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• iPhone: One Object, One Thread

  - by GingerBreadMane

  On the iPhone, I would like to do some operations on an image in a separate thread. Rather than dealing with semiphores, locking, etc., I'd like to use the 'One Object, One Thread' method of safely writing this concurrent operation. I'm not sure what is the correct way to copy my object into a new thread so that the object is not accessed in the main thread. Do I use the 'copy' method? If so, do I do this before the thread or inside the thread? ... -(void)someMethod{ UIImage *myImage; [NSThread detachNewThreadSelector:@selector(getRotatedImage:) toTarget:self withObject:myImage]; } -(void)getRotatedImage:(UIImage *)image{ ... ... UIImage *copiedImage = [image copy]; ... ... }

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• How does one implement a truly asynchronous java thread

  - by Ritesh M Nayak

  I have a function that needs to perfom two operations, one which finishes fast and one which takes a long time to run. I want to be able to delegate the long running operation to a thread and I dont care when the thread finishes, but the threads needs to complete. I implemented this as shown below , but, my secondoperation never gets done as the function exits after the start() call. How I can ensure that the function returns but the second operation thread finishes its execution as well and is not dependent on the parent thread ? public void someFunction(String data) { smallOperation() Blah a = new Blah(); Thread th = new Thread(a); th.Start(); } class SecondOperation implements Runnable { public void run(){ // doSomething long running } }

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• How can I synchronize database access between a write-thread and a read-thread?

  - by Runcible

  My program has two threads: Main execution thread that handles user input and queues up database writes A utility thread that wakes up every second and flushes the writes to the database Inside the main thread, I occasionally need to make reads on the database. When this happens, performance is not important, but correctness is. (In a perfect world, I would be reading from a cache, not making a round-trip to the database - but let's put that aside for the sake of discussion.) How do I make sure that the main thread sees a correct / quiescent database? A standard mutex won't work, since I run the risk of having the main thread grab the mutex before the data gets flushed to the database. This would be a big race condition. What I really want is some sort of mutex that lets the main thread of execution proceed only AFTER the mutex has been grabbed and released once. Does such a thing exist? What's the best way to solve this problem?

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• Can the lock function be used to implement thread-safe enumeration?

  - by Daniel

  I'm working on a thread-safe collection that uses Dictionary as a backing store. In C# you can do the following: private IEnumerable<KeyValuePair<K, V>> Enumerate() { if (_synchronize) { lock (_locker) { foreach (var entry in _dict) yield return entry; } } else { foreach (var entry in _dict) yield return entry; } } The only way I've found to do this in F# is using Monitor, e.g.: let enumerate() = if synchronize then seq { System.Threading.Monitor.Enter(locker) try for entry in dict -> entry finally System.Threading.Monitor.Exit(locker) } else seq { for entry in dict -> entry } Can this be done using the lock function? Or, is there a better way to do this in general? I don't think returning a copy of the collection for iteration will work because I need absolute synchronization.

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• Is this a valid, lazy, thread-safe Singleton implementation for C#?

  - by Matthew

  I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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• Putting a thread to sleep until event X occurs

  - by tipu

  I'm writing to many files in a threaded app and I'm creating one handler per file. I have HandlerFactory class that manages the distribution of these handlers. What I'd like to do is that thread A requests and gets foo.txt's file handle from the HandlerFactory class thread B requests foo.txt's file handler handler class recognizes that this file handle has been checked out handler class puts thread A to sleep thread B closes file handle using a wrapper method from HandlerFactory HandlerFactory notifies sleeping threads thread B wakes and successfully gets foo.txt's file handle This is what I have so far, def get_handler(self, file_path, type): self.lock.acquire() if file_path not in self.handlers: self.handlers[file_path] = open(file_path, type) elif not self.handlers[file_path].closed: time.sleep(1) self.lock.release() return self.handlers[file_path][type] I believe this covers the sleeping and handler retrieval successfully, but I am unsure how to wake up all threads, or even better wake up a specific thread.

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• Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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• [C++] Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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• Running a loop (such as one for a mock webserver) within a thread

  - by bob c

  I'm trying to run a mock webserver within a thread within a class. I've tried passing the class' @server property to the thread block but as soon as I try to do server.accept the thread stops. Is there some way to make this work? I want to basically be able to run a webserver off of this script while still taking user input via stdin.gets. Is this possible? class Server def initialize() @server = TCPServer.new(8080) 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 In the above sample, the thread dies on server.accept

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• What will or won't cause a thread to block (a question from a test)

  - by fingerprint211b

  I've had a test, and there was a question I lost some points on, because I wasn't able to answer it : Which of the following is NOT a condition which can cause a thread to block : Calling an objects's wait() method Waiting for an I/O operation Calling sleep() Calling yield() Calling join() As far as I know, all of these are blocking calls : wait() returns when an something calls notify(), blocks until then If the thread is WAITING for an I/O operation then it's obviously blocked sleep(), obviously, blocks until the time runs out, or something wakes up the thread yield() "cancels the rest of the thread's timeslice" (lacking a better term), and returns only when the thread is active again join() blocks until the thread it's waiting for terminates. Am I missing something here?

