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• Django - Tips to avoid repeating code in views

  - by D Roddis

  I'm moving from a PHP background into Django development via python, mostly for the sake of tackling a MVC (or MVT) that I feel makes the most sense, although in this pattern I've started to notice a lot of repeated code in my views. For example, when logged in I have information regarding the user that I would like to appear on every page, although when using render_to_response and in every view this is required I have to grab the information and pass it to the render_to_response function. I'm wondering what would be the most efficient way to cut down on the duplicate code which would in essence be required in all views in a particular app. Thanks in advance.

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• Lines-of-code counting for many C# solutions

  - by Eric

  I am currently researching a solution for counting lines of code in C#. I pretty much need a combination of the following two tools: http://richnewman.wordpress.com/2007/07/01/c-and-vbnet-line-count-utility/ http://www.locmetrics.com/index.html My problem is that I need to recursively scan a folder containing a lot of visual studio solutions. So can't really use the first tool without any major work on its code, as it's only able to scan a single solution at a time. But I also need to split the results for each solution, preferably even the contained projects. This disqualifies the second tool I found. I also found NDepend which suffers from the same problem. Do you know of any free tools that do what I need? I am unable to find anything suitable.

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• Any Code Review Communities out there?

  - by willcodejavaforfood

  After reading this post I had a look around for 'code review' communities, but I did not really find one. There were a few but they were usually for a very specific technology and not just a programming language specific one. Never really thought of it before, but there sure is a lot of code out there that could benefit from a review. Not only is it a really good way to pick up new skills from your peers (or superiors), but it will also improve quality. Does anyone know of one?

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• Need help converting Ruby code to php code

  - by newprog

  Yesterday I posted this queston. Today I found the code which I need but written in Ruby. Some parts of code I have understood (I don't know Ruby) but there is one part that I can't. I think people who know ruby and php can help me understand this code. def do_create(image) # Clear any old info in case of a re-submit FIELDS_TO_CLEAR.each { |field| image.send(field+'=', nil) } image.save # Compose request vm_params = Hash.new # Submitting a file in ruby requires opening it and then reading the contents into the post body file = File.open(image.filename_in, "rb") # Populate the parameters and compute the signature # Normally you would do this in a subroutine - for maximum clarity all # parameters are explicitly spelled out here. vm_params["image"] = file # Contents will be read by the multipart object created below vm_params["image_checksum"] = image.image_checksum vm_params["start_job"] = 'vectorize' vm_params["image_type"] = image.image_type if image.image_type != 'none' vm_params["image_complexity"] = image.image_complexity if image.image_complexity != 'none' vm_params["image_num_colors"] = image.image_num_colors if image.image_num_colors != '' vm_params["image_colors"] = image.image_colors if image.image_colors != '' vm_params["expire_at"] = image.expire_at if image.expire_at != '' vm_params["licensee_id"] = DEVELOPER_ID #in php it's like this $vm_params["sequence_number"] = -rand(100000000);????? vm_params["sequence_number"] = Kernel.rand(1000000000) # Use a negative value to force an error when calling the test server vm_params["timestamp"] = Time.new.utc.httpdate string_to_sign = CREATE_URL + # Start out with the URL being called... #vm_params["image"].to_s + # ... don't include the file per se - use the checksum instead vm_params["image_checksum"].to_s + # ... then include all regular parameters vm_params["start_job"].to_s + vm_params["image_type"].to_s + vm_params["image_complexity"].to_s + # (nil.to_s => '', so this is fine for vm_params we don't use) vm_params["image_num_colors"].to_s + vm_params["image_colors"].to_s + vm_params["expire_at"].to_s + vm_params["licensee_id"].to_s + # ... then do all the security parameters vm_params["sequence_number"].to_s + vm_params["timestamp"].to_s vm_params["signature"] = sign(string_to_sign) #no problem # Workaround class for handling multipart posts mp = Multipart::MultipartPost.new query, headers = mp.prepare_query(vm_params) # Handles the file parameter in a special way (see /lib/multipart.rb) file.close # mp has read the contents, we can close the file now response = post_form(URI.parse(CREATE_URL), query, headers) logger.info(response.body) response_hash = ActiveSupport::JSON.decode(response.body) # Decode the JSON response string ##I have understood below def sign(string_to_sign) #logger.info("String to sign: '#{string_to_sign}'") Base64.encode64(HMAC::SHA1.digest(DEVELOPER_KEY, string_to_sign)) end # Within Multipart modul I have this: class MultipartPost BOUNDARY = 'tarsiers-rule0000' HEADER = {"Content-type" => "multipart/form-data, boundary=" + BOUNDARY + " "} def prepare_query (params) fp = [] params.each {|k,v| if v.respond_to?(:read) fp.push(FileParam.new(k, v.path, v.read)) else fp.push(Param.new(k,v)) end } query = fp.collect {|p| "--" + BOUNDARY + "\r\n" + p.to_multipart }.join("") + "--" + BOUNDARY + "--" return query, HEADER end end end Thanks for your help.

