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  • Is background tasks the solution for this problem?

    - by Trinca
    Hi. I need to develop an enterprise app that monitors the network traffic. Basically it detects if the user is in wi-fi or cellular data and save the amount of bytes was sent and received in a period of time. I saw an App at the AppStore that do exactly this job. Detecting wi-fi or cellular data is quite simple using the Reachability Sample provided by Apple. My problem is to keep monitoring the bytes sent and received while the app is in background. As it is an enterprise App, I used UIBackgroundModes "voip" to avoid the app to be terminated. I also installed the setKeepAliveTimeout method and I'm able to see the logs each 10 minutes, BUT only for 10 seconds after the method runs. I mean, setKeepAliveTimeout brings my App to run a Timer for 10 seconds each 1o minutes. I'm thinking wether or not a task in background is the best solution for my problem. I'll appreciate any comments. EDIT: Ok guys. Thats the perfect way to do it. First of all you must read this: http://www.christian-fries.de/blog/files/tag-ios.html I tried this and it works really fine. All we need to do is to create a second thread detached from the main one. This way we have a continuos threading running forever. You must see the GCD docs at Apple's website also. Second thing you should consider for an enterprise App is to set it up as a voip App, this way iOS will put your App running even after a reboot. It's a special behavior iOS has to keep voip Apps running. Thats it guys. I hope it can help you.

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  • iPhone - return from an NSOperation

    - by lostInTransit
    Hi I am using a subclass of NSOperation to do some background processes. I want the operation to be cancelled when the user clicks a button. Here's what my NSOperation subclass looks like - (id)init{ self = [super init]; if(self){ //initialization code goes here _isFinished = NO; _isExecuting = NO; } return self; } - (void)start { if (![NSThread isMainThread]) { [self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:NO]; return; } [self willChangeValueForKey:@"isExecuting"]; _isExecuting = YES; [self didChangeValueForKey:@"isExecuting"]; //operation goes here } - (void)finish{ //releasing objects here [self willChangeValueForKey:@"isExecuting"]; [self willChangeValueForKey:@"isFinished"]; _isExecuting = NO; _isFinished = YES; [self didChangeValueForKey:@"isExecuting"]; [self didChangeValueForKey:@"isFinished"]; } - (void)cancel{ [self willChangeValueForKey:@"isCancelled"]; [self didChangeValueForKey:@"isCancelled"]; [self finish]; } And this is how I am adding objects of this class to a queue and listening for KVO notifications operationQueue = [[NSOperationQueue alloc] init]; [operationQueue setMaxConcurrentOperationCount:5]; [operationQueue addObserver:self forKeyPath:@"operations" options:0 context:&OperationsChangedContext]; - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if (context == &OperationsChangedContext) { NSLog(@"Queue size: %u", [[operationQueue operations] count]); } else { [super observeValueForKeyPath:keyPath ofObject:object change:change context:context]; } } To cancel an operation (on a button click for instance), I tried calling -cancel but it doesn't make a difference. Also tried calling -finish but even that doesn't change anything. Every time I add an operation to the queue, the queue size only increases. finish is called (checked using NSLog statements) but it doesn't really end the operation. I'm still not very confident I'm doing this right Can someone please tell me where I am going wrong? Thanks a lot

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  • Looking for a lock-free RT-safe single-reader single-writer structure

    - by moala
    Hi, I'm looking for a lock-free design conforming to these requisites: a single writer writes into a structure and a single reader reads from this structure (this structure exists already and is safe for simultaneous read/write) but at some time, the structure needs to be changed by the writer, which then initialises, switches and writes into a new structure (of the same type but with new content) and at the next time the reader reads, it switches to this new structure (if the writer multiply switches to a new lock-free structure, the reader discards these structures, ignoring their data). The structures must be reused, i.e. no heap memory allocation/free is allowed during write/read/switch operation, for RT purposes. I have currently implemented a ringbuffer containing multiple instances of these structures; but this implementation suffers from the fact that when the writer has used all the structures present in the ringbuffer, there is no more place to change from structure... But the rest of the ringbuffer contains some data which don't have to be read by the reader but can't be re-used by the writer. As a consequence, the ringbuffer does not fit this purpose. Any idea (name or pseudo-implementation) of a lock-free design? Thanks for having considered this problem.

