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  • Django Thread-Safety for templatetags

    - by Acti67
    Hi, I am coming here, because I have a question about Django and Thread. I read the documentation http://docs.djangoproject.com/en/dev/howto/custom-template-tags/#template-tag-thread-safety and I would like to now if the next code could be impacted also, at the rendering context. class ChatterCountNode(NodeBase): def __init__(self, channelname, varname): self.channelname = channelname self.varname = varname def render(self, context): channelname = self.getvalue(context, self.channelname) varname = self.getvalue(context, self.varname) count = get_channel_count(channelname) context[varname] = count return '' Thank you for your time. Stéphane

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  • How to use timer in a thread

    - by Anjaneyulu
    Hi, I would like to send email notifications to users of my project exactly at 8 a.m, Here we are using a thread to send emails to the user. I would like to send some emails exactly at 8 A.M. How can I execute that perticular logic in this Thread. Please help me.

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  • Thread safety with heap-allocated memory

    - by incrediman
    I was reading this: http://en.wikipedia.org/wiki/Thread_safety Is the following function thread-safe? void foo(int y){ int * x = new int[50]; /*...do some stuff with the allocated memory...*/ delete x; } In the article it says that to be thread-safe you can only use variables from the stack. Really? Why? Wouldn't subsequent calls of the above function allocate memory elsewhere?

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  • final fields and thread-safety

    - by pcjuzer
    Should it be all fields, including super-fields, of a purposively immutable java class 'final' in order to be thread-safe or is it enough to have no modifier methods? Suppose I have a POJO with non-final fields where all fields are type of some immutable class. This POJO has getters-setters, and a constructor wich sets some initial value. If I extend this POJO with knocking out modifier methods, thus making it immutable, will extension class be thread-safe?

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  • C++ thread safety - exchange data between worker and controller

    - by peterchen
    I still feel a bit unsafe about the topic and hope you folks can help me - For passing data (configuration or results) between a worker thread polling something and a controlling thread interested in the most recent data, I've ended up using more or less the following pattern repeatedly: Mutex m; tData * stage; // temporary, accessed concurrently // send data, gives up ownership, receives old stage if any tData * Send(tData * newData) { ScopedLock lock(m); swap(newData, stage); return newData; } // receiving thread fetches latest data here tData * Fetch(tData * prev) { ScopedLock lock(m); if (stage != 0) { // ... release prev prev = stage; stage = 0; } return prev; // now current } Note: This is not supposed to be a full producer-consumer queue, only the msot recent data is relevant. Also, I've skimmed ressource management somewhat here. When necessary I'm using two such stages: one to send config changes to the worker, and for sending back results. Now, my questions assuming that ScopedLock implements a full memory barrier: do stage and/or workerData need to be volatile? is volatile necessary for tData members? can I use smart pointers instead of the raw pointers - say boost::shared_ptr? Anything else that can go wrong? I am basically trying to avoid "volatile infection" spreading into tData, and minimize lock contention (a lock free implementation seems possible, too). However, I'm not sure if this is the easiest solution. ScopedLock acts as a full memory barrier. Since all this is more or less platform dependent, let's say Visual C++ x86 or x64, though differences/notes for other platforms are welcome, too. (a prelimenary "thanks but" for recommending libraries such as Intel TBB - I am trying to understand the platform issues here)

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  • Achieving Thread-Safety

    - by Smasher
    Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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  • Returning pointers in a thread-safe way.

    - by Roddy
    Assume I have a thread-safe collection of Things (call it a ThingList), and I want to add the following function. Thing * ThingList::findByName(string name) { return &item[name]; // or something similar.. } But by doing this, I've delegated the responsibility for thread safety to the calling code, which would have to do something like this: try { list.lock(); // NEEDED FOR THREAD SAFETY Thing *foo = list.findByName("wibble"); foo->Bar = 123; list.unlock(); } catch (...) { list.unlock(); throw; } Obviously a RAII lock/unlock object would simplify/remove the try/catch/unlocks, but it's still easy for the caller to forget. There are a few alternatives I've looked at: Return Thing by value, instead of a pointer - fine unless you need to modify the Thing Add function ThingList::setItemBar(string name, int value) - fine, but these tend to proliferate Return a pointerlike object which locks the list on creation and unlocks it again on destruction. Not sure if this is good/bad practice... What's the right approach to dealing with this?

