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  • Distributed transactions

    - by javi
    Hello! I've a question regarding distributed transactions. Let's assume I have 3 transaction programs: Transaction A begin a=read(A) b=read(B) c=a+b write(C,c) commit Transaction B begin a=read(A) a=a+1 write(A,a) commit Transaction C begin c=read(C) c=c*2 write(A,c) commit So there are 5 pairs of critical operations: C2-A5, A2-B4, B4-C4, B2-C4, A2-C4. I should ensure integrity and confidentiality, do you have any idea of how to achieve it? Thank you in advance!

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  • How is dynamic memory allocation handled when extreme reliability is required?

    - by sharptooth
    Looks like dynamic memory allocation without garbage collection is a way to disaster. Dangling pointers there, memory leaks here. Very easy to plant an error that is sometimes hard to find and that has severe consequences. How are these problems addressed when mission-critical programs are written? I mean if I write a program that controls a spaceship like Voyager 1 that has to run for years and leave a smallest leak that leak can accumulate and halt the program sooner or later and when that happens it translates into epic fail. How is dynamic memory allocation handled when a program needs to be extremely reliable?

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  • HttpURLConnection inside a loop

    - by Carlos Garces
    Hi! I'm trying to connect to one URL that I know that exist but I don't know when. I don't have access to this server so I can't change anything to receive a event. The actual code is this. URL url = new URL(urlName); for(int j = 0 ; j< POOLING && disconnected; j++){ HttpURLConnection connection = (HttpURLConnection) url.openConnection(); int status = connection.getResponseCode(); if(status == HttpURLConnection.HTTP_OK || status == HttpURLConnection.HTTP_NOT_MODIFIED){ //Some work }else{ //wait 3s Thread.sleep(3000); } } Java not is my best skill and I'm not sure if this code is good from the point of view of performance. I'm opening a new connection every 3 seconds? or the connection is reused? If I call to disconnect() I ensure that no new connections are open in the loop, but... it will impact in performance?. Suggestions? What is the fast/best ways to know it a URL exist?

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  • Job conditions conflicting with personal principles on software-development - how much is too much?

