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  • Code bacteria: evolving mathematical behavior

    - by Stefano Borini
    It would not be my intention to put a link on my blog, but I don't have any other method to clarify what I really mean. The article is quite long, and it's in three parts (1,2,3), but if you are curious, it's worth the reading. A long time ago (5 years, at least) I programmed a python program which generated "mathematical bacteria". These bacteria are python objects with a simple opcode-based genetic code. You can feed them with a number and they return a number, according to the execution of their code. I generate their genetic codes at random, and apply an environmental selection to those objects producing a result similar to a predefined expected value. Then I let them duplicate, introduce mutations, and evolve them. The result is quite interesting, as their genetic code basically learns how to solve simple equations, even for values different for the training dataset. Now, this thing is just a toy. I had time to waste and I wanted to satisfy my curiosity. however, I assume that something, in terms of research, has been made... I am reinventing the wheel here, I hope. Are you aware of more serious attempts at creating in-silico bacteria like the one I programmed? Please note that this is not really "genetic algorithms". Genetic algorithms is when you use evolution/selection to improve a vector of parameters against a given scoring function. This is kind of different. I optimize the code, not the parameters, against a given scoring function.

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  • Algorithm possible amounts (over)paid for a specific price, based on denominations

    - by Wrikken
    In a current project, people can order goods delivered to their door and choose 'pay on delivery' as a payment option. To make sure the delivery guy has enough change customers are asked to input the amount they will pay (e.g. delivery is 48,13, they will pay with 60,- (3*20,-)). Now, if it were up to me I'd make it a free field, but apparantly higher-ups have decided is should be a selection based on available denominations, without giving amounts that would result in a set of denominations which could be smaller. Example: denominations = [1,2,5,10,20,50] price = 78.12 possibilities: 79 (multitude of options), 80 (e.g. 4*20) 90 (e.g. 50+2*20) 100 (2*50) It's international, so the denominations could change, and the algorithm should be based on that list. The closest I have come which seems to work is this: for all denominations in reversed order (large=>small) add ceil(price/denomination) * denomination to possibles baseprice = floor(price/denomination) * denomination; for all smaller denominations as subdenomination in reversed order add baseprice + (ceil((price - baseprice) / subdenomination) * subdenomination) to possibles end for end for remove doubles sort Is seems to work, but this has emerged after wildly trying all kinds of compact algorithms, and I cannot defend why it works, which could lead to some edge-case / new countries getting wrong options, and it does generate some serious amounts of doubles. As this is probably not a new problem, and Google et al. could not provide me with an answer save for loads of pages calculating how to make exact change, I thought I'd ask SO: have you solved this problem before? Which algorithm? Any proof it will always work?

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  • Spring - Transaction Readonly

    - by AAK
    Hello Gurus! Just wanted your expert opinions on declarative transaction management for Spring. Here is my setup - A. DAO Layer is Plain old JDBC using jdbcTemplete (No hibernate etc) B. Service Layer is POJO with declarative trasnactions as follows - save*, readonly=false, rollback for Throwable Things work fine with above setup. However when I say get*, readonly=true I see errors in my log file saying - Database connection cannot be marked as readonly. This happens for all get* methods in Service Layer. Now my questions - A. Do I have to say get* as readonly? All my get* methods are pure read DB operations. I do not wish to run them in any transaction context. How serious is the above error? B. When I remove the get* confiiguration, I do not see the errors, morever all my simple get* operations are performed without transactions. Is this the way to go? C. Why would anyone want to have transactional methods where readonly = true? Is there any practical significance of this configuration? Thank you! As always your resposes are much appreciated!

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  • How is a relative JMP (x86) implemented in an Assembler?

    - by Pindatjuh
    While building my assembler for the x86 platform I encountered some problems with encoding the JMP instruction: enc inst size in bytes EB cb JMP rel8 2 E9 cw JMP rel16 4 (because of 0x66 16-bit prefix) E9 cd JMP rel32 5 ... (from my favourite x86 instruction website, http://siyobik.info/index.php?module=x86&id=147) All are relative jumps, where the size of each encoding (operation + operand) is in the third column. Now my original (and thus fault because of this) design reserved the maximum (5 bytes) space for each instruction. The operand is not yet known, because it's a jump to a yet unknown location. So I've implemented a "rewrite" mechanism, that rewrites the operands in the correct location in memory, if the location of the jump is known, and fills the rest with NOPs. This is a somewhat serious concern in tight-loops. Now my problem is with the following situation: b: XXX c: JMP a e: XXX ... XXX d: JMP b a: XXX (where XXX is any instruction, depending on the to-be assembled program) The problem is that I want the smallest possible encoding for a JMP instruction (and no NOP filling). I have to know the size of the instruction at c before I can calculate the relative distance between a and b for the operand at d. The same applies for the JMP at c: it needs to know the size of d before it can calculate the relative distance between e and a. How do existing assemblers implement this, or how would you implement this? This is what I am thinking which solves the problem: First encode all the instructions to opcodes between the JMP and it's target, and if this region contains a variable-sized opcode, use the maximum size, i.e. 5 for JMP. Then in some conditions, the JMP is oversized (because it may fit in a smaller encoding): so another pass will search for oversized JMPs, shrink them, and move all instructions ahead), and set absolute branching instructions (i.e. external CALLs) after this pass is completed. I wonder, perhaps this is an over-engineered solution, that's why I ask this question.