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• What would you take into account when you were asked to compare software? [closed]

  - by mstaessen

  For my master's thesis, I am asked to make a comparative study of frameworks for cross-platform mobile development. I want to eliminate the chances of having missed something in my comparison. This is why I want to ask what YOU would value (most) when comparing such frameworks (Like for instance PhoneGap and Appcelerator Titanium). Performance, capabilities and licensing are kind of obvious, but can you think of others?

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• Straight cable or cross over cable?

  - by om sai

  I have pppoe internet connection. My ISP provides connections like this: ISP->media converter(fiber)->8 port switch(TP Link TL-SF1008D)->to individual internet connection account holders (like me) Now the connection between the media converter and the switch is done using 4 pair cross over cat5 cable and I would like to connect the cable running from the switch to the router and through router to my PC. So what type of cable should I use to make the connection between the switch and the router (straight thru cable or cross over cable)? The point I am trying to make is I am able to connect to the internet using straight through cable between the switch and my PC but when I connect the same cable between the switch and the router and from router to my PC I am not able to connect to the internet. Also, if I am using the 2 pair cable (instead of 4) between the switch and the router I am able to connect to the internet but same is not true in case of 4 pair cat5 cable.

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• Cross-match a number of worksheets to one master worksheet

  - by Carter

  Hopefully the title is not too confusing. Basically, I have a master list of addresses and those addresses are listed in multiple columns (Column A - street number, Column B - street name, Column C - street type etc) and I get a another set of addresses on a daily basis with the same address formatting. What I need to do is cross-match the daily changing list of addresses to the first list to remove any matching entries. So, for example, if the first list has 123 Main St on it, I have to ensure that there are no entries of 123 Main St on any subsequent daily lists. I'm using one address as an example but the lists contain upwards of 10000 addresses that have to be cross matched. I don't need them flagged or highlighted, just deleted from the daily lists (though if they have to be flagged or highlighted, I could work with that) Any help here would be much appreciated.

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• How to write a "thread safe" function in C ?

  - by Andrei Ciobanu

  Hello I am writing some data structures in C, and I've realized that their associated functions aren't thread safe. The i am writing code uses only standard C, and I want to achieve some sort of 'synchronization'. I was thinking to do something like this: enum sync_e { TRUE, FALSE }; typedef enum sync_e sync; struct list_s { //Other stuff struct list_node_s *head; struct list_node_s *tail; enum sync_e locked; }; typedef struct list_s list; , to include a "boolean" field in the list structure that indicates the structures state: locked, unlocked. For example an insertion function will be rewritten this way: int list_insert_next(list* l, list_node *e, int x){ while(l->locked == TRUE){ /* Wait */ } l->locked = TRUE; /* Insert element */ /* -------------- */ l->locked = FALSE; return (0); } While operating on the list the 'locked' field will be set to TRUE, not allowing any other alterations. After operation completes the 'locked' field will be again set to 'TRUE'. Is this approach good ? Do you know other approaches (using only standard C).

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• Windows App. Thread Aborting Issue

