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  • how to share a variable between two threads

    - by prmatta
    I just inherited some code, two threads within this code need to perform a system task. One thread should do the system task before the other thread. They should not be performing the system task together. The two threads do not have references to each other. Now, I know I can use some sort of a semaphore to achieve this. But my question is what is the right way to get both threads to access this semaphore. I could create a static variable/method a new class : public class SharedSemaphore { private static Semaphore s = new Semaphore (1, true); public static void performSystemTask () { s.acquire(); } public static void donePerformingSystemTask() { s.release(); } } This would work (right?) but this doesn't seem like the right thing to do. Because, the threads now have access to a semaphore, without ever having a reference to it. This sort of thing doesn't seem like a good programming practice. Am I wrong?

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  • Wait until user press enter in textbox in another form and return value

    - by ekapek
    Hello, I am new to C# and I'm trying to do sth like this: myList = list of 1000+ string values; 1.StartNewThreads(50); //50 is the numbers of new threads 2.DoSth1(next value from myList); 3.DoSth2(); 4. var value = { ShowNewImageForm(); //show only if not another ImageForm is displayed if another is show - wait WaitUntilUserPressEnterInTextBox(); ReturnValueFormTextbox(); } 5.DoSth3(); 6.StartNewThread(); For now I have: foreach(String s in myList ) { DoSth1(s); DoSth2(); DoSth3(); } And now I'm looking for ideas to points 1,3,6 Can You suggest me how to resolve this? How to start 50 threads How to get value from textbox in another form when user press enter

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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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  • Ruby: would using Fibers increase my DB insert throughput?

    - by Zombies
    Currently I am using Ruby 1.9.1 and the 'ruby-mysql' gem, which unlike the 'mysql' gem is written in ruby only. This is pretty slow actually, as it seems to insert at a rate of almost 1 per second (SLOOOOOWWWWWW). And I have a lot of inserts to make too, its pretty much what this script does ultamitely. I am using just 1 connection (since I am using just one thread). I am hoping to speed things up by creating a fiber that will create a new DB connection insert 1-3 records close the DB connection I would imagine launching 20-50 of these would greatly increase DB throughput. Am I correct to go along this route? I feel that this is the best option, as opposed to refactoring all of my DB code :(

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  • java.lang.OutOfMemoryError: unable to create new native thread for multiple threads

    - by Kaustubh Ranjan Singh
    static class solver implements Runnable { static calculator(problem){ //Some code if(condition) {solver s = new solver(newproblem); new Thread(s).start();} } Public solver(int newproblem) { this.problem = newproblem ; } public void run() { // TODO Auto-generated method stub calculator(promblem); } } i am having a big array maze of 100x100 and i am trying to solve it and i am getting an error java.lang.OutOfMemoryError: unable to create new native thread(after running a code for some times). How can solve this , How can i use ExecutorService i think that will solve the problem or i want something like thisIf Number of generated threads4K then stop the first 100 threads

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  • non blocking client server chat application in java using nio

