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• How to manage long running background threads and report progress with DDD

  - by Mr Happy

  Title says most of it. I have found surprising little information about this. I have a long running operation of which the user wants to see the progress (as in, item x of y processed). I also need to be able to pause and stop the operation. (Stopping doesn't rollback the items already processed.) The thing is, it's not that each item takes a long time to get processed, it's that that there are usually a lot of items. And what I've read about so far is that it's somewhat of an anti-pattern to put something like a queue in the DB. I currently don't have any messaging system in place, and I've never worked with one either. Another thing I read somewhere is that progress reporting is something that belongs in the application layer, but it didn't go into the details. So having said all this, what I have in mind is the following. User request with list of items enters the application layer. Application layer gets some information from the domain needed to process the items. Application layer passes the items and the information off to some domain service (should the implementation of this service belong in the infrastructure layer?) This service spins up a worker thread with callbacks for both progress reporting and pausing/stopping it. This worker thread will process each item in it's own UoW. This means the domain information from earlier needs to be stored in some DTO. Since nothing is really persisted, the service should be singleton and thread safe Whenever a user requests a progress report or wants to pause/stop the operation, the application layer will ask the service. Would this be a correct solution? Or am I at least on the right track with this? Especially the singleton and thread safe part makes the whole thing feel icky.

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• Motivation and use of move constructors in C++

  - by Giorgio

  I recently have been reading about move constructors in C++ (see e.g. here) and I am trying to understand how they work and when I should use them. As far as I understand, a move constructor is used to alleviate the performance problems caused by copying large objects. The wikipedia page says: "A chronic performance problem with C++03 is the costly and unnecessary deep copies that can happen implicitly when objects are passed by value." I normally address such situations by passing the objects by reference, or by using smart pointers (e.g. boost::shared_ptr) to pass around the object (the smart pointers get copied instead of the object). What are the situations in which the above two techniques are not sufficient and using a move constructor is more convenient?

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• What is the best way to track / record the current programming project you work on? [duplicate]

  - by user2424160

  This question already has an answer here: Methodology for Documenting Existing Code Base 6 answers When do you start documenting the code? 13 answers Where should a programmer explain the extended logic behind the code? 5 answers I have been in this problem for long time and I want to know how it's done in real / big companies project? Suppose I have the project to build a website. Now I divide the project into sub tasks and do it. But you know that suppose I have task1 in hand like export the page to pdf. Now I spend 3 days to do that , came across various problems, many Stack Overflow questions and in the end I solve it. Now 4 months after someone told me that there is some error in the code. Now by that I completely forgot about (60%) of how I did it and why I do this way. I document the code but I can't write the whole story of that in the code. Then I have to spend much time on code to find what was the problem so that I added this line etc. I want to know that is there any way that i can log steps in completing the project. So that I can see how I end up with code, what errors I got, what questions I asked on SO and etc. How people do it in real time? Which software to use? I know in our project management software called JIRA we have tasks but that does not cover what steps I took to solve that tasks. What is the best way so that when I look back at my 2 year old project, I know how I solve particular task?

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• Algorithm to Solve Most of a Problem

  - by Mike G

  I need an Algorithm/Design Pattern that allows me to try to get the maximum number of rules followed. So I have a couple teams and I need to pair them with a referee and against each other into a round robin. There a rules on who can compete with who and who can judge who so I need to find the configuration that satisfies the most of these. Some rules are more important than others and are "worth more" when evaluating "what satisfies the most of them" There probably isn't a algorithm for this, but is there a design pattern that could help me maximize my chances of finding this configuration?

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• Knowing so much but application is a problem?

  - by Moaz ELdeen

  In my work, my friends always tell me, you know so much about computer science, electronics engineering,..etc. But I have difficulty in applying them and my code is crap. How to solve that problem? Will I be better or programming isn't my career? For example, yes I know OCTree that is used for space partitioning in games and it is used for optimization, did I implement it? No, but I know about it in principle.. Do I know algorithms like Sorting, Searching,..etc? Yes, and I know them pretty well, but didn't implement them.. When I get a task, I struggle in applying the things that I know...

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• Recommened design pattern to handle multiple compression algorithms for a class hierarchy

  - by sgorozco

  For all you OOD experts. What would be the recommended way to model the following scenario? I have a certain class hierarchy similar to the following one: class Base { ... } class Derived1 : Base { ... } class Derived2 : Base { ... } ... Next, I would like to implement different compression/decompression engines for this hierarchy. (I already have code for several strategies that best handle different cases, like file compression, network stream compression, legacy system compression, etc.) I would like the compression strategy to be pluggable and chosen at runtime, however I'm not sure how to handle the class hierarchy. Currently I have a tighly-coupled design that looks like this: interface ICompressor { byte[] Compress(Base instance); } class Strategy1Compressor : ICompressor { byte[] Compress(Base instance) { // Common compression guts for Base class ... // if( instance is Derived1 ) { // Compression guts for Derived1 class } if( instance is Derived2 ) { // Compression guts for Derived2 class } // Additional compression logic to handle other class derivations ... } } As it is, whenever I add a new derived class inheriting from Base, I would have to modify all compression strategies to take into account this new class. Is there a design pattern that allows me to decouple this, and allow me to easily introduce more classes to the Base hierarchy and/or additional compression strategies?

