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• When to start thinking about scalability?

  - by Rits

  I'm having a funny but also terrible problem. I'm about to launch a new (iPhone) app. It's a turn-based multiplayer game running on my own custom backend. But I'm afraid to launch. For some reason, I think it might become something big and that its popularity will kill my poor lonely single server + MySQL database. On one hand I'm thinking that if it's growing, I'd better be prepared and have a scalable infrastructure already in place. On the other hand I just feel like getting it out into the world and see what happens. I often read stuff like "premature optimization is the root of all evil" or people saying that you should just build your killer game now, with the tools at hand, and worry about other stuff like scalability later. I'd love to hear some opinions on this from experts or people with experience with this. Thanks!

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• Testcase runner for parametrized testcases

  - by Razer

  Let me explain my situation. I'm planning a kind of test case runner for doing testcases on external devices, which are microcontroller based. Lets consider the devices: Device 1 Device 2 There exist a lot of test cases which can be run with one of the devices above. For example: Testcase 1 Testcase 2 The main reason that all the testcases can be run with any device is, that the testcases validates some standard and this software should be extensible for future devices. The testcases itself must be runnable with changing parameters. For example Testcase 1 does some Timing Verification the testcase needs as input parameter the datarate: 4800, 9600, 19200. Now hoping you understand the situation, let me explain my design questions. For implementing the test cases I thought about an Attribute based approach, like nunit does it. The more complicated problem is, how to define the parametrized testcases? Like this: Device 1: Testcase 1: datarate: 4800, 9600, 19200 Testcase 2: supply: 1, 2, 3 Device 2: Testcase 1: datarate: 9600, 19200, 38400 Testcase 2: supply: 3, 4, 5 How would you design such a framework? I've done a similar desin in python where I had for every device a XML containing the testcase definitions like: <Testcase="Testcase 1" datarate=4800/> <Testcase="Testcase 1" datarate=9600/> <Testcase="Testcase 1" datarate=19200/>

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• Didatic approaches to teach versioning with Git

  - by Herberth Amaral

  I have already taught versioning with Git, but I think it could be more enjoyable for the guys I teach if I use another approach to teach them. The guys I mentioned before were used to working with SVN and I tried to teach Git based on SVN. Not such a good idea. It seems that some guys/teams which use SVN need a re-education on version control when they're learning Git or another DCVCS. In another attempt, I tried to show a scenario where a development team try to work without a (D)VCS and then I showed how their lives could be easier if they used a (D)VCS. I had the impression that part of the audience left the presentation without a clue what I was talking about. I've taught other classes on other subjects without problems, so I think this is not a issue with me as a teacher, but with my method. I know Git and versioning as well I know the other subjects I've presented to the other classes. So, basically, how to teach Git/DCVCS? Start with some diffs/patches and manual versioning and then teach how it can be more productive with Git? Start with Git object model? Or try to start with some pretty commands and try to save some time? To be clear: I'm looking for approaches on how to teach DCVCS (focusing on Git) effectively, based on real experiences.

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• MVC Validation with ModelState.isValid through a wizard

  - by Emmanuel TOPE

  I'm working on a small educational project on MVC 3, and I'm facing a small problem, when attempting to handle validation in my application through a wizard. I tried to get benefit from the ability of MVC3 to deliver content of a different view using the same URL, when handling an [HttpPost] method on a page. I my case,my main model's class contains about ten [Required] properties, that I would like to expose through a small wizard in 3 steps , So I want that the user may be able to enter his personal informations in the first step, then respond to some questions in the second stepp and finally receive a confirmation mail from the web application whit his credentials in the last step. I can't access the last step, because of the ModelState.isValid method that I use to handle validations, and which can't perform properly if I define some properties as [Required], but don't put them on the first view. As the replies to those questions remain in a couple of choices, I've thinked that I may use some nullable bool? for in order to avoid validation issues, but know that it's not the proper way. Are there someone who would like to help me find a way to extend my validation to those three steps ? Thanks in advance and sorry for my english, I'm not a native speaker.

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• What threading pratice is good 90% of the time?

