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  • Thread safe GUI programming

    - by James
    I have been programming Java with swing for a couple of years now, and always accepted that GUI interactions had to happen on the Event Dispatch Thread. I recently started to use GTK+ for C applications and was unsurprised to find that GUI interactions had to be called on gtk_main. Similarly, I looked at SWT to see in what ways it was different to Swing and to see if it was worth using, and again found the UI thread idea, and I am sure that these 3 are not the only toolkits to use this model. I was wondering if there is a reason for this design i.e. what is the reason for keeping UI modifications isolated to a single thread. I can see why some modifications may cause issues (like modifying a list while it is being drawn), but I do not see why these concerns pass on to the user of the API. Is there a limit imposed by an operating system? Is there a good reason these concerns are not 'hidden' (i.e. some form of synchronization that is invisible to the user)? Is there any (even purely conceptual) way of creating a thread safe graphics library, or is such a thing actually impossible? I found this http://blogs.operationaldynamics.com/andrew/software/gnome-desktop/gtk-thread-awareness which seems to describe GTK differently to how I understood it (although my understanding was the same as many people's) How does this differ to other toolkits? Is it possible to implement this in Swing (as the EDT model does not actually prevent access from other threads, it just often leads to Exceptions)

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  • What happens at control invoke function?

    - by user65909
    A question about form controls invoke function. Control1 is created on thread1. If you want to update something in Control1 from thread2 you must do something like: delegate void SetTextCallback(string txt); void setText(string txt) { if (this.textBox1.InvokeRequired) { SetTextCallback d = new SetTextCallback(setText); this.Invoke(d, new object[] { txt }); } else { // this will run on thread1 even when called from thread2 this.textBox1.AppendText(msg); } }` What happens behind the scenes here? This invoke behaves different from a normal object invoke. When you want to call a function in an object on a specific thread, then that thread must be waiting on some queue of delegates, and execute the incoming delegates. Is it correct that the windows forms control invoke function is completely different from the standard object invoke function?

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  • Clients with multiple proxy and multithreading callbacks

    - by enzom83
    I created a sessionful web service using WCF, and in particular I used the NetTcpBinding binding. In addition to methods to initiate and terminate a session, other methods allow the client to send to one or more tasks to be performed (the results are returned via callback, so the service is duplex), but they also allow you to know the status of the service. Assuming you activate the same service on multiple endpoints, and assuming that the client knows these endpoints (for example, it could maintain a List of endpoints), the client should connect with one or more replicas of the same service. The client periodically updates the status of the service, so when it needs to perform a new task (the task is submitted by the user via UI), it selects the service currently less loaded and sends the task to it. Periodically, the client also initiates a maintenance procedure in order to disconnect from one or more overloaded service and in order to connect with new services. I created a client proxy using the svcutil tool. I wish each proxy can be used simultaneously by different threads, for example, in addition to the thread that submits the tasks using a proxy, there are also the following two threads which act periodically: a thread that periodically sends a request to the service in order to obtain the updated state; a thread that periodically selects a proxy to close and instantiates a new proxy to replace the closed one. To achieve these objectives, is it sufficient to create an array of proxies and manage their opening and closing in separate threads? I think I read that the proxy method calls are thread safe, so I would not need to perform a lock before requesting updates to the service. However, when the maintenance procedure (which is activated on its own thread) decides to close a proxy, should I perform a lock? Finally, each proxy is also associated with an object that implements the callback interface for the service: are the callbacks (invoked on the client) executed on different threads on the client? I would like to wrap the management of the proxy in one or more classes so that it can then easily manage within a WPF application.

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  • Need explanation of hexagonal architecture

    - by Victor Grazi
    I am reading about Alistair Cockburn's Hexagonal Architecture http://alistair.cockburn.us/Hexagonal+architecture with interest. One claim he makes is: "Finally, the automated function regression tests detect any violation of the promise to keep business logic out of the presentation layer. The organization can detect, and then correct, the logic leak." I do not understand this point. Is he saying that because the test is headless, then calls to a ui layer will throw exceptions? That doesn't seem to be a very sound test!

