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• Qt vs .NET - a few comparisons [closed]

  - by Pirate for Profit

  Event Handling In Qt the event handling system you just emit signals when something cool happens and then catch them in slots, for instance emit valueChanged(int percent, bool something); and void MyCatcherObj::valueChanged(int p, bool ok){} blocking them and disconnecting them when needed, doing it across threads... once you get the hang of it, it just seems a lot more natural and intuitive than the way the .NET event handling is set up (you know, object sender, CustomEventArgs e). And I'm not just talking about syntax, because in the end the .NET delegate crap is the bomb. I'm also talking about in more than just reflection (because, yes, .NET obviously has much stronger reflection capabilities). I'm talking about in the way the system feels to a human being. Qt wins hands down i m o. Basically, the footprints make more sense and you can visualize the project easier without the clunky event handling system. I wish I could it explain it better. The only thing is, I do love some of the ease of C# compared to C++ and .NET's assembly architecture. That is a big bonus for modular projects, which are a PITA to do in C++. Database Ease of Doing Crap Also what about datasets and database manipulations. I think .net wins here but I'm not sure. Threading/Conccurency How do you guys think of the threading? In .NET, all I've ever done is make like a list of master worker threads with locks. I like QConcurrentFramework, you don't worry about locks or anything, and with the ease of the signal slot system across threads it's nice to get notified about the progress of things. Memory Usage Also what do you think of the overall memory usage comparison. Is the .NET garbage collector pretty on the ball and quick compared to the instantaneous nature of native memory management? Or does it just let programs leak up a storm and lag the computer then clean it up when it's about to really lag? However, I am a n00b who doesn't know what I'm talking about, please school me on the subject.

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• log4j performance

  - by Bob

  Hi, I'm developing a web app, and I'd like to log some information to help me improve and observe the app. (I'm using Tomcat6) First I thought I would use StringBuilders, append the logs to them and a task would persist them into the database like every 2 minutes. Because I was worried about the out-of-the-box logging system's performance. Then I made some test. Especially with log4j. Here is my code: Main.java public static void main(String[] args) { Thread[] threads = new Thread[LoggerThread.threadsNumber]; for(int i = 0; i < LoggerThread.threadsNumber; ++i){ threads[i] = new Thread(new LoggerThread("name - " + i)); } LoggerThread.startTimestamp = System.currentTimeMillis(); for(int i = 0; i < LoggerThread.threadsNumber; ++i){ threads[i].start(); } LoggerThread.java public class LoggerThread implements Runnable{ public static int threadsNumber = 10; public static long startTimestamp; private static int counter = 0; private String name; public LoggerThread(String name) { this.name = name; } private Logger log = Logger.getLogger(this.getClass()); @Override public void run() { for(int i=0; i<10000; ++i){ log.info(name + ": " + i); if(i == 9999){ int c = increaseCounter(); if(c == threadsNumber){ System.out.println("Elapsed time: " + (System.currentTimeMillis() - startTimestamp)); } } } } private synchronized int increaseCounter(){ return ++counter; } } } log4j.properties log4j.logger.main.LoggerThread=debug, f log4j.appender.f=org.apache.log4j.RollingFileAppender log4j.appender.f.layout=org.apache.log4j.PatternLayout log4j.appender.f.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n log4j.appender.f.File=c:/logs/logging.log log4j.appender.f.MaxFileSize=15000KB log4j.appender.f.MaxBackupIndex=50 I think this is a very common configuration for log4j. First I used log4j 1.2.14 then I realized there was a newer version, so I switched to 1.2.16 Here are the figures (all in millisec) LoggerThread.threadsNumber = 10 1.2.14: 4235, 4267, 4328, 4282 1.2.16: 2780, 2781, 2797, 2781 LoggerThread.threadsNumber = 100 1.2.14: 41312, 41014, 42251 1.2.16: 25606, 25729, 25922 I think this is very fast. Don't forget that: in every cycle the run method not just log into the file, it has to concatenate strings (name + ": " + i), and check an if test (i == 9999). When threadsNumber is 10, there are 100.000 loggings and if tests and concatenations. When it is 100, there are 1.000.000 loggings and if tests and concatenations. (I've read somewhere JVM uses StringBuilder's append for concatenation, not simple concatenation). Did I missed something? Am I doing something wrong? Did I forget any factor that could decrease the performance? If these figures are correct I think, I don't have to worry about log4j's performance even if I heavily log, do I?

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• Do we affect multiple users in ASP.NET when we set the Thread CurrentCulture/CurentUICulture?