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  • Hibernate AssertionFailure in different Threads

    - by bladepit
    I connect to my database with one session. I have always the same session in my hole program. My Thread "1" catches primary data from the database. The user must be allowed to cancel this thread. So if the user presses the cancel button to often or to fast (this is my interpretation) the following error occures: ERROR org.hibernate.AssertionFailure - HHH000099: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session) org.hibernate.AssertionFailure: possible non-threadsafe access to the session The same errors occures if i cancel my thread "2" which is running in the background after my thread "1" ist finished and the try to load another primary data set from the database. Is the failure that i am using the same session in my two threads? What is the right way to solve such a problem?

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  • Running multiple image manipulations in parallel causing OutOfMemory exception

    - by Tom
    I am working on a site where I need to be able to split and image around 4000x6000 into 4 parts (amongst many other tasks) and I need this to be as quick as possible for multiple users. My current code for doing this is var bitmaps = new RenderTargetBitmap[elements.Length]; using (var stream = blobService.Stream(key)) { BitmapImage bi = new BitmapImage(); bi.BeginInit(); bi.StreamSource = stream; bi.EndInit(); for (var i = 0; i < elements.Length; i++) { var element = elements[i]; TransformGroup transformGroup = new TransformGroup(); TranslateTransform translateTransform = new TranslateTransform(); translateTransform.X = -element.Left; translateTransform.Y = -element.Top; transformGroup.Children.Add(translateTransform); DrawingVisual vis = new DrawingVisual(); DrawingContext cont = vis.RenderOpen(); cont.PushTransform(transformGroup); cont.DrawImage(bi, new Rect(new Size(bi.PixelWidth, bi.PixelHeight))); cont.Close(); RenderTargetBitmap rtb = new RenderTargetBitmap(element.Width, element.Height, 96d, 96d, PixelFormats.Default); rtb.Render(vis); bitmaps[i] = rtb; } } for (var i = 0; i < bitmaps.Length; i++) { using (MemoryStream ms = new MemoryStream()) { PngBitmapEncoder encoder = new PngBitmapEncoder(); encoder.Frames.Add(BitmapFrame.Create(bitmaps[i])); encoder.Save(ms); var regionKey = WebPath.Variant(key, elements[i].Id); saveBlobService.Save("image/png", regionKey, ms); } } I am running multiple threads which take jobs off a queue. I am finding that if this part of code is hit by 4 threads at once I get an OutOfMemory exception. I can stop this happening by wrapping all the code above in a lock(obj) but this isn't ideal. I have tried wrapping just the first using block (where the file is read from disk and split) but I still get the out of memory exceptions (this part of the code executes quite quickly). I this normal considering the amount of memory this should be taking up? Are there any optimisations I could make? Can I increase the memory available? UPDATE: My new code as per Moozhe's help public static void GenerateRegions(this IBlobService blobService, string key, Element[] elements) { using (var stream = blobService.Stream(key)) { foreach (var element in elements) { stream.Position = 0; BitmapImage bi = new BitmapImage(); bi.BeginInit(); bi.SourceRect = new Int32Rect(element.Left, element.Top, element.Width, element.Height); bi.StreamSource = stream; bi.EndInit(); DrawingVisual vis = new DrawingVisual(); DrawingContext cont = vis.RenderOpen(); cont.DrawImage(bi, new Rect(new Size(element.Width, element.Height))); cont.Close(); RenderTargetBitmap rtb = new RenderTargetBitmap(element.Width, element.Height, 96d, 96d, PixelFormats.Default); rtb.Render(vis); using (MemoryStream ms = new MemoryStream()) { PngBitmapEncoder encoder = new PngBitmapEncoder(); encoder.Frames.Add(BitmapFrame.Create(rtb)); encoder.Save(ms); var regionKey = WebPath.Variant(key, element.Id); blobService.Save("image/png", regionKey, ms); } } } }

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  • Make Python Socket Server More Efficient

