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• Threading vs single thread

  - by user177883

  Is it always guaranteed that a multi-threaded application would run faster than a single threaded application? I have two threads that populates data from a data source but different entities (eg: database, from two different tables), seems like single threaded version of the application is running faster than the version with two threads. Why would the reason be? when i look at the performance monitor, both cpu s are very spikey ? is this due to context switching? what are the best practices to jack the CPU and fully utilize it? I hope this is not ambiguous.

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• JTextArea thread safe?

  - by Dhaivat Pandya

  Hello everyone, I have some code that does some initialization (including making a JTextArea object), starts three seperate threads, and then these threads try to update the JTextArea (i.e. append() to it), but its not working at all. Nothing shows up on the JTextArea (however, during the initialzation, I print some test lines onto it, and that works fine). What's going on? How can I fix this? Also, each of those threads sleeps a random amount of time every time it has to update the JTextArea. Sorry I haven't provided any code, its all spread out over several files.

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• Java Parallel Programming

  - by user578524

  Dear All, I need to parallelize a CPU intensive Java application on my multicore desktop but I am not so comfortable with threads programming. I looked at Scala but this would imply learning a new language which is really time consuming. I also looked at Ateji PX Java parallel extensions which seem very easy to use but did not have a chance yet to evaluate it. Would anyone recommend it? Other suggestions welcome. Thanks in advance for your help Bill

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• How to interrupt a thread performing a blocking socket connect?

  - by Jason R

  I have some code that spawns a pthread that attempts to maintain a socket connection to a remote host. If the connection is ever lost, it attempts to reconnect using a blocking connect() call on its socket. Since the code runs in a separate thread, I don't really care about the fact that it uses the synchronous socket API. That is, until it comes time for my application to exit. I would like to perform some semblance of an orderly shutdown, so I use thread synchronization primitives to wake up the thread and signal for it to exit, then perform a pthread_join() on the thread to wait for it to complete. This works great, unless the thread is in the middle of a connect() call when I command the shutdown. In that case, I have to wait for the connect to time out, which could be a long time. This makes the application appear to take a long time to shut down. What I would like to do is to interrupt the call to connect() in some way. After the call returns, the thread will notice my exit signal and shut down cleanly. Since connect() is a system call, I thought that I might be able to intentionally interrupt it using a signal (thus making the call return EINTR), but I'm not sure if this is a robust method in a POSIX threads environment. Does anyone have any recommendations on how to do this, either using signals or via some other method? As a note, the connect() call is down in some library code that I cannot modify, so changing to a non-blocking socket is not an option.

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• Create a Task list, with tasks without executing

  - by Ernesto Araya Eguren

  I have an async method private async Task DoSomething(CancellationToken token) a list of Tasks private List<Task> workers = new List<Task>(); and I have to create N threads that runs that method public void CreateThreads(int n) { tokenSource = new CancellationTokenSource(); token = tokenSource.Token; for (int i = 0; i < n; i++) { workers.Add(DoSomething(token)); } } but the problem is that those have to run at a given time public async Task StartAllWorkers() { if (0 < workers.Count) { try { while (0 < workers.Count) { Task finishedWorker = await Task.WhenAny(workers.ToArray()); workers.Remove(finishedWorker); finishedWorker.Dispose(); } if (workers.Count == 0) { tokenSource = null; } } catch (OperationCanceledException) { throw; } } } but actually they run when i call the CreateThreads Method (before the StartAllWorkers). I searched for keywords and problems like mine but couldn't find anything about stopping the task from running. I've tried a lot of different aproaches but anything that could solve my problem entirely. For example, moving the code from DoSomething into a workers.Add(new Task(async () => { }, token)); would run the StartAllWorkers(), but the threads will never actually start. There is another method for calling the tokenSource.Cancel().

