Search Results

Search found 119079 results on 4764 pages for 'code first migrations'.

Page 377/4764 | < Previous Page | 373 374 375 376 377 378 379 380 381 382 383 384  | Next Page >

• How do I deploy Java code on an EC2 instance?

  - by Marianna

  I just started with Amazon web services, and I have an EC2 instance. I downloaded the JAVA SDK and the Eclipse toolbox. I am able to run a sample program locally on my PC and connect to the Amazon databases, etc. My question is, what do I need to do to get this working on my EC2 instance? This may not even be specific to AWS. On Eclipse, I can just "Run as Application" and run any code. On the server side, what do I need to do? Should I ftp over my .java files? Should I export it to a jar and upload that? Do I need to install anything special to actually run it?

  Read the article

• How do shared hosting servers keep executing code from crossing accounts?

  - by acidzombie24

  I am kind of curious, how does a hosting server support multiple users with php but keep each user away from the other code? The 'easy' solution i thought were file permissions. So every user can have www-data belong to their group and the server would have executing access but the users cant access the others file. But then i realize the user running the php would be www-data who has permission to read everyones data. So how does a shared host prevent this from happening? PS: I personally use nginx (with fastcgi php). But i am somewhat familiar on how apache works.

  Read the article

• Should I store my code/projects on my SSD or my secondary drive?

  - by user37467

  I just got a new box. It has an SSD for the primary drive, and a 1TB SATA for the secondary drive. I'm going to run windows and my binaries on the SSD and keep all my downloads/documents/music/etc on the secondary drive. My question is should I also keep my Visual Studio Projects and code on the SSD or keep them on the secondary drive? The faster SSD would presumably be better for compiling and indexed searches, but would it be better to keep it on the 2nd drive for a more parallel disk IO situation?

  Read the article

• Why might a System.String object not cache its hash code?

  - by Dan Tao

  A glance at the source code for string.GetHashCode using Reflector reveals the following (for mscorlib.dll version 4.0): public override unsafe int GetHashCode() { fixed (char* str = ((char*) this)) { char* chPtr = str; int num = 0x15051505; int num2 = num; int* numPtr = (int*) chPtr; for (int i = this.Length; i > 0; i -= 4) { num = (((num << 5) + num) + (num >> 0x1b)) ^ numPtr[0]; if (i <= 2) { break; } num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr[1]; numPtr += 2; } return (num + (num2 * 0x5d588b65)); } } Now, I realize that the implementation of GetHashCode is not specified and is implementation-dependent, so the question "is GetHashCode implemented in the form of X or Y?" is not really answerable. I'm just curious about a few things: If Reflector has disassembled the DLL correctly and this is the implementation of GetHashCode (in my environment), am I correct in interpreting this code to indicate that a string object, based on this particular implementation, would not cache its hash code? Assuming the answer is yes, why would this be? It seems to me that the memory cost would be minimal (one more 32-bit integer, a drop in the pond compared to the size of the string itself) whereas the savings would be significant, especially in cases where, e.g., strings are used as keys in a hashtable-based collection like a Dictionary<string, [...]>. And since the string class is immutable, it isn't like the value returned by GetHashCode will ever even change. What could I be missing? UPDATE: In response to Andras Zoltan's closing remark: There's also the point made in Tim's answer(+1 there). If he's right, and I think he is, then there's no guarantee that a string is actually immutable after construction, therefore to cache the result would be wrong. Whoa, whoa there! This is an interesting point to make (and yes it's very true), but I really doubt that this was taken into consideration in the implementation of GetHashCode. The statement "therefore to cache the result would be wrong" implies to me that the framework's attitude regarding strings is "Well, they're supposed to be immutable, but really if developers want to get sneaky they're mutable so we'll treat them as such." This is definitely not how the framework views strings. It fully relies on their immutability in so many ways (interning of string literals, assignment of all zero-length strings to string.Empty, etc.) that, basically, if you mutate a string, you're writing code whose behavior is entirely undefined and unpredictable. I guess my point is that for the author(s) of this implementation to worry, "What if this string instance is modified between calls, even though the class as it is publicly exposed is immutable?" would be like for someone planning a casual outdoor BBQ to think to him-/herself, "What if someone brings an atomic bomb to the party?" Look, if someone brings an atom bomb, party's over.

  Read the article

• Different setter behavior between DbContext and ObjectContext

  - by Paul

  (This is using EntityFramework 4.2 CTP) I haven't found any references to this on the web yet, although it's likely I'm using the wrong terminology while searching. There's also a very likely scenario where this is 100% expected behavior, just looking for confirmation and would rather not dig through the tt template (still new to this). Assuming I have a class with a boolean field called Active and I have one row that already has this value set to true. I have code that executes to set said field to True regardless of it's existing value. If I use DbContext to update the value to True no update is made. If I use ObjectContext to update the value an update is made regardless of the existing value. This is happening in the exact same EDMX, all I did was change the code generation template from DbContext to EntityObject. Update: Ok, found the confirmation I was looking for...consider this a dupe...next time I'll do MOAR SEARCHING! Entity Framework: Cancel a property change if no change in value ** Update 2: ** Problem: the default tt template wraps the "if (this != value)" in the setter with "if (iskey), so only primarykey fields receive this logic. Solution: it's not the most graceful thing, but I removed this check...we'll see how it pans out in real usage. I included the entire tt template, my changes are denoted with "**"... //////// //////// Write SimpleType Properties. //////// private void WriteSimpleTypeProperty(EdmProperty simpleProperty, CodeGenerationTools code) { MetadataTools ef = new MetadataTools(this); #> /// <summary> /// <#=SummaryComment(simpleProperty)#> /// </summary><#=LongDescriptionCommentElement(simpleProperty, 1)#> [EdmScalarPropertyAttribute(EntityKeyProperty= <#=code.CreateLiteral(ef.IsKey(simpleProperty))#>, IsNullable=<#=code.CreateLiteral(ef.IsNullable(simpleProperty))#>)] [DataMemberAttribute()] <#=code.SpaceAfter(NewModifier(simpleProperty))#><#=Accessibility.ForProperty(simpleProperty)#> <#=MultiSchemaEscape(simpleProperty.TypeUsage, code)#> <#=code.Escape(simpleProperty)#> { <#=code.SpaceAfter(Accessibility.ForGetter(simpleProperty))#>get { <#+ if (ef.ClrType(simpleProperty.TypeUsage) == typeof(byte[])) { #> return StructuralObject.GetValidValue(<#=code.FieldName(simpleProperty)#>); <#+ } else { #> return <#=code.FieldName(simpleProperty)#>; <#+ } #> } <#=code.SpaceAfter(Accessibility.ForSetter((simpleProperty)))#>set { <#+ **//if (ef.IsKey(simpleProperty)) **//{ if (ef.ClrType(simpleProperty.TypeUsage) == typeof(byte[])) { #> if (!StructuralObject.BinaryEquals(<#=code.FieldName(simpleProperty)#>, value)) <#+ } else { #> if (<#=code.FieldName(simpleProperty)#> != value) <#+ } #> { <#+ PushIndent(CodeRegion.GetIndent(1)); **//} #> <#=ChangingMethodName(simpleProperty)#>(value); ReportPropertyChanging("<#=simpleProperty.Name#>"); <#=code.FieldName(simpleProperty)#> = <#=CastToEnumType(simpleProperty.TypeUsage, code)#>StructuralObject.SetValidValue(<#=CastToUnderlyingType(simpleProperty.TypeUsage, code)#>value<#=OptionalNullableParameterForSetValidValue(simpleProperty, code)#>, "<#=simpleProperty.Name#>"); ReportPropertyChanged("<#=simpleProperty.Name#>"); <#=ChangedMethodName(simpleProperty)#>(); <#+ //if (ef.IsKey(simpleProperty)) //{ PopIndent(); #> } <#+ //} #> } }

  Read the article

• Metro: Promises

  - by Stephen.Walther

  The goal of this blog entry is to describe the Promise class in the WinJS library. You can use promises whenever you need to perform an asynchronous operation such as retrieving data from a remote website or a file from the file system. Promises are used extensively in the WinJS library. Asynchronous Programming Some code executes immediately, some code requires time to complete or might never complete at all. For example, retrieving the value of a local variable is an immediate operation. Retrieving data from a remote website takes longer or might not complete at all. When an operation might take a long time to complete, you should write your code so that it executes asynchronously. Instead of waiting for an operation to complete, you should start the operation and then do something else until you receive a signal that the operation is complete. An analogy. Some telephone customer service lines require you to wait on hold – listening to really bad music – until a customer service representative is available. This is synchronous programming and very wasteful of your time. Some newer customer service lines enable you to enter your telephone number so the customer service representative can call you back when a customer representative becomes available. This approach is much less wasteful of your time because you can do useful things while waiting for the callback. There are several patterns that you can use to write code which executes asynchronously. The most popular pattern in JavaScript is the callback pattern. When you call a function which might take a long time to return a result, you pass a callback function to the function. For example, the following code (which uses jQuery) includes a function named getFlickrPhotos which returns photos from the Flickr website which match a set of tags (such as “dog” and “funny”): function getFlickrPhotos(tags, callback) { $.getJSON( "http://api.flickr.com/services/feeds/photos_public.gne?jsoncallback=?", { tags: tags, tagmode: "all", format: "json" }, function (data) { if (callback) { callback(data.items); } } ); } getFlickrPhotos("funny, dogs", function(data) { $.each(data, function(index, item) { console.log(item); }); }); The getFlickr() function includes a callback parameter. When you call the getFlickr() function, you pass a function to the callback parameter which gets executed when the getFlicker() function finishes retrieving the list of photos from the Flickr web service. In the code above, the callback function simply iterates through the results and writes each result to the console. Using callbacks is a natural way to perform asynchronous programming with JavaScript. Instead of waiting for an operation to complete, sitting there and listening to really bad music, you can get a callback when the operation is complete. Using Promises The CommonJS website defines a promise like this (http://wiki.commonjs.org/wiki/Promises): “Promises provide a well-defined interface for interacting with an object that represents the result of an action that is performed asynchronously, and may or may not be finished at any given point in time. By utilizing a standard interface, different components can return promises for asynchronous actions and consumers can utilize the promises in a predictable manner.” A promise provides a standard pattern for specifying callbacks. In the WinJS library, when you create a promise, you can specify three callbacks: a complete callback, a failure callback, and a progress callback. Promises are used extensively in the WinJS library. The methods in the animation library, the control library, and the binding library all use promises. For example, the xhr() method included in the WinJS base library returns a promise. The xhr() method wraps calls to the standard XmlHttpRequest object in a promise. The following code illustrates how you can use the xhr() method to perform an Ajax request which retrieves a file named Photos.txt: var options = { url: "/data/photos.txt" }; WinJS.xhr(options).then( function (xmlHttpRequest) { console.log("success"); var data = JSON.parse(xmlHttpRequest.responseText); console.log(data); }, function(xmlHttpRequest) { console.log("fail"); }, function(xmlHttpRequest) { console.log("progress"); } ) The WinJS.xhr() method returns a promise. The Promise class includes a then() method which accepts three callback functions: a complete callback, an error callback, and a progress callback: Promise.then(completeCallback, errorCallback, progressCallback) In the code above, three anonymous functions are passed to the then() method. The three callbacks simply write a message to the JavaScript Console. The complete callback also dumps all of the data retrieved from the photos.txt file. Creating Promises You can create your own promises by creating a new instance of the Promise class. The constructor for the Promise class requires a function which accepts three parameters: a complete, error, and progress function parameter. For example, the code below illustrates how you can create a method named wait10Seconds() which returns a promise. The progress function is called every second and the complete function is not called until 10 seconds have passed: (function () { "use strict"; var app = WinJS.Application; function wait10Seconds() { return new WinJS.Promise(function (complete, error, progress) { var seconds = 0; var intervalId = window.setInterval(function () { seconds++; progress(seconds); if (seconds > 9) { window.clearInterval(intervalId); complete(); } }, 1000); }); } app.onactivated = function (eventObject) { if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) { wait10Seconds().then( function () { console.log("complete") }, function () { console.log("error") }, function (seconds) { console.log("progress:" + seconds) } ); } } app.start(); })(); All of the work happens in the constructor function for the promise. The window.setInterval() method is used to execute code every second. Every second, the progress() callback method is called. If more than 10 seconds have passed then the complete() callback method is called and the clearInterval() method is called. When you execute the code above, you can see the output in the Visual Studio JavaScript Console. Creating a Timeout Promise In the previous section, we created a custom Promise which uses the window.setInterval() method to complete the promise after 10 seconds. We really did not need to create a custom promise because the Promise class already includes a static method for returning promises which complete after a certain interval. The code below illustrates how you can use the timeout() method. The timeout() method returns a promise which completes after a certain number of milliseconds. WinJS.Promise.timeout(3000).then( function(){console.log("complete")}, function(){console.log("error")}, function(){console.log("progress")} ); In the code above, the Promise completes after 3 seconds (3000 milliseconds). The Promise returned by the timeout() method does not support progress events. Therefore, the only message written to the console is the message “complete” after 10 seconds. Canceling Promises Some promises, but not all, support cancellation. When you cancel a promise, the promise’s error callback is executed. For example, the following code uses the WinJS.xhr() method to perform an Ajax request. However, immediately after the Ajax request is made, the request is cancelled. // Specify Ajax request options var options = { url: "/data/photos.txt" }; // Make the Ajax request var request = WinJS.xhr(options).then( function (xmlHttpRequest) { console.log("success"); }, function (xmlHttpRequest) { console.log("fail"); }, function (xmlHttpRequest) { console.log("progress"); } ); // Cancel the Ajax request request.cancel(); When you run the code above, the message “fail” is written to the Visual Studio JavaScript Console. Composing Promises You can build promises out of other promises. In other words, you can compose promises. There are two static methods of the Promise class which you can use to compose promises: the join() method and the any() method. When you join promises, a promise is complete when all of the joined promises are complete. When you use the any() method, a promise is complete when any of the promises complete. The following code illustrates how to use the join() method. A new promise is created out of two timeout promises. The new promise does not complete until both of the timeout promises complete: WinJS.Promise.join([WinJS.Promise.timeout(1000), WinJS.Promise.timeout(5000)]) .then(function () { console.log("complete"); }); The message “complete” will not be written to the JavaScript Console until both promises passed to the join() method completes. The message won’t be written for 5 seconds (5,000 milliseconds). The any() method completes when any promise passed to the any() method completes: WinJS.Promise.any([WinJS.Promise.timeout(1000), WinJS.Promise.timeout(5000)]) .then(function () { console.log("complete"); }); The code above writes the message “complete” to the JavaScript Console after 1 second (1,000 milliseconds). The message is written to the JavaScript console immediately after the first promise completes and before the second promise completes. Summary The goal of this blog entry was to describe WinJS promises. First, we discussed how promises enable you to easily write code which performs asynchronous actions. You learned how to use a promise when performing an Ajax request. Next, we discussed how you can create your own promises. You learned how to create a new promise by creating a constructor function with complete, error, and progress parameters. Finally, you learned about several advanced methods of promises. You learned how to use the timeout() method to create promises which complete after an interval of time. You also learned how to cancel promises and compose promises from other promises.