    - by BenMills
    I have very little experience working with sockets and multithreaded programming so to learn more I decided to see if I could hack together a little python socket server to power a chat room. I ended up getting it working pretty well but then I noticed my server's CPU usage spiked up over 100% when I had it running in the background. Here is my code in full: http://gist.github.com/332132 I know this is a pretty open ended question so besides just helping with my code are there any good articles I could read that could help me learn more about this? My full code: import select import socket import sys import threading from daemon import Daemon class Server: def __init__(self): self.host = '' self.port = 9998 self.backlog = 5 self.size = 1024 self.server = None self.threads = [] self.send_count = 0 def open_socket(self): try: self.server = socket.socket(socket.AF_INET6, socket.SOCK_STREAM) self.server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) self.server.bind((self.host,self.port)) self.server.listen(5) print "Server Started..." except socket.error, (value,message): if self.server: self.server.close() print "Could not open socket: " + message sys.exit(1) def remove_thread(self, t): t.join() def send_to_children(self, msg): self.send_count = 0 for t in self.threads: t.send_msg(msg) print 'Sent to '+str(self.send_count)+" of "+str(len(self.threads)) def run(self): self.open_socket() input = [self.server,sys.stdin] running = 1 while running: inputready,outputready,exceptready = select.select(input,[],[]) for s in inputready: if s == self.server: # handle the server socket c = Client(self.server.accept(), self) c.start() self.threads.append(c) print "Num of clients: "+str(len(self.threads)) self.server.close() for c in self.threads: c.join() class Client(threading.Thread): def __init__(self,(client,address), server): threading.Thread.__init__(self) self.client = client self.address = address self.size = 1024 self.server = server self.running = True def send_msg(self, msg): if self.running: self.client.send(msg) self.server.send_count += 1 def run(self): while self.running: data = self.client.recv(self.size) if data: print data self.server.send_to_children(data) else: self.running = False self.server.threads.remove(self) self.client.close() """ Run Server """ class DaemonServer(Daemon): def run(self): s = Server() s.run() if __name__ == "__main__": d = DaemonServer('/var/servers/fserver.pid') if len(sys.argv) == 2: if 'start' == sys.argv[1]: d.start() elif 'stop' == sys.argv[1]: d.stop() elif 'restart' == sys.argv[1]: d.restart() else: print "Unknown command" sys.exit(2) sys.exit(0) else: print "usage: %s start|stop|restart" % sys.argv[0] sys.exit(2)

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  • C#: WebBrowser.Navigated Only Fires when I MessageBox.Show();

    - by tsilb
    I have a WebBrowser control which is being instantiated dynamically from a background STA thread because the parent thread is a BackgroundWorker and has lots of other things to do. The problem is that the Navigated event never fires, unless I pop a MessageBox.Show() in the method that told it to .Navigate(). I shall explain: ThreadStart ts = new ThreadStart(GetLandingPageContent_ChildThread); Thread t = new Thread(ts); t.SetApartmentState(ApartmentState.STA); t.Name = "Mailbox Processor"; t.Start(); protected void GetLandingPageContent_ChildThread() { WebBrowser wb = new WebBrowser(); wb.Navigated += new WebBrowserNavigatedEventHandler(wb_Navigated); wb.Navigate(_url); MessageBox.Show("W00t"); } protected void wb_Navigated(object sender, WebBrowserNavigatedEventArgs e) { WebBrowser wb = (WebBrowser)sender; // Breakpoint HtmlDocument hDoc = wb.Document; } This works fine; but the messagebox will get in the way since this is an automation app. When I remove the MessageBox.Show(), the WebBrowser.Navigated event never fires. I've tried supplanting this line with a Thread.Sleep(), and by suspending the parent thread. Once I get this out of the way, I intend to Suspend the parent thread while the WebBrowser is doing its job and find some way of passing the resulting HTML back to the parent thread so it can continue with further logic. Why does it do this? How can I fix it? If someone can provide me with a way to fetch the content of a web page, fill out some data, and return the content of the page on the other side of the submit button, all against a webserver that doesn't support POST verbs nor passing data via QueryString, I'll also accept that answer as this whole exercise will have been unneccessary.

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  • Scala Actors with Java interop to underlying COM libraries

    - by wheaties
    I'm working on a JVM project which uses ESRI components (COM based, wrapped with JIntegra.) The client has requested the JAR files we produce work on the JVM and be accessible to Java code. I'd like to use Scala but I'm worried about how well the library will play with Scala's actors. Particularly I'm worried about the different mechanisms COM and Java employ to pass objects from one thread to another. Does anyone have any experience with this? Will they play nice? Edit: for clarification I noticed that when performing I/O on the ESRI DB that the CPU utilization is roughly 15%. I'd like to read each row and pass that row over to another actor for parsing. Then I could have several threads reading from the DB at once. The problem is that each row retrieved using ESRI's library is actually a Java wrapped COM object.

