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• QProcess, QEventLoop - of any use for parallel-processing

  - by dlib

  I wonder whether I could use QEventLoop (QProcess?) to parallelize multiple calls to same function with Qt. What is precisely the difference with QtConcurrent or QThread? What is a process and an event loop more precisely? I read that QCoreApplication must exec() as early as possible in main() method, so that I wonder why it is different from main Thread. could you point as some efficient reference to processes and thread with Qt? I came through the official doc and those things remain unclear. Thanks and regards.

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• How to solve the Winforms Control.Invoke Error?

  - by omn ohnmar

  How to solve the "Control.Invoke must be used to interact with controls created on a separated thread" Error Exception

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• VS2010 + Resharper 5 performance issues

  - by Jeremy Roberts

  I have been using VS2010 with Resharper 5 for several weeks and am having a performance issue. Sometimes when typing, the cursor will lag and the keystrokes won't show instantaneously. Also, scrolling will lag at times. There is a forum thread started and JetBrains has been responding. Several people (including myself) have added their voice and uploaded some performance profiles. If anyone here has has this issue, I would encourage you to visit the thread and let JetBrains know about it. Has anyone had this problem and have a suggestion to restore performance?

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• Creating a dynamic (video) Overlay on Google Maps on Android 2.1

  - by Soumya

  I'm trying to create a map overlay for displaying a video stream (MJPEG) on top of a Mapview. Currently I've a standalone activity that creates a data thread for fetching MJPEG video frames. I'm using a handler to send a frame (as a Bitmap) from the data thread to the main activity which then updates the UI. I'm not sure how I can implement "refresh" for updating my "overlayed" video stream. EDIT: What I mean by "refresh" is - how can I update the video portion (not the mapview) of my UI whenever I get a new video frame. I plan to paint the video frame (bitmap) in the "draw method" of my implementation of the Overlay subclass. But the "draw" method is not invoked by me directly. Thanks.

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• Scala/Erlang use something like greenThread or not ?

  - by CHAPa

  Hi all, Im reading a lot about how scala/Erlang does lightweight threads and your concurrency model ( Actor Model ). Off course, some doubts appear in my head. Scala/Erlang use a approach similar to the old thread model used by java (greenThread) ? for example, suppose that there is a machine with 2 cores, so the scala/erlang environment will fork one thread per processor ? The other threads will be scheduled by user-space( scala VM / erlang vm ) environment. is it correct ? how under the hood that really work ? thanks a lot.

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• Read vector into CUDA shared memory

  - by Ben

  I am new to CUDA and programming GPUs. I need each thread in my block to use a vector of length ndim. So I thought I might do something like this: extern __shared__ float* smem[]; ... if (threadIddx.x == 0) { for (int d=0; d<ndim; ++d) { smem[d] = vector[d]; } } __syncthreads(); ... This works fine. However, I seems wasteful that a single thread should do all loading, so I changed the code to if (threadIdx.x < ndim) { smem[threadIdx.x] = vector[threadIdx.x]; } __syncthreads(); which does not work. Why? It gives different results than the above code even when ndim << blockDim.x.

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• Deadlock error in INSERT statement

  - by Gnanam

  We've got a web-based application. There is a time-bound database operation (INSERTs and UPDATEs) in the application which takes more time to complete, hence this particular flow has been changed into Java Thread so it will not wait (block) for the complete database operation to be completed. My problem is, if more than 1 user come across this particular flow, I'm facing the following error thrown by PostgreSQL: org.postgresql.util.PSQLException: ERROR: deadlock detected Detail: Process 13560 waits for ShareLock on transaction 3147316424; blocked by process 13566. Process 13566 waits for ShareLock on transaction 3147316408; blocked by process 13560. Above error is consistently thrown in INSERT statements. Additional Information: 1) I have PRIMARY KEY defined in this table. 2) There are FOREIGN KEY references in this table. 3) Separate database connection is passed to each Java Thread. Technologies Web Server: Tomcat v6.0.10 Java v1.6.0 Servlet Database: PostgreSQL v8.2.3 Connection Management: pgpool II

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• how to predict which section have to put in critical section in threading

