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• Why are most really fast servers written in C instead of C++?

  - by orokusaki

  I'm trying to decide which to learn and I've read all the "Which is better" questions/arguments, so I thought I'd get your take on something more specific. Is there a platform dependency issue that C++ developers run into with such applications? Or, is it because there are more C developers out there than C++? I also noticed that many more third party C modules exist for Python even thought C++ modules are supported. From what I've read on different threads the consensus is that C++ is easier and faster to write, and runs just as fast. Am I missing something really big. Examples: NGINX APE (comet server) Apache

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• Using locks inside a loop

  - by Xaqron

  // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Android: Touch seriously slowing my application

  - by Jason Rogers

  Hi all, I've been raking my brains on this one for a while. when I'm running my application (opengl game) eveyrthing goes fine but when I touch the screen my application slows down quite seriously (not noticeable on powerful phones like the nexus one, but on the htc magic it gets quite annoying). I did a trace and found out that the touch events seem to be handled in a different thread and even if it doesn't take so much processing time I think androids ability to switch between threads is not so good... What is the best way to handle touch when speed is an issue ? Currently I'm using : in the GLSurfaceView @Override public boolean onTouchEvent(MotionEvent event) { GameHandler.onTouchEvent(event); return true; } Any ideas are welcome

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• Looking for suggestions about an architecture of a MultiThreaded app.

  - by Dimitri

  Hello everyone. I am looking to develop a multithreaded application that will be running in unconditional loop and processing high volume of data. High volume is 2000+ records per minute. Processing will involve data retrieval, calculations and data updates. I need the application to perform so that there is virtually no back log, meaning i need to be able to finish up all of the 2000 points in one minute or even faster. Our current implementation features a multithreaded application that is spawn multiple times (from 10 to 20) and we are noticing that it's not handling data as expected and i even feel that instances of the application compete with each other for processor time and eventually if not slowing, not benefiting each other for sure. I would like to know what would be the best approach: have a single instance running but maximize threads that can run simultaneously? or is there other ways i don't know? I'm open to suggestions. Thank you in advance

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• Can I safely bind to data on multi-threaded applications?

  - by Paul

  Hi everyone, I'm trying to solve a classic problem - I have a multi-threaded application which runs some processor-intensive calculations, with a GUI interface. Every time one of the threads has completed a task, I'd like to update a status on a table taskID | status I use DataGridView and BindingList in the following way: BindingList<Task> tasks; dataGridView.DataSource = tasks public class Task : INotifyPropertyChanged { ID{get;} Status{get;set;} } Can a background thread safely update a task's status? and changes will be seen in the correct order in the GUI? Second Question: When do I need to call to PropertyChanged? I tried running with and without the call, didn't seem to bother.. Third Question: I've seen on MSDN that dataGridView uses BindingSource as a mediator between DataGridView.DataSource and BindingList Is this really necessary?

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• C# Asynchronous Sockets questions.

  - by ccppjava

  Based on my reading and testing, with asynchronous sockets, the socket itself can be passed using state object (IAsyncResult result), also if store the socket as a private field, it would be captured by the callback methods. I am wondering how the IAysnResult is kepted between the BeginXXX and ReceiveXXX? It looks to me that after the BeginXXX call and the method ends, the state object would be disposed by GC if there is no reference to it. In the case of private field, how the private field is shared between threads? (As far as I know, a callback is executed using a thread from the default thread pool, which would be considered as a new thread.) Many thanks, hope the questions themselves are clear.

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• Visually [Diagrams/movies] Display events and states of System using old logs of Application to trac

  - by singh

  Hi In My Application many process runs. Having multiple threads in each process. Whenever any bug comes, I have to analyze thousands of lines of logs to know exact root-cause. I am thinking of an idea, Please guide me if it is feasible and good enough Each log have Process name , Thread id , and Time stamp along with message. If I can create a intelligence to capture what is happing with time and display in a movie which user can view it like a normal video. Forward – backward etc. It will help to reach root cause fast and bug tracing will become easy. Please guide me on library in c++ using which I can draw diagrams and display as movie

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• Why does my git push hang after successfully pushing?