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• C++ : Efficient code

  - by Alerty

  What code sample is a brilliant example of efficiency in the C++ programming language and its features?

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• Looking for a C# code parser

  - by Blindy

  I'm looking for a set of classes (preferably in the .net framework) that will parse C# code and return a list of functions with parameters, classes with their methods, properties etc. Ideally it would provide all that's needed to build my own intellisense. I have a feeling something like this should be in the .net framework, given all the reflection stuff they offer, but if not then an open source alternative is good enough. What I'm trying to build is basically something like Snippet Compiler, but with a twist. I'm trying to figure out how to get the code dom first. I tried googling for this but I'm not sure what the correct term for this is so I came up empty.

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• Blackberry Code

  - by Haoest

  I have having difficulties protecting my blackberry application persistent data with ControlledAccess object. According to http://www.blackberry.com/developers/docs/4.5.0api/net/rim/device/api/system/PersistentObject.html, I need a PersistentObject, CodeSignKey, and ControlledAccess objects to work. I have everything except one piece: CodeSignKey codeSigningKey = CodeSigningKey.get( "ACME" ); here, I don't know what to replace for "ACME". Is this the PIN code I chose as I filled out the Code Sign Key? Is it my package name, output file name? The Blackberry API documentation doesn't seem to say anything about this particularly important parameter. Help please, thanks.

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• Controlling CodeModel's code output formatting: putting lines between namespace declarations

  - by devoured elysium

  I'm making some experiments with Visual Studio's CodeModel. I tried creating a file with two namespaces in there through VS's Code Model: CodeModel codeModel = projItem.ContainingProject.CodeModel; codeModel.AddNamespace("Namespaces.FirstNamespace", "namespacestest.cs"); codeModel.AddNamespace("Namespaces.SecondNamespace", "namespacestest.cs"); the output of such code is: //file namespacestest.cs namespace Namespaces.FirstNamespace { } namespace Namespaces.SecondNamespace { } Which is almost what I'm looking for. The only catch here is that I'd like to control the spacing: having at least one line between the first and the second namespace. Does by chance anyone know of a way of achieving this? This is what I want: //file namespacestest.cs namespace Namespaces.FirstNamespace { } namespace Namespaces.SecondNamespace { } Thanks

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• migrating C++ code from structures to classes

  - by eSKay

  I am migrating some C++ code from structures to classes. I was using structures mainly for bit-field optimizations which I do not need any more (I am more worried about speed than saving space now). What are the general guidelines for doing this migration? I am still in the planning stage as this is a very big move affecting a major part of the code. I want to plan everything first before doing it. What are all the essential things I should keep in mind?

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• C++ refactor common code with one different statement

  - by user231536

  I have two methods f(vector<int>& x, ....) and g(DBConn& x, ....) where the (....) parameters are all identical. The code inside the two methods are completely identical except for one statement where we do different actions based on the type of x: in f(): we do x.push_back(i) in g(): we do x.DeleteRow(i) What is the simplest way to extract the common code into one method and yet have the two different statements? I am thinking of having a templated functor that overloads operator () (int a) but that seems overkill.

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• Code Golf: Duplicate Character Removal in String

  - by Alex

  The challenge: The shortest code, by character count, that detects and removes duplicate characters in a String. Removal includes ALL instances of the duplicated character (so if you find 3 n's, all three have to go), and original character order needs to be preserved. Example Input 1: nbHHkRvrXbvkn Example Output 1: RrX Example Input 2: nbHHkRbvnrXbvkn Example Output 2: RrX (the second example removes letters that occur three times; some solutions have failed to account for this) (This is based on my other question where I needed the fastest way to do this in C#, but I think it makes good Code Golf across languages.)

