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• Is it possible to use AsyncTask in a Service class ?

  - by Spredzy

  Everything is in the title. On the official documentations it is stated that Note that services, like other application objects, run in the main thread of their hosting process and AsyncTask only works if it is executed in the UIThread. So is it possible to use AsyncTask in a Service class? I am trying to do so but I'm always getting the same error 05-01 18:09:25.487: ERROR/JavaBinder(270): java.lang.ExceptionInInitializerError ... 05-01 18:09:25.487: ERROR/JavaBinder(270): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() Am I doing something wrong or is this just impossible ?

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• How do I let main thread suspend and wait for the System.Timer.Timer running

  - by Kelvin

  Hi I am using System.Timer.Timer I always get NULL after running my programme and it only works if I add this.sleep(6000). Suppose the reason is the main thread ends but the timer hasn't finished ... Here is the class and I call the class from my main form. Class class1 { string finalResult = ""; public string getNumber() { RunTimer(); return finalResult; } pubic void RunTimer () { timer = new System.Timers.Timer(30000); timer.Interval = 1000; timer.Elapsed += new System.Timers.ElapsedEventHandler(cal); timer.Start(); } private void cal(object sender,System.Timers.ElapsedEventArgs e) { finalResult += READFROMCOMPORT; } }

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• Can someone provide an easy explanation of how 'Full Fences' are implemented in .Net using Threading

  - by Kilhoffer

  I'm clear on the usage of MemoryBarrier, but not on what happens behind the scenes in the runtime. Can anyone give a good explanation of what goes on?

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• Android 2.1: Muliple Handlers in a Single Activity

  - by Soumya Simanta

  Hi, I've more than one Handlers in an Activity. I create all the handlers in the onCreate() of the main activity. My understanding is the handlerMessage() method of each handler will never be called at the same time because all messages are put in the same queue (the Activity thread MessageQueue). Therefore, they will be executed in the order in which are put into the Queue. They will also be executed in the main activity thread. Is this correct ? public void onCreate() { this.handler1 = new Handler() { @Override public void handleMessage(Message msg) { //operation 1 : some operation with instanceVariable1 super.handleMessage(msg); } }; this.handler2 = new Handler() { @Override public void handleMessage(Message msg) { //Operation 2: some operation with instanceVariable1 super.handleMessage(msg); } }; this.handler3 = new Handler() { @Override public void handleMessage(Message msg) { //Operation 3: some operation with instanceVariable1 super.handleMessage(msg); } }; }

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• What image processing Library should I use

  - by Swippen

  I have been reading What is the best image manipulation library? And tried a few libraries and are now looking for inputs on what is the best for our need. I will start by describing our current setting and problems. We have a system that needs to resize and crop a large amount of images from big original images. We handle 50 000+ images every day on 2 powerfull servers. Today we use ImageGlue from WebSupergoo but we don't like it at all, it is slow and hangs the service now and then (Its in another unanswered stack overflow question). We have a threaded windows service that uses Microsoft ThreadPool to resize as much as possible on the 8 core machines. I have tried AForge and it went very well it was loads faster and never crashed or anything. But I had problems with quality on a few images. This due to what algorithms I used ofc so can be tweaked. But want to widen our eyes to see if thats the right way to go. so: It needs to be c# .net and run in a windows service. (Since we wont change the rest of the service only image handling) It needs to handle threaded environment well. We have a great need of it being fast since today its too slow. But we also want good quality and small filesize since the images are later displayed on webpage with loads of visitors and needs good quality. So we have a lot of demands on ability to get god quality at a fast pace, and also secondary keep filesizes lowered even if that can be adjusted with compression a bit. Any comments or suggestions on what library to use?

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• Are indivisible operations still indivisible on multiprocessor and multicore systems?

  - by Steve314

  As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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• WPF update binding in a background thread

  - by Mark

  I have a control that has its data bound to a standard ObservableCollection, and I have a background task that calls a service to get more data. I want to, then, update my backing data behind my control, while displaying a "please wait" dialog, but when I add the new items to the collection, the UI thread locks up while it re-binds and updates my controls. Can I get around this so that my animations and stuff keep running on my "please wait" dialog? Or at least give the "appearance" to the user that its not locked up?

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• Is there a chance that sending an email via a thread could ever fail to complete?

  - by Benjamin Dell

  I have a project where I send a couple of emails via a seperet thread, to speed up the process for the end-user. It works successfully, but i was just wondering whether there were any potfalls that i might not have considered? My greatest fear is that the user clicks a button, it says that the message has been sent (as it will have been sent to the thread for sending) but for some reason the thread might fail to send it. Are there any situations where a thread could be aborted prematurely? Please note, that i am not talking about network outages or obvious issues with an email recipient not existing. For simplicites sake please assume that the connect is up, the mail server alive and the recipient valid. Is it possible, for example, for the thread to abort prematurely if the user kills the browser before the thread has completed? This might be a silly question, but i just wanted to make sure i knew the full ramifications of using a thread in this manner. Thanks, in advance, for your help.

