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• Architecture for new ASP.NET web application

  - by Anders Abel

  I'm maintaining an application which currently is just a web service (built with WCF) and a database backend. The web service is built in layers with a linq-to-sql data access part with core functionality in an own assembly and on top of that the web service assembly which contains the WCF code. The core assembly also handles all business logic rules (very few actually). The customer now wants a Web interface for the application instead of just accessing it through other applications which are consuming the web service. I'm quite lost on modern web application design, so I would like some advice on what architecture and frameworks to use for the web application. The web application will be using the same core assembly with business rules and the linq-to-sql data access layer as the web service. Some concepts I've thought about are: ASP.NET MVC Webforms AJAX controls - possibly leting the AJAX controls access the existing web service through JSON. Are there any more concepts I should look into? Which one is the best for a fresh project? The development tools are Visual Studio 2008 Team Edition for Developers targeting .NET 3.5. An upgrade to Visual Studio 2010 Premium (or maybe even Ultimate) is possible if it gives any benefits.

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• Getting my foot in the SCADA door, how?

  - by bibby

  I keep hearing that I should learn SCADA and its PLC language to upgrade my career. While I enjoy currently being a web and mobile development privateer, the prospects of working for a municipality or industrial entity has its appeals (since I am trying to grow a family). Over the years, I've tought myself to skillfully use php, javascript, java, perl, awk, bash. Surely, these language skills can tranfer somewhat to SCADA's logic controller language. Without any formal training in CS (music major!) other than at the workplace, I wouldn't have been able to pick up those languages and run with them had it not been for their open documentation and free-to-install or already-installed interpreters/compilers. I can't see that this is true with SCADA, and I'm hoping that I'm wrong. Ideally, I'd like to be able to apply for a job that requires [A,B,C] and suggest that they hire me because I already know [A & B]; that they wouldn't have to do a ground-up training with someone that's never programmed before. So, finally, the question; How do I "learn" SCADA? Are there sites and docs? What's going to help me get my foot in the door? Any insight is appreciated. Thanks!

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• Optimizing processing and management of large Java data arrays

  - by mikera

  I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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• How to deploy ClickOnce .Net 3.5 application on 3.0 machine

  - by Buthrakaur

  I have .Net 3.5 SP1 WPF application which I'm successfully deploying to client computers using ClickOnce. Now I got new requirement - one of our clients need to run the application on machines equipped just with .Net 3.0 and it's entirely impossible to upgrade or install anything on the machines. I already tried to run the 3.5 application with some of the 3.5FW DLLs copied to the application directory and it worked without any problems. The only problem at the moment is ClickOnce. I already made it to include the 3.5FW System.*.dll files in list of application files, but it always aborts installation on 3.0 machine with this error message: Unable to install or run the application. The application requires that assembly System.Core Version 3.5.0.0 be installed in the Global Assembly Cache (GAC) first. Please contact your system administrator. I already tried to tweak prerequisites on Publish tab of my project, but no combination solved the issue. What part of ClickOnce is responsible for checking prerequisites? I already tried to deploy using mageui.exe, but the 3.5FW error is still present. What should I do to fore ClickOnce to stop checking any prerequisites at all? The project is created using VS2010.

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• Strategy for animating a lot of "LED's" - thread?, UIView animations? NSOperation? (iPhone)

  - by RickiG

  Hi I have to do some different views containing 72 LED lights. I built an LED Class so I can loop through the LED's and set them to different colors (Green, Red, Orange, Blue None etc.). The LED then loads the appropriate .png. This works fine, I loop over the LED's and set them. Now I know that at some time they will need to not just turn on/off change color, but will have to turn on with a small delay. Like an equalizer. I have a 5-10 views containing the 72 LED's and I would like to achieve the above with the minimum amount of memory/CPU strain. for(LED *l in self.ledArray) { [l display:Green]; } I simply loop as shown above and inside the LED is a switch case that does the correct logic. If this were actual LED's and a microController I would use sleep(100) or similar in the loop, but I would really like to avoid stuff like that for obvious reasons. I was thinking that doing a performOnThread withDelay would really be consuming, so would UIView animation changing the alpha and NSOperation would also be a lot of lifting for a small feature. Is there a both efficient and clever way to go around this? Thanks for any inspiration given:)

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• Rails running multiple delayed_job - lock tables

  - by pepernik

  Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

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• What is the performance penalty of XML data type in SQL Server when compared to NVARCHAR(MAX)?

