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  • What is your development checklist for Java low-latency application?

    - by user49767
    I would like to create comprehensive checklist for Java low latency application. Can you add your checklist here? Here is my list 1. Make your objects immutable 2. Try to reduce synchronized method 3. Locking order should be well documented, and handled carefully 4. Use profiler 5. Use Amdhal's law, and find the sequential execution path 6. Use Java 5 concurrency utilities, and locks 7. Avoid Thread priorities as they are platform dependent 8. JVM warmup can be used As per my definition, low-latency application is tuned for every Milli-seconds.

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  • Multiple threads or process with threads

    - by sergiobuj
    Hi, this is for an assignment so I'm not looking for code. I have to simulate a game where each player has turns and needs to 'pay attention' to what's going on. So far, i know I'll need two threads for each player, one that will sleep until the player's turn and the other paying attention. My question is: Should I work each player as a 'fork' and the threads on the fork, or just create some threads for the player and associate them somehow? It's the first time I've worked with concurrency, semaphores and threads so I'm not sure about the good practices and programming style. Thanks!

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  • How can I replace this semaphore with a monitor?

    - by Kurru
    Hi In previous question of mine, someone had meantioned that using Semaphores were expensive in C# compared to using a monitor. So I ask this, how can I replace the semaphore in this code with a monitor? I need function1 to return its value after function2 (in a separate thread) has been completed. I had replaced the Semaphore.WaitOne with a Monitor.Wait and the Semaphore.Release with a Monitor.PulseAll but the PulseAll was being triggered before the Wait causing the program to hang. Any idea how to avoid that race condition? Semaphore semaphore = new Semaphore(0,1); byte b; public byte Function1() { // new thread starting in Function2; semaphore.WaitOne(); return b; } public void Function2() { // do some thing b = 0; semaphore.Release(); }

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  • New to MVVM - Best practices for seperating Data processing thread and UI Thread?

    - by OffApps Cory
    Good day. I have started messing around with the MVVP pattern, and I am having some problems with UI responsiveness versus data processing. I have a program that tracks packages. Shipment and package entities are persisted in SQL database, and are displayed in a WPF view. Upon initial retrieval of the records, there is a noticeable pause before displaying the new shipments view, and I have not even implemented the code that counts shipments that are overdue/active yet (which will necessitate a tracking check via web service, and a lot of time). I have built this with the Ocean framework, and all appears to be doing well, except when I first started my foray into multi-threading. It broke, and it appeared to break something in Ocean... Here is what I did: Private QueryThread As New System.Threading.Thread(AddressOf GetShipments) Public Sub New() ' Insert code required on object creation below this point. Me.New(ViewManagerService.CreateInstance, ViewModelUIService.CreateInstance) 'Perform initial query of shipments 'QueryThread.Start() GetShipments() Console.WriteLine(Me.Shipments.Count) End Sub Public Sub New(ByVal objIViewManagerService As IViewManagerService, ByVal objIViewModelUIService As IViewModelUIService) MyBase.New(objIViewModelUIService) End Sub Public Sub GetShipments() Dim InitialResults = From shipment In db.Shipment.Include("Packages") _ Select shipment Me.Shipments = New ShipmentsCollection(InitialResults, db) End Sub So I declared a new Thread, assigned it the GetShipments method and instanced it in the default constructor. Ocean freaks out at this, so there must be a better way of doing it. I have not had the chance to figure out the usage of the SQL ORM thing in Ocean so I am using Entity Framework (perhaps one of these days i will look at NHibernate or something too). Any information would be greatly appreciated. I have looked at a number of articles and they all have examples of simple uses. Some have mentioned the Dispatcher, but none really go very far into how it is used. Anyone know any good tutorials? Cory

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  • Synchronization requirements for FileStream.(Begin/End)(Read/Write)