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• Measuring CPU time per-thread on Windows

  - by Eli Courtwright

  I'm developing a long-running multi-threaded Python application for Windows, and I want the process to know the CPU time that each of its threads has taken. I can get the overall times for the entire process with os.times() but I need to know the per-thread times. I know that there are external tools such as the Sysinternals Process Explorer, but my program itself needs to have this information. If I were on Linux, I look in the /proc filesystem, as described here. If I were writing C code, I'd use the GetThreadTimes call, as described here. So how can I accomplish this on Windows using Python?

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• C++ threaded class design from non-threaded class

  - by macs

  I'm working on a library doing audio encoding/decoding. The encoder shall be able to use multiple cores (i.e. multiple threads, using boost library), if available. What i have right now is a class that performs all encoding-relevant operations. The next step i want to take is to make that class threaded. So i'm wondering how to do this. I thought about writing a thread-class, creating n threads for n cores and then calling the encoder with the appropriate arguments. But maybe this is an overkill and there is no need for another class, so i'm going to make use of the "user interface" for thread-creation. I hope there are any suggestions.

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• Thread used for ServiceConnection callback (Android)

  - by Jannick

  Hi I'm developing an activity that binds to a local service (in onCreate of the activity): bindService(new Intent(this, CommandService.class), svcConn, BIND_AUTO_CREATE); I would like to be able to call methods through the IBinder in my lifecycle methods, but can not be sure that onServiceConnected have been called prior to these. I'm thinking of handling this by adding a queue of sorts in the ServiceConnection implementation, so that the method calls (Command pattern) will be executed once the connection is established. My questions are then: Is this stupid, any better ways? :) Are there any specification for which thread will be used to execute the ServiceConnection callbacks? More to the point, do I need to worry about synchronizing a queue datastructure? Edit - something like: public void onServiceConnected(ComponentName name, IBinder service) { dispatchService = (DispatchAsync)service; for(ExecutionTask task : queue){ dispatchService.execute(task.getCommand(), task); } }

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• Safest LAMP encrypt method

  - by Adam Kiss

  Hello, what is PHP's safest encrypt/decrypt method, in use with MySQL - to store let's say passwords? Of course, not for portal purposes. I want to do little password (domain/mysql/ftp...) storage for whole team online, but I don't want really to endanger our clients' bussinesses. Hash can't be used for obvious reasons (Doesn't really make sense to run rainbow tables every time :D). Any idea?

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• Using thread in aspx-page making a webrequest

  - by Mike Ribeiro

  Hi, I kind of new to the hole threading stuff so bare with me here.. I have a aspx-page that takes some input and makes a reqest: HttpWebRequest request = (HttpWebRequest)WebRequest.Create(string.Format("{0}?{1}", strPostPath, strPostData)); request.Method = "GET"; request.Timeout = 5000; // set 5 sec. timeout request.ProtocolVersion = HttpVersion.Version11; try { HttpWebResponse response = (HttpWebResponse)request.GetResponse(); /do some with response } catch (WebException exce) { //Log some stuff } The thing is that this function is used ALOT. Is there any advantage to make every request in a separate thread and exactly how would that look like? Thx!

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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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• Force redraw before long running operations

  - by Joshua

  When you have a button, and do something like: Private Function Button_OnClick Button.Enabled = False [LONG OPERATION] End Function Then the button will not be grayed, because the long operation prevents the UI thread from repainting the control. I know the right design is to start a background thread / dispatcher, but sometimes that's too much hassle for a simple operation. So how do I force the button to redraw in disabled state? I tried .UpdateLayout() on the Button, but it didn't have any effects. I also tried System.Windows.Forms.DoEvents() which normally works when using WinForms, but it also had no effect.

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• Where Does A UIAlertView Live While Not Dismissed

  - by Jim Bonner

  Does anyone know in whose subview an active UIAlertView is located or how to find the thread in which it is running?

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• How can you set a time limit for a PowerShell script to run for?

  - by calrain

  I want to set a time limit on a PowerShell (v2) script so it forcibly exits after that time limit has expired. I see in PHP they have commands like set_time_limit and max_execution_time where you can limit how long the script and even a function can execute for. With my script, a do/while loop that is looking at the time isn't appropriate as I am calling an external code library that can just hang for a long time. I want to limit a block of code and only allow it to run for x seconds, after which I will terminate that code block and return a response to the user that the script timed out. I have looked at background jobs but they operate in a different thread so won't have kill rights over the parent thread. Has anyone dealt with this or have a solution? Thanks!

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• What is wrong with locking non-static fields? What is the correct way to lock a particular instance?

  - by smartcaveman

  Why is it considered bad practice to lock non-static fields? And, if I am not locking non-static fields, then how do I lock an instance method without locking the method on all other instances of the same or derived class? I wrote an example to make my question more clear. public abstract class BaseClass { private readonly object NonStaticLockObject = new object(); private static readonly object StaticLockObject = new object(); protected void DoThreadSafeAction<T>(Action<T> action) where T: BaseClass { var derived = this as T; if(derived == null) { throw new Exception(); } lock(NonStaticLockObject) { action(derived); } } } public class DerivedClass :BaseClass { private readonly Queue<object> _queue; public void Enqueue(object obj) { DoThreadSafeAction<DerivedClass>(x=>x._queue.Enqueue(obj)); } } If I make the lock on the StaticLockObject, then the DoThreadSafeAction method will be locked for all instances of all classes that derive from BaseClass and that is not what I want. I want to make sure that no other threads can call a method on a particular instance of an object while it is locked.