  - by Piotr Owsiak

  I have a DB that is going to keep log entries. One of the columns in the log table contains serialized (to XML) objects and a guy on my team proposed to go with XML data type rather than NVARCHAR(MAX). This table will have logs kept "forever" (archiving some very old entries may be considered in the future). I'm a little worried about the CPU overhead, but I'm even more worried that DB can grow faster (FoxyBOA from the referenced question got 70% bigger DB when using XML). I have read this question http://stackoverflow.com/questions/514827/microsoft-sql-server-2005-2008-xml-vs-text-varchar-data-type and it gave me some ideas but I am particulairly interrested in clarification on whether the DB size increases or decreases. Can you please share your insight/experiences in that matter. BTW. I don't currently have any need to depend on XML features within SQL Server (there's nearly zero advantage to me in the specific case). Ocasionally log entries will be extracted, but I prefer to handle the XML using .NET (either by writing a small client or using a function defined in a .NET assembly).

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• Interesting questions related to lighttpd on Amazon EC2

  - by terence410

  This problem appeared today and I have no idea what is going on. Please share you ideas. I have 1 EC2 DB server (MYSQL + NFS File Sharing + Memcached). And I have 3 EC2 Web servers (lighttpd) where it will mounted the NFS folders on the DB server. Everything going smoothly for months but suddenly there is an interesting phenomenon. In every 8 minutes to 10 minutes, PHP file will be unreachable. This will last about 1 minute and then back to normal. Normal files like .html file are unaffected. All servers have the same problem exactly at the same time. I have spent one whole day to analysis the reason. Finally, I find out when the problem appear, the file descriptor of lighttpd suddenly increased a lot. I used ls /proc/1234/fd | wc -l to check the number of fd. The # of fd is around 250 in normal time. However, when the problem appeared, it will be raised to 1500 and then back to normal. It sounds funny, right? Do you have any idea what's going on? ======================== The CPU graph of one of the web server.

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• Access cost of dynamically created objects with dynamically allocated members

  - by user343547

  I'm building an application which will have dynamic allocated objects of type A each with a dynamically allocated member (v) similar to the below class class A { int a; int b; int* v; }; where: The memory for v will be allocated in the constructor. v will be allocated once when an object of type A is created and will never need to be resized. The size of v will vary across all instances of A. The application will potentially have a huge number of such objects and mostly need to stream a large number of these objects through the CPU but only need to perform very simple computations on the members variables. Could having v dynamically allocated could mean that an instance of A and its member v are not located together in memory? What tools and techniques can be used to test if this fragmentation is a performance bottleneck? If such fragmentation is a performance issue, are there any techniques that could allow A and v to allocated in a continuous region of memory? Or are there any techniques to aid memory access such as pre-fetching scheme? for example get an object of type A operate on the other member variables whilst pre-fetching v. If the size of v or an acceptable maximum size could be known at compile time would replacing v with a fixed sized array like int v[max_length] lead to better performance? The target platforms are standard desktop machines with x86/AMD64 processors, Windows or Linux OSes and compiled using either GCC or MSVC compilers.