  - by Nikolay

  When we set the CurrentCulture and/or CurrentUICulture we do this on the current thread like this: Thread.CurrentThread.CurrentCulture = new CultureInfo("en-GB"); Thread.CurrentThread.CurrentUICulture = new CultureInfo("en-GB"); Doest this mean we could affect the culture settings of multiple users of our web application as their requests may reuse the threads from pool? I am working on an ASP.NET MVC application where each user may have own culture setting specified in his/her account data. When the user logs in, the culture setting is retrieved from the database and has to be set as current culture. My worry is that setting the current culture on the current thread may affect another user request reusing this thread. I am even more concerned reading this: ASP.NET not only uses a thread pool, but may switch threads during request processing.

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• C# How to kill parent thread

  - by Royson

  A parent has several child threads. If user click on stop button the parent thread should be killed with all child threads. //calls a main thread mainThread = new Thread(new ThreadStart(startWorking)); mainThread.Start(); //////////////////////////////////////////////// startWorking() { ManualResetEventInstance = new ManualResetEvent(false); ThreadPool.SetMaxThreads(m_ThreadPoolLimit, m_ThreadPoolLimit); for(int i = 0; i < list.count ; i++) { ThreadData obj_ThreadData = new ThreadData(); obj_ThreadData.name = list[i]; m_ThreadCount++; //execute WaitCallback obj_waitCallBack = new WaitCallback(startParsing); ThreadPool.QueueUserWorkItem(obj_waitCallBack, obj_ThreadData); } ManualResetEventInstance.WaitOne(); } I want to kill mainThread.

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• Google groups not finding discussion thread but regular google search does?

  - by Mathias Lin

  I'm having a problem with google groups and finding my own discussion threads. I go to the google group (in my case Android developer group) web view and try to search for my thread by entering the extact title of my thread. But it doesn't appear in the search results. On the other hand, when I search for the same title in the regular google web search, I get the thread right on top of the result list. I thought it might take a while until the groups index all new threads, but still after a few days, it still wouldn't show up. Sample: My thread is here: http://groups.google.com/group/android-developers/browse_thread/thread/0ab41d5056a25ce7 Doing a search for it in Google groups (will give one result, but not mine): http://groups.google.com/group/android-developers/search?group=android-developers&q=Strange+behaviour+with+mediaplayer+and+seekTo&qt_g=Search+this+group Search in Google web search (shows my thread as first result): http://www.google.de/search?sourceid=chrome&ie=UTF-8&q=Strange+behaviour+with+mediaplayer+and+seekTo

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• Unhandled exceptions in BackgroundWorker

  - by edg

  My WinForms app uses a number of BackgroundWorker objects to retrieve information from a database. I'm using BackgroundWorker because it allows the UI to remain unblocked during long-running database queries and it simplifies the threading model for me. I'm getting occasional DatabaseExceptions in some of these background threads, and I have witnessed at least one of these exceptions in a worker thread while debugging. I'm fairly confident these exceptions are timeouts which I suppose its reasonable to expect from time to time. My question is about what happens when an unhandled exception occurs in one of these background worker threads. I don't think I can catch an exception in another thread, but can I expect my WorkerCompleted method to be executed? Is there any property or method of the BackgroundWorker I can interrogate for exceptions?

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• Issue with maxWorkerThreads and thread count

  - by Kartik M

  I have created an ASP.NET application which creates threads in an infinite loop. I set maxWorkerThreads to 20 in processModel in machine.config. When I checked the Thread count in perfmon there was around 7000 threads created in worker process. In PageLoad() I have: using System.Threading; ... int count = 0; var threadList = new System.Collections.Generic.List<System.Threading.Thread>(); try { while (true) { Thread newThread = new Thread(ThreadStart(DummyCall), 1024); newThread.Start(); threadList.Add(newThread); count++; } } catch (Exception ex) { Response.Write(count + " : " + ex.ToString()); } Function: void DummyCall() { System.Threading.Thread.Sleep(1000000000); } How do I restrict thread creation in ASP.NET with IIS6/7?

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• Webapp: safetly update a shared List/Map in the AppContext

  - by al nik

  I've Lists and Maps in my WebAppContext. Most of the time these are only read by multiple Threads but sometimes there's the need to update or add some data. I'm wondering what's the best way to do this without incurring in a ConcurrentModificationException. I think that using CopyOnWriteArrayList I can achieve what I want in terms of - I do not have to sync on every read operation- I can safety update the list while other threads are reading it. Is this the best solution? What about Maps?

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• Is this a correct Interlocked synchronization design?

