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• Best approach to synchronising properties across threads

  - by user290796

  Hi, I'm looking for some advice on the best approach to synchronising access to properties of an object in C++. The application has an internal cache of objects which have 10 properties. These objects are to be requested in sets which can then have their properties modified and be re-saved. They can be accessed by 2-4 threads at any given time but access is not intense so my options are: Lock the property accessors for each object using a critical section. This means lots of critical sections - one for each object. Return copies of the objects when requested and have an update function which locks a single critical section to update the object properties when appropriate. I think option 2 seems the most efficient but I just want to see if I'm missing a hidden 3rd option which would be more appropriate. Thanks, J

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• Swing: How do I run a job from AWT thread, but after a window was layed out?

  - by java.is.for.desktop

  My complete GUI runs inside the AWT thread, because I start the main window using SwingUtilities.invokeAndWait(...). Now I have a JDialog which has just to display a JLabel, which indicates that a certain job is in progress, and close that dialog after the job was finished. The problem is: the label is not displayed. That job seems to be started before JDialog was fully layed-out. When I just let the dialog open without waiting for a job and closing, the label is displayed. The last thing the dialog does in its ctor is setVisible(true). Things such as revalidate(), repaint(), ... don't help either. Even when I start a thread for the monitored job, and wait for it using someThread.join() it doesn't help, because the current thread (which is the AWT thread) is blocked by join, I guess. Replacing JDialog with JFrame doesn't help either. So, is the concept wrong in general? Or can I manage it to do certain job after it is ensured that a JDialog (or JFrame) is fully layed-out? Simplified algorithm of what I'm trying to achieve: Create a subclass of JDialog Ensure that it and its contents are fully layed-out Start a process and wait for it to finish (threaded or not, doesn't matter) Close the dialog I managed to write a reproducible test case: EDIT Problem from an answer is now addressed: This use case does display the label, but it fails to close after the "simulated process", because of dialog's modality. import java.awt.*; import javax.swing.*; public class _DialogTest2 { public static void main(String[] args) throws Exception { SwingUtilities.invokeAndWait(new Runnable() { final JLabel jLabel = new JLabel("Please wait..."); @Override public void run() { JFrame myFrame = new JFrame("Main frame"); myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); myFrame.setSize(750, 500); myFrame.setLocationRelativeTo(null); myFrame.setVisible(true); JDialog d = new JDialog(myFrame, "I'm waiting"); d.setModalityType(Dialog.ModalityType.APPLICATION_MODAL); d.add(jLabel); d.setSize(300, 200); d.setLocationRelativeTo(null); d.setVisible(true); SwingUtilities.invokeLater(new Runnable() { @Override public void run() { try { Thread.sleep(3000); // simulate process jLabel.setText("Done"); } catch (InterruptedException ex) { } } }); d.setVisible(false); d.dispose(); myFrame.setVisible(false); myFrame.dispose(); } }); } }

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• Will lock() statement block all threads in the proccess/appdomain?

  - by MikeJ

  Maybe the question sounds silly, but I don't understand 'something about threads and locking and I would like to get a confirmation (here's why I ask). So, if I have 10 servers and 10 request in the same time come to each server, that's 100 request across the farm. Without locking, thats 100 request to the database. If I do something like this: private static readonly object myLockHolder = new object(); if (Cache[key] == null) { lock(myLockHolder) { if (Cache[key] == null) { Cache[key] = LengthyDatabaseCall(); } } } How many database requests will I do? 10? 100? Or as much as I have threads?

