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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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  • 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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  • Issue with GCD and too many threads

    - by dariaa
    I have an image loader class which provided with NSURL loads and image from the web and executes completion block. Code is actually quite simple - (void)downloadImageWithURL:(NSString *)URLString completion:(BELoadImageCompletionBlock)completion { dispatch_async(_queue, ^{ // dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ UIImage *image = nil; NSURL *URL = [NSURL URLWithString:URLString]; if (URL) { image = [UIImage imageWithData:[NSData dataWithContentsOfURL:URL]]; } dispatch_async(dispatch_get_main_queue(), ^{ completion(image, URLString); }); }); } When I replace dispatch_async(_queue, ^{ with commented out dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ Images are loading much faster, wich is quite logical (before that images would be loaded one at a time, now a bunch of them are loading simultaneously). My issue is that I have perhaps 50 images and I call downloadImageWithURL:completion: method for all of them and when I use global queue instead of _queue my app eventually crashes and I see there are 85+ threads. Can the problem be that my calling dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0) 50 times in a row makes GCD create too many threads? I thought that gcd handles all the treading and makes sure the number of threads is not huge, but if it's not the case is there any way I can influence number of threads?

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  • C - How to use both aio_read() and aio_write().

    - by Slav
    I implement game server where I need to both read and write. So I accept incoming connection and start reading from it using aio_read() but when I need to send something, I stop reading using aio_cancel() and then use aio_write(). Within write's callback I resume reading. So, I do read all the time but when I need to send something - I pause reading. It works for ~20% of time - in other case call to aio_cancel() fails with "Operation now in progress" - and I cannot cancel it (even within permanent while cycle). So, my added write operation never happens. How to use these functions well? What did I missed? EDIT: Used under Linux 2.6.35. Ubuntu 10 - 32 bit. Example code: void handle_read(union sigval sigev_value) { /* handle data or disconnection */ } void handle_write(union sigval sigev_value) { /* free writing buffer memory */ } void start() { const int acceptorSocket = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in addr; memset(&addr, 0, sizeof(struct sockaddr_in)); addr.sin_family = AF_INET; addr.sin_addr.s_addr = INADDR_ANY; addr.sin_port = htons(port); bind(acceptorSocket, (struct sockaddr*)&addr, sizeof(struct sockaddr_in)); listen(acceptorSocket, SOMAXCONN); struct sockaddr_in address; socklen_t addressLen = sizeof(struct sockaddr_in); for(;;) { const int incomingSocket = accept(acceptorSocket, (struct sockaddr*)&address, &addressLen); if(incomingSocket == -1) { /* handle error ... */} else { //say socket to append outcoming messages at writing: const int currentFlags = fcntl(incomingSocket, F_GETFL, 0); if(currentFlags < 0) { /* handle error ... */ } if(fcntl(incomingSocket, F_SETFL, currentFlags | O_APPEND) == -1) { /* handle another error ... */ } //start reading: struct aiocb* readingAiocb = new struct aiocb; memset(readingAiocb, 0, sizeof(struct aiocb)); readingAiocb->aio_nbytes = MY_SOME_BUFFER_SIZE; readingAiocb->aio_fildes = socketDesc; readingAiocb->aio_buf = mySomeReadBuffer; readingAiocb->aio_sigevent.sigev_notify = SIGEV_THREAD; readingAiocb->aio_sigevent.sigev_value.sival_ptr = (void*)mySomeData; readingAiocb->aio_sigevent.sigev_notify_function = handle_read; if(aio_read(readingAiocb) != 0) { /* handle error ... */ } } } } //called at any time from server side: send(void* data, const size_t dataLength) { //... some thread-safety precautions not needed here ... const int cancellingResult = aio_cancel(socketDesc, readingAiocb); if(cancellingResult != AIO_CANCELED) { //this one happens ~80% of the time - embracing previous call to permanent while cycle does not help: if(cancellingResult == AIO_NOTCANCELED) { puts(strerror(aio_return(readingAiocb))); // "Operation now in progress" /* don't know what to do... */ } } //otherwise it's okay to send: else { aio_write(...); } }

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  • What are some good ways to do intermachine locking?