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• RegisterStartupScript not working after upgrading to framework 3.5

  - by AaronS

  I'm trying to upgrade an asp.net c# web project from framework 2.0 to 3.5. When I do this, the client side script that gets written using RegisterStartupScript isn't rendered on the client page. This works perfectly when I compile for 2.0, and for 3.0, but not when I compile for 3.5. Here is the code that isn't getting rendered: Page myPage = (Page)HttpContext.Current.Handler; ScriptManager.RegisterStartupScript(myPage, myPage.GetType(), "alertscript", "alert('test');", true); This is called from a class project, and not the web project itself, which is why I'm using the HttpContext.Current.Handler. There are no errors getting generated from the compiler, the CLR, and there are no client side JavaScript errors. If I do a search for the "alertscript" in my rendered page, the above code actually isn't there. Anyone have ideas as to what is going on? -Edit- This seems to be an issue when I'm trying to register the script from an external project. If I use the exact same code in a class file in the web project (not the code behind), it works. However, if I make a call to a method in a class from another project, it does not work. Does the ScriptManager.RegisterStartupScript not get registered correctly if performed from somewhere besides the web project itself?

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• JAVASCRIPT ENABLED [closed]

  - by kirchoffs415

  HI, I hope somebody can help, i keep getting the following message when i log on-- Your Javascript is disabled. Limited functionality is available. it will stay for maybe a day sometimes two.I have uninstalled javascript and reinstalled but still the same. Iam using chrome. any help would be gratefull many thanks Dominic p.s. my system spec is as follows System InformationOS Name Microsoft® Windows Vista™ Home Premium Version 6.0.6002 Service Pack 2 Build 6002 Other OS Description Not Available OS Manufacturer Microsoft Corporation System Name DOM-PC System Manufacturer Dell Inc. System Model Inspiron 1545 System Type X86-based PC Processor Pentium(R) Dual-Core CPU T4200 @ 2.00GHz, 2000 Mhz, 2 Core(s), 2 Logical Processor(s) BIOS Version/Date Dell Inc. A05, 25/02/2009 SMBIOS Version 2.4 Windows Directory C:\Windows System Directory C:\Windows\system32 Boot Device \Device\HarddiskVolume3 Locale United Kingdom Hardware Abstraction Layer Version = "6.0.6002.18005" User Name DOM-PC\DOM Time Zone GMT Standard Time Installed Physical Memory (RAM) 3.00 GB Total Physical Memory 2.96 GB Available Physical Memory 1.38 GB Total Virtual Memory 5.89 GB Available Virtual Memory 4.25 GB Page File Space 3.00 GB Page File C:\pagefile.sys My System Specs

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• question about MySQL database migration

  - by WilliamLou

  Hi there: If I have a MySQL database with several tables on a live server, now I would like to migrate this database to another server. Of course, the migration I mean here involves some database tables, for example: add some new columns to several tables, add some new tables etc.. Now, the only method I can think of is to use some php/python(two scripts I know) script, connect two databases, dump the data from the old database, and then write into the new database. However, this method is not efficient at all. For example: in old database, table A has 28 columns; in new database, table A has 29 columns, but the extra column will have default value 0 for all the old rows. My script still needs to dump the data row by row and insert each row into the new database. Is there any tools or a better method than writing a script yourself? Here, I dont need to worry about multithread writing problems etc.., I mean the old database will be down (not open to public usage etc.., only for upgrade ) for a while. Thanks!!

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• Using SVN post-commit hook to update only files that have been commited

  - by fondie

  I am using an SVN repository for my web development work. I have a development site set up which holds a checkout of the repository. I have set up an SVN post-commit hook so that whenever a commit is made to the repository the development site is updated: cd /home/www/dev_ssl /usr/bin/svn up This works fine but due to the size of the repository the updates take a long time (approx. 3 minutes) which is rather frustrating when making regular commits. What I'd like is to change the post-commit hook to only update those files/directories that have been committed but I don't know how to go about doing this. Updating the "lowest common directory" would probably be the best solution, e.g. If committing the follow files: /branches/feature_x/images/logo.jpg /branches/feature_x/css/screen.css It would update the directory: /branches/feature_x/ Can anyone help me create a solution that achieves this please? Thanks! Update: The repository and development site are located on the same server so network issues shouldn't be involved. CPU usage is very low, and I/O should be ok (it's running on hi-spec dedicated server) The development site is approx. 7.5GB in size and contains approx. 600,000 items, this is mainly due to having multiple branches/tags

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• Should a setter return immediately if assigned the same value?