  Read the article

• Visual Studio Shortcut: Surround With

  - by Jeff Widmer

  I learned a new Visual Studio keyboard shortcut today that is really awesome; the “Surround With” shortcut.  You can trigger the Surround With context menu by pressing the Ctrl-K, Ctrl-S key combination when on a line of code. Ctrl-K, Ctrl-S means to hold down the Control key and then press K and then while still holding down the Control key press S. Here is where this comes in handy: You type a line of code and then realize you need to put it within an if statement block. So you type “if” and hit tab twice to insert the if statement code snippet.  Then you highlight the previous line of code that you typed, and then either drag and drop it into the if-then block or cut and paste it.  That is not too bad but it is a lot of extra key clicks and mouse moves. Now try the same with the Surround With keyboard shortcut.  Just highlight that line of code that you just typed and press Ctrl-K, Ctrl-S and choose the if statement code snippet, hit tab, and POW!... you are done!  No more code moving/indenting required. Here is what the Surround With context menu looks like: Just up or down arrow inside the drop down list to the code snippet that you want to surround your currently selected text with.  Did I mention this is AWESOME! Now it is so simple to surround lines of code with an if-then block or a try-catch-finally block... things that usually took several key clicks and maybe one or two mouse moves. And this works in both Visual Studio 2008 and Visual Studio 2010 which means it has been around for a long time and I never knew about it.   Technorati Tags: Visual Studio Keyboard Shortcut

  Read the article

• Click Once Deployment Process and Issue Resolution

  - by Geordie

  Introduction We are adopting Click Once as a deployment standard for Thick .Net application clients.  The latest version of this tool has matured it to a point where it can be used in an enterprise environment.  This guide will identify how to use Click Once deployment and promote code trough the dev, test and production environments. Why Use Click Once over SCCM If we already use SCCM why add Click Once to the deployment options.  The advantages of Click Once are their ability to update the code in a single location and have the update flow automatically down to the user community.  There have been challenges in the past with getting configuration updates to download but these can now be achieved.  With SCCM you can do the same thing but it then needs to be packages and pushed out to users.  Each time a new user is added to an application, time needs to be spent by an administrator, to push out any required application packages.  With Click Once the user would go to a web link and the application and pre requisites will automatically get installed. New Deployment Steps Overview The deployment in an enterprise environment includes several steps as the solution moves through the development life cycle before being released into production.  To make mitigate risk during the release phase, it is important to ensure the solution is not deployed directly into production from the development tools.  Although this is the easiest path, it can introduce untested code into production and result in unexpected results. 1. Deploy the client application to a development web server using Visual Studio 2008 Click Once deployment tools.  Once potential production versions of the solution are being generated, ensure the production install URL is specified when deploying code from Visual Studio.  (For details see ‘Deploying Click Once Code from Visual Studio’) 2. xCopy the code to the test server.  Run the MageUI tool to update the URLs, signing and version numbers to match the test server. (For details see ‘Moving Click Once Code to a new Server without using Visual Studio’) 3. xCopy the code to the production server.  Run the MageUI tool to update the URLs, signing and version numbers to match the production server. The certificate used to sign the code should be provided by a certificate authority that will be trusted by the client machines.  Finally make sure the setup.exe contains the production install URL.  If not redeploy the solution from Visual Studio to the dev environment specifying the production install URL.  Then xcopy the install.exe file from dev to production.  (For details see ‘Moving Click Once Code to a new Server without using Visual Studio’) Detailed Deployment Steps Deploying Click Once Code From Visual Studio Open Visual Studio and create a new WinForms or WPF project.   In the solution explorer right click on the project and select ‘Publish’ in the context menu.   The ‘Publish Wizard’ will start.  Enter the development deployment path.  This could be a local directory or web site.  When first publishing the solution set this to a development web site and Visual basic will create a site with an install.htm page.  Click Next.  Select weather the application will be available both online and offline. Then click Finish. Once the initial deployment is completed, republish the solution this time mapping to the directory that holds the code that was just published.  This time the Publish Wizard contains and additional option.   The setup.exe file that is created has the install URL hardcoded in it.  It is this screen that allows you to specify the URL to use.  At some point a setup.exe file must be generated for production.  Enter the production URL and deploy the solution to the dev folder.  This file can then be saved for latter use in deployment to production.  During development this URL should be pointing to development site to avoid accidently installing the production application. Visual studio will publish the application to the desired location in the process it will create an anonymous ‘pfx’ certificate to sign the deployment configuration files.  A production certificate should be acquired in preparation for deployment to production.   Directory structure created by Visual Studio     Application files created by Visual Studio   Development web site (install.htm) created by Visual Studio Migrating Click Once Code to a new Server without using Visual Studio To migrate the Click Once application code to a new server, a tool called MageUI is needed to modify the .application and .manifest files.  The MageUI tool is usually located – ‘C:\Program Files\Microsoft SDKs\Windows\v6.0A\Bin’ folder or can be downloaded from the web. When deploying to a new environment copy all files in the project folder to the new server.  In this case the ‘ClickOnceSample’ folder and contents.  The old application versions can be deleted, in this case ‘ClickOnceSample_1_0_0_0’ and ‘ClickOnceSample_1_0_0_1’.  Open IIS Manager and create a virtual directory that points to the project folder.  Also make the publish.htm the default web page.   Run the ManeUI tool and then open the .application file in the root project folder (in this case in the ‘ClickOnceSample’ folder). Click on the Deployment Options in the left hand list and update the URL to the new server URL and save the changes.   When MageUI tries to save the file it will prompt for the file to be signed.   This step cannot be bypassed if you want the Click Once deployment to work from a web site.  The easiest solution to this for test is to use the auto generated certificate that Visual Studio created for the project.  This certificate can be found with the project source code.   To save time go to File>Preferences and configure the ‘Use default signing certificate’ fields.   Future deployments will only require application files to be transferred to the new server.  The only difference is then updating the .application file the ‘Version’ must be updated to match the new version and the ‘Application Reference’ has to be update to point to the new .manifest file.     Updating the Configuration File of a Click Once Deployment Package without using Visual Studio When an update to the configuration file is required, modifying the ClickOnceSample.exe.config.deploy file will not result in current users getting the new configurations.  We do not want to go back to Visual Studio and generate a new version as this might introduce unexpected code changes.  A new version of the application can be created by copying the folder (in this case ClickOnceSample_1_0_0_2) and pasting it into the application Files directory.  Rename the directory ‘ClickOnceSample_1_0_0_3’.  In the new folder open the configuration file in notepad and make the configuration changes. Run MageUI and open the manifest file in the newly copied directory (ClickOnceSample_1_0_0_3).   Edit the manifest version to reflect the newly copied files (in this case 1.0.0.3).  Then save the file.  Open the .application file in the root folder.  Again update the version to 1.0.0.3.  Since the file has not changed the Deployment Options/Start Location URL should still be correct.  The application Reference needs to be updated to point to the new versions .manifest file.  Save the file. Next time a user runs the application the new version of the configuration file will be down loaded.  It is worth noting that there are 2 different types of configuration parameter; application and user.  With Click Once deployment the difference is significant.  When an application is downloaded the configuration file is also brought down to the client machine.  The developer may have written code to update the user parameters in the application.  As a result each time a new version of the application is down loaded the user parameters are at risk of being overwritten.  With Click Once deployment the system knows if the user parameters are still the default values.  If they are they will be overwritten with the new default values in the configuration file.  If they have been updated by the user, they will not be overwritten. Settings configuration view in Visual Studio Production Deployment When deploying the code to production it is prudent to disable the development and test deployment sites.  This will allow errors such as incorrect URL to be quickly identified in the initial testing after deployment.  If the sites are active there is no way to know if the application was downloaded from the production deployment and not redirected to test or dev.   Troubleshooting Clicking the install button on the install.htm page fails. Error: URLDownloadToCacheFile failed with HRESULT '-2146697210' Error: An error occurred trying to download <file>   This is due to the setup.exe file pointing to the wrong location. ‘The setup.exe file that is created has the install URL hardcoded in it.  It is this screen that allows you to specify the URL to use.  At some point a setup.exe file must be generated for production.  Enter the production URL and deploy the solution to the dev folder.  This file can then be saved for latter use in deployment to production.  During development this URL should be pointing to development site to avoid accidently installing the production application.’

  Read the article

• Is "White-Board-Coding" inappropriate during interviews?

  - by Eoin Campbell

  This is a somewhat subjective quesiton but I'd love to hear feedback/opinions from either interviewers/interviewees on the topic. We split our technical part into 4 parts. Write Code, Read & Analyse Code, Design Session & Code on the white board. For the last part what we ask interviewees to do is write a small code snippet (4-5 lines) on the whiteboard and explain as they go through it. Let me be clear the purpose is not to catch people out. We're not looking for perfect syntax. Hell it can even be pseudo-code. but the point is to give them a very simple problem and see if their brain can communicate the solution to us. By simple problems I mean "Reverse a string", "FizzBuzz" etc... EDIT Just with regards the comment about Pseudo-Code. We always ask for an explicit language first. We;re a .NET C# house. we've only said "pseudo-code" where someone has been blanking/really struggling with the code. My question is "Is it innappropriate / unreasonable to expect a programmer to write a code snippet on a whiteboard during an interview ?"

