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• Am I correct in my assumption about synchronized block?

  - by kunjaan

  I have a method shout() with a synchronized block. private void shout(){ System.out.println("SHOUT " + Thread.currentThread().getName()); synchronized(this){ System.out.println("Synchronized Shout" + Thread.currentThread().getName()); try { Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Synchronized Shout" + Thread.currentThread().getName()); } } If I have two Threads that run this method, am I correct in assuming that the two "Synchronized Shout" will always appear one after the other? There can be no other statements in between the "Synchronized Shout"?

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• ConcurrentLinkedQueue$Node remains in heap after remove()

  - by action8

  I have a multithreaded app writing and reading a ConcurrentLinkedQueue, which is conceptually used to back entries in a list/table. I originally used a ConcurrentHashMap for this, which worked well. A new requirement required tracking the order entries came in, so they could be removed in oldest first order, depending on some conditions. ConcurrentLinkedQueue appeared to be a good choice, and functionally it works well. A configurable amount of entries are held in memory, and when a new entry is offered when the limit is reached, the queue is searched in oldest-first order for one that can be removed. Certain entries are not to be removed by the system and wait for client interaction. What appears to be happening is I have an entry at the front of the queue that occurred, say 100K entries ago. The queue appears to have the limited number of configured entries (size() == 100), but when profiling, I found that there were ~100K ConcurrentLinkedQueue$Node objects in memory. This appears to be by design, just glancing at the source for ConcurrentLinkedQueue, a remove merely removes the reference to the object being stored but leaves the linked list in place for iteration. Finally my question: Is there a "better" lazy way to handle a collection of this nature? I love the speed of the ConcurrentLinkedQueue, I just cant afford the unbounded leak that appears to be possible in this case. If not, it seems like I'd have to create a second structure to track order and may have the same issues, plus a synchronization concern.

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• Is there an existing solution to the multithreaded data structure problem?

  - by thr

  I've had the need for a multi-threaded data structure that supports these claims: Allows multiple concurrent readers and writers Is sorted Is easy to reason about Fulfilling multiple readers and one writer is a lot easier, but I really would wan't to allow multiple writers. I've been doing research into this area, and I'm aware of ConcurrentSkipList (by Lea based on work by Fraser and Harris) as it's implemented in Java SE 6. I've also implemented my own version of a concurrent Skip List based on A Provably Correct Scalable Concurrent Skip List by Herlihy, Lev, Luchangco and Shavit. These two implementations are developed by people that are light years smarter then me, but I still (somewhat ashamed, because it is amazing work) have to ask the question if these are the two only viable implementations of a concurrent multi reader/writer data structures available today?

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• How can I save an NSDocument concurrently?

  - by Paperflyer

  I have a document based application. Saving the document can take a few seconds, so I want to enable the user to continue using the program while it saves the document in the background. Due to the document architecture, my application is asked to save to a temporary location and that temporary file is then copied over the old file. However, this means that I can not just run my file saving code in the background and return way before it is done, since the temporary file has to be written completely before it can be copied. Is there a way to disable this temporary-file-behavior or otherwise enable file saving in the background?

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• Will thread.join() block other clients also?

  - by maxp

  In an asp.net web application, say everytime the user makes the request, and the page loads, a thread is fired off that uses thread.join() to block execution until it's finished. Say this thread takes 10 seconds to complete. Does this mean that if 5 totally seperate users make a request to this page, mere miliseconds after the last, does this mean the last user is going to wait 50 seconds to finish their request? Or is each client request threaded?

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• Actionscript 3 : XML cached in local testing

  - by Boun

  Hi, My question is about XML loading. I need to avoid xml caching. On a web server, the technique is adding a random param to reload each time the XML file. But on local testing (in Flash CS4 IDE, CTRL + Enter), the following lines are not possible : var my_date : Date; path = "toto.xml?time="+my_date.getSeconds()+my_date.getMilliseconds(); Is there any trick to bypass this issue ? I've read on different forum about the "delete" method, we delete the xml object and then recreate one new. In my case, I put : myXML = null; myXML = new XML ( loadedData ); But it doesn't work at all. I spent many hours on that problem, if anyone has a good solution... Thank you.

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• Help with java executors: wait for task termination.

  - by Raffo

  I need to submit a number of task and then wait for them until all results are available. Each of them adds a String to a Vector (that is synchronized by default). Then I need to start a new task for each result in the Vector but I need to do this only when all the previous tasks have stopped doing their job. I want to use Java Executor, in particular I tried using Executors.newFixedThreadPool(100) in order to use a fixed number of thread (I have a variable number of task that can be 10 or 500) but I'm new with executors and I don't know how to wait for task termination. This is something like a pseudocode of what my program needs to do: EecutorService e = Executors.newFixedThreadPool(100); while(true){ /*do something*/ for(...){ <start task> } <wait for all task termination> for each String in result{ <start task> } <wait for all task termination> } I can't do a e.shutdown because I'm in a while(true) and I need to reuse the executorService... Can you help me? Can you suggest me a guide/book about java executors??