  - by Dan Bryant

  I have a system that takes Samples. I have multiple client threads in the application that are interested in these Samples, but the actual process of taking a Sample can only occur in one context. It's fast enough that it's okay for it to block the calling process until Sampling is done, but slow enough that I don't want multiple threads piling up requests. I came up with this design (stripped down to minimal details): public class Sample { private static Sample _lastSample; private static int _isSampling; public static Sample TakeSample(AutomationManager automation) { //Only start sampling if not already sampling in some other context if (Interlocked.CompareExchange(ref _isSampling, 0, 1) == 0) { try { Sample sample = new Sample(); sample.PerformSampling(automation); _lastSample = sample; } finally { //We're done sampling _isSampling = 0; } } return _lastSample; } private void PerformSampling(AutomationManager automation) { //Lots of stuff going on that shouldn't be run in more than one context at the same time } } Is this safe for use in the scenario I described?

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• What is design principle behind Servlets being Singleton

  - by Sandeep Jindal

  A servlet container "generally" create one instance of a servlet and different threads of the same instance to serve multiple requests. (I know this can be changed using deprecated SingleThreadModel and other features, but this is the usual way). I thought, the simple reason behind this is performance gain, as creating threads is better than creating instances. But it seems this is not the reason. On the other hand, creating instances have little advantage that developers never have to worry about thread safety. I am trying to understand the reason for this decision over the trade-off of thread-safety.

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• Java synchronized method lock on object, or method?

  - by wuntee

  If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as specific as the variables inside the synchronized method? Example: class x{ private int a; private int b; public synchronized void addA(){ a++; } public synchronized void addB(){ b++; } } Can 2 threads access the same instance of class x performing x.addA() and x.addB() at the same time?

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• Coroutines in Java

  - by JUST MY correct OPINION

  I would like to do some stuff in Java that would be clearer if written using concurrent routines, but for which full-on threads are serious overkill. The answer, of course, is the use of coroutines, but there doesn't appear to be any coroutine support in the standard Java libraries and a quick Google on it brings up tantalising hints here or there, but nothing substantial. Here's what I've found so far: JSIM has a coroutine class, but it looks pretty heavyweight and conflates, seemingly, with threads at points. The point of this is to reduce the complexity of full-on threading, not to add to it. Further I'm not sure that the class can be extracted from the library and used independently. Xalan has a coroutine set class that does coroutine-like stuff, but again it's dubious if this can be meaningfully extracted from the overall library. It also looks like it's implemented as a tightly-controlled form of thread pool, not as actual coroutines. There's a Google Code project which looks like what I'm after, but if anything it looks more heavyweight than using threads would be. I'm basically nervous of something that requires software to dynamically change the JVM bytecode at runtime to do its work. This looks like overkill and like something that will cause more problems than coroutines would solve. Further it looks like it doesn't implement the whole coroutine concept. By my glance-over it gives a yield feature that just returns to the invoker. Proper coroutines allow yields to transfer control to any known coroutine directly. Basically this library, heavyweight and scary as it is, only gives you support for iterators, not fully-general coroutines. The promisingly-named Coroutine for Java fails because it's a platform-specific (obviously using JNI) solution. And that's about all I've found. I know about the native JVM support for coroutines in the Da Vinci Machine and I also know about the JNI continuations trick for doing this. These are not really good solutions for me, however, as I would not necessarily have control over which VM or platform my code would run on. (Indeed any bytecode manipulation system would suffer similar problems -- it would be best were this pure Java if possible. Runtime bytecode manipulation would restrict me from using this on Android, for example.) So does anybody have any pointers? Is this even possible? If not, will it be possible in Java 7?

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• How to use SMS content provider? Where are the docs?

  - by Mark

  Hi, I'd like to be able to read the system's SMS content provider. Basically I wanted to make an SMS messaging app, but it would only be useful if I could see past threads etc. It seems like there's a content provider for this, but I can't find documentation for it - anyone know where that is? Thanks -------- edit ----------- Ok I found a way to get the sms inbox provider, and I just dumped all the column names in that provider, looks like this: Uri uriSms = Uri.parse("content://sms/inbox"); Cursor c = context.getContentResolver().query(uriSms, null,null,null,null); // column names for above provider: 0: _id 1: thread_id 2: address 3: person 4: date 5: protocol 6: read 7: status 8: type 9: reply_path_present 10: subject 11: body 12: service_center 13: locked I'm just piecing this together from random threads I find around the net, I'm really wondering where this is all documented (if at all)? Thanks again

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• Is there a technical way to speed up a general program above current PC speed limit?