  - by John

  On a newly set up ssh git repo, whenever I push, I get normal output like this: ? git push Counting objects: 15, done. Delta compression using up to 4 threads. Compressing objects: 100% (9/9), done. Writing objects: 100% (9/9), 989 bytes, done. Total 9 (delta 7), reused 0 (delta 0) It happens very quickly, and the changes are immediately available on the server repo. But the output hangs there for about a minute, and then finishes with: To [email protected]:baz.git c8c391c..1de5e80 branch_name -> branch_name If I control-c before it finishes, everything seems to continue to be normal and healthy, locally and remotely. What is it doing while hanging? Is something configured incorrectly on the server side?

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• How can I implement a download rate limited in Java?

  - by JohnWithoutArms

  Hello, I'm going to implement a (simple) downloader application in Java as a personal exercise. It is going to run several jobs in different threads, in a way that I will be downloading a few files at the same time at all times during execution. I want to be able to define a download rate limit that is shared between all the download jobs, but I don't know how to do it even for a single download task. How should I go about doing this? What are the solutions I should try implementing? Thanks.

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• c++ thread running time

  - by chnet

  I want to know whether I can calculate the running time for each thread. I implement a multithread program in C++ using pthread. As we know, each thread will compete the CPU. Can I use clock() function to calculate the actual number of CPU clocks each thread consumes? my program looks like: Class Thread () { Start(); Run(); Computing(); }; Start() is to start multiple threads. Then each thread will run Computing function to do something. My question is how I can calculate the running time of each thread for Computing function

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• Saving core data in a thread, how to ensure its done writing before quitting?

  - by Shizam

  So I'm saving small images to core data which take a really short amount of time to save, like .2 seconds but I'm doing it while the user is flipping through a scroll view so in order to improve responsiveness I'm moving the saving to a thread. This works great, everything gets saved and the app is responsive. However, there is one thing in the core-data + multithreading doco that worries me: "In Cocoa, only the main thread is not-detached. If you need to save on other threads, you must write additional code such that the main thread prevents the application from quitting until all the save operation is complete." Ok, how do you do that? It only needs to last ~ .2 seconds and its rarely going to happen since the chance of the app quitting as something is saving is very low. How do I run something on the main thread that'll prevent the app from quitting AND not block the gui? Thanks

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• Can't select database table even though the code is right

  - by Lisa

  I am trying to display a list of my vbulliten threads on a non-vbulliten portion of my site. However I can't select the vbulliten database: <?php $host = "localhost"; $user = "my username"; $pass = "my password"; $dbname = "tableprefix_forum"; mysql_connect($host, $user, $pass) or die ("Could not connect to database server."); mysql_select_db($dbname) or die ("Could not select database."); ?> I am substituting some things here in this example but all my credentials are correct including my db server username, password and forum db name. So what is the problem? Is it due to some internal security feature in vbulliten, does this system not allow you to connect to it's db if the page trying to connect to it is a non-vbulliten page?

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• What to use to wait on a indeterminate number of tasks?

  - by Scott Chamberlain

  I am still fairly new to parallel computing so I am not too sure which tool to use for the job. I have a System.Threading.Tasks.Task that needs to wait for n number number of tasks to finish before starting. The tricky part is some of its dependencies may start after this task starts (You are guaranteed to never hit 0 dependent tasks until they are all done). Here is kind of what is happening Parent thread creates somewhere between 1 and (NUMBER_OF_CPU_CORES - 1) tasks. Parent thread creates task to be run when all of the worker tasks are finished. Parent thread creates a monitoring thread Monitoring thread may kill a worker task or spawn a new task depending on load. I can figure out everything up to step 4. How do I get the task from step 2 to wait to run until any new worker threads created in step 4 finish?

