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  • Fastest way to become a MySQL expert?

    - by Kerry
    I have been using MySQL for years, mainly on smaller projects until the last year or so. I'm not sure if it's the nature of the language or my lack of real tutorials that gives me the feeling of being unsure if what I'm writing is the proper way for optimization purposes and scaling purposes. While self-taught in PHP I'm very sure of myself and the code I write, easily can compare it to others and so on. With MySQL, I'm not sure whether (and in what cases) an INNER JOIN or LEFT JOIN should be used, nor am I aware of the large amount of functionality that it has. While I've written code for databases that handled tens of millions of records, I don't know if it's optimum. I often find that a small tweak will make a query take less than 1/10 of the original time... but how do I know that my current query isn't also slow? I would like to become completely confident in this field in the ability to optimize databases and be scalable. Use is not a problem -- I use it on a daily basis in a number of different ways. So, the question is, what's the path? Reading a book? Website/tutorials? Recommendations?

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  • Rewarding iOS app beta testers with in app purchase?

    - by Partridge
    My iOS app is going to be free, but with additional functionality enabled via in app purchase. Currently beta testers are doing a great job finding bugs and I want to reward them for their hard work. I think the least I can do is give them a full version of the app so that they don't have to buy the functionality themselves. However, I'm not sure what the best way to do this is. There do not appear to be promo codes for in app purchase so I can't just email out promo codes. I have all the tester device UDIDs so when the app launches I could grab the device UDID and compare it to an internal list of 'approved' UDIDs. Is this what other developers do? My concerns: The in app purchase content would not be tied to their iTunes account, so if beta testers move to a new device they would not be able to enable the content unless I released a new build in the app store with their new UDID. So they may have to buy it eventually anyway. Having an internal list leaves a hole for hackers to modify the list and add themselves to it. What would you do?

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  • Arrays not matching correctly

    - by Nick Gibson
    userAnswer[] holds the string of the answer the user types in and is comparing it to answers[] to see if they match up and then spits out correct or wrong. j is equal to the question number. So if j was question 6, answers[j] should refer to answers[6] right? Then userAnswer[6] should compare to answers[6] and match if its correct. But its giving me wrong answers and displaying the answer I typed as correct. int abc, loopCount = 100; int j = quesNum, overValue, forLoop = 100; for (int loop = 1; loop < loopCount; loop++) { aa = r.nextInt(10+1); abc = (int) aa; String[] userAnswer = new String[x]; JOptionPane.showMessageDialog(null,abc); if(abc < x) { userAnswer[j] = JOptionPane.showInputDialog(null,"Question "+quesNum+"\n"+questions[abc]+"\n\nA: "+a[abc]+"\nB: "+b[abc]+"\nC: "+c[abc]+"\nD: "+d[abc]); if(userAnswer[j].equals(answers[j])) { JOptionPane.showMessageDialog(null,"Correct. \nThe Correct Answer is "+answers[abc]); } else { JOptionPane.showMessageDialog(null,"Wrong. \n The Correct Answer is "+answers[abc]); }//else }//if }//for

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  • Calculating a consecutive streak in data

    - by Jura25
    I’m trying to calculate the maximum winning and losing streak in a dataset (i.e. the highest number of consecutive positive or negative values). I’ve found a somewhat related question here on StackOverflow and even though that gave me some good suggestions, the angle of that question is different, and I’m not (yet) experienced enough to translate and apply that information to this problem. So I was hoping you could help me out, even an suggestion would be great. My data set look like this: > subRes Instrument TradeResult.Currency. 1 JPM -3 2 JPM 264 3 JPM 284 4 JPM 69 5 JPM 283 6 JPM -219 7 JPM -91 8 JPM 165 9 JPM -35 10 JPM -294 11 KFT -8 12 KFT -48 13 KFT 125 14 KFT -150 15 KFT -206 16 KFT 107 17 KFT 107 18 KFT 56 19 KFT -26 20 KFT 189 > split(subRes[,2],subRes[,1]) $JPM [1] -3 264 284 69 283 -219 -91 165 -35 -294 $KFT [1] -8 -48 125 -150 -206 107 107 56 -26 189 In this case, the maximum (winning) streak for JPM is four (namely the 264, 284, 69 and 283 consecutive positive results) and for KFT this value is 3 (107, 107, 56). My goal is to create a function which gives the maximum winning streaks per instrument (i.e. JPM: 4, KFT: 3). To achieve that: R needs to compare the current result with the previous result, and if it is higher then there is a streak of at least 2 consecutive positive results. Then R needs to look at the next value, and if this is also higher: add 1 to the already found value of 2. If this value isn’t higher, R needs to move on to the next value, while remembering 2 as the intermediate maximum. I’ve tried cumsum and cummax in accordance with conditional summing (like cumsum(c(TRUE, diff(subRes[,2]) > 0))), which didn’t work out. Also rle in accordance with lapply (like lapply(rle(subRes$TradeResult.Currency.), function(x) diff(x) > 0)) didn’t work. How can I make this work?

