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• Detect aborted connection during ASIO request

  - by Tim Sylvester

  Is there an established way to determine whether the other end of a TCP connection is closed in the asio framework without sending any data? Using Boost.asio for a server process, if the client times out or otherwise disconnects before the server has responded to a request, the server doesn't find this out until it has finished the request and generated a response to send, when the send immediately generates a connection-aborted error. For some long-running requests, this can lead to clients canceling and retrying over and over, piling up many instances of the same request running in parallel, making them take even longer and "snowballing" into an avalanche that makes the server unusable. Essentially hitting F5 over and over is a denial-of-service attack. Unfortunately I can't start sending a response until the request is complete, so "streaming" the result out is not an option, I need to be able to check at key points during the request processing and stop that processing if the client has given up.

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• F# return type coercion

  - by Alex

  Hi, In F# I have a function that returns System.Linq.Expression instances: and System.Object with member this.ToExpression() = match this with | :? System.Int32 -> Expression.Constant(this) :> Expression | :? System.Boolean -> Expression.Constant(this) :> Expression | :? Tml.Runtime.Seq as s -> s.ToExpression() | _ -> failwith "bad expression" If I omit the type coercions on the return values F# will infer the return type of the function to ConstantExpression. My first thought was to explicitly mark the return type as being : #Expression, but that didn't work. Is there a more elegant way of doing this that doesn't involve manually casting return types to the most generic type? Thanks.

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• Findbugs warning: Equals method should not assume anything about the type of its argument

  - by Uri

  When running FindBugs on my project, I got a few instances of the error described above. Namely, my overriding versions of equals cast the RHS object into the same type as the object in which the overriding version is defined. However, I'm not sure whether a better design is possible, since AFAIK Java does not allow variance in method parameters, so it is not possible to define any other type for the equals parameter. Am I doing something very wrong, or is FindBugs too eager? A different way to phrase this question is: what is the correct behavior if the object passed to equals is not the same type as an LHS: Is this a false, or should there be an exception? For example: public boolean equals(Object rhs) { MyType rhsMyType = (MyType)rhs; // Should throw exception if(this.field1().equals(rhsMyType.field1())... // Or whatever }

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• IS NULL doesn't work as expected in SQL Server 2000 with no Service Pack on it

  - by user306825

  The following batch executed on different instances of SQL Server 2000 illustrates the problem. select @@version create table a (a int) create table b (b int) insert into a(a) values (1) insert into a(a) values (2) insert into a(a) values (3) insert into b(b) values (1) insert into b(b) values (2) select * from a left outer join (select 1 as test, b from b) as j on j.b = a.a where j.test IS NULL drop table a drop table b Output 1: Microsoft SQL Server 2000 - 8.00.194 (Intel X86) Aug 6 2000 00:57:48 Copyright (c) 1988-2000 Microsoft Corporation Developer Edition on Windows NT 6.1 (Build 7600: ) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) a test b ----------- ----------- ----------- (0 row(s) affected) Output 2: Microsoft SQL Server 2000 - 8.00.2039 (Intel X86) May 3 2005 23:18:38 Copyright (c) 1988-2003 Microsoft Corporation Developer Edition on Windows NT 5.2 (Build 3790: Service Pack 2) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) (1 row(s) affected) a test b ----------- ----------- ----------- 3 NULL NULL (1 row(s) affected) If someone encounters the same problem - make sure you have the SP installed!

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• Fixing javascript Array functions in Internet Explorer (indexOf, forEach, etc)

  - by Chas Emerick

  As detailed elsewhere, and otherwise apparently well-known, Internet Explorer (definitely 7, and in some instances, 8) do not implement key functions, in particular on Array (such as forEach, indexOf, etc). There are a number of workarounds here and there, but I'd like to fold a proper, canonical set of implementations into our site rather than copy and paste or hack away at our own implementations. I've found js-methods, which looks promising, but thought I'd post here to see whether another library comes more highly-recommended. A couple of misc. criteria: the lib should just be a no-op for those functions that a browser already has implementations for (js-methods appears to do quite well here) non-GPL, please, though LGPL is acceptable

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• Handling undo and edit flag on window with several model objects

  - by Rui Pacheco

  Hi, I've a window that will hold several instances of a model object, listed in a table. The model object is updated using a text view. What is the best way to keep the edit flag and undo manager in synch with the content of the different model objects? I'm thinking creating an instance of the undo manager on the model object and manually set the undo manager for the text view every time the user choses a new model object. Does the undo manager also handle the edited flag?