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• Help me understand the code snippet in c#

  - by Benny

  I am reading this blog: Pipes and filters pattern I am confused by this code snippet: public class Pipeline<T> { private readonly List<IOperation<T>> operations = new List<IOperation<T>>(); public Pipeline<T> Register(IOperation<T> operation) { operations.Add(operation); return this; } public void Execute() { IEnumerable<T> current = new List<T>(); foreach (IOperation<T> operation in operations) { current = operation.Execute(current); } IEnumerator<T> enumerator = current.GetEnumerator(); while (enumerator.MoveNext()); } } what is the purpose of this statement: while (enumerator.MoveNext());? seems this code is a noop.

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• Using Gridview in aspx.vb (code-behind)

  - by Tauron Xavenberg

  I need to create a gridview based on 2 different datasources: main and sub-cathegory. And I need to list them like below: Productinfo sub-product 1 sub-product 2 Productinfo sub-product 1 sub-product 2 sub-product 3 sub-product 4 Etc... the thing is that both the "productinfo" and the "sub-product" are dynamic as the number of both can vary, so I would have to create a gridview within a gridview, plus the necessary filters too. For this reason I thought it was best to do it all in code-behind, but I can't understand how to use the gridview-class in codebehind and bind it so that it actually shows something in the main aspx page. Basically what I'm asking for is a simple example of how, when you have nothing but <asp:GridView/> in the aspx -page, can you add components to it and show it, from code-behind (vb)? Thanks.

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• Add code to html pages automatically

  - by piede

  I need to add some code to the of several html contained in a folder on my desktop. How can i do that? I am using a prototyping tool (Axure) on Mac and I want to add some html meta tags to the generated pages. These pages can be overwritten every time I generate the prototype. What I need is a sort of script that I can launch after re-generating the prototype, to reinsert the code. There is something for windows but it doesn't work on Mac: http://joshuamorse.com/2009/01/14/axure-protonotes-an-alternative-to-protoshare/ thanks

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• UNIX Signal lost

  - by user309506

  Hello, Is there any situation in which classic UNIX signals are lost? Thank you!

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• Login fails when recreating database with Code First

  - by Mun

  I'm using ASP.NET Entity Framework's Code First to create my database from the model, and the login seems to fail when the database needs to be recreated after the model changes. In Global.asax, I've got the following: protected void Application_Start() { Database.SetInitializer(new DropCreateDatabaseIfModelChanges<EntriesContext>()); // ... } In my controller, I've got the following: public ActionResult Index() { // This is just to force the database to be created var context = new EntriesContext(); var all = (from e in context.Entries select e).ToList(); } When the database doesn't exist, it is created with no problems. However, when I make a change to the model, rebuild and refresh, I get the following error: Login failed for user 'sa'. My connection string looks like this: <add name="EntriesContext" connectionString="Server=(LOCAL);Database=MyDB;User Id=sa;Password=password" providerName="System.Data.SqlClient" /> The login definitely works as I can connect to the server and the database from Management Studio using these credentials. If I delete the database manually, everything works correctly and the database is recreated as expected with the schema reflecting the changes made to the model. It seems like either the password or access to the database is being lost. Is there something else I need to do to get this working?

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• A Simple Approach For Presenting With Code Samples