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• multi-threading in MFC

  - by kiddo

  Hello all,in my application there is a small part of function,in which it will read files to get some information,the number of filecount would be utleast 50,So I thought of implementing threading.Say if the user is giving 50 files,I wanted to separate it as 5 *10, 5 thread should be created,so that each thread can handle 10 files which can speed up the process.And also from the below code you can see that some variables are common.I read some articles about threading and I am aware that only one thread should access a variable/contorl at a me(CCriticalStiuation can be used for that).For me as a beginner,I am finding hard to imlplement what I have learned about threading.Somebody please give me some idea with code shown below..thanks in advance file read function:// void CMyClass::GetWorkFilesInfo(CStringArray& dataFilesArray,CString* dataFilesB, int* check,DWORD noOfFiles,LPWSTR path) { CString cFilePath; int cIndex =0; int exceptionInd = 0; wchar_t** filesForWork = new wchar_t*[noOfFiles]; int tempCheck; int localIndex =0; for(int index = 0;index < noOfFiles; index++) { tempCheck = *(check + index); if(tempCheck == NOCHECKBOX) { *(filesForWork+cIndex) = new TCHAR[MAX_PATH]; wcscpy(*(filesForWork+cIndex),*(dataFilesB +index)); cIndex++; } else//CHECKED or UNCHECKED { dataFilesArray.Add(*(dataFilesB+index)); *(check + localIndex) = *(check + index); localIndex++; } } WorkFiles(&cFilePath,dataFilesArray,filesForWork, path, cIndex); dataFilesArray.Add(cFilePath); *(check + localIndex) = CHECKED; }

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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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• Is thread-safe to use the 'yield' operator inside an extension method'?

  - by SDReyes

  Would be thread-safe to use the yield operator inside an extension method? For example: public static CartItem GetItems( this Cart cart ) { { while( cart.hasNext() ) yield return cart.GetNextItem( ); } }

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• Is this use of PreparedStatements in a Thread in JAVA correct?

  - by Gormcito

  I'm still an undergrad just working part time and so I'm always trying to be aware of better ways to do things. Recently I had to write a program for work where the main thread of the program would spawn "task" threads (for each db "task" record) which would perform some operations and then update the record to say that it has finished. Therefore I needed a database connection object and PreparedStatement objects in or available to the ThreadedTask objects. This is roughly what I ended up writing, is creating a PreparedStatement object per thread a waste? I thought static PreparedStatments could create race conditions... Thread A stmt.setInt(); Thread B stmt.setInt(); Thread A stmt.execute(); Thread B stmt.execute(); A´s version never gets execed.. Is this thread safe? Is creating and destroying PreparedStatement objects that are always the same not a huge waste? public class ThreadedTask implements runnable { private final PreparedStatement taskCompleteStmt; public ThreadedTask() { //... taskCompleteStmt = Main.db.prepareStatement(...); } public run() { //... taskCompleteStmt.executeUpdate(); } } public class Main { public static final db = DriverManager.getConnection(...); }

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• Threads in PHP.

  - by Muhammad Sajid

  Hello.. I am creating a web application using zend, here i create an interface from where user-A can send email to more than one user(s) & it works excellent but it slow the execution time because of which user-A wait too much for the "acknowledged response" ( which will show after the emails have sent. ) In Java there are "Threads" by which we can perform that task (send emails) & it does not slow the rest application. Is there any technique in PHP/Zend just like in Java by which we can divide our tasks which could take much time eg: sending emails. Thanks..

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• Why is my BeginInvoke method not async?

  - by Petr

  Hi, In order to avoid freezing of GUI, I wanted to run method connecting to DB asynchronously. Therefore I have written this: DelegatLoginu dl = ConnectDB; IAsyncResult ar=dl.BeginInvoke(null, null); bool result = (bool)dl.EndInvoke(ar); But it is still freezing and I do not understand why - I though BeginInvoke assures that method it references is run in another thread. Thank you!

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• XNA Multi-Thread Jitters

  - by Ice Phoenix

  Hi guys, brand new question. Just implemented multi-threading into my XNA game as it was unable to keep up with using 1 processor. MT is all implemented fine and everything, however the player seems to jitter all over the spot every now and then. I originally thought it was a loss of data between the update and render, but even when i did the player update in the render it did the same thing. It's not a memory/processor issue as i'm no where near maxing out my RAM or processors. It's strange aswell because none of the other entities in the game seem to have any of these issues. Any ideas at all??

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• Serialized task distribution: use thread or epoll?

  - by hpsmouse

  Now I'm in such a situation that there is a group of predefined tasks for multiple clients to do(any client can take any task). When a client connects to the server, server choose a task from the uncompleted tasks and send it to the client. It takes a while for the client to finish the task and send the result back to the server. Since a task should be sent to only one client, server should process requests in a serialized way. Now I have two plans to do it: create a thread for each client connection and all the threads take turns accessing the task pool, or use epoll listening on all the connection and process for each event of clients. Which one is better for the job? Or is there any other ideas? The server will be run on a multi-core machine.