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  • Using Java Executor on AppEngine causes AccessControlException

    - by Drew
    How do you get java.util.concurrent.Executor or CompletionService to work on Google AppEngine? The classes are all officially white-listed, but I get a runtime security error when trying to submit asynchronous tasks. Code: // uses the async API but this factory makes it so that tasks really // happen sequentially Executor executor = java.util.concurrent.Executors.newSingleThreadExecutor(); // wrap Executor in CompletionService CompletionService<String> completionService = new ExecutorCompletionService<String>(executor); final SomeTask someTask = new SomeTask(); // this line throws exception completionService.submit(new Callable<String>(){ public String call() { return someTask.doNothing("blah"); } }); // alternately, send Runnable task directly to Executor, // which also throws an exception executor.execute(new Runnable(){ public void run() { someTask.doNothing("blah"); } }); } private class SomeTask{ public String doNothing(String message){ return message; } } Exception: java.security.AccessControlException: access denied (java.lang.RuntimePermission modifyThreadGroup) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:323) at java.security.AccessController.checkPermission(AccessController.java:546) at java.lang.SecurityManager.checkPermission(SecurityManager.java:532) at com.google.appengine.tools.development.DevAppServerFactory$CustomSecurityManager.checkPermission(DevAppServerFactory.java:166) at com.google.appengine.tools.development.DevAppServerFactory$CustomSecurityManager.checkAccess(DevAppServerFactory.java:191) at java.lang.ThreadGroup.checkAccess(ThreadGroup.java:288) at java.lang.Thread.init(Thread.java:332) at java.lang.Thread.(Thread.java:565) at java.util.concurrent.Executors$DefaultThreadFactory.newThread(Executors.java:542) at java.util.concurrent.ThreadPoolExecutor.addThread(ThreadPoolExecutor.java:672) at java.util.concurrent.ThreadPoolExecutor.addIfUnderCorePoolSize(ThreadPoolExecutor.java:697) at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:652) at java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:590) at java.util.concurrent.ExecutorCompletionService.submit(ExecutorCompletionService.java:152) This code works fine when run on Tomcat or via command-line JVM. However, it chokes in the AppEngine SDK Jetty container (tried with Eclipse plugin and the maven-gae-plugin). AppEngine is likely designed to not allow potentially dangerous programs to run, so I could see them completely disabling thread creation. However, why would Google allow you to create a class, but not allow you to call methods on it? White-listing java.util.concurrent is misleading. Is there some other way to do parallel/simultaneous/concurrent tasks on GAE?

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  • Databinding in WinForms performing async data import

    - by burnside
    I have a scenario where I have a collection of objects bound to a datagrid in winforms. If a user drags and drops an item on to the grid, I need to add a placeholder row into the grid and kick off a lengthy async import process. I need to communicate the status of the async import process back to the UI, updating the row in the grid and have the UI remain responsive to allow the user to edit the other rows. What's the best practice for doing this? My current solution is: binding a thread safe implementation of BindingList to the grid, filled with the objects that are displayed as rows in the grid. When a user drags and drops an item on to the grid, I create a new object containing the sparse info obtained from the dropped item and add that to the BindingList, disabling the editing of that row. I then fire off a separate thread to do the import, passing it the newly bound object I have just created to fill with data. The import process, periodically sets the status of the object and fires an event which is subscribed to by the UI telling it to refresh the grid to see the new properties on the object. Should I be passing the same object that is bound to the grid to the import process thread to operate on, or should I be creating a copy and merging back the changes to the object on the UI thread using BeginInvoke? Any problems or advice with this implementation? Thanks

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  • .NET or Windows Synchronization Primitives Performance Specifications

    - by ovanes
    Hello *, I am currently writing a scientific article, where I need to be very exact with citation. Can someone point me to either MSDN, MSDN article, some published article source or a book, where I can find performance comparison of Windows or .NET Synchronization primitives. I know that these are in the descending performance order: Interlocked API, Critical Section, .NET lock-statement, Monitor, Mutex, EventWaitHandle, Semaphore. Many Thanks, Ovanes P.S. I found a great book: Concurrent Programming on Windows by Joe Duffy. This book is written by one of the head concurrency developers for .NET Framework and is simply brilliant with lots of explanations, how things work or were implemented.

