, both pro and con!), succinctness, etc. Note, I'm of the school of rigorous quality and readability in code having worked on huge projects where code convention and quality is paramount (the write once read a thousand times paradigm).

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  • Avoid XmlDocument validating namespaces in C#

    - by Abbey Kingston
    Hello, I'm trying to find a way of indenting a HTML file, I've been using XMLDocument and just using a XmlTextWriter. However I am unable to format it correctly for HTML documents because it checks the doctype and tries to download it. Is there a "dumb" indenting mechanism that doesnt validate or check the document and does a best effort indentation? The files are 4-10Mb in size and they are autogenerated, we have to handle it internal - its fine, the user can wait, I just want to avoid forking to a new process etc. Essentially, right now I use a MemoryStream, XmlTextWriter and XmlDocument, once indented I read it back from the MemoryStream and return it as a string. Failures happen for XHTML documents and some HTML 4 documents because its trying to grab the dtds. I tried setting XmlResolver as null but to no avail :(

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  • Big Data – Various Learning Resources – How to Start with Big Data? – Day 20 of 21

    - by Pinal Dave
    In yesterday’s blog post we learned how to become a Data Scientist for Big Data. In this article we will go over various learning resources related to Big Data. In this series we have covered many of the most essential details about Big Data. At the beginning of this series, I have encouraged readers to send me questions. One of the most popular questions is - “I want to learn more about Big Data. Where can I learn it?” This is indeed a great question as there are plenty of resources out to learn about Big Data and it is indeed difficult to select on one resource to learn Big Data. Hence I decided to write here a few of the very important resources which are related to Big Data. Learn from Pluralsight Pluralsight is a global leader in high-quality online training for hardcore developers.  It has fantastic Big Data Courses and I started to learn about Big Data with the help of Pluralsight. Here are few of the courses which are directly related to Big Data. Big Data: The Big Picture Big Data Analytics with Tableau NoSQL: The Big Picture Understanding NoSQL Data Analysis Fundamentals with Tableau I encourage all of you start with this video course as they are fantastic fundamentals to learn Big Data. Learn from Apache Resources at Apache are single point the most authentic learning resources. If you want to learn fundamentals and go deep about every aspect of the Big Data, I believe you must understand various concepts in Apache’s library. I am pretty impressed with the documentation and I am personally referencing it every single day when I work with Big Data. I strongly encourage all of you to bookmark following all the links for authentic big data learning. Haddop - The Apache Hadoop® project develops open-source software for reliable, scalable, distributed computing. Ambari: A web-based tool for provisioning, managing, and monitoring Apache Hadoop clusters which include support for Hadoop HDFS, Hadoop MapReduce, Hive, HCatalog, HBase, ZooKeeper, Oozie, Pig and Sqoop. Ambari also provides a dashboard for viewing cluster health such as heat maps and ability to view MapReduce, Pig and Hive applications visually along with features to diagnose their performance characteristics in a user-friendly manner. Avro: A data serialization system. Cassandra: A scalable multi-master database with no single points of failure. Chukwa: A data collection system for managing large distributed systems. HBase: A scalable, distributed database that supports structured data storage for large tables. Hive: A data warehouse infrastructure that provides data summarization and ad hoc querying. Mahout: A Scalable machine learning and data mining library. Pig: A high-level data-flow language and execution framework for parallel computation. ZooKeeper: A high-performance coordination service for distributed applications. Learn from Vendors One of the biggest issues with about learning Big Data is setting up the environment. Every Big Data vendor has different environment request and there are lots of things require to set up Big Data framework. Many of the users do not start with Big Data as they are afraid about the resources required to set up framework as well as a time commitment. Here Hortonworks have created fantastic learning environment. They have created Sandbox with everything one person needs to learn Big Data and also have provided excellent tutoring along with it. Sandbox comes with a dozen hands-on tutorial that will guide you through the basics of Hadoop as well it contains the Hortonworks Data Platform. I think Hortonworks did a fantastic job building this Sandbox and Tutorial. Though there are plenty of different Big Data Vendors I have decided to list only Hortonworks due to their unique setup. Please leave a comment if there are any other such platform to learn Big Data. I will include them over here as well. Learn from Books There are indeed few good books out there which one can refer to learn Big Data. Here are few good books which I have read. I will update the list as I will learn more. Ethics of Big Data Balancing Risk and Innovation Big Data for Dummies Head First Data Analysis: A Learner’s Guide to Big Numbers, Statistics, and Good Decisions If you search on Amazon there are millions of the books but I think above three books are a great set of books and it will give you great ideas about Big Data. Once you go through above books, you will have a clear idea about what is the next step you should follow in this series. You will be capable enough to make the right decision for yourself. Tomorrow In tomorrow’s blog post we will wrap up this series of Big Data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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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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