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• [Android] Thread Button sleep

  - by user557475

  Hello For my project,i´am trying to execute a Method every 10 seconds when i click a button "A" and it should stop when i click the button again (kind of on/off). this is what i reached :-/ : ButtonA.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Handler handler = new Handler(); handler.postDelayed(new Runnable() { public void run() { showCurrentLocation(); Methodexecute(); } }, 10000); } } }); how can i repeat executing this method every 10 seconds until the button is clicked again. thanks

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• Threadpool with pasistant worker instances

  - by Matt Smokey-waters Holmes

  So basically what im trying to do is queue up tasks in a thread pool to be executed as soon as a worker becomes free, i have found various examples of this but in all cases the examples have been setup to use a new Worker instance for each job, i want persistent workers. Im trying to make a ftp backup tool, i have it working but because of the limitations of a single connection it is slow. What i ideally want to do is have a single connection for scanning directories and building up a file list then four workers to download said files. Here is an example of my worker /** * FTP Worker */ public class Worker implements Runnable { protected FTPClient _ftp; // Connection details protected String _host = ""; protected String _user = ""; protected String _pass = ""; // worker status protected boolean _working = false; public Worker(String host, String user, String pass) { this._host = host; this._user = user; this._pass = pass; } // Check if the worker is in use public boolean inUse() { return this._working; } @Override public void run() { this._ftp = new FTPClient(); this._connect(); } // Download a file from the ftp server public boolean download(String base, String path, String file) { this._working = true; boolean outcome = true; //create directory if not exists File pathDir = new File(base + path); if (!pathDir.exists()) { pathDir.mkdirs(); } //download file try { OutputStream output = new FileOutputStream(base + path + file); this._ftp.retrieveFile(file, output); output.close(); } catch (Exception e) { outcome = false; } finally { this._working = false; return outcome; } } // Connect to the server protected boolean _connect() { try { this._ftp.connect(this._host); this._ftp.login(this._user, this._pass); } catch (Exception e) { return false; } return this._ftp.isConnected(); } // Disconnect from the server protected void _disconnect() { try { this._ftp.disconnect(); } catch (Exception e) { /* do nothing */ } } } and basically i want to be able to call Worker.download(...) for each task in a queue whenever a worker becomes available without having to create a new connection to the ftp server for each download Any help would be appreciated as iv'e never used threads before and I'm going round in circles at the moment

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• Manually Increasing the Amount of CPU a Java Application Uses

  - by SkylineAddict

  I've just made a program with Eclipse that takes a really long time to execute. It's taking even longer because it's loading my CPU to 25% only (I'm assuming that is because I'm using a quad-core and the program is only using one core). Is there any way to make the program use all 4 cores to max it out? Java is supposed to be natively multi-threaded, so I don't understand why it would only use 25%.

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• Thread in android

  - by ravi adhikari

  Hi experts, I need some help as i am just calling a method in a thread. now what i want is wait for reply form getData() method only for 15 seconds. If it reply before 15 seconds it should be terminated otherwise after 15 seconds it should be terminated. The code is given below: boolean networkStatus; private Runnable runnable; private ProgressDialog m_ProgressDialog = null; private Runnable returnRes = new Runnable() { @Override public void run() { if(networkStatus){ setData(); m_ProgressDialog.dismiss(); } }; private void callGetdata(){ runnable = new Runnable() { @Override public void run() { networkStatus = getData(); runOnUiThread(returnRes); } }; Thread thread = new Thread(null, runnable, "MovetoBackground"); thread.start(); m_ProgressDialog = ProgressDialog.show(this, "", getString(R.string.loadMsg), true); }

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• Thread Code...anything wrong with this, must use java 1.4

