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• Help with porting thread functionality: Win32 --> .Net

  - by JimDaniel

  Hi, I am responsible for porting a class from legacy Win32 code to .Net and I have come across a threading model that I'm not sure how best to implement in .Net. Basically the Win32 has one worker thread, which calls WaitForMultipleObjects() and executes the particular piece of code when a particular object has been triggered. This has a sort of first-come-first-serve effect that I need to emulate in my own code. But I'm not sure how best to do this in .Net. Does anyone have any idea? I see that there is no equivalent of WaitForMultipleObjects() in .Net, only the ThreadPool class, which seems to provide most of what I need, but I'm not sure if it's the best, since I only have four objects total to wait and execute code for. Thanks, Daniel

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• "too many threads error" in blackberry OS-4.5

  - by SWATI

  hi in my application i have 20 icons(bitmap fields) on the home screen When i click on any icon an HTTP request is made in a separate thread. I have used invoke later method wherever necessary to take care of multi-threading problems. But still the number of threads goes beyond 16 and an error pops up indicating too many threads error and applications needs to be restarted!! can anybody tell me how to destroy these threads when they are no longer in use. I don't understand why they don't destroy on their own as usually they do.

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• Design Stock Server Application in C++

  - by Avinash

  [Queston asked in ML Interview] Design an server/application which handle multiple incoming stock information ( stock symbol and values ) Server need to store the information in some cache ( need to design the data structure ), There are multiple client connected to server using tcp/ip socket. They will subscribe to particular request say stock symbol XYZ , and may be for more then one. As and when there is change the stock symbol server should broadcast the information to subscribed client. If tcp/ip write failed, server should handle the unregistration of the client. What various data structures will be used and how threading model will be ?

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• SQL Querying for Threaded Messages

  - by Harper

  My site has a messaging feature where one user may message another. The messages support threading - a parent message may have any number of children but only one level deep. The messages table looks like this: Messages - Id (PK, Auto-increment int) - UserId (FK, Users.Id) - FromUserId (FK, Users.Id) - ParentMessageId (FK to Messages.Id) - MessageText (varchar 200) I'd like to show messages on a page with each 'parent' message followed by a collapsed view of the children messages. Can I use the GROUP BY clause or similar construct to retrieve parent messages and children messages all in one query? Right now I am retrieving parent messages only, then looping through them and performing another query for each to get all related children messages. I'd like to get messages like this: Parent1 Child1 Child2 Child3 Parent2 Child1 Parent3 Child1 Child2

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• How to know who kills my threads

  - by mcabral

  I got a thread that is just banishing.. i'd like to know who is killing my thread and why. It occurs to me my thread is being killed by the OS, but i'd like to confirm this and if possible to know why it's killing it. As for the thread, i can assert it has at least 40 min of execution before dying, but it suddenly dies around 5 min. public void RunWorker() { Thread worker = new Thread(delegate() { DoSomethingForALongLongTime(); }); worker.IsBackground = true; worker.SetApartmentState(System.Threading.ApartmentState.STA); worker.Start(); }

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• How to pass around event as parameter in c#

  - by Jerry Liu

  Am writing unit test for a multi-threading application, where I need to wait until a specific event triggered so that I know the asyn operation is done. E.g. When I call repository.add(something), I wait for event AfterChange before doing any assertion. So I write a util function to do that. public static void SyncAction(EventHandler event_, Action action_) { var signal = new object(); EventHandler callback = null; callback = new EventHandler((s, e) => { lock (signal) { Monitor.Pulse(signal); } event_ -= callback; }); event_ += callback; lock (signal) { action_(); Assert.IsTrue(Monitor.Wait(signal, 10000)); } } However, the compiler prevents from passing event out of the class. Is there a way to achieve that?

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• sqlite3.OperationalError: database is locked - non-threaded application

  - by James C

  Hi, I have a Python application which throws the standard sqlite3.OperationalError: database is locked error. I have looked around the internet and could not find any solution which worked (please note that there is no multiprocesses/threading going on, and as you can see I have tried raising the timeout parameter). The sqlite file is stored on the local hard drive. The following function is one of many which accesses the sqlite database, and runs fine the first time it is called, but throws the above error the second time it is called (it is called as part of a for loop in another function): def update_index(filepath): path = get_setting('Local', 'web') stat = os.stat(filepath) modified = stat.st_mtime index_file = get_setting('Local', 'index') connection = sqlite3.connect(index_file, 30) cursor = connection.cursor() head, tail = os.path.split(filepath) cursor.execute('UPDATE hwlive SET date=? WHERE path=? AND name=?;', (modified, head, tail)) connection.commit() connection.close() Many thanks.