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• How to Perform Continues Iteration over Shared Dictionary in Multi-threaded Environment

  - by Mubashar Ahmad

  Dear Gurus. Note Pls do not tell me regarding alternative to custom session, Pls answer only relative to the Pattern Scenario I have Done Custom Session Management in my application(WCF Service) for this I have a Dictionary shared to all thread. When a specific function Gets called I add a New Session and Issue SessionId to the client so it can use that sessionId for rest of his calls until it calls another specific function, which terminates this session and removes the session from the Dictionary. Due to any reason Client may not call session terminator function so i have to implement time expiration logic so that i can remove all such sessions from the memory. For this I added a Timer Object which calls ClearExpiredSessions function after the specific period of time. which iterates on the dictionary. Problem: As this dictionary gets modified every time new client comes and leaves so i can't lock the whole dictionary while iterating over it. And if i do not lock the dictionary while iteration, if dictionary gets modified from other thread while iterating, Enumerator will throw exception on MoveNext(). So can anybody tell me what kind of Design i should follow in this case. Is there any standard pattern available.

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• asp.net Background Threads Exception Handling

  - by Chris

  In my 3.5 .net web application I have a background thread that does a lot of work (the application is similar to mint.com in that it does a lot of account aggregation on background threads). I do extensive exception handling within the thread performing the aggregation but there's always the chance an unhandled exception will be thrown and my entire application will die. I've read some articles about this topic but they all seem fairly outdated and none of them implement a standard approach. Is there a standard approach to this nowadays? Is there any nicer way to handle this in ASP.NET 4.0?

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• ruby thread programming , ruby equivalent of java wait/notify/notifyAll

  - by Geo

  I would like to know what are ruby's alternatives to the Java methods : wait notify notifyAll Could you please post a small snippet or some links ?

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• Impossible to be const-correct when combining data and it's lock?

  - by Graeme

  I've been looking at ways to combine a piece of data which will be accessed by multiple threads alongside the lock provisioned for thread-safety. I think I've got to a point where I don't think its possible to do this whilst maintaining const-correctness. Take the following class for example: template <typename TType, typename TMutex> class basic_lockable_type { public: typedef TMutex lock_type; public: template <typename... TArgs> explicit basic_lockable_type(TArgs&&... args) : TType(std::forward<TArgs...>(args)...) {} TType& data() { return data_; } const TType& data() const { return data_; } void lock() { mutex_.lock(); } void unlock() { mutex_.unlock(); } private: TType data_; mutable TMutex mutex_; }; typedef basic_lockable_type<std::vector<int>, std::mutex> vector_with_lock; In this I try to combine the data and lock, marking mutex_ as mutable. Unfortunately this isn't enough as I see it because when used, vector_with_lock would have to be marked as mutable in order for a read operation to be performed from a const function which isn't entirely correct (data_ should be mutable from a const). void print_values() const { std::lock_guard<vector_with_lock>(values_); for(const int val : values_) { std::cout << val << std::endl; } } vector_with_lock values_; Can anyone see anyway around this such that const-correctness is maintained whilst combining data and lock? Also, have I made any incorrect assumptions here?

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• Thread local storage with __declspec(thread) fails in C++/CLI

  - by EFrank

  I'm working on a project where we mix .NET code and native C++ code via a C++/CLI layer. In this solution I want to use Thread Local Storage via the __declspec(thread) declaration: __declspec(thread) int lastId = 0; However, at the first access of the variable, I get a NullReferenceException. To be more precise, the declaration is done within a ref class (a .NET class implemented in C++/CLI). I have already read something about __declspec(thread) does not work with delay loaded DLLs. Am I using delay loaded DLLs automatically if I use .NET?

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• remote function with pthread

  - by user311130

  Hi all, I wrote some code in c, using pthread (I configured the linker and compiler in eclipse IDE first). #include <pthread.h> #include "starter.h" #include "UI.h" Page* MM; Page* Disk; PCB* all_pcb_array; void* display_prompt(void *id){ printf("Hello111\n"); return NULL; } int main(int argc, char** argv) { printf("Hello\n"); pthread_t *thread = (pthread_t*) malloc (sizeof(pthread_t)); pthread_create(thread, NULL, display_prompt, NULL); printf("Hello\n"); return 1; } that works fine. However, when I move display_prompt to UI.h no "Hello111 " output is printed. anyone know how to solve that? Elad

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• Are indivisible operations still indivisible on multiprocessor and multicore systems?

  - by Steve314

  As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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• How to save objects using Multi-Threading in Core Data?