    - by Amith
    I built a simple chat application using nio channels. I am very much new to networking as well as threads. This application is for communicating with server (Server / Client chat application). My problem is that multiple clients are not supported by the server. How do I solve this problem? What's the bug in my code? public class Clientcore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void coreClient() { System.out.println("please enter the text"); BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in)); SocketChannel sc = null; try { sc = SocketChannel.open(); sc.configureBlocking(false); sc.connect(new InetSocketAddress(8888)); int i=0; while (!sc.finishConnect()) { } for(int ii=0;ii>-22;ii++) { System.out.println("Enter the text"); String HELLO_REQUEST =stdin.readLine().toString(); if(HELLO_REQUEST.equalsIgnoreCase("end")) { break; } System.out.println("Sending a request to HelloServer"); ByteBuffer buffer = ByteBuffer.wrap(HELLO_REQUEST.getBytes()); sc.write(buffer); } } catch (IOException e) { e.printStackTrace(); } finally { if (sc != null) { try { sc.close(); } catch (Exception e) { e.printStackTrace(); } } } } public void run() { try { coreClient(); } catch(Exception ej) { ej.printStackTrace(); }}} public class ServerCore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void run() { try { coreServer(); } catch(Exception ej) { ej.printStackTrace(); } } private void coreServer() { try { ServerSocketChannel ssc = ServerSocketChannel.open(); try { ssc.socket().bind(new InetSocketAddress(8888)); while (true) { sckt_manager=SelectorProvider.provider().openSelector(); ssc.configureBlocking(false); SocketChannel sc = ssc.accept(); register_server(ssc,SelectionKey.OP_ACCEPT); if (sc == null) { } else { System.out.println("Received an incoming connection from " + sc.socket().getRemoteSocketAddress()); printRequest(sc); System.err.println("testing 1"); String HELLO_REPLY = "Sample Display"; ByteBuffer buffer = ByteBuffer.wrap(HELLO_REPLY.getBytes()); System.err.println("testing 2"); sc.write(buffer); System.err.println("testing 3"); sc.close(); }}} catch (IOException e) { e.printStackTrace(); } finally { if (ssc != null) { try { ssc.close(); } catch (IOException e) { e.printStackTrace(); } } } } catch(Exception E) { System.out.println("Ex in servCORE "+E); } } private static void printRequest(SocketChannel sc) throws IOException { ReadableByteChannel rbc = Channels.newChannel(sc.socket().getInputStream()); WritableByteChannel wbc = Channels.newChannel(System.out); ByteBuffer b = ByteBuffer.allocate(1024); // read 1024 bytes while (rbc.read(b) != -1) { b.flip(); while (b.hasRemaining()) { wbc.write(b); System.out.println(); } b.clear(); } } public void register_server(ServerSocketChannel ssc,int selectionkey_ops)throws Exception { ssc.register(sckt_manager,selectionkey_ops); }} public class HelloClient { public void coreClientChat() { Clientcore t=new Clientcore(); new Thread(t).start(); } public static void main(String[] args)throws Exception { HelloClient cl= new HelloClient(); cl.coreClientChat(); }} public class HelloServer { public void coreServerChat() { ServerCore t=new ServerCore(); new Thread(t).start(); } public static void main(String[] args) { HelloServer st= new HelloServer(); st.coreServerChat(); }}

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  • stop thread that does not get interrupted

    - by prmatta
    I have a thread that sits and reads objects off of an ObjectInputStream: public void run() { try { ois = new ObjectInputStream(clientSocket.getInputStream()); Object o; while ((o = ois.readObject()) != null) { //do something with object } } catch (Exception ex) { //Log exception } } readObject does not throw InterruptedException and as far as I can tell, no exception is thrown when this thread is interrupted. How do I stop this thread?

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  • Physical Cores vs Virtual Cores in Parallelism

    - by Code Curiosity
    When it comes to virtualization, I have been deliberating on the relationship between the physical cores and the virtual cores, especially in how it effects applications employing parallelism. For example, in a VM scenario, if there are less physical cores than there are virtual cores, if that's possible, what's the effect or limits placed on the application's parallel processing? I'm asking, because in my environment, it's not disclosed as to what the physical architecture is. Is there still much advantage to parallelizing if the application lives on a dual core VM hosted on a single core physical machine?

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  • How to implement a Mutex in Python when using Gtk with PyGTK

    - by Julian
    Hi, I have an application that starts several threads using gobject.timeout_add(delay, function) Now in my function I want to test and set on some variable, e.g. def function(self): if flag == True: flag = False doSomething() Now to make this threadsafe, I would have to lock the function using some mutex lock. Is this possible with Gtk? Or can I use the Python Lock objects from threading?