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  • What's wrong with debugging in Eclipse on Android?

    - by Sebastian Dwornik
    I've obviously been spoiled by Visual Studio, because although I'm just learning Android and the Eclipse environment, debugging apps in Eclipse is becoming a serious detriment to further development. For example, Eclipse will compile this divide by zero just fine: public class Lesson2Main extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate (savedInstanceState); int i = 1 / 0; TextView tv = new TextView (this); tv.setText ("Hello, Android!"); setContentView (tv); } } And then, when it executes it under the debugger, I will get a full screen of useless debug info, non of which actually points me to the specific line containing the error. The stackTrace is null within the exception ('e') info tree, and it simply states a message stating 'ArithmeticException'. (that's nice, how about you point me in the direction of where you found it!?) I've looked all over the screen and am baffled that this IDE can't get this right. Does developing with Eclipse resort everyone back to 1991 with printf() like logging at every interval then to track down bugs? Seriously. Is there a configuration or plug-in that I'm missing to help with this? I haven't tested this case with XCode, but if the iPhone dev. IDE handles this more like Visual Studio, then no wonder the Android marketplace has so few apps. I'm excited about Android, but it seems that Eclipse is getting in the way.

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  • Mysql Server Optimization

    - by Ish Kumar
    Hi Geeks, We are having serious MySQL(InnoDB) performance issues at a moment when we do: (10-20) insertions on TABLE1 (10-20) updates on TABLE2 Note: Both above operations happens within fraction of a second. And this occurs every few (10-15) minutes. And all online users (approx 400-600) doing read operation on join of TABLE1 & TABLE2 every 1 second. Here is our mysql configuration info: http://docs.google.com/View?id=dfrswh7c_117fmgcmb44 Issues: Lot queries wait and expire later (saw it from phpmyadmin / processes). My poor MySQL server crashes sometimes Questions Q1: Any suggestions to optimize at MySQL level? Q2: I thinking to use persistent connections at application level, is it right? Info Added Later: Database Engine: InnoDB TABLE1 : 400,000 rows (inserting 8,000 daily) & TABLE2: 8,000 rows 1 second query: SELECT b.id, b.user_id, b.description, b.debit, b.created, b.price, u.username, u.email, u.mobile FROM TABLE1 b, TABLE2 u WHERE b.credit = 0 AND b.user_id = u.id AND b.auction_id = "12345" ORDER BY b.id DESC LIMIT 10; // there are few more but they are not so critical. Indexing is good, we are using them wisely. In above query all id's are indexed And TABLE1 has frequent insertions and TABLE2 has frequent updates.

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  • Git as mercurial client? Why no git-hg?

    - by aapeli
    This is a question that's been bothering me for a while. I've done my homework and checked stackoverflow and found at least these two topics about my question: Git for Mercurial like git-svn and Git interoperability with a Mercurial repository I've done some serious googling to solve this issue, but so far with no luck. I've also read the Git Internals book, and the Mercurial Definitive Behind the Scenes to try to figure this out. I'm still a bit puzzled why I haven't been able to find any suitable git-hg type of a tool. From my perspective hg-svn is one of the main features, why I've chosen to use git over mercurial also at work. It allows me to use a workflow I like, and nobody else needs to bother, if they don't care. I just don't see the point in using the intermediate hg repo to convert back and forth, as suggested in one of the chains. So anyway, from what I've read hg and git seem very similar in conceptual design. There are differences under the hood, but none of those should prevent creating a git client for hg. As it seems to me, remote tracking branches and octopus merges make git even more powerful than hg is. So, the real question, is there any real reason why git-hg does not exist (or at least is very hard to find)? Is there some animosity from git users (and developers) towards their hg counterparts that has caused the lack of the git-hg tool? Do any of you have any plans to develop something like this, and go public with it? I could volunteer (although with very feeble C-skills) to participate to get this done. I just don't possess the full knowledge to start this up myself. Could this be the tool to end all DVCS wars for good?

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  • http server implentation, the page does not show properly

