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• iPhone: How to Determine Average Light/Dark of an Area of an UIImage

  - by TechZen

  I need to place labels with a transparent background over a variable-content UIImage. Readability will vary significantly depending on the relationship between the color of the label's text and the color/luminosity of the area of the image displayed under the label. Since the image will be constantly changing, the color of the label's text needs to change in sync. I have found several techniques for determining the color, perceived luminosity etc of a single pixel. However, I need to rather quickly (while a view loads) determine the rough perceived color/luminosity of an area of the UIImage under the frame of the UILabel. I presume I will also need to measure the alpha because the same color/luminosity looks different at different alpha values. Is there a way to calculate such a value for an area? Will I be reduced to simply summing pixels? If it comes to that, is there an algorithm to accomplish this? I've thought of two possible approaches: Perform some "folding" operations i.e. combining pixels from one half of the area to the other half. Then repeat until I get a single value. Would this be practical? How would you logically combine pixels to average their perceived color/luminosity? Sample a statistically significant number of pixels in the area and then combine them (somehow) to get a rough measure. I think this problem comes up a lot these days with people being so found of customizing backgrounds. Seems like something that would be worth my time to bang out a category or class to handle this and then share it around.

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• ReaderWriterLockSlim and Pulse/Wait

  - by Jono

  Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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• iPhone: Does it ever make sense for an object to retain its delegate?

  - by randombits

  According to the rules of memory management in a non garbage collected world, one is not supposed to retain a the calling object in a delegate. Scenario goes like this: I have a class that inherits from UITableViewController and contains a search bar. I run expensive search operations in a secondary thread. This is all done with an NSOperationQueue and subclasses NSOperation instances. I pass the controller as a delegate that adheres to a callback protocol into the NSOperation. There are edge cases when the application crashes because once an item is selected from the UITableViewController, I dismiss it and thus its retain count goes to 0 and dealloc gets invoked on it. The delegate didn't get to send its message in time as the results are being passed at about the same time the dealloc happens. Should I design this differently? Should I call retain on my controller from the delegate to ensure it exists until the NSOperation itself is dealloc'd? Will this cause a memory leak? Right now if I put a retain on the controller, the crashes goes away. I don't want to leak memory though and need to understand if there are cases where retaining the delegate makes sense. Just to recap. UITableViewController creates an NSOperationQueue and NSOperation that gets embedded into the queue. The UITableViewController passes itself as a delegate to NSOperation. NSOperation calls a method on UITableViewController when it's ready. If I retain the UITableViewController, I guarantee it's there, but I'm not sure if I'm leaking memory. If I only use an assign property, edge cases occur where the UITableViewController gets dealloc'd and objc_msgSend() gets called on an object that doesn't exist in memory and a crash is imminent.

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• How can I improve the performance of LinqToSql queries that use EntitySet properties?

  - by DanM

  I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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• Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

  - by mihi

  Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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• Plist data OK in iPhone simulator but disappears after installation onto device

  - by user183804

  I am testing an application on a first-generation iPod running OS 3.1.3 with a tableview populated from a plist. The application works well on the simulator. Initially after installation onto the iPod for testing, the tableview was blank (scrollable lines present, but empty rows). After searching this site, I found one issue to be a case-sensitive problem in the name of the plist file ("Data.plist in resources; "data.plist" in code). When the problem persisted, I again found on this site the advice to "Clean all Targets" prior to installation. I now have found that after performing a "Clean all Targets" operation twice, quitting XCode in between operations, the problem resolves, and the tableview appears properly populated after installation. I am wondering whether this issue signifies a corrupted plist file, prior to making the application available on the App store. Re-creating the plist file from scratch and then testing it likely would take several hours of work, so I do not want to do so unless absolutely necessary. Thanks in advance for any help.