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• JScript JSON Object Check

  - by George

  I'm trying to check if json[0]['DATA']['name'][0]['DATA']['first_0'] exists or not when in some instances json[0]['DATA']['name'] contains nothing. I can check json[0]['DATA']['name'] using if (json[0]['DATA']['name'] == '') { // DOES NOT EXIST } however if (json[0]['DATA']['name'][0]['DATA']['first_0'] == '' || json[0]['DATA']['name'][0]['DATA']['first_0'] == 'undefined') { // DOES NOT EXIST } returns json[0]['DATA']['name'][0]['DATA'] is null or not an object. I understand this is because the array 'name' doesn't contain anything in this case, but in other cases first_0 does exist and json[0]['DATA']['name'] does return a value. Is there a way that I can check json[0]['DATA']['name'][0]['DATA']['first_0'] directly without having to do the following? if (json[0]['DATA']['name'] == '') { if (json[0]['DATA']['name'][0]['DATA']['first_0'] != 'undefined') { // OBJECT EXISTS } }

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• cross-user C# mutex

  - by Martin

  My app is forced to use a 3rd party module which will blue-screen Windows if two instances are started at the same time on the same machine. To work around the issue, my C# app has a mutex: static Mutex mutex = new Mutex(true, "{MyApp_b9d19f99-b83e-4755-9b11-d204dbd6d096}"); And I check if it's present - and if so I show an error message and close the app: bool IsAnotherInstanceRunning() { if (mutex.WaitOne(TimeSpan.Zero, true)) return (true); else return (false); } The problem is if two users can log in and open the application at the same time, and IsAnotherInstanceRunning() will return false. How do I get around this?

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• mongodb read/write performance and mongo hosting in the cloud

  - by z3cko

  we are currently developing a high traffic rails application with facebooker (facebook game). since amazon simpledb (aws-sdb) is really slow, we are thinking of using a dedicated mongodb server as offered by mongoHQ for example. questions: what is the read/writes peak value for a mongodb server running on a amazon ec2 instance? what would be a recommended setup for a ec2 hosted app with mongodb - a master on amazon EBS and replicas on the ec2 instances? any examples or experiences? is there a company that offers mongodb hosting in the cloud? thanks, mz

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• Should a Unit-test replicate functionality or Test output?

  - by Daniel Beardsley

  I've run into this dilemma several times. Should my unit-tests duplicate the functionality of the method they are testing to verify it's integrity? OR Should unit tests strive to test the method with numerous manually created instances of inputs and expected outputs? I'm mainly asking the question for situations where the method you are testing is reasonably simple and it's proper operation can be verified by glancing at the code for a minute. Simplified example (in ruby): def concat_strings(str1, str2) return str1 + " AND " + str2 end Simplified functionality-replicating test for the above method: def test_concat_strings 10.times do str1 = random_string_generator str2 = random_string_generator assert_equal (str1 + " AND " + str2), concat_strings(str1, str2) end end I understand that most times the method you are testing won't be simple enough to justify doing it this way. But my question remains; is this a valid methodology in some circumstances (why or why not)?

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• Java: Non-static nested classes and instance.super()

  - by Kiv

  I'm having a hard time wrapping my head around non-static nested classes in Java. Consider the following example, which prints "Inner" and then "Child". class Outer { class Inner { Inner() { System.out.println("Inner"); } } } public class Child extends Outer.Inner { Child(Outer o) { o.super(); System.out.println("Child"); } public static void main(String args[]) { new Child(new Outer()); } } I understand that instances of Inner always have to be associated with an Outer instance, and that that applies to Child too since it extends Inner. My question is what the o.super() syntax means - why does it call the Inner constructor? I've only seen a plain super(args) used to call the superclass constructor and super.method() to call the superclass version of an overridden method, but never something of the form instance.super().

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• The best way to assign an immutable instance to a Collection in Java

  - by Ali

  Today I was reading through some Hibernate code and I encounter something interesting. There is a class called CollectionHelper that defines the following constant varibale: public final class CollectionHelper { public static final List EMPTY_LIST = Collections.unmodifiableList( new ArrayList(0 ) ; public static final Collection EMPTY_COLLECTION = Collections.unmodifiableCollection(new ArrayList(0) ); public static final Map EMPTY_MAP = Collections.unmodifiableMap( new HashMap(0) ); They have used these constants to initialize collections with immutable instances. Why they didn't simply use the Collections.EMPTY_LIST for initializing lists? Is there a benefit in using the following method?

