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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• Is it a good idea to apply some basic macros to simplify code in a large project?

  - by DoctorT

  I've been working on a foundational c++ library for some time now, and there are a variety of ideas I've had that could really simplify the code writing and managing process. One of these is the concept of introducing some macros to help simplify statements that appear very often, but are a bit more complicated than should be necessary. For example, I've come up with this basic macro to simplify the most common type of for loop: #define loop(v,n) for(unsigned long v=0; v<n; ++v) This would enable you to replace those clunky for loops you see so much of: for (int i = 0, i < max_things; i++) With something much easier to write, and even slightly more efficient: loop (i, max_things) Is it a good idea to use conventions like this? Are there any problems you might run into with different types of compilers? Would it just be too confusing for someone unfamiliar with the macro(s)?

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• Is scala functional programming slower than traditional coding?

  - by Fred Haslam

  In one of my first attempts to create functional code, I ran into a performance issue. I started with a common task - multiply the elements of two arrays and sum up the results: var first:Array[Float] ... var second:Array[Float] ... var sum=0f; for(ix<-0 until first.length) sum += first(ix) * second(ix); Here is how I reformed the work: sum = first.zip(second).map{ case (a,b) => a*b }.reduceLeft(_+_) When I benchmarked the two approaches, the second method takes 40 times as long to complete! Why does the second method take so much longer? How can I reform the work to be both speed efficient and use functional programming style?

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• How can an SQL query return data from multiple tables

  - by Fluffeh

  I would like to know how to get data from multiple tables in my database, what types of methods are there to do this, what are joins and unions and how are they different from one another? When should I use each one compared to the others? I am planning to use this in my (for example - PHP) application, but don't want to run multiple queries against the database, what options do I have to get data from multiple tables in a single query? Note: I am writing this as I would like to be able to link to a well written guide on the numerous questions that I constantly come across in the PHP queue, so I can link to this for further detail when I post an answer. The answers cover off the following: Part 1 - Joins and Unions Part 2 - Subqueries Part 3 - Tricks and Efficient Code

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• JavaScript BubbleSort

  - by Alyn

  Hi, Have a bubblesort routine similar the this. I need to make it more efficient by stopping the loop when the array is sorted or if the array is already sorted. function sortNumbers(listbox) { var x, y, holder; // The Bubble Sort method. for(x = 0; x < ranarray.length; x++) { for(y = 0; y < (ranarray.length-1); y++) { if(ranarray[y] > ranarray[y+1]) { holder = ranarray[y+1]; ranarray[y+1] = ranarray[y]; ranarray[y] = holder; } } }

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• Design best practice - best way to handle user selection

  - by user1457227

  I'm an experienced developer (WPF) moving over to Android development. My question: an app I am developing allows the user to browse their local storage (such as SDCARD) and select a file. Now, should I simply create a new Activity (after the user has made a selection) to handle what I want to have the app do with that chosen file, -or- is the better approach to pass the path/name of the selected file back to the main Activity and let IT launch the next Activity? In other words, is the better practice to have the main Activity launch other (support) activities, or is it perfectly ok and normal to have one activity chain to another and on and on? Thanks!

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• C# GroupJoin efficiency

  - by bsnote

  without using GroupJoin: var playersDictionary = players.ToDictionary(player => player.Id, element => new PlayerDto { Rounds = new List<RoundDto>() }); foreach (var round in rounds) { PlayerDto playerDto; playersDictionary.TryGetValue(round.PlayerId, out playerDto); if (playerDto != null) { playerDto.Rounds.Add(new RoundDto { }); } } var playerDtoItems = playersDictionary.Values; using GroupJoin: var playerDtoItems = from player in players join round in rounds on player.Id equals round.PlayerId into playerRounds select new PlayerDto { Rounds = playerRounds.Select(playerRound => new RoundDto {}) }; Which of these two pieces is more efficient?

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• url and nameserver question

  - by aristotaly

  i have hosting accout in go daddy its a delux plan so i can assign more than one url right now i got two of them they both registerd throgh go daddy in the same account. right now i would like to give some storage space to a freind that have a url ( also go ddady) in a different account . and i do not know how to do it . i think he needs to set up his name servers as my name servers so he did and than i should add his url in the domain maneger i did that also and even installed joomla on this particular folder that i assinged to his url nothing happenend . am i missing somthing ? plz help if you can :)

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• Pre-loading external files (CSS, JavaScript) for other pages

  - by Jason Young

  I'm curious if there is an efficient way to wait for the front page of a site to load, and then pre-load CSS and script files that I know will likely be needed for the other pages on the site. I want the front page of the site to be as fast as possible (lean and mean). It's likely that the user will not immediately click on a link. Since there will likely be some idle time, this seems like an opportune time to pre-load some of the external assets. Pre-loading should cause them to become cached. When the user does click on another page, the only request needed will be for the content and possibly some images, etc. Has anyone done this? Is it a bad idea? Is there an elegant way to implement it?