    - by Doug McClean
    Is the following pattern of multi-threaded calls acceptable to a .Net FileStream? Several threads calling a method like this: ulong offset = whatever; // different for each thread byte[] buffer = new byte[8192]; object state = someState; // unique for each call, hence also for each thread lock(theFile) { theFile.Seek(whatever, SeekOrigin.Begin); IAsyncResult result = theFile.BeginRead(buffer, 0, 8192, AcceptResults, state); } if(result.CompletedSynchronously) { // is it required for us to call AcceptResults ourselves in this case? // or did BeginRead already call it for us, on this thread or another? } Where AcceptResults is: void AcceptResults(IAsyncResult result) { lock(theFile) { int bytesRead = theFile.EndRead(result); // if we guarantee that the offset of the original call was at least 8192 bytes from // the end of the file, and thus all 8192 bytes exist, can the FileStream read still // actually read fewer bytes than that? // either: if(bytesRead != 8192) { Panic("Page read borked"); } // or: // issue a new call to begin read, moving the offsets into the FileStream and // the buffer, and decreasing the requested size of the read to whatever remains of the buffer } } I'm confused because the documentation seems unclear to me. For example, the FileStream class says: Any public static members of this type are thread safe. Any instance members are not guaranteed to be thread safe. But the documentation for BeginRead seems to contemplate having multiple read requests in flight: Multiple simultaneous asynchronous requests render the request completion order uncertain. Are multiple reads permitted to be in flight or not? Writes? Is this the appropriate way to secure the location of the Position of the stream between the call to Seek and the call to BeginRead? Or does that lock need to be held all the way to EndRead, hence only one read or write in flight at a time? I understand that the callback will occur on a different thread, and my handling of state, buffer handle that in a way that would permit multiple in flight reads. Further, does anyone know where in the documentation to find the answers to these questions? Or an article written by someone in the know? I've been searching and can't find anything. Relevant documentation: FileStream class Seek method BeginRead method EndRead IAsyncResult interface

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  • Winforms: Attempted to read or write protected memory. This is often an indication that other memory is corrupt

    - by mamcx
    I have a bunch of background events. All of them call a log: private void log(string text, params object[] values) { if (editLog.InvokeRequired) { editLog.BeginInvoke( (MethodInvoker)delegate { this.log(text, values); }); } else { text = string.Format(text, values) + Environment.NewLine; lock (editLog) { editLog.AppendText(text); editLog.SelectionStart = editLog.TextLength; editLog.ScrollToCaret(); } } } Sometimes I get this, but other times not: System.AccessViolationException was unhandled Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt. Source=System.Windows.Forms StackTrace: at System.Windows.Forms.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam) at System.Windows.Forms.NativeWindow.DefWndProc(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.RichTextBox.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.SendMessage(HandleRef hWnd, Int32 msg, Int32 wParam, Object& editOle) at System.Windows.Forms.TextBoxBase.ScrollToCaret() at Program1.frmMain.log(String text, Object[] values) in ... ... ... P.D: Not always stop at this line, randomly will be one of the three times editLog methods/properties are used. Not always a exception is throw. Sometimes look like the thing freeze. But not the main UI, just the flow of messages (ie: log look like is never called again) The app is a single form, with background process. I can't see what I doing wrong with this...

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  • Spawning BackgroundWorkers

    - by washtik
    We have a business case that would be perfect for multiple BackgroundWorkers. As an example, we have a form with a "Save" button on it. Normally we would run all the save commands (Save is an example) synchronously and then close the form. We would like to now split the work onto separate threads using backgroundworker. We will loop through each "Save" required (could be many and/or different number of commands that need executing) creating a BackgroundWorker for each command required. The question is ... how do we wait for ALL the BackgroundWorkers to complete before we close the form. We understand how to wait for a single BackgroundWorker to complete but when we have X number of BackgroundWorkers operating, how do we wait until all are complete before closing the UI form?

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  • .NET 1.0 ThreadPool Question

    - by dotnet-practitioner
    I am trying to spawn a thread to take care of DoWork task that should take less than 3 seconds. Inside DoWork its taking 15 seconds. I want to abort DoWork and transfer the control back to main thread. I have copied the code as follows and its not working. Instead of aborting DoWork, it still finishes DoWork and then transfers the control back to main thread. What am I doing wrong? class Class1 { /// <summary> /// The main entry point for the application. /// </summary> /// private static System.Threading.ManualResetEvent[] resetEvents; [STAThread] static void Main(string[] args) { resetEvents = new ManualResetEvent[1]; int i = 0; resetEvents[i] = new ManualResetEvent(false); ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork),(object)i); Thread.CurrentThread.Name = "main thread"; Console.WriteLine("[{0}] waiting in the main method", Thread.CurrentThread.Name); DateTime start = DateTime.Now; DateTime end ; TimeSpan span = DateTime.Now.Subtract(start); //abort dowork method if it takes more than 3 seconds //and transfer control to the main thread. do { if (span.Seconds < 3) WaitHandle.WaitAll(resetEvents); else resetEvents[0].Set(); end = DateTime.Now; span = end.Subtract(start); }while (span.Seconds < 2); Console.WriteLine(span.Seconds); Console.WriteLine("[{0}] all done in the main method",Thread.CurrentThread.Name); Console.ReadLine(); } static void DoWork(object o) { int index = (int)o; Thread.CurrentThread.Name = "do work thread"; //simulate heavy duty work. Thread.Sleep(15000); //work is done.. resetEvents[index].Set(); Console.WriteLine("[{0}] do work finished",Thread.CurrentThread.Name); } }