    - by none
    well, as i am doing a small project of coding an http server. the code is at http://code.google.com/p/reactor/ the current puzzle is when asked to parse a page with java script and css. As an http server it just sends a page (copied from another website) and it parsed inproperly. when a simple html page is been parse , by my firefox, it shows ok, however when parsing a more complex page(css+javascript) the page is all wired like this : ???? ????? if(getCookie('pais999')==null){varisToplayerDouble="True";isToplayerDouble=(isToplayerDouble=="True")?true:falsevarToplayerCookieName='pais999';varTopLayerCookieExpiredDays=1;varToplayerLink='http://xads.zedo.com/ads2/c?a=239671;g=0;c=455000000;i=0;x=7168;n=455;s=0;k=http://www.pais.co.il/Pais/Games/Lotto/';varToplayerImpression='http://l4.zedo.com/log/p.gif?a=239671;c=455000000;x=7168;n=455;e=i;i=0;s=0;z='+Math.random();varToplayerBigPath='pais/January2007/98one_toplayer.swf';varToplayerSmallPath='pais/January2007/98one_reminder.swf';varToplayerBigWidth=1005;varToplayerBigHeight=500;varToplayerSmallWidth=100;varToplayerSmallHeight=100;varToplayerBigLeft=(0==0)?resWidth/2-ToplayerBigWidth/2:resWidth/2-ToplayerBigWidth/2+0varToplayerBigTop=0;varToplayerSmallLeft=resWidth-ToplayerSmallWidth-0;varToplayerSmallTop=0;varSecondsToChangeBigToSmall=15;}elseif(getCookie('NF999')==null){varisToplayerDouble="True";isToplayerDouble=(isToplayerDouble=="True")?true:falsevarToplayerCookieName='NF999';varTopLayerCookieExpiredDays=1;varToplayerLink='http://xads.zedo.com/ads2/c?a=238663;g=0;c=455000000;i=0;x=7168;n=455;s=0;k=http://www.new-pharm.co.il/SkiGame/?ToolID=OLJD8O';varToplayerImpression='http://l4.zedo.com/log/p.gif?a=238663;c=455000000;x=7168;n=455;e=i;i=0;s=0;z='+Math.random();varToplayerBigPath='NewFarm/Ski/995ONE_TopLayer_550x360.swf';varToplayerSmallPath='NewFarm/Ski/995ONE_Reminder_100x100.swf';varToplayerBigWidth=550;varToplayerBigHeight=360;varToplayerSmallWidth=100;varToplayerSmallHeight=100;varToplayerBigLeft=(0==0)?resWidth/2-ToplayerBigWidth/2:resWidth/2-ToplayerBigWidth/2+0varToplayerBigTop=0;varToplayerSmallLeft=resWidth-ToplayerSmallWidth-0;varToplayerSmallTop=0;varSecondsToChangeBigToSmall=15;}elseif(1==0){}$("divToplayerBig").style.width=ToplayerBigWidth;$("divToplayerBig").style.height=ToplayerBigHeight;$("divToplayerBig").style.left=resWidth/2-ToplayerBigWidth/2;$("divToplayerSmall").style.width=ToplayerSmallWidth;$("divToplayerSmall").style.height=ToplayerSmallHeight;$("divToplayerSmall").style.right=ToplayerSmallWidthvartopOff=0;if(ToplayerBigTop0)topOff=resHeight-ToplayerBigHeight+ToplayerBigTop;varisMain=false;#divToplayerBig{position:absolute;right:20px;bottom:1px;}bodydiv#divToplayerBig{position:fixed;}#divToplayerSmall{position:absolute;right:20px;bottom:10px;}bodydiv#divToplayerSmall{position:fixed;}????|??????LIVE|???????????|ONE???????|ONETV |????'??|BigONE|?????????| CrazyONE | where the source code of the html is : ONE:???:??????????????????????????? ????  ????? if(getCookie('pais999')==null){varisToplayerDouble="True";isToplayerDouble=(isToplayerDouble=="True")?true:falsevarToplayerCookieName='pais999';varTopLayerCookieExpiredDays=1;varToplayerLink='http://xads.zedo.com/ads2/c?a=239671;g=0;c=455000000;i=0;x=7168;n=455;s=0;k=http://www.pais.co.il/Pais/Games/Lotto/';varToplayerImpression='http://l4.zedo.com/log/p.gif?a=239671;c=455000000;x=7168;n=455;e=i;i=0;s=0;z='+Math.random();varToplayerBigPath='pais/January2007/98one_toplayer.swf';varToplayerSmallPath='pais/January2007/98one_reminder.swf';varToplayerBigWidth=1005;varToplayerBigHeight=500;varToplayerSmallWidth=100;varToplayerSmallHeight=100;varToplayerBigLeft=(0==0)?resWidth/2-ToplayerBigWidth/2:resWidth/2-ToplayerBigWidth/2+0varToplayerBigTop=0;varToplayerSmallLeft=resWidth-ToplayerSmallWidth-0;varToplayerSmallTop=0;varSecondsToChangeBigToSmall=15;}elseif(getCookie('NF999')==null){varisToplayerDouble="True";isToplayerDouble=(isToplayerDouble=="True")?true:falsevarToplayerCookieName='NF999';varTopLayerCookieExpiredDays=1;varToplayerLink='http://xads.zedo.com/ads2/c?a=238663;g=0;c=455000000;i=0;x=7168;n=455;s=0;k=http://www.new-pharm.co.il/SkiGame/?ToolID=OLJD8O';varToplayerImpression='http://l4.zedo.com/log/p.gif?a=238663;c=455000000;x=7168;n=455;e=i;i=0;s=0;z='+Math.random();varToplayerBigPath='NewFarm/Ski/995ONE_TopLayer_550x360.swf';varToplayerSmallPath='NewFarm/Ski/995ONE_Reminder_100x100.swf';varToplayerBigWidth=550;varToplayerBigHeight=360;varToplayerSmallWidth=100;varToplayerSmallHeight=100;varToplayerBigLeft=(0==0)?resWidth/2-ToplayerBigWidth/2:resWidth/2-ToplayerBigWidth/2+0varToplayerBigTop=0;varToplayerSmallLeft=resWidth-ToplayerSmallWidth-0;varToplayerSmallTop=0;varSecondsToChangeBigToSmall=15;}elseif(1==0){}$("divToplayerBig").style.width=ToplayerBigWidth;$("divToplayerBig").style.height=ToplayerBigHeight;$("divToplayerBig").style.left=resWidth/2-ToplayerBigWidth/2;$("divToplayerSmall").style.width=ToplayerSmallWidth;$("divToplayerSmall").style.height=ToplayerSmallHeight;$("divToplayerSmall").style.right=ToplayerSmallWidthvartopOff=0;if(ToplayerBigTop0)topOff=resHeight-ToplayerBigHeight+ToplayerBigTop;varisMain=false;#divToplayerBig{position:absolute;right:20px;bottom:1px;}bodydiv#divToplayerBig{position:fixed;}div#divToplayerBig{right:auto;bottom:auto;left:expression((-20-divToplayerBig.offsetWidth+(document.documentElement.clientWidth?document.documentElement.clientWidth:document.body.clientWidth)+(ignoreMe2=document.documentElement.scrollLeft?document.documentElement.scrollLeft:document.body.scrollLeft))+'px');top:expression((0-divToplayerBig.offsetHeight-topOff+(document.documentElement.clientHeight?document.documentElement.clientHeight:document.body.clientHeight)+(ignoreMe=document.documentElement.scrollTop?document.documentElement.scrollTop:document.body.scrollTop))+'px');}#divToplayerSmall{position:absolute;right:20px;bottom:10px;}bodydiv#divToplayerSmall{position:fixed;}div#divToplayerSmall{right:auto;bottom:auto;left:expression((-20-divToplayerSmall.offsetWidth+(document.documentElement.clientWidth?document.documentElement.clientWidth:document.body.clientWidth)+(ignoreMe2=document.documentElement.scrollLeft?document.documentElement.scrollLeft:document.body.scrollLeft))+'px');top:expression((0-divToplayerSmall.offsetHeight+(document.documentElement.clientHeight?document.documentElement.clientHeight:document.body.clientHeight)+(ignoreMe=document.documentElement.scrollTop?document.documentElement.scrollTop:document.body.scrollTop))+'px');}varisTopTrans=(ToplayerBigPath.indexOf("transparent")-1)?false:true;varisRemTrans=(ToplayerSmallPath.indexOf("transparent")-1)?false:true;vartop1session=3;vartop2session=5;InitToplayer(isTopTrans,isRemTrans);window.onload=StartToplayer;????|??????LIVE|???????????|ONE???????|ONETV |????'??|BigONE|?????????|  CrazyONE |????????????????????????????????????????????????????????19/01/07  19:30?????????????????????-?????:?????????????????????????19/01/07  18:43??????????????:??????????????????????19/01/07  17:41???:??????????????????????????????????19/01/07  16:49?????:??????"?????????????/?????1:2,??????"??????19/01/07  16:45????????????????????????????,?????2.5???????????????19/01/07  16:37???????:???"?????????????????-19:30?????????????19/01/07  14:32?????"?????????-18:30?????????"????????,????'??????19/01/07  14:45????????????????????????????????"?:??????????????19/01/07  14:37??????????:??????????????????????????????0:019/01/07  13:46varswfPeleSmall=newSWFObject("http://images.one.co.il/images/PeleEmulator/emulator_pelephone_01a.swf","peleSmall",160,470,"6","#FFFFFF");swfPeleSmall.addParam("quality","high");swfPeleSmall.addParam("wmode","transparent");swfPeleSmall.write("divPeleSmall");varswfPeleBig=newSWFObject("http://images.one.co.il/images/PeleEmulator/emulator_pelephone_02d.swf","peleBig",400,470,"6","#FFFFFF");swfPeleBig.addParam("quality","high");swfPeleBig.addParam("wmode","transparent");swfPeleBig.write("divWithBig");???:???????????????????????????????????????-ONE????????????????????????????????????????????.????????,???????????1:2,?????????????:"???????????"DisplayFlash("W_S_round_border_pic.swf","156","201","1","style=position:absolute");?????????????????????????(??????)?????????                          19/01/20077:26???????????????(????)????????????????????????????6:3,5:7?-5:7???????????????????????,???????23?????.?????,????????????????????????????????,???????????????????????????????????????????,????????????????????.??????????????????????????,??????????????????????????.????????????????????????????-1:1?????????.?????????????????????????????'?????????????????????????????.?????????????.???????????????????????????????(16???????),???????????????????????????????????????3???????,???????????????????????.????????- (only part of of the page presentation in firefox and page source html) why is it happening? what is midding in the http response? StringBuffer tResponse = new StringBuffer(); tResponse.append("HTTP/1.1 200 OK\n"); tResponse.append("Date: "+new Date().toString() +'\n'); tResponse.append("server: http-reactor/0.1-dev\n"); tResponse.append("last-Modified:"+ d.toString() +'\n'); tResponse.append("Content-Type: text/html; charset=windows-1255\n"); tResponse.append("Accept-Language: he; q=1.0, en; q=0.5:); tResponse.append("Content-Length: "+tFileContent.length()+'\n'); tResponse.append('\n'); tResponse.append(tFileContent); public StringBuffer FetchData(String FileName) throws FileNotFoundException{ StringBuffer tFileContent = new StringBuffer(); if (FileName.contains("../")) throw new SecurityException(); if (FileName.equals("/")) FileName = "\\index.html"; FileName.replace('/', '\\'); File f = new File(_root + FileName); Scanner scanner = new Scanner(f); while(scanner.hasNext()) tFileContent.append(scanner.next()); return generateResponse(tFileContent,f.lastModified()); } private StringBuffer generateResponse(StringBuffer tFileContent, long l) { StringBuffer tResponse = new StringBuffer(); Date d = new Date(l); tResponse.append("HTTP/1.1 200 OK\n"); tResponse.append("Date: "+new Date().toString() +'\n'); tResponse.append("server: http-reactor/0.1-dev\n"); tResponse.append("last-Modified:"+ d.toString() +'\n'); tResponse.append("Content-Type: text/html; charset=windows-1255\n"); tResponse.append("Accept-Language: he; q=1.0, en; q=0.5:); tResponse.append("Content-Length: "+tFileContent.length()+'\n'); tResponse.append('\n'); tResponse.append(tFileContent); return tResponse; }