  - by acidzombie24

  Since my SO thread was closed i guess i can ask it here. What practice or practices are good 90% of the time when working with threading with multiple cores? Personally all i have done was share immutable classes and pass (copy) data to a queue to the destine thread. Note: This is for research and when i say 90% of the time i dont mean it is allowed to fail 10% of the time (thats ridiculous!) i mean 90% it is a good solution while the other 10% it is not so desirable due to implementation or efficiently reasons (or plainly another technique fits the problem domain a lot better).

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• Efficient Trie implementation for unicode strings

  - by U Mad

  I have been looking for an efficient String trie implementation. Mostly I have found code like this: Referential implementation in Java (per wikipedia) I dislike these implementations for mostly two reasons: They support only 256 ASCII characters. I need to cover things like cyrillic. They are extremely memory inefficient. Each node contains an array of 256 references, which is 4096 bytes on a 64 bit machine in Java. Each of these nodes can have up to 256 subnodes with 4096 bytes of references each. So a full Trie for every ASCII 2 character string would require a bit over 1MB. Three character strings? 256MB just for arrays in nodes. And so on. Of course I don't intend to have all of 16 million three character strings in my Trie, so a lot of space is just wasted. Most of these arrays are just null references as their capacity far exceeds the actual number of inserted keys. And if I add unicode, the arrays get even larger (char has 64k values instead of 256 in Java). Is there any hope of making an efficient trie for strings? I have considered a couple of improvements over these types of implementations: Instead of using array of references, I could use an array of primitive integer type, which indexes into an array of references to nodes whose size is close to the number of actual nodes. I could break strings into 4 bit parts which would allow for node arrays of size 16 at the cost of a deeper tree.

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• WWDC 2012 announced features on iOS 5?

  - by Arnold Sakhnov

  I am relatively new to iOS development, so after watching a bunch of WWDC videos announcing new awesome features for the iPhone SDK, I still got a few questions regarding their support for older devices. Specifically: Do the new compiler features (such as literals support, auto-synthesize, etc) require iOS 6 on the target device, or can the new style code be deployed to iOS 5 devices? Auto-layout for iOS, same question. Will it only be supported on iOS 6, or 5 as well? If it's 6 only, what kind of fallback are we expected to implement? Would really appreciate if someone could clarify this for me, as I'm thinking about rewriting my older unfinished project and I would love to use some of that improved SDK functionality.

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• Materialized View does not import properly when importing on a second instance of a database

  - by marinus

  When I import a database with materialized view mv_mt in just one database (Oracle) everything is ok. create materialized view mv_mt refresh complete next trunc( sysdate ) + 1 as SELECT sysdate, media_type.* from media_type; But when I try to import the same database to a copy in another schema I get the following errors: IMP-00017: following statement failed with ORACLE error 1: "BEGIN DBMS_JOB.ISUBMIT(JOB=438,WHAT='dbms_refresh.refresh(''"ALEXANDRA"" "."MV_MT"'');',NEXT_DATE=TO_DATE('2012-07-02:14:22:36','YYYY-MM-DD:HH24:MI:" "SS'),INTERVAL='sysdate + 1 / 24 / 60 / 6 ',NO_PARSE=TRUE); END;" IMP-00003: ORACLE error 1 encountered ORA-00001: unique constraint (SYS.I_JOB_JOB) violated ORA-06512: at "SYS.DBMS_JOB", line 100 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23421: "BEGIN dbms_refresh.make('"ALEXANDRA"."MV_MT"',list=null,next_date=null," "interval=null,implicit_destroy=TRUE,lax=FALSE,job=438,rollback_seg=NUL" "L,push_deferred_rpc=TRUE,refresh_after_errors=FALSE,purge_option = 1,par" "allelism = 0,heap_size = 0); END;" IMP-00003: ORACLE error 23421 encountered ORA-23421: job number 438 is not a job in the job queue ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86 ORA-06512: at "SYS.DBMS_IJOB", line 793 ORA-06512: at "SYS.DBMS_REFRESH", line 86 ORA-06512: at "SYS.DBMS_REFRESH", line 62 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23410: "BEGIN dbms_refresh.add(name='"ALEXANDRA"."MV_MT"',list='"ALEXANDRA"."MV" "_MT"',siteid=0,export_db='ORCL01'); END;" IMP-00003: ORACLE error 23410 encountered ORA-23410: materialized view "ALEXANDRA"."MV_MT" is already in a refresh group ORA-06512: at "SYS.DBMS_SYS_ERROR", line 95 ORA-06512: at "SYS.DBMS_IREFRESH", line 484 ORA-06512: at "SYS.DBMS_REFRESH", line 140 ORA-06512: at "SYS.DBMS_REFRESH", line 125 ORA-06512: at line 1 Anyone any ideas? Regards, Marinus

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• What is a good support knowledge base tool?