  - by Patrick

  I'm working on an application that has to make specific decisions based on files that are placed into a folder being watched by a file watcher. Part of this decision making process involves renaming files before moving them off to another folder to be processed. Since I'm working with files of all different sizes I created an object that checks the file in a seperate thread to verify that it is "available" and when it is it fires an event. When I run the rename code from inside this available event it works. public void RenameFile_Test() { string psFilePath = @"C:\File1.xlsx"; tgt_File target = new FileObject(psFilePath); target.FileAvailable += new FileEventHandler(OnFileAvailable); target.FileUnAvailable += new FileEventHandler(OnFileUnavailable); } private void OnFileAvailable(object source, FileEventArgs e) { ((FileObject)source).RenameFile(@"C:\File2.xlsx"); } The problem I'm running into is that when the extensions are different from the source file and the rename to file I am making a call to a conversion factory that returns a factory object based on the type of conversion and then converts the file accordingly before doing the rename. When I run that particular piece of code in unit test it works, the factory object is returned, and the conversion happens correctly. But when I run it within the process I get up to the... moExcelApp = new Application(); part of converting an .xls or .xlsx to a .csv and i get a "Thread was being Aborted" error. Any thoughts? Update: There is a bit more information and a bit of map of how the application works currently. Client Application running FSW On File Created event Creates a FileObject passing in the path of the file. On construction the file is validated: if file exists is true then, Thread toAvailableCheck = new Thread(new ThreadStart(AvailableCheck)); toAvailableCheck.Start(); The AvailableCheck Method repeatedly tries to open a streamreader to the file until the reader is either created or the number of attempts times out. If the reader is opened, it fires the FileAvailable event, if not it fires the FileUnAvailable event, passing back itself in the event. The client application is wired to catch those events from inside the Oncreated event of the FSW. the OnFileAvailable method then calls the rename functionality which contains the excel interop call. If the file is being renamed (not converted, extensions stay the same) it does a move to change the name from the old file name to the new, and if its a conversion it runs a conversion factory object which returns the correct type of conversion based on the extensions of the source file and the destination file name. If it is a simple rename it works w/o a problem. If its a conversion (which is the XLS to CSV object that is returned as a part of the factory) the very first thing it does is create a new application object. That is where the application bombs. When i test the factory and conversion/rename process outside of the thread and in its own unit test the process works w/o a problem. Update: I tested the Excel Interop inside a thread by doing this: [TestMethod()] public void ExcelInteropTest() { Thread toExcelInteropThreadTest = new Thread(new ThreadStart(Instantiate_App)); toExcelInteropThreadTest.Start(); } private void Instantiate_App() { Application moExcelApp = new Application(); moExcelApp.Quit(); } And on the line where the application is instatntiated I got the 'A first chance exception of type 'System.Threading.ThreadAbortException' error. So I added; toExcelInteropThreadTest.SetApartmentState(ApartmentState.MTA); after the thread instantiation and before the thread start call and still got the same error. I'm getting the notion that I'm going to have to reconsider the design.

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• An unspecified error occurred on the render thread. (NotifyPartitionIsZombie)

  - by red-X

  oke heres the problem, I have a ContentControl3D object from thriple in that im creating a LibraryStack with images it runs fine, until i run the function where the LibraryStack gets created and filled. when i click on any of the objects inside i get the following error An unspecified error occurred on the render thread. with stacktrace at System.Windows.Media.MediaContext.NotifyPartitionIsZombie(Int32 failureCode) at System.Windows.Media.MediaContext.NotifyChannelMessage() at System.Windows.Interop.HwndTarget.HandleMessage(Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Interop.HwndSource.HwndTargetFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter) at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.Run() at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run(Window window) at System.Windows.Application.Run() at WelkoMap.App.Main() in F:\MediaGarde\Surface\Development\WelkoMap\WelkoMap\obj\Debug\App.g.cs:line 0 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() heres the code that adds and creates the LibraryStack and fills it public void ReplaceBackContent(List<Image> images, List<MediaElement> videos) { ContentControl3D control = this.TryFindParent<ContentControl3D>(); if (control == null) { return; } LibraryStack stack = new LibraryStack(); foreach (Image image in images) { if (image.Parent != null) { continue; } LibraryStackItem item = new LibraryStackItem(); item.Content = image; stack.Items.Add(item); } control.BackContent = stack; } Since it has the NotifyPartitionIsZombie error i already installed windows update KB967634 which had absolutely no effect at all

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• What's the best way to do cross browser testing?

  - by Doug

  What's the best way for me to check if my website is compatible in IE7,8, Safari, FF, and Chrome without having to install each and everyone? I mainly want to check the CSS, HTML, and JavaScript. Update I put a bounty in hopes there is a more practical solution for someone like myself. I am using Windows 7 Home Premium x64. Update2 I don't mind installing these browsers now, but I can't even if I wanted to. Windows 7 doesn't allow me to install IE7.

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• Which cross threading invoke function is better for a control that is inherited?

  - by Stevoni

  I have a relatively simple question regarding the best way to call the DataGridView.Rows.Add function when it is inherited into the current control. Which is the best way to make the call to the inherited control? Call it directly in the invoke or call it using recursive-like function? They both seem to produce the same result, a row gets added and the quantity is returned, but which is the most efficient? The delegate: Private Delegate Function ReturnDelegate() As Object The two ways are: A) Private Overloads Function AddRow() As Integer If InvokeRequired Then Return CInt(Invoke(New ReturnDelegate(AddressOf AddRow))) Else Return Rows.Add() End If End Function Or B) Private Function RowsAdd() As Integer If Me.InvokeRequired Then Return CInt(Me.Invoke(New ReturnDelegate(AddressOf MyBase.Rows.Add))) Else Return MyBase.Rows.Add End If End Function

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• Can you cross-site ping another site using C# or JS/Ajax?