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• Dowloading a bunch of files asynchronous wait till last finished

  - by Casper Broeren

  I'm trying to download a lot of files after downloading a sql statement must insert a record. I'm using System.Net.Client to download each file synchronously, still it could be done asynchronous. There's no relation or dependency between each download. At first I just tried to use WebClient.DownloadFileAsync but that shutted the program down and killed all the download processes/threads. Second I tried to create a wait routine something like this; while (processedFiles < totalFiles) Thread.Sleep(1000) This freezed everything. So could someone tell me which aproach to take to implement this Async?

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• What is wrong with my @synchronized block?

  - by hyn

  I have 2 threads in my application, a game update thread and render/IO/main thread. My update thread updates the game state, and the render thread renders the scene based on the updated values of the game state models and a few other variables stored inside an object (gameEngine). The render thread gets executed while the game thread is still updating, which is a problem, so it appeared to me the solution is to use @synchronized like this: @synchronized(gameEngine) { [gameEngine update]; nextUpdate = now + GAME_UPDATE_INTERVAL; gameEngine.lastGameUpdateInterval = now - lastUpdate; gameEngine.lastGameUpdateTime = now; lastUpdate = now; } But the render thread still accesses the gameEngine object between -update and the last 3 lines of the block. Why is this?

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• How do I prevent race condition WITHOUT using locks in C++?

  - by Hristo

  How do I prevent a race condition WITHOUT locking or using mutexes/semaphors in C++? I'm dealing with a nested for loop in which I will be setting a value in an array: for (int i = 0; i < m; ++i) for (int j = 0; j < n; ++j) for (int k = 0; k < o; ++k) array[k] += foo(...); More or less, I want to deal with this so that I can ensure different threads running at the same time don't write to array[k] at the same time. Any suggestions on how to approach this? Edit: I am running on a Linux machine and I also have to use the Intel compiler. I will be using "icc" instead of "gcc" to compile the code.

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• Representing a very large array of bits in little memory

  - by user614624

  Hello, I would like to represent a structure containing 250 M states(1 bit each) somehow into as less memory as possible (100 k maximum). The operations on it are set/get. I cold not say that it's dense or sparse, it may vary. The language I want to use is C. I looked at other threads here to find something suitable also. A probabilistic structure like Bloom filter for example would not fit because of the possible false answers. Any suggestions please?

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• ConcurentModificationException in Java HashMap

  - by Bear

  Suppose I have two methods in my classes, writeToMap() and processKey() and both methods are called by multiple threads. writeToMap is a method to write something in hashmap and processKey() is used to do sth based on the keySet of HashMap. Inside processKey, I first copy the originalMap before getting the key set. new HashMap<String, Map<String,String>(originalMap).get("xx").keySet(); But I am still getting ConcurrentModificationException even though I always copy the hashmap. Whats the problem?

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• C++ boost thread id and Singleton

  - by aaa

  hi. Sorry to flood so many questions this week. I assume thread index returned by thread.get_id is implementation specific. In case of the pthreads, is index reused? IE, if thread 0 runs and joins, is thread launched afterwords going to have a different ID? the reason I ask this is a need to implement Singleton pattern with a twist: each thread gets its own instance. I know it sounds very crazy, but threads control hardware (cuda) which does not permit device memory sharing. What is a good way to implement such pattern?

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• Avoid stuck calling callback

  - by andlomba

  Hello all, This is a question about generic c++ event driven applications design. Lets assume that we have two threads, a "Dispatcher" (or "Engine"...) and a "Listener" (or "Client"...). Let's assume that I write the Dispatcher code, and release it as a library. I also write the Listener interface, of course. When the Dispatcher executes (after Listener registration) listenerInstance.onSomeEvent(); the event handling code will actually be executed by the Dispatcher thread, so if the person that implements the Listener writes something like void Listener::onSomeEvent() { while(true) ; } The Dispatcher will stuck forever. Is there a "plain old c++" (I mean no boost or libsigc++) way to "decouple" the two classes, so I can be sure that my Dispatcher will work fine whatever the Listeners does in the callbacks? bye and thanks in advance, Andrea