  - by Guillaume

  I have been searching for a tool to help my team organize its knowledge for resolving recurring support cases. I know this question will probably be closed, but I'll try my change anyway because I know that I can have some good answers about that. Context: our team is developing and supporting an huge applications (lots of different screens and workflow processes. We already have a good tool for managing our documentation, but we are struggling with support cases. Support action involve often quite a lot of manual steps to fix stuff and the knowledge for these actions is more 'oral transmission' than modern tools. We need an efficient way to store them in a knowledge base to be able to retrieve similar cases based on patterns (a stacktrace, an error message, a component name, a workflow step, ...) and ranked by similarity. Our wiki search is not very powerful when it come to this kind of search and the team members don't want to 'waste' time writing a report that will never be found... Do you know efficient knowledge base tool for this kind of use case ?

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• How to handle mutiple API calls using javascript/jquery

  - by James Privett

  I need to build a service that will call multiple API's at the same time and then output the results on the page (Think of how a price comparison site works for example). The idea being that as each API call completes the results are sent to the browser immediately and the page would get progressively bigger until all process are complete. Because these API calls may take several seconds each to return I would like to do this via javascript/jquery in order to create a better user experience. I have never done anything like this before using javascript/jquery so I was wondering if there was any frameworks/advice that anyone would be willing to share.

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• Isolating test data in acceptance tests

  - by Matt Phillips

  I'm looking for guidance on how to keep my acceptance tests isolated. Right now the issue I'm having with being able to run the tests in parallel is the database records that are manipulated in the tests. I've written helpers that take care of doing inserts and deletes before tests are executed, to make sure the state is correct. But now I can't run them in parallel against the same database without uniquely generating the test data fields for each test. For example. Testing creating a row i'll delete everything where column A = foo and column B = bar Then I'll navigate through the UI in the test and create a record with column A = foo and column B = bar. Testing that a duplicate row is not allowed to be created. I'll insert a row with column A = foo and column B = bar and then use the UI to try and do the exact same thing. This will display an error message in the UI as expected. These tests work perfectly when ran separately and serially. But I can't run them at the same time for fear that one will create or delete a record the other is expecting. Any tips on how to structure them better so they can be run in parallel?

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• Cloning existing software for commercial purposes - legal implications

  - by user2036256

  I have been asked to clone some existing software for a company. Basically its an old 16 bit DOS console app, which was supplied free of charge in I believe the late 80's. Having replaced the machine that needs to run it with a box running Win7 x64 they can't get it to work. It crashes every couple of minutes under DOSbox. The company that supplied it appears to no longer exist - if they did the company asking me to do this would almost certainly know about it. Its undetermined whether they have gone entirely or are just trading under a different name. If the latter they seem to have withdrawn from the market related to this product (because again, niche area, we should know about everyone there). What is the status to this with regards to copyright etc.? The main concern for the company involved is they want an identical interface to what they already have so I would have to clone this entirely. Having no source code / indication of the underlying mechanisms these would be written from scratch. Is an interface covered by copyright? / Does that still hold 30 years later? What is the assumed license when none at all is provided? Under UK law would I be under any serious risk were I to take on the project? How would this pan out if I then decided to sell the software on to other companies? Thanks

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• Use adapter pattern for coupled classes

  - by kaiseroskilo

  I need (for unit testing purposes) to create adapters for external library classes.ExchangeService and ContactsFolder are Microsoft's implementations in its' EWS library. So I created my adapters that implement my interfaces, but it seems that contactsFolder has a dependency for ExchangeService in its' constructor. The problem is that I cannot instantiate ContactsFolderAdapter without somehow accessing the actual ExchangeService instance (I see only ExchangeServiceAdapter in scope). Is there a better pattern for this that retains the adapter classes? Or should I "infect" ExchangeServiceAdapter with some kind of GetActualObject method?

