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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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  • Java - Call to start method on thread : how does it route to Runnable interface's run () ?

    - by Bhaskar
    Ok , I know the two standard ways to create a new thread and run it in Java : 1 Implement Runnable in a class , define run method ,and pass an instance of the class to a new Thread. When the start method on the thread instance is called , the run method of the class instance will be invoked. 2 Let the class derive from Thread, so it can to override the method run() and then when a new instance's start method is called , the call is routed to overridden method. In both methods , basically a new Thread object is created and its start method invoked. However , while in the second method , the mechanism of the call being routed to the user defined run() method is very clear ,( its a simple runtime polymorphism in play ), I dont understand how the call to start method on the Thread object gets routed to run() method of the class implementing Runnable interface. Does the Thread class have an private field of Type Runnable which it checks first , and if it is set then invokes the run method if it set to an object ? that would be a strange mechanism IMO. How does the call to start() on a thread get routed to the run method of the Runnable interface implemented by the class whose object is passed as a parameter when contructing the thread ?

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  • Class initialization and synchronized class method

    - by nybon
    Hi there, In my application, there is a class like below: public class Client { public synchronized static print() { System.out.println("hello"); } static { doSomething(); // which will take some time to complete } } This class will be used in a multi thread environment, many threads may call the Client.print() method simultaneously. I wonder if there is any chance that thread-1 triggers the class initialization, and before the class initialization complete, thread-2 enters into print method and print out the "hello" string? I see this behavior in a production system (64 bit JVM + Windows 2008R2), however, I cannot reproduce this behavior with a simple program in any environments. In Java language spec, section 12.4.1 (http://java.sun.com/docs/books/jls/second_edition/html/execution.doc.html), it says: A class or interface type T will be initialized immediately before the first occurrence of any one of the following: T is a class and an instance of T is created. T is a class and a static method declared by T is invoked. A static field declared by T is assigned. A static field declared by T is used and the reference to the field is not a compile-time constant (§15.28). References to compile-time constants must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field never cause initialization. According to this paragraph, the class initialization will take place before the invocation of the static method, however, it is not clear if the class initialization need to be completed before the invocation of the static method. JVM should mandate the completion of class initialization before entering its static method according to my intuition, and some of my experiment supports my guess. However, I did see the opposite behavior in another environment. Can someone shed me some light on this? Any help is appreciated, thanks.

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  • C# parameter count mismatch when trying to add AsyncCallback into BeginInvoke()

    - by PunX
    I have main form (PrenosForm) and I am trying to run Form2 asynchronously. It works without callback delegate: this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, null); //works 1. Doesn't work with callback delegate (parameter count mismatch): this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, new AsyncCallback(callBackDelegate), null); //doesn't work parameter count mismatch 2. Works with callback delegate if I do it like this: cp.BeginInvoke(datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt, new AsyncCallback(callBackDelegate), null); //works 3. My question is why does one way work and the other doesn't? I'm new at this. Would anyone be so kind as to answer my question and point out my mistakes? private delegate void copyDelegat(List<ListViewItem> datoteke, string path, PrenosForm forma, DragDropEffects efekt); private delegate void callBackDelegat(IAsyncResult a); public void doCopy(List<ListViewItem> datoteke, string path, PrenosForm forma, DragDropEffects efekt) { new Form2(datoteke, path, forma, efekt); } public void callBackFunc(IAsyncResult a) { AsyncResult res = a.AsyncState as AsyncResult; copyDelegat delegat = res.AsyncDelegate as copyDelegat; delegat.EndInvoke(a); } public void kopiraj(List<ListViewItem> datoteke, DragDropEffects efekt) { copyDelegat cp = new copyDelegat(doCopy); callBackDelegat callBackDelegate = new callBackDelegat(callBackFunc); this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, new AsyncCallback(callBackDelegate), null); //doesn't work parameter count missmatch 2. this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, null); //works 1. cp.BeginInvoke(datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt, new AsyncCallback(callBackDelegate), null); //works 3. }

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  • Does my Dictionary must use locking mechanism?

    - by theateist
    Many threads have access to summary. Each thread will have an unique key for accessing the dictionary; Dictionary<string, List<Result>> summary; Do I need locking for following operations? summary[key] = new List<Result>() summary[key].Add(new Result()); It seems that I don't need locking because each thread will access dictionary with different key, but won't the (1) be problematic because of adding concurrently new record to dictionary with other treads?

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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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  • Best way to identify and dispose locked thread in java.

    - by Bala R
    I have to call a function 3rd party module on a new thread. From what I've seen, the call either completes quickly if everything went well or it just hangs for ever locking up the thread. What's a good way to start the thread and make the call and wait for a few secs and if the thread is still alive, then assuming it's locked up, kill (or stop or abandon) the thread without using any deprecated methods. I have something like this for now, but I'm not sure if this is the best way to do it and I want to avoid calling Thread.stop() as it's deprecated. Thanks. private void foo() throws Exception { Runnable runnable = new Runnable() { @Override public void run() { // stuff that could potentially lock up the thread. } }; Thread thread; thread = new Thread(runnable); thread.start(); thread.join(3500); if (thread.isAlive()) { thread.stop(); throw new Exception(); } }

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  • Polling servers at the same port - Threads and Java