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  • Killing a deadlocked Task in .NET 4 TPL

    - by Dan Bryant
    I'd like to start using the Task Parallel Library, as this is the recommended framework going forward for performing asynchronous operations. One thing I haven't been able to find is any means of forcible Abort, such as what Thread.Abort provides. My particular concern is that I schedule tasks running code that I don't wish to completely trust. In particular, I can't be sure this untrusted code won't deadlock and therefore I can't be certain if a Task I schedule using this code will ever complete. I want to stay away from true AppDomain isolation (due to the overhead and complexity of marshaling), but I also don't want to leave a Task thread hanging around, deadlocked. Is there a way to do this in TPL?

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  • Identify high CPU consumed thread for Java app

    - by Vincent Ma
    Following java code to emulate busy and Idle thread and start it. import java.util.concurrent.*;import java.lang.*; public class ThreadTest {    public static void main(String[] args) {        new Thread(new Idle(), "Idle").start();        new Thread(new Busy(), "Busy").start();    }}class Idle implements Runnable {    @Override    public void run() {        try {            TimeUnit.HOURS.sleep(1);        } catch (InterruptedException e) {        }    }}class Busy implements Runnable {    @Override    public void run() {        while(true) {            "Test".matches("T.*");        }    }} Using Processor Explorer to get this busy java processor and get Thread id it cost lots of CPU see the following screenshot: Cover to 4044 to Hexadecimal is oxfcc. Using VistulVM to dump thread and get that thread. see the following screenshot In Linux you can use  top -H to get Thread information. That it! Any question let me know. Thanks

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  • Boost.Thread throws bad_alloc exception in VS2010

    - by the_drow
    Upon including <boost/thread.hpp> I get this exception: First-chance exception at 0x7c812afb in CSF.exe: Microsoft C++ exception: boost::exception_detail::clone_impl<boost::exception_detail::bad_alloc_> at memory location 0x0012fc3c.. First-chance exception at 0x7c812afb in CSF.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.. I can't catch it, breaking at the memory location brings me to kernel32.dll and at this point I cannot say what's going on but it appears that the exception is thrown after the program ends and VS is capable of catching it. The testcase: #include <boost/thread.hpp> int main() { return 0; }

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  • NSInvocationOperation and main thread

    - by kpower
    Imagine that I have a view with some UIKit object as its subview (for example, UIActivityIndicatorView - this doesn't matter). This view also has a selector, called doSomething, which somehow manages UIKit object (in our example it can start or stop indicator view). I create NSInvocationOperation (from view's code parts) with initWithTarget:self selector:@selector(doSomething) object:nil. Then add it to NSOperationQueue. And all works fine. How?! It should be a new thread and non-thread-safe UIKit object! Why no error found (and no crash happened)?

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  • How to use thread in Django

    - by zomboid
    I want to check users' subscribed dates for certain period. And send mail to users whose subscription is finishing (ex. reminds two days). I think the best way is using thread and timer to check dates. But I have no idea how to call this function. I don't want to make a separate program or shell. I want to combine this procedure to my django code. I tried to call this function in my settings.py file. But it seems it is not a good idea. It calls the fucntion and creates thread everytime i imported settings.

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  • Thread vs ThreadPool - .Net 2.0

    - by NLV
    Hello I'm not able to understand the difference between Thread vs ThreadPool. Consider i've to manipulate 50,000 records using threads. In case of threads i need to either predefine no of threads or no of records per threads. Either of them has to be constant. In case of threadpool we dont need to set any of them theoretically. But practically we need to assign the number of records per thread, because the no of threads may grow extremely large if the input no of records is huge. Any insights on this?

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  • Adding row to DataGridView from Thread

    - by she hates me
    Hello, I would like to add rows to DataGridView from two seperate threads. I tried something with delegates and BeginInvoke but doesn't work. Here is my row updater function which is called from another function in a thread. public delegate void GRIDLOGDelegate(string ulke, string url, string ip = ""); private void GRIDLOG(string ulke, string url, string ip = "") { if (this.InvokeRequired) { // Pass the same function to BeginInvoke, // but the call would come on the correct // thread and InvokeRequired will be false. object[] myArray = new object[3]; myArray[0] = ulke; myArray[1] = url; myArray[2] = ip; this.BeginInvoke(new GRIDLOGDelegate(GRIDLOG), new object[] { myArray }); return; } //Yeni bir satir daha olustur string[] newRow = new string[] { ulke, url, ip }; dgLogGrid.Rows.Add(newRow); }

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  • localtime_r supposed to be thread safe, but causing errors in Valgrind DRD

    - by Nik
    I searched google as much as I could but I couldn't find any good answers to this. localtime_r is supposed to be a thread-safe function for getting the system time. However, when checking my application with Valgrind --tool=drd, it consistantly tells me that there is a data race condition on this function. Are the common search results lying to me, or am I just missing something? It doesn't seem efficient to surround each localtime_r call with a mutex, especially if it is supposed to by thread safe in the first place. here is how i'm using it: timeval handlerTime; gettimeofday(&handlerTime,NULL); tm handlerTm; localtime_r(&handlerTime.tv_sec,&handlerTm); Any ideas?

