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• In linux, is it possible to do partial reads on a regular file

  - by Jimm

  I need to write an application that spits out log entries to a regular file at a very fast rate. Also, there will be another process, that can read the same file concurrently at the time, other process would be writing to it. I have following questions How does read() determine EOF, specially in the case, where the underlying file could be concurrently being modified? Is it possible for read() to return partially written data from the other process write? For example, the write process wrote half a line and read would pick that half line and return? The application would be written in C on linux 2.6.x using Ex4 filesystem UPDATE: Below link points to the patch, that locks inode in EXT4, before reading and writing. http://patchwork.ozlabs.org/patch/91834/

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• how-to initialize 'const std::vector<T>' like a c array

  - by vscharf

  Is there an elegant way to create and initialize a const std::vector<const T> like const T a[] = { ... } to a fixed (and small) number of values? I need to call a function frequently which expects a vector<T>, but these values will never change in my case. In principle I thought of something like namespace { const std::vector<const T> v(??); } since v won't be used outside of this compilation unit.

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• C# - can you name a matrix with the contents of a string

  - by RHodgett

  Basically I have x amount of matrices I need to establish of y by y size. I was hoping to name the matrices: matrixnumber1 matrixnumber2..matrixnumbern I cannot use an array as its matrices I have to form. Is it possible to use a string to name a string (or a matrix in this case)? Thank you in advance for any help on this! for (int i = 1; i <= numberofmatricesrequired; i++) { string number = Convert.ToString(i); Matrix (matrixnumber+number) = new Matrix(matrixsize, matrixsize); }

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• Multithreading - are the multi-core processors really doing parallel processing?

  - by so.very.tired

  Are the modern multi-core processors really doing parallel processing? Like, take for example, Intel's core i7 processors. some of them has #of Cores: 4 and #of Threads: 8 (taken from Intel's specifications pages). If I to write a program (say in Java or C) that has multiple threads of execution, will they really be processed concurrently? My instructor said that "it is not always the case with multi-core processors", but didn't gave to much details. And why do Intel have to specify both #of Cores and #of Threads? Isn't thread just a term that describe a program-related abstraction, unlike "cores" which are actual hardware? ("Every thread runs on different core").

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• Where to find viterbi algorithm transition values for natural language processing?

  - by Rodrigo Salazar

  I just watched a video where they used Viterbi algorithm to determine whether certain words in a sentence are intended to be nouns/verbs/adjs etc, they used transition and emission probabilities, for example the probability of the word 'Time' being used as a verb is known (emission) and the probability of a noun leading onto a verb (transition). http://www.youtube.com/watch?v=O_q82UMtjoM&feature=relmfu (The video) How can I find a good dataset of transition and emission probabilities for this use-case? Or EVEN just a single example with all the probabilities displayed, I want to use realistic numbers in a demonstration.

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• When should I define an hash code function for my types?

  - by devoured elysium

  Is there any other reason for implementing an hash code function for my types other than allowing for good use of hash tables? Let's say I am designing some types that I intend to use internally. I know that types are "internal" to the system, and I also know I will never use those types in hash tables. In spite of this, I decide I will have to redefine the equals() method. Theory says I should also redefine the hash code method, but I can't see any reason why, in this case, I should do it. Can anyone point me out any other reason? This question can be rephrased to : in which situations should we implement a hash code method in our types. PS : I am not asking how to implement one. I am asking when.

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• Removing rows from MySQL table where the timestamp is over one day old?

  - by Rob

  I found the exact same question here. But it isn't working for me. I've modified it a bit, manipulated it, and I can't figure it out. I'm trying to remove rows that are over a day old. Here is my code: if (isset($_POST['prune'])) { $sql = "DELETE FROM logs WHERE time < date('now', '-1 days')"; mysql_query($sql); echo 'Logs older than one day removed.'; } Fairly simple question I suppose, but its bugging the hell out of me. I would appreciate any help. In case it makes a difference, the column is a TIMESTAMP type.