  - by Konstantin

  I'm getting some data from the web service and saving it in the core data. This workflow looks like this: get xml feed go over every item in that feed, create a new ManagedObject for every feed item download some big binary data for every item and save it into ManagedObject call [managedObjectContext save:] Now, the problem is of course the performance - everything runs on the main thread. I'd like to re-factor as much as possible to another thread, but I'm not sure where I should start. Is it OK to put everything (1-4) to the separate thread?

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• C++ VB6 interfacing problem

  - by Roshan

  Hi, I'm tearing my hair out trying to solve this one, any insights will be much appreciated: I have a C++ exe which acquires data from some hardware in the main thread and processes it in another thread (thread 2). I use a c++ dll to supply some data processing functions which are called from thread 2. I have a requirement to make another set of data processing functions in VB6. I have thus created a VB6 dll, using the add-in vbAdvance to create a standard dll. When I call functions from within this VB6 dll from the main thread, everything works exactly as expected. When I call functions from this VB6 dll in thread 2, I get an access violation. I've traced the error to the CopyMemory command, it would seem that if this is used within the call from the main thread, it's fine but in a call from the process thread, it causes an exception. Why should this be so? As far as I understand, threads share the same address space. Here is the code from my VB dll Public Sub UserFunInterface(ByVal in1ptr As Long, ByVal out1ptr As Long, ByRef nsamples As Long) Dim myarray1() As Single Dim myarray2() As Single Dim i As Integer ReDim myarray1(0 To nsamples - 1) As Single ReDim myarray2(0 To nsamples - 1) As Single With tsa1din(0) ' defined as safearray1d in a global definitions module .cDims = 1 .cbElements = 4 .cElements = nsamples .pvData = in1ptr End With With tsa1dout .cDims = 1 .cbElements = 4 .cElements = nsamples .pvData = out1ptr End With CopyMemory ByVal VarPtrArray(myarray1), VarPtr(tsa1din(0)), 4 CopyMemory ByVal VarPtrArray(myarray2), VarPtr(tsa1dout), 4 For i = 0 To nsamples - 1 myarray2(i) = myarray1(i) * 2 Next i ZeroMemory ByVal VarPtrArray(myarray1), 4 ZeroMemory ByVal VarPtrArray(myarray2), 4 End Sub

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• What is Erlang's concurrency model actually ?

  - by arun_suresh

  I was reading a paper recently Why Events are Bad. The paper is a comparative study of Event based and thread based highly concurrent servers and finally concludes stating that Threads are better than events in that scenario. I find that I am not able to classify what sort of concurrency model erlang exposes. Erlang provides Light Weight Processes, but those processes are suspended most of the time until it has received some event/message of some sort. /Arun

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• Different standard streams per POSIX thread

  - by Roman Nikitchenko

  Is there any possibility to achieve different redirections for standard output like printf(3) for different POSIX thread? What about standard input? I have lot of code based on standard input/output and I only can separate this code into different POSIX thread, not process. Linux operation system, C standard library. I know I can refactor code to replace printf() to fprintf() and further in this style. But in this case I need to provide some kind of context which old code doesn't have. So doesn't anybody have better idea (look into code below)? #include <pthread.h> #include <stdio.h> void* different_thread(void*) { // Something to redirect standard output which doesn't affect main thread. // ... // printf() shall go to different stream. printf("subthread test\n"); return NULL; } int main() { pthread_t id; pthread_create(&id, NULL, different_thread, NULL); // In main thread things should be printed normally... printf("main thread test\n"); pthread_join(id, NULL); return 0; }

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• Multi threading in WCF RIA Services

  - by synergetic

  I use WCF RIA Services to update customer database. In domain service: public void UpdateCustomer(Customer customer) { this.ObjectContext.Customers.AttachAsModified(customer); syncCustomer(customer); } After update, a database trigger launches and depending on the columns updated it may insert a new record in CustomerChange table. syncCustomer(customer) method is executed to check for a new record in the CustomerChange table and if found it will create a text file which contains customer information and forwards that file to external system for import. Now this synchronization may take a time so I wanted to execute it in different thread. So: private void syncCustomer(Customer customer) { this.ObjectContext.SaveChanges(); new Thread(() => syncCustomerInfo(customer.CustomerID)) { IsBackground = true }.Start(); } private void syncCustomerInfo(int customerID) { //Thread.Sleep(2000); //does real job here ... ... } The problem is in most cases syncCustomerInfo method cannot find any new CustomerChange record even if it was definitely there. If I force thread sleep then it finds a new record. I also looked Entity Framework events but the only event provided by object context is SavingChanges which occur before changes are saved. Please suggest me what else to try.