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  • Scalable Architecture for modern Web Development [on hold]

    - by Jhilke Dai
    I am doing research about Scalable architecture for Web Development, the research is solely to support Modern Web Development with flexible architecture which can scale up/down according to the needs without losing any core functionality. By Modern Web I mean to support all the Devices used to access websites, but the loading mechanism for all devices would be different. My quest of architecture is: For PC: Accessing web in PC is faster but it also depends on the Geo-location, so, the application would check by default the capacity of Internet/Browser and load the page according to it. For Mobile: Most of the mobile design these days either hide information or use different version of same application. eg: facebook uses m.facebook.com which is completely different than PC version. Hiding the things from Mobile using JavaScript or CSS is not a solution as it'll consume the bandwidth and make the application slow. So, my architecture research is about Serving one Application, which has different stack. When the application receives the request it'd send the Packaged Stack to the received request. This way the load time for end users would be faster and maintenance of application for developers would be easier. I am researching about for 4-tier(layered) architecture like: Presentation Layer Application Logic Layer -- The main Logic layer which stores the Presentation Stack Business Logic Layer Data Layer Main Question: Have you come across of similar architecture? If so, then can you list the links here, I'm very much interested to learn about those implementations specially in real world scenario. Have you thought about similar architectures and tried your own ideas, or if you have any ideas regarding this, then I urge to share. I am open to any discussions regarding this, so, please feel free to comment/answer.

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  • Best open source ASP.NET MVC e-commerce projects

    - by Øyvind Knobloch-Bråthen
    I need to get a e-commerce site up and running, but I really don't want to program it from the bottom up if I don't need to. I want to program it using ASP.NET MVC. I'm looking for a good open source alternative (or one for purchase if it's modular enough) that I can use as a base and enhance with the needed functions? It has to have all "normal" e-commerce functions, and also the possibility to integrate with a credit card API of my choice. If anyone have any recommendations for me here, I would appreciate it :)

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  • Search network device from LAN through my C++ application and change the IP address

    - by Arun Kumar K S
    I am developing an application in C++ to communicate with my network device. I used UDP classes to search the device from the network. I done the code in such a way that from my application a broadcast message will send to the local network. The device will respond to the broadcast message and the application will get the IP address from that response. After establishing a network communication send a message to the device for changing the IP address. That worked fine if my devices IP address is correct. But when I set a wrong IP address and subnet to the device. My application will never get any messages from the device. So I can't able communicate to the device and not able get the device and unable to change the IP address etc. Say example IP address of the device 20.1.1.1 Subnet Mask 255.0.0.0 And in my system that runs the application IP address 192.168.1.23 Subnet Mask 255.255.255.0 I tried the Lantronix device installation software with their Lantronix device in network. It listed the device from the network and I am able to change the IP address from their software. Any one know how this is done in this type of software? How I can search in network to find the device and change the IP address when its IP address is not in range? Which protocol they used to find the device?

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  • Precising definition of programming paradigm

    - by Kazark
    Wikipedia defines programming paradigm thus: a fundamental style of computer programming which is echoed in the descriptive text of the paradigms tag on this site. I find this a disappointing definition. Anyone who knows the words programming and paradigm could do about that well without knowing anything else about it. There are many styles of computer programming at many level of abstraction; within any given programming paradigm, multiple styles are possible. For example, Bob Martin says in Clean Code (13), Consider this book a description of the Object Mentor School of Clean Code. The techniques and teachings within are the way that we practice our art. We are willing to claim that if you follow these teachings, you will enjoy the benefits that we have enjoyed, and you will learn to write code that is clean and professional. But don't make the mistake of thinking that we are somehow "right" in any absolute sense. Thus Bob Martin is not claiming to have the correct style of Object-Oriented programming, even though he, if anyone, might have some claim to doing so. But even within his school of programming, we might have different styles of formatting the code (K&R, etc). There are many styles of programming at many levels. Sp how can we define programming paradigm rigorously, to distinguish it from other categories of programming styles? Fundamental is somewhat helpful, but not specific. How can we define the phrase in a way that will communicate more than the separate meanings of each of the two words—in other words, how can we define it in a way that will provide additional meaning for someone who speaks English but isn't familiar with a variety of paradigms?

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  • Write a program consisting of a main module and three other modules

    - by user106080
    The owner of a super supermarket would like to have a program that computes the monthly gross pay of their employees as well as the employees’s net pay. The input for this program is the employee id number, hourly rate of pay, and number of regular and overtime hours hours worked. Gross pay is the sum of the wages earnes from regular hours; overtime is 1.5 times the regular rate. Net pay is gross pay hours; overtime is paid at 1.5 times the regular rate. Net pay is the gross pay minus deductions. Assume that deduction are taken for tax withholding (50 percent of gross pay) and parking ($10.00 per month) you will need the following variables: EmployeeID (a string) HourRate is (a float) RegHours (a float) ; GrossPay (a float);Tax (afloat) Parking (a float) OverTimeHours (a float) NetPay (a float) GrossPay = Regularhours* HourRate+OverTimeHours*(HourRate*1.5) NetPay= GrossPay – (GrossPay*Tax) – Parking

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  • How should I make progress further as a programmer?