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• Singleton design potential leak

  - by iBrad Apps

  I have downloaded a library off of github and have noticed that in the main singleton of the library there is a possible leak in this bit of code: +(DDGameKitHelper*) sharedGameKitHelper { @synchronized(self) { if (instanceOfGameKitHelper == nil) { [[DDGameKitHelper alloc] init]; } return instanceOfGameKitHelper; } return nil; } Now obviously there is no release or autorelease anywhere so I must do it but how and in what way properly? I have looked at various Singleton design patterns on the Internet and they just assign, in this case, instanceOfGameKitHelper to the alloc and init line. Anyway how would I properly fix this? Thanks!

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• Check for changes with jquery and a database

  - by Steve

  I am doing a notification system. When a new post is published, users will be notified immediately by an small notification on the screen. I am currently using this: setInterval(function(){ checkForChanges(); }, 2*1000); function checkForChanges(){ $.post("http://"+ document.domain + "/posts/checkForChanges/", function(dat){ if(dat>0){ .... /*create notification*/ } }); } And i was wondering if this is the correct way to do it or not. Because, this is calling a PHP function every 2 seconds and making a query to the database. In case there are no new changes, it won't do anything... Thanks.

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• Rails - set POST request limit (file upload)

  - by Fabiano PS

  I am building a file uploader for Rails, using CarrierWave. I am pretty happy about it's API, except that I don't seem to be able to cut file uploads that exceed a limit on the fly. I found this plugin for validation, but the problem is that it happens after the upload is completed. It is completely unacceptable in my case, as any user could take the site down by uploading a huge file. So, I figure that the way would be to use some Rack configuration or middleware that will limit POST body size as it receives. I am hosting on Heroku, as context. *I am aware of https://github.com/dwilkie/carrierwave_direct but it doesn't solve my issue as I have to resize first and discard the original large image.

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• mysql_close(): supplied argument is not a valid MySQL-Link resource

  - by maxedison

  I'm trying to get the hang of using custom session handlers to store session data in a MySQL database. However, I keep getting the following warning: mysql_close(): supplied argument is not a valid MySQL-Link resource Here's the code I'm using, which I got from here: function _open(){ global $_sess_db; $_sess_db = mysql_connect("localhost", "root", "******"); if ($_sess_db) { return mysql_select_db('style', $_sess_db); } return false; } function _close(){ global $_sess_db; return mysql_close($_sess_db); //error happens here } The full text of the error message ultimately points to the final "return mysql_close($_sess_db);" line. I can confirm that the mysql_connect info does in fact work, and I do have the rest of the session handler functions defined as well. And in case it helps, I get these errors immediately upon page load, without actually calling any of the session handler functions, and without having any current sessions open.

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• conditional beginReceive

  - by sbenderli

  I am writing a client program that uses Sockets. I would like the client to receive asyncronously UNLESS it is expecting a response, in which case I would like to receive syncronously. My current problem is that because I have to make a call to socket.BeginReceive which waits until there's data on the buffer, the async call always happens prior to the sync call.. How could I temporarily stop BeginReceive from executing? Is there a way to call EndReceive and then once I am done receiving syncronously, I can continue to receive asnycronously?

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• Insert a row and avoiding race condition (PHP/MySQL)

  - by justkevin

  I'm working on a multiplayer game which has a lobby-like area where players select "sectors" to enter. The lobby gateway is powered by PHP, while actual gameplay is handled by one or more Java servers. The datastore is MySQL. The happy path: A player chooses a sector and tells the lobby he'd like to enter. The lobby checks whether this is okay, including checking whether there are too many players in the sector (compares the entry count in sector assignments for that sector against the sector's max_players value). The player is added to the sector_assignments table pairing him with the sector. The player client receives a passkey that will let him connect to the appropriate game server. The race condition: If two players request access to the same sector at close to same time, I can envision a case where they are both added because there was one space free when their check was started and max players gets exceeded. Is the best solution LOCK TABLE on sector_assignments? Is there another option?

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• Android on Desktop tutorials/resources

  - by Ascension Systems

  I'm aware of the android-x86 project and as far as the end result (bootable live/install iso), I am looking to do the same thing. The difference is, I'm looking to do this with the ice cream sandwich branch from android master repo. Ice cream sandwich adds full support for x86 hardware and even sports a build target specifically for running the OS in virtualbox. So my question is, is anyone aware of any documentation for building and deploying to that target? Just in case it's not clear, I'm not just using the android-x86 project because they haven't yet put up a build for anything later than android 3.