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  • finding common prefix of array of strings

    - by bumperbox
    I have an array like this $sports = array( 'Softball - Counties', 'Softball - Eastern', 'Softball - North Harbour', 'Softball - South', 'Softball - Western' ); and i would like to find the longest common part of the string so in this instance, it would be 'Softball - '; I am thinking that I would follow the this process $i = 1; // loop to the length of the first string while ($i < strlen($sports[0]) { // grab the left most part up to i in length $match = substr($sports[0], 0, $i); // loop through all the values in array, and compare if they match foreach ($sports as $sport) { if ($match != substr($sport, 0, $i) { // didn't match, return the part that did match return substr($sport, 0, $i-1); } } // foreach // increase string length $i++; } // while // if you got to here, then all of them must be identical Questions is there a built in function or much simpler way of doing this ? for my 5 line array that is probably fine, but if i were to do several thousand line arrays, there would be a lot of overhead, so i would have to be move calculated with my starting values of $i, eg $i = halfway of string, if it fails, then $i/2 until it works, then increment $i by 1 until we succeed. so that we are doing the least number of comparisons to get a result If there a formula/algorithm out already out there for this kind of problem ? thanks alex

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  • Is there a table of OpenGL extensions, versions, and hardware support somewhere?

    - by Thomas
    I'm looking for some resource that can help me decide what OpenGL version my game needs at minimum, and what features to support through extensions. Ideally, a table of the following format: 1.0 1.1 1.2 1.2.1 1.3 ... multitexture - ARB ARB core core texture_float - EXT EXT ARB ARB ... (Not sure about the values I put in, but you get the idea.) The extension specs themselves, at opengl.org, list the minimum OpenGL version they need, so that part is easy. However, many extensions have been accepted and became core standard in subsequent OpenGL versions, but it is very hard to find when that happened. The only way I could find is to compare the full OpenGL standards document for each version. On a related note, I would also very much like to know which extensions/features are supported by which hardware, to help me decide what features I can safely use in my game, and which ones I need to make optional. For example, a big honkin' table like this: MAX_TEXTURE_IMAGE_UNITS MAX_VERTEX_TEXTURE_IMAGE_UNITS ... GeForce 6xxx 8 4 GeForce 7xxx 16 8 ATi x300 8 4 ... (Again, I'm making the values up.) The table could list hardware limitations from glGet but also support for particular extensions, and limitations of such extension support (e.g. what floating-point texture formats are supported in hardware). Any pointers to these or similar resources would be hugely appreciated!

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  • search algorithm using sentinel

    - by davit-datuashvili
    i am trying to do search algorithm using sentinel which reduce time to 3.87n nanoseconds for example compare to this code int search (int t ){ for (int i=0;i<n;i++) if (x[i]==t) return i; return -1; } it takes 4.06 nanoseconds so i am trying to optimize it here is code public class Search{ public static int search(int a[],int t){ int i; int p=0; int n=a.length; int hold; hold=a[n-1]; a[n-1]=t; for ( i=0;;i++) if (a[i]==t) break; a[n-1]=t; if (i==n){ p= -1; } else{ p= i; } return p; } public static void main(String[]args){ int t=-1; int a[]=new int[]{4,5,2,6,8,7,9}; System.out.println(search(a,t)); } } but is show me that 9 is at position 6 which is correct but if t =1 or something else which is not array it show me position 6 too please help

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  • What are major differences between C# and Java?