  Read the article

• Why unhandled exceptions are useful

  - by Simon Cooper

  It’s the bane of most programmers’ lives – an unhandled exception causes your application or webapp to crash, an ugly dialog gets displayed to the user, and they come complaining to you. Then, somehow, you need to figure out what went wrong. Hopefully, you’ve got a log file, or some other way of reporting unhandled exceptions (obligatory employer plug: SmartAssembly reports an application’s unhandled exceptions straight to you, along with the entire state of the stack and variables at that point). If not, you have to try and replicate it yourself, or do some psychic debugging to try and figure out what’s wrong. However, it’s good that the program crashed. Or, more precisely, it is correct behaviour. An unhandled exception in your application means that, somewhere in your code, there is an assumption that you made that is actually invalid. Coding assumptions Let me explain a bit more. Every method, every line of code you write, depends on implicit assumptions that you have made. Take this following simple method, that copies a collection to an array and includes an item if it isn’t in the collection already, using a supplied IEqualityComparer: public static T[] ToArrayWithItem( ICollection<T> coll, T obj, IEqualityComparer<T> comparer) { // check if the object is in collection already // using the supplied comparer foreach (var item in coll) { if (comparer.Equals(item, obj)) { // it's in the collection already // simply copy the collection to an array // and return it T[] array = new T[coll.Count]; coll.CopyTo(array, 0); return array; } } // not in the collection // copy coll to an array, and add obj to it // then return it T[] array = new T[coll.Count+1]; coll.CopyTo(array, 0); array[array.Length-1] = obj; return array; } What’s all the assumptions made by this fairly simple bit of code? coll is never null comparer is never null coll.CopyTo(array, 0) will copy all the items in the collection into the array, in the order defined for the collection, starting at the first item in the array. The enumerator for coll returns all the items in the collection, in the order defined for the collection comparer.Equals returns true if the items are equal (for whatever definition of ‘equal’ the comparer uses), false otherwise comparer.Equals, coll.CopyTo, and the coll enumerator will never throw an exception or hang for any possible input and any possible values of T coll will have less than 4 billion items in it (this is a built-in limit of the CLR) array won’t be more than 2GB, both on 32 and 64-bit systems, for any possible values of T (again, a limit of the CLR) There are no threads that will modify coll while this method is running and, more esoterically: The C# compiler will compile this code to IL according to the C# specification The CLR and JIT compiler will produce machine code to execute the IL on the user’s computer The computer will execute the machine code correctly That’s a lot of assumptions. Now, it could be that all these assumptions are valid for the situations this method is called. But if this does crash out with an exception, or crash later on, then that shows one of the assumptions has been invalidated somehow. An unhandled exception shows that your code is running in a situation which you did not anticipate, and there is something about how your code runs that you do not understand. Debugging the problem is the process of learning more about the new situation and how your code interacts with it. When you understand the problem, the solution is (usually) obvious. The solution may be a one-line fix, the rewrite of a method or class, or a large-scale refactoring of the codebase, but whatever it is, the fix for the crash will incorporate the new information you’ve gained about your own code, along with the modified assumptions. When code is running with an assumption or invariant it depended on broken, then the result is ‘undefined behaviour’. Anything can happen, up to and including formatting the entire disk or making the user’s computer sentient and start doing a good impression of Skynet. You might think that those can’t happen, but at Halting problem levels of generality, as soon as an assumption the code depended on is broken, the program can do anything. That is why it’s important to fail-fast and stop the program as soon as an invariant is broken, to minimise the damage that is done. What does this mean in practice? To start with, document and check your assumptions. As with most things, there is a level of judgement required. How you check and document your assumptions depends on how the code is used (that’s some more assumptions you’ve made), how likely it is a method will be passed invalid arguments or called in an invalid state, how likely it is the assumptions will be broken, how expensive it is to check the assumptions, and how bad things are likely to get if the assumptions are broken. Now, some assumptions you can assume unless proven otherwise. You can safely assume the C# compiler, CLR, and computer all run the method correctly, unless you have evidence of a compiler, CLR or processor bug. You can also assume that interface implementations work the way you expect them to; implementing an interface is more than simply declaring methods with certain signatures in your type. The behaviour of those methods, and how they work, is part of the interface contract as well. For example, for members of a public API, it is very important to document your assumptions and check your state before running the bulk of the method, throwing ArgumentException, ArgumentNullException, InvalidOperationException, or another exception type as appropriate if the input or state is wrong. For internal and private methods, it is less important. If a private method expects collection items in a certain order, then you don’t necessarily need to explicitly check it in code, but you can add comments or documentation specifying what state you expect the collection to be in at a certain point. That way, anyone debugging your code can immediately see what’s wrong if this does ever become an issue. You can also use DEBUG preprocessor blocks and Debug.Assert to document and check your assumptions without incurring a performance hit in release builds. On my coding soapbox… A few pet peeves of mine around assumptions. Firstly, catch-all try blocks: try { ... } catch { } A catch-all hides exceptions generated by broken assumptions, and lets the program carry on in an unknown state. Later, an exception is likely to be generated due to further broken assumptions due to the unknown state, causing difficulties when debugging as the catch-all has hidden the original problem. It’s much better to let the program crash straight away, so you know where the problem is. You should only use a catch-all if you are sure that any exception generated in the try block is safe to ignore. That’s a pretty big ask! Secondly, using as when you should be casting. Doing this: (obj as IFoo).Method(); or this: IFoo foo = obj as IFoo; ... foo.Method(); when you should be doing this: ((IFoo)obj).Method(); or this: IFoo foo = (IFoo)obj; ... foo.Method(); There’s an assumption here that obj will always implement IFoo. If it doesn’t, then by using as instead of a cast you’ve turned an obvious InvalidCastException at the point of the cast that will probably tell you what type obj actually is, into a non-obvious NullReferenceException at some later point that gives you no information at all. If you believe obj is always an IFoo, then say so in code! Let it fail-fast if not, then it’s far easier to figure out what’s wrong. Thirdly, document your assumptions. If an algorithm depends on a non-trivial relationship between several objects or variables, then say so. A single-line comment will do. Don’t leave it up to whoever’s debugging your code after you to figure it out. Conclusion It’s better to crash out and fail-fast when an assumption is broken. If it doesn’t, then there’s likely to be further crashes along the way that hide the original problem. Or, even worse, your program will be running in an undefined state, where anything can happen. Unhandled exceptions aren’t good per-se, but they give you some very useful information about your code that you didn’t know before. And that can only be a good thing.

  Read the article

• Another Twig Improvements

  - by Ondrej Brejla

  Hi all! We are here again to intorduce you some of our new NetBeans 7.3 features. Today we'll show you some another Twig improvements. So let's start! Code Templates First feature is about Code Templates. We added some basic templates to improve your Editor experience. You will be really fast with it! If someone don't know what Code Templates are, they are piece of code (snippet) which is inserted into editor after typing its abbreviation and pressing Tab key (or another one which you define in Tools -> Options -> Editor -> Code Templates -> Expand Template on) to epxand it. All default Twig Code Templates can be found in Tools -> Options -> Editor -> Code Templates -> Twig Markup. You can add your custom templates there as well. Note: Twig Markup code templates have to be expanded inside Twig delimiters (i.e. { and }). If you try to expand them outside of delimiters, it will not work, because then you are in HTML context. If you want to add a template which will contain Twig delimiter too, you have to add it directly into Tools -> Options -> Editor -> Code Templates -> HTML/XHTML. Don't add them into Twig File, it will not work. Interpolation Coloring The second, minor, feature is, that we know how to colorize Twig Interpolation. It's a small feature, but usefull :-) And that's all for today and as usual, please test it and if you find something strange, don't hesitate to file a new issue (product php, component Twig). Thanks a lot!

  Read the article

• Series On Embedded Development (Part 3) - Runtime Optionality

  - by Darryl Mocek

  What is runtime optionality? Runtime optionality means writing and packaging your code in such a way that all of the features are available at runtime, but aren't loaded and used if the feature isn't used. The code is separate, and you can even remove the code to save persistent storage if you know the feature will not be used. In native programming terms, it's splitting your application into separate shared libraries so you only have to load what you're using, which means it only impacts volatile memory when enabled at runtime. All the functionality is there, but if it's not used at runtime, it's not loaded. A good example of this in Java is JVMTI, Java's Virtual Machine Tool Interface. On smaller, embedded platforms, these libraries may not be there. If the libraries are not there, there's no effect on the runtime as long as you don't try to use the JVMTI features. There is a trade-off between size/performance and flexibility here. Putting code in separate libraries means loading that code will take longer and it will typically take up more persistent space. However, if the code is rarely used, you can save volatile memory by including it in a separate library. You can also use this method in Java by putting rarely-used code into one or more separate JAR's. Loading a JAR and parsing it takes CPU cycles and volatile memory. Putting all of your application's code into a single JAR means more processing for that JAR. Consider putting rarely-used code in a separate library/JAR.

  Read the article

• iphone: Help with AudioToolbox Leak: Stack trace/code included here...

