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  • Is it safe to draw three separate QImages in three separate QThreads?

    - by yan bellavance
    I have a QMainWindow with three widgets inside that are promoted to a class containing a subclassed QThread. They each draw on a local QImage in their rexpective qthread which is sent with a signal once its drawn and then rendered by calling update (mandlebrot example) from the slot. Is this safe or dangerous? They do not share any data, at least none that I am generating and am wondering what data they could be sharing that is outside of my coding range ie that is generated by Qt automatically.

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  • The simplest concurrency pattern

    - by Ilya Kogan
    Please, would you help me in reminding me of one of the simplest parallel programming techniques. How do I do the following in C#: Initial state: semaphore counter = 0 Thread 1: // Block until semaphore is signalled semaphore.Wait(); // wait until semaphore counter is 1 Thread 2: // Allow thread 1 to run: semaphore.Signal(); // increments from 0 to 1 It's not a mutex because there is no critical section, or rather you can say there is an infinite critical section. So what is it?

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  • Pyqt - QMenu dynamically populated and clicked

    - by mleep
    I need to be able to know what item I've clicked in a dynamically generated menu system. I only want to know what I've clicked on, even if it's simply a string representation. def populateShotInfoMenus(self): self.menuFilms = QMenu() films = self.getList() for film in films: menuItem_Film = self.menuFilms.addAction(film) self.connect(menuItem_Film, SIGNAL('triggered()'), self.onFilmSet) self.menuFilms.addAction(menuItem_Film) def onFilmRightClick(self, value): self.menuFilms.exec_(self.group1_inputFilm.mapToGlobal(value)) def onFilmSet(self, value): print 'Menu Clicked ', value

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  • Connecting slots and events in PyQt4 in a loop

    - by LukaD
    Im trying to build a calculator with PyQt4 and connecting the 'clicked()' signals from the buttons doesn't as expected. Im creating my buttons for the numbers inside a for loop where i try to connect them afterwards. def __init__(self): for i in range(0,10): self._numberButtons += [QPushButton(str(i), self)] self.connect(self._numberButtons[i], SIGNAL('clicked()'), lambda : self._number(i)) def _number(self, x): print(x) When I click on the buttons all of them print out '9'. Why is that so and how can i fix this?

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  • Compiling VIM on OS X Mountain Lion

    - by Lauri L
    Compiling VIM on Mountain Lion does not work for me. I compile VIM with the following sequence: hg clone https://vim.googlecode.com/hg/ vim cd vim ./configure --enable-rubyinterp --with-features=huge -prefix=/usr make I then try to start the compiled binary with src/vim, but it crashes like this: $ src/vim Vim: Caught deadly signal SEGV Vim: Finished. Segmentation fault: 11 What am I missing here?

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  • Do you use an exception class in your Perl programs? Why or why not?

    - by daotoad
    I've got a bunch of questions about how people use exceptions in Perl. I've included some background notes on exceptions, skip this if you want, but please take a moment to read the questions and respond to them. Thanks. Background on Perl Exceptions Perl has a very basic built-in exception system that provides a spring-board for more sophisticated usage. For example die "I ate a bug.\n"; throws an exception with a string assigned to $@. You can also throw an object, instead of a string: die BadBug->new('I ate a bug.'); You can even install a signal handler to catch the SIGDIE psuedo-signal. Here's a handler that rethrows exceptions as objects if they aren't already. $SIG{__DIE__} = sub { my $e = shift; $e = ExceptionObject->new( $e ) unless blessed $e; die $e; } This pattern is used in a number of CPAN modules. but perlvar says: Due to an implementation glitch, the $SIG{DIE} hook is called even inside an eval(). Do not use this to rewrite a pending exception in $@ , or as a bizarre substitute for overriding CORE::GLOBAL::die() . This strange action at a distance may be fixed in a future release so that $SIG{DIE} is only called if your program is about to exit, as was the original intent. Any other use is deprecated. So now I wonder if objectifying exceptions in sigdie is evil. The Questions Do you use exception objects? If so, which one and why? If not, why not? If you don't use exception objects, what would entice you to use them? If you do use exception objects, what do you hate about them, and what could be better? Is objectifying exceptions in the DIE handler a bad idea? Where should I objectify my exceptions? In my eval{} wrapper? In a sigdie handler? Are there any papers, articles or other resources on exceptions in general and in Perl that you find useful or enlightening.

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  • Execute Slot in different class

    - by sijith
    Hi, I want to execute a slot in different class. Is it possible UI_CDSK Obj; connect(Obj.penDrive,SIGNAL(clicked()),this,SLOT( Obj.caller())); This code is in different class and from this class i want to execute slot of different class(UI_CDSK ) Here penDrive and caller belongs to function UI_CDSK class and the mentioned code is in other class

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  • EXC_BAD_ACCESS when simply casting a pointer in Obj-C

    - by AlexChilcott
    Hi all, Frequent visitor but first post here on StackOverflow, I'm hoping that you guys might be able to help me out with this. I'm fairly new to Obj-C and XCode, and I'm faced with this really... weird... problem. Googling hasn't turned up anything whatsoever. Basically, I get an EXC_BAD_ACCESS signal on a line that doesn't do any dereferencing or anything like that that I can see. Wondering if you guys have any idea where to look for this. I've found a work around, but no idea why this works... The line the broken version barfs out on is the line: LevelEntity *le = entity; where I get my bad access signal. Here goes: THIS VERSION WORKS NSArray *contacts = [self.body getContacts]; for (PhysicsContact *contact in contacts) { PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } THIS VERSION DOESNT WORK NSArray *contacts = [self.body getContacts]; for (NSUInteger i = 0; i < [contacts count]; i++) { PhysicsContact *contact = [contacts objectAtIndex:i]; PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } Here, the only difference between the two examples is the way I enumerate through my array. In the first version (which works) I use for (... in ...), where as in the second I use for (...; ...; ...). As far as I can see, these should be the same. This is seriously weirding me out. Anyone have any similar experience or idea whats going on here? Would be really great :) Cheers, Alex

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  • Command line semaphore utility

    - by compie
    I want to write a command line utility that can be used to synchronize the execution off programs in different consoles. Console A: $ first_program && semaphore -signal Console B: $ semaphore -wait && second_program The first program takes a long take to complete. The second program can only start when the first program has finished. Which synchronization object do I need to implement this?