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• How to end a thread in java?

  - by beagleguy

  hi all, I have 2 pools of threads ioThreads = (ThreadPoolExecutor)Executors.newCachedThreadPool(); cpuThreads = (ThreadPoolExecutor)Executors.newFixedThreadPool(numCpus); I have a simple web crawler that I want to create an iothread, pass it a url, it will then fetch the url and pass the contents over to a cpuThread to be processed and the ioThread will then fetch another url, etc... At some point the IO thread will not have any new pages to crawl and I want to update my database that this session is complete. How can I best tell when the threads are all done processing and the program can be ended?

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• SslStream.ReadByte() blocks thread?

  - by alex

  I'm trying to write an Imap4 client. For that I use a SslStream to Connect to the Server. Everything's fine until I send the "Login" command. When I try to get an Answer to it, SslStream.ReadByte() block the thread. The result is that my programm crashes always. Whats happening here?? Code: if (ssl) { s = stream; } int cc = 0; MessageBox.Show("entered"); while (true) { int xs = s.ReadByte(); MessageBox.Show(xs.ToString()); if (xs > 0) { buf.Add((byte)xs); cc++; if (xs == '\n') { break; } if (cc > 10) MessageBox.Show(en.GetString(buf.ToArray())); } else { break; } } MessageBox.Show("left");

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• DOM Storage and locks

  - by user535759

  Since DOM storage and its equivalencies persist in between tabs and windows, I've thought about using it for message passing. The problem is that fetch and store are different operations, and therefore not atomic. I have models that rely on UUID generation, conflict resolutions, and beaconing to do the small subset of what I need to do, but my real question is this: Since the local storage is a shared memory resource, what are the locking mechanisms available for mutual access?

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• Best practices about creating a generic object dictionary in C#? Is this bad?

  - by JimDaniel

  For clarity I am using C# 3.5/Asp.Net MVC 2 Here is what I have done: I wanted the ability to add/remove functionality to an object at run-time. So I simply added a generic object dictionary to my class like this: public Dictionary<int, object> Components { get; set; } Then I can add/remove any kind of .Net object into this dictionary at run-time. To insert an object I do something like this: var tag = new Tag(); myObject.Components.Add((int)Types.Components.Tag, tag); Then to retrieve I just do this: if(myObject.Components.ContainsKey((int)Types.Components.Tag)) { var tag = myObject.Components[(int)Types.Components.Tag] as Tag; if(tag != null) { //do stuff } } Somehow I feel sneaky doing this. It works okay, but I am wondering what you guys think about it as a best practice. Thanks for your input, Daniel

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• ThreadStateException when using QueueUserWorkItem in a Timer

  - by Tim

  Hi all, I have a ThreadStateException in my winforms application. Step to reproduce : Create simple winforms app Add a button In click event, do : timer1.Interval = 1000; timer1.Tick += timer1_Tick; timer1.Start(); void timer1_Tick(object sender, EventArgs e) { ThreadPool.QueueUserWorkItem(delegate { StringCollection paths = new StringCollection { @"c:\my.txt", @"c:\my.png" }; Clipboard.SetFileDropList(paths); }); } The exception tells me : Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it. But the main has already the [STAThread] attribute. How to solve it ? Thanks in advance for any help

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• C++ Static Initializer - Is it thread safe

  - by Yan Cheng CHEOK

  Usually, when I try to initialize a static variable class Test2 { public: static vector<string> stringList; private: static bool __init; static bool init() { stringList.push_back("string1"); stringList.push_back("string2"); stringList.push_back("string3"); return true; } }; // Implement vector<string> Test2::stringList; bool Test2::__init = Test2::init(); Is the following code thread safe, during static variable initialization? Is there any better way to static initialize stringlist, instead of using a seperate static function (init)?

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• Are static delegates thread-safe?

  - by leypascua

  Consider this code snippet: public static class ApplicationContext { private static Func<TService> Uninitialized<TService>() { throw new InvalidOperationException(); } public static Func<IAuthenticationProvider> AuthenticationProvider = Uninitialized<IAuthenticationProvider>(); public static Func<IUnitOfWorkFactory> UnitOfWorkFactory = Uninitialized<IUnitOfWorkFactory>(); } //can also be in global.asax if used in a web app. public static void Main(string[] args) { ApplicationContext.AuthenticationProvider = () => new LdapAuthenticationProvider(); ApplicationContext.UnitOfWorkFactory = () => new EFUnitOfWorkFactory(); } //somewhere in the code.. say an ASP.NET MVC controller ApplicationContext.AuthenticationProvider().SignIn(username, true); Are delegates in the static class ApplicationContext thread-safe in the sense that multiple-threads can invoke them? What potential problems will I face if I pursue this approach?

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