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• How can I selectively update XNA GameComponents?

  - by Bill

  I have a small 2D game I'm working on in XNA. So far, I have a player-controlled ship that operates on vector thrust and is terribly fun to spin around in circles. I've implemented this as a DrawableGameComponent and registered it with the game using game.Components.Add(this) in the Ship object constructor. How can I implement features like pausing and a menu system with my current implementation? Is it possible to set certain GameComponents to not update? Is this something for which I should even be using a DrawableGameComponent? If not, what are more appropriate uses for this?

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• programming manner to solve problem

  - by gcc

  Everyone has style(s)/technique(s) to approach/solve real world problems. This/these technique(s) distinguish(es) us from other people or other programmers. (Actually, I think it make us a wanted/ great programmer/computer science ) To improve, we read a lot of books (ex : programming style, how to solve program, how to approach problem, software and algorithm). Can I learn your technique? In other words, if someone gives you a problem, at first step, what are you doing to solve it? (In all honesty, I want learn in what manner you are looking problem )

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• Maintainability of Boolean logic - Is nesting if statements needed?

  - by Vaccano

  Which of these is better for maintainability? if (byteArrayVariable != null) if (byteArrayVariable .Length != 0) //Do something with byteArrayVariable OR if ((byteArrayVariable != null) && (byteArrayVariable.Length != 0)) //Do something with byteArrayVariable I prefer reading and writing the second, but I recall reading in code complete that doing things like that is bad for maintainability. This is because you are relying on the language to not evaluate the second part of the if if the first part is false and not all languages do that. (The second part will throw an exception if evaluated with a null byteArrayVariable.) I don't know if that is really something to worry about or not, and I would like general feedback on the question. Thanks.

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• Default values - are they good or evil?

  - by Andrew

  The question about default values in general - default return function values, default parameter values, default logic for when something is missing, default logic for handling exceptions, default logic for handling the edge conditions etc. For a long time I considered default values to be a "pure evil" thing, something that "cloaks the catastrophe" and results in a very hard do find bugs. But recently I started to think about default values as some sort of a technical debt ... which is not a straight bad thing but something that could provide some "short term financing" get us to survive the project (how many of us could afford to buy a house without taking out the mortgage?). When I say a "short term" - I don't mean - "do something quickly first and do refactor it out later before it hits the production". No - I am talking about relying on a hardcoded default values in a production software. Granted - it could cause some issues, but what if it only going to cause a single trouble in a whole year. Again - I am talking about the "average" mainstream software here (not a software for a nuclear power station) - the average web site or a UI application for the accounting software, meaning that people lives are not at stake, nor millions of dollars. Again, from my experience, business users would rather live with the software which "works somehow", rather then wait for a perfect one. And the use of default values helps a lot if you develop a software in a RAD style. But again - the longest debug sessions I have spent were because of the bugs introduced by a default value which either stopped being "a default" along the way or because a small subsystem has recently been upgraded and as a result of this upgrade it does not handle the default correctly (e.g. empty list vs null, or null string vs empty string). So my question is - are the default values good or evil. And if they are a technical debt - how do measure up how much you can borrow so you can afford the repayments? Would really appreciate any input. Cheers. EDIT: If I am using the default values as a way to cut the corners during the development - and if the corners cutting results in a bugs and issues - what is the methodology to recover from these issues?

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• Best practice in setting return value (use else or?)

  - by Deckard

  Whenever you want to return a value from a method, but whatever you return depends on some other value, you typically use branching: int calculateSomething() { if (a == b) { return x; } else { return y; } } Another way to write this is: int calculateSomething() { if (a == b) { return x; } return y; } Is there any reason to avoid one or the other? Both allow adding "else if"-clauses without problems. Both typically generate compiler errors if you add anything at the bottom. Note: I couldn't find any duplicates, although multiple questions exist about whether the accompanying curly braces should be on their own line. So let's not get into that.