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  • [WPF] The calling thread cannot access this object because a different thread owns it.

    - by zunyite
    Why I can't create CroppedBitmap in the following code ? I got an exception : The calling thread cannot access this object because a different thread owns it. public MainWindow() { InitializeComponent(); ThreadPool.QueueUserWorkItem((o) => { //load a large image file var bf = BitmapFrame.Create( new Uri("D:\\1172735642.jpg"), BitmapCreateOptions.DelayCreation | BitmapCreateOptions.IgnoreColorProfile, BitmapCacheOption.None); bf.Freeze(); Dispatcher.BeginInvoke( new Action(() => { CroppedBitmap cb = new CroppedBitmap(bf, new Int32Rect(1,1,5,5)); cb.Freeze(); //set Image's source to cb.... }), System.Windows.Threading.DispatcherPriority.ApplicationIdle); } ); }

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  • Java Thread - Synchronization issue

    - by Yatendra Goel
    From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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  • Python Threading, loading one thread after another

    - by Michael
    Hi, I'm working on a media player and am able to load in a single .wav and play it. As seen in the code below. foo = wx.FileDialog(self, message="Open a .wav file...", defaultDir=os.getcwd(), defaultFile="", style=wx.FD_MULTIPLE) foo.ShowModal() queue = foo.GetPaths() self.playing_thread = threading.Thread(target=self.playFile, args=(queue[0], 'msg')) self.playing_thread.start() But the problem is, when I try to make the above code into a loop for multiple .wav files. Such that while playing_thread.isActive == True, create and .start() the thread. Then if .isActive == False, pop queue[0] and load the next .wav file. Problem is, my UI will lock up and I'll have to terminate the program. Any ideas would be appreciated.

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  • Static dictionary in .Net Thread safety

    - by Emmanuel
    Reading msdn documentation for dictionaries it says : "Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." Those this mean that with a dictionary such as this : static object syncObject = new object(); static Dictionary<string,MyObject> mydictionary= new Dictionary<string, MyObject>(); Is doing something like the code below unnecessary? lock (syncObject) { context = new TDataContext(); mydictionary.Add("key", myObject); }

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  • Optimal strategy to make a C++ hash table, thread safe

    - by Ajeet
    (I am interested in design of implementation NOT a readymade construct that will do it all.) Suppose we have a class HashTable (not hash-map implemented as a tree but hash-table) and say there are eight threads. Suppose read to write ratio is about 100:1 or even better 1000:1. Case A) Only one thread is a writer and others including writer can read from HashTable(they may simply iterate over entire hash table) Case B) All threads are identical and all could read/write. Can someone suggest best strategy to make the class thread safe with following consideration 1. Top priority to least lock contention 2. Second priority to least number of locks My understanding so far is thus : One BIG reader-writer lock(semaphore). Specialize the semaphore so that there could be eight instances writer-resource for case B, where each each writer resource locks one row(or range for that matter). (so i guess 1+8 mutexes) Please let me know if I am thinking on the correct line, and how could we improve on this solution.

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  • OIM 11g : Multi-thread approach for writing custom scheduled job