  - by Lalit Dhake

  Hi , I am using the console application i used multi threading in the same. I just want to know which section have to put inside critical section my code is : .------------------------------------------------------------------------------. public class SendBusReachSMS { public void SchedularEntryPoint() { try { List<ActiveBusAndItsPathInfo> ActiveBusAndItsPathInfoList = BusinessLayer.GetActiveBusAndItsPathInfoList(); if (ActiveBusAndItsPathInfoList != null) { //SMSThreadEntryPoint smsentrypoint = new SMSThreadEntryPoint(); while (true) { foreach (ActiveBusAndItsPathInfo ActiveBusAndItsPathInfoObj in ActiveBusAndItsPathInfoList) { if (ActiveBusAndItsPathInfoObj.isSMSThreadActive == false) { DateTime CurrentTime = System.DateTime.Now; DateTime Bustime = Convert.ToDateTime(ActiveBusAndItsPathInfoObj.busObj.Timing); TimeSpan tsa = Bustime - CurrentTime; if (tsa.TotalMinutes > 0 && tsa.TotalMinutes < 5) { ThreadStart starter = delegate { SMSThreadEntryPointFunction(ActiveBusAndItsPathInfoObj); }; Thread t = new Thread(starter); t.Start(); t.Join(); } } } } } } catch (Exception ex) { Console.WriteLine("==========================================="); Console.WriteLine(ex.Message); Console.WriteLine(ex.InnerException); Console.WriteLine("==========================================="); } } public void SMSThreadEntryPointFunction(ActiveBusAndItsPathInfo objActiveBusAndItsPathInfo) { try { //mutThrd.WaitOne(); String consoleString = "Thread for " + objActiveBusAndItsPathInfo.busObj.Number + "\t" + " on path " + "\t" + objActiveBusAndItsPathInfo.pathObj.PathId; Console.WriteLine(consoleString); TrackingInfo trackingObj = new TrackingInfo(); string strTempBusTime = objActiveBusAndItsPathInfo.busObj.Timing; while (true) { trackingObj = BusinessLayer.get_TrackingInfoForSendingSMS(objActiveBusAndItsPathInfo.busObj.Number); if (trackingObj.latitude != 0.0 && trackingObj.longitude != 0.0) { //calculate distance double distanceOfCurrentToDestination = 4.45; TimeSpan CurrentTime = System.DateTime.Now.TimeOfDay; TimeSpan timeLimit = objActiveBusAndItsPathInfo.sessionInTime - CurrentTime; if ((distanceOfCurrentToDestination <= 5) && (timeLimit.TotalMinutes <= 5)) { Console.WriteLine("Message sent to bus number's parents: " + objActiveBusAndItsPathInfo.busObj.Number); break; } } } // mutThrd.ReleaseMutex(); } catch (Exception ex) { //throw; Console.WriteLine("==========================================="); Console.WriteLine(ex.Message); Console.WriteLine(ex.InnerException); Console.WriteLine("==========================================="); } } } Please help me in multithreading. new topic for me in .net

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• SQLiteException Unknown error

  - by -providergeoff.bruckner

  Does anyone know what this means? I'm trying to start a transaction in onActivityResult() to insert a row based on the received result. 03-05 15:39:51.937: ERROR/Database(2387): Failure 21 (out of memory) on 0x0 when preparing 'BEGIN EXCLUSIVE;'. 03-05 15:39:51.967: DEBUG/AndroidRuntime(2387): Shutting down VM 03-05 15:39:51.967: WARN/dalvikvm(2387): threadid=3: thread exiting with uncaught exception (group=0x40013140) 03-05 15:39:51.967: ERROR/AndroidRuntime(2387): Uncaught handler: thread main exiting due to uncaught exception 03-05 15:39:52.137: ERROR/AndroidRuntime(2387): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { (has extras) }} to activity {com.ozdroid/com.ozdroid.load.LoadView}: android.database.sqlite.SQLiteException: unknown error: BEGIN EXCLUSIVE; ... 03-05 15:39:52.137: ERROR/AndroidRuntime(2387): Caused by: android.database.sqlite.SQLiteException: unknown error: BEGIN EXCLUSIVE; ... 03-05 15:39:52.137: ERROR/AndroidRuntime(2387): at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:434)

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• How is 6 trits equal to 9.5 bits?

  - by eSKay

  This reddit thread says 6 trits ~ 9.5 bits. How is 6 trits ~ 9.5 bits?