  - by editor guy

  Part of this app is a "Scream" button that plays random screams from cast members of a TV show. I have to bang on the app quite a while to see a memory leak in Instruments, but it's there, occasionally coming up (every 45 seconds to 2 minutes.) The leak is 3.50kb when it occurs. Haven't been able to crack it for several hours. Any help appreciated. Instruments says this is the offending code line: [appSoundPlayer play]; that's linked to from line 9 of the below stack trace: 0 libSystem.B.dylib malloc 1 libSystem.B.dylib pthread_create 2 AudioToolbox CAPThread::Start() 3 AudioToolbox GenericRunLoopThread::Start() 4 AudioToolbox AudioQueueNew(bool, AudioStreamBasicDescription const*, TCACallback const&, CACallbackTarget const&, unsigned long, OpaqueAudioQueue*) 5 AudioToolbox AudioQueueNewOutput 6 AVFoundation allocAudioQueue(AVAudioPlayer, AudioPlayerImpl*) 7 AVFoundation prepareToPlayQueue(AVAudioPlayer*, AudioPlayerImpl*) 8 AVFoundation -[AVAudioPlayer prepareToPlay] 9 Scream Queens -[ScreamViewController scream:] /Users/laptop2/Desktop/ScreamQueens Versions/ScreamQueens25/Scream Queens/Classes/../ScreamViewController.m:210 10 CoreFoundation -[NSObject performSelector:withObject:withObject:] 11 UIKit -[UIApplication sendAction:to:from:forEvent:] 12 UIKit -[UIApplication sendAction:toTarget:fromSender:forEvent:] 13 UIKit -[UIControl sendAction:to:forEvent:] 14 UIKit -[UIControl(Internal) _sendActionsForEvents:withEvent:] 15 UIKit -[UIControl touchesEnded:withEvent:] 16 UIKit -[UIWindow _sendTouchesForEvent:] 17 UIKit -[UIWindow sendEvent:] 18 UIKit -[UIApplication sendEvent:] 19 UIKit _UIApplicationHandleEvent 20 GraphicsServices PurpleEventCallback 21 CoreFoundation CFRunLoopRunSpecific 22 CoreFoundation CFRunLoopRunInMode 23 GraphicsServices GSEventRunModal 24 UIKit -[UIApplication _run] 25 UIKit UIApplicationMain 26 Scream Queens main /Users/laptop2/Desktop/ScreamQueens Versions/ScreamQueens25/Scream Queens/main.m:14 27 Scream Queens start Here's .h: #import <UIKit/UIKit.h> #import <AVFoundation/AVFoundation.h> #import <MediaPlayer/MediaPlayer.h> #import <AudioToolbox/AudioToolbox.h> #import <MessageUI/MessageUI.h> #import <MessageUI/MFMailComposeViewController.h> @interface ScreamViewController : UIViewController <UIApplicationDelegate, AVAudioPlayerDelegate, MFMailComposeViewControllerDelegate> { //AudioPlayer related AVAudioPlayer *appSoundPlayer; NSURL *soundFileURL; BOOL interruptedOnPlayback; BOOL playing; //Scream button related IBOutlet UIButton *screamButton; int currentScreamIndex; NSString *currentScream; NSMutableArray *screams; NSMutableArray *personScreaming; NSMutableArray *photoArray; int currentSayingsIndex; NSString *currentButtonSaying; NSMutableArray *funnyButtonSayings; IBOutlet UILabel *funnyButtonSayingsLabel; IBOutlet UILabel *personScreamingField; IBOutlet UIImageView *personScreamingImage; //Mailing the scream related IBOutlet UILabel *mailStatusMessage; IBOutlet UIButton *shareButton; } //AudioPlayer related @property (nonatomic, retain) AVAudioPlayer *appSoundPlayer; @property (nonatomic, retain) NSURL *soundFileURL; @property (readwrite) BOOL interruptedOnPlayback; @property (readwrite) BOOL playing; //Scream button related @property (nonatomic, retain) UIButton *screamButton; @property (nonatomic, retain) NSMutableArray *screams; @property (nonatomic, retain) NSMutableArray *personScreaming; @property (nonatomic, retain) NSMutableArray *photoArray; @property (nonatomic, retain) UILabel *personScreamingField; @property (nonatomic, retain) UIImageView *personScreamingImage; @property (nonatomic, retain) NSMutableArray *funnyButtonSayings; @property (nonatomic, retain) UILabel *funnyButtonSayingsLabel; //Mailing the scream related @property (nonatomic, retain) IBOutlet UILabel *mailStatusMessage; @property (nonatomic, retain) IBOutlet UIButton *shareButton; //Scream Button - (IBAction) scream: (id) sender; //Mail the scream - (IBAction) showPicker: (id)sender; - (void)displayComposerSheet; - (void)launchMailAppOnDevice; @end Here's the top of .m: #import "ScreamViewController.h" //top of code has Audio session callback function for responding to audio route changes (from Apple's code), then my code continues... @implementation ScreamViewController @synthesize appSoundPlayer; // AVAudioPlayer object for playing the selected scream @synthesize soundFileURL; // Path to the scream @synthesize interruptedOnPlayback; // Was application interrupted during audio playback @synthesize playing; // Track playing/not playing state @synthesize screamButton; //Press this button, girls scream. @synthesize screams; //Mutable array holding strings pointing to sound files of screams. @synthesize personScreaming; //Mutable array tracking the person doing the screaming @synthesize photoArray; //Mutable array holding strings pointing to photos of screaming girls @synthesize personScreamingField; //Field updates to announce which girl is screaming. @synthesize personScreamingImage; //Updates to show image of the screamer. @synthesize funnyButtonSayings; //Mutable array holding the sayings @synthesize funnyButtonSayingsLabel; //Label that updates with the funnyButtonSayings @synthesize mailStatusMessage; //did the email go out @synthesize shareButton; //share scream via email Next line begins the block with the offending code: - (IBAction) scream: (id) sender { //Play a click sound effect SystemSoundID soundID; NSString *sfxPath = [[NSBundle mainBundle] pathForResource:@"aClick" ofType:@"caf"]; AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:sfxPath],&soundID); AudioServicesPlaySystemSound (soundID); // Because someone may slam the scream button over and over, //must stop current sound, then begin next if ([self appSoundPlayer] != nil) { [[self appSoundPlayer] setDelegate:nil]; [[self appSoundPlayer] stop]; [self setAppSoundPlayer: nil]; } //after selecting a random index in the array (did that in View Did Load), //we move to the next scream on each click. //First check... //Are we past the end of the array? if (currentScreamIndex == [screams count]) { currentScreamIndex = 0; } //Get the string at the index in the personScreaming array currentScream = [screams objectAtIndex: currentScreamIndex]; //Get the string at the index in the personScreaming array NSString *screamer = [personScreaming objectAtIndex:currentScreamIndex]; //Log the string to the console NSLog (@"playing scream: %@", screamer); // Display the string in the personScreamingField field NSString *listScreamer = [NSString stringWithFormat:@"scream by: %@", screamer]; [personScreamingField setText:listScreamer]; // Gets the file system path to the scream to play. NSString *soundFilePath = [[NSBundle mainBundle] pathForResource: currentScream ofType: @"caf"]; // Converts the sound's file path to an NSURL object NSURL *newURL = [[NSURL alloc] initFileURLWithPath: soundFilePath]; self.soundFileURL = newURL; [newURL release]; [[AVAudioSession sharedInstance] setDelegate: self]; [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayback error: nil]; // Registers the audio route change listener callback function AudioSessionAddPropertyListener ( kAudioSessionProperty_AudioRouteChange, audioRouteChangeListenerCallback, self ); // Activates the audio session. NSError *activationError = nil; [[AVAudioSession sharedInstance] setActive: YES error: &activationError]; // Instantiates the AVAudioPlayer object, initializing it with the sound AVAudioPlayer *newPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL: soundFileURL error: nil]; //Error check and continue if (newPlayer != nil) { self.appSoundPlayer = newPlayer; [newPlayer release]; [appSoundPlayer prepareToPlay]; [appSoundPlayer setVolume: 1.0]; [appSoundPlayer setDelegate:self]; //NEXT LINE IS FLAGGED BY INSTRUMENTS AS LEAKY [appSoundPlayer play]; playing = YES; //Get the string at the index in the photoArray array NSString *screamerPic = [photoArray objectAtIndex:currentScreamIndex]; //Log the string to the console NSLog (@"displaying photo: %@", screamerPic); // Display the image of the person screaming personScreamingImage.image = [UIImage imageNamed:screamerPic]; //show the share button shareButton.hidden = NO; mailStatusMessage.hidden = NO; mailStatusMessage.text = @"share!"; //Get the string at the index in the funnySayings array currentSayingsIndex = random() % [funnyButtonSayings count]; currentButtonSaying = [funnyButtonSayings objectAtIndex: currentSayingsIndex]; NSString *theSaying = [funnyButtonSayings objectAtIndex:currentSayingsIndex]; [funnyButtonSayingsLabel setText: theSaying]; currentScreamIndex++; } } Here's my dealloc: - (void)dealloc { [appSoundPlayer stop]; [appSoundPlayer release], appSoundPlayer = nil; [screamButton release], screamButton = nil; [mailStatusMessage release], mailStatusMessage = nil; [personScreamingField release], personScreamingField = nil; [personScreamingImage release], personScreamingImage = nil; [funnyButtonSayings release], funnyButtonSayings = nil; [funnyButtonSayingsLabel release], funnyButtonSayingsLabel = nil; [screams release], screams = nil; [personScreaming release], personScreaming = nil; [soundFileURL release]; [super dealloc]; } @end Thanks so much for reading this far! Any input appreciated.

  Read the article

• Something is making my page perform an Ajax call multiple times... [read: I've never been more frust

  - by Jack Webb-Heller

  NOTE: This is a long question. I've explained all the 'basics' at the top and then there's some further (optional) information for if you need it. Hi folks Basically last night this started happening at about 9PM whilst I was trying to restructure my code to make it a bit nicer for the designer to add a few bits to. I tried to fix it until 2AM at which point I gave up. Came back to it this morning, still baffled. I'll be honest with you, I'm a pretty bad Javascript developer. Since starting this project Javascript has been completely new to me and I've just learn as I went along. So please forgive me if my code structure is really bad (perhaps give a couple of pointers on how to improve it?). So, to the problem: to reproduce it, visit http://furnace.howcode.com (it's far from complete). This problem is a little confusing but I'd really appreciate the help. So in the second column you'll see three tabs The 'Newest' tab is selected by default. Scroll to the bottom, and 3 further results should be dynamically fetched via Ajax. Now click on the 'Top Rated' tab. You'll see all the results, but ordered by rating Scroll to the bottom of 'Top Rated'. You'll see SIX results returned. This is where it goes wrong. Only a further three should be returned (there are 18 entries in total). If you're observant you'll notice two 'blocks' of 3 returned. The first 'block' is the second page of results from the 'Newest' tab. The second block is what I just want returned. Did that make any sense? Never mind! So basically I checked this out in Firebug. What happens is, from a 'Clean' page (first load, nothing done) it calls ONE POST request to http://furnace.howcode.com/code/loadmore . But every time you load a new one of the tabs, it makes an ADDITIONAL POST request each time where there should normally only be ONE. So, can you help me? I'd really appreciate it! At this point you could start independent investigation or read on for a little further (optional) information. Thanks! Jack Further Info (may be irrelevant but here for reference): It's almost like there's some Javascript code or something being left behind that duplicates it each time. I thought it might be this code that I use to detect when the browser is scrolled to the bottom: var col = $('#col2'); col.scroll(function(){ if (col.outerHeight() == (col.get(0).scrollHeight - col.scrollTop())) loadMore(1); }); So what I thought was that code was left behind, and so every time you scroll #col2 (which contains different data for each tab) it detected that and added it for #newest as well. So, I made each tab click give #col2 a dynamic class - either .newestcol, .featuredcol, or .topratedcol. And then I changed the var col=$('.newestcol');dynamically so it would only detect it individually for each tab (makin' any sense?!). But hey, that didn't do anything. Another useful tidbit: here's the PHP for http://furnace.howcode.com/code/loadmore: $kind = $this->input->post('kind'); if ($kind == 1){ // kind is 1 - newest $start = $this->input->post('currentpage'); $data['query'] = "SELECT code.id AS codeid, code.title AS codetitle, code.summary AS codesummary, code.author AS codeauthor, code.rating AS rating, code.date, code_tags.*, tags.*, users.firstname AS authorname, users.id AS authorid, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS taggroup FROM code, code_tags, tags, users WHERE users.id = code.author AND code_tags.code_id = code.id AND tags.id = code_tags.tag_id GROUP BY code_id ORDER BY date DESC LIMIT $start, 15 "; $this->load->view('code/ajaxlist',$data); } elseif ($kind == 2) { // kind is 2 - featured So my jQuery code sends a variable 'kind'. If it's 1, it runs the query for Newest, etc. etc. The PHP code for furnace.howcode.com/code/ajaxlist is: <?php // Our query base // SELECT * FROM code ORDER BY date DESC $query = $this->db->query($query); foreach($query->result() as $row) { ?> <script type="text/javascript"> $('#title-<?php echo $row->codeid;?>').click(function() { var form_data = { id: <?php echo $row->codeid; ?> }; $('#col3').fadeOut('slow', function() { $.ajax({ url: "<?php echo site_url('code/viewajax');?>", type: 'POST', data: form_data, success: function(msg) { $('#col3').html(msg); $('#col3').fadeIn('fast'); } }); }); }); </script> <div class="result"> <div class="resulttext"> <div id="title-<?php echo $row->codeid; ?>" class="title"> <?php echo anchor('#',$row->codetitle); ?> </div> <div class="summary"> <?php echo $row->codesummary; ?> </div> <!-- Now insert the 5-star rating system --> <?php include($_SERVER['DOCUMENT_ROOT']."/fivestars/5star.php");?> <div class="bottom"> <div class="author"> Submitted by <?php echo anchor('auth/profile/'.$row->authorid,''.$row->authorname);?> </div> <?php // Now we need to take the GROUP_CONCATted tags and split them using the magic of PHP into seperate tags $tagarray = explode(", ", $row->taggroup); foreach ($tagarray as $tag) { ?> <div class="tagbutton" href="#"> <span><?php echo $tag; ?></span> </div> <?php } ?> </div> </div> </div> <?php } echo "&nbsp;";?> <script type="text/javascript"> var newpage = <?php echo $this->input->post('currentpage') + 15;?>; </script> So that's everything in PHP. The rest you should be able to view with Firebug or by viewing the Source code. I've put all the Tab/clicking/Ajaxloading bits in the tags at the very bottom. There's a comment before it all kicks off. Thanks so much for your help!