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  • how to write silverlight threading function in another file or project

    - by Piyush
    I am using three tier architecture.I have SilverlightUI and UIController two projects.SilverlightUI contains only UI pages and controls while UIController contains all proxies of WCF services. Now I have created threads to update my controls dynamically and to do processing parallel.AS the requirement I want to define all functionality of threads in UIController projects.What should I do? Currenty what I am doing - private void Button_Click(object sender, RoutedEventArgs e) { StartThreads(); } private void StartThreads() { private Thread _thread1; _thread1 = new Thread(DoThread1); _thread1.Start(); } public static void DoThread1() { _data1.Dispatcher.BeginInvoke(delegate() { _data1.Text = _count1.ToString(); }); System.Threading.Thread.Sleep(1000); } I Want to write DoThread1() method in UIController project and call that function from here button_click()

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  • Efficient implementation of threads in the given scenario

    - by shadeMe
    I've got a winforms application that is set up in the following manner: 2 buttons, a textbox, a collection K, function X and another function, Y. Function X parses a large database and enumerates some of its data in the global collection. Button 1 calls function X. Function Y walks through the above collection and prints out the data in the textbox. Button 2 calls function Y. I'd like to call function X through a worker thread in such a way that: The form remains responsive to user input. This comes intrinsically from the use of a separate thread. There is never more than a single instance of function X running at any point in time. K can be accessed by both functions at all times. What would be the most efficient implementation of the above environment ?

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  • Delegates And Cross Thread Exception

    - by Neo
    Whenever i am updating UI in windows form using delegate it gives me cross thread exception why it is happening like this? is there new thread started for each delegate call ? void Port_DataReceived(object sender, SerialDataReceivedEventArgs e) { //this call delegate to display data clsConnect(statusMsg); } protected void displayResponse(string resp) { //here cross thread exception occur if directly set to lblMsgResp.Text="Test"; if (lblMsgResp.InvokeRequired) { lblMsgResp.Invoke(new MethodInvoker(delegate { lblMsgResp.Text = resp; })); } }

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  • Parallel Processing Simulation in Javascript

    - by le_havre
    Hello, I'm new to JavaScript so forgive me for being a n00b. When there's intensive calculation required, it more than likely involves loops that are recursive or otherwise. Sometimes this may mean having am recursive loop that runs four functions and maybe each of those functions walks the entire DOM tree, read positions and do some math for collision detection or whatever. While the first function is walking the DOM tree, the next one will have to wait its for the first one to finish, and so forth. Instead of doing this, why not launch those loops-within-loops separately, outside the programs, and act on their calculations in another loop that runs slower because it isn't doing those calculations itself? Retarded or clever? Thanks in advance!

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  • ThreadPoolExecutor fixed thread pool with custom behaviour

    - by Simone Margaritelli
    i'm new to this topic ... i'm using a ThreadPoolExecutor created with Executors.newFixedThreadPool( 10 ) and after the pool is full i'm starting to get a RejectedExecutionException . Is there a way to "force" the executor to put the new task in a "wait" status instead of rejecting it and starting it when the pool is freed ? Thanks Issue regarding this https://github.com/evilsocket/dsploit/issues/159 Line of code involved https://github.com/evilsocket/dsploit/blob/master/src/it/evilsocket/dsploit/net/NetworkDiscovery.java#L150

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  • Implement a threading to prevent UI block on a bug in an async function

    - by Marcx
    I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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  • Is it safe to draw three separate QImages in three separate QThreads?

    - by yan bellavance
    I have a QMainWindow with three widgets inside that are promoted to a class containing a subclassed QThread. They each draw on a local QImage in their rexpective qthread which is sent with a signal once its drawn and then rendered by calling update (mandlebrot example) from the slot. Is this safe or dangerous? They do not share any data, at least none that I am generating and am wondering what data they could be sharing that is outside of my coding range ie that is generated by Qt automatically.