    - by enba
    I just want to clarify one thing. This is not a question on which one is better, that part I leave to someone else to discuss. I don't care about it. I've been asked this question on my job interview and I thought it might be useful to learn a bit more. These are the ones I could come up with: Java is "platform independent". Well nowadays you could say there is the Mono project so C# could be considered too but I believe it is a bit exaggerating. Why? Well, when a new release of Java is done it is simultaneously available on all platforms it supports, on the other hand how many features of C# 3.0 are still missing in the Mono implementation? Or is it really CLR vs. JRE that we should compare here? Java doesn't support events and delegates. As far as I know. In Java all methods are virtual Development tools: I believe there isn't such a tool yet as Visual Studio. Especially if you've worked with team editions you'll know what I mean. Please add others you think are relevant. Update: Just popped up my mind, Java doesn't have something like custom attributes on classes, methods etc. Or does it?

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  • values not equal in sqlite and json array in android

    - by Venkat
    I am trying to compare the value in sqlite table and id of the webservice what i have done so far is if(data_exist!=bookProduct.length()){ Log.i("in update","m here"); Cursor cursors = getRawEvents("select id from bcuk_book"); try{ for (int i = 0; i < bookProduct.length(); i++) { JSONObject c = bookProduct.getJSONObject(i); String Bid = c.getString(TAG_ID); ArrayList<String> mapId = new ArrayList<String>(); while(cursors.moveToNext()) { Log.e("cursors",cursors.getString(0)); Log.i(Bid,Bid); if(cursors.getString(0)!=c.getString(TAG_ID)){ Log.e("fas",Bid); } } mapId.add(TAG_ID); Log.e(Bid,Bid); } } My issue is i am getting same values in logs.. if(cursors.getString(0)!=c.getString(TAG_ID)){ this condition says if they are not equal then print the log..But the issue is i am entering into that block even i am getting same values from sqlite and TAG_ID i.e from json webservice..How to solve this.Where i done wrong?

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  • Coordinating typedefs and structs in std::multiset (C++)

    - by Sarah
    I'm not a professional programmer, so please don't hesitate to state the obvious. My goal is to use a std::multiset container (typedef EventMultiSet) called currentEvents to organize a list of structs, of type Event, and to have members of class Host occasionally add new Event structs to currentEvents. The structs are supposed to be sorted by one of their members, time. I am not sure how much of what I am trying to do is legal; the g++ compiler reports (in "Host.h") "error: 'EventMultiSet' has not been declared." Here's what I'm doing: // Event.h struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } double time; int eventID; int hostID; }; // Host.h ... void calcLifeHist( double, EventMultiSet * ); // produces compiler error ... void addEvent( double, int, int, EventMultiSet * ); // produces compiler error // Host.cpp #include "Event.h" ... // main.cpp #include "Event.h" ... typedef std::multiset< Event, std::less< Event > > EventMultiSet; EventMultiSet currentEvents; EventMultiSet * cePtr = &currentEvents; ... Major questions Where should I include the EventMultiSet typedef? Are my EventMultiSet pointers obviously problematic? Is the compare function within my Event struct (in theory) okay? Thank you very much in advance.

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  • Dynamic evaluation of a table column within an insert before trigger

    - by Tim Garver
    HI All, I have 3 tables, main, types and linked. main has an id column and 32 type columns. types has id, type linked has id, main_id, type_id I want to create an insert before trigger on the main table. It needs to compare its 32 type columns to the values in the types table if the main table column has an 'X' for its value and insert the main_id and types_id into the linked table. i have done a lot of searching, and it looks like a prepared statement would be the way to go, but i wanted to ask the experts. The issue, is i dont want to write 32 IF statements, and even if i did, i need to query the types table to get the ID for that type, seems like a huge waist of resources. Ideally i want to do this inside of my trigger: BEGIN DECLARE @types results_set -- (not sure if this is a valid type); -- (iam sure my loop syntax is all wrong here)... SET @types = (select * from types) for i=0;i<types.records;i++ { IF NEW.[i.type] = 'X' THEN insert into linked (main_id,type_id) values (new.ID, i.id); END IF; } END; Anyway, This is what i was hoping to do, maybe there is a way to dynamically set the field name inside of a results loop, but i cant find a good example of this. Thanks in advance Tim

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  • MySQL LIMIT 1 but query 15 rows?