  - by bmw0128

  I have a servlet automatically firing up when the app server starts, and in its init(), I'm making another thread: init(){ new FooThread() } in FooThread(), i want to periodically check the status of a DB value, then depending on the value, make a web service call. When these two tasks complete, I want the thread to sleep to wait a certain period then repeat. This cycle would just continue forever. FooThread: public class FooThread implements Runnable{ Thread t; FooThread(){ t = new Thread(this, "BBSThread"); logger.info("*** about to start " + t.getName()); t.start(); logger.info("*** started: " + t); } public void run() { try{ while(true){ //do the db check, then conditionally do the web services call logger.info("*** calling sleep() ***"); Thread.sleep(50000); logger.info("*** now awake ***"); } } catch (InterruptedException e) { System.out.println("*** FooThread interrupted"); } } }

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• Multithreaded update of multiple ProgressBars

  - by ClaudeS

  I have developped an application that can process data (in my case image algorithms performed on videos). I have developed different ProcessingMethods. Sometimes several videos are processed in parallel. Each process runs in a seperate thread. I have a GUI with several ProgressBars, one for each thread that is processing data. What is a good way to update the ProgressBar? Today my GUI is creating all the processing threads and one progressBars for each thread. Then I pass those progressBars to the threads, which pass them to the ProcessingMethod. The ProcessingMethod will then update the progressbar (using Invoke(..)). I have different processingMethods. Within each of these methods I have copy-paste code to update the progressBar. Although I am a new to programming, I know copy-paste is not good. What is a good way to make it better?

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• What is the absolute fastest way to implement a concurrent queue with ONLY one consumer and one producer?

  - by JohnPristine

  java.util.concurrent.ConcurrentLinkedQueue comes to mind, but is it really optimum for this two-thread scenario? I am looking for the minimum latency possible on both sides (producer and consumer). If the queue is empty you can immediately return null AND if the queue is full you can immediately discard the entry you are offering. Does ConcurrentLinkedQueue use super fast and light locks (AtomicBoolean) ? Has anyone benchmarked ConcurrentLinkedQueue or knows about the ultimate fastest way of doing that? Additional Details: I imagine the queue should be a fair one, meaning the consumer should not make the consumer wait any longer than it needs (by front-running it) and vice-versa.

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• Windows App. Thread Aborting Issue

  - by Patrick

  I'm working on an application that has to make specific decisions based on files that are placed into a folder being watched by a file watcher. Part of this decision making process involves renaming files before moving them off to another folder to be processed. Since I'm working with files of all different sizes I created an object that checks the file in a seperate thread to verify that it is "available" and when it is it fires an event. When I run the rename code from inside this available event it works. public void RenameFile_Test() { string psFilePath = @"C:\File1.xlsx"; tgt_File target = new FileObject(psFilePath); target.FileAvailable += new FileEventHandler(OnFileAvailable); target.FileUnAvailable += new FileEventHandler(OnFileUnavailable); } private void OnFileAvailable(object source, FileEventArgs e) { ((FileObject)source).RenameFile(@"C:\File2.xlsx"); } The problem I'm running into is that when the extensions are different from the source file and the rename to file I am making a call to a conversion factory that returns a factory object based on the type of conversion and then converts the file accordingly before doing the rename. When I run that particular piece of code in unit test it works, the factory object is returned, and the conversion happens correctly. But when I run it within the process I get up to the... moExcelApp = new Application(); part of converting an .xls or .xlsx to a .csv and i get a "Thread was being Aborted" error. Any thoughts? Update: There is a bit more information and a bit of map of how the application works currently. Client Application running FSW On File Created event Creates a FileObject passing in the path of the file. On construction the file is validated: if file exists is true then, Thread toAvailableCheck = new Thread(new ThreadStart(AvailableCheck)); toAvailableCheck.Start(); The AvailableCheck Method repeatedly tries to open a streamreader to the file until the reader is either created or the number of attempts times out. If the reader is opened, it fires the FileAvailable event, if not it fires the FileUnAvailable event, passing back itself in the event. The client application is wired to catch those events from inside the Oncreated event of the FSW. the OnFileAvailable method then calls the rename functionality which contains the excel interop call. If the file is being renamed (not converted, extensions stay the same) it does a move to change the name from the old file name to the new, and if its a conversion it runs a conversion factory object which returns the correct type of conversion based on the extensions of the source file and the destination file name. If it is a simple rename it works w/o a problem. If its a conversion (which is the XLS to CSV object that is returned as a part of the factory) the very first thing it does is create a new application object. That is where the application bombs. When i test the factory and conversion/rename process outside of the thread and in its own unit test the process works w/o a problem. Update: I tested the Excel Interop inside a thread by doing this: [TestMethod()] public void ExcelInteropTest() { Thread toExcelInteropThreadTest = new Thread(new ThreadStart(Instantiate_App)); toExcelInteropThreadTest.Start(); } private void Instantiate_App() { Application moExcelApp = new Application(); moExcelApp.Quit(); } And on the line where the application is instatntiated I got the 'A first chance exception of type 'System.Threading.ThreadAbortException' error. So I added; toExcelInteropThreadTest.SetApartmentState(ApartmentState.MTA); after the thread instantiation and before the thread start call and still got the same error. I'm getting the notion that I'm going to have to reconsider the design.