    - by mike
    Our server cluster consists of 20 machines, each with 10 pids of 5 threads. We'd like some way to prevent any two threads, in any pid, on any machine, from modifying the same object at the same time. Our code's written in Python and runs on Linux, if that helps narrow things down. Also, it's a pretty rare case that two such threads want to do this, so we'd prefer something that optimizes the "only one thread needs this object" case to be really fast, even if it means that the "one thread has locked this object and another one needs it" case isn't great. What are some of the best practices?

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  • Using lock(obj) inside a recursive call

    - by Amby
    As per my understanding a lock is not released until the runtime completes the code block of the lock(obj) ( because when the block completes it calls Monitor.Exit(obj). With this understanding i am not able to understand the reason behind the behaviour of the following code. private static string obj = ""; private static void RecurseSome(int number) { Console.WriteLine(number); lock (obj) { RecurseSome(++number); } } //Call: RecurseSome(0) //Output: 0 1 2 3...... stack overflow exception There must be some concept that i am missing. Please help.

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  • Multithreaded Delegates/Events

    - by Matt
    I am trying to disable parts of the UI in a .NET app based on polling done on a background thread. The background thread checks to see if the global database connection the app uses is still open and operable. What I need to do, and would prefer to do it without polling on the UI thread, is to add an event handler that can be raised by the background thread if the connection status changes. That way, any form can have a handler that will disable those parts of the UI that require the connection to function. Attempting to use a straight event declaration in the class that holds the thread sub, and raising the event in the background thread causing cross-thread execution errors regarding accessing UI controls from other threads. Obviously, there is a correct way to do this, but we have limited experience with events (single threaded apps mainly), and almost none with delegates. I've read through documentation and examples for delegates, and it seems to be closer to what we need, but I'm not sure how to make it work in this instance. The app is written mainly in VB.NET, but an example or help in C# is fine too.

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  • Parallel software?

    - by mavric
    What is the meaning of "parallel software" and what are the differences between "parallel software" and "regular software"? What are its advantages and disadvantages? Does writing "parallel software" require a specific hardware or programming language ?

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  • Best way to implement game loop without freezing UI thread

    - by Matt H
    I'm trying to make a simple 2D game in Java. So far I have a JFrame, with a menubar, and a class which extends JPanel and overrides it's paint method. Now, I need to get a game loop going, where I will update the position of images and so on. However, I'm stuck at how best to achieve this. Should I use multi-threading, because surely, if you put an infinite loop on the main thread, the UI (and thus my menu bar) will freeze up? Here's my code so far: import java.awt.Color; import java.awt.Graphics; import javax.swing.JPanel; @SuppressWarnings("serial") public class GameCanvas extends JPanel { public void paint(Graphics g) { while (true) { g.setColor(Color.DARK_GRAY); try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } } } } import javax.swing.JFrame; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; @SuppressWarnings("serial") public class Main extends JFrame { GameCanvas canvas = new GameCanvas(); final int FRAME_HEIGHT = 400; final int FRAME_WIDTH = 400; public static void main(String args[]) { new Main(); } public Main() { super("Game"); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem startMenuItem = new JMenuItem("Pause"); menuBar.add(fileMenu); fileMenu.add(startMenuItem); super.add(canvas); super.setVisible(true); super.setSize(FRAME_WIDTH, FRAME_WIDTH); super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); super.setJMenuBar(menuBar); } } Any pointers/tips? Also, where should I put my loop? In my main class, or my GameCanvas class? Any help is appreciated, thanks.

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  • VB.NET Two different approaches to generic cross-threaded operations; which is better?