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• "Collection was modified; enumeration operation may not execute." on form disposal.

  - by cyclotis04

  "Collection was modified; enumeration operation may not execute." appears to be a common error with foreach loops, but I can't figure mine out. I have two classes of forms. One is begun on startup, and a button creates new instances of the second form, and displays them. When I close the secondary forms, I get an InvalidOperationException. FirstForm.cs public partial class FirstForm : Form { SecondForm frmSecond; ... private void button1_Click(object sender, EventArgs e) { frmSecond= new SecondForm (); frmSecond.Show(); } } SecondForm.designer.cs partial class SecondForm { ... protected override void Dispose(bool disposing) { if (disposing && (components != null)) { components.Dispose(); } base.Dispose(disposing); // InvalidOperationException thrown here. } }

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• Using property file in hibernate mapping

  - by Zoltan Hamori

  Hi, I have a two nodes environment using the same database. In the database there is a resource table like RESOURCE_ID, CODE, NODE The content of the NODE column can be 1 or 2 depending on which node can use it. As I need to deploy the same ear to the two nodes, I would like to map this table like this: <hibernate-mapping> <class name="ResourceVO" table="RESOURCE" dynamic-update="true" optimistic-lock="dirty" where="NODE=${node.value}" > I would like to store the node.value property on the file system, so the instances could identify which resource to use. Is it possible in hibernate?

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• Hitting a memory limit slows down the .Net application

  - by derdo

  We have a 64bit C#/.Net3.0 application that runs on a 64bit Windows server. From time to time the app can use large amount of memory which is available. In some instances the application stops allocating additional memory and slows down significantly (500+ times slower).When I check the memory from the task manager the amount of the memory used barely changes. The application keeps on running very slowly and never gives an out of memory exception. Any ideas? Let me know if more data is needed.

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• tomcat 6 - Cluster / BackupManager

  - by Kevin

  Hi, I have a question regarding Clustering (session replication/failover) in tomcat 6 using BackupManager. Reason I chose BackupManager, is because it replicates the session to only one other server. I am going to run through the example below to try and explain my question. I have 6 nodes setup in a tomcat 6 cluster with BackupManager. The front end is one Apache server using mod_jk with sticky session enabled Each node has 1 session each. node1 has a session from client1 node2 has a session from client2 .. .. Now lets say node1 goes down ; assuming node2 is the backup, node2 now has two sessions (for client2 and client1) The next time client1 makes a request, what exactly happens ? Does Apache "know" that node1 is down and does it send the request directly to node2 ? =OR= does it try each of the 6 instances and find out the hard way who the backup is ?

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• Factory Method pattern and public constructor

  - by H4mm3rHead

  Hi, Im making a factory method that returns new instances of my objects. I would like to prevent anyone using my code from using a public constructor on my objects. Is there any way of doing this? How is this typically accomplished: public abstract class CarFactory { public abstract ICar CreateSUV(); } public class MercedesFactory : CarFactory { public override ICar CreateSUV() { return new Mercedes4WD(); } } I then would like to limit/prevent the other developers (including me in a few months) from making an instance of Mercedes4WD. But make them call my factory method. How to?

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• Memory leak with WPF & ItemsControl (VB.NET)

  - by Matt H.

  I have an ItemsControl that uses a DataTemplate to display properties in my customClass that implements INotifyPropertyChanged... Pretty straightforward... Some items in the DataTemplate use CommandBindings (such as buttons), and a few have some code-behind (yuck). When I empty the ItemsControl and set all instances of customClass = Nothing , no memory is released from my program. This becomes a problem pretty quickly! Any idea where I should start looking? I've even gone so far as to completely traverse the visual tree of each DataTemplate instance and set each Visual = Nothing. I'm not really if that's supposed to have any effect though.

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• Differences between query using LINQ and IQueryable interface directly?

  - by JohnMetta

  Using Entity Framework 4, and given: ObjectSet<Thing> AllThings = Context.CreateObjectSet<Thing>; public IQueryable<Thing> ByNameA(String name) { IQueryable<Thing> query = from o in AllThings where o.Name == name select o; return query; } public IQueryable<Thing> ByNameB(String name) { return AllThings.Where((o) => o.Name == name); } Both return IQueryable< instances, and thus the query doesn't hit the server until something like ToList() is called, right? Is it purely readability that is the difference, or are the using fundamentally different technologies on the back-end?