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  • C# threads - Posting messages between threads

    - by Harsha
    Hi All, I am working on a project which involves reusing as well as migrating some of the existing MFC code to C#. The current code in MFC, creates some threads and uses ::PostthreadeMessage() and ON_THREAD_MESSAGE(msg,func) for inter thread asynchronous communication through messages. ::PostthreadeMessage() - sends a message to a particular thread id. ON_THREAD_MESSAGE(msg,func) - calls the function(func) when a message(msg) is received. Since i am not much aware of the threading interfaces in C#, i tried to search for similar API's in C#, but was not able to find any. It would be great, if somebody can help me in finding the appropriate functions for this purpose in C# Thanks, Harsha

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  • Multi-threading mechanisms to run some lengthy operations from winforms code and communication with

    - by tmarouda
    What do I want to achieve: I want to perform some time consuming operations from my MDI winforms application (C# - .NET). An MDI child form may create the thread with the operation, which may take long time (from 0.1 seconds, to even half hour) to complete. In the meantime I want the UI to respond to user actions, including manipulation of data in some other MDI child form. When the operation completes, the thread should notify the MDI child that the calculations are done, so that the MDI child can perform the post-processing. How can I achieve this: Should I use explicit threading (i.e., create explicit threads), thread pools? Or simply just propose your solution. Should I create foreground or background threads? And how does the thread communicates with the GUI, according the solution you propose? If you know of a working example that handles a similar situation, please make a note.

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  • Is ACE reactor timer managment thread safe?

    - by idimba
    I have a module that manages timers in my aplication. This class has basibly three functions: Instance of ACE_Reactor is used internally by the module to manage the timers. schedule timer - calls ACE_Reactor::schedule_timer(). One of the arguments is a callback, called upon timer experation. cancel timer - calls ACE_Reactor::cancel_timer() The reactor executed in private timer of execution, so schedule/cancel and timeout callback are executed in different threads. ACE_Reactor::schedule_timer() receives a heap allocatec structure ( arg argument). This structure later deleted when canceling timer or when timeout handler is called. But since cancel and timeout handler are executed in different threads it looks like there's cases that the structure is deleted twice. Isn't it responsibility of reactor to ensure that timer is canceled when timeout handler is called?

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  • Timer or Thread?

    - by Pradeep Singh
    I have a method(say method1) that writes to database(sqlserver)and another method(say method2) that tries to access the same database after some time and updates the data row that was created by method1. The problem arises when method1 fails to access db due to the LAN being disconnected (this is not an exception this is a scenario that will definitely arise in my software, getting into details will make the question too complex) if method1 fails to access db method2 cannot work. What I want to do is to make method1 store values to local db instead of server if the LAN is disconnected and as soon as it enters value in local db the application should start trying to access the server after ever 10-15 seconds. What should I use timer or create a new thread?

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  • Ruby - Immutable Objects

    - by Chris Bunch
    I've got a highly multithreaded app written in Ruby that shares a few instance variables. Writes to these variables are rare (1%) while reads are very common (99%). What is the best way (either in your opinion or in the idiomatic Ruby fashion) to ensure that these threads always see the most up-to-date values involved? Here's some ideas so far that I had (although I'd like your input before I overhaul this): Have a lock that most be used before reading or writing any of these variables (from Java Concurrency in Practice). The downside of this is that it puts a lot of synchronize blocks in my code and I don't see an easy way to avoid it. Use Ruby's freeze method (see here), although it looks equally cumbersome and doesn't give me any of the synchronization benefits that the first option gives. These options both seem pretty similar but hopefully anyone out there will have a better idea (or can argue well for one of these ideas). I'd also be fine with making the objects immutable so they aren't corrupted or altered in the middle of an operation, but I don't know Ruby well enough to make the call on my own and this question seems to argue that objects are highly mutable.