    - by Baelnorn
    Sorry for the incoming wall'o'text (and for my probably bad English) but I just need to get this off somehow. I also accept that this question will be probably closed as subjective and argumentative, but I need to know one thing: "how much BS are programmers supposed to put up with before breaking?" My background I'm 27 years old and have a B.Sc. in Computer engineering with a graduation grade of 1.8 from a university of applied science. I went looking for a job right after graduation. I got three offers right away, with two offers paying vastly more than the last one, but that last one seemed more interesting so I went for that. My situation I've been working for the company now for 17 months now, but it feels like a drag more and more each day. Primarily because the company (which has only 5 other developers but me, and of these I work with 4) turned out to be pretty much the anti-thesis of what I expected (and was taught in university) from a modern software company. I agreed to accept less than half of the usual payment appropriate for my qualification for the first year because I was promised a trainee program. However, the trainee program turned out to be "here you got a computer, there's some links on the stuff we use, and now do what you colleagues tell you". Further, during my whole time there (trainee or not) I haven't been given the grace of even a single code-review - apparently nobody's interested in my work as long as it "just works". I was told in the job interview that "Microsoft technology played a central role in the company" yet I've been slowly eroding my congnitive functions with Flex/Actionscript/Cairngorm ever since I started (despite having applied as a C#/.NET developer). Actually, the company's primary projects are based on Java/XSLT and Flex/Actionscript (with some SAP/ABAP stuff here and there but I'm not involved in that) and they've been working on these before I even applied. Having had no experience either with that particular technology nor the framework nor the field (RIA) nor in developing business scale applications I obviously made several mistakes. However, my boss told me that he let me make those mistakes (which ate at least 2 months of development time on their own) on purpose to provide some "learning experience". Even when I was still a trainee I was already tasked with working on a business-critical application. On my own. Without supervision. Without code-reviews. My boss thinks agile methods are a waste of time/money and deems putting more than one developer on any project not efficient. Documentation is not necessary and each developer should only document what he himself needs for his work. Recently he wanted us to do bug tracking with Excel and Email instead of using an already existing Bugzilla, overriding an unanimous decision made by all developers and testers involved in the process - only after another senior developer had another hour-long private discussion with him he agreed to let us use the bugtracker. Project management is basically not present, there are only a few Excel sheets floating around where the senior developer lists some things (not all, mind you) with a time estimate ranging from days to months, trying to at least somehow organize the whole mess. A development process is also basically not present, each developer just works on his own however he wants. There are not even coding conventions in the company. Testing is done manually with a single tester (sometimes two testers) per project because automated testing wasn't given the least thought when the whole project was started. I guess it's not a big surprise when I say that each developer also has his own share of hundreds of overhours (which are, of course, unpaid). Each developer is tasked with working on his own project(s) which in turn leads to a very extensive knowledge monopolization - if one developer was to have an accident or become ill there would be absolutely no one who could even hope to do his work. Considering that each developer has his own business-critical application to work on, I guess that's a pretty bad situation. I've been trying to change things for the better. I tried to introduce a development process, but my first attempt was pretty much shot down by my boss with "I don't want to discuss agile methods". After that I put together a process that at least resembled how most of the developers were already working and then include stuff like automated (or at least organized) testing, coding conventions, etc. However, this was also shot down because it wasn't "simple" enought to be shown on a business slide (actually, I wasn't even given the 15 minutes I'd have needed to present the process in the meeting). My problem I can't stand working there any longer. Seriously, I consider to resign on monday, which still leaves me with 3 months to work there due to the cancelation period. My primary goal since I started studying computer science was being a good computer scientist, working with modern technologies and adhering to modern and proven principles and methods. However, the company I'm working for seems to make that impossible. Some days I feel as if was living in a perverted real-life version of the Dilbert comics. My question Am I overreacting? Is this the reality each graduate from university has to face? Should I betray my sound principles and just accept these working conditions? Or should I gtfo of there? What's the opinion of other developers on this matter. Would you put up with all that stuff?

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  • Advice needed from PHP/Cake PHP expert

    - by Hiro
    I'm very new to programming (besides SQL and databases), but I ultimately want to master Cake PHP for web development. Now, given how new I am, I'm rather lost as to how I get started. Down the road, I want to use MVC framework so that I help myself be disciplined in the way I build. However, I know basic knowledge of PHP and OOP PHP are required. So my question is this: what are the right steps to mastering Cake PHP? I don't want to skip critical phases of learning before learning to Cake PHP. At the same time, I don't want to spend more time than required learning PHP if I can learn it directly through Cake PHP knowledge. Any advice would be appreciated.

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  • What should every developer know about databases?

    - by Aaronaught
    Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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  • Setting up DomainKeys/DKIM in a PHP-based SMTP client

    - by Alex
    It looks like there are some great libraries out there to do DomainKeys signing of emails on C#/.NET, but I'm having a really hard time finding the same kind of support for PHP. Maybe I'm not looking in the right place? The only one I found is http://php-dkim.sourceforge.net/; it looks incredibly hacky and supports PHP4 only. Considering how popular PHP is, and how critical DomainKeys are for email classification as non-spam, I'd expect better tools; do you know of any? Any other tricks you'd recommend?

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  • How can I limit access to a particular class to one caller at a time in an ASMX web service?

    - by MusiGenesis
    I have a web service method in which I create a particular type of object, use it for a few seconds, and then dispose it. Because of problems arising from multiple threads creating and using instances of this class at the same time, I need to restrict the method so that only one caller at a time ever has one of these objects. To do this, I am creating a private static object: private static object _lock = new object(); ... and then inside the web service method I do this around the critical code: lock (_lock) { using (DangerousObject do = new DangerousObject()) { do.MakeABigMess(); do.CleanItUp(); } } I'm not sure this is working, though. Do I have this right? Will this code ensure that only one instance of DangerousObject is instantiated and in use at a time? Or does each caller get their own copy of _lock, rendering my code here laughable?