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  • Is it any loose coupling mechanism in Objective-C + Cocoa like C# delegates or C++Qt signals+slots?

    - by Eye of Hell
    Hello. For a large programs, the standard way to chalenge a complexity is to divide a program code into small objects. Most of the actual programming languages offer this functionality via classes, so is Objective-C. But after source code is separated into small object, the second challenge is to somehow connect them with each over. Standard approaches, supported by most languages are compositon (one object is a member field of another), inheritance, templates (generics) and callbacks. More cryptic techniques include method-level delagates (C#) and signals+slots (C++Qt). I like the delegates / signals idea, since while connecting two objects i can connect individual methods with each over, without objects knowing anything of each over. For C#, it will look like this: var object1 = new CObject1(); var object2 = new CObject2(); object1.SomethingHappened += object2.HandleSomething; In this code, is object1 calls it's SomethingHappened delegate (like a normal method call) the HandleSomething method of object2 will be called. For C++Qt, it will look like this: var object1 = new CObject1(); var object2 = new CObject2(); connect( object1, SIGNAL(SomethingHappened()), object2, SLOT(HandleSomething()) ); The result will be exactly the same. This technique has some advantages and disadvantages, but generally i like it more than interfaces since if program code base grows i can change connections and add new ones without creating tons of interfaces. After examination of Objective-C i havn't found any way to use this technique i like :(. It seems that Objective-C supports message passing perfectly well, but it requres for object1 to have a pointer to object2 in order to pass it a message. If some object needs to be connected to lots of other objects, in Objective-C i will be forced to give him pointers to each of the objects it must be connected. So, the question :). Is it any approach in Objective-C programming that will closely resemble delegate / signal+slot types of connection, not a 'give first object an entire pointer to second object so it can pass a message to it'. Method-level connections are a bit more preferable to me than object-level connection ^_^.

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  • Django updating a single model

    - by Hellnar
    Hello How can I use the update() method on a single model which I retrieved via Queryset.get() ? It seems like model. Model doesn't have an update() method yet I cannot invoke .save() as I have a pre-save signals which messes things up. EDIT: An idea would be passing some parameter to the save method and catching it at the pre_save signal, so that I can understand the purpose, how can this be done ? Thanks

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  • Analyzing data for noisy arrays

    - by jimbo
    Using MATLAB I filtered a very noisy m x n array with a low-pass Gaussian filter, cleaned it up pretty well but still not well enough to analyze my data. What would the next step be? I'm thinking that signal enhancement, but am not sure how to go about this.

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  • Bluetooth communications with C#

    - by Abdulaziz
    hello, I want to write 2 programs with C# one work on PC, the other work on a windows mobile phone. So I want the PC program to send a signal via Bluetooth ( 1 byte maybe) to the windows mobile phone. and the mobile program (which work on background) handles and accepts this byte without the need of pairing. how to code this? please I need any kind of help.

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  • Safe Cross Thread Signals/Slot C++

    - by JP
    It seem that the only implementation that provide Safe Cross-Thread Signals for both the Signal class and what's being called in the slot is QT. (Maybe I'm wrong?). But I cannot use QT in the project I'm doing. So how could I provide safe Slots call from a different thread (Using Boost::signals2 for example)? Are mutex inside the slot the only way? I think signals2 protect themself but not what's being done inside the slot. Thanks

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  • Qt, Color Picker Dialog?

    - by high6
    Is there a color picker dialog for Qt like the following? Also it needs to have a OnColorChanged signal which is called when ever the selected color changes. I want to give a live preview when they are changing the colors, that is why. Using google I could only find this one that was a triangle in side of a circle and personally I think it looks ugly.

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  • No clock with FTDIchip FT2232 MPSSE mode

    - by Simi
    Hello, I'm trying to write/read to an extern device connected to a FTDIchip FT2232 MPSSE mode using SPI. I'm using the SPI function given by FTDI for Labview. I'm doing this: Open_Device - Init_Device - Write/Read - Close_Device The problem is that I don't have a clock signal on the scope when I try to read/write. Do you have a solution? Thanks

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  • How to create a status bar icon on the right side? (Android)

    - by yuku
    Notification and NotificationManager are used to create icons to be placed on the top-left position of the screen. A Notification also need to have an entry on the status bar pull-down. However, icons on the right side such as the battery, signal strength, wireless indicators do not need any entry on the status bar. How do I make such icons without any entry in the status bar pull-down?

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  • event handling in C++

    - by Max
    Hi. I'm writing a game in C++, and I'm trying to get it to recognize keyboard and mouse events. Google tells me that boost.signal is suitable for event handling, but none of the code samples or tutorials I've found tell me how to associate a keypress or mouseclick with a function. Can anyone shed any light on this?

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