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• How to configure Spring-DM OSGi service for new instance per call?

  - by Bhav

  I'm starting to delve into using Spring DM and OSGi services in an RCP application. I've created a service which is used by another bundle in the RCP application. It does a lookup of the service via calls to getBundleContext().getServiceReference() using the explicit bundle names and service class names. I'm not using DI anywhere yet. The issue I'm running into is that the service that is returned in the requesting bundle is a singleton. At times I notice a threading issue since it is a "stateful" service. How do I configure the application to get back a new service instance with each call? Here is my spring xml file contents which registers the service: <bean id="myServBean" class="com.xyz.ClassImpl"/> <osgi:service ref="myServBean" class="com.xyz.Class"/>

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• Combining RequiresSTA and Timeout attributes on a test fails

  - by Peter Lillevold

  I have a test that opens and closes a WPF Window and thus requires the STA threading apartment. To safeguard the test against the window staying open (and thus hang the test indefinitely) I wanted to use the Timeout attribute. The problem is that applying the Timeout attribute causes the test to fail on timeout regardless of whether the test works or not. Without the attribute everything works fine. My theory is that Timeout causes the test to be executed on a new thread that does not inherit the STA apartment. Is there another way to have both STA and the timeout safeguard in NUnit? My test looks something like this: [Test, RequiresSTA, Timeout(300)] public void Construct() { var window = new WindowView(); window.Loaded += (sender, args) => window.Close(); var app = new Application(); app.Run(window); try { // ...run system under test } finally { app.Shutdown(); } }

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• Run java with highest security setting

  - by Ankiov Spetsnaz

  I'm currently writing an in house coding challenge web application and I am wondering if there is any other security precaution I would need to have other than below java option at runtime. java -Djava.security.manager=default Basically, challenges would be more of single threaded math and algorithm focused. So I would need to enable basic data structure objects and disable any file, sockets, threading or any thing that might be not so important. Based on my quick search turning on security manager as above seems to be a solution but since this is a security related I would like to be sure before it goes alive. Is there anything else I could do more?

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• What's the advantage for 'attach to process' compared with 'Start Debugging'?

  - by Nano HE

  Hi. I am new to programming. I know only Start debug before. Maybe start debug suit for some small application develop better. I found Visual studio IDE provide another method of attach to process for using. When & Why must I use the attach debugging? Such as multi-threading application debugging. Client/Service application debugging. etc. Thank you.

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• Good simple C/C++ FTP and SFTP client library recommendation for embedded Linux

  - by Roman Nikitchenko

  Could anyone recommend FTP / SFTP client C/C++ library for Linux-based embedded system? I know about Curl library but I need something as simple as possible just to download files from FTP / SFTP servers. Is there any recommendation to look for? Yes, SFTP support is critical. Actually I can even sacrifice multi-threading because I need only one stream at a time. And I'd like it to be able to work through memory buffers but this should be not a problem. Thank you in advance.

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• "Cannot use fixed local inside lambda expression"

  - by JulianR

  I have an XNA 3.0 project that compiled just fine in VS2008, but that gives compile errors in VS2010 (with XNA 4.0 CTP). The error: Cannot use fixed local 'depthPtr' inside an anonymous method, lambda expression, or query expression depthPtr is a fixed float* into an array, that is used inside a Parallel.For lambda expression from System.Threading. As I said, this compiled and ran just fine on VS2008, but it does not on VS2010, even when targeting .NET 3.5. Has this changed in .NET 4.0, and even so, shouldn't it still compile when I choose .NET 3.5 as the target framework? Searching for the term "Cannot use fixed local" yields exactly one (useless) result, both in Google and Bing. If this has changed, what is the reason for this? I can imagine capturing a fixed pointer-type in a closure could get a bit weird, is that why? So I'm guessing this is bad practice? And before anyone asks: no, the use of pointers is not absolutely critical here. I would still like to know though :)

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• How to program a connection pool?