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• Detaching all entities of T to get fresh data

  - by Goran

  Lets take an example where there are two type of entites loaded: Product and Category, Product.CategoryId - Category.Id. We have available CRUD operations on products (not Categories). If on another screen Categories are updated (or from another user in the network), we would like to be able to reload the Categories, while preserving the context we currently use, since we could be in the middle of editing data, and we do not want changes to be lost (and we cannot depend on saving, since we have incomplete data). Since there is no easy way to tell EF to get fresh data (added, removed and modified), we thought of twp possible ways: 1) Getting products attached to context, and categories detached from context. This would mean that we loose the ability to access Product.Category.Name, which we do sometimes require, so we would need to manually resolve it (example when printing data). 2) detaching / attaching all Categories from current context. Context.ChangeTracker.Entries().Where(x => x.Entity.GetType() == typeof(T)).ForEach(x => x.State = EntityState.Detached); And then reload the categories, which will get fresh data. Do you find any problem with this second approach? We understand that this will require all constraints to be put on foreign keys, and not navigation properties, since when detaching all Categories, Product.Category navigation properties would be reset to null also. Also, there could be a potential performance problem, which we did not test, since there could be couple of thousand products loaded, and all would need to resolve navigation property when reloading. Which of the two do you prefer, and is there a better way (EF6 + .NET 4.0)?

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• How to efficiently store and update binary data in Mongodb?

  - by Rocketman

  I am storing a large binary array within a document. I wish to continually add bytes to this array and sometimes change the value of existing bytes. I was looking for some $append_bytes and $replace_bytes type of modifiers but it appears that the best I can do is $push for arrays. It seems like this would be doable by performing seek-write type operations if I had access somehow to the underlying bson on disk, but it does not appear to me that there is anyway to do this in mongodb (and probably for good reason). If I were instead to just query this binary array, edit or add to it, and then update the document by rewriting the entire field, how costly will this be? Each binary array will be on the order of 1-2MB, and updates occur once every 5 minutes and across 1000s of documents. Worse, yet there is no easy way to spread these out (in time) and they will usually be happening close to one another on the 5 minute intervals. Does anyone have a good feel for how disastrous this will be? Seems like it would be problematic. An alternative would be to store this binary data as separate files on disk, implement a thread pool to efficiently manipulate the files on disk, and reference the filename from my mongodb document. (I'm using python and pymongo so I was looking at pytables). I'd prefer to avoid this though if possible. Is there any other alternative that I am overlooking here? Thanks in advnace.

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• What should i do for accomodating large scale data storage and retrieval?

  - by kailashbuki

  There's two columns in the table inside mysql database. First column contains the fingerprint while the second one contains the list of documents which have that fingerprint. It's much like an inverted index built by search engines. An instance of a record inside the table is shown below; 34 "doc1, doc2, doc45" The number of fingerprints is very large(can range up to trillions). There are basically following operations in the database: inserting/updating the record & retrieving the record accoring to the match in fingerprint. The table definition python snippet is: self.cursor.execute("CREATE TABLE IF NOT EXISTS `fingerprint` (fp BIGINT, documents TEXT)") And the snippet for insert/update operation is: if self.cursor.execute("UPDATE `fingerprint` SET documents=CONCAT(documents,%s) WHERE fp=%s",(","+newDocId, thisFP))== 0L: self.cursor.execute("INSERT INTO `fingerprint` VALUES (%s, %s)", (thisFP,newDocId)) The only bottleneck i have observed so far is the query time in mysql. My whole application is web based. So time is a critical factor. I have also thought of using cassandra but have less knowledge of it. Please suggest me a better way to tackle this problem.

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• How do I add code automatically to a derived function in C++

  - by Ian

  I have code that's meant to manage operations on both a networked client and a server, since there is significant overlap between the two. However, there are a few functions here and there that are meant to be exclusively called by the client or server, and accidentally calling a client function on the server (or vice versa) is a significant source of bugs. To reduce these sorts of programming errors, I'm trying to tag functions so that they'll raise a ruckus if they're misused. My current solution is a simple macro at the start of each function that calls an assert if the client or server accesses members they shouldn't. However, this runs into problems when there are multiple derived instances of classes, in that I have to tag the implementation as client or server side in EVERY child class. What I'd like to be able to do is put a tag in the virtual member's signature in the base class, so that I only have to tag it once and not run into errors by forgetting to do it repeatedly. I've considered putting a check in a base class implementation and then referring to it with something like base::functionName, but that runs into the same issue as far as needing to manually add the function call to every implementation. Ideally, I'd be able to have parent versions of the function called automatically like default constructors do. Does anybody know how to achieve something like this in C++? Is there an alternate approach I should be considering? Thanks!