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  • Effective thread Synchronization in C#

    - by n0vic3c0d3r
    I have a scenario where I need to search from many binary files (using keys) and combine the results (strings). Until now, I have been doing it in a for loop one file after the other. foreach (string file in FileSources.Keys) { aggregatedDefinitions.Append(DefinitionLookup(txtSearchWord.Text, file)); } Since this operation is very slow, I was thinking of using threads, so that I could do IO operations in parallel. Is threading the right way to go. If I use threading, how can I ensure that I get the results in the order I want. I haven't used Threading until now. It would be very helpful if you could suggest some materials/books that would help me solve my problem.

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  • running multi threads in Java

    - by owca
    My task is to simulate activity of couple of persons. Each of them has few activities to perform in some random time: fast (0-5s), medium(5-10s), slow(10-20s) and very slow(20-30s). Each person performs its task independently in the same time. At the beginning of new task I should print it's random time, start the task and then after time passes show next task's time and start it. I've written run() function that counts time, but now it looks like threads are done one after another and not in the same time or maybe they're just printed in this way. public class People{ public static void main(String[] args){ Task tasksA[]={new Task("washing","fast"), new Task("reading","slow"), new Task("shopping","medium")}; Task tasksM[]={new Task("sleeping zzzzzzzzzz","very slow"), new Task("learning","slow"), new Task(" :** ","slow"), new Task("passing an exam","slow") }; Task tasksJ[]={new Task("listening music","medium"), new Task("doing nothing","slow"), new Task("walking","medium") }; BusyPerson friends[]={ new BusyPerson("Alice",tasksA), new BusyPerson("Mark",tasksM), new BusyPerson("John",tasksJ)}; System.out.println("STARTING....................."); for(BusyPerson f: friends) (new Thread(f)).start(); System.out.println("DONE........................."); } } class Task { private String task; private int time; private Task[]tasks; public Task(String t, String s){ task = t; Speed speed = new Speed(); time = speed.getSpeed(s); } public Task(Task[]tab){ Task[]table=new Task[tab.length]; for(int i=0; i < tab.length; i++){ table[i] = tab[i]; } this.tasks = table; } } class Speed { private static String[]hows = {"fast","medium","slow","very slow"}; private static int[]maxs = {5000, 10000, 20000, 30000}; public Speed(){ } public static int getSpeed( String speedString){ String s = speedString; int up_limit=0; int down_limit=0; int time=0; //get limits of time for(int i=0; i<hows.length; i++){ if(s.equals(hows[i])){ up_limit = maxs[i]; if(i>0){ down_limit = maxs[i-1]; } else{ down_limit = 0; } } } //get random time within the limits Random rand = new Random(); time = rand.nextInt(up_limit) + down_limit; return time; } } class BusyPerson implements Runnable { private String name; private Task[] person_tasks; private BusyPerson[]persons; public BusyPerson(String s, Task[]t){ name = s; person_tasks = t; } public BusyPerson(BusyPerson[]tab){ BusyPerson[]table=new BusyPerson[tab.length]; for(int i=0; i < tab.length; i++){ table[i] = tab[i]; } this.persons = table; } public void run() { int time = 0; double t1=0; for(Task t: person_tasks){ t1 = (double)t.time/1000; System.out.println(name+" is... "+t.task+" "+t.speed+ " ("+t1+" sec)"); while (time == t.time) { try { Thread.sleep(10); } catch(InterruptedException exc) { System.out.println("End of thread."); return; } time = time + 100; } } } } And my output : STARTING..................... DONE......................... Mark is... sleeping zzzzzzzzzz very slow (36.715 sec) Mark is... learning slow (10.117 sec) Mark is... :** slow (29.543 sec) Mark is... passing an exam slow (23.429 sec) Alice is... washing fast (1.209 sec) Alice is... reading slow (23.21 sec) Alice is... shopping medium (11.237 sec) John is... listening music medium (8.263 sec) John is... doing nothing slow (13.576 sec) John is... walking medium (11.322 sec) Whilst it should be like this : STARTING..................... DONE......................... John is... listening music medium (7.05 sec) Alice is... washing fast (3.268 sec) Mark is... sleeping zzzzzzzzzz very slow (23.71 sec) Alice is... reading slow (15.516 sec) John is... doing nothing slow (13.692 sec) Alice is... shopping medium (8.371 sec) Mark is... learning slow (13.904 sec) John is... walking medium (5.172 sec) Mark is... :** slow (12.322 sec) Mark is... passing an exam very slow (27.1 sec)

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  • multi thread in c question

    - by REALFREE
    Does mutex guarantee to execute thread in order of arriving? that is, if, thread 2 and thread 3 arrive is waiting while thread 1 is in critical section what exactly happen after thread 1 exit critical section if thread 2 arrive at mutex lock before thread 3, thread 2 will be allowed to enter critical section before thread 3 ? or race condition will be occurred?

