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Search found 164 results on 7 pages for 'misha zaslavsky'.

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  • Example of contravariance

    - by Misha
    I am thinking of the following example to illustrate why contravariance is useful. Let's consider a GUI framework with Widgets, Events, and Event Listeners. abstract class Event; class KeyEvent extends Event class MouseEvent extends Event trait EventListener[-Event] { def listen(e:Event) } Let Widgets define the following methods: def addKeyEventListener(listener:EventListener[KeyEvent]) def addMouseEventListener(listener:EventListener[MouseEvent]) These methods accept only "specific" event listeners, which is fine. However I would like to define also "kitchen-sink" listeners, which listen to all events, and pass such listeners to the "add listener" methods above. For instance, I would like to define LogEventListener to log all incoming events class LogEventListener extends EventListener[Event] { def listen(e:Event) { log(event) } } Since the trait EventListener is contravariant in Event we can pass LogEventListener to all those "add listener" methods without losing their type safety. Does it make sense ?

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  • Java: Making concurrent MySQL queries from multiple clients synchronised

    - by Misha Gale
    I work at a gaming cybercafe, and we've got a system here (smartlaunch) which keeps track of game licenses. I've written a program which interfaces with this system (actually, with it's backend MySQL database). The program is meant to be run on a client PC and (1) query the database to select an unused license from the pool available, then (2) mark this license as in use by the client PC. The problem is, I've got a concurrency bug. The program is meant to be launched simultaneously on multiple machines, and when this happens, some machines often try and acquire the same license. I think that this is because steps (1) and (2) are not synchronised, i.e. one program determines that license #5 is available and selects it, but before it can mark #5 as in use another copy of the program on another PC tries to grab that same license. I've tried to solve this problem by using transactions and table locking, but it doesn't seem to make any difference - Am I doing this right? Here follows the code in question: public LicenseKey Acquire() throws SmartLaunchException, SQLException { Connection conn = SmartLaunchDB.getConnection(); int PCID = SmartLaunchDB.getCurrentPCID(); conn.createStatement().execute("LOCK TABLE `licensekeys` WRITE"); String sql = "SELECT * FROM `licensekeys` WHERE `InUseByPC` = 0 AND LicenseSetupID = ? ORDER BY `ID` DESC LIMIT 1"; PreparedStatement statement = conn.prepareStatement(sql); statement.setInt(1, this.id); ResultSet results = statement.executeQuery(); if (results.next()) { int licenseID = results.getInt("ID"); sql = "UPDATE `licensekeys` SET `InUseByPC` = ? WHERE `ID` = ?"; statement = conn.prepareStatement(sql); statement.setInt(1, PCID); statement.setInt(2, licenseID); statement.executeUpdate(); statement.close(); conn.commit(); conn.createStatement().execute("UNLOCK TABLES"); return new LicenseKey(results.getInt("ID"), this, results.getString("LicenseKey"), results.getInt("LicenseKeyType")); } else { throw new SmartLaunchException("All licenses of type " + this.name + "are in use"); } }

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  • Rails 3: How not to include column's name in a validation message without plugins ?

    - by Misha Moroshko
    I have the following validation: validates_presence_of :price, :message => "my message" and I get the following error when the price is blank: Price my message Is there a way not to include the column name (price) in the message ? I tried to do: validates_presence_of :price, :message => "^ my message" as suggested here, but it didn't work for me. I got the following message: Price ^ my message

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  • How to run Rails 3 application on localhost/<my_port> ?

    - by Misha Moroshko
    To run Rails application on Windows I do: cd < app_dir rails server I see the following: => Booting WEBrick => Rails 3.0.1 application starting in development on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server [2011-01-12 20:32:07] INFO WEBrick 1.3.1 [2011-01-12 20:32:07] INFO ruby 1.9.2 (2010-08-18) [i386-mingw32] [2011-01-12 20:32:07] INFO WEBrick::HTTPServer#start: pid=5812 port=3000 Question 1 Why port 3000 is selected ? Where is it configured ? Question 2 How could I run 2 applications in parallel ? I guess I need to configure one of them to be on other port (like 3001). How should I do this ?