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• How to check what the value of app concurrent requests are in IIS

  - by Shiraz Bhaiji

  In step 4 of this link there is a description of how to set the maximum concurrent request in IIS throught scripts. Is it possible to see what these values are set to, either through the IIS UI, or in the registry?

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• Python sock.listen(...)

  - by Ian

  All the examples I've seen of sock.listen(5) in the python documentation suggest I should set the max backlog number to be 5. This is causing a problem for my app since I'm expecting some very high volume (many concurrent connections). I set it to 200 and haven't seen any problems on my system, but was wondering how high I can set it before it causes problems.. Anyone know?

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• App only spawns one thread

  - by tipu

  I have what I thought was a thread-friendly app, and after doing some output I've concluded that of the 15 threads I am attempting to run, only one does. I have if __name__ == "__main__": fhf = FileHandlerFactory() tweet_manager = TweetManager("C:/Documents and Settings/Administrator/My Documents/My Dropbox/workspace/trie/Tweet Search Engine/data/partitioned_raw_tweets/raw_tweets.txt.001") start = time.time() for i in range(15): Indexer(tweet_manager, fhf).start() Then in my thread-entry point, I do def run(self): print(threading.current_thread()) self.index() That results in this: <Indexer(Thread-3, started 1168)> So of 15 threads that I thought were running, I'm only running one. Any idea as to why? Edit: code

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• Find messages[from-to]

  - by Alfred

  I would like to return all messages from certain key to a certain key. The class should be thread-safe and old keys should be able to be deleted say for example after 30 seconds. I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the items from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement this or maybe use a library?

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• C# Is it possible to interrupt a specific thread inside a ThreadPool?

  - by Lirik

  Suppose that I've queued a work item in a ThreadPool, but the work item blocks if there is no data to process (reading from a BlockingQueue). If the queue is empty and there will be no more work going into the queue, then I must call the Thread.Interrupt method if I want to interrupt the blocking task, but how does one do the same thing with a ThreadPool? The code might look like this: void Run() { try { while(true) { blockingQueue.Dequeue(); doSomething(); } } finally { countDownLatch.Signal(); } } I'm aware that the best thing to do in this situation is use a regular Thread, but I'm wondering if there is a ThreadPool equivalent way to interrupt a work item.

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• Mongomapper - unit testing with shoulda on rails 2.3.5

  - by egarcia

  I'm trying to implement shoulda unit tests on a rails 2.3.5 app using mongomapper. So far I've: Configured a rails app that uses mongomapper (the app works) Added shoulda to my gems, and installed it with rake gems:install Added config.frameworks -= [ :active_record, :active_resource ] to config/environment.rb so ActiveRecord isn't used. My models look like this: class Account include MongoMapper::Document key :name, String, :required => true key :description, String key :company_id, ObjectId key :_type, String belongs_to :company many :operations end My test for that model is this one: class AccountTest < Test::Unit::TestCase should_belong_to :company should_have_many :operations should_validate_presence_of :name end It fails on the first should_belong_to: ./test/unit/account_test.rb:3: undefined method `should_belong_to' for AccountTest:Class (NoMethodError) Any ideas why this doesn't work? Should I try something different from shoulda? I must point out that this is the first time I try to use shoulda, and I'm pretty new to testing itself.

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• XCode - Copy sqlite DB from simulator and copy onto device for testing

  - by Neal L

  Hello, I am working on a Core Data app, and have populated the sqlite file in the iPhone Simulator with all of the fixtures/data that I use to test the app. I would like to use that sqlite file as a standardized set of testing data. The devices that I test the app on all have different data sets, and I would like to standardize on the one in the simulator. Is there a way in XCode (3 or 4) to add a step to the build/install process that will copy the sqlite file from the iPhone Simulator and install it over the file on the phone (if one exists)? Thanks, Neal

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• Cross Browser Testing on Virtual Machines - Issues?

  - by codemate2112

  I am part of an organization in which there is contention amongst some very competent folks as to whether or not testing cross-browser behavior for JavaScript applications on virtual machines (for IE6/7/8, FF2/3, Chrome on XP/Vista/7) is reliable. This is using VMWare server on a Linux box host. While the discrepancies seen are few, there are cases in which it has proven difficult to tell if it is a product of virtualization or just different machine configurations. My question to the community is, what is people experience with this? Is there any credence to the claim that VM pose inconsistencies, or are they generally spot-on reliable? Can we trust them?

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• automatic enter login credentials while testing my app (from visual studio 2008)

  - by Michel

  Hi all, this is something that i don't want to program, but i was looking for a handy way of logging on to my web app. i'm building (and testing and running) my webapp over and over again, and here i've been provided a strong password. needless to say it's not so nice to enter my full user name + strong password 30 times a day. is there a nifty tool which lives in the background and when i open page localhost/mytestpage.aspx, it will say: "hey, let me type in michel and sdfs%^%gfhg in these two textboxes"?