  - by Maksee

  Let's imagine I developed a Windows console application implementing some algorithm calculating something. Let's say it doesn't use any threads, just straightforward linear approach with ifs, loops and so on. Is there any technical way to make if run it 100x times faster than on the most advanced current PC? For example one of the way would be to run it on a super computer that emulates i386 faster than any of the existing PCs. But in this case the question what computer and does it really have ability to emulate Windows. In other words, is there real examples of such approach? Although in general it looks useless, but if there is a way, one could develop some program on his general home computer and pay for running it much faster on some other hardware. I suppose that this question could be asked on superuser.com, but since there are possible specific with such things as assembler instructions or threads, I thought that stackoverflow.com is better

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• What is a good method to use with multithreading to simulate this?

  - by user1504257

  I am writing a program in c++ in visual studio to be able to handle a line at a park. I have all of my customers in a line at the park and I want to be able to service them using multithreading with openmp. When I put the pragma and such in, I have multiple threads servicing the same customer at the same time for each and every customer I create, not what I want. I want for example, if I had two threads and four customers, that thread one to do customer one while thread 2 does customer 2. Then I would like thread 1 to do customer 3 and thread 2 customer 4 at the same time. I don't know if its possible or if there is a better way, but I need to use openmp. Thanks for your input.

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• C++ threaded class design from non-threaded class

  - by macs

  I'm working on a library doing audio encoding/decoding. The encoder shall be able to use multiple cores (i.e. multiple threads, using boost library), if available. What i have right now is a class that performs all encoding-relevant operations. The next step i want to take is to make that class threaded. So i'm wondering how to do this. I thought about writing a thread-class, creating n threads for n cores and then calling the encoder with the appropriate arguments. But maybe this is an overkill and there is no need for another class, so i'm going to make use of the "user interface" for thread-creation. I hope there are any suggestions.

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• Multithreading using C on PIC18

  - by M3

  How does one create threads that run in parallel while programming PIC18, since there is no OS?

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• CUDA small kernel 2d convolution - how to do it

  - by paulAl

  I've been experimenting with CUDA kernels for days to perform a fast 2D convolution between a 500x500 image (but I could also vary the dimensions) and a very small 2D kernel (a laplacian 2d kernel, so it's a 3x3 kernel.. too small to take a huge advantage with all the cuda threads). I created a CPU classic implementation (two for loops, as easy as you would think) and then I started creating CUDA kernels. After a few disappointing attempts to perform a faster convolution I ended up with this code: http://www.evl.uic.edu/sjames/cs525/final.html (see the Shared Memory section), it basically lets a 16x16 threads block load all the convolution data he needs in the shared memory and then performs the convolution. Nothing, the CPU is still a lot faster. I didn't try the FFT approach because the CUDA SDK states that it is efficient with large kernel sizes. Whether or not you read everything I wrote, my question is: how can I perform a fast 2D convolution between a relatively large image and a very small kernel (3x3) with CUDA?

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• Is ReaderWriterLockSlim.EnterUpgradeableReadLock() essentially the same as Monitor.Enter()?

  - by Neil Barnwell

  So I have a situation where I may have many, many reads and only the occasional write to a resource shared between multiple threads. A long time ago I read about ReaderWriterLock, and have read about ReaderWriterGate which attempts to mitigate the issue where many writes coming in trump reads and hurt performance. However, now I've become aware of ReaderWriterLockSlim... From the docs, I believe that there can only be one thread in "upgradeable mode" at any one time. In a situation where the only access I'm using is EnterUpgradeableReadLock() (which is appropriate for my scenario) then is there much difference to just sticking with lock(){}? Here's the excerpt: A thread that tries to enter upgradeable mode blocks if there is already a thread in upgradeable mode, if there are threads waiting to enter write mode, or if there is a single thread in write mode. Or, does the recursion policy make any difference to this?

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• NSAutoreleasePool carrying across methods?

  - by Tim

  I'm building an iPhone application where I detach some threads to do long-running work in the background so as not to hang the UI. I understand that threads need NSAutoreleasePool instances for memory management. What I'm not sure about is if the threaded method calls another method - does that method also need an NSAutoreleasePool? Example code: - (void)primaryMethod { [self performSelectorInBackground:@selector(threadedMethod) withObject:nil]; } - (void)threadedMethod { NSAutoreleasePool *aPool = [[NSAutoreleasePool alloc] init]; // Some code here [self anotherMethod]; // Maybe more code here [aPool drain]; } - (void)anotherMethod { // More code here } The reason I ask is I'm receiving errors that objects are being autoreleased with no pool in place, and are "just leaking." I've seen other questions where people didn't have autorelease pools in place at all, and I understand why an autorelease pool is needed. I'm specifically interested in finding out whether an autorelease pool created in (in this example) threadedMethod applies to objects created in anotherMethod.