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• Log RuntimeException thrown from thread created by Spring via the @Async annotation

  - by Eugen

  I'm having some difficulty logging RuntimeException from a thread. My system is: Java 7 (b118), Spring 3.0.5. The threads are not created by hand, but via Spring's @Async annotation, which creates it's own executor behind the scenes, so I don't really have the option of overriding any methods of the thread, FutureTask or anything low level. So my question is if Spring has any support or if there are any best practices for handling (logging) these type of exceptions? Any suggestions are appreciated. Thanks.

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• Bluetooth in Java Mobile: Handling connections that go out of range

  - by Albus Dumbledore

  I am trying to implement a server-client connection over the spp. After initializing the server, I start a thread that first listens for clients and then receives data from them. It looks like that: public final void run() { while (alive) { try { /* * Await client connection */ System.out.println("Awaiting client connection..."); client = server.acceptAndOpen(); /* * Start receiving data */ int read; byte[] buffer = new byte[128]; DataInputStream receive = client.openDataInputStream(); try { while ((read = receive.read(buffer)) > 0) { System.out.println("[Recieved]: " + new String(buffer, 0, read)); if (!alive) { return; } } } finally { System.out.println("Closing connection..."); receive.close(); } } catch (IOException e){ e.printStackTrace(); } } } It's working fine for I am able to receive messages. What's troubling me is how would the thread eventually die when a device goes out of range? Firstly, the call to receive.read(buffer) blocks so that the thread waits until it receives any data. If the device goes out of range, it would never proceed onward to check if meanwhile it has been interrupted. Secondly, it would never close the connection, i.e. the server would not accept the device once it goes back in range. Thanks! Any ideas would be highly appreciated! Merry Christmas!

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• Printdialog in multithreaded wpf window thrown TargetInvocationException

  - by Nils

  I have designed a multithreaded app, which is starting most windows in an dedicated thread like this: Thread newWindowThread = new Thread(new ThreadStart(ThreadStartingPoint)); newWindowThread.SetApartmentState(ApartmentState.STA); newWindowThread.IsBackground = true; newWindowThread.Start(); However, if in one of those window-in-own-thread I try to print something by simply calling PrintDialog pDialog = new PrintDialog(); bool? doPrint = pDialog.ShowDialog(); I get a TargetInvocationException - it does look like the PrintDialog does not reside in the same thread as my window. Is there any way to create a thread-agnostic (or "thread-save") PrinterDialog ?

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• Multi-threaded library calls in ASP.NET page request.

  - by ProfK

  I have an ASP.NET app, very basic, but right now too much code to post if we're lucky and I don't have to. We have a class called ReportGenerator. On a button click, method GenerateReports is called. It makes an async call to InternalGenerateReports using ThreadPool.QueueUserWorkItem and returns, ending the ASP.NET response. It doesn't provide any completion callback or anything. InternalGenerateReports creates and maintains five threads in the threadpool, one report per thread, also using QueueUserWorkItem, by 'creating' five threads, also with and waiting until calls on all of them complete, in a loop. Each thread uses an ASP.NET ReportViewer control to render a report to HTML. That is, for 200 reports, InternalGenerateReports should create 5 threads 40 times. As threads complete, report data is queued, and when all five have completed, report data is flushed to disk. My biggest problems are that after running for just one report, the aspnet process is 'hung', and also that at around 200 reports, the app just hangs. I just simplified this code to run in a single thread, and this works fine. Before we get into details like my code, is there anything obvious in the above scendario that might be wrong?