  - by Jesse Taber

  Originally posted on: http://geekswithblogs.net/GruffCode/archive/2013/07/31/a-simple-approach-for-presenting-with-code-samples.aspxI’ve been getting ready for a presentation and have been struggling a bit with the best way to show and execute code samples. I don’t present often (hardly ever), but when I do I like the presentation to have a lot of succinct and executable code snippets to help illustrate the points that I’m making. Depending on what the presentation is about, I might just want to build an entire sample application that I would run during the presentation. In other cases, however, building a full-blown application might not really be the best way to present the code. The presentation I’m working on now is for an open source utility library for dealing with dates and times. I could have probably cooked up a sample app for accepting date and time input and then contrived ways in which it could put the library through its paces, but I had trouble coming up with one app that would illustrate all of the various features of the library that I wanted to highlight. I finally decided that what I really needed was an approach that met the following criteria: Simple: I didn’t want the user interface or overall architecture of a sample application to serve as a distraction from the demonstration of the syntax of the library that the presentation is about. I want to be able to present small bits of code that are focused on accomplishing a single task. Several of these examples will look similar, and that’s OK. I want each sample to “stand on its own” and not rely much on external classes or methods (other than the library that is being presented, of course). “Debuggable” (not really a word, I know): I want to be able to easily run the sample with the debugger attached in Visual Studio should I want to step through any bits of code and show what certain values might be at run time. As far as I know this rules out something like LinqPad, though using LinqPad to present code samples like this is actually a very interesting idea that I might explore another time. Flexible and Selectable: I’m going to have lots of code samples to show, and I want to be able to just package them all up into a single project or module and have an easy way to just run the sample that I want on-demand. Since I’m presenting on a .NET framework library, one of the simplest ways in which I could execute some code samples would be to just create a Console application and use Console.WriteLine to output the pertinent info at run time. This gives me a “no frills” harness from which to run my code samples, and I just hit ‘F5’ to run it with the debugger. This satisfies numbers 1 and 2 from my list of criteria above, but item 3 is a little harder. By default, just running a console application is going to execute the ‘main’ method, and then terminate the program after all code is executed. If I want to have several different code samples and run them one at a time, it would be cumbersome to keep swapping the code I want in and out of the ‘main’ method of the console application. What I really want is an easy way to keep the console app running throughout the whole presentation and just have it run the samples I want when I want. I could setup a simple Windows Forms or WPF desktop application with buttons for the different samples, but then I’m getting away from my first criteria of keeping things as simple as possible. Infinite Loops To The Rescue I found a way to have a simple console application satisfy all three of my requirements above, and it involves using an infinite loop and some Console.ReadLine calls that will give the user an opportunity to break out and exit the program. (All programs that need to run until they are closed explicitly (or crash!) likely use similar constructs behind the scenes. Create a new Windows Forms project, look in the ‘Program.cs’ that gets generated, and then check out the docs for the Application.Run method that it calls.). Here’s how the main method might look: 1: static void Main(string[] args) 2: { 3: do 4: { 5: Console.Write("Enter command or 'exit' to quit: > "); 6: var command = Console.ReadLine(); 7: if ((command ?? string.Empty).Equals("exit", StringComparison.OrdinalIgnoreCase)) 8: { 9: Console.WriteLine("Quitting."); 10: break; 11: } 12: 13: } while (true); 14: } The idea here is the app prompts me for the command I want to run, or I can type in ‘exit’ to break out of the loop and let the application close. The only trick now is to create a set of commands that map to each of the code samples that I’m going to want to run. Each sample is already encapsulated in a single public method in a separate class, so I could just write a big switch statement or create a hashtable/dictionary that maps command text to an Action that will invoke the proper method, but why re-invent the wheel? CLAP For Your Own Presentation I’ve blogged about the CLAP library before, and it turns out that it’s a great fit for satisfying criteria #3 from my list above. CLAP lets you decorate methods in a class with an attribute and then easily invoke those methods from within a console application. CLAP was designed to take the arguments passed into the console app from the command line and parse them to determine which method to run and what arguments to pass to that method, but there’s no reason you can’t re-purpose it to accept command input from within the infinite loop defined above and invoke the corresponding method. Here’s how you might define a couple of different methods to contain two different code samples that you want to run during your presentation: 1: public static class CodeSamples 2: { 3: [Verb(Aliases="one")] 4: public static void SampleOne() 5: { 6: Console.WriteLine("This is sample 1"); 7: } 8:   9: [Verb(Aliases="two")] 10: public static void SampleTwo() 11: { 12: Console.WriteLine("This is sample 2"); 13: } 14: } A couple of things to note about the sample above: I’m using static methods. You don’t actually need to use static methods with CLAP, but the syntax ends up being a bit simpler and static methods happen to lend themselves well to the “one self-contained method per code sample” approach that I want to use. The methods are decorated with a ‘Verb’ attribute. This tells CLAP that they are eligible targets for commands. The “Aliases” argument lets me give them short and easy-to-remember aliases that can be used to invoke them. By default, CLAP just uses the full method name as the command name, but with aliases you can simply the usage a bit. I’m not using any parameters. CLAP’s main feature is its ability to parse out arguments from a command line invocation of a console application and automatically pass them in as parameters to the target methods. My code samples don’t need parameters ,and honestly having them would complicate giving the presentation, so this is a good thing. You could use this same approach to invoke methods with parameters, but you’d have a couple of things to figure out. When you invoke a .NET application from the command line, Windows will parse the arguments and pass them in as a string array (called ‘args’ in the boilerplate console project Program.cs). The parsing that gets done here is smart enough to deal with things like treating strings in double quotes as one argument, and you’d have to re-create that within your infinite loop if you wanted to use parameters. I plan on either submitting a pull request to CLAP to add this capability or maybe just making a small utility class/extension method to do it and posting that here in the future. So I now have a simple class with static methods to contain my code samples, and an infinite loop in my ‘main’ method that can accept text commands. Wiring this all up together is pretty easy: 1: static void Main(string[] args) 2: { 3: do 4: { 5: try 6: { 7: Console.Write("Enter command or 'exit' to quit: > "); 8: var command = Console.ReadLine(); 9: if ((command ?? string.Empty).Equals("exit", StringComparison.OrdinalIgnoreCase)) 10: { 11: Console.WriteLine("Quitting."); 12: break; 13: } 14:   15: Parser.Run<CodeSamples>(new[] { command }); 16: Console.WriteLine("---------------------------------------------------------"); 17: } 18: catch (Exception ex) 19: { 20: Console.Error.WriteLine("Error: " + ex.Message); 21: } 22:   23: } while (true); 24: } Note that I’m now passing the ‘CodeSamples’ class into the CLAP ‘Parser.Run’ as a type argument. This tells CLAP to inspect that class for methods that might be able to handle the commands passed in. I’m also throwing in a little “----“ style line separator and some basic error handling (because I happen to know that some of the samples are going to throw exceptions for demonstration purposes) and I’m good to go. Now during my presentation I can just have the console application running the whole time with the debugger attached and just type in the alias of the code sample method that I want to run when I want to run it.