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  • Thread and two dimensional array in objective C?

    - by mactonny
    Hey, guys, I am just starting to wrap my head around objective C and I am doing a little project on Iphone. And I just encountered a weird problem. I had to deal with images in my program so I have a lot local variables declared like temp[width][height]. If I am not using NSThread to perform image processing, it works all fine. However, if I use NSThread, it'll keep giving me EXC_BAD_ACCESS on whenever I try to access a 2-D array declared like temp[widht][height]. So I have to allocate memory from heap in order to have a 2-D array. That'll solve the problem but I still don't get it. My first thought would be stack over flow, but it worked all fine with one thread. I just don't get it.

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  • multi thread apps crashes in release mode

    - by etzarfat
    Hello, I'm using Visual Studio 2008 (programming in c). I've a weird problem I worte a program that has 2 threads that runs simultaneously, a recording thread (using audio card to record into memory) and a translation thread (using a speech engine to recognize the words). when I run my program in debug mode (aka setting a breakpoint in the code) it runs great, however when I run in debug mode or release mode (outside the visual studio enviroment) it crashes and give me the following exception: "Unhandled exception at 0x7c911129 in LowLevel.exe: 0xC0000005: Access violation reading location 0x014c7245." My stack looks: LowLevel.exe!__set_flsgetvalue() Line 256 + 0xc bytes C LowLevel.exe!_isleadbyte_l(int c=4359676, localeinfo_struct * plocinfo=0x00000001) Line 57 C++ 014b00d8() LowLevel.exe!PlayDateOfExam(int option=1) Line 2240 + 0x7 bytes C++ LowLevel.exe!NSCThread(void * arg=0x00000000) Line 1585 + 0xb bytes C++ kernel32.dll!7c80b729() winmm.dll!76b5b294() I uses the following file in my project "nsc.lib" and WinMM.lib" I'm not really familiar with threads I used a sample (which works great) and built on it. I saw a similiar question year on the forum but I didn't really understand the answers since I'm not familiar with with threads. Can someone help me? Thanks

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  • Can a call to WaitHandle.SignalAndWait be ignored for performance profiling purposes?

    - by Dan Tao
    I just downloaded the trial version of ANTS Performance Profiler from Red Gate and am investigating some of my team's code. Immediately I notice that there's a particular section of code that ANTS is reporting as eating up to 99% CPU time. I am completely unfamiliar with ANTS or performance profiling in general (that is, aside from self-profiling using what I'm sure are extremely crude and frowned-upon methods such as double timeToComplete = (endTime - startTime).TotalSeconds), so I'm still fiddling around with the application and figuring out how it's used. But I did call the developer responsible for the code in question and his immediate reaction was "Yeah, that doesn't surprise me that it says that; but that code calls SignalAndWait [which I could see for myself, thanks to ANTS], which doesn't use any CPU, it just sits there waiting for something to do." He advised me to simply ignore that code and look for anything ELSE I could find. My question: is it true that SignalAndWait requires NO CPU overhead (and if so, how is this possible?), and is it reasonable that a performance profiler would view it as taking up 99% CPU time? I find this particularly curious because, if it's at 99%, that would suggest that our application is often idle, wouldn't it? And yet its performance has become rather sluggish lately. Like I said, I really am just a beginner when it comes to this tool, and I don't know anything about the WaitHandle class. So ANY information to help me to understand what's going on here would be appreciated.