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• Diffrernce between BackgroundWorker.ReportProgress() and Control.Invoke()

  - by ohadsc

  What is the difference between options 1 and 2 in the following? private void BGW_DoWork(object sender, DoWorkEventArgs e) { for (int i=1; i<=100; i++) { string txt = i.ToString(); if (Test_Check.Checked) //OPTION 1 Test_BackgroundWorker.ReportProgress(i, txt); else //OPTION 2 this.Invoke((Action<int, string>)UpdateGUI, new object[] {i, txt}); } } private void BGW_ProgressChanged(object sender, ProgressChangedEventArgs e) { UpdateGUI(e.ProgressPercentage, (string)e.UserState); } private void UpdateGUI(int percent, string txt) { Test_ProgressBar.Value = percent; Test_RichTextBox.AppendText(txt + Environment.NewLine); } Looking at reflector, the Control.Invoke() appears to use: this.FindMarshalingControl().MarshaledInvoke(this, method, args, 1); whereas BackgroundWorker.Invoke() appears to use: this.asyncOperation.Post(this.progressReporter, args); (I'm just guessing these are the relevant function calls.) If I understand correctly, BGW Posts to the WinForms window its progress report request, whereas Control.Invoke uses a CLR mechanism to invoke on the right thread. Am I close? And if so, what are the repercussions of using either ? Thanks

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• c# multi threaded file processing

  - by user177883

  There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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• Setting the default stack size on Linux globally for the program

  - by wowus

  So I've noticed that the default stack size for threads on linux is 8MB (if I'm wrong, PLEASE correct me), and, incidentally, 1MB on Windows. This is quite bad for my application, as on a 4-core processor that means 64 MB is space is used JUST for threads! The worst part is, I'm never using more than 100kb of stack per thread (I abuse the heap a LOT ;)). My solution right now is to limit the stack size of threads. However, I have no idea how to do this portably. Just for context, I'm using Boost.Thread for my threading needs. I'm okay with a little bit of #ifdef hell, but I'd like to know how to do it easily first. Basically, I want something like this (where windows_* is linked on windows builds, and posix_* is linked under linux builds) // windows_stack_limiter.c int limit_stack_size() { // Windows impl. return 0; } // posix_stack_limiter.c int limit_stack_size() { // Linux impl. return 0; } // stack_limiter.cpp int limit_stack_size(); static volatile int placeholder = limit_stack_size(); How do I flesh out those functions? Or, alternatively, am I just doing this entirely wrong? Remember I have no control over the actual thread creation (no new params to CreateThread on Windows), as I'm using Boost.Thread.

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• HttpWebResponse get mixed up when used inside multiple threads

  - by Holli

  In my Application I have a few threads who will get data from a web service. Basically I just open an URL and get an XML output. I have a few threads who do this continuously but with different URLs. Sometimes the results are mixed up. The XML output doesn't belong to the URL of a thread but to the URL of another thread. In each thread I create an instance of the class GetWebPage and call the method Get from this instance. The method is very simple and based mostly on code from the MSDN documentation. (See below. I removed my error handling here!) public string Get(string userAgent, string url, string user, string pass, int timeout, int readwriteTimeout, WebHeaderCollection whc) { string buffer = string.Empty; HttpWebRequest myWebRequest = (HttpWebRequest)WebRequest.Create(url); if (!string.IsNullOrEmpty(userAgent)) myWebRequest.UserAgent = userAgent; myWebRequest.Timeout = timeout; myWebRequest.ReadWriteTimeout = readwriteTimeout; myWebRequest.Credentials = new NetworkCredential(user, pass); string[] headers = whc.AllKeys; foreach (string s in headers) { myWebRequest.Headers.Add(s, whc.Get(s)); } using (HttpWebResponse myWebResponse = (HttpWebResponse)myWebRequest.GetResponse()) { using (Stream ReceiveStream = myWebResponse.GetResponseStream()) { Encoding encode = Encoding.GetEncoding("utf-8"); StreamReader readStream = new StreamReader(ReceiveStream, encode); // Read 1024 characters at a time. Char[] read = new Char[1024]; int count = readStream.Read(read, 0, 1024); int break_counter = 0; while (count > 0 && break_counter < 10000) { String str = new String(read, 0, count); buffer += str; count = readStream.Read(read, 0, 1024); break_counter++; } } } return buffer; As you can see I have no public properties or any other shared resources. At least I don't see any. The url is the service I call in the internet and buffer is the XML Output from the server. Like I said I have multiple instances of this class/method in a few threads (10 to 12) and sometimes buffer does not belong the the url of the same thread but another thread.

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