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• Java: Implement own message queue (threadsafe)

  - by derMax

  The task is to implement my own messagequeue that is thread safe. My approach: public class MessageQueue { /** * Number of strings (messages) that can be stored in the queue. */ private int capacity; /** * The queue itself, all incoming messages are stored in here. */ private Vector<String> queue = new Vector<String>(capacity); /** * Constructor, initializes the queue. * * @param capacity The number of messages allowed in the queue. */ public MessageQueue(int capacity) { this.capacity = capacity; } /** * Adds a new message to the queue. If the queue is full, it waits until a message is released. * * @param message */ public synchronized void send(String message) { //TODO check } /** * Receives a new message and removes it from the queue. * * @return */ public synchronized String receive() { //TODO check return "0"; } } If the queue is empty and I call remove(), I want to call wait() so that another thread can use the send() method. Respectively, I have to call notifyAll() after every iteration. Question: Is that possible? I mean does it work that when I say wait() in one method of an object, that I can then execute another method of the same object? And another question: Does that seem to be clever?

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• Registry corrupted for testing?

  - by Emile

  Hi. Forgive my ignorance. I'm a lowly LAMP stack developer and this is my first post for "c++". We had an Internet Explorer add-on commissioned but then lost support. Allegedly each version has to be have been tested "on a fresh computer since old add-ons could have cause registry errors." I'm not familiar with IE add-on development (or c++ dev). Is this common? Can't one simply reverse registry errors? How to continue testing iterations on one machine? Thanks!

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• Scala and the Java Memory Model

  - by Ben Lings

  The Java Memory Model (since 1.5) treats final fields differently to non-final fields. In particular, provided the this reference doesn't escape during construction, writes to final fields in the constructor are guaranteed to be visible on other threads even if the object is made available to the other thread via a data race. (Writes to non-final fields aren't guaranteed to be visible, so if you improperly publish them, another thread could see them in a partially constructed state.) Is there any documentation on how/if the Scala compiler creates final (rather than non-final) backing fields for classes? I've looked through the language specification and searched the web but can't find any definitive answers. (In comparison the @scala.volatile annotation is documented to mark a field as volatile)

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• How does volatile actually work?

  - by FredOverflow

  Marking a variable as volatile in Java ensures that every thread sees the value that was last written to it instead of some stale value. I was wondering how this is actually achieved. Does the JVM emit special instructions that flush the CPU cashes or something?

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• Java - Multithreading !

  - by Gogi

  If a thread holds a lock , what happens when the thread needs to enter another critical section controlled by the same lock?

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• Webapp: safetly update a shared List/Map in the AppContext

  - by al nik

  I've Lists and Maps in my WebAppContext. Most of the time these are only read by multiple Threads but sometimes there's the need to update or add some data. I'm wondering what's the best way to do this without incurring in a ConcurrentModificationException. I think that using CopyOnWriteArrayList I can achieve what I want in terms of - I do not have to sync on every read operation- I can safety update the list while other threads are reading it. Is this the best solution? What about Maps?

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• Watin testing of FckEditor

  - by Iyyengar

  I have been working on the integration testing of a webapp using watin. The webapp uses fckeditor as one of the richtext controls. Here is the piece of html of the viewsource of my webapp that includes fckeditor iframe id="ctl00_HeaderMain_txtSafetyNetDescription___Frame" src="/FCKEditor/editor/fckeditor.html?InstanceName=ctl00_HeaderMain_txtSafetyNetDescription&Toolbar=myApp" width="100%" height="200px" frameborder="no" scrolling="no" /iframe By using the watin script ... i am able to get the frame object with the following code. Frame frame = ie.Frame(Find.ById("ctl00_HeaderMain_txtSafetyNetDescription___Frame")) ; Now I want to write some text to the fckeditor. But i am not sure how to write to the fckeditor as it is a frame -- can someone help me on this. Thanks. Iyyengar.

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• Must all Concurrent Data Store (CDB) locks be explicitly released when closing a Berkeley DB?

  - by Steve Emmerson

  I have an application that comprises multiple processes each accessing a single Berkeley DB Concurrent Data Store (CDB) database. Each process is single-threaded and does no explicit locking of the database. When each process terminates normally, it calls DB-close() and DB_ENV-close(). When all processes have terminated, there should be no locks on the database. Episodically, however, the database behaves as if some process was holding a write-lock on it even though all processes have terminated normally. Does each process need to explicitly release all locks before calling DB_ENV-close()? If so, how does the process obtain the "locker" parameter for the call to DB_ENV-loc_vec()?

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• Testing file existence using NSURL

  - by Peter Hosey

  Snow Leopard introduced many new methods to use NSURL objects to refer to files, not pathnames or Core Services' FSRefs. However, there's one task I can't find a URL-based method for: Testing whether a file exists. I'm looking for a URL-based version of -[NSFileManager fileExistsAtPath:]. Like that method, it should return YES if the URL describes anything, whether it's a regular file, a directory, or anything else. I could attempt to look up various resource values, but none of them are explicitly guaranteed to not exist if the file doesn't, and some of them (e.g., NSURLEffectiveIconKey) could be costly if it does. I could just use NSFileManager's fileExistsAtPath:, but if there's a more modern method, I'd prefer to use that. Is there a simple method or function in Cocoa, CF, or Core Services that's guaranteed/documented to tell me whether a given file (or file-reference) URL refers to a file-system object that exists?

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