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• Creating a form on non-gui thread

  - by luntain

  You can't access gui controls from a thread they were not created on, at least so says the message of an exception that is sometimes raised when you do it. Recently I was puzzled by seeing that forms created on background threads work just fine. My mental model was that all actions initiated by UI input is handled on the GUI thread. Clicking on a button on such a form should raise the dreaded exception (the form and all its controls were created on a background thread not the gui thread), but it doesn't. Something is wrong with my map. (*) well to be honest I have seen one problem where opening the standard open file dialog was blocking everything

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• Handling file upload in a non-blocking manner

  - by Kaliyug Antagonist

  The background thread is here Just to make objective clear - the user will upload a large file and must be redirected immediately to another page for proceeding different operations. But the file being large, will take time to be read from the controller's InputStream. So I unwillingly decided to fork a new Thread to handle this I/O. The code is as follows : The controller servlet /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse * response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub System.out.println("In Controller.doPost(...)"); TempModel tempModel = new TempModel(); tempModel.uploadSegYFile(request, response); System.out.println("Forwarding to Accepted.jsp"); /*try { Thread.sleep(1000 * 60); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); }*/ request.getRequestDispatcher("/jsp/Accepted.jsp").forward(request, response); } The model class package com.model; import java.io.IOException; import java.util.concurrent.ExecutionException; import java.util.concurrent.Future; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.utils.ProcessUtils; public class TempModel { public void uploadSegYFile(HttpServletRequest request, HttpServletResponse response) { // TODO Auto-generated method stub System.out.println("In TempModel.uploadSegYFile(...)"); /* * Trigger the upload/processing code in a thread, return immediately * and notify when the thread completes */ try { FileUploaderRunnable fileUploadRunnable = new FileUploaderRunnable( request.getInputStream()); /* * Future<FileUploaderRunnable> future = ProcessUtils.submitTask( * fileUploadRunnable, fileUploadRunnable); * * FileUploaderRunnable processed = future.get(); * * System.out.println("Is file uploaded : " + * processed.isFileUploaded()); */ Thread uploadThread = new Thread(fileUploadRunnable); uploadThread.start(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* * catch (InterruptedException e) { // TODO Auto-generated catch block * e.printStackTrace(); } catch (ExecutionException e) { // TODO * Auto-generated catch block e.printStackTrace(); } */ System.out.println("Returning from TempModel.uploadSegYFile(...)"); } } The Runnable package com.model; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.nio.ByteBuffer; import java.nio.channels.Channels; import java.nio.channels.ReadableByteChannel; public class FileUploaderRunnable implements Runnable { private boolean isFileUploaded = false; private InputStream inputStream = null; public FileUploaderRunnable(InputStream inputStream) { // TODO Auto-generated constructor stub this.inputStream = inputStream; } public void run() { // TODO Auto-generated method stub /* Read from InputStream. If success, set isFileUploaded = true */ System.out.println("Starting upload in a thread"); File outputFile = new File("D:/06c01_output.seg");/* * This will be changed * later */ FileOutputStream fos; ReadableByteChannel readable = Channels.newChannel(inputStream); ByteBuffer buffer = ByteBuffer.allocate(1000000); try { fos = new FileOutputStream(outputFile); while (readable.read(buffer) != -1) { fos.write(buffer.array()); buffer.clear(); } fos.flush(); fos.close(); readable.close(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("File upload thread completed"); } public boolean isFileUploaded() { return isFileUploaded; } } My queries/doubts : Spawning threads manually from the Servlet makes sense to me logically but scares me coding wise - the container isn't aware of these threads after all(I think so!) The current code is giving an Exception which is quite obvious - the stream is inaccessible as the doPost(...) method returns before the run() method completes : In Controller.doPost(...) In TempModel.uploadSegYFile(...) Returning from TempModel.uploadSegYFile(...) Forwarding to Accepted.jsp Starting upload in a thread Exception in thread "Thread-4" java.lang.NullPointerException at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:512) at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:497) at org.apache.coyote.http11.InternalInputBuffer$InputStreamInputBuffer.doRead(InternalInputBuffer.java:559) at org.apache.coyote.http11.AbstractInputBuffer.doRead(AbstractInputBuffer.java:324) at org.apache.coyote.Request.doRead(Request.java:422) at org.apache.catalina.connector.InputBuffer.realReadBytes(InputBuffer.java:287) at org.apache.tomcat.util.buf.ByteChunk.substract(ByteChunk.java:407) at org.apache.catalina.connector.InputBuffer.read(InputBuffer.java:310) at org.apache.catalina.connector.CoyoteInputStream.read(CoyoteInputStream.java:202) at java.nio.channels.Channels$ReadableByteChannelImpl.read(Unknown Source) at com.model.FileUploaderRunnable.run(FileUploaderRunnable.java:39) at java.lang.Thread.run(Unknown Source) Keeping in mind the point 1., does the use of Executor framework help me in anyway ? package com.utils; import java.util.concurrent.Future; import java.util.concurrent.ScheduledThreadPoolExecutor; public final class ProcessUtils { /* Ensure that no more than 2 uploads,processing req. are allowed */ private static final ScheduledThreadPoolExecutor threadPoolExec = new ScheduledThreadPoolExecutor( 2); public static <T> Future<T> submitTask(Runnable task, T result) { return threadPoolExec.submit(task, result); } } So how should I ensure that the user doesn't block and the stream remains accessible so that the (uploaded)file can be read from it?