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• C#: Converting string to namespace

  - by Am

  Hi, I have an interface named IHarvester. There are 3 implementations of that interface, each under their own namespace: Google Yahoo Bing A HarvesterManager uses the given harvester. It knows the interface and all 3 implementations. I want some way of letting the class user say in which harvester it wants to use. And in the code select that implementation, without a switch-case implementation. Can reflection save my day? Here is the code bits: // repeat for each harvester namespace Harvester.Google { public abstract class Fetcher : BaseHarvester, IInfoHarvester {...} } public enum HarvestingSource { Google, Yahoo, Bing, } class HarvesterManager { public HarvestingSource PreferedSource {get;set;} public HarvestSomthing() { switch (PreferedSource) .... // awful... } } Thanks.

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• WndProc to detect device unplug and plug

  - by Kev Fixx

  How can I know a devices is plug or unplug in WPF? I am using the code below to detect device changes: private void OnSourceInitialized(object sender, EventArgs e) { IntPtr windowHandle = (new WindowInteropHelper(this)).Handle; HwndSource src = HwndSource.FromHwnd(windowHandle); src.AddHook(new HwndSourceHook(WndProc)); } private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) { // Handle WM_DEVICECHANGE... if (msg == 0x219) { InitHead(); } return IntPtr.Zero; } Thank you. EDITED: I did the below, still not working: if (msg == 0x0219) { switch (wParam.ToInt32()) { case 0x8000: { InitHead(); } break; } }

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• How can I convert my Stream (image data) back into a file

  - by James Hay

  I have a WCF restful service that I'm trying to upload an image to. I have a very basic metod that accepts a stream as it's only parameter and is defined in the contract as: [OperationContract] [WebInvoke(UriTemplate = "ReviewImage", BodyStyle = WebMessageBodyStyle.Bare, Method = "POST")] ReviewImage UploadImage(Stream data); I'm actually consuming this service from flash (which is fairly inconsequntial) which selects a file from the file system and uploads it through the service url. It all works seems to work, adding a breakpoint to the UploadImage method breaks as expected. If I wanted to save this file back to disk, is it just a case of reading this Stream object into a FileStream object that creates the file somewhere? A bit like the this? When i do actually do this the file can not be opened as an image. I'm sure i'm missing a key piece of knowledge here. Does my stream actually contain just the image bytes or does it contain more than that?

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• How do I run compiled java classes with GPU libraries (Jogamp JOCL)?

  - by jam383

  Does anyone know how to run the java code from the command line with dependency on GPU libraries in this case Jogamps JOCL. I have compiled a test program HelloJOCL.java but I get an error during run time. I tried javac -classpath "./lib/jocl.jar:./lib/jocl-natives-macosx-universal.jar:./lib/jocl-natives-linux-i586.jar:./lib/jocl-natives-linux-amd64.jar:./lib/gluegen-rt.jar:./lib/gluegen-rt-natives-linux-amd64.jar:./lib/gluegen-rt-natives-macosx-universal.jar:./lib/gluegen-rt-natives-linux-i586.jar" ./HelloJOCL.java java -classpath "./lib/jocl.jar:./lib/jocl-natives-macosx-universal.jar:./lib/jocl-natives-linux-i586.jar:./lib/jocl-natives-linux-amd64.jar:./lib/gluegen-rt.jar:./lib/gluegen-rt-natives-linux-amd64.jar:./lib/gluegen-rt-natives-macosx-universal.jar:./lib/gluegen-rt-natives-linux-i586.jar:." HelloJOCL but get this error Exception in thread "main" java.lang.NoClassDefFoundError: com/jogamp/opencl/CLContext at java.lang.Class.getDeclaredMethods0(Native Method)

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• Selecting distinct values from mysql with largest timestamp