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• Automated architecture validation

  - by P.Brian.Mackey

  I am aware of the fact that TFS 2010 ultimate edition can create and validate architecture diagrams. For example, I can create a new modeling project add Layer Diagram Add Layer called View Add BL Layer Add DL layer. Then I can validate this architecture as part of the build process when someone tries to check code into TFS. In other words, if the View references the DL then the compilation process will fail and the checkin will not be allowed. For those without an MSDN ultimate license, can FxCop or some 3rd party utility be used to validate architecture in an automated fashion? I prefer a TFS install-able plugin, but a local VS plugin will do.

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• On a queue, which end is the "head"?

  - by Aidan Cully

  I had always thought that the "head" of a queue as the next element to be read, and never really questioned that usage. So a linked-list library I wrote, which is used for maintaining queues, codified that terminology: we have a list1_head macro that retrieves the first element; when using this library in a queue, this will be the first element to be removed. But a new developer on the team was used to having queues implemented the other way around. He described a queue as behaving like a dog: you insert at the head, and remove at the tail. This is a clever enough description that I feel like his usage must be more widespread, and I don't have a similarly evocative description of my preferred usage. So, I guess, there are two related questions: 1, what does the "head" of a queue mean to you? and 2, why do we use the word "head" to describe that concept?

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• What are the IEEE and ACM good for?

  - by Joshua Fox

  Membership in the IEEE and ACM is sometimes portrayed as a sign of professionalism. But all that is involved, as far as I can tell, is sending them your money. In return, besides the potential resume line, these organizations sponsor conferences and journals. I can always attend a conference or subscribe to or submit a paper to a journal, whether I am a member or not. If being a member makes some of that cheaper, or is a prerequisite for admission then OK, but I still don't see the purpose of these organizations. The answer, as far as I can gather, is that their most important value is to provide some reading material. I'd suggest that this is not worth the money given the wide availability of other valuable reading materials.

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• Functional programming readability

  - by Jimmy Hoffa

  I'm curious about this because I recall before learning any functional languages, I thought them all horribly, awfully, terribly unreadable. Now that I know Haskell and f#, I find it takes a little longer to read less code, but that little code does far more than an equivalent amount would in an imperative language, so it feels like a net gain and I'm not extremely practiced in functional. Here's my question, I constantly hear from OOP folks that functional style is terribly unreadable. I'm curious if this is the case and I'm deluding myself, or if they took the time to learn a functional language, the whole style would no longer be more unreadable than OOP? Has anybody seen any evidence or got any anecdotes where they saw this go one way or another with frequency enough to possibly say? If writing functionally really is of lower readability than I don't want to keep using it, but I really don't know if that's the case or not..

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• How important is Discrete Mathematics for a Computer Scientist?

  - by mort

  As the title says, How important is Discrete Mathematics for a Computer Scientist? Background: I'm pursuing a Master's degree with a focus on fundamentals such as Algorithms, Complexity and Computability Theory and Programming Languages to get a good foundation for working in the field of Parallel Computing. Some more background: My university grants a lot of freedom in the choices of courses for my Master's degree. It's officially called "Software Engineering", but due to a the broad range of electives, a different focus is possible. Interestingly, none of the electives is a lecture in Math! I'm thinking about doing a course about Discrete Mathematics that would take half a semester to complete successfully, even if I can't use it for my degree. So with this question I'm trying to find out if the effort is justifiable.

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• What was the first consumer-oriented hardware/software solution?

  - by Maksee

  We all know the story of the personal computer as a consumer-oriented product. But I just thought that real end user solution should have appeared before that time. So a product that was probably expensive, but allowed using it as a service charging for it, for example computer-terminal for transport time-table access or game machine. On the other site, the video terminals as we know them appeared not so long ago. So if there was something like this, this could be hardware/software most likely offering no interactivity, but probably printing some information based on user actions.

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• How do you update copyright notices?

  - by James

  So now it's 2011, and as I carry on coding on our active projects it's time to update some copyright notices. eg. Copyright Widgets Ltd 2010 to Copyright Widgets Ltd 2010, 2011 My question is when do you update the copyright notices? Do you change the notice in the head of a file the first time you work on that file? Since a module is one piece of code consisting of many files that work together, do you update all notices in that module when you change a single file in that module? Since a program is one piece of code (maybe consisting of many modules), do you update all notices in that program when you change a single file in that program? Or do you just go through and change en-mass over your morning coffee on the grounds your about to start programming and updateing things?

