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  • How would you implement this "WorkerChain" functionality in .NET?

    - by Dan Tao
    Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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  • How do I create a thread-safe write-once read-many value in Java?

    - by Software Monkey
    This is a problem I encounter frequently in working with more complex systems and which I have never figured out a good way to solve. It usually involves variations on the theme of a shared object whose construction and initialization are necessarily two distinct steps. This is generally because of architectural requirements, similar to applets, so answers that suggest I consolidate construction and initialization are not useful. By way of example, let's say I have a class that is structured to fit into an application framework like so: public class MyClass { private /*ideally-final*/ SomeObject someObject; MyClass() { someObject=null; } public void startup() { someObject=new SomeObject(...arguments from environment which are not available until startup is called...); } public void shutdown() { someObject=null; // this is not necessary, I am just expressing the intended scope of someObject explicitly } } I can't make someObject final since it can't be set until startup() is invoked. But I would really like it to reflect it's write-once semantics and be able to directly access it from multiple threads, preferably avoiding synchronization. The idea being to express and enforce a degree of finalness, I conjecture that I could create a generic container, like so: public class WoRmObject<T> { private T object; WoRmObject() { object=null; } public WoRmObject set(T val) { object=val; return this; } public T get() { return object; } } and then in MyClass, above, do: private final WoRmObject<SomeObject> someObject; MyClass() { someObject=new WoRmObject<SomeObject>(); } public void startup() { someObject.set(SomeObject(...arguments from environment which are not available until startup is called...)); } Which raises some questions for me: Is there a better way, or existing Java object (would have to be available in Java 4)? Is this thread-safe provided that no other thread accesses someObject.get() until after it's set() has been called. The other threads will only invoke methods on MyClass between startup() and shutdown() - the framework guarantees this. Given the completely unsynchronized WoRmObject container, it is ever possible under either JMM to see a value of object which is neither null nor a reference to a SomeObject? In other words, does has the JMM always guaranteed that no thread can observe the memory of an object to be whatever values happened to be on the heap when the object was allocated.

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  • Issue accessing class variable from thread.

    - by James
    Hello, The code below is meant to take an arraylist of product objects as an input, spun thread for each product(and add the product to the arraylist 'products'), check product image(product.imageURL) availability, remove the products without images(remove the product from the arraylist 'products'), and return an arraylist of products with image available. package com.catgen.thread; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import com.catgen.Product; import com.catgen.Utils; public class ProductFilterThread extends Thread{ private Product product; private List<Product> products = new ArrayList<Product>(); public ProductFilterThread(){ } public ProductFilterThread(Product product){ this.product = product; } public synchronized void addProduct(Product product){ System.out.println("Before add: "+getProducts().size()); getProducts().add(product); System.out.println("After add: "+getProducts().size()); } public synchronized void removeProduct(Product product){ System.out.println("Before rem: "+getProducts().size()); getProducts().remove(product); System.out.println("After rem: "+getProducts().size()); } public synchronized List<Product> getProducts(){ return this.products; } public synchronized void setProducts(List<Product> products){ this.products = products; } public void run(){ boolean imageExists = Utils.fileExists(this.product.ImageURL); if(!imageExists){ System.out.println(this.product.ImageURL); removeProduct(this.product); } } public List<Product> getProductsWithImageOnly(List<Product> products){ ProductFilterThread pft = null; try{ List<ProductFilterThread> threads = new ArrayList<ProductFilterThread>(); for(Product product: products){ pft = new ProductFilterThread(product); addProduct(product); pft.start(); threads.add(pft); } Iterator<ProductFilterThread> threadsIter = threads.iterator(); while(threadsIter.hasNext()){ ProductFilterThread thread = threadsIter.next(); thread.join(); } }catch(Exception e){ e.printStackTrace(); } System.out.println("Total returned products = "+getProducts().size()); return getProducts(); } } Calling statement: displayProducts = new ProductFilterThread().getProductsWithImageOnly(displayProducts); Here, when addProduct(product) is called from within getProductsWithImageOnly(), getProducts() returns the list of products, but that's not the case(no products are returned) when the method removeProduct() is called by a thread, because of which the products without images are never removed. As a result, all the products are returned by the module whether or not the contained products have images. What can be the problem here? Thanks in advance. James.