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• Configurability for windows application built in C#

  - by Sam

  Hi, I am working on a windows application which is developed in C#. I am kinda new in windows world. I want to restrict number of parallel threads running for this application at a given point of time. This number can be changed by user on a beefier machine. What is the best way to do this configuration and how it can be achieved. I can think of following approaches. 1. Use ConfigurationManager to read the configuration value. If user exists more than N number of threads show a message and give option there to modify the value of N. 2. Use registery entry? Thanks in Advance! Sam

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• Forum board example schema in YAML format - modify for Nested set?

  - by takeshin

  I have created a forum board app, based on YAML schema found in 'real world examples' of Doctrine Manual, which looks similar to this: --- Forum_Category: columns: root_category_id: integer(10) parent_category_id: integer(10) name: string(50) description: string(99999) relations: Subcategory: class: Forum_Category local: parent_category_id foreign: id Rootcategory: class: Forum_Category local: root_category_id foreign: id Forum_Board: columns: category_id: integer(10) name: string(100) description: string(5000) relations: Category: class: Forum_Category local: category_id foreign: id Threads: class: Forum_Thread local: id foreign: board_id Forum_Entry: columns: author: string(50) topic: string(100) message: string(99999) parent_entry_id: integer(10) thread_id: integer(10) date: integer(10) relations: Parent: class: Forum_Entry local: parent_entry_id foreign: id Thread: class: Forum_Thread local: thread_id foreign: id Forum_Thread: columns: board_id: integer(10) updated: integer(10) closed: integer(1) relations: Board: class: Forum_Board local: board_id foreign: id Entries: class: Forum_Entry local: id foreign: thread_id How to modify this schema, to use NestedSet (Tree structure of threads and entries)?

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• Can you have too many Delegate.BeginInvoke calls at once?

  - by stewsha

  I am cleaning up some old code converting it to work asynchronously. psDelegate.GetStops decStops = psLoadRetrieve.GetLoadStopsByLoadID; var arStops = decStops.BeginInvoke(loadID, null, null); WaitHandle.WaitAll(new WaitHandle[] { arStops.AsyncWaitHandle }); var stops = decStops.EndInvoke(arStops); Above is a single example of what I am doing for asynchronous work. My plan is to have close to 20 different delegates running. All will call BeginInvoke and wait until they are all complete before calling EndInvoke. My question is will having so many delegates running cause problems? I understand that BeginInvoke uses the ThreadPool to do work and that has a limit of 25 threads. 20 is under that limit but it is very likely that other parts of the system could be using any number of threads from the ThreadPool as well. Thanks!

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• Unresponsive UI when using BeginInvoke

  - by Kazoom

  Bckground I have a networked application written in C#. my server program has a UI and several communication threads, that read from tcp sockets and display messages on controller UI. Communication with each client is done through a seprate thread. When i recieve some stream of messages from one client , the thread for that client writes on UI, which is a richtextbox on a Form. I call SetTextHelper(string text) method of the form. which looks like this private delegate void MyTextUpdateHandler(string text); public void SetTextHelper(string text) { BeginInvoke(new MyTextUpdateHandler(SetText), new object[] { text }); } public setText(string text) { richtext.Text= text; } Question - If i use BeginInvoke my UI is entirely unresponsive when i m writing large stream of data to UI - Invoke solves that problem, but i read that for multi threaded environment where many thereads are sharing same resource Invoke can lead to deadlocks I share the common ichtextbox between around 16 threads - What would be a good desing for my situation?

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• Can getAttribute() method of Tomcat ServletContext implementation be called without synchronization?

  - by oo_olo_oo

  I would like to read some parameters during servlet initializtion (in init() method), and store them among servlet context attributes (using getServletContext().setAttribute()). I would like to read these parameters later - during some request processing (using getServletContext().getAttribute()). So, the multiple threads could do this simultaneously. My question is if such an attempt is safe? Could I be sure that multi threaded calls to the getAttribute() don't mess up any internal state of the servlet context? Please take into account that I'm not going to call the setAttribute() anywhere besides the initialization. So, only calls to the getAttribute() are going to be done from multiple threads. But depending on the internal implementation, this also could be dangerous. So, any information about Tomcat's implementation would be appreciated.

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