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• What's a good algorithm for searching arrays N and M, in order to find elements in N that also exist

  - by GenTiradentes

  I have two arrays, N and M. they are both arbitrarily sized, though N is usually smaller than M. I want to find out what elements in N also exist in M, in the fastest way possible. To give you an example of one possible instance of the program, N is an array 12 units in size, and M is an array 1,000 units in size. I want to find which elements in N also exist in M. (There may not be any matches.) The more parallel the solution, the better. I used to use a hash map for this, but it's not quite as efficient as I'd like it to be. Typing this out, I just thought of running a binary search of M on sizeof(N) independent threads. (Using CUDA) I'll see how this works, though other suggestions are welcome.

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• how to find out how much application memory django process is (or will be) taking?

  - by photographer

  There are different "Application memory" options (like 80MB...200MB) in django-friendly hosting called webfaction and I'm confused deciding which one I should buy. Could someone please walk me through the ideas on how to figure out how much memory my project might require (excluding operating system, the main apache server and the database servers memory requirements)? I understand in theory I'll need to perform some kind of load testing, but thought there might be ways to calculate that in advance with some simple/relatively easy understandable approach. I don't know how hard they enforce application memory usage limit, and another question is: what will happen if more users came to the site and more threads started than what I expected? Will the application crash? Or will delays just become uncomfortable? And - no, application is not ready yet (I can't measure anything right now). Development environment if it matters is Winodows 7, 64-bit. Hosting itself is some kind of Linux I think. (Sorry if it's not a stackoverflow question.)

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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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• 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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• 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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• Fast way to pass a simple java object from one thread to another

  - by Adal

  I have a callback which receives an object. I make a copy of this object, and I must pass it on to another thread for further processing. It's very important for the callback to return as fast as possible. Ideally, the callback will write the copy to some sort of lock-free container. I only have the callback called from a single thread and one processing thread. I only need to pass a bunch of doubles to the other thread, and I know the maximum number of doubles (around 40). Any ideas? I'm not very familiar with Java, so I don't know the usual ways to pass stuff between threads.

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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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• Git svn - no changes, no branches (except master), rebase/info is not working

  - by ex3v

  I know that similar questions were asked before, but I think my is a little bit different, so please don't point me to existing threads. I'm migrating our old svn repo to git. I did git svn clone path --authors-file abc.txt and everything seemend legit to me. Then I did git remote add origin xyz and git push --all origin and it also worked. I created this repo as test one, with only me having access to both local repo and origin. No changes were made in project held on this repo, nothing to commit, no pushing and so on. There is also only one branch, because someone initialized svn years ago without creating proper folder structure (branches, trunk, tags). Meanwhile someone pushed their work to svn, so I tried to git svn fetch (which worked), and git svn rebase which didn't, giving me error: Unable to determine upstream SVN information from working tree history Is there any reason why git svn decided to stop working?

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• Millisecond-Accurate Scheduling of Future Events in C++/CLI

  - by A Grad Student at a University

  I need to create a C++/CLI mixed assembly that can schedule future calls into a native DLL with millisecond accuracy. This will, of course, mean setting a timer (what kind?) for a millisecond or three beforehand, then spinning until the moment and calling the native DLL function. Based on what I've read, I would guess that the callback that the timer calls will need to be native to make sure there are no thunks or GC to delay handling the timer callback. Will the entire thread or process need to be native and CLR-free, though, or can this be done just as accurately with #pragma unmanaged or setting one file of the assembly to compile as native? If so, how? If there is indeed no way to do this in mixed-mode C++/CLI, what would be the easiest way to set up an app/thread (ie, DLL or exe?) to handle it and to get the data back and forth between the native and managed threads/apps?

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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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• 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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• 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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• 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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• 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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• 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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• memcpy() safety on adjacent memory regions

  - by JaredC

  I recently asked a question on using volatile and was directed to read some very informative articles from Intel and others discussing memory barriers and their uses. After reading these articles I have become quite paranoid though. I have a 64-bit machine. Is it safe to memcpy into adjacent, non-overlapping regions of memory from multiple threads? For example, say I have a buffer: char buff[10]; Is it always safe for one thread to memcpy into the first 5 bytes while a second thread copies into the last 5 bytes? My gut reaction (and some simple tests) indicate that this is completely safe, but I have been unable to find documentation anywhere that can completely convince me.

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• Take advantage of multiple cores executing SQL statements

  - by willvv

  I have a small application that reads XML files and inserts the information on a SQL DB. There are ~ 300 000 files to import, each one with ~ 1000 records. I started the application on 20% of the files and it has been running for 18 hours now, I hope I can improve this time for the rest of the files. I'm not using a multi-thread approach, but since the computer I'm running the process on has 4 cores I was thinking on doing it to get some improvement on the performance (although I guess the main problem is the I/O and not only the processing). I was thinking on using the BeginExecutingNonQuery() method on the SqlCommand object I create for each insertion, but I don't know if I should limit the max amount of simultaneous threads (nor I know how to do it). What's your advice to get the best CPU utilization? Thanks

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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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• x86 linux - how to create custom malloc with address hint

  - by nandu

  Hi, I want to create a custom malloc which allocates memory blocks within a given address range. I am writing a pthreads application in which threads are bound to unique cores on a many-core machine. The memory controllers are statically mapped, so that certain range of addresses on main memory are electrically closer to a core. I want to minimize the latency of communication between cores and main memory by allocating thread memory on these "closer" regions. Any ideas would be most appreciated. Thank you! Nandu

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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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• 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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• 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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• 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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• 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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• Updating a module level shared dictionary

  - by Vishal

  Hi, A module level dictionary 'd' and is accessed by different threads/requests in a django web application. I need to update 'd' every minute with a new data and the process takes about 5 seconds. What could be best solution where I want the users to get either the old value or the new value of d and nothing in between. I can think of a solution where a temp dictionary is constructed with a new data and assigned to 'd' but not sure how this works! Appreciate your ideas. Thanks

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