    - by BASnappl
    VB.NET 2010, .NET 4 Hello, I recently read about using SynchronizationContext objects to control the execution thread for some code. I have been using a generic subroutine to handle (possibly) cross-thread calls for things like updating UI controls that utilizes Invoke. I'm an amateur and have a hard time understanding the pros and cons of any particular approach. I am looking for some insight on which approach might be preferable and why. Update: This question is motivated, in part, by statements such as the following from the MSDN page on Control.InvokeRequired. An even better solution is to use the SynchronizationContext returned by SynchronizationContext rather than a control for cross-thread marshaling. Method 1: Public Sub InvokeControl(Of T As Control)(ByVal Control As T, ByVal Action As Action(Of T)) If Control.InvokeRequired Then Control.Invoke(New Action(Of T, Action(Of T))(AddressOf InvokeControl), New Object() {Control, Action}) Else Action(Control) End If End Sub Method 2: Public Sub UIAction(Of T As Control)(ByVal Control As T, ByVal Action As Action(Of Control)) SyncContext.Send(New Threading.SendOrPostCallback(Sub() Action(Control)), Nothing) End Sub Where SyncContext is a Threading.SynchronizationContext object defined in the constructor of my UI form: Public Sub New() InitializeComponent() SyncContext = WindowsFormsSynchronizationContext.Current End Sub Then, if I wanted to update a control (e.g., Label1) on the UI form, I would do: InvokeControl(Label1, Sub(x) x.Text = "hello") or UIAction(Label1, Sub(x) x.Text = "hello") So, what do y'all think? Is one way preferred or does it depend on the context? If you have the time, verbosity would be appreciated! Thanks in advance, Brian

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  • Using the windows api and C++, how could I load an exe from the hard drive and run it in its own thread?

    - by returneax
    For the sake of learning I'm trying to do what the OS does when launching a program ie. parsing a PE file and giving it a thread of execution. If I have two exe's one called foo.exe and the other bar.exe, how could I have foo.exe load the contents of bar.exe into memory then have it execute from there in its own thread? I know how to get it into memory using MapViewOfFile or by simple loading the contents on the hard drive into a buffer. I'm assuming simply copying the contents of bar.exe on disk into its own suspended thread and running it wouldn't work. I am semi-familiar with PE file internals. All help is very much appreciated, of course :)

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  • How can I use multi-threading with a "for" or "foreach" loop?

    - by saafh
    I am trying to run the for loop in a separate thread so that the UI should be responsive and the progress bar is visible. The problem is that I don't know how to do that :). In this code, the process starts in a separate thread, but the next part of the code is executed at the same time. The messageBox is displayed and the results are never returned (e.g. the listbox's selected index property is never set). It doesn't work even if I use, "taskEx.delay()". TaskEx.Run(() => { for (int i = 0; i < sResults.Count(); i++) { if (sResults.ElementAt(i).DisplayIndexForSearchListBox.Trim().Contains(ayaStr)) { lstGoto.SelectedIndex = i; lstGoto_SelectionChanged(lstReadingSearchResults, null); IsIndexMatched = true; break; } } }); //TaskEx.delay(1000); if (IsIndexMatched == true) stkPanelGoto.Visibility = Visibility.Collapsed; else //the index didn't match { MessagePrompt.ShowMessage("The test'" + ayaStr + "' does not exist.", "Warning!"); } Could anyone please tell me how can I use multi-threading with a "for" or "foreach" loop?

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  • synchronized in java - Proper use