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  • What is the simplest way to implement multithredding in c# to existing code

    - by Kaeso
    I have already implemented a functionnal application that parses 26 pages of html all at once to produce an xml file with data contained on the web pages. I would need to implement a thread so that this method can work in the background without causing my app to seems unresponsive. Secondly, I have another function that is decoupled from the first one which compares two xml files to produce a third one and then transform this third xml file to produce an html page using XSLT. This would have to be on a thread, where I can click Cancel to stop the thread whithout crashing the app. What is the easiest best way to do this using WPF forms in VS 2010 ? Note: I cannot use the BackgroundWorker component as it is grayed out in the toolbox.

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  • perl threading problem

    - by Alice Wozownik
    I'm writing a multithreaded website uptime checker in perl, and here is the basic code so far (includes only threading part): !/usr/bin/perl use LWP::UserAgent; use Getopt::Std; use threads; use threads::shared; my $maxthreads :shared = 50; my $threads :shared = 0; print "Website Uptime Checker\n"; my $infilename = $ARGV[0]; chomp($infilename); open(INFILE, $infilename); my $outfilename = $ARGV[1]; chomp($outfilename); open(OUTFILE, "" . $outfilename); OUTFILE-autoflush(1); while ($site = ) { chomp($site); while (1) { if ($threads < $maxthreads) { $threads++; my $thr = threads-create(\&check_site, $site); $thr-detach(); last; } else { sleep(1); } } } while ($threads 0) { sleep(1); } sub check_site { $server = $_[0]; print "$server\n"; $threads--; } It gives an error after a while: Can't call method "detach" on an undefined value at C:\perl\webchecker.pl line 28, line 245. What causes this error? I know it is at detach, but what am I doing wrong in my code? Windows shows lots of free memory, so it should not be the computer running out of memory, this error occurs even if I set $maxthreads as low as 10 or possibly even lower.

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  • Script stops while waiting for user input from STDIN.gets

    - by bob c
    I'm trying to do something like this, where I have two loops going in seperate threads. The problem I am having is that in the main thread, when I use gets and the script is waiting for user input, the other thread is stopped to wait as well. class Server def initialize() @server = TCPServer.new(8080) run end def run() @thread = Thread.new(@server) { |server| while true newsock = server.accept puts "some stuff after accept!" next if !newsock # some other stuff end } end end def processCommand() # some user commands here end test = Server.new while true do processCommand(STDIN.gets) end The above is just a sample of what I want to do. Is there a way to make the main thread block while waiting for user input?

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  • Threading Issue with WCF Service

    - by helixed
    I'm new to both WCF and threading, so please bear with me. I have a WCF service set up. The service has multiple threads, all of which act upon a single array. This works without a problem so far. However, this service has a method, which, when called, will return the array. My questions: The array is serialized when it is transferred to the client by WCF. Is this a thread safe operation? In other words, can I count on WCF to block all threads from accessing this array while it's being serialized? If I can't count on WCF to do this, then how can I implement it manually? I don't really understand how WCF would facilitate this since the serialization happens after I return from my method call. How can I guarantee a thread will not modify the array after it's been returned by my method but before WCF serializes it?

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  • Threading best practice when using SFTP in C#

    - by Christian
    Ok, this is more one of these "conceptual questions", but I hope I got some pointers in the right direction. First the desired scenario: I want to query an SFTP server for directory and file lists I want to upload or download files simulaneously Both things are pretty easy using a SFTP class provided by Tamir.SharpSsh, but if I only use one thread, it is kind of slow. Especially the recursion into subdirs gets very "UI blocking", because we are talking about 10.000 of directories. My basic approach is simple, create some kind of "pool" where I keep 10 open SFTP connections. Then query the first worker for a list of dirs. If this list was obtained, send the next free workers (e.g. 1-10, first one is also free again) to get the subdirectory details. As soon as there is a worker free, send him for the subsubdirs. And so on... I know the ThreadPool, simple Threads and did some Tests. What confuses me a little bit is the following: I basically need... A list of threads I create, say 10 Connect all threads to the server If a connection drops, create a new thread / sftp client If there is work to do, take the first free thread and handle the work I am currently not sure about the implementation details, especially the "work to do" and the "maintain list of threads" parts. Is it a good idea to: Enclose the work in an object, containing a job description (path) and a callback Send the threads into an infinite loop with 100ms wait to wait for work If SFTP is dead, either revive it, or kill the whole thread and create a new one How to encapsulate this, do I write my own "10ThreadsManager" or are there some out Ok, so far... Btw, I could also use PRISM events and commands, but I think the problem is unrelated. Perhaps the EventModel to signal a done processing of a "work package"... Thanks for any ideas, critic.. Chris

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  • What is the correct way to synchronize a shared, static object in Java?