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  • GUI toolkit for Unicode text app?

    - by wrp
    In developing a tool for processing text in exotic scripts, I'm having trouble choosing a GUI toolkit. The main part of the interface is to be a text editor, not much more elaborate than Notepad, but with its own input method editor. It is to be extensible in a scripting language so that non-programmers can develop their own input methods and display routines. It will be assumed that all files are UTF-8. More elaborate support like regexes is not needed. The main sticking points are: characters beyond the Basic Multilingual Plane right-to-left and bi-directional text extension in a scripting language cross-platform Linux/Windows/OS X My first choice was Tcl/Tk, but it lacks bidi and going beyond the BMP seems dodgy. At the other extreme, I've considered Qt with embedded ECMAScript, but that might be heavier and less malleable than I would like. I'm even thinking about making it browser based, but I'm concerned that the IM for large scripts would be too heavy for client-side processing. I've also looked at a few similar projects in Java, but the quality of the font rendering in SWING has been unacceptable. What are your experiences in handling Unicode with various toolkits? Are there other serious issues I haven't considered? What would you recommend for doing this in the lightest way?

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  • UTF8 charset, diacritical elements, conversion problems - and Zend Framework form escaping

    - by imanc
    Hey, I am writing a webapp in ZF and am having serious issues with UTF8. It's using multi lingual content through Zend Form and it seems that ZF heavily escapes all of these characters and basically just won't show a field if there's diacritical elements 'é' and if I use the HTML entity equivalent e.g. é it gets escaped so that the user will see 'é'. Zend Form allows for having non escaped data, but trying to use this is confusing, and it seems it'd need to be used all over the place. So, I have been told that if the page and the text is in UTF8, no conversion to htmlentities is required. Is this true? And if the last question is true, then how do I convert the source text to UTF8? I am comfortable setting up apache so that it sends a default UTF8 charset heading, and also adding the charset meta tag to the html, but doing this I am still getting messed up encoding. I have also tried opening the translation csv file in TextWrangler on OSX as UTF8, but it has done nothing. Thanks! L

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  • Thoughts on GoGrid vs EC2

    - by Jason
    I am currently hosting my SaaS application at GoGrid (Microsoft stack). Here's what I have: Database Server - physical box, 12 GB RAM, 2 X Quad Core CPU (2.13 GHz Xeon E5506) 2 Web / App servers - cloud servers, 2 GB RAM, 2 VCPUs 300 GB monthly bandwidth I am paying around $900 / month for this. My web / app servers are busting at the seams and need to be upgraded to 4 GB of RAM. I also need a firewall, and GoGrid just added this service for an additional $200. After the upgrade, I will be paying around $1,400. I started looking at Amazon EC2, specifically this config: Database server - "High Memory Double Extra Large Instance" - 34 GB RAM, 13 EC2 compute units 2 Web / App servers - "Large Instance" - 7.5 GB RAM, 4 EC2 compute units If I go with 1 year reserved instances, my upfront cost would be $4,500 and my monthly would be $700. This comes to $1,075 / month when amortized. Amazon also includes a firewall for free. Here are my questions: Do any of you have experience running a database (especially SQL Server) on an EC2 instance? How did it perform compared to a dedicated machine? One of my major concerns is with disk I/O. Amazon's description of a compute unit is fairly vague. Any ideas on how the CPU performance on the database servers would compare? I am hoping that the Amazon solution will provide significantly better performance than my current or even improved GoGrid setup. Having a virtual database server would also be nice in terms of availability. Right now I would be in serious trouble if I had any hardware issues. Thanks for any insight...

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  • Good guidelines for developing an ecommerce application

    - by kaciula
    I'm making an ecommerce application on Android and, as it is my first serious project, I'm trying to figure out beforehand the best approach to do this. The application talks to a web service (magento api, meaning soap or xml rpc unfortunately) and gets all the content on the phone (product categories, product details, user credentials etc.). I think it should do lazy loading or something like that. So, I was thinking to keep the user credentials in a custom Object which will be kept in a SharedPreferences so that every Activity cand easily access it. I'll use a couple of ListViews to show the content and AsyncTask to fetch the data needed. Should I keep all the data in memory in objects or should I use some sort of cache or a local database? Also, I'm planning to use a HashMap with SoftReferences to hold the bitmaps I am downloading. But wouldn't this eat a lot of memory? How cand all the activities have access to all these objects (ecommerce basket etc.)? I'm thinking of passing them using Intents but this doesn't seem right to me. Can SharedPreferences be used for a lot of objects and are there any concurrency issues? Any pointers would be really appreciated. What are some good guidelines? What classes should I look into? Do you know of any resources on the Internet for me to check out?