    - by mushfiq
    Hello, I have just left my college after doing graduation in computer engineering,during my college life I tried to do some freelancing in local market.I succeeded in the last year and earned some small amounts based on joomla,wordpress and visual basic based job.I had some small projects on php,mysql also. After finishing my undergrad life,I sat for an written test for post of python programmer and luckily I got the job and is working there(Its a small software firm do most of the task in python).Day by day I have gained some experience with core python. Meanwhile an USA based web service firm called me for the interview and after finishing three steps(oral+mini coding project+final oral)they selected me(i was wondered!).And I am going to join their with in few days.There I have to work in python(based on Django framework,I know only basic of this framework). My problem is when I started to work with python simultaneously I worked in Odesk as a wordpress,joomla,drupal,php developer. Now a days I am feeling that I am getting "Jack of all trades master of none". My current situation is i am familiar with several popular web technologies but not an expert.I want to make myself skilled. How should I organize myself to be a skilled web programmer?

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  • Does Microsoft really offer "support"?

    - by SpashHit
    One of the arguments against using Open Source is that there is no "support". However, do big vendors (e.g. Microsoft) really offer "support" of any kind? I'm sure there is some sort of 4-figure-per-hour "paid support" option out there, but is that really an "option" for any problem short of one that is going to bankrupt your business? To put it more concretely... I buy a Microsoft product... it has a bug... now what? And how is that better than what I get from Open Source?

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  • UML Diagrams of Multi-Threaded Applications

    - by PersonalNexus
    For single-threaded applications I like to use class diagrams to get an overview of the architecture of that application. This type of diagram, however, hasn’t been very helpful when trying to understand heavily multi-threaded/concurrent applications, for instance because different instances of a class "live" on different threads (meaning accessing an instance is save only from the one thread it lives on). Consequently, associations between classes don’t necessarily mean that I can call methods on those objects, but instead I have to make that call on the target object's thread. Most literature I have dug up on the topic such as Designing Concurrent, Distributed, and Real-Time Applications with UML by Hassan Gomaa had some nice ideas, such as drawing thread boundaries into object diagrams, but overall seemed a bit too academic and wordy to be really useful. I don’t want to use these diagrams as a high-level view of the problem domain, but rather as a detailed description of my classes/objects, their interactions and the limitations due to thread-boundaries I mentioned above. I would therefore like to know: What types of diagrams have you found to be most helpful in understanding multi-threaded applications? Are there any extensions to classic UML that take into account the peculiarities of multi-threaded applications, e.g. through annotations illustrating that some objects might live in a certain thread while others have no thread-affinity; some fields of an object may be read from any thread, but written to only from one; some methods are synchronous and return a result while others are asynchronous that get requests queued up and return results for instance via a callback on a different thread.

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  • I don't understand why algorithms are so special

    - by Jessica
    I'm a student of computer science trying to soak up as much information on the topic as I can during my free time. I keep returning to algorithms time and again in various formats (online course, book, web tutorial), but the concept fails to sustain my attention. I just don't understand: why are algorithms so special? I can tell you why fractals are awesome, why the golden ratio is awesome, why origami is awesome and scientific applications of all the above. Heck I even love Newton's laws and conical sections. But when it comes to algorithms, I'm just not astounded. They are not insightful in new ways about human cognition at all. I was expecting algorithms to be shattering preconceptions and mind-altering but time and time again they fail miserably. What am I doing wrong in my approach? Can someone tell me why algorithms are so awesome?

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  • How many questions is it appropriate to ask as an intern?

    - by Casey Patton
    So, I just started an internship, and I'm worried that I'm asking too many questions. My mentor assigns me projects and helps me learn all the company's technologies and methodologies. However, there's so much new material for me to learn while doing this project that I have a lot of questions. I generally ask questions over instant messages or E-mail (those are the primary modes of communication for my company). I'm trying to be careful not to ask too many questions: I don't want to come off as annoying or dumb. How many questions are appropriate to ask? Once an hour? More? Less? Keep in mind, my mentor is also a fellow programmer who has his own responsibilities.

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  • The perfect crossfade

    - by epologee
    I find it hard to describe this problem in words, which is why I made a video (45 seconds) to illustrate it. Here's a preview of the questions, please have a look at it on Vimeo: http://vimeo.com/epologee/perfect-crossfade The issue of creating a flawless crossfade or dissolve of two images or shapes has been recurring to me in a number of fields over the last decade. First in video editing, then in Flash animation and now in iOS programming. When you start googling it, there are many workarounds to be found, but I really want to solve this without a hack this time. The summary: What is the name of the technique or curve to apply in crossfading two semi-transparent, same-colored bitmaps, if you want the resulting transparency to match the original of either one? Is there a (mathematical) function to calculate the neccessary partial transparency/alpha values during the fade? Are there programming languages that have these functions as a preset, similar to the ease in, ease out or ease in out functions found in ActionScript or Cocoa?