    - by johnrock
    This is a question concerning what is the proper way to synchronize a shared object in java. One caveat is that the object that I want to share must be accessed from static methods. My question is, If I synchronize on a static field, does that lock the class the field belongs to similar to the way a synchronized static method would? Or, will this only lock the field itself? In my specific example I am asking: Will calling PayloadService.getPayload() or PayloadService.setPayload() lock PayloadService.payload? Or will it lock the entire PayloadService class? public class PayloadService extends Service { private static PayloadDTO payload = new PayloadDTO(); public static void setPayload(PayloadDTO payload){ synchronized(PayloadService.payload){ PayloadService.payload = payload; } } public static PayloadDTO getPayload() { synchronized(PayloadService.payload){ return PayloadService.payload ; } } ... Is this a correct/acceptable approach ? In my example the PayloadService is a separate thread, updating the payload object at regular intervals - other threads need to call PayloadService.getPayload() at random intervals to get the latest data and I need to make sure that they don't lock the PayloadService from carrying out its timer task

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  • Tomcat threads vs Java threads

    - by black666
    When using java threads, one has to take care of the basic problems that come with concurrency through synchronization etc. AFAIK Tomcat also works with threads to handle its workload. Why is it, that I don't have to think about making my code threadsafe when it is running in Tomcat?

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  • WPF Background Thread Invocation

    - by jeffn825
    Maybe I'm mis-remembering how Winforms works or I'm overcomplicating the hell out of this, but here's my problem. I have a WPF client app application that talks to a server over WCF. The current user may "log out" of the WPF client, which closes all open screens, leaves only the navigation pane, and minimizes the program window. When the user re-maximizes the program window, they are prompted to log in. Simple. But sometimes things happen on background threads - like every 5 minutes the client tries to make a WCF calls that refreshes some cached data. And what if the user is logged out when this 5 minute timer triggers? Well, then the user should be prompted to log back in...and this must of course happen on the UI thread. private static ISecurityContext securityContext; public static ISecurityContext SecurityContext { get { if (securityContext == null) { // Login method shows a window and prompts the user to log in Application.Current.Dispatcher.Invoke((Action)Login); } return securityContext; } } So far so good, right? But what happens when multiple threads hit this spot of code? Well, my first intuition was that since I'm syncrhonizing across the Application.Current.Dispatcher, I should be fine, and whichever thread hit first would be responsible for showing the login form and getting the user logged in... Not the case... Thread 1 will hit the code and call ShowDialog on the login form Thread 2 will also hit the code and will call Login as soon as Thread 1 has called ShowDialog, since calling ShowDialog unblocked Thread 1 (I believe because of the way the WPF message pump works) All I want is a synchronized way of getting the user logged back into the application...what am I missing here? Thanks in advance.

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  • async handler deleted by the wrong thread in django

    - by user3480706
    I'm run this algorithm in my django application.when i run several time from my GUI django local server will stopped and i got this error Exception RuntimeError: RuntimeError('main thread is not in main loop',) in ignored Tcl_AsyncDelete: async handler deleted by the wrong thread Aborted (core dumped) code print "Learning the sin function" network =MLP.MLP(2,10,1) samples = np.zeros(2000, dtype=[('x', float, 1), ('y', float, 1)]) samples['x'] = np.linspace(-5,5,2000) samples['y'] = np.sin(samples['x']) #samples['y'] = np.linspace(-4,4,2500) for i in range(100000): n = np.random.randint(samples.size) network.propagate_forward(samples['x'][n]) network.propagate_backward(samples['y'][n]) plt.figure(figsize=(10,5)) # Draw real function x = samples['x'] y = samples['y'] #x=np.linspace(-6.0,7.0,50) plt.plot(x,y,color='b',lw=1) samples1 = np.zeros(2000, dtype=[('x1', float, 1), ('y1', float, 1)]) samples1['x1'] = np.linspace(-4,4,2000) samples1['y1'] = np.sin(samples1['x1']) # Draw network approximated function for i in range(samples1.size): samples1['y1'][i] = network.propagate_forward(samples1['x1'][i]) plt.plot(samples1['x1'],samples1['y1'],color='r',lw=3) plt.axis([-2,2,-2,2]) plt.show() plt.close() return HttpResponseRedirect('/charts/charts') how can i fix this error ?need a quick help