  Read the article

• C#/.NET Little Wonders: The Concurrent Collections (1 of 3)

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In the next few weeks, we will discuss the concurrent collections and how they have changed the face of concurrent programming. This week’s post will begin with a general introduction and discuss the ConcurrentStack<T> and ConcurrentQueue<T>.  Then in the following post we’ll discuss the ConcurrentDictionary<T> and ConcurrentBag<T>.  Finally, we shall close on the third post with a discussion of the BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. A brief history of collections In the beginning was the .NET 1.0 Framework.  And out of this framework emerged the System.Collections namespace, and it was good.  It contained all the basic things a growing programming language needs like the ArrayList and Hashtable collections.  The main problem, of course, with these original collections is that they held items of type object which means you had to be disciplined enough to use them correctly or you could end up with runtime errors if you got an object of a type you weren't expecting. Then came .NET 2.0 and generics and our world changed forever!  With generics the C# language finally got an equivalent of the very powerful C++ templates.  As such, the System.Collections.Generic was born and we got type-safe versions of all are favorite collections.  The List<T> succeeded the ArrayList and the Dictionary<TKey,TValue> succeeded the Hashtable and so on.  The new versions of the library were not only safer because they checked types at compile-time, in many cases they were more performant as well.  So much so that it's Microsoft's recommendation that the System.Collections original collections only be used for backwards compatibility. So we as developers came to know and love the generic collections and took them into our hearts and embraced them.  The problem is, thread safety in both the original collections and the generic collections can be problematic, for very different reasons. Now, if you are only doing single-threaded development you may not care – after all, no locking is required.  Even if you do have multiple threads, if a collection is “load-once, read-many” you don’t need to do anything to protect that container from multi-threaded access, as illustrated below: 1: public static class OrderTypeTranslator 2: { 3: // because this dictionary is loaded once before it is ever accessed, we don't need to synchronize 4: // multi-threaded read access 5: private static readonly Dictionary<string, char> _translator = new Dictionary<string, char> 6: { 7: {"New", 'N'}, 8: {"Update", 'U'}, 9: {"Cancel", 'X'} 10: }; 11:  12: // the only public interface into the dictionary is for reading, so inherently thread-safe 13: public static char? Translate(string orderType) 14: { 15: char charValue; 16: if (_translator.TryGetValue(orderType, out charValue)) 17: { 18: return charValue; 19: } 20:  21: return null; 22: } 23: } Unfortunately, most of our computer science problems cannot get by with just single-threaded applications or with multi-threading in a load-once manner.  Looking at  today's trends, it's clear to see that computers are not so much getting faster because of faster processor speeds -- we've nearly reached the limits we can push through with today's technologies -- but more because we're adding more cores to the boxes.  With this new hardware paradigm, it is even more important to use multi-threaded applications to take full advantage of parallel processing to achieve higher application speeds. So let's look at how to use collections in a thread-safe manner. Using historical collections in a concurrent fashion The early .NET collections (System.Collections) had a Synchronized() static method that could be used to wrap the early collections to make them completely thread-safe.  This paradigm was dropped in the generic collections (System.Collections.Generic) because having a synchronized wrapper resulted in atomic locks for all operations, which could prove overkill in many multithreading situations.  Thus the paradigm shifted to having the user of the collection specify their own locking, usually with an external object: 1: public class OrderAggregator 2: { 3: private static readonly Dictionary<string, List<Order>> _orders = new Dictionary<string, List<Order>>(); 4: private static readonly _orderLock = new object(); 5:  6: public void Add(string accountNumber, Order newOrder) 7: { 8: List<Order> ordersForAccount; 9:  10: // a complex operation like this should all be protected 11: lock (_orderLock) 12: { 13: if (!_orders.TryGetValue(accountNumber, out ordersForAccount)) 14: { 15: _orders.Add(accountNumber, ordersForAccount = new List<Order>()); 16: } 17:  18: ordersForAccount.Add(newOrder); 19: } 20: } 21: } Notice how we’re performing several operations on the dictionary under one lock.  With the Synchronized() static methods of the early collections, you wouldn’t be able to specify this level of locking (a more macro-level).  So in the generic collections, it was decided that if a user needed synchronization, they could implement their own locking scheme instead so that they could provide synchronization as needed. The need for better concurrent access to collections Here’s the problem: it’s relatively easy to write a collection that locks itself down completely for access, but anything more complex than that can be difficult and error-prone to write, and much less to make it perform efficiently!  For example, what if you have a Dictionary that has frequent reads but in-frequent updates?  Do you want to lock down the entire Dictionary for every access?  This would be overkill and would prevent concurrent reads.  In such cases you could use something like a ReaderWriterLockSlim which allows for multiple readers in a lock, and then once a writer grabs the lock it blocks all further readers until the writer is done (in a nutshell).  This is all very complex stuff to consider. Fortunately, this is where the Concurrent Collections come in.  The Parallel Computing Platform team at Microsoft went through great pains to determine how to make a set of concurrent collections that would have the best performance characteristics for general case multi-threaded use. Now, as in all things involving threading, you should always make sure you evaluate all your container options based on the particular usage scenario and the degree of parallelism you wish to acheive. This article should not be taken to understand that these collections are always supperior to the generic collections. Each fills a particular need for a particular situation. Understanding what each container is optimized for is key to the success of your application whether it be single-threaded or multi-threaded. General points to consider with the concurrent collections The MSDN points out that the concurrent collections all support the ICollection interface. However, since the collections are already synchronized, the IsSynchronized property always returns false, and SyncRoot always returns null.  Thus you should not attempt to use these properties for synchronization purposes. Note that since the concurrent collections also may have different operations than the traditional data structures you may be used to.  Now you may ask why they did this, but it was done out of necessity to keep operations safe and atomic.  For example, in order to do a Pop() on a stack you have to know the stack is non-empty, but between the time you check the stack’s IsEmpty property and then do the Pop() another thread may have come in and made the stack empty!  This is why some of the traditional operations have been changed to make them safe for concurrent use. In addition, some properties and methods in the concurrent collections achieve concurrency by creating a snapshot of the collection, which means that some operations that were traditionally O(1) may now be O(n) in the concurrent models.  I’ll try to point these out as we talk about each collection so you can be aware of any potential performance impacts.  Finally, all the concurrent containers are safe for enumeration even while being modified, but some of the containers support this in different ways (snapshot vs. dirty iteration).  Once again I’ll highlight how thread-safe enumeration works for each collection. ConcurrentStack<T>: The thread-safe LIFO container The ConcurrentStack<T> is the thread-safe counterpart to the System.Collections.Generic.Stack<T>, which as you may remember is your standard last-in-first-out container.  If you think of algorithms that favor stack usage (for example, depth-first searches of graphs and trees) then you can see how using a thread-safe stack would be of benefit. The ConcurrentStack<T> achieves thread-safe access by using System.Threading.Interlocked operations.  This means that the multi-threaded access to the stack requires no traditional locking and is very, very fast! For the most part, the ConcurrentStack<T> behaves like it’s Stack<T> counterpart with a few differences: Pop() was removed in favor of TryPop() Returns true if an item existed and was popped and false if empty. PushRange() and TryPopRange() were added Allows you to push multiple items and pop multiple items atomically. Count takes a snapshot of the stack and then counts the items. This means it is a O(n) operation, if you just want to check for an empty stack, call IsEmpty instead which is O(1). ToArray() and GetEnumerator() both also take snapshots. This means that iteration over a stack will give you a static view at the time of the call and will not reflect updates. Pushing on a ConcurrentStack<T> works just like you’d expect except for the aforementioned PushRange() method that was added to allow you to push a range of items concurrently. 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: // but you can also push multiple items in one atomic operation (no interleaves) 7: stack.PushRange(new [] { "Second", "Third", "Fourth" }); For looking at the top item of the stack (without removing it) the Peek() method has been removed in favor of a TryPeek().  This is because in order to do a peek the stack must be non-empty, but between the time you check for empty and the time you execute the peek the stack contents may have changed.  Thus the TryPeek() was created to be an atomic check for empty, and then peek if not empty: 1: // to look at top item of stack without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (stack.TryPeek(out item)) 5: { 6: Console.WriteLine("Top item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Stack was empty."); 11: } Finally, to remove items from the stack, we have the TryPop() for single, and TryPopRange() for multiple items.  Just like the TryPeek(), these operations replace Pop() since we need to ensure atomically that the stack is non-empty before we pop from it: 1: // to remove items, use TryPop or TryPopRange to get multiple items atomically (no interleaves) 2: if (stack.TryPop(out item)) 3: { 4: Console.WriteLine("Popped " + item); 5: } 6:  7: // TryPopRange will only pop up to the number of spaces in the array, the actual number popped is returned. 8: var poppedItems = new string[2]; 9: int numPopped = stack.TryPopRange(poppedItems); 10:  11: foreach (var theItem in poppedItems.Take(numPopped)) 12: { 13: Console.WriteLine("Popped " + theItem); 14: } Finally, note that as stated before, GetEnumerator() and ToArray() gets a snapshot of the data at the time of the call.  That means if you are enumerating the stack you will get a snapshot of the stack at the time of the call.  This is illustrated below: 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: var results = stack.GetEnumerator(); 7:  8: // but you can also push multiple items in one atomic operation (no interleaves) 9: stack.PushRange(new [] { "Second", "Third", "Fourth" }); 10:  11: while(results.MoveNext()) 12: { 13: Console.WriteLine("Stack only has: " + results.Current); 14: } The only item that will be printed out in the above code is "First" because the snapshot was taken before the other items were added. This may sound like an issue, but it’s really for safety and is more correct.  You don’t want to enumerate a stack and have half a view of the stack before an update and half a view of the stack after an update, after all.  In addition, note that this is still thread-safe, whereas iterating through a non-concurrent collection while updating it in the old collections would cause an exception. ConcurrentQueue<T>: The thread-safe FIFO container The ConcurrentQueue<T> is the thread-safe counterpart of the System.Collections.Generic.Queue<T> class.  The concurrent queue uses an underlying list of small arrays and lock-free System.Threading.Interlocked operations on the head and tail arrays.  Once again, this allows us to do thread-safe operations without the need for heavy locks! The ConcurrentQueue<T> (like the ConcurrentStack<T>) has some departures from the non-concurrent counterpart.  Most notably: Dequeue() was removed in favor of TryDequeue(). Returns true if an item existed and was dequeued and false if empty. Count does not take a snapshot It subtracts the head and tail index to get the count.  This results overall in a O(1) complexity which is quite good.  It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. ToArray() and GetEnumerator() both take snapshots. This means that iteration over a queue will give you a static view at the time of the call and will not reflect updates. The Enqueue() method on the ConcurrentQueue<T> works much the same as the generic Queue<T>: 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5: queue.Enqueue("Second"); 6: queue.Enqueue("Third"); For front item access, the TryPeek() method must be used to attempt to see the first item if the queue.  There is no Peek() method since, as you’ll remember, we can only peek on a non-empty queue, so we must have an atomic TryPeek() that checks for empty and then returns the first item if the queue is non-empty. 1: // to look at first item in queue without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (queue.TryPeek(out item)) 5: { 6: Console.WriteLine("First item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Queue was empty."); 11: } Then, to remove items you use TryDequeue().  Once again this is for the same reason we have TryPeek() and not Peek(): 1: // to remove items, use TryDequeue. If queue is empty returns false. 2: if (queue.TryDequeue(out item)) 3: { 4: Console.WriteLine("Dequeued first item " + item); 5: } Just like the concurrent stack, the ConcurrentQueue<T> takes a snapshot when you call ToArray() or GetEnumerator() which means that subsequent updates to the queue will not be seen when you iterate over the results.  Thus once again the code below will only show the first item, since the other items were added after the snapshot. 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5:  6: var iterator = queue.GetEnumerator(); 7:  8: queue.Enqueue("Second"); 9: queue.Enqueue("Third"); 10:  11: // only shows First 12: while (iterator.MoveNext()) 13: { 14: Console.WriteLine("Dequeued item " + iterator.Current); 15: } Using collections concurrently You’ll notice in the examples above I stuck to using single-threaded examples so as to make them deterministic and the results obvious.  Of course, if we used these collections in a truly multi-threaded way the results would be less deterministic, but would still be thread-safe and with no locking on your part required! For example, say you have an order processor that takes an IEnumerable<Order> and handles each other in a multi-threaded fashion, then groups the responses together in a concurrent collection for aggregation.  This can be done easily with the TPL’s Parallel.ForEach(): 1: public static IEnumerable<OrderResult> ProcessOrders(IEnumerable<Order> orderList) 2: { 3: var proxy = new OrderProxy(); 4: var results = new ConcurrentQueue<OrderResult>(); 5:  6: // notice that we can process all these in parallel and put the results 7: // into our concurrent collection without needing any external locking! 8: Parallel.ForEach(orderList, 9: order => 10: { 11: var result = proxy.PlaceOrder(order); 12:  13: results.Enqueue(result); 14: }); 15:  16: return results; 17: } Summary Obviously, if you do not need multi-threaded safety, you don’t need to use these collections, but when you do need multi-threaded collections these are just the ticket! The plethora of features (I always think of the movie The Three Amigos when I say plethora) built into these containers and the amazing way they acheive thread-safe access in an efficient manner is wonderful to behold. Stay tuned next week where we’ll continue our discussion with the ConcurrentBag<T> and the ConcurrentDictionary<TKey,TValue>. For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here.   Tweet Technorati Tags: C#,.NET,Concurrent Collections,Collections,Multi-Threading,Little Wonders,BlackRabbitCoder,James Michael Hare