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• Providing custom database functionality to custom asp.net membership provider

  - by IrfanRaza

  Hello friends, I am creating custom membership provider for my asp.net application. I have also created a separate class "DBConnect" that provides database functionality such as Executing SQL statement, Executing SPs, Executing SPs or Query and returning SqlDataReader and so on... I have created instance of DBConnect class within Session_Start of Global.asax and stored to a session. Later using a static class I am providing the database functionality throughout the application using the same single session. In short I am providing a single point for all database operations from any asp.net page. I know that i can write my own code to connect/disconnect database and execute SPs within from the methods i need to override. Please look at the code below - public class SGI_MembershipProvider : MembershipProvider { ...... public override bool ChangePassword(string username, string oldPassword, string newPassword) { if (!ValidateUser(username, oldPassword)) return false; ValidatePasswordEventArgs args = new ValidatePasswordEventArgs(username, newPassword, true); OnValidatingPassword(args); if (args.Cancel) { if (args.FailureInformation != null) { throw args.FailureInformation; } else { throw new Exception("Change password canceled due to new password validation failure."); } } ..... //Database connectivity and code execution to change password. } .... } MY PROBLEM - Now what i need is to execute the database part within all these overriden methods from the same database point as described on the top. That is i have to pass the instance of DBConnect existing in the session to this class, so that i can access the methods. Could anyone provide solution on this. There might be some better techniques i am not aware of that. The approach i am using might be wrong. Your suggessions are always welcome. Thanks for sharing your valuable time.

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• Generics vs inheritance (when no collection classes are involved)

  - by Ram

  This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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• Doing a POST to a Service Operation in ADO.NET data services

  - by DataServices123

  Is it possible to POST to a service operation defined in an ADO.NET data service (it is decorated with WebInvoke)? I had no problem calling the service operation as an HTTP GET. However, when I switched to doing a POST, the stack trace consistently comes back with "Parameter cannot be NULL". I am using the jQuery syntax below, and sending the POST as JSON (though I'm not including the $.ajax call, the parameter names line up exactly). It would be possible to try this with WCF, as opposed to ADO.NET data services (newly renamed as WCF data services). However, my preference would be to use this approach first. I have tried this with and without the stringify method. Most examples online only show how to use a POST to entities (i.e. for handling CRUD operations). However, in this case we are POSTing to a Service Operation. function PostToDataService() { varType = "POST"; varUrl = "http://dev-server/MyServices/MyService.svc/SampleSO"; varData = { CustomMessage: $("#TextBox1").val() }; varData = JSON.stringify(varData); varContentType = "application/json; charset=utf-8"; varDataType = "json"; varProcessData = true; CallService(); }

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• What is the fastest way to do division in C for 8bit MCUs?

  - by Jordan S

  I am working on the firmware for a device that uses an 8bit mcu (8051 architecture). I am using SDCC (Small Device C Compiler). I have a function that I use to set the speed of a stepper motor that my circuit is driving. The speed is set by loading a desired value into the reload register for a timer. I have a variable, MotorSpeed that is in the range of 0 to 1200 which represents pulses per second to the motor. My function to convert MotorSpeed to the correct 16bit reload value is shown below. I know that float point operations are pretty slow and I am wondering if there is a faster way of doing this... void SetSpeed() { float t = MotorSpeed; unsigned int j = 0; t = 1/t ; t = t / 0.000001; j = MaxInt - t; TMR3RL = j; // Set reload register for desired freq return; }

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• HTTP POST with URL query parameters -- good idea or not?