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  • Thread resource sharing

    - by David
    I'm struggling with multi-threaded programming... I have an application that talks to an external device via a CAN to USB module. I've got the application talking on the CAN bus just fine, but there is a requirement for the application to transmit a "heartbeat" message every second. This sounds like a perfect time to use threads, so I created a thread that wakes up every second and sends the heartbeat. The problem I'm having is sharing the CAN bus interface. The heartbeat must only be sent when the bus is idle. How do I share the resource? Here is pseudo code showing what I have so far: TMainThread { Init: CanBusApi =new TCanBusApi; MutexMain =CreateMutex( "CanBusApiMutexName" ); HeartbeatThread =new THeartbeatThread( CanBusApi ); Execution: WaitForSingleObject( MutexMain ); CanBusApi->DoSomething(); ReleaseMutex( MutexMain ); } THeartbeatThread( CanBusApi ) { Init: MutexHeart =CreateMutex( "CanBusApiMutexName" ); Execution: Sleep( 1000 ); WaitForSingleObject( MutexHeart ); CanBusApi->DoHeartBeat(); ReleaseMutex( MutexHeart ); } The problem I'm seeing is that when DoHeartBeat is called, it causes the main thread to block while waiting for MutexMain as expected, but DoHeartBeat also stops. DoHeartBeat doesn't complete until after WaitForSingleObject(MutexMain) times out in failure. Does DoHeartBeat execute in the context of the MainThread or HeartBeatThread? It seems to be executing in MainThread. What am I doing wrong? Is there a better way? Thanks, David

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  • Crash: iPhone Threading with Blocks