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  • Does a CS PhD Help for Software Engineering Career?

    - by SiLent SoNG
    I would like to seek advice on whether or not to take a PhD offer from a good university. My only concern is the PhD will take at least 4 year's commitment. During the period I won't have good monetary income. I am also concerned whether the PhD will help my future career development. My career goal is software engineering only. Some of the PhD info: The PhD is CS related. The research area is Information Retrieval, Machine Learning, and Nature Language Processing. More specifically, the research topic is Deep Web search. Some of backgrounds: I worked in Oracle for 3 years in database development after obtained a CS degree from some good university. In last year I received an email telling an interesting project from a professor and thereafter I was lured into his research team. The team consists of 4 PhD students; those students have little or no industry experiences and their coding skills are really really bad. By saying bad I mean they do not know some common patterns and they do not know pitfalls of the programming languages as well as idioms for doing things right. I guess a at least 4 year commitment is worth of serious consideration. I am 27 at this moment. If I take the offer, that implies I will be 31+ upon graduation. Wah... becoming.. what to say, no longer young. Hence, here I am seeking advice on whether it is good or not to take the PhD offer, and whether a CS PhD is good for my future career growth as a software engineer? I do not intent to go for academia.

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  • Why are references compacted inside Perl lists?

    - by parkan
    Putting a precompiled regex inside two different hashes referenced in a list: my @list = (); my $regex = qr/ABC/; push @list, { 'one' => $regex }; push @list, { 'two' => $regex }; use Data::Dumper; print Dumper(\@list); I'd expect: $VAR1 = [ { 'one' => qr/(?-xism:ABC)/ }, { 'two' => qr/(?-xism:ABC)/ } ]; But instead we get a circular reference: $VAR1 = [ { 'one' => qr/(?-xism:ABC)/ }, { 'two' => $VAR1->[0]{'one'} } ]; This will happen with indefinitely nested hash references and shallowly copied $regex. I'm assuming the basic reason is that precompiled regexes are actually references, and references inside the same list structure are compacted as an optimization (\$scalar behaves the same way). I don't entirely see the utility of doing this (presumably a reference to a reference has the same memory footprint), but maybe there's a reason based on the internal representation Is this the correct behavior? Can I stop it from happening? Aside from probably making GC more difficult, these circular structures create pretty serious headaches. For example, iterating over a list of queries that may sometimes contain the same regular expression will crash the MongoDB driver with a nasty segfault (see https://rt.cpan.org/Public/Bug/Display.html?id=58500)

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  • why MVC instead of good old asp.net? Still not grasping why I should go this route??

    - by RJ
    I know this question has been asked before and I read all the answers but they still don't give me the answers I am looking for. I need something concrete. I volunteered to give a presentation on MVC to other developers in our group which forces me to learn it. The big question everyone has is: "What can MVC bring to the table that we can't do in asp.net or MVC can do faster. I have just gone through Nerd Dinner and actually created a complete website that sort of mimics Nerd Dinner. But as great a job that Scott Guthrie did on it, there are big gaps that aren't answered such as, how do I throw a textbox on the listing page with a button and do a simple search. In asp.net, I would throw a textbox, button and grid on the page and bind it to a sproc and away I go. What is the equivalent in MVC. I guess I need a really good tutorial on how to use MVC without using Linq-to-Sql. I know I am sort of babbling on about this but it is a very serious question that still seems to go unanswered. On a side note, the View page of MVC brings back nightmares of classic asp with all the in-line code that we got away from way back when with code behind pages. Yes, MVC has Controller and Model classes which are great but I still don't like the classic asp tags in the html. Help me out here, I really like the concept of MVC and want it to be successful but I need more!

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  • One big executable or many small DLL's?

    - by Patrick
    Over the years my application has grown from 1MB to 25MB and I expect it to grow further to 40, 50 MB. I don't use DLL's, but put everything in this one big executable. Having one big executable has certain advantages: Installing my application at the customer is really: copy and run. Upgrades can be easily zipped and sent to the customer There is no risk of having conflicting DLL's (where the customer has version X of the EXE, but version Y of the DLL) The big disadvantage of the big EXE is that linking times seem to grow exponentially. Additional problem is that a part of the code (let's say about 40%) is shared with another application. Again, the advantages are that: There is no risk on having a mix of incorrect DLL versions Every developer can make changes on the common code which speeds up developments. But again, this has a serious impact on compilation times (everyone compiles the common code again on his PC) and on linking times. The question http://stackoverflow.com/questions/2387908/grouping-dlls-for-use-in-executable mentions the possibility of mixing DLL's in one executable, but it looks like this still requires you to link all functions manually in your application (using LoadLibrary, GetProcAddress, ...). What is your opinion on executable sizes, the use of DLL's and the best 'balance' between easy deployment and easy/fast development?