  - by Steven Huwig

  I'm designing an API to go over HTTP and I am wondering if using the HTTP POST command, but with URL query parameters only and no request body, is a good way to go. Considerations: "Good Web design" requires non-idempotent actions to be sent via POST. This is a non-idempotent action. It is easier to develop and debug this app when the request parameters are present in the URL. The API is not intended for widespread use. It seems like making a POST request with no body will take a bit more work, e.g. a Content-Length: 0 header must be explicitly added. It also seems to me that a POST with no body is a bit counter to most developer's and HTTP frameworks' expectations. Are there any more pitfalls or advantages to sending parameters on a POST request via the URL query rather than the request body? Edit: The reason this is under consideration is that the operations are not idempotent and have side effects other than retrieval. See the HTTP spec: In particular, the convention has been established that the GET and HEAD methods SHOULD NOT have the significance of taking an action other than retrieval. These methods ought to be considered "safe". This allows user agents to represent other methods, such as POST, PUT and DELETE, in a special way, so that the user is made aware of the fact that a possibly unsafe action is being requested. ... Methods can also have the property of "idempotence" in that (aside from error or expiration issues) the side-effects of N 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also, the methods OPTIONS and TRACE SHOULD NOT have side effects, and so are inherently idempotent.

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• Parallel.For Batching

  - by chibacity

  Is there built-in support in the TPL for batching operations? I was recently playing with a routine to carry out character replacement on a character array which required a lookup table i.e. transliteration: for (int i = 0; i < chars.Length; i++) { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } } I could see that this could be trivially parallelized, so jumped in with a first stab which I knew would perform worse as the tasks were too fine-grained: Parallel.For(0, chars.Length, i => { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } }); I then reworked the algorithm to use batching so that the work could be chunked onto different threads in less fine-grained batches. This made use of threads as expected and I got some near linear speed up. I'm sure that there must be built-in support for batching in the TPL. What is the syntax, and how do I use it? const int CharBatch = 100; int charLen = chars.Length; Parallel.For(0, ((charLen / CharBatch) + 1), i => { int batchUpper = ((i + 1) * CharBatch); for (int j = i * CharBatch; j < batchUpper && j < charLen; j++) { char replaceChar; if (lookup.TryGetValue(chars[j], out replaceChar)) { chars[j] = replaceChar; } } });

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• jQuery: one-liner for removing all children but one

  - by user1352530

  HTML code is: <li> <a href="#" /> <ul> <li> <a href="#"/> </li> </ul> </li> I want to delete any node under $(this) = li that is not a link. If there are more than one link, just the first one is saved, and if there are links inside the ul tag, they are not included because they are descendants and no childrens. Something like this (I am cloning and outputting html): $(this).clone().remove('not(a:first)').html(); //Assuming remove looks for "a" as a first child Does not work, so I try with this: $(this).clone().children().remove('not(a:first)').parent().html(); Does not work so I try with this: $(this).clone().remove('not(>a:first)').html(); I need the original element as a reference after removal for chaining more operations EDIT: Ok! Second one works with a little syntax correction as some appointed (:not( instead of not() but I would like to know if there is any other solution similar to the third line so I don't have to do children().remove().parent(). Thank you!

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• How can I find out if the MainActivity is being paused from my Java class?

  - by quinestor

  I am using motion sensor detection in my application. My design is this: a class gets the sensor services references from the main activity and then it implements SensorEventListener. That is, the MainActivity does not listen for sensor event changes: public void onCreate(Bundle savedInstanceState) { // ... code mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE); mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); // The following is my java class, it does not extends any android fragment/activty mShakeUtil = new ShakeUtil(mSensorManager,mAccelerometer,this); // ..more code.. } I can't redesign ShakeUtil so it is a fragment nor activity, unfortunately. Now to illustrate the problem consider: MainActivity is on its way to be destroyed/paused. I.e screen rotation ShakeUtil's onSensorChanged(SensorEvent event) gets called in the process.. One of the things that happen inside onSensorChanged is a dialog interaction, which gives the error: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState When the previous happens between MainActivity's onSaveInstanceState and onPause. I know this can be prevented if I successfully detect that MainActivity is being pause in ShakeUtil. How can I detect that MainActivity is being paused or onSaveInstanceState was called from ShakeUtil? Alternatively, how can I avoid this issue without making Shakeutil extend activity? So far I have tried with flag variables but that isn't good enough, I guess these are not atomic operations. I tried using Activity's isChangingConfigurations(), but I get an undocummented "NoSuchMethodFound" error.. I am unregistering the sensors by calling ShakeUtil when onPause in main ACtivity

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• WCF Custom SOAP Header Issues