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• What are the arguments against parsing the Cthulhu way?

  - by smarmy53

  I have been assigned the task of implementing a Domain Specific Language for a tool that may become quite important for the company. The language is simple but not trivial, it already allows nested loops, string concatenation, etc. and it is practically sure that other constructs will be added as the project advances. I know by experience that writing a lexer/parser by hand -unless the grammar is trivial- is a time consuming and error prone process. So I was left with two options: a parser generator à la yacc or a combinator library like Parsec. The former was good as well but I picked the latter for various reasons, and implemented the solution in a functional language. The result is pretty spectacular to my eyes, the code is very concise, elegant and readable/fluent. I concede it may look a bit weird if you never programmed in anything other than java/c#, but then this would be true of anything not written in java/c#. At some point however, I've been literally attacked by a co-worker. After a quick glance at my screen he declared that the code is uncomprehensible and that I should not reinvent parsing but just use a stack and String.Split like everybody does. He made a lot of noise, and I could not convince him, partially because I've been taken by surprise and had no clear explanation, partially because his opinion was immutable (no pun intended). I even offered to explain him the language, but to no avail. I'm positive the discussion is going to re-surface in front of management, so I'm preparing some solid arguments. These are the first few reasons that come to my mind to avoid a String.Split-based solution: you need lot of ifs to handle special cases and things quickly spiral out of control lots of hardcoded array indexes makes maintenance painful extremely difficult to handle things like a function call as a method argument (ex. add( (add a, b), c) very difficult to provide meaningful error messages in case of syntax errors (very likely to happen) I'm all for simplicity, clarity and avoiding unnecessary smart-cryptic stuff, but I also believe it's a mistake to dumb down every part of the codebase so that even a burger flipper can understand it. It's the same argument I hear for not using interfaces, not adopting separation of concerns, copying-pasting code around, etc. A minimum of technical competence and willingness to learn is required to work on a software project after all. (I won't use this argument as it will probably sound offensive, and starting a war is not going to help anybody) What are your favorite arguments against parsing the Cthulhu way?* *of course if you can convince me he's right I'll be perfectly happy as well

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• Is an 'if password == XXXXXXX' enough for minimum security?

  - by Morgan Herlocker

  If I create a login for an app that has middle to low security risk (in other words, its not a banking app or anything), is it acceptable for me to verify a password entered by the user by just saying something like: if(enteredPassword == verifiedPassword) SendToRestrictedArea(); else DisplayPasswordUnknownMessage(); It seems to easy to be effective, but I certainly would not mind if that was all that was required. Is a simple check on username/password combo enough? Update: The particular project happens to be a web service, the verification is entirely server side, and it is not open-source. Does the domain change how you would deal with this?

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• How to properly install libsvm-3.11?

  - by Gomathi

  I'm using libvm-3.11. I downloaded it at http://www.csie.ntu.edu.tw/~cjlin/libsvm/ and extracted. Then I set path in Matlb. After that whenever I run my program, it gives the same error always. ??? Invalid MEX-file 'E:\Gomu\Gomu General\final yr Project\proj\libsvm-3.11\windows\svmtrain.mexw32': The specified module could not be found. . Error in == trysvm at 6 svmStruct = svmtrain(T,TrainMat,'showplot',true); What should I do?

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• Runtime analysis

  - by Joe Smith

  can someone please help me with the analysis of the following function (for inputs of size n). The part that confuses me the most is the inner for loop. def prefix_sums(L): # Total cost = ? pSum = [] #cost = 1 for a in range(len(L)+1): # range + body of function = (n+1) + (n+1)*(body) ? s = 0 #cost = 1 for b in range(a): # cost = ? s = s + L[b] #cost = operation + accessing list = 2 pSum.append(s) #cost = 1 return pSum #cost = 1 What I need to do is figure out the cost of each statement.

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• Code Smell: Inheritance Abuse

  - by dsimcha

  It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of delegating everything to a base class unless explicitly overridden and is therefore extremely convenient and useful. Delegation can often (though not always) be verbose and brittle. The most obvious and IMHO surest sign of inheritance abuse is violation of the Liskov Substitution Principle. What are some other signs that inheritance is The Wrong Tool for the Job even if it seems convenient?

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