  - by Andrei Rinea

  In classes that implement INotifyPropertyChanged I often see this pattern : public string FirstName { get { return _customer.FirstName; } set { if (value == _customer.FirstName) return; _customer.FirstName = value; base.OnPropertyChanged("FirstName"); } } Precisely the lines if (value == _customer.FirstName) return; are bothering me. I've often did this but I am not that sure it's needed nor good. After all if a caller assigns the very same value I don't want to reassign the field and, especially, notify my subscribers that the property has changed when, semantically it didn't. Except saving some CPU/RAM/etc by freeing the UI from updating something that will probably look the same on the screen/whatever_medium what do we obtain? Could some people force a refresh by reassigning the same value on a property (NOT THAT THIS WOULD BE A GOOD PRACTICE HOWEVER)? 1. Should we do it or shouldn't we? 2. Why?

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• How to check the backtrace of a "USER process" in the Linux Kernel Crash Dump

  - by Biswajit

  I was trying to debug a USER Process in Linux Crash Dump. The normal steps to go to the crash dump are: Go to the path where the dump is located. Use the command crash kernel_link dump.201104181135. Where kernel_link is a soft link I have created for vmlinux image. Now you will be in the CRASH prompt. If you run the command foreach <PID Of the process> bt Eg: crash> **foreach 6920 bt** **PID: 6920 TASK: ffff88013caaa800 CPU: 1 COMMAND: **"**climmon**"**** #0 [ffff88012d2cd9c8] **schedule** at ffffffff8130b76a #1 [ffff88012d2cdab0] **schedule_timeout** at ffffffff8130bbe7 #2 [ffff88012d2cdb50] **schedule_timeout_uninterruptible** at ffffffff8130bc2a #3 [ffff88012d2cdb60] **__alloc_pages_nodemask** at ffffffff810b9e45 #4 [ffff88012d2cdc60] **alloc_pages_curren**t at ffffffff810e1c8c #5 [ffff88012d2cdc90] **__page_cache_alloc** at ffffffff810b395a #6 [ffff88012d2cdcb0] **__do_page_cache_readahead** at ffffffff810bb592 #7 [ffff88012d2cdd30] **ra_submit** at ffffffff810bb6ba #8 [ffff88012d2cdd40] **filemap_fault** at ffffffff810b3e4e #9 [ffff88012d2cdda0] **__do_fault** at ffffffff810caa5f #10 [ffff88012d2cde50] **handle_mm_fault** at ffffffff810cce69 #11 [ffff88012d2cdf00] **do_page_fault** at ffffffff8130f560 #12 [ffff88012d2cdf50] **page_fault** at ffffffff8130d3f5 RIP: 00007fd02b7e9071 RSP: 0000000040e86ea0 RFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007fd02b7e9071 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040e86ec0 RBP: 0000000040e87140 R8: 0000000000000800 R9: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff16ec43d0 R13: 00007fd02bcadf00 R14: 0000000040e87950 R15: 0000000000001000 ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b If you check the above backtrace it shows the kernel functions used for scheduling/handling page fault but not the functions that were executed in the USER process (here eg. climmon). So I am not able to debug this process as I am not able to see the functions executed in that process. Can any one help me with this case?

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• Button Onclick event (which is in codbehind) doesn't get triggered in MVC 2

  - by rksprst

  I had an MVC 1.0 web application that was in VS 2008; I just upgraded the project to VS 2010 which automatically upgraded MVC to 2.0. I have a bunch of viewpages have codebehind files that were manually added. The project worked fine before the upgrade, but now the onclick even't don't get triggered. I.e. I have an asp:button with an onclick event that points to a method in the codebehind. When you click the button, the onclick event doesn't get triggered. In fact, when you look at the Page variable, IsPostBack is false. This is really bizarre and I'm wondering if anyone know what happened and how to fix it. I'm thinking it has something to do with the changes in MVC 2.0; but I'm not sure. Any help is really appreciated, I've been trying to figure this out for a while. (deleting the codebehinds and moving that to the controller is not really an option since there is so many pages, moving back to vs 2008 is a last resort as I want to make use of some of the VS 2010 features like performance testing.)