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• How Java Runtime Maps to Targets

  - by zharvey

  According to the Javadocs for Runtime here: Every Java application has a single instance of class Runtime that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the getRuntime method. An application cannot create its own instance of this class. My question is: what's their definition of an application? Is each JAR/WAR/EAR considered a standalone application? What about a plain ole' Driver.class class with a main() method? What about JEE containers that house EARs and EJBs? I guess I'm trying to understand how many Runtime instances could be up and running inside a complex (JEE) system. And understanding that requires me to understand what specific "things" constitute an "application" in Java terminology. Thanks in advance!

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• How can I copy a queryset to a new model in django admin?

  - by user3806832

  I'm trying to write an action that allows the user to select the queryset and copy it to a new table. So: John, Mark, James, Tyler and Joe are in a table 1( called round 1) The user selects the action that say to "move to next round" and those same instances that were chosen are now also in the table for "round 2". I started trying with an action but don't really know where to go from here: def Round_2(modeladmin, request, queryset): For X in queryset: X.pk = None perform.short_description = "Move to Round 2" How can I copy them to the next table with all of their information (pk doesn't have to be the same)? Thanks

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• Search for Variable Usage In SSIS tasks

  - by yoni.s

  Hi all: As what seems to be some sort of penance for sins in a prior life, I have been tasked with maintaining some SSIS packages. (NO! NO BADMOUTHING SSIS!! BAD PROGRAMMMER! NO DOUGHNUT!). Anyhoo, I many of the packages have variables, defined in an outer container, which are used in multiple inner containers, in script tasks. What I want to do, is find out all the places in a package a variable being used; in other words, search for instances of variable usage in all tasks of a package. This would be a huge help, but I cannot for the life of me find out how this can be done in BIDS. (this is SSIS/BIDS 2008) Thanks for any help, YS

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• Chaning coding style due to Android GC performance, how far is too far?

  - by Benju

  I keep hearing that Android applications should try to limit the number of objects created in order to reduce the workload on the garbage collector. It makes sense that you may not want to created massive numbers of objects to track on a limited memory footprint, for example on a traditional server application created 100,000 objects within a few seconds would not be unheard of. The problem is how far should I take this? I've seen tons of examples of Android applications relying on static state in order supposedly "speed things up". Does increasing the number of instances that need to be garbage collected from dozens to hundreds really make that big of a difference? I can imagine changing my coding style to now created hundreds of thousands of objects like you might have on a full-blown Java-EE server but relying on a bunch of static state to (supposedly) reduce the number of objects to be garbage collected seems odd. How much is it really necessary to change your coding style in order to create performance Android apps?

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• Code equivalence between Javascript and PHP

  - by xdevel2000

  I'm trying to learn PHP and I wish to know if there are some function equivalence constructs: In JS I can do: var t = function() {}; t(); myObj.DoStuff = function() {} // here I add a method at run-time myObj.DoStuff(); myObj["DoStuff"](); var j = myObj.DoStuff; j(); and so other things with function evaluation. In Js objects are associative arrays so every properties is accessible with the subscript notation... Can I add a method at run-time to a class template so next its object instances can have it? In JS I can do that via a prototype function property.

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• StructureMap: Wiring (generic) implementations to an implementation of another type

  - by Jeremy Frey

  If I have an interface: public interface IRepository<T> And an abstract class: public abstract class LinqToSqlRepository<T, TContext> : IRepository<T> where T : class where TContext : DataContext And a whole bunch of implementations of IRepository / LinqToSqlRepository (e.g. AccountRepository, ContactRepository, etc.), what's the best way to to use StructureMap (2.5.3) to generically wire them all up? e.g., I want this code to pass: [Test] public void ShouldWireUpAccountRepositories { var accountRepo = ObjectFactory.GetInstance<IRepository<Account>>(); Assert.IsInstanceOf<AccountRepository>(accountRepo); } Without explicitly writing this: ObjectFactory.Configure(x => x.ForRequestedType<IRepository<Account>>() .TheDefaultIsConcreteType<AccountRepository>()); In the past, we've always created a specific interface on each repository that inherited from the generic one, and used the default scanner to automatically wire all of those instances, but I'd like to be able to ask specifically for an IRepository<Account> without cluttering up the project with additional interfaces / configurations.

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