  - by the_drow

  Is there a known algorithm for implementing a connection pool? If not what are the known algorithms and what are their trade-offs? What design patterns are common when designing and programming a connection pool? Are there any code examples implement a connection pool using boost.asio? Is it a good idea to use a connection pool for presisting connections (not http)? How is threading related to connection pooling? When do you need a new thread?

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• Simple prime number program - Weird issue with threads C#

  - by Para

  Hi! This is my code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading; namespace FirePrime { class Program { static bool[] ThreadsFinished; static bool[] nums; static bool AllThreadsFinished() { bool allThreadsFinished = false; foreach (var threadFinished in ThreadsFinished) { allThreadsFinished &= threadFinished; } return allThreadsFinished; } static bool isPrime(int n) { if (n < 2) { return false; } if (n == 2) { return true; } if (n % 2 == 0) { return false; } int d = 3; while (d * d <= n) { if (n % d == 0) { return false; } d += 2; } return true; } static void MarkPrimes(int startNumber,int stopNumber,int ThreadNr) { for (int j = startNumber; j < stopNumber; j++) nums[j] = isPrime(j); lock (typeof(Program)) { ThreadsFinished[ThreadNr] = true; } } static void Main(string[] args) { int nrNums = 100; int nrThreads = 10; //var threadStartNums = new List<int>(); ThreadsFinished = new bool[nrThreads]; nums = new bool[nrNums]; //var nums = new List<bool>(); nums[0] = false; nums[1] = false; for(int i=2;i<nrNums;i++) nums[i] = true; int interval = (int)(nrNums / nrThreads); //threadStartNums.Add(2); //int aux = firstStartNum; //int i = 2; //while (aux < interval) //{ // aux = interval*i; // i=i+1; // threadStartNums.Add(aux); //} int startNum = 0; for (int i = 0; i < nrThreads; i++) { var _thread = new System.Threading.Thread(() => MarkPrimes(startNum, Math.Min(startNum + interval, nrNums), i)); startNum = startNum + interval; //set the thread to run in the background _thread.IsBackground = true; //start our thread _thread.Start(); } while (!AllThreadsFinished()) { Thread.Sleep(1); } for (int i = 0; i < nrNums; i++) if(nums[i]) Console.WriteLine(i); } } } This should be a pretty simple program that is supposed to find and output the first nrNums prime numbers using nrThreads threads working in parallel. So, I just split nrNums into nrThreads equal chunks (well, the last one won't be equal; if nrThreads doesn't divide by nrNums, it will also contain the remainder, of course). I start nrThreads threads. They all test each number in their respective chunk and see if it is prime or not; they mark everything out in a bool array that keeps a tab on all the primes. The threads all turn a specific element in another boolean array ThreadsFinished to true when they finish. Now the weird part begins: The threads never all end. If I debug, I find that ThreadNr is not what I assign to it in the loop but another value. I guess this is normal since the threads execute afterwards and the counter (the variable i) is already increased by then but I cannot understand how to make the code be right. Can anyone help? Thank you in advance. P.S.: I know the algorithm is not very efficient; I am aiming at a solution using the sieve of Eratosthenes also with x given threads. But for now I can't even get this one to work and I haven't found any examples of any implementations of that algorithm anywhere in a language that I can understand.

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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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• mutliprocessing.Pool.add_sync() eating up memory

  - by Austin

  I want to use multithreading to make my script faster... I'm still new to this. The Python doc assumes you already understand threading and what-not. So... I have code that looks like this from itertools import izip from multiprocessing import Pool p = Pool() for i, j in izip(hugeseta, hugesetb): p.apply_async(number_crunching, (i, j)) Which gives me great speed! However, hugeseta and hugesetb are really huge. Pool keeps all of the _i_s and _j_s in memory after they've finished their job (basically, print output to stdout). Is there any to del i, and j after they complete?

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• Custom Control with Localization Support in WP7

  - by Ponmalar

  I have created the DateTimePicker control. Now i want to add localization Support with this. I have followed the below steps. Created CustomControls.de-DE.resx inside the ResourceFolder. added some commonly used strings in that resx file changed the access modifier to Public added <SupportedCulture>de-DE;</SupportedCulture> in the csproj file. set System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("de-DE"); in sample.cs file before IntializeComponent(). my DateTimevalue was " 2 Day(s): 3 Hr (s): 5 Min(s) : 32 Sec (s) Getting only default language that is english. What i did wrong? Please help me anyone. Is anything i missed?