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• Override onDraw to change how the drawing occurs (Android)

  - by Casebash

  I want to change how my UI elements display, so I am overriding onDraw. The following code allows me to change a View to be drawn using PorterDuff.Mode.DARKEN. Unfortunately, this method involves creating a bitmap the size of the entire screen, then drawing to it then drawing this large bitmap the main screen again, for each UI element. This isn't at all efficient. Is it possible to achieve this in a more effecient way? @Override protected void onDraw(Canvas canvas) { //TODO: Reduce the burden from multiple drawing Bitmap bitmap=Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Config.ARGB_8888); Log.e("tmp",canvas.getClipBounds().toString()); Canvas offscreen=new Canvas(bitmap); super.onDraw(offscreen); //Then draw onscreen Paint p=new Paint(); p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN)); canvas.drawBitmap(bitmap, 0, 0, p); }

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• ColdFusion Timeout Error

  - by Jason

  I have a scheduled task that runs once a day that builds an XML file that I pass off to another group. Recently the amount of data has greatly increased and is now causing the task to time out (I think). I have tried to optimize my script as much as possible but with no luck. It times out long before an hour and I don't get any kind of ColdFusion error. Instead I get a "This page cannot be found" after it runs. Could this be a timeout someplace other than Coldfusion? Is there a more efficient way to build this XML file? select PersonID, FirstName, LastName from People select d.DepartmentID, DepartmentName, pd.PersonID from Department d inner join PersonDepartment pd on d.DepartmentID = pd.DepartmentID select PaperID, PaperTitle, PaperDescription, pp.PersonID from Paper p inner join PersonPaper pp on p.PaperID = pp.PaperID select DepartmentID, DepartmentName from getDepartments where PersonID = #getPeople.PersonID# select PaperID, PaperDescription from getpapers where PersonID = #getPeople.PersonID# #getPeople.PersonID# #getPeople.Firstname# #getPeople.LastName# #getPersonDepartments.DepartmentID# #getPersonDepartments.DepartmentName# #getPersonPapers.PaperID# #getPersonPapers.PaperDescription# Done!

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• How to Implement chat application for Android?

  - by user396530

  I am working on a chat application for android. This chat application is for sending messages from one device to another using internet(GPRS,3G,etc) from this application. please tell me a way to implement this. I thought using web services is more data(internet) consuming and less efficient.is this right? I worked on server and client sockets. I ran both server and client classes in single device and messages can be transfered from client socket to server socket and vice versa.Now i want to message between two devices using server socket on web server and how to connect to server from Android Devices. please help me thank you very much.

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• Simple, Custom Parsing with c++

  - by bradkovach

  Hi! I have been reading SO for some time now, but I truly cannot find any help for my problem. I have a c++ assignment to create an IAS simulator. Here is some sample code... 0 1 a 1 2 b 2 c 3 1 10 begin 11 . load a, subtract b and offset by -1 for jump+ 11 load M(0) 12 sub M(1) 13 sub M(3) 14 halt Using c++, I need to be able to read these lines and store them in a "memory register" class that I already have constructed... For example, the first line would need to store "1 a" in register zero. How can I parse out the number at the line beginning and then store the rest as a string? I have setup storage using a class that is called using mem.set(int, string);. int is the memory location at the beginning of the line and string is the stored instruction.

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• How can I efficiently retrieve a large number of database settings as PHP variables?

  - by Steven

  Currently all of my script's settings are located in a PHP file which I 'include'. I'm in the process of moving these settings (about 100) to a database table called 'settings'. However I'm struggling to find an efficient way of retrieving all of them into the file. The settings table has 3 columns: ID (autoincrements) name value Two example rows might be: 1 admin_user john 2 admin_email_address [email protected] The only way I can think of retrieving each setting is like this: $result = mysql_query("SELECT value FROM settings WHERE name = 'admin_user'"); $row = mysql_fetch_array($result); $admin_user = $row['value']; $result = mysql_query("SELECT value FROM settings WHERE name = 'admin_email_address'"); $row = mysql_fetch_array($result); $admin_email_address = $row['value']; etc etc Doing it this way will take up a lot of code and will likely be slow. Is there a better way? Thanks.

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• Is select() Ok to implemnet single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Hibernate Query - Get latest versions by timestamp?

  - by Slim

  I have a database that is being used as a sort of version control system. That is, instead of ever updating any rows, I add a new row with the same information. Each row also contains a version column that is a date timestamp, so the only difference is the new row will have a more recent timestamp. What I'm having trouble with is writing an efficient hibernate query to return the latest version of these rows. For the sake of example, these are rows in a table called Product, the timestamped column is version. There are multiple versions of multiple products in the table. So there may be multiple versions (rows) of ProductA, multiple versions of ProductB, etc. And I would like to grab the latest version of each. Can I do this in just a single hibernate query? session.createQuery("select product from Product product where...?"); Or would this require some intermediate steps?

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• Convert unusual string into date time

  - by BlueChippy

  I have a system that outputs dates in the format "1{yy}{MM}{dd}" and I am trying to find a good way to parse it back into a real date. At the moment I am using this: var value = "1110825"; var z = Enumerable.Range(1,3).Select(i => int.Parse(value.Substring(i, 2))).ToList(); var d = new DateTime(2000 + z[0], z[1], z[2]); but I'm sure there's a cleaner/more efficient way to do it? I've tried DT.ParseExact, but can't find a suitable format string to use.