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• Compiling zip component for PHP 5.2.11 in MAMP PRO

  - by Zlatoroh

  Helo I installed MAMP PRO on my Macbook Pro (10.6) some time ago. Now I would like to use zip functions in php. I found that I must add zip.so to my extension folder and edited php.ini. On my computer I have two different versions of PHP one in MAMP folder and other in user/lib which was pre-installed on my system. Now I wish to compile my zip library for MAMP version. I got zip sources for my version of PHP then in terminal called function /Applications/MAMP/bin/php5/bin/phpize so it uses mamp php version ./configure make then I moved compile zip.so to extensions/no-debug-non-zts-20060613. When MAMP is launched it returns this error: [11-Apr-2010 16:33:27] PHP Warning: PHP Startup: zip: Unable to initialize module Module compiled with module API=20090626, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 Can some body explain to me how to do this the right way.

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• iPhone: Speeding up a search that's polling 17,000 Core Data objects

  - by randombits

  I have a class that conforms to UISearchDisplayDelegate and contains a UISearchBar. This view is responsible for allowing the user to poll a store of about 17,000 objects that are currently managed by Core Data. Everytime the user types in a character, I created an instance of a SearchOperation (subclasses NSOperation) that queries Core Data to find results that might match the search. The code in the search controller looks something like: - (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope { // Update the filtered array based on the search text and scope in a secondary thread if ([searchText length] < 3) { [filteredList removeAllObjects]; // First clear the filtered array. [self setFilteredList:NULL]; [self.tableView reloadData]; return; } NSDictionary *searchdict = [NSDictionary dictionaryWithObjectsAndKeys:scope, @"scope", searchText, @"searchText", nil]; [aSearchQueue cancelAllOperations]; SearchOperation *searchOp = [[SearchOperation alloc] initWithDelegate:self dataDict:searchdict]; [aSearchQueue addOperation:searchOp]; } And my search is rather straight forward. SearchOperation is a subclass of NSOperation. I overwrote the main method with the following code: - (void)main { if ([self isCancelled]) { return; } NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"MyEntity" inManagedObjectContext:managedObjectContext]; NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; [fetchRequest setEntity:entity]; NSPredicate *predicate = NULL; predicate = [NSPredicate predicateWithFormat:@"(someattr contains[cd] %@)", searchText]; [fetchRequest setPredicate:predicate]; NSError *error = NULL; NSArray *fetchResults = [managedObjectContext executeFetchRequest:fetchRequest error:&error]; [fetchRequest release]; if (self.delegate != nil) [self.delegate didFinishSearching:fetchResults]; [pool drain]; } This code works, but it has several issues. It's slow. Even though I have the search happening in a separate thread other than the UI thread, querying 17,000 objects is clearly not optimal. If I'm not careful, crashes can happen. I set the max concurrent searches in my NSOperationQueue to 1 to avoid this. What else can I do to make this search faster? I think preloading all 17,000 objects into memory might be risky. There has to be a smarter way to conduct this search to give results back to the user faster.

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• Asynchronous vs Synchronous vs Threading in an iPhone App

  - by Coocoo4Cocoa

  I'm in the design stage for an app which will utilize a REST web service and sort of have a dilemma in as far as using asynchronous vs synchronous vs threading. Here's the scenario. Say you have three options to drill down into, each one having its own REST-based resource. I can either lazily load each one with a synchronous request, but that'll block the UI and prevent the user from hitting a back navigation button while data is retrieved. This case applies almost anywhere except for when your application requires a login screen. I can't see any reason to use synchronous HTTP requests vs asynchronous because of that reason alone. The only time it makes sense is to have a worker thread make your synchronous request, and notify the main thread when the request is done. This will prevent the block. The question then is bench marking your code and seeing which has more overhead, a threaded synchronous request or an asynchronous request. The problem with asynchronous requests is you need to either setup a smart notification or delegate system as you can have multiple requests for multiple resources happening at any given time. The other problem with them is if I have a class, say a singleton which is handling all of my data, I can't use asynchronous requests in a getter method. Meaning the following won't go: - (NSArray *)users { if(users == nil) users = do_async_request // NO GOOD return users; } whereas the following: - (NSArray *)users { if(users == nil) users == do_sync_request // OK. return users; } You also might have priority. What I mean by priority is if you look at Apple's Mail application on the iPhone, you'll notice they first suck down your entire POP/IMAP tree before making a second request to retrieve the first 2 lines (the default) of your message. I suppose my question to you experts is this. When are you using asynchronous, synchronous, threads -- and when are you using either async/sync in a thread? What kind of delegation system do you have setup to know what to do when a async request completes? Are you prioritizing your async requests? There's a gamut of solutions to this all too common problem. It's simple to hack something out. The problem is, I don't want to hack and I want to have something that's simple and easy to maintain.