    - by jtbandes
    I have some convenience methods set up for threading with blocks (using PLBlocks). Then in the main portion of my code, I call the method -fetchArrivalsForLocationIDs:callback:errback:, which runs some web API calls in the background. Here's the problem: when I comment out the 2 NSAutoreleasePool-related lines in JTBlockThreading.m, of course I get lots of Object 0x6b31280 of class __NSArrayM autoreleased with no pool in place - just leaking errors. However, if I uncomment them, the app frequently crashes on the [pool release]; line, sometimes saying malloc: *** error for object 0x6e3ae10: pointer being freed was not allocated" *** set a breakpoint in malloc_error_break to debug. I assume I've made a horrible mistake/assumption in threading somewhere, but can anyone figure out what exactly the problem is? // JTBlockThreading.h #import <Foundation/Foundation.h> #import <PLBlocks/Block.h> #define JT_BLOCKTHREAD_BACKGROUND [self invokeBlockInBackground:^{ #define JT_BLOCKTHREAD_MAIN [self invokeBlockOnMainThread:^{ #define JT_BLOCKTHREAD_END }]; #define JT_BLOCKTHREAD_BACKGROUND_END_WAIT } waitUntilDone:YES]; @interface NSObject (JTBlockThreading) - (void)invokeBlockInBackground:(void (^)())block; - (void)invokeBlockOnMainThread:(void (^)())block; - (void)invokeBlockOnMainThread:(void (^)())block waitUntilDone:(BOOL)wait; - (void)invokeBlock:(void (^)())block; @end // JTBlockThreading.m #import "JTBlockThreading.h" @implementation NSObject (JTBlockThreading) - (void)invokeBlockInBackground:(void (^)())block { [self performSelectorInBackground:@selector(invokeBlock:) withObject:[block copy]]; } - (void)invokeBlockOnMainThread:(void (^)())block { [self invokeBlockOnMainThread:block waitUntilDone:NO]; } - (void)invokeBlockOnMainThread:(void (^)())block waitUntilDone:(BOOL)wait { [self performSelectorOnMainThread:@selector(invokeBlock:) withObject:[block copy] waitUntilDone:wait]; } - (void)invokeBlock:(void (^)())block { //NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; block(); [block release]; //[pool release]; } @end - (void)fetchArrivalsForLocationIDs:(NSString *)locIDs callback:(JTWSCallback)callback errback:(JTWSErrback)errback { JT_PUSH_NETWORK(); JT_BLOCKTHREAD_BACKGROUND NSError *error = nil; // Create API call URL NSURL *url = [NSURL URLWithString: [NSString stringWithFormat:@"%@/arrivals/appID/%@/locIDs/%@", TRIMET_BASE_URL, appID, locIDs]]; if (!url) { JT_BLOCKTHREAD_MAIN errback(@"That’s not a valid Stop ID!"); JT_POP_NETWORK(); JT_BLOCKTHREAD_END return; } // Call API NSData *data = [NSData dataWithContentsOfURL:url options:0 error:&error]; if (!data) { JT_BLOCKTHREAD_MAIN errback([NSString stringWithFormat: @"Had trouble downloading the arrival data! %@", [error localizedDescription]]); JT_POP_NETWORK(); JT_BLOCKTHREAD_END return; } CXMLDocument *doc = [[CXMLDocument alloc] initWithData:data options:0 error:&error]; if (!doc) { JT_BLOCKTHREAD_MAIN // TODO: further error description // (TouchXML doesn't provide information with the error) errback(@"Had trouble reading the arrival data!"); JT_POP_NETWORK(); JT_BLOCKTHREAD_END return; } NSArray *nodes = nil; CXMLElement *resultSet = [doc rootElement]; // Begin building the response model JTWSResponseArrivalData *response = [[[JTWSResponseArrivalData alloc] init] autorelease]; response.queryTime = [NSDate JT_dateWithTriMetWSTimestamp: [[resultSet attributeValueForName:@"queryTime"] longLongValue]]; if (!response.queryTime) { // TODO: further error check? NSLog(@"Hm, query time is nil in %s... response %@, resultSet %@", __PRETTY_FUNCTION__, response, resultSet); } nodes = [resultSet nodesForXPath:@"//arrivals:errorMessage" namespaceMappings:namespaceMappings error:&error]; if ([nodes count] > 0) { NSString *message = [[nodes objectAtIndex:0] stringValue]; response.errorMessage = message; // TODO: this probably won't be used... JT_BLOCKTHREAD_MAIN errback([NSString stringWithFormat: @"TriMet error: “%@”", message]); JT_POP_NETWORK(); JT_BLOCKTHREAD_END return; } // Build location models nodes = [resultSet nodesForXPath:@"/arrivals:location" namespaceMappings:namespaceMappings error:&error]; if ([nodes count] <= 0) { NSLog(@"Hm, no locations returned in %s... xpath error %@, response %@, resultSet %@", __PRETTY_FUNCTION__, error, response, resultSet); } NSMutableArray *locations = [NSMutableArray arrayWithCapacity:[nodes count]]; for (CXMLElement *loc in nodes) { JTWSLocation *location = [[[JTWSLocation alloc] init] autorelease]; location.desc = [loc attributeValueForName:@"desc"]; location.dir = [loc attributeValueForName:@"dir"]; location.position = [[[CLLocation alloc] initWithLatitude:[[loc attributeValueForName:@"lat"] doubleValue] longitude:[[loc attributeValueForName:@"lng"] doubleValue]] autorelease]; location.locID = [[loc attributeValueForName:@"locid"] integerValue]; } // Build arrival models nodes = [resultSet nodesForXPath:@"/arrivals:arrival" namespaceMappings:namespaceMappings error:&error]; if ([nodes count] <= 0) { NSLog(@"Hm, no arrivals returned in %s... xpath error %@, response %@, resultSet %@", __PRETTY_FUNCTION__, error, response, resultSet); } NSMutableArray *arrivals = [[NSMutableArray alloc] initWithCapacity:[nodes count]]; for (CXMLElement *arv in nodes) { JTWSArrival *arrival = [[JTWSArrival alloc] init]; arrival.block = [[arv attributeValueForName:@"block"] integerValue]; arrival.piece = [[arv