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• Search in big text log files

  - by 0xFF

  Hi, let's say you have an game server which creating text log files of gamers actions, and from time to time you need to lookup something in those logs files (like investigating an scam or loosing an item). Just for example you have 100 files and each file have size between 20MB and 50MB - How you would search them quickly? What I have already tried to do is create several threads and each invidual thread will map his own file to memory (let say memory should not be problem if it not exceed 500MB of ram) perform search here, result was something around 1 second per file : File:a26.log - read in: 0.891, lines: 625282, matches: 78848 Is there better way how to do that ? - because it seems to me kinda slow. thanks. (java was used for this case)

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• Serialized task distribution: use thread or epoll?

  - by hpsmouse

  Now I'm in such a situation that there is a group of predefined tasks for multiple clients to do(any client can take any task). When a client connects to the server, server choose a task from the uncompleted tasks and send it to the client. It takes a while for the client to finish the task and send the result back to the server. Since a task should be sent to only one client, server should process requests in a serialized way. Now I have two plans to do it: create a thread for each client connection and all the threads take turns accessing the task pool, or use epoll listening on all the connection and process for each event of clients. Which one is better for the job? Or is there any other ideas? The server will be run on a multi-core machine.

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• How to move file pointer to a particular location using fseek()?

  - by Noge

  My intention is to read every elements in the 2nd column into a buffer[] from the following .txt file: 9992891234 09.920 15.771 11.909 9992345971 07.892 12.234 09.234 9992348971 64.567 70.456 50.987 9992348231 89.234 85.890 58.982 I have know of a way to do it by using fscanf(): for (int i=0;i<4;i++) { fscanf(pFile, "%lld", &junk); fscanf(pFile, "%f", &buffer[i]); fscanf(pFile, "%f", &junk); fscanf(pFile, "%f", &junk); } However, since I'm doing parallel programing which requires me to use different Windows Threads to read different columns, so I'll need to read the elements in the 2nd column directly using fseek(). The question here is, what should I put in the 2nd argument in fseek() in the code below to move my file pointer to read the 2nd element of the 2nd line? fscanf(pFile, "%llf", &junk);//<------this is used to skip the 1st data for (int i=0;i<4;i++) { fscanf(pFile, "%f", &buffer[i]); fseek ( pFile , ??, SEEK_CUR );//<----how do I calculate this offset? }

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