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  • Which async call use for DB connection and still responsive GUI?--

    - by Jade
    Hi, My application connects to MSSQL but sometimes it takes a while and the GUI is getting frozen. I would like to do the connection on the other thread, I guess BeginInvoke would be the best way (I know about background worker but I would like to learn this). I have studied MSDN page but I did not understand what is the best way to use? They also say that you can use only callback when the thread that called the async.method does not need to know the results...I dont understand it as I believe I can set some variable in the other thread to "pass" the result well. I would just need the GUI to be not frozen while the connection is being established. Thank you for your advice.

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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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  • Creating new process with Lua interpreater, failures in passing argumets

    - by user1131997
    I need help with passing arguments in CreateProcess() //Windows I want to: BOOL status = CreateProcess(L"C:\\Program Files (x86)\\Lua\\lua52.exe", NULL, NULL, NULL, FALSE, NULL, NULL, NULL, &si, &pi); But with passing some arguments.... Lua interpreater accepts file with lua-scripts, so I have prepared it and want to do: lua52 C:\1.lua for example... I have the path of some lua-script and want the interpreater of Lua to interpreate it and than get the result of program on Lua from Created process. I have tried in some ways to do it, but no success. Please, help! Thank you!

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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 improve multi-threaded access to Cache (custom implementation)

    - by Andy
    I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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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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  • WinForm-style Invoke() in unmanaged C++

    - by Matt Green
    I've been playing with a DataBus-type design for a hobby project, and I ran into an issue. Back-end components need to notify the UI that something has happened. My implementation of the bus delivers the messages synchronously with respect to the sender. In other words, when you call Send(), the method blocks until all the handlers have called. (This allows callers to use stack memory management for event objects.) However, consider the case where an event handler updates the GUI in response to an event. If the handler is called, and the message sender lives on another thread, then the handler cannot update the GUI due to Win32's GUI elements having thread affinity. More dynamic platforms such as .NET allow you to handle this by calling a special Invoke() method to move the method call (and the arguments) to the UI thread. I'm guessing they use the .NET parking window or the like for these sorts of things. A morbid curiosity was born: can we do this in C++, even if we limit the scope of the problem? Can we make it nicer than existing solutions? I know Qt does something similar with the moveToThread() function. By nicer, I'll mention that I'm specifically trying to avoid code of the following form: if(! this->IsUIThread()) { Invoke(MainWindowPresenter::OnTracksAdded, e); return; } being at the top of every UI method. This dance was common in WinForms when dealing with this issue. I think this sort of concern should be isolated from the domain-specific code and a wrapper object made to deal with it. My implementation consists of: DeferredFunction - functor that stores the target method in a FastDelegate, and deep copies the single event argument. This is the object that is sent across thread boundaries. UIEventHandler - responsible for dispatching a single event from the bus. When the Execute() method is called, it checks the thread ID. If it does not match the UI thread ID (set at construction time), a DeferredFunction is allocated on the heap with the instance, method, and event argument. A pointer to it is sent to the UI thread via PostThreadMessage(). Finally, a hook function for the thread's message pump is used to call the DeferredFunction and de-allocate it. Alternatively, I can use a message loop filter, since my UI framework (WTL) supports them. Ultimately, is this a good idea? The whole message hooking thing makes me leery. The intent is certainly noble, but are there are any pitfalls I should know about? Or is there an easier way to do this?

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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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  • multi-thread in MS Access, async processing

    - by LanguaFlash
    I know that title sounds crazy but here is my situation. After a certain user event I need to update a couple tables that are "unrelated" to what the user is currently doing. Currently this takes a couple seconds to execute and causes the user a certain amount of frustration. Is there a way to perform my update in a second process or in a manner that doesn't "freeze" the UI of my app while it is processing? Thanks

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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 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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  • 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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  • 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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  • Invoking different methods on threads

    - by Kraken
    I have a main process main. It creates 10 threads (say) and then what i want to do is the following: while(required){ Thread t= new Thread(new ClassImplementingRunnable()); t.start(); counter++; } Now i have the list of these threads, and for each thread i want to do a set of process, same for all, hence i put that implementation in the run method of ClassImplementingRunnable. Now after the threads have done their execution, i wan to wait for all of them to stop, and then evoke them again, but this time i want to do them serially not in parallel. for this I join each thread, to wait for them to finish execution but after that i am not sure how to evoke them again and run that piece of code serially. Can i do something like for(each thread){ t.reevoke(); //how can i do that. t.doThis(); // Also where does `dothis()` go, given that my ClassImplementingRunnable is an inner class. } Also, i want to use the same thread, i.e. i want the to continue from where they left off, but in a serial manner. I am not sure how to go about the last piece of pseudo code. Kindly help. Working with with java.

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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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  • 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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