    - by Ian
    Basically what I'm trying to do is compare the ID's of rows against 15 results in MySQL, eliminating all but 1 (using NOT IN) and then pull that result. Now normally this would be fine by itself, however the order of the 15 rows I'm doing the SQL query for are constantly changing based on a ranking, so there is a possibility that between the time the ranking updates, and the ajax request (which I submit the ID's for NOT IN) more than just one ID has changed, which would of course bring back more than one row which I do not want. So in short, is there a way in which I can query 15 rows, but only return one? Without having to run two separate queries. Any help is appreciated, thank you. EXAMPLE: Say I have 7 items in my database, and I'm displaying 5 on the page to the user. These are what are being displayed to the user: Apple Orange Kiwi Banana Grape But in the database I also have Peach Blackberry Now what I want to do is if the user deletes an item from their list, it will add another item (based on a ranking they have) Now the issue is, in order to know what they have on their list at the moment I send the remaining items to the database (say they deleted Kiwi, I would send Apple, Orange, Banana, and Grape) So now I select the highest ranked 5 items from are remaining six items, make sure they are not the ones already displayed on the page, and then add the new one to list (either Peach or Blackberry) All good and well, except that if both peach and blackberry now outrank grape, then I will be returning two results instead of just one. Because it would've searched... Apple Orange Banana Peach Blackberry and excluded... Apple Orange Banana Grape Which leaves us with both Peach and Blackberry, instead of just Peach or Blackberry

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  • On the search for my next great .Net Read

    - by user127954
    Just got done with "The art of unit testing". It was a great read and i think everyone should go buy a copy. With that said i think the next book I'm like to read would be a architecture / Design type book that would focus heavily on building your objects / software in such a way that it would be: Low Coupling High Cohesion Easily Maintainable / Extended Easy to test Easy to Navigate / Debug The above characteristcs are the most important ones but also maybe it would also include (but not necessary) designing for: Performance - Don't want to design a system at at the end find out its dog slow :) Scalability - Again don't want to design something at the end find out it won't scale. I'd also prefer (but not necessary again): Something newer - Architectural principles seem to gradually evolve / improve over time and id like something with current thinking. .Net as illustrating language - like i said above its not mandatory but since its what i use every day id prefer it to be in .net. Doesn't really matter if its in vb.net or c# Some of the topics that would be talked about its how to minimize dependencies and using interfaces throughout your solution rather than concrete classes. Maybe it would constract /compare some of the newest design principles like DDD, Repository Pattern, Ect... I already have "Clean Code" (don't know if its this type of book or not) and "Working effectively with legacy code" on my radar but id like to read a book based upon the topic i talked about above first. Is there such a book?

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  • Uniquing with Existing Core Data Entities

    - by warrenm
    I'm using Core Data to store a lot (1000s) of items. A pair of properties on each item are used to determine uniqueness, so when a new item comes in, I compare it against the existing items before inserting it. Since the incoming data is in the form of an RSS feed, there are often many duplicates, and the cost of the uniquing step is O(N^2), which has become significant. Right now, I create a set of existing items before iterating over the list of (possible) new items. My theory is that on the first iteration, all the items will be faulted in, and assuming we aren't pressed for memory, most of those items will remain resident over the course of the iteration. I see my options thusly: Use string comparison for uniquing, iterating over all "new" items and comparing to all existing items (Current approach) Use a predicate to filter the set of existing items against the properties of the "new" items. Use a predicate with Core Data to determine uniqueness of each "new" item (without retrieving the set of existing items). Is option 3 likely to be faster than my current approach? Do you know of a better way?

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  • File.Replace throwing IOException

    - by WebDevHobo
    I have an app that can make modify images. In some cases, this makes the filesize smaller, in some cases bigger. The program doesn't have an option to "not replace the file if result has a bigger filesize". So I wrote a little C# app to try and solve this. Instead of overwriting the files, I make the app write the result to a folder under the current one and name that folder Test. The C# app I wrote compares grabs the contents of both folders and puts the full path to the file(s) in two List objects. I then compare and replace. The replacing isn't working however. I get the following IOException: Unable to remove the file to be replaced The location is on an external hard-drive, on which I have full rights. Now, I know I can just do File.Delete and File.Move in that order, but this exception has gotten me interested in why this particular setup wont work. Here's the source code: http://pastebin.com/4Vq82Umu And yes, the file specified as last argument of the Replace function does exist.