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• How to debug ConcurrentModificationException?

  - by Dani

  I encountered ConcurrentModificationException and by looking at it I can't see the reason why it's happening; the area throwing the exception and all the places modifying the collection are surrounded by synchronized (this.locks.get(id)) { ... } // locks is a HashMap<String, Object>; I tried to catch the the pesky thread but all I could nail (by setting a breakpoint in the exception) is that the throwing thread owns the monitor while the other thread (there are two threads in the program) sleeps. How should I proceed? What do you usually do when you encounter similar threading issues?

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• Is there a straightforward way to have a ThreadStatic instance member?

  - by Dan Tao

  With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there some corresponding attribute that provides the same functionality, but for instance members? In other words, that allows me to have one instance of the object, per thread, per instance of the containing class?

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• Debug.writeline locks

  - by Carra

  My program frequently stops with a deadlock. When I do a break-all and look at the threads I see that three threads are stuck in our logging function: public class Logging { public static void WriteClientLog(LogLevel logLevel, string message) { #if DEBUG System.Diagnostics.Debug.WriteLine(String.Format("{0} {1}", DateTime.Now.ToString("HH:mm:ss"), message)); //LOCK #endif //...Log4net logging } } If I let the program continue the threads are still stuck on that line. I can't see where this can lock. The debug class, string class & datetime class seem to be thread safe. The error goes away when I remove the "#if DEBUG System... #endif" code but I'm curious why this behavior happens. Thread one: public void CleanCache() { Logging.WriteClientLog(LogLevel.Debug, "Start clean cache.");//Stuck } Thread two: private void AliveThread() { Logging.WriteClientLog(LogLevel.Debug, "Check connection");//Stuck }

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• boost scoped_lock mutex crashes

  - by JahSumbar

  hello, I have protected a std::queue's access functions, push, pop, size, with boost::mutexes and boost::mutex::scoped_lock in these functions from time to time it crashes in a scoped lock the call stack is this: 0 0x0040f005 boost::detail::win32::interlocked_bit_test_and_set include/boost/thread/win32/thread_primitives.hpp 361 1 0x0040e879 boost::detail::basic_timed_mutex::timed_lock include/boost/thread/win32/basic_timed_mutex.hpp 68 2 0x0040e9d3 boost::detail::basic_timed_mutex::lock include/boost/thread/win32/basic_timed_mutex.hpp 64 3 0x0040b96b boost::unique_lock<boost::mutex>::lock include/boost/thread/locks.hpp 349 4 0x0040b998 unique_lock include/boost/thread/locks.hpp 227 5 0x00403837 MyClass::inboxSize - this is my inboxSize function that uses this code: MyClass::inboxSize () { boost::mutex::scoped_lock scoped_lock(m_inboxMutex); return m_inbox.size(); } and the mutex is declared like this: boost::mutex m_inboxMutex; it crashes at the last pasted line in this function: inline bool interlocked_bit_test_and_set(long* x,long bit) { long const value=1<<bit; long old=*x; and x has this value: 0xababac17 Thanks for the help

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• Is this a valid, lazy, thread-safe Singleton implementation for C#?

  - by Matthew

  I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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• Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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