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• VirtualTreeView add roots with Threads

  - by Benjamin Weiss

  I would like to add roots to a VirtualTreeView http://www.delphi-gems.com/index.php/controls/virtual-treeview with a thread like this: function AddRoot ( p : TForm1 ) : Integer; stdcall; begin p.VirtualStringTree1.AddChild(NIL); end; var Dummy : DWORD; i : Integer; begin for i := 0 to 2000 do begin CloseHandle(CreateThread(NIL,0, @ADDROOT, Self,0, Dummy)); end; end; The reason for this is that I want to add all connections from my INDY Server to the TreeView. Indy's onexecute/onconnect get's called as a thread. So if 3+ connections come in at the same time the app crashes due to the TreeView. Same is if a client gets disconnected and I want to delete the Node. I am using Delphi7 and Indy9 Any Idea how to fix that?

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• How can I pause a BackgroundWorker? Or something similar...

  - by juan

  I was using a BackgroundWorker to download some web sites by calling WebClient.DownloadString inside a loop. I wanted the option for the user to cancel in the middle of downloading stuff, so I called CancelAsync whenever I found that CancellationPending was on in the middle of the loop. But now I noticed that the function DownloadString kinda freezes sometimes, so I decided to use DownloadStringAsync instead (all this inside the other thread created with BackgroundWorker). An since and don't want to rewrite my whole code by having to exit the loop and the function after calling DownloadStringAsync, I made a while loop right after calling it that does nothing but checks for a variable bool Stop that I turn true either when the DownloadStringCompleted event handler is called or when the user request to cancel the operation. Now, the weird thing is that it works fine on the debug version, but on the release one, the program freezes in the while loop like if it were the main thread.

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• what is a dispatcher

  - by taher chhabra

  can anyone please explain the concept of dispatcher, is it one dispatcher per thread or anything else

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• May the FileInputStream.available foolish me?

  - by Tom Brito

  This FileInputStream.available() javadoc says: Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks. I'm not sure if in this check: if (new FileInputStream(xmlFile).available() == 0) can I rely that empty files will always return zero?

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• custom MSSQL driver

  - by hoodoos

  I had a crazy thought about writing my own MSSQL driver to make it work something like non-blocking http client, so it won't be thread thirsty and could handle lots of db queries within one thread. I tried to look over google for some guidelines about implementing MSSQL client protocol, but found none really, where do those guys get information about it when they write own implementations for PHP or python? I need a really low level to be documented so I can implement all phases of working with a connection through sockets. And would be really nice to have a an example in c# langauge. :)

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• Is there a Java equivalent to libevent?

  - by JoelPM

  I've written a high-throughput server that handles each request in its own thread. For requests coming in it is occasionally necessary to do RPCs to one or more back-ends. These back-end RPCs are handled by a separate queue and thread-pool, which provides some bounding on the number of threads created and the maximum number of connections to the back-end (it does some caching to reuse clients and save the overhead of constantly creating connections). Having done all this, though, I'm beginning to think an event-based architecture would be more efficient. In searching around I haven't found any equivalents to libevent for Java, but maybe I'm not looking in the right place? Mina-statemachine from Apache was the closest thing I found, but it looks more verbose than I need and there's no real release available. Any suggestions?

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• PyQt4, QThread and opening big files without freezing the GUI

  - by jmrbcu

  Hi, I would like to ask how to read a big file from disk and maintain the PyQt4 UI responsive (not blocked). I had moved the load of the file to a QThread subclass but my GUI thread get freezed. Any suggestions? I think it must be something with the GIL but I don't know how to sort it? EDIT: I am using vtkGDCMImageReader from the GDCM project to read a multiframe DICOM image and display it with vtk and pyqt4. I do this load in a different thread (QThread) but my app freeze until the image is loaded. here is an example code: class ReadThread(QThread): def __init__(self, file_name): super(ReadThread, self).__init__(self) self.file_name = file_name self.reader.vtkgdcm.vtkGDCMImageReader() def run(self): self.reader.SetFileName(self.file_name) self.reader.Update() self.emit(QtCore.SIGNAL('image_loaded'), self.reader.GetOutput())

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• Does a multithreaded crawler in Python really speed things up?