    - by ZoharYosef
    I'm building a simple program to use in multi processes (Threads). My question is more to understand - when I have to use a reserved word synchronized? Do I need to use this word in any method that affects the bone variables? I know I can put it on any method that is not static, but I want to understand more. thank you! here is the code: public class Container { // *** data members *** public static final int INIT_SIZE=10; // the first (init) size of the set. public static final int RESCALE=10; // the re-scale factor of this set. private int _sp=0; public Object[] _data; /************ Constructors ************/ public Container(){ _sp=0; _data = new Object[INIT_SIZE]; } public Container(Container other) { // copy constructor this(); for(int i=0;i<other.size();i++) this.add(other.at(i)); } /** return true is this collection is empty, else return false. */ public synchronized boolean isEmpty() {return _sp==0;} /** add an Object to this set */ public synchronized void add (Object p){ if (_sp==_data.length) rescale(RESCALE); _data[_sp] = p; // shellow copy semantic. _sp++; } /** returns the actual amount of Objects contained in this collection */ public synchronized int size() {return _sp;} /** returns true if this container contains an element which is equals to ob */ public synchronized boolean isMember(Object ob) { return get(ob)!=-1; } /** return the index of the first object which equals ob, if none returns -1 */ public synchronized int get(Object ob) { int ans=-1; for(int i=0;i<size();i=i+1) if(at(i).equals(ob)) return i; return ans; } /** returns the element located at the ind place in this container (null if out of range) */ public synchronized Object at(int p){ if (p>=0 && p<size()) return _data[p]; else return null; }

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  • Do really need a count lock on Multi threads with one CPU core?

    - by MrROY
    If i have some code looks like this(Please ignore the syntax, i want to understand it without a specified language): count = 0 def countDown(): count += 1 if __name__ == '__main__': thread1(countDown) thread2(countDown) thread3(countDown) Here i have a CPU with only one core, do i really need a lock to the variable count in case of it could be over-written by other threads. I don't know, but if the language cares a lot, please explain it under Java?C and Python, So many thanks.

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  • Ensuring all waiting threads complete

    - by Daniel
    I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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  • different thread accessing MemoryStream

    - by Wayne
    There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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  • Java Thread - Memory consistency errors

    - by Yatendra Goel
    I was reading a Sun's tutorial on Concurrency. But I couldn't understand exactly what memory consistency errors are? I googled about that but didn't find any helpful tutorial or article about that. I know that this question is a subjective one, so you can provide me links to articles on the above topic. It would be great if you explain it with a simple example.

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  • multi-thread access MySQL error

    - by user188916
    I have written a simple multi-threaded C program to access MySQL,it works fine except when i add usleep() or sleep() function in each thread function. i created two pthreads in the main method, int main(){ mysql_library_init(0,NULL,NULL); printf("Hello world!\n"); init_pool(&p,100); pthread_t producer; pthread_t consumer_1; pthread_t consumer_2; pthread_create(&producer,NULL,produce_fun,NULL); pthread_create(&consumer_1,NULL,consume_fun,NULL); pthread_create(&consumer_2,NULL,consume_fun,NULL); mysql_library_end(); } void * produce_fun(void *arg){ pthread_detach(pthread_self()); //procedure while(1){ usleep(500000); printf("producer...\n"); produce(&p,cnt++); } pthread_exit(NULL); } void * consume_fun(void *arg){ pthread_detach(pthread_self()); MYSQL db; MYSQL *ptr_db=mysql_init(&db); mysql_real_connect(); //procedure while(1){ usleep(1000000); printf("consumer..."); int item=consume(&p); addRecord_d(ptr_db,"test",item); } mysql_thread_end(); pthread_exit(NULL); } void addRecord_d(MYSQL *ptr_db,const char *t_name,int item){ char query_buffer[100]; sprintf(query_buffer,"insert into %s values(0,%d)",t_name,item); //pthread_mutex_lock(&db_t_lock); int ret=mysql_query(ptr_db,query_buffer); if(ret){ fprintf(stderr,"%s%s\n","cannot add record to ",t_name); return; } unsigned long long update_id=mysql_insert_id(ptr_db); // pthread_mutex_unlock(&db_t_lock); printf("add record (%llu,%d) ok.",update_id,item); } the program output errors like: [Thread debugging using libthread_db enabled] [New Thread 0xb7ae3b70 (LWP 7712)] Hello world! [New Thread 0xb72d6b70 (LWP 7713)] [New Thread 0xb6ad5b70 (LWP 7714)] [New Thread 0xb62d4b70 (LWP 7715)] [Thread 0xb7ae3b70 (LWP 7712) exited] producer... producer... consumer...consumer...add record (31441,0) ok.add record (31442,1) ok.producer... producer... consumer...consumer...add record (31443,2) ok.add record (31444,3) ok.producer... producer... consumer...consumer...add record (31445,4) ok.add record (31446,5) ok.producer... producer... consumer...consumer...add record (31447,6) ok.add record (31448,7) ok.producer... Error in my_thread_global_end(): 2 threads didn't exit [Thread 0xb72d6b70 (LWP 7713) exited] [Thread 0xb6ad5b70 (LWP 7714) exited] [Thread 0xb62d4b70 (LWP 7715) exited] Program exited normally. and when i add pthread_mutex_lock in function addRecord_d,the error still exists. So what exactly the problem is?