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  • Design of std::ifstream class

    - by Nawaz
    Those of us who have seen the beauty of STL try to use it as much as possible, and also encourage others to use it wherever we see them using raw pointers and arrays. Scott Meyers have written a whole book on STL, with title Effective STL. Yet what happened to the developers of ifstream that they preferred char* over std::string. I wonder why the first parameter of ifstream::open() is of type const char*, instead of const std::string &. Please have a look at it's signature: void open(const char * filename, ios_base::openmode mode = ios_base::in ); Why this? Why not this: void open(const string & filename, ios_base::openmode mode = ios_base::in ); Is this a serious mistake with the design? Or this design is deliberate? What could be the reason? I don't see any reason why they have preferred char* over std::string. Note we could still pass char* to the latter function that takes std::string. That's not a problem! By the way, I'm aware that ifstream is a typedef, so no comment on my title.:P. It looks short that is why I used it. The actual class template is : template<class _Elem,class _Traits> class basic_ifstream;

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  • Using SetParent to steal the main window of another process but keeping the message loops separate

    - by insta
    Background: My coworker and I are maintaining a million-line legacy application we inherited. Its frontend is written in VB6, and as we're devoting almost all of our resources to converting it to C#, we are looking for quick & dirty solutions to our specific problem. The application behaves in a plugin-ish manner. There are up to 20ish separate ActiveX controls that can be loaded at once in a grid-style layout. The problem is that the ActiveX controls do all of their processing on their own UI thread, and as a lot of it is blocking waiting on network access, the UI gets very soupy. When our hosting C# app loads these controls, it becomes unresponsive because of how many controls are chewing up UI resources doing nothing. To top it off, the controls are fragile and will crash at the slightest provocation. When they are hosted in the main C# app, it creates serious instability. The best my coworker and I have come up with so far is starting a process per ActiveX control. This process, which we call the proxy, is another winforms app. It uses named pipes to communicate with the hosting process. The hosting process creates a window, loads an ActiveX control of our choice (via some reflections & AxHost magic), and tells the main process what its window handle is via the named pipe. The main process uses a combination of SetParent, and SetWindowPos to move the proxy application into itself to emulate a plugin. Size updates are sent via the named pipe. This works well enough until the ActiveX application does some sort of lengthy process and we click around on the main window while it's working. For awhile the main window is responsive, but eventually it becomes unresponsive as the child window waits for its UI thread. How can we keep the child windows on their own complete thread while still getting the benefits of SetParent? (please let me know if anything isn't clear!)

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  • Max Daily Budget exceeded and Billing Status "Changing Daily Budget"

    - by draftpik
    We've exceeded the Max Daily Budget for our app, but we can't increase the budget due to a serious flaw in Google's billing system. Google App Engine and Google Wallet do not have very capable support for multiple sign-in. As a result, I went to change the budget, but it used the wrong Google Wallet account (a different Google Account I was signed in as). I had to go back and try again, but now our GAE app shows the following status: Billing Status: Changing Daily Budget Your account has been locked while we process your budget changes. If you were redirected to Google Checkout but did not complete the process, your settings will remain unchanged. (You will be able to make changes to your budget settings again once the outstanding payment is processed.) Now I'm completely prevented from making any billing changes, our app is shut off (over quota), and I have NOTHING I can do to fix it. This is a seriously fundamental flaw in App Engine's billing system and Google Wallet integration. Has anyone run into this before? Is there a workaround anyone is aware of? Right now, our production app is completely down thanks to this issue. Any help you can offer would be greatly appreciated? If you're from Google and you might be able to help on the backend, our app id is "nhldraftpik". Thanks! Brian

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  • PHP GD imagecreatefromstring discards transparency

    - by meustrus
    I've been trying to get transparency to work with my application (which dynamically resizes images before storing them) and I think I've finally narrowed down the problem after much misdirection about imagealphablending and imagesavealpha. The source image is never loaded with proper transparency! // With this line, the output image has no transparency (where it should be // transparent, colors bleed out randomly or it's completely black, depending // on the image) $img = imagecreatefromstring($fileData); // With this line, it works as expected. $img = imagecreatefrompng($fileName); // Blah blah blah, lots of image resize code into $img2 goes here; I finally // tried just outputting $img instead. header('Content-Type: image/png'); imagealphablending($img, FALSE); imagesavealpha($img, TRUE); imagepng($img); imagedestroy($img); It would be some serious architectural difficulty to load the image from a file; this code is being used with a JSON API that gets queried from an iPhone app, and it's easier in this case (and more consistent) to upload images as base64-encoded strings in the POST data. Do I absolutely need to somehow store the image as a file (just so that PHP can load it into memory again)? Is there maybe a way to create a Stream from $fileData that can be passed to imagecreatefrompng?

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  • How to ensure DB security for a Windows Forms application?

    - by Vilx-
    The basic setup is classic - you're creating a Windows Forms application that connects to a DB and does all kinds of enterprise-y stuff. Naturally, such an application will have many users with different access rights in the DB, and each with their own login name and password. So how do you implement this? One way is to create a DB login for every application user, but that's a pretty serious thing to do, which even requires admin rights on the DB server, etc. If the DB server hosts several applications, the admins are quite likely not to be happy with this. In the web world typically one creates his own "Users" table which contains all the necessary info, and uses one fixed DB login for all interaction. That is all nice for a web app, but a windows forms can't hide this master login information, negating security altogether. (It can try to hide, but all such attempts are easily broken with a bit of effort). So... is there some middle way? Perhaps logging in with a fixed login, and then elevating priviledges from a special stored procedure which checks the username and password?