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  • Easiest way to retrofit retry logic on LINQ to SQL migration to SQL Azure

    - by Pat James
    I have a couple of existing ASP .NET web forms and MVC applications that currently use LINQ to SQL with a SQL Server 2008 Express database on a Windows VPS: one VPS for both IIS and SQL. I am starting to outgrow the VPS's ability to effectively host both SQL and IIS and am getting ready to split them up. I am considering migrating the database to SQL Azure and keeping IIS on the VPS. After doing initial research it sounds like implementing retry logic in the data access layer is a must-do when adopting SQL Azure. I suspect this is even more critical to implement in my situation where IIS will be on a VPS outside of the Azure infrastructure. I am looking for pointers on how to do this with the least effort and impact on my existing code base. Is there a good retry pattern that can be applied once at the LINQ to SQL data access layer, as opposed to having to wrap all of my LINQ to SQL operations in try/catch/wait/retry logic?

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  • What are some programming techniques for converting SD images to HD images

    - by Dr Dork
    I'm taking programming class and instructor loves to work with images so most of our assignments involve manipulating raw RGB image data. One of our assignments is to implement a standard image converter that converts SD images to HD images and vice versa. I always take advantage of these types of assignments to go a little beyond what we were asked to do, so I added a basic anti-aliasing process that uses the average pixel color of the 3x3 surrounding pixels to improve the converted image. While it helps a bit, the resulting image still doesn't look good, which is ok because it's not expected to for the assignment. I've learned that converting an SD to HD images has shown to be much harder than down sampling to SD from HD just because SD to HD effectively involves increasing resolution when it is not there. Obviously, it is hard to create pixels from nothing, but I'd like enhance my anti-aliasing to something that provides better results when upscaling an image. Most of the techniques I find and read on the internet are far beyond my level of image processing and programming. Can anybody suggest any better methods or processes to create good HD content from SD content that may be within my programming skill level? I know that's a difficult thing to gauge since you don't know me, but perhaps knowing that I can write c++ code to read in raw RGB data and upscale/downscale it with simple average-anti-aliasing will give you an idea. Thanks in advance for all your help!

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  • Add Core Data Index to certain Attributes via migration

    - by steipete
    For performance reasons, i want to set the Indexed Attribute to some of my entities. I created a new core data model version to perform the changes. Core Data detects the changes and migrates my model to the new version, however, NO INDEXES ARE GENERATED. If I recreate the database from scratch, the indexes are there. I checked with SQLite Browser both on the iPhone and on the Simulator. The problem only occurs if a database in the prior format is already there. Is there a way to manually add the indexes? Write some sql for that? Or am I missing something? I did already some more critical migrations, no problems there. But those missing indexes are bugging me. Thanks for helping!

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  • Methods for ensuring security between users in multi-user applications

    - by Emilio
    I'm writing a multiuser application (.NET - C#) in which each user's data is separated from the others and there is no data that's common between users. It's critical to ensure that no user has access to another user's data. What are some approaches for implementing security at the database level and/or in the application architecture to to accomplish this? For example (and this is totally made up - I'm not suggesting it's a good or bad approach) including a userID column in all data tables might be an approach. I'm developing the app in C# (asp.net) and SQL Server 2008. I'm looking for options that are are either native in the tools I'm using or general patterns.

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  • Global find object references in NHibernate

    - by Miral
    Is it possible to perform a global reversed-find on NHibernate-managed objects? Specifically, I have a persistent class called "Io". There are a huge number of fields across multiple tables which can potentially contain an object of that type. Is there a way (given a specific instance of an Io object), to retrieve a list of objects (of any type) that actually do reference that specific object? (Bonus points if it can identify which specific fields actually contain the reference, but that's not critical.) Since the NHibernate mappings define all the links (and the underlying database has corresponding foreign key links), there ought to be some way to do it.