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• .NET Code Evolution

  - by Alois Kraus

  Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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• Jquery validation does not stop execution of "code behind" code of asp.net button

  - by shahk26

  Hi, I have a asp.net button which has click event which basically adds data into datbase. I also have a radiobuttonlist(i.e Approve / Decline) and a textbox. If user selects decline, the textbox becomes visible. I want to run validation that when user clicks on submit button, if the decline is selected then the textbox can not blank. I have used jquery validation for that. when I click button, the message apppears next to textbox that the field is required but it does not stop the execution of code behind. i.e.It adds data into database. Here is my code. <script type="text/javascript" language="javascript"> $(function() { $('#declinediv').hide(); //////// var $radBtn = $("table.rblist input:radio"); $radBtn.click(function() { var $radChecked = $(':radio:checked'); var value = $radChecked.val(); if (value == 'Decline' || value == 'Approve') { if (value == 'Decline') $('#declinediv').show(); else $('#declinediv').hide(); } else { $('#declinediv').hide(); } }); ////////////////////////// $("#aspnetForm").validate({ rules: { <%=txtdeclinereason.UniqueID %>: { minlength: 2, required: true } }, messages: { <%=txtdeclinereason.UniqueID %>:{ required: "* Required Field *", minlength: "* Please enter atleast 2 characters *" } }, onsubmit: true }); ////////////////////////////////// $('#btnsubmit').click(function(evt){ var isValid = $("#aspnetForm").valid(); if (!isValid) { evt.preventDefault(); } }); }); function myredirect(v, m, f) { window.location.href = v; } </script> <table style="border: 1px black solid; text-align: center; vertical-align: middle" width="100%"> <tr> <td> <asp:RadioButtonList ID="rbtnlstapprover" runat="server" RepeatDirection="Horizontal" CssClass="rblist" DataTextField="username" DataValueField="emailaddress"> <asp:ListItem Text="Approve" Value="Approve" /> <asp:ListItem Text="Decline" Value="Decline" /> </asp:RadioButtonList> <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="rbtnlstapprover" Text="*" ErrorMessage="Please select atleast one Approver" ValidationGroup="approvalgroup" Display="Dynamic" /> </td> </tr> <tr> <td> <div id="declinediv"> <asp:TextBox ID="txtdeclinereason" runat="server" TextMode="MultiLine" Columns="80" Rows="5" /> </div> </td> </tr> <tr> <td> <asp:Button ID="btnsubmit" runat="server" Text="Submit" CssClass="RegularButton" CausesValidation="true" ValidationGroup="approvalgroup" OnClick="btnsubmit_Click" /> </td> </tr> </table> How do I stop the execution of code behind? Thanks for your help.