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• What happened to the .NET version definition with v4.0?

  - by Tom Tresansky

  I'm building a C# class library, and using the beta 2 of Visual Web Developer/Visual C# 2010. I'm trying to save information about what version of .NET the library was built under. In the past, I was able to use this: // What version of .net was it built under? #if NET_1_0 public const string NETFrameworkVersion = ".NET 1.0"; #elif NET_1_1 public const string NETFrameworkVersion = ".NET 1.1"; #elif NET_2_0 public const string NETFrameworkVersion = ".NET 2.0"; #elif NET_3_5 public const string NETFrameworkVersion = ".NET 3.5"; #else public const string NETFrameworkVersion = ".NET version unknown"; #endif So I figured I could just add: #elif NET_4_0 public const string NETFrameworkVersion = ".NET 4.0"; Now, in Project-Properties, my target Framework is ".NET Framework 4". If I check: Assembly.GetExecutingAssembly().ImageRuntimeVersion I can see my runtime version is v4.0.21006 (so I know I have .NET 4.0 installed on my CPU). I naturally expect to see that my NETFrameworkVersion variable holds ".NET 4.0". It does not. It holds ".NET version unknown". So my question is, why is NET_4_0 not defined? Did the naming convention change? Is there some simple other way to determine .NET framework build version in versions 3.5?

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• Changing character encoding in MySQL, PHP scripts, HTML

  - by Sandman

  So, I have built on this system for quite some time, and it is currently outputting Latin1 (ISO-8859-1) to the web browser, and this is the components: MySQL - all data is stored with the Latin1 character set PHP - All PHP text files are stored on disk with Latin1 encoding HTML - The output has the http-equiv="content-type" content="text/html; charset=iso-8859-1" meta tag So, I'm trying to understand how the encoding of the different parts come into play in my workflow. If I open a PHP script and change its encoding within the text editor to UTF-8 and save it back to disk and reload the web browser, the text is all messed up - unless the text comes from the DB. If I change the encoding of the DB to UTF-8 and keep the PHP files in latin1 I have to use utf8_decode() for the data to display correctly. And if I change the HTML code the browser will read it incorrectly. So yeah, I realise that if I want to "upgrade" to UTF8, I have to update all three parts of this setup for it to work correctly, but since it's a huge system with some 180k lines of PHP code and millions of posts in a lot of databases/tables, I don't want to start something like this without understanding everything correctly. What haven't I thought about? What could mess this up beyond fixing? What are the procedures for changing the encoding of an entire MySQL installation and what's the easiest way to change the encoding of hundreds or thousands of PHP files on disk? The META tag is luckily added dynamically, so I'll change that in one place only :) Let me hear about your experiences with this.

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• Excel 2010 64 bit can't create .net object

  - by aboes81

  I have a simple class library that I use in Excel. Here is a simplification of my class... using System; using System.Runtime.InteropServices; namespace SimpleLibrary { [ComVisible(true)] public interface ISixGenerator { int Six(); } public class SixGenerator : ISixGenerator { public int Six() { return 6; } } } In Excel 2007 I would create a macro enabled workbook and add a module with the following code: Public Function GetSix() Dim lib As SimpleLibrary.SixGenerator lib = New SimpleLibrary.SixGenerator Six = lib.Six End Function Then in Excel I could call the function GetSix() and it would return six. This no longer works in Excel 2010 64bit. I get a Run-time error '429': ActiveX component can't create object. I tried changing the platform target to x64 instead of Any CPU but then my code wouldn't compile unless I unchecked the Register for COM interop option, doing so makes it so my macro enable workbook cannot see SimpleLibrary.dll as it is no longer regsitered. Any ideas how I can use my library with Excel 2010 64 bit?