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  • Struct in C, are they efficient?

    - by pygabriel
    I'm reading some C code like that: double function( int lena,double xa,double ya, double za, double *acoefs, ..., int lenb,double xb,double yb, double zb, double *bcoefs, ..., same for c, same for d ) This function is called in the code mor than 100.000 times so it's performance-critical. I'm trying to extend this code but I want to know if it's efficient or not (and how much this influences the speed) to encapsulate all the parameters in a struct like this struct PGTO { int len; double x,y,z ; double *acoefs } and then access the parameters in the function.

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  • JQUERY POST, UI to show if status is "saving" "still saving" "error" "complete"

    - by nobosh
    I have a JQUERY Post call which is posting critical data to the server. Which if isn't posted successfully, results in a huge loss of important data. I have a save banner UI show on the page before the JQUERY POST, after the JQUERY Post it has the Save Banner go away. I'd like an inbetween state, where if the save is taking longer than 1 second, it updates from "saving" to "saving..." but if it doesn't save within 4 seconds, it says "error, try again" something like that. Any ideas on how to accomplish this with JQUERY?

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  • What to implement today to help yourself fixing bugs in the future?

    - by Heinrich Ulbricht
    Assume you are in the process of developing some really cool software. It will be deployed to a lot of customers. They will need this software and they will use it in time-critical situations. So if something goes wrong they will call (you). And you or your team will be the ones who have to resolve the issue. Fast. You know out of experience this will happen. Now if you could decide what to implement to aid your future self - what would that be?

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  • Java/Swing: the fast/slow UI binding problem

    - by Jason S
    I need a way to bind UI indicators to rapidly-changing values. I have a class NumberCruncher which does a bunch of heavy processing in a critical non-UI thread, thousands of iterations of a loop per second, and some number of those result in changes to a set of parameters I care about. (think of them as a key-value store) I want to display those at a slower rate in the UI thread; 10-20Hz would be fine. How can I add MVC-style notification so that my NumberCruncher code doesn't need to know about the UI code/binding?

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  • allowDefinition='MachineToApplication' error when publishing from VS2010 (but only after a previous

    - by burnt_hand
    I can run my Asp.Net MVC 2 application without an issue on my local computer. Just Run / Debug. But if I have already built it, I can't publish it! I have to clean the solution and publish it again. I know this is not system critical, but it's really annoying. "One Click Publish" is not "Clean solution and then One click publish" The exact error is as follows: Error 11 It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS. I suspect it's something to do with the Web.Config in the Views folder, but then why only after I build once previously. And just to note, the app works fine once published.

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  • What is a TFS Agile Issue?

    - by Jaxidian
    With TFS2010 using the "MSF for Agile Software Development v5" process template, I'm having some difficulty in understanding exactly what an Issue is. The most specific documentation I've been able to find is this. Is an Issue a higher-level item for which we will probably generate a Bug for after some investigation in code/requirements? Or is an Issue something different than a Bug because it has not actually a mistake in code but is more of a critical oversight in design (for example, there was never an attempt to create a datepicker for all date fields and this is a UX issue but not really a bug) and therefore a change request of sorts? Or is it something different?

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  • How can I reuse my javascript code between client and server?

    - by Chris Farmer
    I have some javascript code that includes an ANTLR-generated lexer and parser, and some associated syntax tree evaluation functionality. This code runs in the browser in my web app to support users who author code snippets which process scientific data. Now I'd like to do some additional background processing on the server using the same generated parser. I would prefer not to have to re-implement this stuff in C# and have multiple bits of code that did the exact same thing. Performance isn't as critical to me as eliminating duplication, since this is a background process. So, how can I call into my javascript code from C#? And how can I format my script so that it plays nicely with my .NET web app?

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  • SQL Query to delete oldest rows over a certain row count?