    - by Saravanan V S
    In this post I have shared my experience of designing and developing an OIM schedule job that uses multi threaded approach for updating data in OIM using APIs.  I have used thread pool (in particular fixed thread pool) pattern in developing the OIM schedule job. The thread pooling pattern has noted advantages compared to thread per task approach. I have listed few of the advantage here ·         Threads are reused ·         Creation and tear-down cost of thread is reduced ·         Task execution latency is reduced ·         Improved performance ·         Controlled and efficient management of memory and resources used by threads More about java thread pool http://docs.oracle.com/javase/tutorial/essential/concurrency/pools.html The following diagram depicts the high-level architectural diagram of the schedule job that process input from a flat file to update OIM process form data using fixed thread pool approach    The custom scheduled job shared in this post is developed to meet following requirement 1)      Need to process a CSV extract that contains identity, account identifying key and list of data to be updated on an existing OIM resource account. 2)      CSV file can contain data for multiple resources configured in OIM 3)      List of attribute to update and mapping between CSV column to OIM fields may vary between resources The following are three Java class developed for this requirement (I have given only prototype of the code that explains how to use thread pools in schedule task) CustomScheduler.java - Implementation of TaskSupport class that reads and passes the parameters configured on the schedule job to Thread Executor class. package com.oracle.oim.scheduler; import java.util.HashMap; import com.oracle.oim.bo.MultiThreadDataRecon; import oracle.iam.scheduler.vo.TaskSupport; public class CustomScheduler extends TaskSupport {      public void execute(HashMap options) throws Exception {             /*  Read Schedule Job Parameters */             String param1 = (String) options.get(“Parameter1”);             .             int noOfThread = (int) options.get(“No of Threads”);             .             String paramn = (int) options.get(“ParamterN”); /* Provide all the required input configured on schedule job to Thread Pool Executor implementation class like 1) Name of the file, 2) Delimiter 3) Header Row Numer 4) Line Escape character 5) Config and resource map lookup 6) No the thread to create */ new MultiThreadDataRecon(all_required_parameters, noOfThreads).reconcile();       }       public HashMap getAttributes() { return null; }       public void setAttributes() {       } } MultiThreadDataRecon.java – Helper class that reads data from input file, initialize the thread executor and builds the task queue. package com.oracle.oim.bo; import <required file IO classes>; import  <required java.util classes>; import  <required OIM API classes>; import <csv reader api>; public class MultiThreadDataRecon {  private int noOfThreads;  private ExecutorService threadExecutor = null;  public MetaDataRecon(<required params>, int noOfThreads)  {       //Store parameters locally       .       .       this.noOfThread = noOfThread;  }        /**        *  Initialize         */  private void init() throws Exception {       try {             // Initialize CSV file reader API objects             // Initialize OIM API objects             /* Initialize Fixed Thread Pool Executor class if no of threads                 configured is more than 1 */             if (noOfThreads > 1) {                   threadExecutor = Executors.newFixedThreadPool(noOfThreads);             } else {                   threadExecutor = Executors.newSingleThreadExecutor();             }             /* Initialize TaskProcess clas s which will be executing task                 from the Queue */                TaskProcessor.initializeConfig(params);       } catch (***Exception e) {                   // TO DO       }  }       /**        *  Method to reconcile data from CSV to OIM        */ public void reconcile() throws Exception {        try {             init();             while(<csv file has line>){                   processRow(line);             }             /* Initiate thread shutdown */             threadExecutor.shutdown();             while (!threadExecutor.isTerminated()) {                 // Wait for all task to complete.             }            } catch (Exception e) {                   // TO DO            } finally {                   try {                         //Close all the file handles                   } catch (IOException e) {                         //TO DO                   }             }       }       /**        * Method to process         */       private void processRow(String row) {             // Create task processor instance with the row data              // Following code push the task to work queue and wait for next                available thread to execute             threadExecutor.execute(new TaskProcessor(rowData));       } } TaskProcessor.java – Implementation of “Runnable” interface that executes the required business logic to update data in OIM. package com.oracle.oim.bo; import <required APIs> class TaskProcessor implements Runnable {       //Initialize required member variables       /**        * Constructor        */       public TaskProcessor(<row data>) {             // Initialize and parse csv row       }       /*       *  Method to initialize required object for task execution       */       public static void initializeConfig(<params>) {             // Process param and initialize the required configs and object       }           /*        * (non-Javadoc)        *         * @see java.lang.Runnable#run()        */            public void run() {             if (<is csv data valid>){                   processData();             }       }  /**   * Process the the received CSV input   */  private void processData() {     try{       //Find the user in OIM using the identity matching key value from CSV       // Find the account to be update from user’s account based on account identifying key on CSV       // Update the account with data from CSV       }catch(***Exception e){           //TO DO       }   } }

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  • Is a 1:* write:read thread system safe?

    - by Di-0xide
    Theoretically, thread-safe code should fix race conditions. Race conditions, as I understand it, occur because two threads attempt to write to the same location at the same time. However, what about a threading model in which a single thread is designed to write to a location, and several slave/worker threads simply read from the location? Assuming the value/timing at which they read the data isn't relevant/doesn't hinder the worker thread's outcome, wouldn't this be considered 'thread safe', or am I missing something in my logic?

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