  - by WayneC

  I'm trying to implement an endpoint behavior which injects a custom SOAP header into all messages to and from a service. I've gotten pretty close by implementing the approach from the accepted answer of this question: http://stackoverflow.com/questions/986455/wcf-wsdl-soap-header-on-all-operations/995951#995951 After implementing that solution, my custom SOAP header does indeed show up in the WSDL; however, when I try to call the methods on my service, I get the following exception/fault: <ExceptionDetail xmlns="http://schemas.datacontract.org/2004/07/System.ServiceModel" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"> <HelpLink i:nil="true" /> <InnerException i:nil="true" /> <Message>Index was outside the bounds of the array.</Message> <StackTrace> at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.AddHeadersToMessage(Message message, MessageDescription messageDescription, Object[] parameters, Boolean isRequest) at System.ServiceModel.Dispatcher.OperationFormatter.SerializeReply(MessageVersion messageVersion, Object[] parameters, Object result) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.SerializeOutputs(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc&amp; rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)</StackTrace> <Type>System.IndexOutOfRangeException</Type> </ExceptionDetail> Looking in Reflector at the DataContractSerializerOperationFormatter.AddHeadersToMessage method thats throwing the exception, leads me to believe that the following snippet is causing the problem...but I'm not sure why. MessageHeaderDescription description = (MessageHeaderDescription) headerPart.Description; object parameterValue = parameters[description.Index]; I think the last line above is throwing the exception. The parameters variable is from IDispatchFormatter.SerializeReply What's going on?!?!! Any help would be greatly appreciated...

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• Ember Data Sycn - LocalStorage+REST+RealTime+Online/Offline

  - by Miguel Madero

  We have a combination of requirements in terms o data access. Pre-load some reference data. We need reference data to survive browser restarts instead of just living in memory to avoid loading it all the time. I'm currently using the LocalStorageAdapter for that. Once we have it, we would like to sync changes (polling or using Socket.IO in the background and updating the LocalStorage could do the trick) There're other models that are more transactional, where we would need to directly go to the Server and get/save them. It would be nice to use something like the RESTAdapter for that. Lastly, there're some operations that should work off-line and changes should be synced later. To make it more concrete: * We pre-load vendor and "favorite products" into Local Storage. We work offline with those. * We need to sync server changes to vendor and product information. * If they search the full catalog, that requires them to be online. * When offline, we need to allow users to add something to their cart or even submit and order. We would like to queue this action and submit it when they have an Internet Connection. So a few questions are derived from this: * Is there a way to user RESTAdapter in combination with LocalStorage? * Is there some Socket.IO support? (Happy to do this part manually) * Is there Queueing support? Ideally at the Ember-Data level. I know we will have to do a lot of this manually and pull together the different lego pieces, but I wanted to ask for some perspective from experience Ember devs.

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• .NET 3.5 C# does not offer what I need for locking: Count async saves until 0 again.

  - by Frank Michael Kraft

  I have some records, that I want to save to database asynchronously. I organize them into batches, then send them. As time passes, the batches are processed. In the meanwhile the user can work on. There are some critical operations, that I want to lock him out from, while any save batch is still running asynchronously. The save is done using a TableServiceContext and method .BeginSave() - but I think this should be irrelevant. What I want to do is whenever an async save is started, increase a lock count, and when it completes, decrease the lock count so that it will be zero as soon as all have finished. I want to lock out the critical operation as long as the count is not zero. Furthermore I want to qualify the lock - by business object - for example. I did not find a .NET 3.5 c# locking method, that does fulfil this requirement. A semaphore does not contain a method to check, if the count is 0. Otherwise a semaphore with unlimited max count would do.

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• Groovy as a substitute for Java when using BigDecimal?

