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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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• 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 can one use multi threading in php applications

  - by Steve Obbayi

  Is there a realistic way of implementing a multi-threaded model in php whether truly or just simulating it. Some time back it was suggested that you can force the operating system to load another instance of the php executable and handle other simultaneous processes. The problem with this is that when the php code finished executing the php instance remains in memory because there is no way to kill it from within php. so if you are simulating several threads you can imagine whats going to happen. So am still looking for a way multi-threading can be done or simulated effectively from within php. Any ideas?

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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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• 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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• Postgresql Output column from another table

  - by muffin

  i'm using Postgresql, my question is specifically about querying from a table that's in another table and i'm really having trouble with this one. In fact, i'm absolutely mentally blocked. I'll try to define the relations of the tables as much as I can. I have a table entry which is like this: Each of the entries has a group_id; when they are 'advanced' to the next stage, the old entries are marked is_active = false, and a new assignment is done, so C & D are advanced stages of A & B. I have another table (which acts as a record keeper) , in which the storage_log_id refers to, this is the storage_log table : But then I have another table, to really find out where the entries are actually stored - storage table : To define my problem properly. Each entry has a storage_log_id (but some doesn't have yet), and a storage_log has a storage_id to refer to the actual table and find the storage label. The sql query i'm trying to do should output this one: Where The actual storage label is shown instead of the log id. This is so far what i've done: select e.id, e.group_id, e.name, e.stage, s.label from operational.entry e, operational.storage_log sl, operational.storage s where e.storage_log_id = sl.id and sl.storage_id = s.id But this just returns 3 rows, showing only the ones that have the seed_storage_log_id set; I should be able to see even those without logs, and especially the active ones. adding e.is_active = true to the condition makes the results empty. So, yeah i'm stuck. Need help, Thanks guys!

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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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• 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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• 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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• 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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• 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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• why can't I set a new instance's delegate as self?

  - by Guille10k

  I have a uipickerview, which appears with an ActionSheet. All this is in a class "MultiPicker". I create a new instance from "FirstViewController" this way: multiPicker *multiPic = [[multiPicker alloc]init]; multiPic.delegate = self; [multiPic action:aRunIndex]; And inside "multiPicker", in "action:" UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:title delegate:otroDelegate cancelButtonTitle:nil destructiveButtonTitle:@"Cancel" otherButtonTitles:@"Done", nil]; UIPickerView *pickerView = [[[UIPickerView alloc] init] autorelease]; pickerView.tag = 101; pickerView.delegate = self; pickerView.dataSource = self; pickerView.showsSelectionIndicator = YES; [actionSheet addSubview:pickerView]; [actionSheet showInView:self.view]; I need "FirstViewController" when MultiPicker finishes, so I can update a table in FirstView. I tried setting a new delegate to MultiPicker so, it tells FirstView when it finishes. But the instruction "multipic.delegate = self" in the first piece of code mades the app crash and says "Terminating due to uncaught exception". If I simply put all "MultiPicker" code inside FirstViewController class, not in a separate one, the action sheet stay blocked when I try to push a button different from "Cancel" Any idea? Thank u

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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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• 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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• 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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• 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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• 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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• C++: is it safe to read an integer variable that's being concurrently modified without locking?

  - by Hongli

  Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect reads too? I've heard that there are some hardware architectures on which, if one thread modifies a variable, and another thread reads it, then the read result will be garbage; in this case I do need to protect reads. I've never seen such architectures though. This question assumes that a single transaction only consists of updating a single integer variable so I'm not worried about the states of any other variables that might also be involved in a transaction.

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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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• How to find root cause for "too many connections" error in MySQL/PHP

  - by Nir

  I'm running a web service which runs algorithms that serve millions of calls daily and run some background processing as well. Every now and than I see "Too many connections" error in attempts to connect to the MySQL box" for a few seconds. However this is not necessarily attributed to high traffic times or anything I can put my finger on. I want to find the bottleneck causing it. Other than in the specific times this happens the server isn't too loaded in terms of CPU and Memory, and has 2-3 connections (threads) open and everything works smoothly. (I use Zabbix for monitoring) Any creative ideas on how to trace it?

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• Django AND .htaccess rewrites/redirects, is this possible?

  - by Infinity

  Is it possible to have Apache htaccess rewrites take effect before it hits django? For example so I can redirect iPhone users to a completely different domain without even hitting django. We're using apache2 with mod_wsgi and the apache vhost looks like this: <VirtualHost *:80> DocumentRoot /usr/local/www/site/static Alias /css/ /usr/local/www/site/static/css/ Alias /js/ /usr/local/www/site/static/js/ Alias /img/ /usr/local/www/site/static/img/ Alias /flash/ /usr/local/www/site/static/flash/ <Directory /usr/local/www/site/static> AllowOverride All Order allow,deny Allow from all </Directory> WSGIDaemonProcess mallorca-site threads=15 WSGIScriptAlias / /usr/local/www/site/config/dev/dev.wsgi </VirtualHost> Thanks

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• How is executed a SendMessage from a different thread?

  - by Lorenzo

  When we send a message, "if the specified window was created by the calling thread, the window procedure is called immediately as a subroutine". But "if the specified window was created by a different thread, the system switches to that thread and calls the appropriate window procedure. Messages sent between threads are processed only when the receiving thread executes message retrieval code." (taken from MSDN documentation for SendMessage). Now, I don't understand how (or, more appropriately, when) the target windows procedure is called. Of course the target thread will not be preempted (the program counter is not changed). I presume that the call will happen during some wait function (like GetMessage or PeekMessage), it is true? That process is documented in detail somewhere?

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• matplotlib plot window won't appear

  - by user1518837

  I'm using Python 2.7.3 in 64-bit. I installed pandas as well as matplotlib 1.1.1, both for 64-bit. Right now, none of my plots are showing. After attempting to plot from several different dataframes, I gave up in frustration and tried the following first example from http://pandas.pydata.org/pandas-docs/dev/visualization.html: INPUT: import matplotlib.pyplot as plt ts = Series(randn(1000), index=date_range ('1/1/2000', periods=1000)) ts = ts.cumsum() ts.plot() pylab.show() OUTPUT: Axes(0.125,0.1;0.775x0.8) And no plot window appeared. Other StackOverflow threads I've read suggested I might be missing DLLs. Any suggestions?

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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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• How can I close my software in a save way?

  - by Roman

  Up to now I used my application as a stand alone product. So, when user pressed "Stop" button I called System.exit(0); and it was fine. Now my application will be called (in a programmatic way) from another program. So, I afraid that System.exit(0); will kill not only my process but also the external software which started my program. So, what is the correct way to shutdown my application if a corresponding request from an external software is received? My application is an GUI application. So, I want to close the window but I also want to close all processes performed by my program. ADDED: To be more specific, I want to close all threads started by my program. My program does not start any OS process or any other program.

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