  - by beagleguy

  Was looking to write a little web crawler in python. I was starting to investigate writing it as a multithreaded script, one pool of threads downloading and one pool processing results. Due to the GIL would it actually do simultaneous downloading? How does the GIL affect a web crawler? Would each thread pick some data off the socket, then move on to the next thread, let it pick some data off the socket, etc..? Basically I'm asking is doing a multi-threaded crawler in python really going to buy me much performance vs single threaded? thanks!

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• Cleaning up temp folder after long-running subprocess exits

  - by dbr

  I have a Python script (running inside another application) which generates a bunch of temporary images. I then use subprocess to launch an application to view these. When the image-viewing process exists, I want to remove the temporary images. I can't do this from Python, as the Python process may have exited before the subprocess completes. I.e I cannot do the following: p = subprocess.Popen(["imgviewer", "/example/image1.jpg", "/example/image1.jpg"]) p.communicate() os.unlink("/example/image1.jpg") os.unlink("/example/image2.jpg") ..as this blocks the main thread, nor could I check for the pid exiting in a thread etc The only solution I can think of means I have to use shell=True, which I would rather avoid: cmd = ['imgviewer'] cmd.append("/example/image2.jpg") for x in cleanup: cmd.extend(["&&", "rm", x]) cmdstr = " ".join(cmd) subprocess.Popen(cmdstr, shell = True) This works, but is hardly elegant, and will fail with filenames containing spaces etc.. Basically, I have a background subprocess, and want to remove the temp files when it exits, even if the Python process no longer exists.

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• Crash in Reachability API

  - by Marc

  I'm using the Reachability sample code provided by Apple to check the network connectivity and get notified of changes (Reachability Sample code). I had a look at some crash locks of my app. It seems that some crashes are due to the Reachability/SystemConfiguration Reachablity API stuff (see below). SCNetworkReachabilityGetFlags is only used in the Reachability class provided by Apple. Or am I misinterpreting the crash log? Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x00000000, 0x00000000 Crashed Thread: 0 Thread 0 Crashed: 0 libSystem.B.dylib 0x00000e70 mach_msg_trap + 20 1 libSystem.B.dylib 0x00003354 mach_msg + 60 2 SystemConfiguration 0x0001f480 configopen + 168 3 SystemConfiguration 0x00004d08 SCDynamicStoreCreateWithOptions + 272 4 SystemConfiguration 0x00004e54 SCDynamicStoreCreate + 24 5 SystemConfiguration 0x00015244 updateReachabilityStoreInfo + 152 6 SystemConfiguration 0x00016f04 updateCommCenterStatus + 32 7 SystemConfiguration 0x00017678 checkAddress + 1368 8 SystemConfiguration 0x0001a260 __SCNetworkReachabilityGetFlags + 1992 9 SystemConfiguration 0x0001b00c rlsPerform + 132 10 CoreFoundation 0x00058266 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 8 11 CoreFoundation 0x00028692 __CFRunLoopDoSources0 + 214 12 CoreFoundation 0x00027f62 __CFRunLoopRun + 258 13 CoreFoundation 0x00027d74 CFRunLoopRunSpecific + 220 14 CoreFoundation 0x00027c82 CFRunLoopRunInMode + 54 15 GraphicsServices 0x00004e84 GSEventRunModal + 188 16 UIKit 0x00004f8c -[UIApplication _run] + 564 17 UIKit 0x000024cc UIApplicationMain + 964 18 MyApp 0x0000f80c main (main.m:21) 19 MyApp 0x0000f77c start + 44

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• What are the pros and cons of using an in memeory DB rather than a ThreadLocal

  - by Pangea

  we have been using ThreadLocal so far to carry some data so as to not clutter the API. However below are some of issues of using thread local that which I dont like 1) over the years the data items being carried in thread local has increased 2) Since we started using threads (for some light weight processing), we have also migrating these data to the threads in the pool and copying them back again I am thinking of using an in memory DB for these (we doesnt want to add this to the API). I wondering if this approach is good. What r the pros and cons. thx in advance.

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• Java Future and infinite computation

  - by Chris

  I'm trying to optimize an (infinite) computation algorithm. I have an infinte Sum to calculate ( Summ_{n- infinity} (....) ) My idea was to create several threads using the Future < construct, then combine the intermediate results together. My problem hoewer is that I need a certain precision. So I need to constantly calculate the current result while other threads keep calculating. My question is: Is there some sort of result queue where each finished thread can put its results in, while a main thread can receive those results and then either lets the computation continues or terminate the whole ExecutorService? Any Help would really be appreciated! Thanks!

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