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  • Do something else if ReadWriteSlimlock is held

    - by user43838
    Hi everyone, I have implemented ReaderWriterLockSlim, Now i don't want it to wait at the lock. I want to do something else if the lock is held. I considered using is isWriterLockHeld but it does not makes much sense to me, Since if two threads come in at the same time and enter the if statement at the same time one will still be waiting at the lock here is my code. ReaderWriterLockSlim rw = GetLoadingLock(parameters); rw = GetLoadingLock(parameters); try { rw.EnterWriteLock(); item = this.retrieveCacheItem(parameters.ToString(), false); if (item != null) { parameters.DataCameFromCache = true; // if the data was found in the cache, return it immediately return item.data; } else { try { object loaditem = null; itemsLoading[parameters.ToString()] = true; loaditem = this.retrieveDataFromStore(parameters); return loaditem; } finally { itemsLoading.Remove(parameters.ToString()); } } } finally { rw.ExitWriteLock(); } Can anyone please guide me in the right direction with this. Thanks

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  • Java, Massive message processing with queue manager (trading)

    - by Ronny
    Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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  • Is a new thread in a Visual Studio test project aborted when the test ends?

    - by Michel
    Hi, i have to do some message exchange with a 3rd party (in a website). When the client posts a page, i start the message exchange. When that doesn't succeed for some reason, i report this to the client by rendering the page with a message. On the background, in a separate thread, i start a process to send abort messages to the 3rd party. I can't do this while the user is waiting for the page to come back, because it might take a few minutes. But in a test project, the test ends when the message to the 3rd party is sent, and after the new thread is started. But it seems that the new thread also ends, when the test is done. Is that normal behaviour? I do start the thread in a new class with a reference to 2 objects from the class which tries to send the message in the first place, may that be a problem?

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  • Is private method in spring service implement class thread safe

    - by Roger Ray
    I got a service in an project using Spring framework. public class MyServiceImpl implements IMyService { public MyObject foo(SomeObject obj) { MyObject myobj = this.mapToMyObject(obj); myobj.setLastUpdatedDate(new Date()); return myobj; } private MyObject mapToMyObject(SomeObject obj){ MyObject myojb = new MyObject(); ConvertUtils.register(new MyNullConvertor(), String.class); ConvertUtils.register(new StringConvertorForDateType(), Date.class); BeanUtils.copyProperties(myojb , obj); ConvertUtils.deregister(Date.class); return myojb; } } Then I got a class to call foo() in multi-thread; There goes the problem. In some of the threads, I got error when calling BeanUtils.copyProperties(myojb , obj); saying Cannot invoke com.my.MyObject.setStartDate - java.lang.ClassCastException@2da93171 obviously, this is caused by ConvertUtils.deregister(Date.class) which is supposed to be called after BeanUtils.copyProperties(myojb , obj);. It looks like one of the threads deregistered the Date class out while another thread was just about to call BeanUtils.copyProperties(myojb , obj);. So My question is how do I make the private method mapToMyObject() thread safe? Or simply make the BeanUtils thread safe when it's used in a private method. And will the problem still be there if I keep the code this way but instead I call this foo() method in sevlet? If many sevlets call at the same time, would this be a multi-thread case as well?

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