    - by John
    Hi there. I'm currently busy working on an IP ban tool for the early versions of Call of Duty 1. (Apparently such a feature wasn't implemented in these versions). I've finished a single threaded application but it won't perform well enough for multiple servers, which is why I am trying to implement threading. Right now, each server has its own thread. I have a Networking class, which has a method; "GetStatus" -- this method is synchronized. This method uses a DatagramSocket to communicate with the server. Since this method is static and synchronized, I shouldn't get in trouble and receive a whole bunch of "Address already in use" exceptions. However, I have a second method named "SendMessage". This method is supposed to send a message to the server. How can I make sure "SendMessage" cannot be invoked when there's already a thread running in "GetStatus", and the other way around? If I make both synchronized, I will still get in trouble if Thread A is opening a socket on Port 99999 and invoking "SendMessage" while Thread B is opening a socket on the same port and invoking "GetStatus"? (Game servers are usually hosted on the same ports) I guess what I am really after is a way to make an entire class synchronized, so that only one method can be invoked and run at a time by a single thread. Hope that what I am trying to accomplish/avoid is made clear in this text. Any help is greatly appreciated.

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  • Have threads run indefinitely in a java application

    - by TP
    I am trying to program a game in which I have a Table class and each person sitting at the table is a separate thread. The game involves the people passing tokens around and then stopping when the party chime sounds. how do i program the run() method so that once I start the person threads, they do not die and are alive until the end of the game One solution that I tried was having a while (true) {} loop in the run() method but that increases my CPU utilization to around 60-70 percent. Is there a better method?

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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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  • java thread - run() and start() methods

    - by JavaUser
    Please explain the output of the below code: If I call th1.run() ,the output is EXTENDS RUN RUNNABLE RUN If I call th1.start() , the output is : RUNNABLE RUN EXTENDS RUN Why this inconsistency . Please explain. class ThreadExample extends Thread{ public void run(){ System.out.println("EXTENDS RUN"); } } class ThreadExampleRunnable implements Runnable { public void run(){ System.out.println("RUNNABLE RUN "); } } class ThreadExampleMain{ public static void main(String[] args){ ThreadExample th1 = new ThreadExample(); //th1.start(); th1.run(); ThreadExampleRunnable th2 = new ThreadExampleRunnable(); th2.run(); } }

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  • performSelectorInBackground, notify other viewcontroller when done.

    - by Michiel
    Hi, I have a method used to save an image when the user clicks Save. I use performSelectorInBackground to save the image, the viewcontroller is popped and the previous viewcontroller is shown. I want the table (on the previousUIViewController) to reload its data when the imagesaving is done. How can I do this? The save method is called like this: [self performSelectorInBackground:@selector(saveImage) withObject:nil]; [self.navigationController popViewControllerAnimated:YES];

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  • Java: How to test methods that call System.exit()?

    - by Chris Conway
    I've got a few methods that should call System.exit() on certain inputs. Unfortunately, testing these cases causes JUnit to terminate! Putting the method calls in a new Thread doesn't seem to help, since System.exit() terminates the JVM, not just the current thread. Are there any common patterns for dealing with this? For example, can I subsitute a stub for System.exit()? [EDIT] The class in question is actually a command-line tool which I'm attempting to test inside JUnit. Maybe JUnit is simply not the right tool for the job? Suggestions for complementary regression testing tools are welcome (preferably something that integrates well with JUnit and EclEmma).

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  • Protecting critical sections based on a condition in C#

    - by NAADEV
    Hello, I'm dealing with a courious scenario. I'm using EntityFramework to save (insert/update) into a SQL database in a multithreaded environment. The problem is i need to access database to see whether a register with a particular key has been already created in order to set a field value (executing) or it's new to set a different value (pending). Those registers are identified by a unique guid. I've solved this problem by setting a lock since i do know entity will not be present in any other process, in other words, i will not have same guid in different processes and it seems to be working fine. It looks something like that: static readonly object LockableObject = new object(); static void SaveElement(Entity e) { lock(LockableObject) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } But this implies when i have a huge ammount of requests to be saved, they will be queued. I wonder if there is something like that (please, take it just as an idea): static void SaveElement(Entity e) { (using ThisWouldBeAClassToProtectBasedOnACondition protector = new ThisWouldBeAClassToProtectBasedOnACondition(e => e.UniqueId) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } The idea would be having a kind of protection that protected based on a condition so each entity e would have its own lock based on e.UniqueId property. Any idea?

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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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  • Is it multitasking?

    - by Newbie
    Consider the below program myThread = new Thread( new ThreadStart( delegate { Method1(); Method2(); } ) ); Is it that 2 threads are getting called parallely(multitasking) or a single thread is calling the methods sequentially? It's urgent.

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  • Unresponsive UI when using BeginInvoke

    - by Kazoom
    Bckground I have a networked application written in C#. my server program has a UI and several communication threads, that read from tcp sockets and display messages on controller UI. Communication with each client is done through a seprate thread. When i recieve some stream of messages from one client , the thread for that client writes on UI, which is a richtextbox on a Form. I call SetTextHelper(string text) method of the form. which looks like this private delegate void MyTextUpdateHandler(string text); public void SetTextHelper(string text) { BeginInvoke(new MyTextUpdateHandler(SetText), new object[] { text }); } public setText(string text) { richtext.Text= text; } Question - If i use BeginInvoke my UI is entirely unresponsive when i m writing large stream of data to UI - Invoke solves that problem, but i read that for multi threaded environment where many thereads are sharing same resource Invoke can lead to deadlocks I share the common ichtextbox between around 16 threads - What would be a good desing for my situation?

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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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  • 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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  • 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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