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• Pattern for a class that does only one thing

  - by Heinzi

  Let's say I have a procedure that does stuff: void doStuff(initalParams) { ... } Now I discover that "doing stuff" is quite a compex operation. The procedure becomes large, I split it up into multiple smaller procedures and soon I realize that having some kind of state would be useful while doing stuff, so that I need to pass less parameters between the small procedures. So, I factor it out into its own class: class StuffDoer { private someInternalState; public Start(initalParams) { ... } // some private helper procedures here ... } And then I call it like this: new StuffDoer().Start(initialParams); or like this: new StuffDoer(initialParams).Start(); And this is what feels wrong. When using the .NET or Java API, I always never call new SomeApiClass().Start(...);, which makes me suspect that I'm doing it wrong. Sure, I could make StuffDoer's constructor private and add a static helper method: public static DoStuff(initalParams) { new StuffDoer().Start(initialParams); } But then I'd have a class whose external interface consists of only one static method, which also feels weird. Hence my question: Is there a well-established pattern for this type of classes that have only one entry point and have no "externally recognizable" state, i.e., instance state is only required during execution of that one entry point?

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• How to play many sounds at once in OpenAL

  - by Krom

  Hello, I'm developing an RTS game and I would like to add sounds to it. My choice has landed on OpenAL. I have plenty of units which from time to time make sounds: fSound.Play(sfx_shoot, location). Sounds often repeat, e.g. when squad of archers shoots arrows, but they are not synced with each other. My questions are: What is the common design pattern to play multiple sounds in OpenAL, when some of them are duplicate? What are the hardware limitations on sounds count and tricks to overcome them?

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• Identifying the best pattern

  - by Daniel Grillo

  I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern.

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• Relative encapsulation design

  - by taher1992

  Let's say I am doing a 2D application with the following design: There is the Level object that manages the world, and there are world objects which are entities inside the Level object. A world object has a location and velocity, as well as size and a texture. However, a world object only exposes get properties. The set properties are private (or protected) and are only available to inherited classes. But of course, Level is responsible for these world objects, and must somehow be able to manipulate at least some of its private setters. But as of now, Level has no access, meaning world objects must change its private setters to public (violating encapsulation). How to tackle this problem? Should I just make everything public? Currently what I'm doing is having a inner class inside game object that does the set work. So when Level needs to update an objects location it goes something like this: void ChangeObject(GameObject targetObject, int newX, int newY){ // targetObject.SetX and targetObject.SetY cannot be set directly var setter = new GameObject.Setter(targetObject); setter.SetX(newX); setter.SetY(newY); } This code feels like overkill, but it doesn't feel right to have everything public so that anything can change an objects location for example.

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• Is there a name for the Builder Pattern where the Builder is implemented via interfaces so certain parameters are required?

  - by Zipper

  So we implemented the builder pattern for most of our domain to help in understandability of what actually being passed to a constructor, and for the normal advantages that a builder gives. The one twist was that we exposed the builder through interfaces so we could chain required functions and unrequired functions to make sure that the correct parameters were passed. I was curious if there was an existing pattern like this. Example below: public class Foo { private int someThing; private int someThing2; private DateTime someThing3; private Foo(Builder builder) { this.someThing = builder.someThing; this.someThing2 = builder.someThing2; this.someThing3 = builder.someThing3; } public static RequiredSomething getBuilder() { return new Builder(); } public interface RequiredSomething { public RequiredDateTime withSomething (int value); } public interface RequiredDateTime { public OptionalParamters withDateTime (DateTime value); } public interface OptionalParamters { public OptionalParamters withSeomthing2 (int value); public Foo Build ();} public static class Builder implements RequiredSomething, RequiredDateTime, OptionalParamters { private int someThing; private int someThing2; private DateTime someThing3; public RequiredDateTime withSomething (int value) {someThing = value; return this;} public OptionalParamters withDateTime (int value) {someThing = value; return this;} public OptionalParamters withSeomthing2 (int value) {someThing = value; return this;} public Foo build(){return new Foo(this);} } } Example of how it's called: Foo foo = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).build(); Foo foo2 = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).withSomething2(3).build();

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• Software development magazines [closed]

  - by Sebastian

  Ive spent the last hour or so browsing the web for professional development magazines. I am mostly interested in the java platform, agile methods, "programming in general" (tutorials on languages or whatever, "hot new stuff" etc) and software craftmanship. My best finding yet was pragpub and maybe MSDN magazine. I am willing to pay and have a Zinio account if anyone knows a magazine about programming that is distributed by them. Ive already browsed a couple of related threads here on stackexchange. ACM and IEEE does not seem relevant, as Im not interested in research articles. Maybe conferences like OOPSLA as somebody mentioned in another thread. PS. I prefer if they are in pdf or readable on kindle or a tablet. DS. BR Sebastian

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• Quick Tip - Speed a Slow Restore from the Transaction Log

  - by KKline

  Here's a quick tip for you: During some restore operations on Microsoft SQL Server, the transaction log redo step might be taking an unusually long time. Depending somewhat on the version and edition of SQL Server you've installed, you may be able to increase performance by tinkering with the readahead performance for the redo operations. To do this, you should use the MAXTRANSFERSIZE parameter of the RESTORE statement. For example, if you set MAXTRANSFERSIZE=1048576, it'll use 1MB buffers. If you...(read more)

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• Making dummy applications while not involved in LIVE work [closed]

  - by Ratan Sharma

  I know this is subjective but I am looking for some real time helpful points/advice here, which will be helpful for some to get motivated. In our company so many people are on bench(not assigned with real time work) and they do not want to experiment things by their own. What would be a good motivation for them to keep their learning spirit? I personally feel that one can learn and give more effort in live client work than regular practicing things and making dummies. Am I right here or it is just my thinking only?