  - by geejay

  I have just completed an evaluation of Java, Groovy and Scala. The factors I considered were: readability, precision The factors I would like to know: performance, ease of integration I needed a BigDecimal level of precision. Here are my results: Java void someOp() { BigDecimal del_theta_1 = toDec(6); BigDecimal del_theta_2 = toDec(2); BigDecimal del_theta_m = toDec(0); del_theta_m = abs(del_theta_1.subtract(del_theta_2)) .divide(log(del_theta_1.divide(del_theta_2))); } Groovy void someOp() { def del_theta_1 = 6.0 def del_theta_2 = 2.0 def del_theta_m = 0.0 del_theta_m = Math.abs(del_theta_1 - del_theta_2) / Math.log(del_theta_1 / del_theta_2); } Scala def other(){ var del_theta_1 = toDec(6); var del_theta_2 = toDec(2); var del_theta_m = toDec(0); del_theta_m = ( abs(del_theta_1 - del_theta_2) / log(del_theta_1 / del_theta_2) ) } Note that in Java and Scala I used static imports. Java: Pros: it is Java Cons: no operator overloading (lots o methods), barely readable/codeable Groovy: Pros: default BigDecimal means no visible typing, least surprising BigDecimal support for all operations (division included) Cons: another language to learn Scala: Pros: has operator overloading for BigDecimal Cons: some surprising behaviour with division (fixed with Decimal128), another language to learn

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• Read/Write/Find/Replace huge csv file

  - by notapipe

  I have a huge (4,5 GB) csv file.. I need to perform basic cut and paste, replace operations for some columns.. the data is pretty well organized.. the only problem is I cannot play with it with Excel because of the size (2000 rows, 550000 columns). here is some part of the data: ID,Affection,Sex,DRB1_1,DRB1_2,SENum,SEStatus,AntiCCP,RFUW,rs3094315,rs12562034,rs3934834,rs9442372,rs3737728 D0024949,0,F,0101,0401,SS,yes,?,?,A_A,A_A,G_G,G_G D0024302,0,F,0101,7,SN,yes,?,?,A_A,G_G,A_G,?_? D0023151,0,F,0101,11,SN,yes,?,?,A_A,G_G,G_G,G_G I need to remove 4th, 5th, 6th, 7th, 8th and 9th columns; I need to find every _ character from column 10 onwards and replace it with a space ( ) character; I need to replace every ? with zero (0); I need to replace every comma with a tab; I need to remove first row (that has column names; I need to replace every 0 with 1, every 1 with 2 and every ? with 0 in 2nd column; I need to replace F with 2, M with 1 and ? with 0 in 3rd column; so that in the resulting file the output reads: D0024949 1 2 A A A A G G G G D0024302 1 2 A A G G A G 0 0 D0023151 1 2 A A G G G G G G (both input and output should read one line per row, ne extra blank row) Is there a memory efficient way of doing that with java(and I need a code to do that) or a usable tool for playing with this large data so that I can easily apply Excel functionality..

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• Using SMO to call Database.ExecuteNonQuery() concurrently?

  - by JimDaniel

  I have been banging my head against the wall trying to figure out how I can run update scripts concurrently against multiple databases in a single SQL Server instance using SMO. Our environments have an ever-increasing number of databases which need updating, and iterating through one at a time is becoming a problem (too slow). From what I understand SMO does not support concurrent operations, and my tests have bore that out. There seems to be shared memory at the Server object level, for things like DataReader context, keeps throwing exceptions such as "reader is already open." I apologize for not having the exact exceptions I am getting. I will try to get them and update this post. I am no expert on SMO and just feeling my way through to be honest. Not really sure I am approaching it the right way, but it's something that has to be done, or our productivity will slow to a crawl. So how would you guys do something like this? Am I using the wrong technology with SMO? All I am wanting to do is execute sql scripts against databases in a single sql server instance in parallel. Thanks for any help you can give, Daniel

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• WPF and LINQ/SQL - how and where to keep track of changes?

  - by Groky

  I have a WPF application built using the MVVM pattern: My Models come from LINQ to SQL. I use the Repository Pattern to abstract away the DataContext. My ViewModels have a reference to a Model. Setting a property on the ViewModel causes that value to be written through to the Model. As you can see, my data is stored in my Model, and changes are therefore tracked by my DataContext. However, in this question I read: The guidelines from the MSDN documentation on the DataContext class are what I would recommend following: In general, a DataContext instance is designed to last for one "unit of work" however your application defines that term. A DataContext is lightweight and is not expensive to create. A typical LINQ to SQL application creates DataContext instances at method scope or as a member of short-lived classes that represent a logical set of related database operations. How do you track your changes? In your DataContext? In your ViewModel? Elsewhere?

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