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  • What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

    - by Robert S. Barnes
    Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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  • java will this threading setup work or what can i be doing wrong

    - by Erik
    Im a bit unsure and have to get advice. I have the: public class MyApp extends JFrame{ And from there i do; MyServer = new MyServer (this); MyServer.execute(); MyServer is a: public class MyServer extends SwingWorker<String, Object> { MyServer is doing listen_socket.accept() in the doInBackground() and on connection it create a new class Connection implements Runnable { I have the belove DbHelper that are a singleton. It holds an Sqlite connected. Im initiating it in the above MyApp and passing references all the way in to my runnable: class Connection implements Runnable { My question is what will happen if there are two simultaneous read or `write? My thought here was the all methods in the singleton are synchronized and would put all calls in the queue waiting to get a lock on the synchronized method. Will this work or what can i change? public final class DbHelper { private boolean initalized = false; private String HomePath = ""; private File DBFile; private static final String SYSTEM_TABLE = "systemtable"; Connection con = null; private Statement stmt; private static final ContentProviderHelper instance = new ContentProviderHelper (); public static ContentProviderHelper getInstance() { return instance; } private DbHelper () { if (!initalized) { initDB(); initalized = true; } } private void initDB() { DBFile = locateDBFile(); try { Class.forName("org.sqlite.JDBC"); // create a database connection con = DriverManager.getConnection("jdbc:sqlite:J:/workspace/workComputer/user_ptpp"); } catch (SQLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } private File locateDBFile() { File f = null; try{ HomePath = System.getProperty("user.dir"); System.out.println("HomePath: " + HomePath); f = new File(HomePath + "/user_ptpp"); if (f.canRead()) return f; else { boolean success = f.createNewFile(); if (success) { System.out.println("File did not exist and was created " + HomePath); // File did not exist and was created } else { System.out.println("File already exists " + HomePath); // File already exists } } } catch (IOException e) { System.out.println("Maybe try a new directory. " + HomePath); //Maybe try a new directory. } return f; } public String getHomePath() { return HomePath; } private synchronized String getDate(){ SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date date = new Date(); return dateFormat.format(date); } public synchronized String getSelectedSystemTableColumn( String column) { String query = "select "+ column + " from " + SYSTEM_TABLE ; try { stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY); ResultSet rs = stmt.executeQuery(query); while (rs.next()) { String value = rs.getString(column); if(value == null || value == "") return ""; else return value; } } catch (SQLException e ) { e.printStackTrace(); return ""; } finally { } return ""; } }

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  • Thread synchronization and aborting.

    - by kubal5003
    Hello, I've got a little problem with ending the work of one of my threads. First things first so here's the app "layout": Thread 1 - worker thread (C++/CLI) - runs and terminates as expected for(...) { try { if(TabuStop) return; System::Threading::Monitor::Enter("Lock1"); //some work, unmanaged code } finally { if(stop) { System::Threading::Monitor::Pulse("Lock1"); } else { System::Threading::Monitor::Pulse("Lock1"); System::Threading::Monitor::Wait("Lock1"); } } } Thread 2 - display results thread (C#) while (WorkerThread.IsAlive) { lock ("Lock1") { if (TabuEngine.TabuStop) { Monitor.Pulse("Lock1"); } else { Dispatcher.BeginInvoke(RefreshAction); Monitor.Pulse("Lock1"); Monitor.Wait("Lock1", 5000); } } // Thread.Sleep(5000); } I'm trying to shut the whole thing down from app main thread like this: TabuEngine.TabuStop = true; //terminates nicely the worker thread and if (DisplayThread.IsAlive) { DisplayThread.Abort(); } I also tried using DisplayThread.Interrupt, but it always blocks on Monitor.Wait("Lock1", 5000); and I can't get rid of it. What is wrong here? How am I supposed to perform the synchronization and let it do the work that it is supposed to do? //edit I'm not even sure now if the trick with using "Lock1" string is really working and locks are placed on the same object..

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