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  • Questions about Code Reviews

    - by bamboocha
    My team plans to do Code Review and asked me to make a concept what and how we are going to make our Code Reviews. We are a little group of 6 team members. We use an SVN repository and write programs in different languages (mostly: VB.NET, Java, C#), but the reviews should be also possible for others, yet not defined. Basically I am asking you, how are you doing it, to be more precise I made a list of some questions I got: 1. Peer Meetings vs Ticket System? Would you tend to do meetings with all members, rather than something like a ticket system, where the developer can add a new code change and some or all need to check and approve it? 1. What tool? I made some researches on my own and it showed that Rietveld seems to be the program to use for non-git solutions. Do you agree/disagree and why? 2. A good workflow to follow? 3. Are there good ways to minimize the effort for those meetings even more? 4. What are good questions, every code reviewer should follow? I already made a list with some questions, what would you append/remove? are there any magic numbers in the code? do all variable and method names make sense and are easily understandable? are all querys using prepared statement? are all objects disposed/closed when they are not needed anymore? 5. What are your general experiences with it? What's important? Things to consider/prevent/watch out?

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  • Who is likely to need the most this high-quality, measurable, reliable approach to software? [closed]

    - by Marek Cruz
    Software engineering is the application of principles of engineering to software. Trouble is, most of those who like to flatter with the title "software engineer" don't do that. They just keep writing code and patching it until it's stable enough to foist off on users. That's not software engineering. Who is likely to need the most the practice of software engineering? (with all the project planning, requirements engineering, software design, implementation based on the design, testing, deployment, awareness of IEEE standards, metrics, security, dependability, usability, etc.)

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  • Eyes easily get dry and itchy [closed]

    - by Lo Wai Lun
    I have currently working as a programmer for half a year Very often, I often looking the monitors with natural contrast and brightness. Still when the weather is getting cold, my eyes feel dry and itchy. Sometimes I can see some red 'tree-roots' (capillaries) near iris. At home, i sometimes use my notebook for 13" or Galaxy Nexus Brightness are also natural contrast and brightness , a bit dim How should we take care of our eyes under this scenario?

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  • Designing Content-Based ETL Process with .NET and SFDC

    - by Patrick
    As my firm makes the transition to using SFDC as our main operational system, we've spun together a couple of SFDC portals where we can post customer-specific documents to be viewed at will. As such, we've had the need for pseudo-ETL applications to be implemented that are able to extract metadata from the documents our analysts generate internally (most are industry-standard PDFs, XML, or MS Office formats) and place in networked "queue" folders. From there, our applications scoop of the queued documents and upload them to the appropriate SFDC CRM Content Library along with some select pieces of metadata. I've mostly used DbAmp to broker communication with SFDC (DbAmp is a Linked Server provider that allows you to use SQL conventions to interact with your SFDC Org data). I've been able to create [console] applications in C# that work pretty well, and they're usually structured something like this: static void Main() { // Load parameters from app.config. // Get documents from queue. var files = someInterface.GetFiles(someFilterOrRegexPattern); foreach (var file in files) { // Extract metadata from the file. // Validate some attributes of the file; add any validation errors to an in-memory // structure (e.g. List<ValidationErrors>). if (isValid) { // Upload using some wrapper for an ORM an someInterface.Upload(meta.Param1, meta.Param2, ...); } else { // Bounce the file } } // Report any validation errors (via message bus or SMTP or some such). } And that's pretty much it. Most of the time I wrap all these operations in a "Worker" class that takes the needed interfaces as constructor parameters. This approach has worked reasonably well, but I just get this feeling in my gut that there's something awful about it and would love some feedback. Is writing an ETL process as a C# Console app a bad idea? I'm also wondering if there are some design patterns that would be useful in this scenario that I'm clearly overlooking. Thanks in advance!

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  • If your unit test code "smells" does it really matter?

    - by Buttons840
    Usually I just throw my unit tests together using copy and paste and all kind of other bad practices. The unit tests usually end up looking quite ugly, they're full of "code smell," but does this really matter? I always tell myself as long as the "real" code is "good" that's all that matters. Plus, unit testing usually requires various "smelly hacks" like stubbing functions. How concerned should I be over poorly designed ("smelly") unit tests?