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  • How can I speed up the "finally get it" process?

    - by Earlz
    Hello, I am a hobby programmer and began when I was about 13. I'm currently going to college(freshman) for my computer science degree(which means, I'm still in the stuff I already know such as for loops). I've been programming professionally for a start up for about 9 months or so now. I have a serious problem though. I think that almost all of the code I write is perfect. Now I remember reading an article somewhere where there is like 3 stages of learning programming You don't know anything and you know you don't know anything. You don't know anything but you think you do. You finally get and accept that you don't know anything. (if someone finds that article tell me and I'll give a link) So right now, I'm at stage 2. How can I get to stage 3 quicker? The more and more of some people's code I read I think "this is complete rubbish, I would've done it like..." and I really dislike how I think that way. (and this fairly recently began happening, like over the past year)

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  • What's a good Java-based Master-Slave communication mechanism?

    - by plecong
    I'm creating a Java application that requires master-slave communication between JVMs, possibly residing on the same physical machine. There will be a "master" server running inside a JEE application server (i.e. JBoss) that will have "slave" clients connect to it and dynamically register itself for communication (that is the master will not know the IP addresses/ports of the slaves so cannot be configured in advance). The master server acts as a controller that will dole work out to the slaves and the slaves will periodically respond with notifications, so there would be bi-directional communication. I was originally thinking of RPC-based systems where each side would be a server, but it could get complicated, so I'd prefer a mechanism where there's an open socket and they talk back and forth. I'm looking for a communication mechanism that would be low-latency where the messages would be mostly primitive types, so no serious serialization is necessary. Here's what I've looked at: RMI JMS: Built-in to Java, the "slave" clients would connect to the existing ConnectionFactory in the application server. JAX-WS/RS: Both master and slave would be servers exposing an RPC interface for bi-directional communication. JGroups/Hazelcast: Use shared distributed data structures to facilitate communication. Memcached/MongoDB: Use these as "queues" to facilitate communication, though the clients would have to poll so there would be some latency. Thrift: This does seem to keep a persistent connection, but not sure how to integrate/embed a Thrift server into JBoss WebSocket/Raw Socket: This would work, but require a lot more custom code than I'd like. Is there any technology I'm missing? Edit: Also looked at: JMX: Have the client connect to JBoss' JMX server and receive JMX notifications for bidirectional comms.

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  • Serializing and deserializing a map with key as string

    - by Grace K
    Hi! I am intending to serialize and deserialize a hashmap whose key is a string. From Josh Bloch's Effective Java, I understand the following. P.222 "For example, consider the case of a harsh table. The physical representation is a sequence of hash buckets containing key-value entries. Which bucket an entry is placed in is a function of the hash code of the key, which is not, in general guaranteed to be the same from JVM implementation to JVM implementation. In fact, it isn't even guranteed to be the same from run to run on the same JVM implementation. Therefore accepting the default serialized form for a hash table would constitute a serious bug. Serializing and deserializing the hash table could yield an object whose invariants were seriously corrupt." My questions are: 1) In general, would overriding the equals and hashcode of the key class of the map resolve this issue and the map can be correctly restored? 2) If my key is a String and the String class is already overriding the hashCode() method, would I still have problem described above. (I am seeing a bug which makes me think this is probably still a problem even though the key is String with overriding hashCode.) 3)Previously, I get around this issue by serializing an array of entries (key, value) and when deserializing I would reconstruct the map. I am wondering if there is a better approach. 4) If the answers to question 1 and 2 are that I still can't be guaranteed. Could someone explain why? If the hashCodes are the same would they go to the same buckets across JVMs? Thanks, Grace

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  • (nested) user controls within a mvp pattern causing sporadic problems

    - by LLEA
    hi everyone, I have a serious problem with nested user controls (UCs) in WinForms while trying to implement the mvp pattern (passive view). The project consists of one model (designed as a singleton) and a set of different presenters with corresponding view interfaces. To avoid one huge view interface and therefore an overloaded main UI, I decided to make use of a set of different UCs. Each UC has one view interface and one presenter that can access the model. But there are nested UCs: meaning that one specialised UC implements sort of a basic UC. The main UI just represents a container for all those UCs. So far, so good (if not, please ask)?! There are two problems that I am facing now (but I guess both are of the same origin): From time to time it is not possible anymore to load the UCs and test them within the Visual Studio 2008 User Control Test Container. The error message just says that a project with an output type of class library cannot be started directly etc. I can "handle" that by unloading all UC projects and reloading them afterwards. (I guess the references to all mvp components and other UCs are then updated). Assuming that the implementation of my mvp pattern is okay and all those UCs are testable within the VS Test Container at a certain time - there is the biggest problem still left: I am not able to add any UC (even the basic and unnested ones) to a simple Form (UI). The error message: error message.jpg Could it be that my basic UC causes all these Problems?! It consists of two simple ComboBoxes and implements a basic presenter and basic view interface. Whenever I add this UC to a different UC the VS designer adds two references to the public getter methods of the UC as resources. I then manually remove those resources from the resx-file and commend the corresponding lines in the designer file. thx in advance

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