attributeValueForName:@"piece"] integerValue]; arrival.locID = [[arv attributeValueForName:@"locid"] integerValue]; arrival.departed = [[arv attributeValueForName:@"departed"] boolValue]; // TODO: verify arrival.detour = [[arv attributeValueForName:@"detour"] boolValue]; // TODO: verify arrival.direction = (JTWSRouteDirection)[[arv attributeValueForName:@"dir"] integerValue]; arrival.estimated = [NSDate JT_dateWithTriMetWSTimestamp: [[arv attributeValueForName:@"estimated"] longLongValue]]; arrival.scheduled = [NSDate JT_dateWithTriMetWSTimestamp: [[arv attributeValueForName:@"scheduled"] longLongValue]]; arrival.fullSign = [arv attributeValueForName:@"fullSign"]; arrival.shortSign = [arv attributeValueForName:@"shortSign"]; NSString *status = [arv attributeValueForName:@"status"]; if ([status isEqualToString:@"estimated"]) { arrival.status = JTWSArrivalStatusEstimated; } else if ([status isEqualToString:@"scheduled"]) { arrival.status = JTWSArrivalStatusScheduled; } else if ([status isEqualToString:@"delayed"]) { arrival.status = JTWSArrivalStatusDelayed; } else if ([status isEqualToString:@"canceled"]) { arrival.status = JTWSArrivalStatusCanceled; } else { NSLog(@"Unknown arrival status %s in %@... response %@, arrival %@", status, __PRETTY_FUNCTION__, response, arv); } NSArray *blockPositions = [arv nodesForXPath:@"/arrivals:blockPosition" namespaceMappings:namespaceMappings error:&error]; if ([blockPositions count] > 1) { // The schema allows for any number of blockPosition elements, // but I'm really not sure why... NSLog(@"Hm, more than one blockPosition in %s... response %@, arrival %@", __PRETTY_FUNCTION__, response, arv); } if ([blockPositions count] > 0) { CXMLElement *bpos = [blockPositions objectAtIndex:0]; JTWSBlockPosition *blockPosition = [[JTWSBlockPosition alloc] init]; blockPosition.reported = [NSDate JT_dateWithTriMetWSTimestamp: [[bpos attributeValueForName:@"at"] longLongValue]]; blockPosition.feet = [[bpos attributeValueForName:@"feet"] integerValue]; blockPosition.position = [[[CLLocation alloc] initWithLatitude:[[bpos attributeValueForName:@"lat"] doubleValue] longitude:[[bpos attributeValueForName:@"lng"] doubleValue]] autorelease]; NSString *headingStr = [bpos attributeValueForName:@"heading"]; if (headingStr) { // Valid CLLocationDirections are > 0 CLLocationDirection heading = [headingStr integerValue]; while (heading < 0) heading += 360.0; blockPosition.heading = heading; } else { blockPosition.heading = -1; // indicates invalid heading } NSArray *tripData = [bpos nodesForXPath:@"/arrivals:trip" namespaceMappings:namespaceMappings error:&error]; NSMutableArray *trips = [[NSMutableArray alloc] initWithCapacity:[tripData count]]; for (CXMLElement *tripDatum in tripData) { JTWSTrip *trip = [[JTWSTrip alloc] init]; trip.desc = [tripDatum attributeValueForName:@"desc"]; trip.destDist = [[tripDatum attributeValueForName:@"destDist"] integerValue]; trip.direction = (JTWSRouteDirection)[[tripDatum attributeValueForName:@"dir"] integerValue]; trip.pattern = [[tripDatum attributeValueForName:@"pattern"] integerValue]; trip.progress = [[tripDatum attributeValueForName:@"progress"] integerValue]; trip.route = [[tripDatum attributeValueForName:@"route"] integerValue]; [trips addObject:trip]; [trip release]; } blockPosition.trips = trips; [trips release]; NSArray *layoverData = [bpos nodesForXPath:@"/arrivals:layover" namespaceMappings:namespaceMappings error:&error]; NSMutableArray *layovers = [[NSMutableArray alloc] initWithCapacity:[layoverData count]]; for (CXMLElement *layoverDatum in layoverData) { JTWSLayover *layover = [[JTWSLayover alloc] init]; layover.start = [NSDate JT_dateWithTriMetWSTimestamp: [[layoverDatum attributeValueForName:@"start"] longLongValue]]; layover.end = [NSDate JT_dateWithTriMetWSTimestamp: [[layoverDatum attributeValueForName:@"end"] longLongValue]]; // TODO: it seems the API can send a <location> inside a layover (undocumented)... support? [layovers addObject:layover]; [layover release]; } blockPosition.layovers = layovers; [layovers release]; arrival.blockPosition = blockPosition; [blockPosition release]; } [arrivals addObject:arrival]; [arrival release]; } // Add arrivals to corresponding locations for (JTWSLocation *loc in locations) { loc.arrivals = [arrivals selectWithBlock:^BOOL (id arv) { return loc.locID == ((JTWSArrival *)arv).locID; }]; } [arrivals release]; response.locations = locations; [locations release]; // Build route status models (used in inclement weather) nodes = [resultSet nodesForXPath:@"/arrivals:routeStatus" namespaceMappings:namespaceMappings error:&error]; NSMutableArray *routeStatuses = [NSMutableArray arrayWithCapacity:[nodes count]]; for (CXMLElement *stat in nodes) { JTWSRouteStatus *status = [[JTWSRouteStatus alloc] init]; status.route = [[stat attributeValueForName:@"route"] integerValue]; NSString *statusStr = [stat attributeValueForName:@"status"]; if ([statusStr isEqualToString:@"estimatedOnly"]) { status.status = JTWSRouteStatusTypeEstimatedOnly; } else if ([statusStr isEqualToString:@"off"]) { status.status = JTWSRouteStatusTypeOff; } else { NSLog(@"Unknown route status type %s in %@... response %@, routeStatus %@", status, __PRETTY_FUNCTION__, response, stat); } [routeStatuses addObject:status]; [status release]; } response.routeStatuses = routeStatuses; [routeStatuses release]; JT_BLOCKTHREAD_MAIN callback(response); JT_POP_NETWORK(); JT_BLOCKTHREAD_END JT_BLOCKTHREAD_END }