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• How to start coding the "Dining Philosophers" simulation?

  - by GrizzlyGuru

  I'm not a beginner at C# but I really need to increase my understanding, so I've picked a classic deadlock problem to code to help teach myself some of the more advanced concepts of C#. The Dining Philosophers Problem seems like a good one, but I need a little help to get started. I know I need to approach the "diners" as objects, but to simulate the random delays between eating, should I look to threading with each diner in a separate thread? Do I need some kind of "master" to monitor all the actions? Any general design concept advice is welcome, but I'd like to do the grunt programming as an exercise. Thanks!

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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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• Re-ordering C++ template functions

  - by DeadMG

  In C++, I have a certain template function that, on a given condition, calls a template function in another class. The trouble is that the other class requires the full definition of the first class to be implemented, as it creates the second class and stores them and manages them in similar fashions. The trouble is that naturally, they fall as one class, and thus have some tight interop, except that I need them to be two classes for threading reasons. A sort of, master for all threads, one child per thread, system. Any advice on how this can be implemented?

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• In game programming are global variables bad?

  - by Joe.F

  I know my gut reaction to global variables is "badd!" but in the two game development courses I've taken at my college globals were used extensively, and now in the DirectX 9 game programming tutorial I am using (www.directxtutorial.com) I'm being told globals are okay in game programming ...? The site also recommends using only structs if you can when doing game programming to help keep things simple. I'm really confused on this issue, and all the research I've been trying to do is very confusing. I realize there are issues when using global variables (threading issues, they make code harder to maintain, the state of them is hard to track etc) but also there is a cost associated with not using globals, I'd have to pass a loooot of information around very often which can be confusing and I imagine time-costing, although I guess pointers would speed the process up (this is my first time writing a game in C++.) Anyway, I realize there is probably no "right" or "wrong" answer here since both ways work, but I want my code to be as proper as I can so any input would be good, thank you very much!

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• Why did the C# designers attach three different meanings to the 'using' keyword?

  - by gWiz

  The using keyword has three disparate meanings: type/namespace aliasing namespace import syntactic sugar for ensuring Dispose is called The documentation calls the first two definitions directives (which I'm guessing means they are preprocessing in nature), while the last is a statement. Regardless of the fact that they are distinguished by their syntaxes, why would the language developers complicate the semantics of the keyword by attaching three different meanings to it? For example, (disclaimer: off the top of my head, there may certainly be better examples) why not add keywords like alias and import? Technical, theoretical, or historical reasons? Keyword quota? ;-) Contrived sample: import System.Timers; alias LiteTimer=System.Threading.Timer; alias WinForms=System.Windows.Forms; public class Sample { public void Action { var elapsed = false; using(var t = new LiteTimer.Timer(_ => elapsed = true) { while (!elapsed) CallSomeFinickyApi(); } } } "Using" is such a vague word.

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• C# Spawn Multiple Threads for work then wait until all finished

  - by pharoc

  just want some advice on "best practice" regarding multi-threading tasks. as an example, we have a C# application that upon startup reads data from various "type" table in our database and stores the information in a collection which we pass around the application. this prevents us from hitting the database each time this information is required. at the moment the application is reading data from 10 tables synchronously. i would really like to have the application read from each table in a different thread all running in parallel. the application would wait for all the threads to complete before continuing with the startup of the application. i have looked into BackGroundWorker but just want some advice on accomplishing the above. Does the method sound logical in order to speed up the startup time of our application How can we best handle all the threads keeping in mind that each thread's work is independent of one another, we just need to wait for all the threads to complete before continuing. i look forward to some answers

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• thread destructors in C++0x vs boost

  - by Abruzzo Forte e Gentile

  Hi All These days I am reading the pdf Designing MT programs . It explains that the user MUST explicitly call detach() on an object of class std::thread in C++0x before that object gets out of scope. If you don't call it std::terminate() will be called and the application will die. I usually use boost::thread for threading in C++. Correct me if I am wrong but a boost::thread object detaches automatically when it get out of scope. Is seems to me that the boost approach follow a RAII principle and the std doesn't. Do you know if there is some particular reason for this? Kind Regards AFG

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