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  • cannot modify header information puzzler

    - by outofmyleague_lucy
    hi im out of my league i have written what has now become identical code for two sites hosted on different servers. the first worked perfectly and i have therefore used it to compare the second to.from a login for i am directing to a loginaction.php when i include the db_connect.php ie <?php session_start(); include 'db_connect.php'; $user=$_POST['formUser'] $password=$_POST['formPassword']etc ? i am returning cannot modify header information header info already sent, but when i include the content of the db_connect ie <?php session_start(); $connect = mysql_connect("localhost", "user", "pass"); mysql_select_db(db_name, $connection); $user=$_POST['formUser'] $password=$_POST['formPassword']etc ? it works. any ideas? edit - requested error message Warning: Cannot modify header information - headers already sent by (output started at /home/avenncou/public_html/include/db_connect.php:4) in /home/avenncou/public_html/include/loginaction.php on line 14 at line 14 the is a header("Location: {$_SERVER["HTTP_REFERER"]}"); edit - requested db_connect.php <?php $connection = mysql_connect("localhost", "user", "pass");// or die ("Unable to connect!"); mysql_select_db("db", $connection);// or die ("Unable to select database!"); ?> that is all of it (dies commented out in case thats where the error was)!!!

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  • How Best to Replace PL/SQL with C#?

    - by Mike
    Hi, I write a lot of one-off Oracle SQL queries/reports (in Toad), and sometimes they can get complex, involving lots of unions, joins, and subqueries, and/or requiring dynamic SQL, and/or procedural logic. PL/SQL is custom made for handling these situations, but as a language it does not compare to C#, and even if it did, it's tooling does not, and if even that did, forcing yet another language on the team is something to be avoided whenever possible. Experience has shown me that using SQL for the set based processing, coupled with C# for the procedural processing, is a powerful combination indeed, and far more readable, maintainable and enhanceable than PL/SQL. So, we end up with a number of small C# programs which typically would construct a SQL query string piece by piece and/or run several queries and process them as needed. This kind of code could easily be a disaster, but a good developer can make this work out quite well, and end up with very readable code. So, I don't think it's a bad way to code for smaller DB focused projects. My main question is, how best to create and package all these little C# programs that run ad hoc queries and reports against the database? Right now I create little report objects in a DLL, developed and tested with NUnit, but then I continue to use NUnit as the GUI to select and run them. NUnit just happens to provide a nice GUI for this kind of thing, even after testing has been completed. I'm also interested in suggestions for reporting apps generally. I feel like there is a missing piece or product. The perfect tool would allow writing and running C# inside of Toad, or SQL inside of Visual Studio, along with simple reporting facilities. All ideas will be appreciated, but let's make the assumption that PL/SQL is not the solution.

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  • Aggregating a list of dates to start and end date

    - by Joe Mako
    I have a list of dates and IDs, and I would like to roll them up into periods of consucitutive dates, within each ID. For a table with the columns "testid" and "pulldate" in a table called "data": | A79 | 2010-06-02 | | A79 | 2010-06-03 | | A79 | 2010-06-04 | | B72 | 2010-04-22 | | B72 | 2010-06-03 | | B72 | 2010-06-04 | | C94 | 2010-04-09 | | C94 | 2010-04-10 | | C94 | 2010-04-11 | | C94 | 2010-04-12 | | C94 | 2010-04-13 | | C94 | 2010-04-14 | | C94 | 2010-06-02 | | C94 | 2010-06-03 | | C94 | 2010-06-04 | I want to generate a table with the columns "testid", "group", "start_date", "end_date": | A79 | 1 | 2010-06-02 | 2010-06-04 | | B72 | 2 | 2010-04-22 | 2010-04-22 | | B72 | 3 | 2010-06-03 | 2010-06-04 | | C94 | 4 | 2010-04-09 | 2010-04-14 | | C94 | 5 | 2010-06-02 | 2010-06-04 | This is the the code I came up with: SELECT t2.testid, t2.group, MIN(t2.pulldate) AS start_date, MAX(t2.pulldate) AS end_date FROM(SELECT t1.pulldate, t1.testid, SUM(t1.check) OVER (ORDER BY t1.testid,t1.pulldate) AS group FROM(SELECT data.pulldate, data.testid, CASE WHEN data.testid=LAG(data.testid,1) OVER (ORDER BY data.testid,data.pulldate) AND data.pulldate=date (LAG(data.pulldate,1) OVER (PARTITION BY data.testid ORDER BY data.pulldate)) + integer '1' THEN 0 ELSE 1 END AS check FROM data ORDER BY data.testid, data.pulldate) AS t1) AS t2 GROUP BY t2.testid,t2.group ORDER BY t2.group; I use the use the LAG windowing function to compare each row to the previous, putting a 1 if I need to increment to start a new group, I then do a running sum of that column, and then aggregate to the combinations of "group" and "testid". Is there a better way to accomplish my goal, or does this operation have a name? I am using PostgreSQL 8.4

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  • Cannot pass null to server using jQuery AJAX. Value received at the server is the string "null".