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• Advanced All In One .NET Framework

  - by alfredo dobrekk

  Hi, i m starting a new project that would basically take input from user and save them to database among about 30 screens, and i would like to find a framework that will allow the maximum number of these features out of the box : .net c#. windows form. unit testing continuous integration screens with lists, combo boxes, text boxes, add, delete, save, cancel that are easy to update when you add a property to your classes or a field to your database. auto completion on controls to help user find its way use of an orm like nhibernate easy multithreading and display of wait screens for user easy undo redo tabbed child windows search forms ability to grant access to some functionnalities according to user profiles mvp/mvvm or whatever design patterns either some code generation from database to c# classe or generation of database schema from c# classes some kind of database versioning / upgrade to easily update database when i release patches to application once in production automatic control resizing code metrics analysis some code generator i can use against my entities that would generate some rough form i can rearrange after code documentation generator ... Any ideas ? I know its lot but i really would like to use existing code to build upon so i can focus on business rules. Could splitting the requirements on 3 or 4 existing open source framework be possible ? Do u have any suggestion to add to the list before starting ? What open source tools would u use to achieve these ?

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• EC2 persistence of machine

  - by Seagull

  I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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• .NET multithreading, volatile and memory model

  - by fedor-serdukov

  Assume that we have the following code: class Program { static volatile bool flag1; static volatile bool flag2; static volatile int val; static void Main(string[] args) { for (int i = 0; i < 10000 * 10000; i++) { if (i % 500000 == 0) { Console.WriteLine("{0:#,0}",i); } flag1 = false; flag2 = false; val = 0; Parallel.Invoke(A1, A2); if (val == 0) throw new Exception(string.Format("{0:#,0}: {1}, {2}", i, flag1, flag2)); } } static void A1() { flag2 = true; if (flag1) val = 1; } static void A2() { flag1 = true; if (flag2) val = 2; } } } It's fault! The main quastion is Why... I suppose that CPU reorder operations with flag1 = true; and if(flag2) statement, but variables flag1 and flag2 marked as volatile fields...

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• Is there a way to get number of connections in Signalr hub group?

  - by pajo

  Here is my problem, I want to track if user is online or offline and notify other clients about it. I'm using hubs and implemented both IConnected and IDisconnect interfaces. My idea was to send notification to all clients when hub detects connect or disconnect. By default when user refreshes page he will get new connection id and eventually previous connection will call disconnect notifying other clients user is offline even though he's actually online. I tired to use my own ConnectionIdFactory returning username for connection id but with multiple tabs opened at some point it will detect user connectionid disconnected and after that client side hub will try to unsuccessfully connect to the hub in endless loop wasting memory and cpu making browser almost unusable. I needed to fix it fast so I removed my factory and now I add every new connection to the group using username, so I can easily notify single user on all connections, but then I have problem of detecting if user is online or offline as I don't know how many active connection user is having. So I'm wondering is there a way to get number of connections in one group? Or if anybody has some better idea how to track when user goes offline? I'm using Signalr 0.4

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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• IE not rendering div contents

  - by The.Anti.9

  I've written an app using HTML 5 and I wan't to show an error box instead of the page when someone visits from IE. When it detects navigator.appName as Microsoft Internet Explorer it hides everything and shows the error div that started out hidden. The div is as follows: <div id='ieerror' style='display:none;width:500px;height:500px;border:3px solid #ff0000;position:absolute;top:50%;left:50%;margin-top:-250px;margin-left:-250px;'> <center> <h1 style='font-size: 30px;'>Internet Explorer is not supported by Aud!</h1><br /><br /> <p>Internet Explorer does not support HTML 5 and therefore this application cannot run.<br /> Please upgrade your browser. We suggest <a href='http://www.google.com/chrome'>Google Chrome</a>!</p> </center> </div> The problem is that when I visit the page in IE, the div pops up with the border, but it has no contents. Nothing is inside of it. I went to view->source and looked at it, and the code is still there, but none of it is rendered. How do I fix this?

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