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• Twin edges - Half edge data structure

  - by Pradeep Kumar

  I have implemented a Half-edge data structure for loading 3d objects. I find that the part of assigning twin/pair edges takes the longest computation time (especially for objects which have hundreds of thousands half edges). The reason is that I use nested loops to accomplish this. Is there a simpler and efficient way of doing this? Below is the code which I've written. HE is the half-edge data structure. hearr is a vector containing all the half edges. vert is the starting vertex and end is the ending vertex. Thanks!! HE *e1,*e2; for(size_t i=0;i<hearr.size();i++){ e1=hearr[i]; for(size_t j=1;j<hearr.size();j++){ e2=hearr[j]; if((e1->vert==e2->end)&&(e2->vert==e1->end)){ e1->twin=e2; e2->twin=e1; } } }

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• Android card based game, need help to start

  - by user331296

  Hello, I'm just setting out in android development. I want to make a kind of card based game. I'm just looking for suggestions really on how I might start it. I know I have to make the menu layout and view, then use an Intent from that to get to the main game view. My sticking points are: -There's going to be a deck of cards. It's going to be a set number so I was thinking I could just have each card defined as a button in the layout. I don't know if that is the right way to do it though. -Storage of card details. I'm thinking of using an xml file to store these. Thanks in advance.

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• Query with multiple IN-statements but without the cartesian product

  - by Janne

  How could I make this kind of query e.g. in MySQL SELECT * FROM Table t WHERE t.a IN (1,2,3) AND t.b IN (4,5,6) AND t.c IN (7,8,9) ... so that the result would contain only the three rows: t.a|t.b|t.c ---+---+--- 1 | 4 | 7 2 | 5 | 8 3 | 6 | 9 The above query of course returns all the combinations of the values in the IN clauses but I would like to get just the ones where the first elements of each tuple match, second elements of each tuple match and so on. Is there any efficient way to do this? By the way is there some common term for this kind of query or concept? I'm having hard time coming up with the question's title because I can't put this into words..

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• Algorithm to Group All the Cycles Together

  - by Ngu Soon Hui

  I have a lot of cycles ( indicated by numeric values, for example, 1-2-3-4 corresponds to a cycle, with 4 edges, edge 1 is {1:2}, edge 2 is {2:3}, edge 3 is {3,4}, edge 4 is {4,1}, and so on). A cycle is said to be connected to another cycle if they share one and only one edge. For example, let's say I have two cycles 1-2-3-4 and 5-6-7-8, then there are two cycle groups because these two cycles are not connecting to each other. If I have two cycles 1-2-3-4 and 3-4-5-6, then I have only one cycle group because these two cycles share the same edge. What is the most efficient way to find all the cycle groups?

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• More intelligent Context Menus in Visual Studio 2008 Database Projects

  - by Mike C.

  I'm using a SQL Server 2008 Database Project, and I'm finding it's very cumbersome to add certain items. For example, if I right click on Tables = Keys and navigate to the Add item, I'd expect to see the different kinds of keys that I can add. Instead, I see the stock items that don't apply, and I'm forced to navigate the Add New Item screen to find Primary Key. Is there a way to make this more efficient? I have Resharper; can I leverage templates somehow (kind of a noob with these). Thanks!

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• Ruby on Rails: Best way to save search queries in a database

  - by Adam Templeton

  For a RoR app I'm helping develop, I need to save all search queries in a database so I can analyze them later. My plan right now is to create a Result model and table, and just save each search query's text in that table, along with a user's ID, the time, etc. However, the app has about 15,000 users, so I'm afraid the single table approach won't be super efficient when it comes time to parse that data. (The database is setup via MySQL, if that factors in at all.) Am I just being paranoid? Is there a Ruby gem that handles this sort of thing, or a better approach I could take? Any input would be appreciated.

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• Is `auto int i` valid C++0x?

  - by Motti

  In answering this question the question arose as to whether the traditional C meaning of the keyword auto (automatic storage) is still valid in C++0x now that it means type deduction. I remember that the old meaning of auto should remain where relevant but others disagreed. auto char c = 42; // either compilation error or c = '*' Looking at compilers I see the current division. Old meaning of auto is no longer allowed VS10 g++ Old meaning of auto is used where relevant Comeau Do you know which is the correct behaviour?

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• Generate custom marker (icon) out of two images in Leaflet

  - by Rmatt

  In Javascript/CoffeeScript, using Leaflet to display a map, I would like to have custom markers out of a two custom images, and also featuring a shadow for the pin : I want to have a "background" image with a color (or shape) to identify the category On top, I want to have inside this image a specific image (logo) for each pin I didn't find out how I could do that... Setting one image is quite easy but I don't know how to overlay them. I could also consider using a tool to superpose/group/overlay these images (locally ?) before in order to send only one to the Icon Leaflet Class, but also there, I wouldn't know which tool to use. Nevertheless, I still think that a double overlay would be more efficient and that my case could be useful for several people.

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