  - by user987048

  I am building a mail system. The inbox is only supposed to grab the last message (one with the highest time value) of a concatenation of user and sender, where the user or sender is the user ID. Here is the table structure: CREATE TABLE IF NOT EXISTS `mail` ( `user` int(11) NOT NULL, `sender` int(11) NOT NULL, `body` text NOT NULL, `new` enum('0','1') NOT NULL default '1', `time` int(11) NOT NULL, KEY `user` (`user`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; So, with a table with the following data: user sender new time ***************************************** 1 0 0 5 1 0 0 6 2 1 0 7 1 0 1 8 1 2 0 9 1 0 1 11 1 2 1 12 I want to select the following: WHERE USER OR SENDER = X (in this case, 1) user sender new time ***************************************** 2 1 0 7 1 2 0 9 1 0 1 11 How would I go about doing something like this?

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• Hi, i have a c programming doubt? I want to know the difference between the two and where one is use

  - by aks

  Hi, i have a c programming doubt? I want to know the difference between the two and where one is useful over other? suppose i have a struct called employee as below: struct emp{ char first_name[10]; char last_name[10]; char key[10]; }; Now, i want to store the table of employee records, then which method should i use: struct emp e1[100]; // Or struct emp * e1[100]; I know the two are not same but would like to know a use case where second declaration would be of interest and more advantageous to use? Can someone clarify?

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• how do indices in mysql tables (MyISAM) work?

  - by understack

  Few basic doubts I have: 1. Is primary key column automatically indexed? 2. What should be criteria to select index column? 3. When should I club multiple columns? 4. Does MyISAM or InnoDB has any affect on this? 5. Are they really required, specially in case if primary key column is automatically indexed? Thanks.

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• How should I set up UITableViewCell subclasses with UIControls in them?

  - by GeneralMike

  I have a dynamically generated UITableView (so I have to use prototype cells, not static cells) with many cells on it. Each cell will have a UILabel on it. Additionally, each cell will also have at least one UIControl (as of right now, it could be a UITextfield or a UISegmentedControl, but I want to keep it flexible in case I add something else in the future). I'm going to need to be able to send the text in that label, and get either the text in the textfield, or the title of the selected segment index, etc. For the cells with multiple controls, I'm going to have to also let it know what control I'm interested in for that call. What would be the best way to set this up?

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• .NET (C#): Getting child windows when you only have a process handle or PID?

  - by shea241

  Kind of a special case problem: I start a process with System.Diagnostics.Process.Start(..) The process opens a splash screen -- this splash screen becomes the main window. The splash screen closes and the 'real' UI is shown. The main window (splash screen) is now invalid. I still have the Process object, and I can query its handle, module, etc. But the main window handle is now invalid. I need to get the process's UI (or UI handle) at this point. Assume I cannot change the behavior of the process to make this any easier (or saner). I have looked around online but I'll admit I didn't look for more than an hour. Seemed like it should be somewhat trivial :-( Thanks

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• Ruby - overriding/enabling multiple assignment (e.g. `a, b, c = d, e, f`)

  - by nicholaides

  In ruby, you can do this: d = [1, 2, 3] a, b, c = d a, b, and c, will receive the values 1, 2, and 3, respectively. d, in this case in an Array and ruby knows to assign it's contents to a, b, and c. But, if d were a Fixnum, for example, only a would be assigned to the value of d while b and c would be assigned nil. What properties of d allow it to be used for multiple assignment? In my exploring so far, I've only been able to make instances of subclasses of Array behave in this way.

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• RESTful enums. string or Id?

  - by GazTheDestroyer

  I have a RESTful service that exposes enums. Should I expose them as localised strings, or plain integers? My leaning is toward integers for easy conversion at the service end, but in that case the client needs to grab a list of localised strings from somewhere in order to know what the enums mean. Am I just creating extra steps for nothing? There seems to be little information I can find about which is commonly done in RESTful APIs. EDIT: OK. Let's say I'm writing a website that stores information about people's pets. I could have an AnimalType enum 0 Dog 1 Cat 2 Rabbit etc. When people grab a particular pet resource, say /pets/1, I can either provide a meaningful localised string for the animal type, or just provide the ID and force them to do another look up via a /pets/types resource. Or should I provide both?

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