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  • Actor model to replace the threading model?

    - by prosseek
    I read a chapter in a book (Seven languages in Seven Weeks by Bruce A. Tate) about Matz (Inventor of Ruby) saying that 'I would remove the thread and add actors, or some other more advanced concurrency features'. Why and how an actor model can be an advanced concurrency model that replaces the threading? What other models are the 'advanced concurrency model'?

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  • atomic writes to ehcache

    - by Jacques René Mesrine
    Context I am storing a java.util.List inside ehcache. Key(String) --> List<UserDetail> The ordered List contains a Top 10 ranking of my most active users. Problem Concurrent 3rd party clients might be requesting for this list. I have a requirement to be as current as possible with regards to the ranking. Thus if the ranking is changed due the activities of users, the ordered List in the cache must not be left stale for very long. Once I've recalculated a new List, I want to replace the one in cache immediately. Consider a busy scenario whereby multiple concurrent clients are requesting for the ranking; how can I replace the cache item in an fashion such that: Clients can continue to pull a possibly stale snapshot. They should never get a null value. There will only be 1 server thread that writes to the cache.

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  • Large number of simultaneous long-running operations in Qt

    - by Hostile Fork
    I have some long-running operations that number in the hundreds. At the moment they are each on their own thread. My main goal in using threads is not to speed these operations up. The more important thing in this case is that they appear to run simultaneously. I'm aware of cooperative multitasking and fibers. However, I'm trying to avoid anything that would require touching the code in the operations, e.g. peppering them with things like yieldToScheduler(). I also don't want to prescribe that these routines be stylized to be coded to emit queues of bite-sized task items...I want to treat them as black boxes. For the moment I can live with these downsides: Maximum # of threads tend to be O(1000) Cost per thread is O(1MB) To address the bad cache performance due to context-switches, I did have the idea of a timer which would juggle the priorities such that only idealThreadCount() threads were ever at Normal priority, with all the rest set to Idle. This would let me widen the timeslices, which would mean fewer context switches and still be okay for my purposes. Question #1: Is that a good idea at all? One certain downside is it won't work on Linux (docs say no QThread::setPriority() there). Question #2: Any other ideas or approaches? Is QtConcurrent thinking about this scenario? (Some related reading: how-many-threads-does-it-take-to-make-them-a-bad-choice, many-threads-or-as-few-threads-as-possible, maximum-number-of-threads-per-process-in-linux)

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  • SerialPort ReadLine() after Thread.Sleep() goes crazy

    - by Mat
    Hi everybody, I've been fighting with this issue for a day and I can't find answer for it. I am trying to read data from GPS device trough COM port in Compact Framework C#. I am using SerialPort class (actually my own ComPort class boxing SerialPort, but it adds only two fields I need, nothing special). Anyway.. I am running while loop in a separate thread which reads line from the port, analyze NMEA data, print them, catch all exceptions and then I Sleep(200) the thread, cause I need CPU for other threads... Without Sleep it works fine, but uses 100% CPU.. When I dont use Sleep after few minutes the output from COM port looks like this: GPGSA,A,3,09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F GSA,A,3,09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F A,A,3,09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F ,18,12,271,24,24,05,020,24,14,04,326,25,11,03,023,*76 A,3,09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F 3,09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F 09,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F ,12,22,17,15,27,,,,,,,2.6,1.6,2.1*3F as you can see the same message is read few times but cut. I wonder what I'm doing wrong... My port configuration: port.ReadBufferSize = 4096; port.BaudRate = 4800; port.DataBits = 8; port.Parity = Parity.None; port.StopBits = StopBits.One; port.NewLine = "\r\n"; port.ReadTimeout = 1000; port.ReceivedBytesThreshold = 100000; And my reading function: private void processGps(){ while (!closing) { //reconnect if needed try { string sentence = port.ReadLine(); //here print the sentence //analyze the sentence (this takes some time 50-100ms) } catch (TimeoutException) { Thread.Sleep(0); } catch (IOException ioex) { //handling IO exception (some info on the screen) } Thread.Sleep(200); } } There is some more stuff in this function like reconnection if the device is lost etc.. but it is not called when the GPS is connected properly.. I was trying port.DiscardInBuffer(); after some blocks of code (in TimeoutException, after read..) Did anyone had similar problem? I really dont know what I'm doing wrong.. The only way to get rig of it is removing the last Sleep... Thanks in advance! Best Regards, Mat

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