  Read the article

• SpaceX’s Falcon 9 Launch Success And Reusable Rockets Test Partially Successful

  - by Gopinath

  Elon Musk’s SpaceX is closing on the dream of developing reusable rockets and likely in an year or two space launch rockets will be reusable just like flights, ships and cars. Today SpaceX launched an upgraded Falcon 9 rocket in to space to deliver satellites as well as to test their reusable rocket launching technology. All on board satellites were released on to the orbit and the first stage of rocket partially succeeded in returning back to Earth. This is a huge leap in space technology.   Couple of years ago reusable rockets were considered as impossible. NASA, Russian Space Agency, China, India or for that matter any other space agency never even attempted to build reusable rockets. But SpaceX’s revolutionary technology partially succeeded in doing the impossible! Elon Musk founded SpaceX with the goal of building reusable rockets and transporting humans to & from other planets like Mars. He says If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred.  A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space. Normally the first stage of a rocket falls back to Earth after burning out and is destroyed. But today SpaceX reignited first stage rocket after its separation and attempted to descend smoothly on to ocean’s surface. Though it did not fully succeed, the test was partially successful and SpaceX was able to recovers portions of first stage. Rocket booster relit twice (supersonic retro & landing), but spun up due to aero torque, so fuel centrifuged & we flamed out — Elon Musk (@elonmusk) September 29, 2013 With the partial success of recovering first stage, SpaceX gathered huge amount of information and experience it can use to improve Falcon 9 and build a fully reusable rocket. In post launch press conference Musk said if things go "super well", could refly a Falcon 9 1st stage by the end of next year. Falcon 9 Launch Video Next reusable first tests delayed by at least two launches SpaceX has a busy schedule for next several months with more than 50 missions scheduled using the new Falcon 9 rocket. Ten of those missions are to fly cargo to the International Space Shuttle for NASA.  SpaceX announced that they will not attempt to recover the first stage of Falcon 9 in next two missions. The next test will be conducted on  the fourth mission of Falcon 9 which is planned to carry cargo to Internation Space Station sometime next year. This will give time required for SpaceX to analyze the information gathered from today’s mission and improve first stage reentry systems. More reading Here are few interesting sources to read more about today’s SpaceX launch SpaceX post mission press conference details and discussion on Reddit Giant Leaps for Space Firms Orbital, SpaceX Hacker News community discussion on SpaceX launch SpaceX Launches Next-Generation Private Falcon 9 Rocket on Big Test Flight

  Read the article

• The SSIS tuning tip that everyone misses

  - by Rob Farley

  I know that everyone misses this, because I’m yet to find someone who doesn’t have a bit of an epiphany when I describe this. When tuning Data Flows in SQL Server Integration Services, people see the Data Flow as moving from the Source to the Destination, passing through a number of transformations. What people don’t consider is the Source, getting the data out of a database. Remember, the source of data for your Data Flow is not your Source Component. It’s wherever the data is, within your database, probably on a disk somewhere. You need to tune your query to optimise it for SSIS, and this is what most people fail to do. I’m not suggesting that people don’t tune their queries – there’s plenty of information out there about making sure that your queries run as fast as possible. But for SSIS, it’s not about how fast your query runs. Let me say that again, but in bolder text: The speed of an SSIS Source is not about how fast your query runs. If your query is used in a Source component for SSIS, the thing that matters is how fast it starts returning data. In particular, those first 10,000 rows to populate that first buffer, ready to pass down the rest of the transformations on its way to the Destination. Let’s look at a very simple query as an example, using the AdventureWorks database: We’re picking the different Weight values out of the Product table, and it’s doing this by scanning the table and doing a Sort. It’s a Distinct Sort, which means that the duplicates are discarded. It'll be no surprise to see that the data produced is sorted. Obvious, I know, but I'm making a comparison to what I'll do later. Before I explain the problem here, let me jump back into the SSIS world... If you’ve investigated how to tune an SSIS flow, then you’ll know that some SSIS Data Flow Transformations are known to be Blocking, some are Partially Blocking, and some are simply Row transformations. Take the SSIS Sort transformation, for example. I’m using a larger data set for this, because my small list of Weights won’t demonstrate it well enough. Seven buffers of data came out of the source, but none of them could be pushed past the Sort operator, just in case the last buffer contained the data that would be sorted into the first buffer. This is a blocking operation. Back in the land of T-SQL, we consider our Distinct Sort operator. It’s also blocking. It won’t let data through until it’s seen all of it. If you weren’t okay with blocking operations in SSIS, why would you be happy with them in an execution plan? The source of your data is not your OLE DB Source. Remember this. The source of your data is the NCIX/CIX/Heap from which it’s being pulled. Picture it like this... the data flowing from the Clustered Index, through the Distinct Sort operator, into the SELECT operator, where a series of SSIS Buffers are populated, flowing (as they get full) down through the SSIS transformations. Alright, I know that I’m taking some liberties here, because the two queries aren’t the same, but consider the visual. The data is flowing from your disk and through your execution plan before it reaches SSIS, so you could easily find that a blocking operation in your plan is just as painful as a blocking operation in your SSIS Data Flow. Luckily, T-SQL gives us a brilliant query hint to help avoid this. OPTION (FAST 10000) This hint means that it will choose a query which will optimise for the first 10,000 rows – the default SSIS buffer size. And the effect can be quite significant. First let’s consider a simple example, then we’ll look at a larger one. Consider our weights. We don’t have 10,000, so I’m going to use OPTION (FAST 1) instead. You’ll notice that the query is more expensive, using a Flow Distinct operator instead of the Distinct Sort. This operator is consuming 84% of the query, instead of the 59% we saw from the Distinct Sort. But the first row could be returned quicker – a Flow Distinct operator is non-blocking. The data here isn’t sorted, of course. It’s in the same order that it came out of the index, just with duplicates removed. As soon as a Flow Distinct sees a value that it hasn’t come across before, it pushes it out to the operator on its left. It still has to maintain the list of what it’s seen so far, but by handling it one row at a time, it can push rows through quicker. Overall, it’s a lot more work than the Distinct Sort, but if the priority is the first few rows, then perhaps that’s exactly what we want. The Query Optimizer seems to do this by optimising the query as if there were only one row coming through: This 1 row estimation is caused by the Query Optimizer imagining the SELECT operation saying “Give me one row” first, and this message being passed all the way along. The request might not make it all the way back to the source, but in my simple example, it does. I hope this simple example has helped you understand the significance of the blocking operator. Now I’m going to show you an example on a much larger data set. This data was fetching about 780,000 rows, and these are the Estimated Plans. The data needed to be Sorted, to support further SSIS operations that needed that. First, without the hint. ...and now with OPTION (FAST 10000): A very different plan, I’m sure you’ll agree. In case you’re curious, those arrows in the top one are 780,000 rows in size. In the second, they’re estimated to be 10,000, although the Actual figures end up being 780,000. The top one definitely runs faster. It finished several times faster than the second one. With the amount of data being considered, these numbers were in minutes. Look at the second one – it’s doing Nested Loops, across 780,000 rows! That’s not generally recommended at all. That’s “Go and make yourself a coffee” time. In this case, it was about six or seven minutes. The faster one finished in about a minute. But in SSIS-land, things are different. The particular data flow that was consuming this data was significant. It was being pumped into a Script Component to process each row based on previous rows, creating about a dozen different flows. The data flow would take roughly ten minutes to run – ten minutes from when the data first appeared. The query that completes faster – chosen by the Query Optimizer with no hints, based on accurate statistics (rather than pretending the numbers are smaller) – would take a minute to start getting the data into SSIS, at which point the ten-minute flow would start, taking eleven minutes to complete. The query that took longer – chosen by the Query Optimizer pretending it only wanted the first 10,000 rows – would take only ten seconds to fill the first buffer. Despite the fact that it might have taken the database another six or seven minutes to get the data out, SSIS didn’t care. Every time it wanted the next buffer of data, it was already available, and the whole process finished in about ten minutes and ten seconds. When debugging SSIS, you run the package, and sit there waiting to see the Debug information start appearing. You look for the numbers on the data flow, and seeing operators going Yellow and Green. Without the hint, I’d sit there for a minute. With the hint, just ten seconds. You can imagine which one I preferred. By adding this hint, it felt like a magic wand had been waved across the query, to make it run several times faster. It wasn’t the case at all – but it felt like it to SSIS.

  Read the article

• SQL University: What and why of database refactoring

  - by Mladen Prajdic

  This is a post for a great idea called SQL University started by Jorge Segarra also famously known as SqlChicken on Twitter. It’s a collection of blog posts on different database related topics contributed by several smart people all over the world. So this week is mine and we’ll be talking about database testing and refactoring. In 3 posts we’ll cover: SQLU part 1 - What and why of database testing SQLU part 2 - What and why of database refactoring SQLU part 3 - Tools of the trade This is a second part of the series and in it we’ll take a look at what database refactoring is and why do it. Why refactor a database To know why refactor we first have to know what refactoring actually is. Code refactoring is a process where we change module internals in a way that does not change that module’s input/output behavior. For successful refactoring there is one crucial thing we absolutely must have: Tests. Automated unit tests are the only guarantee we have that we haven’t broken the input/output behavior before refactoring. If you haven’t go back ad read my post on the matter. Then start writing them. Next thing you need is a code module. Those are views, UDFs and stored procedures. By having direct table access we can kiss fast and sweet refactoring good bye. One more point to have a database abstraction layer. And no, ORM’s don’t fall into that category. But also know that refactoring is NOT adding new functionality to your code. Many have fallen into this trap. Don’t be one of them and resist the lure of the dark side. And it’s a strong lure. We developers in general love to add new stuff to our code, but hate fixing our own mistakes or changing existing code for no apparent reason. To be a good refactorer one needs discipline and focus. Now we know that refactoring is all about changing inner workings of existing code. This can be due to performance optimizations, changing internal code workflows or some other reason. This is a typical black box scenario to the outside world. If we upgrade the car engine it still has to drive on the road (preferably faster) and not fly (no matter how cool that would be). Also be aware that white box tests will break when we refactor. What to refactor in a database Refactoring databases doesn’t happen that often but when it does it can include a lot of stuff. Let us look at a few common cases. Adding or removing database schema objects Adding, removing or changing table columns in any way, adding constraints, keys, etc… All of these can be counted as internal changes not visible to the data consumer. But each of these carries a potential input/output behavior change. Dropping a column can result in views not working anymore or stored procedure logic crashing. Adding a unique constraint shows duplicated data that shouldn’t exist. Foreign keys break a truncate table command executed from an application that runs once a month. All these scenarios are very real and can happen. With the proper database abstraction layer fully covered with black box tests we can make sure something like that does not happen (hopefully at all). Changing physical structures Physical structures include heaps, indexes and partitions. We can pretty much add or remove those without changing the data returned by the database. But the performance can be affected. So here we use our performance tests. We do have them, right? Just by adding a single index we can achieve orders of magnitude performance improvement. Won’t that make users happy? But what if that index causes our write operations to crawl to a stop. again we have to test this. There are a lot of things to think about and have tests for. Without tests we can’t do successful refactoring! Fixing bad code We all have some bad code in our systems. We usually refer to that code as code smell as they violate good coding practices. Examples of such code smells are SQL injection, use of SELECT *, scalar UDFs or cursors, etc… Each of those is huge code smell and can result in major code changes. Take SELECT * from example. If we remove a column from a table the client using that SELECT * statement won’t have a clue about that until it runs. Then it will gracefully crash and burn. Not to mention the widely unknown SELECT * view refresh problem that Tomas LaRock (@SQLRockstar on Twitter) and Colin Stasiuk (@BenchmarkIT on Twitter) talk about in detail. Go read about it, it’s informative. Refactoring this includes replacing the * with column names and most likely change to application using the database. Breaking apart huge stored procedures Have you ever seen seen a stored procedure that was 2000 lines long? I have. It’s not pretty. It hurts the eyes and sucks the will to live the next 10 minutes. They are a maintenance nightmare and turn into things no one dares to touch. I’m willing to bet that 100% of time they don’t have a single test on them. Large stored procedures (and functions) are a clear sign that they contain business logic. General opinion on good database coding practices says that business logic has no business in the database. That’s the applications part. Refactoring such behemoths requires writing lots of edge case tests for the stored procedure input/output behavior and then start to refactor it. First we split the logic inside into smaller parts like new stored procedures and UDFs. Those then get called from the master stored procedure. Once we’ve successfully modularized the database code it’s best to transfer that logic into the applications consuming it. This only leaves the stored procedure with common data manipulation logic. Of course this isn’t always possible so having a plethora of performance and behavior unit tests is absolutely necessary to confirm we’ve actually improved the codebase in some way.   Refactoring is not a popular chore amongst developers or managers. The former don’t like fixing old code, the latter can’t see the financial benefit. Remember how we talked about being lousy at estimating future costs in the previous post? But there comes a time when it must be done. Hopefully I’ve given you some ideas how to get started. In the last post of the series we’ll take a look at the tools to use and an example of testing and refactoring.