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• Best Creational Pattern for loggers in a multi-threaded system?

  - by Dipan Mehta

  This is a follow up question on my past questions : Concurrency pattern of logger in multithreaded application As suggested by others, I am putting this question separately. As the learning from the last question. In a multi-threaded environment, the logger should be made thread safe and probably asynchronous (where in messages are queued while a background thread does writing releasing the requesting object thread). The logger could be signleton or it can be a per-group logger which is a generalization of the above. Now, the question that arise is how does logger should be assigned to the object? There are two options I can think of: 1. Object requesting for the logger: Should each of the object call some global API such as get_logger()? Such an API returns "the" singleton or the group logger. However, I feel this involves assumption about the Application environment to implement the logger -which I think is some kind of coupling. If the same object needs to be used by other application - this new application also need to implement such a method. 2. Assign logger through some known API The other alternative approach is to create a kind of virtual class which is implemented by application based on App's own structure and assign the object sometime in the constructor. This is more generalized method. Unfortunately, when there are so many objects - and rather a tree of objects passing on the logger objects to each level is quite messy. My question is there a better way to do this? If you need to pick any one of the above, which approach is would you pick and why? Other questions remain open about how to configure them: How do objects' names or ID are assigned so that will be used for printing on the log messages (as the module names) How do these objects find the appropriate properties (such as log levels, and other such parameters) In the first approach, the central API needs to deal with all this varieties. In the second approach - there needs to be additional work. Hence, I want to understand from the real experience of people, as to how to write logger effectively in such an environment.

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• Why is nesting or piggybacking errors within errors bad in general?

  - by dietbuddha

  Why is nesting or piggybacking errors within errors bad in general? To me it seems bad intuitively, but I'm suspicious in that I cannot adequately articulate why it is bad. This may be because it is not in general bad and that it is only bad in specific instances. Why is it detrimental to design error/exception handling in such a way. The specific instance is that of a REST service. There is a desire by some to use http errors (specifically the 500 response) as a way to indicate any problem with specific instances of a resource. An example of an instance resource in this case would be: http://server/ticket/80 # instance http://server/ticket # not an instance So this is the behavior that is being proposed. If ticket 80 does not exist return a http response code of 500. Within the body of the error return the "real" error as an additional error code and description. If the ticket resource doesn't exist return a response code of 404.

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• Use Those Schemas, People!

  - by BuckWoody

  Database Schemas are just containers – they aren’t users or anything else – think of a sub-directory on the hard drive. In early versions of SQL Server we “hid” schemas, placing all objects under “dbo”, which gave the erroneous perception that Schemas are users. In SQL Server 2005, we “un-hid” or re-introduced schemas within the database. Users can have a default schema (a place where their new objects go), you can add new schemas and transfer objects between them, and they have many other benefits. But I still see a lot of applications, developed by shops I know as well as vendors, that don’t make use of a Schema. Everything is piled under dbo. I completely understand this – since permissions can be granted to a schema, they feel a lot like a user, so it’s just easier not to worry about both users and schemas when you create a database. But if you’ll use them properly you can make your application more understandable and portable. You should at least take a few minutes and read more about them – you owe it to your users: http://msdn.microsoft.com/en-us/library/ms190387.aspx Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Recommendation for Improving Programming Skills

  - by Moaz ELdeen

  I'm 25, I know C++ syntax since 9 years.. but It seems that I have copied so much code, and I didn't learn that much and didn't solve a lot of algorithms in my own. Currently I'm working for computer vision programmer as a junior and I have difficulity of doing algorithms like blob tracking or object tracking, writing algorithms like KNN, Quadtree,..etc. I don't know what to do, or what to improve, I tried to write asteriods game, I have finished it, and here you can watch it https://www.youtube.com/watch?v=jw0L4aCB4TU What should I do more to enhance my skills ?

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• How do you author code

  - by garbagecollector

  This is something I was never taught. I have seen alot of different types of authoring styles. I code primarily in Java and Python. I was wondering if there was a standard authoring style or if everything is freestyle. Also if you answer would you mind attaching the style you use to author files that your create at home or at work. I usually just go @author garbagecollector @company garbage inc.

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