    - by Casey
    I have a table that contains log entries for a program I'm writing. I'm looking for ideas on an SQL query (I'm using SQL Server Express 2005) that will keep the newest X number of records, and delete the rest. I have a datetime column that is a timestamp for the log entry. I figure something like the following would work, but I'm not sure of the performance with the IN clause for larger numbers of records. Performance isn't critical, but I might as well do the best I can the first time. DELETE FROM MyTable WHERE PrimaryKey NOT IN (SELECT TOP 10,000 PrimaryKey FROM MyTable ORDER BY TimeStamp DESC)

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  • Representing a schedule in a database

    - by David Pfeffer
    I have the interesting problem of representing complex schedule data in a database. I need to be able to represent the entirety of what the iCalendar (ics) format can represent, but in my database. I don't care about insertion efficiency but query efficiency is critical. The operation I will be doing most often is providing either a single date/time or a date/time range, and trying to determine if the defined schedule matches any part of the date/time range. Other operations can be slower. For those unfamiliar, ics allows representation of a single event or a reoccuring event based on multiple times per day, days of the week, week of a month, month, year, or some combination of those. For example, the third Thursday in November, or the 25th of December, or every two weeks starting November 2nd and continuing until September the following year. Any suggestions?

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  • Python: create a function to modify a list by reference not value

    - by Jonathan
    Hey all- I'm doing some performance-critical Python work and want to create a function that removes a few elements from a list if they meet certain criteria. I'd rather not create any copies of the list because it's filled with a lot of really large objects. Functionality I want to implement: def listCleanup(listOfElements): i = 0 for element in listOfElements: if(element.meetsCriteria()): del(listOfElements[i]) i += 1 return listOfElements myList = range(10000) myList = listCleanup(listOfElements) I'm not familiar with the low-level workings of Python. Is myList being passed by value or by reference? How can I make this faster? Is it possible to somehow extend the list class and implement listCleanup() within that? myList = range(10000) myList.listCleanup() Thanks- Jonathan

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  • PHP - Best practice to retain form values across postback

    - by Adam
    Hello, Complete PHP novice here, almost all my previous work was in ASP.NET. I am now working on a PHP project, and the first rock I have stumbled upon is retaining values across postback. For the most simple yet still realistic example, i have 10 dropdowns. They are not even databound yet, as that is my next step. They are simple dropdowns. I have my entire page inclosed in a tag. the onclick() event for each dropdown, calls a javascript function that will populate the corrosponding dropdowns hidden element, with the dropdowns selected value. Then, upon page reload, if that hidden value is not empty, i set the selected option = that of my hidden. This works great for a single postback. However, when another dropdown is changed, the original 1'st dropdown loses its value, due to its corrosponding hidden value losing its value as well! This draws me to look into using querystring, or sessions, or... some other idea. Could someone point me in the right direction, as to which option is the best in my situation? I am a PHP novice, however I am being required to do some pretty intense stuff for my skill level, so I need something flexable and preferribly somewhat easy to use. Thanks! -----edit----- A little more clarification on my question :) When i say 'PostBack' I am referring to the page/form being submitted. The control is passed back to the server, and the HTML/PHP code is executed again. As for the dropdowns & hiddens, the reason I used hidden variables to retain the "selected value" or "selected index", is so that when the page is submitted, I am able to redraw the dropdown with the previous selection, instead of defaulting back to the first index. When I use the $_POST[] command, I am unable to retrieve the dropdown by name, but I am able to retrieve the hidden value by name. This is why upon dropdown-changed event, I call javascript which sets the selected value from the dropdown into its corrosponding hidden.

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  • Unsuccessful error detection of improperly declared method in GCC 4.2 compiler

    - by sam
    I am using C++ compiler GCC 4.2 in XCode 3.2.2. I have noted that the compiler will successfully compile a method foo even though there are no ellipses. The header and method are properly declared as foo(), but when I do a find and replace either by file or by program-wide it will miss approximately 2-3% of the changes [foo to foo(). This would not be critical if the compiler did not give an erroneous successful build. I have not found that this to occur with: foo(any parameter). Does anyone have any solution? Thank you.

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