  Read the article

• Source-control 'wet-work'?

  - by Phil Factor

  When a design or creative work is flawed beyond remedy, it is often best to destroy it and start again. The other day, I lost the code to a long and intricate SQL batch I was working on. I’d thought it was impossible, but it happened. With all the technology around that is designed to prevent this occurring, this sort of accident has become a rare event.  If it weren’t for a deranged laptop, and my distraction, the code wouldn’t have been lost this time.  As always, I sighed, had a soothing cup of tea, and typed it all in again.  The new code I hastily tapped in  was much better: I’d held in my head the essence of how the code should work rather than the details: I now knew for certain  the start point, the end, and how it should be achieved. Instantly the detritus of half-baked thoughts fell away and I was able to write logical code that performed better.  Because I could work so quickly, I was able to hold the details of all the columns and variables in my head, and the dynamics of the flow of data. It was, in fact, easier and quicker to start from scratch rather than tidy up and refactor the existing code with its inevitable fumbling and half-baked ideas. What a shame that technology is now so good that developers rarely experience the cleansing shock of losing one’s code and having to rewrite it from scratch.  If you’ve never accidentally lost  your code, then it is worth doing it deliberately once for the experience. Creative people have, until Technology mistakenly prevented it, torn up their drafts or sketches, threw them in the bin, and started again from scratch.  Leonardo’s obsessive reworking of the Mona Lisa was renowned because it was so unusual:  Most artists have been utterly ruthless in destroying work that didn’t quite make it. Authors are particularly keen on writing afresh, and the results are generally positive. Lawrence of Arabia actually lost the entire 250,000 word manuscript of ‘The Seven Pillars of Wisdom’ by accidentally leaving it on a train at Reading station, before rewriting a much better version.  Now, any writer or artist is seduced by technology into altering or refining their work rather than casting it dramatically in the bin or setting a light to it on a bonfire, and rewriting it from the blank page.  It is easy to pick away at a flawed work, but the real creative process is far more brutal. Once, many years ago whilst running a software house that supplied commercial software to local businesses, I’d been supervising an accounting system for a farming cooperative. No packaged system met their needs, and it was all hand-cut code.  For us, it represented a breakthrough as it was for a government organisation, and success would guarantee more contracts. As you’ve probably guessed, the code got mangled in a disk crash just a week before the deadline for delivery, and the many backups all proved to be entirely corrupted by a faulty tape drive.  There were some fragments left on individual machines, but they were all of different versions.  The developers were in despair.  Strangely, I managed to re-write the bulk of a three-month project in a manic and caffeine-soaked weekend.  Sure, that elegant universally-applicable input-form routine was‘nt quite so elegant, but it didn’t really need to be as we knew what forms it needed to support.  Yes, the code lacked architectural elegance and reusability. By dawn on Monday, the application passed its integration tests. The developers rose to the occasion after I’d collapsed, and tidied up what I’d done, though they were reproachful that some of the style and elegance had gone out of the application. By the delivery date, we were able to install it. It was a smaller, faster application than the beta they’d seen and the user-interface had a new, rather Spartan, appearance that we swore was done to conform to the latest in user-interface guidelines. (we switched to Helvetica font to look more ‘Bauhaus’ ). The client was so delighted that he forgave the new bugs that had crept in. I still have the disk that crashed, up in the attic. In IT, we have had mixed experiences from complete re-writes. Lotus 123 never really recovered from a complete rewrite from assembler into C, Borland made the mistake with Arago and Quattro Pro  and Netscape’s complete rewrite of their Navigator 4 browser was a white-knuckle ride. In all cases, the decision to rewrite was a result of extreme circumstances where no other course of action seemed possible.   The rewrite didn’t come out of the blue. I prefer to remember the rewrite of Minix by young Linus Torvalds, or the rewrite of Bitkeeper by a slightly older Linus.  The rewrite of CP/M didn’t do too badly either, did it? Come to think of it, the guy who decided to rewrite the windowing system of the Xerox Star never regretted the decision. I’ll agree that one should often resist calls for a rewrite. One of the worst habits of the more inexperienced programmer is to denigrate whatever code he or she inherits, and then call loudly for a complete rewrite. They are buoyed up by the mistaken belief that they can do better. This, however, is a different psychological phenomenon, more related to the idea of some motorcyclists that they are operating on infinite lives, or the occasional squaddies that if they charge the machine-guns determinedly enough all will be well. Grim experience brings out the humility in any experienced programmer.  I’m referring to quite different circumstances here. Where a team knows the requirements perfectly, are of one mind on methodology and coding standards, and they already have a solution, then what is wrong with considering  a complete rewrite? Rewrites are so painful in the early stages, until that point where one realises the payoff, that even I quail at the thought. One needs a natural disaster to push one over the edge. The trouble is that source-control systems, and disaster recovery systems, are just too good nowadays.   If I were to lose this draft of this very blog post, I know I’d rewrite it much better. However, if you read this, you’ll know I didn’t have the nerve to delete it and start again.  There was a time that one prayed that unreliable hardware would deliver you from an unmaintainable mess of a codebase, but now technology has made us almost entirely immune to such a merciful act of God. An old friend of mine with long experience in the software industry has long had the idea of the ‘source-control wet-work’,  where one hires a malicious hacker in some wild eastern country to hack into one’s own  source control system to destroy all trace of the source to an application. Alas, backup systems are just too good to make this any more than a pipedream. Somehow, it would be difficult to promote the idea. As an alternative, could one construct a source control system that, on doing all the code-quality metrics, would systematically destroy all trace of source code that failed the quality test? Alas, I can’t see many managers buying into the idea. In reading the full story of the near-loss of Toy Story 2, it set me thinking. It turned out that the lucky restoration of the code wasn’t the happy ending one first imagined it to be, because they eventually came to the conclusion that the plot was fundamentally flawed and it all had to be rewritten anyway.  Was this an early  case of the ‘source-control wet-job’?’ It is very hard nowadays to do a rapid U-turn in a development project because we are far too prone to cling to our existing source-code.

  Read the article

• Refactoring Part 1 : Intuitive Investments

  - by Wes McClure

  Fear, it’s what turns maintaining applications into a nightmare.  Technology moves on, teams move on, someone is left to operate the application, what was green is now perceived brown.  Eventually the business will evolve and changes will need to be made.  The approach to those changes often dictates the long term viability of the application.  Fear of change, lack of passion and a lack of interest in understanding the domain often leads to a paranoia to do anything that doesn’t involve duct tape and bailing twine.  Don’t get me wrong, those have a place in the short term viability of a project but they don’t have a place in the long term.  Add to it “us versus them” in regards to the original team and those that maintain it, internal politics and other factors and you have a recipe for disaster.  This results in code that quickly becomes unmanageable.  Even the most clever of designs will eventually become sub optimal and debt will amount that exponentially makes changes difficult.  This is where refactoring comes in, and it’s something I’m very passionate about.  Refactoring is about improving the process whereby we make change, it’s an exponential investment in the process of change. Without it we will incur exponential complexity that halts productivity. Investments, especially in the long term, require intuition and reflection.  How can we tackle new development effectively via evolving the original design and paying off debt that has been incurred? The longer we wait to ask and answer this question, the more it will cost us.  Small requests don’t warrant big changes, but realizing when changes now will pay off in the long term, and especially in the short term, is valuable. I have done my fair share of maintaining applications and continuously refactoring as needed, but recently I’ve begun work on a project that hasn’t had much debt, if any, paid down in years.  This is the first in a series of blog posts to try to capture the process which is largely driven by intuition of smaller refactorings from other projects. Signs that refactoring could help: Testability How can decreasing test time not pay dividends? One of the first things I found was that a very important piece often takes 30+ minutes to test.  I can only imagine how much time this has cost historically, but more importantly the time it might cost in the coming weeks: I estimate at least 10-20 hours per person!  This is simply unacceptable for almost any situation.  As it turns out, about 6 hours of working with this part of the application and I was able to cut the time down to under 30 seconds!  In less than the lost time of one week, I was able to fix the problem for all future weeks! If we can’t test fast then we can’t change fast, nor with confidence. Code is used by end users and it’s also used by developers, consider your own needs in terms of the code base.  Adding logic to enable/disable features during testing can help decouple parts of an application and lead to massive improvements.  What exactly is so wrong about test code in real code?  Often, these become features for operators and sometimes end users.  If you cannot run an integration test within a test runner in your IDE, it’s time to refactor. Readability Are variables named meaningfully via a ubiquitous language? Is the code segmented functionally or behaviorally so as to minimize the complexity of any one area? Are aspects properly segmented to avoid confusion (security, logging, transactions, translations, dependency management etc) Is the code declarative (what) or imperative (how)?  What matters, not how.  LINQ is a great abstraction of the what, not how, of collection manipulation.  The Reactive framework is a great example of the what, not how, of managing streams of data. Are constants abstracted and named, or are they just inline? Do people constantly bitch about the code/design? If the code is hard to understand, it will be hard to change with confidence.  It’s a large undertaking if the original designers didn’t pay much attention to readability and as such will never be done to “completion.”  Make sure not to go over board, instead use this as you change an application, not in lieu of changes (like with testability). Complexity Simplicity will never be achieved, it’s highly subjective.  That said, a lot of code can be significantly simplified, tidy it up as you go.  Refactoring will often converge upon a simplification step after enough time, keep an eye out for this. Understandability In the process of changing code, one often gains a better understanding of it.  Refactoring code is a good way to learn how it works.  However, it’s usually best in combination with other reasons, in effect killing two birds with one stone.  Often this is done when readability is poor, in which case understandability is usually poor as well.  In the large undertaking we are making with this legacy application, we will be replacing it.  Therefore, understanding all of its features is important and this refactoring technique will come in very handy. Unused code How can deleting things not help? This is a freebie in refactoring, it’s very easy to detect with modern tools, especially in statically typed languages.  We have VCS for a reason, if in doubt, delete it out (ok that was cheesy)! If you don’t know where to start when refactoring, this is an excellent starting point! Duplication Do not pray and sacrifice to the anti-duplication gods, there are excellent examples where consolidated code is a horrible idea, usually with divergent domains.  That said, mediocre developers live by copy/paste.  Other times features converge and aren’t combined.  Tools for finding similar code are great in the example of copy/paste problems.  Knowledge of the domain helps identify convergent concepts that often lead to convergent solutions and will give intuition for where to look for conceptual repetition. 80/20 and the Boy Scouts It’s often said that 80% of the time 20% of the application is used most.  These tend to be the parts that are changed.  There are also parts of the code where 80% of the time is spent changing 20% (probably for all the refactoring smells above).  I focus on these areas any time I make a change and follow the philosophy of the Boy Scout in cleaning up more than I messed up.  If I spend 2 hours changing an application, in the 20%, I’ll always spend at least 15 minutes cleaning it or nearby areas. This gives a huge productivity edge on developers that don’t. Ironically after a short period of time the 20% shrinks enough that we don’t have to spend 80% of our time there and can move on to other areas.   Refactoring is highly subjective, never attempt to refactor to completion!  Learn to be comfortable with leaving one part of the application in a better state than others.  It’s an evolution, not a revolution.  These are some simple areas to look into when making changes and can help get one started in the process.  I’ve often found that refactoring is a convergent process towards simplicity that sometimes spans a few hours but often can lead to massive simplifications over the timespan of weeks and months of regular development.

  Read the article

• Source-control 'wet-work'?