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  • .NET Process.Kill() in a safe way

    - by Orborde
    I'm controlling a creaky old FORTRAN simulator from a VB.NET GUI, using redirected I/O to communicate with the simulator executable. The GUI pops up a "status" window with a progress bar, estimated time, and a "STOP" button (Button_Stop). Now, I want the Button_Stop to terminate the simulator process immediately. The obvious way to do this is to call Kill() on the Child Process object. This gives an exception if it's done after the process has exited, but I can test whether the process is exited before trying to kill it, right? OK, so I do the following when the button is clicked: If Not Child.HasExited Then Child.Kill() Button_Stop.Enabled = False End If However, what if the process happens to exit between the test and the call to Kill()? In that case, I get an exception. The next thing to occur to me was that I can do Button_Stop.Enabled = False in the Process.Exited event handler, and thus prevent the Child.Kill() call in the Button_Stop.Clicked handler. But since the Process.Exited handler is called on a different thread, that still leaves the following possible interleaving: Child process exits. Process.Exited fires, calls Invoke to schedule the Button_Stop.Enabled = False User clicks on Button_Stop, triggering Child.Kill() Button_Stop.Enabled = False actually happens. An exception would then be thrown on step 3. How do I kill the process without any race conditions? Am I thinking about this entirely wrong?

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  • How to use pthread_atfork() and pthread_once() to reinitialize mutexes in child processes

    - by Blair Zajac
    We have a C++ shared library that uses ZeroC's Ice library for RPC and unless we shut down Ice's runtime, we've observed child processes hanging on random mutexes. The Ice runtime starts threads, has many internal mutexes and keeps open file descriptors to servers. Additionally, we have a few of mutexes of our own to protect our internal state. Our shared library is used by hundreds of internal applications so we don't have control over when the process calls fork(), so we need a way to safely shutdown Ice and lock our mutexes while the process forks. Reading the POSIX standard on pthread_atfork() on handling mutexes and internal state: Alternatively, some libraries might have been able to supply just a child routine that reinitializes the mutexes in the library and all associated states to some known value (for example, what it was when the image was originally executed). This approach is not possible, though, because implementations are allowed to fail *_init() and *_destroy() calls for mutexes and locks if the mutex or lock is still locked. In this case, the child routine is not able to reinitialize the mutexes and locks. On Linux, the this test C program returns EPERM from pthread_mutex_unlock() in the child pthread_atfork() handler. Linux requires adding _NP to the PTHREAD_MUTEX_ERRORCHECK macro for it to compile. This program is linked from this good thread. Given that it's technically not safe or legal to unlock or destroy a mutex in the child, I'm thinking it's better to have pointers to mutexes and then have the child make new pthread_mutex_t on the heap and leave the parent's mutexes alone, thereby having a small memory leak. The only issue is how to reinitialize the state of the library and I'm thinking of reseting a pthread_once_t. Maybe because POSIX has an initializer for pthread_once_t that it can be reset to its initial state. #include <pthread.h> #include <stdlib.h> #include <string.h> static pthread_once_t once_control = PTHREAD_ONCE_INIT; static pthread_mutex_t *mutex_ptr = 0; static void setup_new_mutex() { mutex_ptr = malloc(sizeof(*mutex_ptr)); pthread_mutex_init(mutex_ptr, 0); } static void prepare() { pthread_mutex_lock(mutex_ptr); } static void parent() { pthread_mutex_unlock(mutex_ptr); } static void child() { // Reset the once control. pthread_once_t once = PTHREAD_ONCE_INIT; memcpy(&once_control, &once, sizeof(once_control)); setup_new_mutex(); } static void init() { setup_new_mutex(); pthread_atfork(&prepare, &parent, &child); } int my_library_call(int arg) { pthread_once(&once_control, &init); pthread_mutex_lock(mutex_ptr); // Do something here that requires the lock. int result = 2*arg; pthread_mutex_unlock(mutex_ptr); return result; } In the above sample in the child() I only reset the pthread_once_t by making a copy of a fresh pthread_once_t initialized with PTHREAD_ONCE_INIT. A new pthread_mutex_t is only created when the library function is invoked in the child process. This is hacky but maybe the best way of dealing with this skirting the standards. If the pthread_once_t contains a mutex then the system must have a way of initializing it from its PTHREAD_ONCE_INIT state. If it contains a pointer to a mutex allocated on the heap than it'll be forced to allocate a new one and set the address in the pthread_once_t. I'm hoping it doesn't use the address of the pthread_once_t for anything special which would defeat this. Searching comp.programming.threads group for pthread_atfork() shows a lot of good discussion and how little the POSIX standards really provides to solve this problem. There's also the issue that one should only call async-signal-safe functions from pthread_atfork() handlers, and it appears the most important one is the child handler, where only a memcpy() is done. Does this work? Is there a better way of dealing with the requirements of our shared library?

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