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• Need a hand understanding this Java code please :-)

  - by Brian

  Hi all, Just wondering if anyone would be able to take a look at this code for implementing the quicksort algorithm and answer me a few questions, please :-) public class Run { /*************************************************************************** * Quicksort code from Sedgewick 7.1, 7.2. **************************************************************************/ public static void quicksort(double[] a) { //shuffle(a); // to guard against worst-case quicksort(a, 0, a.length - 1, 0); } static void quicksort(final double[] a, final int left, final int right, final int tdepth) { if (right <= left) return; final int i = partition(a, left, right); if ((tdepth < 4) && ((i - left) > 1000)) { final Thread t = new Thread() { public void run() { quicksort(a, left, i - 1, tdepth + 1); } }; t.start(); quicksort(a, i + 1, right, tdepth + 1); try { t.join(); } catch (InterruptedException e) { throw new RuntimeException("Cancelled", e); } } else { quicksort(a, left, i - 1, tdepth); quicksort(a, i + 1, right, tdepth); } } // partition a[left] to a[right], assumes left < right private static int partition(double[] a, int left, int right) { int i = left - 1; int j = right; while (true) { while (less(a[++i], a[right])) // find item on left to swap ; // a[right] acts as sentinel while (less(a[right], a[--j])) // find item on right to swap if (j == left) break; // don't go out-of-bounds if (i >= j) break; // check if pointers cross exch(a, i, j); // swap two elements into place } exch(a, i, right); // swap with partition element return i; } // is x < y ? private static boolean less(double x, double y) { return (x < y); } // exchange a[i] and a[j] private static void exch(double[] a, int i, int j) { double swap = a[i]; a[i] = a[j]; a[j] = swap; } // shuffle the array a[] private static void shuffle(double[] a) { int N = a.length; for (int i = 0; i < N; i++) { int r = i + (int) (Math.random() * (N - i)); // between i and N-1 exch(a, i, r); } } // test client public static void main(String[] args) { int N = 5000000; // Integer.parseInt(args[0]); // generate N random real numbers between 0 and 1 long start = System.currentTimeMillis(); double[] a = new double[N]; for (int i = 0; i < N; i++) a[i] = Math.random(); long stop = System.currentTimeMillis(); double elapsed = (stop - start) / 1000.0; System.out.println("Generating input: " + elapsed + " seconds"); // sort them start = System.currentTimeMillis(); quicksort(a); stop = System.currentTimeMillis(); elapsed = (stop - start) / 1000.0; System.out.println("Quicksort: " + elapsed + " seconds"); } } My questions are: What is the purpose of the variable tdepth? Is this considered a "proper" implementation of a parallel quicksort? I ask becuase it doesn't use implements Runnable or extends Thread... If it doesn't already, is it possible to modify this code to use multiple threads? By passing in the number of threads you want to use as a parameter, for example...? Many thanks, Brian

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• Code Golf: 1x1 black pixel

  - by Joey Adams

  Recently, I used my favorite image editor to make a 1x1 black pixel (which can come in handy when you want to draw solid boxes in HTML cheaply). Even though I made it a monochrome PNG, it came out to be 120 bytes! I mean, that's kind of steep. 120 bytes. For one pixel. I then converted it to a GIF, which dropped the size down to 43 bytes. Much better, but still... Challenge The shortest image file or program that is or generates a 1x1 black pixel. A submission may be: An image file that represents a 1x1 black pixel. The format chosen must be able to represent larger images than 1x1, and cannot be ad-hoc (that is, it can't be an image format you just made up for code golf). Image files will be ranked by byte count. A program that generates such an image file. Programs will be ranked by character count, as usual in code golf. As long as an answer falls into one of these two categories, anything is fair game.