  - by Josh Harris

  On our web application I am trying to ping a 3rd party site to see if it is up before redirecting our customers to it. So far I have not seen a way to do this other than from a desktop app or system console. Is this possible? I have heard that there was an image trick in original ASP. Currently we are using .NET MVC with Javascript. Thank you, Josh

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• How to deal with Unicode strings in C/C++ in a cross-platform friendly way?

  - by Sorin Sbarnea

  On platforms different than Windows you could easily use char * strings and treat them as UTF-8. The problem is that on Windows you are required to accept and send messages using wchar* strings (W). If you'll use the ANSI functions (A) you will not support Unicode. So if you want to write truly portable application you need to compile it as Unicode on Windows. Now, In order to keep the code clean I would like to see what is the recommended way of dealing with strings, a way that minimize ugliness in the code. Type of strings you may need: std::string, std::wstring, std::tstring,char *,wchat_t *, TCHAR*, CString (ATL one). Issues you may encounter: cout/cerr/cin and their Unicode variants wcout,wcerr,wcin all renamed wide string functions and their TCHAR macros - like strcmp, wcscmp and _tcscmp. constant strings inside code, with TCHAR you will have to fill your code with _T() macros. What approach do you see as being best? (examples are welcome) Personally I would go for a std::tstring approach but I would like to see how would do to the conversions where they are necessary.

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• How do I begin with making a small cross-site AJAX script using someone's API?

  - by Daddy Warbox

  Let's say I want to use this API: http://hiveminder.com/help/reference/API.html The instructions walk through its use via. the curl command line tool, which I'm unfamiliar with. I want to access this API through a simple script on my own page. What are the steps I need to do this?

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• What is a lightweight cross platform WAV playing library?

  - by Lokkju

  I'm looking for a lightweight way to make my program (written in C) be able to play audio files on either windows or linux. I am currently using windows native calls, which is essentially just a single call that is passed a filename. I would like something similar that works on linux. The audio files are Microsoft PCM, Single channel, 22Khz Any Suggestions?

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• How to deal with forward declaration / #import in Cocoa Touch (Objective-C cross C++) correctly?

  - by unknownthreat

  I am trying to write this header file: //@class AQPlayer; //#import "AQPlayer.h" @interface AQ_PWN_iPhoneViewController : UIViewController { AQPlayer* player; } @end AQPlayer is a .mm file written in C++. I tried to make a class forward declaration here, but it complains to me: error: cannot find interface declaration for 'AQPlayer' So I tried to "#import" the header file instead, but it complains something completely off and weird. Here's a slice of the error complained: In file included from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQPlayer.h:51, from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQ_PWN_iPhoneViewController.h:12, from /Users/akaraphan/Desktop/SpecialTopic1/AQ_PWN_iPhone/Classes/AQ_PWN_iPhoneAppDelegate.m:10: /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:78: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAStreamBasicDescription' /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:230: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:231: error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:233: error: expected '=', ',', ';', 'asm' or '__attribute__' before '!=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:234: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:235: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>=' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:236: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>' token /Developer/Examples/CoreAudio/PublicUtility/CAStreamBasicDescription.h:239: error: expected ';', ',' or ')' before '&' token Am I missing something? Can't I do a forward declaration for this?

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• What's the cross-browser way to capture all single clicks on a button?

  - by sany

  What's the best way to execute a function exactly once every time a button is clicked, regardless of click speed and browser? Simply binding a "click" handler works perfectly in all browsers except IE. In IE, when the user clicks too fast, only "dblclick" fires, so the "click" handler is never executed. Other browsers trigger both events so it's not a problem for them. The obvious solution/hack (to me at least) is to attach a dblclick handler in IE that triggers my click handler twice. Another idea is to track clicks myself with mousedown/mouseup, which seems pretty primitive and probably belongs in a framework rather than my application. So, what's the best/usual/right way of handling this? (pure javascript or jQuery preferred)

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• What would you do if you coded a C++/OO cross-platform framework and realize its laying on your disk

  - by Manuel

  This project started as a development platform because i wanted to be able to write games for mobile devices, but also being able to run and debug the code on my desktop machine too (ie, the EPOC device emulator was so bad): the platforms it currently supports are: Window-desktop WinCE Symbian iPhone The architecture it's quite complete with 16bit 565 video framebuffer, blitters, basic raster ops, software pixel shaders, audio mixer with shaders (dsp fx), basic input, a simple virtual file system... although this thing is at it's first write and so there are places where some refactoring would be needed. Everything has been abstracted away and the guiding principle are: mostly clean code, as if it was a book to just be read object-orientation, without sacrifying performances mobile centric The idea was to open source it, but without being able to manage it, i doubt the software itself would benefit from this move.. Nevertheless, i myself have learned a lot from unmaintained projects. So, thanking you in advance for reading all this... really, what would you do?

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