    - by Tom
    I am converting a javascript/php/ajax application to use jQuery to ensure compatibility with browsers other than Firefox. I am having trouble passing true, false, and null values using jQuery's ajax function. Javascript code: $.ajax ( { url : <server_url>, dataType: 'json', type : 'POST', success : receiveAjaxMessage, data: { valueTrue : true, valueFalse : false, valueNull : null } } ); PHP code: var_dump($_POST); Server output: array(3) { ["valueTrue"]=> string(4) "true" ["valueFalse"]=> string(5) "false" ["valueNull"]=> string(4) "null" } The problem is that the null, true, and false values are being converted to strings. The Javascript AJAX code currently in use passes null, true, and false correctly but only works in Firefox. Does anyone know how to solve this problem using jQuery? Here is some working code (not using jQuery) to compare with the code not-working code given above. Javascript Code: ajaxPort.send ( <server_url>, { valueTrue : true, valueFalse : false, valueNull : null } ); PHP code: var_dump(json_decode(file_get_contents('php://input'), true)); Server output: array(3) { ["valueTrue"]=> bool(true) ["valueFalse"]=> bool(false) ["valueNull"]=> NULL } Note that the null, true, and false values are correctly received. Note also that in the second method the $_POST array is not used in the PHP code. I think this is the key to the problem, but I cannot find a way to replicate this behavior using jQuery.

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  • Does the managed main UI thread stay on the same (unmanaged) Operation System thread?

    - by Daniel Rose
    I am creating a managed WPF UI front-end to a legacy Win32-application. The WPF front-end is the executable; as part of its startup routines I start the legacy app as a DLL in a second thread. Any UI-operation (including CreateWindowsEx, etc.) by the legacy app is invoked back on the main UI-thread. As part of the shutdown process of the app I want to clean up properly. Among other things, I want to call DestroyWindow on all unmanaged windows, so they can properly clean themselves up. Thus, during shutdown I use EnumWindows to try to find all my unmanaged windows. Then I call DestroyWindow one the list I generate. These run on the main UI-thread. After this background knowledge, on to my actual question: In the enumeration procedure of EnumWindows, I have to check if one of the returned top-level windows is one of my unmanaged windows. I do this by calling GetWindowThreadProcessId to get the process id and thread id of the window's creator. I can compare the process id with Process.GetCurrentProcess().Id to check if my app created it. For additional security, I also want to see if my main UI-thread created the window. However, the returned thread id is the OS's ThreadId (which is different than the managed thread id). As explained in this question, the CLR reserves the right to re-schedule the managed thread to different OS threads. Can I rely on the CLR to be "smart enough" to never do this for the main UI thread (due to thread-affinity of the UI)? Then I could call GetCurrentThreadId to get the main UI-thread's unmanaged thread id for comparison.

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  • Multithreaded linked list traversal

    - by Rob Bryce
    Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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  • File size monitoring in C#

    - by manemawanna
    Hello, I work in the Systems & admin team and have been given the task of creating a quota management application to try and encourage users to better manage there resources as we currently have issues with disc space and don't enforce hard quotas. At the moment I'm using the code below to go through all the files in a users homespace to retrieve the overall amount of space they are using. As from what I've seen else where theres no other way to do this in C#, the issue with it is theirs quite a high overhead while it retireves the size of each file then creates a total. try { long dirSize = 0; FileInfo[] FI = new DirectoryInfo("I:\\").GetFiles("*.*", SearchOption.AllDirectories); foreach (FileInfo F1 in FI) { dirSize += F1.Length; } return dirSize; } So I'm looking for a quicker way to do this or a quick way to monitor changes in the size of files while using the options avaliable through FileSystemWatcher. At the moment the only thing I can think of is creating a hashtable containing the file location and size of each file, so when a size changed event occurs I can compare the old size against the new one and update the total. Any suggestions would be greatly appreciated.