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• Code Golf: Leibniz formula for Pi

  - by Greg Beech

  I recently posted one of my favourite interview whiteboard coding questions in "What's your more controversial programming opinion", which is to write a function that computes Pi using the Leibniz formula. It can be approached in a number of different ways, and the exit condition takes a bit of thought, so I thought it might make an interesting code golf question. Shortest code wins! Given that Pi can be estimated using the function 4 * (1 - 1/3 + 1/5 - 1/7 + ...) with more terms giving greater accuracy, write a function that calculates Pi to within 0.00001. Edit: 3 Jan 2008 As suggested in the comments I changed the exit condition to be within 0.00001 as that's what I really meant (an accuracy 5 decimal places is much harder due to rounding and so I wouldn't want to ask that in an interview, whereas within 0.00001 is an easier to understand and implement exit condition). Also, to answer the comments, I guess my intention was that the solution should compute the number of iterations, or check when it had done enough, but there's nothing to prevent you from pre-computing the number of iterations and using that number. I really asked the question out of interest to see what people would come up with.

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• Programming language shootout: code most like pseudocode for Dijkstra's Algorithm

  - by Casebash

  Okay, so this question here asked which language is most like executable pseudocode, so why not find out by actually writing some code! Here we have a competition where I will award a 100 point bounty (I know its not much, but I am poor after the recalc) to the code which most resembles this pseudocode. I've read through this a few times so I'm pretty sure that this pseudocode below is correct and about as unambiguous as pseudocode can be. Personally, I'm going to have a go in Python and probably Haskell as well, but I'm just learning the later so my attempt will probably be pretty poor. Note: Obviously to implement anything looking like this you'll have to define quite a few library functions. define DirectedGraph G with: Vertices as V, Edges as E define Vertex A, Z declare each e in E as having properties: Boolean fixed with: initial=false Real minSoFar with: initial=0 for A else infinity define PriorityQueue pq with: objects=V initial=A priority v=v.minSoFar create triggers for v in V: when v.minSoFar event reduced then pq.addOrUpdate v when v.fixed event becomesTrue then pq.remove v Repeat until Z.fixed==True: define Vertex U=pq.pop() U.fixed=True for Edge E adjacentTo U with other Vertex V: V.minSoFar=U.minSoFar+length(E) if reducesValue return Z.name, Z.minSoFar

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• Code Golf: Tic Tac Toe

  - by Aistina

  Post your shortest code, by character count, to check if a player has won, and if so, which. Assume you have an integer array in a variable b (board), which holds the Tic Tac Toe board, and the moves of the players where: 0 = nothing set 1 = player 1 (X) 2 = player 2 (O) So, given the array b = [ 1, 2, 1, 0, 1, 2, 1, 0, 2 ] would represent the board X|O|X -+-+- |X|O -+-+- X| |O For that situation, your code should output 1 to indicate player 1 has won. If no-one has won you can output 0 or false. My own (Ruby) solution will be up soon. Edit: Sorry, forgot to mark it as community wiki. You can assume the input is well formed and does not have to be error checked. Update: Please post your solution in the form of a function. Most people have done this already, but some haven't, which isn't entirely fair. The board is supplied to your function as the parameter. The result should be returned by the function. The function can have a name of your choosing.

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• Code Golf: Connect 4

  - by Matthieu M.

  If you don't know the Connect 4 game, follow the link :) I used to play it a lot when I was a child. At least until my little sister got bored with me winning... Anyway I was reading the Code Golf: Tic Tac Toe the other day and I thought that solving the Tic Tac Toe problem was simpler than solving the Connect 4... and wondered how much this would reflect on the number of characters a solution would yield. I thus propose a similar challenge: Find the winner The grid is given under the form of a string meant to passed as a parameter to a function. The goal of the code golf is to write the body of the function, the parameter will be b, of string type The image in the wikipedia article leads to the following representation: "....... ..RY... ..YYYR. ..RRYY. ..RYRY. .YRRRYR" (6 rows of 7 elements) but is obviously incomplete (Yellow has not won yet) There is a winner in the grid passed, no need to do error checking Remember that it might not be exactly 4 The expected output is the letter representing the winner (either R or Y) I expect perl mongers to produce the most unreadable script (along with Ook and whitespace, of course), but I am most interested in reading innovative solutions. I must admit the magic square solution for Tic Tac Toe was my personal fav and I wonder if there is a way to build a similar one with this. Well, happy Easter weekend :) Now I just have a few days to come up with a solution of my own!

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