  - by Phil Factor

  When a design or creative work is flawed beyond remedy, it is often best to destroy it and start again. The other day, I lost the code to a long and intricate SQL batch I was working on. I’d thought it was impossible, but it happened. With all the technology around that is designed to prevent this occurring, this sort of accident has become a rare event.  If it weren’t for a deranged laptop, and my distraction, the code wouldn’t have been lost this time.  As always, I sighed, had a soothing cup of tea, and typed it all in again.  The new code I hastily tapped in  was much better: I’d held in my head the essence of how the code should work rather than the details: I now knew for certain  the start point, the end, and how it should be achieved. Instantly the detritus of half-baked thoughts fell away and I was able to write logical code that performed better.  Because I could work so quickly, I was able to hold the details of all the columns and variables in my head, and the dynamics of the flow of data. It was, in fact, easier and quicker to start from scratch rather than tidy up and refactor the existing code with its inevitable fumbling and half-baked ideas. What a shame that technology is now so good that developers rarely experience the cleansing shock of losing one’s code and having to rewrite it from scratch.  If you’ve never accidentally lost  your code, then it is worth doing it deliberately once for the experience. Creative people have, until Technology mistakenly prevented it, torn up their drafts or sketches, threw them in the bin, and started again from scratch.  Leonardo’s obsessive reworking of the Mona Lisa was renowned because it was so unusual:  Most artists have been utterly ruthless in destroying work that didn’t quite make it. Authors are particularly keen on writing afresh, and the results are generally positive. Lawrence of Arabia actually lost the entire 250,000 word manuscript of ‘The Seven Pillars of Wisdom’ by accidentally leaving it on a train at Reading station, before rewriting a much better version.  Now, any writer or artist is seduced by technology into altering or refining their work rather than casting it dramatically in the bin or setting a light to it on a bonfire, and rewriting it from the blank page.  It is easy to pick away at a flawed work, but the real creative process is far more brutal. Once, many years ago whilst running a software house that supplied commercial software to local businesses, I’d been supervising an accounting system for a farming cooperative. No packaged system met their needs, and it was all hand-cut code.  For us, it represented a breakthrough as it was for a government organisation, and success would guarantee more contracts. As you’ve probably guessed, the code got mangled in a disk crash just a week before the deadline for delivery, and the many backups all proved to be entirely corrupted by a faulty tape drive.  There were some fragments left on individual machines, but they were all of different versions.  The developers were in despair.  Strangely, I managed to re-write the bulk of a three-month project in a manic and caffeine-soaked weekend.  Sure, that elegant universally-applicable input-form routine was‘nt quite so elegant, but it didn’t really need to be as we knew what forms it needed to support.  Yes, the code lacked architectural elegance and reusability. By dawn on Monday, the application passed its integration tests. The developers rose to the occasion after I’d collapsed, and tidied up what I’d done, though they were reproachful that some of the style and elegance had gone out of the application. By the delivery date, we were able to install it. It was a smaller, faster application than the beta they’d seen and the user-interface had a new, rather Spartan, appearance that we swore was done to conform to the latest in user-interface guidelines. (we switched to Helvetica font to look more ‘Bauhaus’ ). The client was so delighted that he forgave the new bugs that had crept in. I still have the disk that crashed, up in the attic. In IT, we have had mixed experiences from complete re-writes. Lotus 123 never really recovered from a complete rewrite from assembler into C, Borland made the mistake with Arago and Quattro Pro  and Netscape’s complete rewrite of their Navigator 4 browser was a white-knuckle ride. In all cases, the decision to rewrite was a result of extreme circumstances where no other course of action seemed possible.   The rewrite didn’t come out of the blue. I prefer to remember the rewrite of Minix by young Linus Torvalds, or the rewrite of Bitkeeper by a slightly older Linus.  The rewrite of CP/M didn’t do too badly either, did it? Come to think of it, the guy who decided to rewrite the windowing system of the Xerox Star never regretted the decision. I’ll agree that one should often resist calls for a rewrite. One of the worst habits of the more inexperienced programmer is to denigrate whatever code he or she inherits, and then call loudly for a complete rewrite. They are buoyed up by the mistaken belief that they can do better. This, however, is a different psychological phenomenon, more related to the idea of some motorcyclists that they are operating on infinite lives, or the occasional squaddies that if they charge the machine-guns determinedly enough all will be well. Grim experience brings out the humility in any experienced programmer.  I’m referring to quite different circumstances here. Where a team knows the requirements perfectly, are of one mind on methodology and coding standards, and they already have a solution, then what is wrong with considering  a complete rewrite? Rewrites are so painful in the early stages, until that point where one realises the payoff, that even I quail at the thought. One needs a natural disaster to push one over the edge. The trouble is that source-control systems, and disaster recovery systems, are just too good nowadays.   If I were to lose this draft of this very blog post, I know I’d rewrite it much better. However, if you read this, you’ll know I didn’t have the nerve to delete it and start again.  There was a time that one prayed that unreliable hardware would deliver you from an unmaintainable mess of a codebase, but now technology has made us almost entirely immune to such a merciful act of God. An old friend of mine with long experience in the software industry has long had the idea of the ‘source-control wet-work’,  where one hires a malicious hacker in some wild eastern country to hack into one’s own  source control system to destroy all trace of the source to an application. Alas, backup systems are just too good to make this any more than a pipedream. Somehow, it would be difficult to promote the idea. As an alternative, could one construct a source control system that, on doing all the code-quality metrics, would systematically destroy all trace of source code that failed the quality test? Alas, I can’t see many managers buying into the idea. In reading the full story of the near-loss of Toy Story 2, it set me thinking. It turned out that the lucky restoration of the code wasn’t the happy ending one first imagined it to be, because they eventually came to the conclusion that the plot was fundamentally flawed and it all had to be rewritten anyway.  Was this an early  case of the ‘source-control wet-job’?’ It is very hard nowadays to do a rapid U-turn in a development project because we are far too prone to cling to our existing source-code.

  Read the article

• Event Driven Behavior Tree: deterministic traversal order with parallel

  - by Heisenbug

  I've studied several articles and listen some talks about behavior trees (mostly the resources available on AIGameDev by Alex J. Champandard). I'm particularly interested on event driven behavior trees, but I have still some doubts on how to implement them correctly using a scheduler. Just a quick recap: Standard Behavior Tree Each execution tick the tree is traversed from the root in depth-first order The execution order is implicitly expressed by the tree structure. So in the case of behaviors parented to a parallel node, even if both children are executed during the same traversing, the first leaf is always evaluated first. Event Driven BT During the first traversal the nodes (tasks) are enqueued using a scheduler which is responsible for updating only running ones every update The first traversal implicitly produce a depth-first ordered queue in the scheduler Non leaf nodes stays suspended mostly of the time. When a leaf node terminate(either with success or fail status) the parent (observer) is waked up allowing the tree traversing to continue and new tasks will be enqueued in the scheduler Without parallel nodes in the tree there will be up to 1 task running in the scheduler Without parallel nodes, the tasks in the queue(excluding dynamic priority implementation) will be always ordered in a depth-first order (is this right?) Now, from what is my understanding of a possible implementation, there are 2 requirements I think must be respected(I'm not sure though): Now, some requirements I think needs to be guaranteed by a correct implementation are: The result of the traversing should be independent from which implementation strategy is used. The traversing result must be deterministic. I'm struggling trying to guarantee both in the case of parallel nodes. Here's an example: Parallel_1 -->Sequence_1 ---->leaf_A ---->leaf_B -->leaf_C Considering a FIFO policy of the scheduler, before leaf_A node terminates the tasks in the scheduler are: P1(suspended),S1(suspended),leaf_A(running),leaf_C(running) When leaf_A terminate leaf_B will be scheduled (at the end of the queue), so the queue will become: P1(suspended),S1(suspended),leaf_C(running),leaf_B(running) In this case leaf_B will be executed after leaf_C at every update, meanwhile with a non event-driven traversing from the root node, the leaf_B will always be evaluated before leaf_A. So I have a couple of question: do I have understand correctly how event driven BT work? How can I guarantee the depth first order is respected with such an implementation? is this a common issue or am I missing something?

  Read the article

• How to merge many text files data in databse

  - by Mirage

  i have around 100 text files. The files have questions and 3 choices. FIles are like below ab001.txt -- contains question ab001a.txt -- is the first choice ab001b.txt ---is second choice ab001c.txt --- is third choice There are thousnad files like this. now i want to insert them in sql or first may in excel like First columns questions and other three columns as answers First two characters are same for soom files , looks like it signifies osme category so around every 30 questioons have same first charaters Any ideas

  Read the article

• Any way to loop through FPDF code with proper XY coordinates?

  - by JM4

  At the end of a form collection, I provide the consumer a printable PDF with the information they just entered. I already run through a loop to store the variables themselves but am wondering if it is at all possible to build a loop that builds on itself for FPDF. The catch is this, each new variable (#1, #2, #3) will change location by a determined amount of space. For example: I print the Member #1 First name at coordinate at coordinate (95, 101). I print Member #2 First name at coordinate (95, 110)... and so on. Each known variable will be 9.5mm greater than its previous entry (therefor Member #9 will be 40mm higher than Member 6) My sample code for the FPDF itself is: $pdf->SetFont('Arial','', 7); $pdf->SetXY(8,76.5); $pdf->Cell(20,0,$f1name); $pdf->SetFont('Arial','', 5); $pdf->SetXY(50.5,76.5); $pdf->Cell(20,0,$f1address); $pdf->SetFont('Arial','', 7); $pdf->SetXY(95.7,76.5); $pdf->Cell(20,0,$f1city); $pdf->SetXY(129.5,76.5); $pdf->Cell(20,0,$f1state); $pdf->SetXY(139.1,76.5); $pdf->Cell(20,0,$f1zip); $pdf->SetXY(151,76.5); $pdf->Cell(20,0,$f1dob); $pdf->SetXY(168,76.5); $pdf->Cell(20,0,$f1ssn); $pdf->SetXY(186,76.5); $pdf->Cell(20,0,$f1phone); $pdf->SetXY(55,81.1); $pdf->Cell(20,0,$f1email); $pdf->SetXY(129,81.1); $pdf->Cell(20,0,$f1fednum); Ideally, all Y variables with $f2 would be 9.5mm greater than f1's Y values.

  Read the article

• Compiling cpp code in netbeans produce errors, how to solve it ?

  - by Rupertt Wind

  i use the netbeans with MinGW and MYSY make /debugger but when i compile a basic cpp code in it and run it it produces two erorrs this is the code runned and the output![alt text][1] box #include <iostream> void main() { cout << "Hello World!" << endl; cout << "Welcome to C++ Programming" << endl; } output is /usr/bin/make -f nbproject/Makefile-Debug.mk SUBPROJECTS= .build-conf make[1]: Entering directory `/d/Users/Home/Documents/NetBeansProjects/newApp' /usr/bin/make -f nbproject/Makefile-Debug.mk dist/Debug/MinGW-Windows/newapp.exe make[2]: Entering directory `/d/Users/Home/Documents/NetBeansProjects/newApp' mkdir -p dist/Debug/MinGW-Windows g++.exe -o dist/Debug/MinGW-Windows/newapp build/Debug/MinGW-Windows/newmain.o build/Debug/MinGW-Windows/newfile.o build/Debug/MinGW-Windows/main.o build/Debug/MinGW-Windows/newfile.o: In function `main': D:/Users/Home/Documents/NetBeansProjects/newApp/newfile.cpp:5: multiple definition of `main' build/Debug/MinGW-Windows/newmain.o:D:/Users/Home/Documents/NetBeansProjects/newApp/newmain.c:15: first defined here build/Debug/MinGW-Windows/main.o: In function `main': D:/Users/Home/Documents/NetBeansProjects/newApp/main.cpp:13: multiple definition of `main' build/Debug/MinGW-Windows/newmain.o:D:/Users/Home/Documents/NetBeansProjects/newApp/newmain.c:15: first defined here collect2: ld returned 1 exit status make[2]: *** [dist/Debug/MinGW-Windows/newapp.exe] Error 1 make[2]: Leaving directory `/d/Users/Home/Documents/NetBeansProjects/newApp' make[1]: *** [.build-conf] Error 2 make[1]: Leaving directory `/d/Users/Home/Documents/NetBeansProjects/newApp' make: *** [.build-impl] Error 2 BUILD FAILED (exit value 2, total time: 1s) how can i solve this ?

  Read the article

< Previous Page | 373 374 375 376 377 378 379 380 381 382 383 384  | Next Page >