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  • Out-of-memory algorithms for addressing large arrays

    - by reve_etrange
    I am trying to deal with a very large dataset. I have k = ~4200 matrices (varying sizes) which must be compared combinatorially, skipping non-unique and self comparisons. Each of k(k-1)/2 comparisons produces a matrix, which must be indexed against its parents (i.e. can find out where it came from). The convenient way to do this is to (triangularly) fill a k-by-k cell array with the result of each comparison. These are ~100 X ~100 matrices, on average. Using single precision floats, it works out to 400 GB overall. I need to 1) generate the cell array or pieces of it without trying to place the whole thing in memory and 2) access its elements (and their elements) in like fashion. My attempts have been inefficient due to reliance on MATLAB's eval() as well as save and clear occurring in loops. for i=1:k [~,m] = size(data{i}); cur_var = ['H' int2str(i)]; %# if i == 1; save('FileName'); end; %# If using a single MAT file and need to create it. eval([cur_var ' = cell(1,k-i);']); for j=i+1:k [~,n] = size(data{j}); eval([cur_var '{i,j} = zeros(m,n,''single'');']); eval([cur_var '{i,j} = compare(data{i},data{j});']); end save(cur_var,cur_var); %# Add '-append' when using a single MAT file. clear(cur_var); end The other thing I have done is to perform the split when mod((i+j-1)/2,max(factor(k(k-1)/2))) == 0. This divides the result into the largest number of same-size pieces, which seems logical. The indexing is a little more complicated, but not too bad because a linear index could be used. Does anyone know/see a better way?

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  • Copy only files that are newer

    - by ErocM
    I am currently using this code: if (!Directory.Exists(command2)) Directory.CreateDirectory(command2); if (Directory.Exists(vmdaydir)) Directory.Delete(vmdaydir,true); if (!Directory.Exists(vmdaydir)) Directory.CreateDirectory(vmdaydir); var dir = Path.GetDirectoryName(args[0]); sb.AppendLine("Backing Up VM: " + DateTime.Now.ToString(CultureInfo.InvariantCulture)); Microsoft.VisualBasic.FileIO.FileSystem.CopyDirectory(dir, vmdaydir); sb.AppendLine("VM Backed Up: " + DateTime.Now.ToString(CultureInfo.InvariantCulture)); As you can see, I am deleting the directory, then I am copying the folder back. This is taking way to long since the directory is ~80gb in size. I realized that I do not need to copy all the files, only the ones that have changed. How would I copy the files from one folder to another but only copying the files that are newer? Anyone have any suggestions? ==== edit ==== I assume I can just do a file compare of each file and then copy it to the new directory, iterating through each folder/file? Is there a simpler way to do this?

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  • What changed in the DataGrid that means it won't work anymore?

    - by Jeff Yates
    I have a Silverlight app with a DataGrid containing some custom columns and all was working well. Then I updated to Silverlight 3 tools for VS 2008 SP1 and rebuilt it. Now it has the following problems: Rows aren't added when the collection is modified. The ItemsSource property is (and always has been) set to an ObservableCollection instance, which notifies when its contents change. This worked fine for Silverlight 2. However, in Silverlight 3 to get this working at all, I now have to null and then re-set ItemsSource - this seems like I'm hiding a bigger issue but I can't work out what that might be. I cannot select a row or a cell anymore. If I'm lucky, I can select one whole row before it stops working. I can't edit anything. I suspect this is related to the previous point. I'll post some source when I am able, but first I have to strip it down to the bare minimum. In the meantime, I was hoping someone might have some idea of what may be going on here. My gut feeling on the second two points is that my bindings are no longer working, but that's just a guess and if it is the case, I have no idea which ones. Thanks for any help anyone might be able to provide. Update So, I finally reduced my problem down to a simple works/doesn't work comparison. The problem seems to occur if I override Equals in my element type. As soon as I do that, something happens strangely in the ObservableCollection that contains that type, it seems, and my application breaks. To make it more interesting, there is a check to make sure that duplicate items don't even get close to being added to the collection. I don't exactly know why ObservableCollection needs to compare equality when inserting items (the stack trace indicates it is using IndexAt) but this seems to cause the issue. So, any thoughts?

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