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  • Avoiding Object Oriented Pitfalls, Migrating from C, What Worked for You?

    - by Stephen
    I've been programming in procedural languages for quite some time now, and my first reaction to a problem is to start breaking it down into tasks to perform rather than to consider the different entities (objects) that exist and their relationships. I have had a university course in OOP, and understand the fundamentals of encapsulation, data abstraction, polymorphism, modularity and inheritance. I read Learning to think in the Object Oriented Way and Learning object oriented thinking, and will be looking at some of the books pointed to in those answers. I think that several of my medium to large sized projects will benefit from effective use of OOP but as a novice I would like to avoid time consuming, common errors. Based on your experiences, what are these pitfalls and what are reasonable ways around them? If you could explain why they are pitfalls, and how your suggestion is effective in addressing the issue it'd be appreciated. I'm thinking along the lines of something like "Is it common to have a fair number of observer and modifier methods and use private variables or are there techniques for consolidating/reducing them?" I'm not worried about using C++ as a pure OO language, if there are good reasons to mix methods. (Reminiscent of the reasons to use GOTOs, albeit sparingly.) Thank you!

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  • SQL query. An unusual join. DB implemented in sqlite-3

    - by user02814
    This is essentially a question about constructing an SQL query. The db is implemented with sqlite3. I am a relatively new user of SQL. I have two tables and want to join them in an unusual way. The following is an example to explain the problem. Table 1 (t1): id year name ------------------------- 297 2010 Charles 298 2011 David 300 2010 Peter 301 2011 Richard Table 2 (t2) id year food --------------------------- 296 2009 Bananas 296 2011 Bananas 297 2009 Melon 297 2010 Coffee 297 2012 Cheese 298 2007 Sugar 298 2008 Cereal 298 2012 Chocolate 299 2000 Peas 300 2007 Barley 300 2011 Beans 300 2012 Chickpeas 301 2010 Watermelon I want to join the tables on id and year. The catch is that (1) id must match exactly, but if there is no exact match in Table 2 for the year in Table 1, then I want to choose the year that is the next (lower) available. A selection of the kind that I want to produce would give the following result id year matchyr name food ------------------------------------------------- 297 2010 2010 Charles Coffee 298 2011 2008 David Cereal 300 2010 2007 Peter Barley 301 2011 2010 Richard Watermelon To summarise, id=297 had an exact match for year=2010 given in Table 1, so the corresponding line for id=297, year=2010 is chosen from Table 2. id=298, year=2011 did not have a matching year in Table 2, so the next available year (less than 2011) is chosen. As you can see, I would also like to know what that matched year (whether exactly , or inexactly) actually was. I would very much appreciate (1) an indication (yes/no answer) of whether this is possible to do in SQL alone, or whether I need to look outside SQL, and (2) a solution, if that is not too onerous.

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  • Where do service implementations fit into the Microsoft Application Architecture guidelines?

    - by tuespetre
    The guidelines discuss the service layer with its service interfaces and data/message/fault contracts. They also discuss the business layer with its logic/workflow components and entities as well as the 'optional' application facade. What is unclear still to me after studying this guide is where the implementations of the service interfaces belong. Does the application facade in the business layer implement these interfaces, or does a separate 'service facade' exist to make calls to the business layer and it's facade/raw components? (With the former, there would be less seemingly trivial calls to yet another layer, though with the latter I could see how the service layer could remove the concerns of translating business entities to data contracts from the business layer.)

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  • Should you charge clients hours spent on the wrong track?

    - by Lea Verou
    I took up a small CSS challenge to solve for a client and I'm going to be paid on a hourly rate. I eventually solved it, it took 4 hours but I spent roughly 30% of the time in the wrong track, trying a CSS3 solution that only worked in recent browsers and finally discovering that no fallback is possible via JS (like I originally thought). Should I charge the client that 30%? More details: I didn't provide an estimate, I liked the challenge per se, so I started working on it before giving an estimate (but I have worked with him before, so I know he's not one of those people that have unrealistic expectations). At the very worst I will have spent 4 unpaid hours on an intriguing CSS challenge. And I will give the fairest possible estimate for both of us, since I will have already done the work. :)

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  • Extreme Programming Dying? [closed]

    - by jonny
    Is Extreme Programming Dying? I've been reviewing my fellow students reports on extreme programming.(I am a student myself) Some students are claiming that extreme programming lacks in empirical evidences, and is relevantly new, hence lacking in empirical evidence. XP is already 13 years old it should be considered as new, from my perspective. I guess the practices of XP has been tweaked and used in newer methodologies such as scrum. What are your point of view on this, do you guys think XP is Dying?

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