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  • Pass variable name to a function in r

    - by Misha
    Is it possible to pass just a variable name in a function call and have it utilised as such within the function?? pseudocode: q<-function(A){ b<-(w%in%A.2|w%in%A.7) factor(b,levels=c(F,T),labels=c("non-"A,A))} w<-c(0:10) e.2<-c(1,2) e.7<-c(6,7) what I´d like to do is q(e) and have returned non-e,e,e,non-e,non-e,e,e,non-e,non-e //M q<-function(A) { a2<-get(paste(a,".2",sep="")) a7<-get(paste(a,".7",sep="")) b<-(w%in%a2|%in%a7) factor(b,levels=c(F,T),labels=c(paste("non-",a,sep=""),a)) } q("e") Thx, M

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  • How not to lose focus on a login page

    - by Misha Moroshko
    I have a simple login form with 2 input fields: "username" and "password". "username" field is focused by default. The problem is that when user clicks outside "username" or "password" fields, the focus is gone (it is neither on "username" nor on "password" fields"). How can I force the focus to be on these 2 fields only ? In my case, this is a really annoying behavior, so I really want to do this :) Can I do something like: $("*").focus(function() { if (!$(this).hasClass("my_inputs_class")) { // How to stop the focusing process here ? } }); ?

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  • jQuery .parent() does not work

    - by Misha Moroshko
    Why the following code fails with: Error: class_a_jquery_objects[0].parent is not a function ? HTML: <div> <div class='a b'></div> <div class='b c'></div> <div class='c a'></div> </div> <div id='log'></div> JS: $(function() { var class_a_jquery_objects = $(".a"); $("#log").append(class_a_jquery_objects.length + "<br />"); $("#log").append(class_a_jquery_objects[0] + "<br />"); $("#log").append(class_a_jquery_objects[0].parent() + "<br />"); });

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  • How to set cell's background in HTML table ?

    - by misha-moroshko
    I would like to set the background of a cell in HTML table to be like this. What are my options besides using an image as background ? Are there any predefined backgrounds like this ? Maybe dotted, or diagonal lines backgrounds ? In case of image background, if I don't know in advance what would be the size of the cell, what image size should I take ? How to make it be repetitive so it would look nice ? Any HTML/CSS/Javascript/jQuery suggestions are welcome :)

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  • Extracting DCT coefficients from encoded images and video

    - by misha
    Is there a way to easily extract the DCT coefficients (and quantization parameters) from encoded images and video? Any decoder software must be using them to decode block-DCT encoded images and video. So I'm pretty sure the decoder knows what they are. Is there a way to expose them to whomever is using the decoder? I'm implementing some video quality assessment algorithms that work directly in the DCT domain. Currently, the majority of my code uses OpenCV, so it would be great if anyone knows of a solution using that framework. I don't mind using other libraries (perhaps libjpeg, but that seems to be for still images only), but my primary concern is to do as little format-specific work as possible (I don't want to reinvent the wheel and write my own decoders). I want to be able to open any video/image (H.264, MPEG, JPEG, etc) that OpenCV can open, and if it's block DCT-encoded, to get the DCT coefficients. In the worst case, I know that I can write up my own block DCT code, run the decompressed frames/images through it and then I'd be back in the DCT domain. That's hardly an elegant solution, and I hope I can do better. Presently, I use the fairly common OpenCV boilerplate to open images: IplImage *image = cvLoadImage(filename); // Run quality assessment metric The code I'm using for video is equally trivial: CvCapture *capture = cvCaptureFromAVI(filename); while (cvGrabFrame(capture)) { IplImage *frame = cvRetrieveFrame(capture); // Run quality assessment metric on frame } cvReleaseCapture(&capture); In both cases, I get a 3-channel IplImage in BGR format. Is there any way I can get the DCT coefficients as well?

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  • Rails 3: How to validate that A < B where A and B are both model attributes ?

    - by Misha Moroshko
    I would like to validate that customer_price >= my_price. I tried the following: class Product < ActiveRecord::Base attr_accessor :my_price validates_numericality_of :customer_price, :greater_than_or_equal_to => my_price ... end (customer_price is a column in the Products table in the database, while my_price isn't.) Here is the result: NameError in ProductsController#index undefined local variable or method `my_price' for #<Class:0x313b648> What is the right way to do this in Rails 3 ?

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  • Long task in Javascript

    - by Misha Moroshko
    Why in the following code I see the whole page at once ? Thanks ! HTML: <div></div> CSS: div { width: 100px; height: 300px; border: 1px solid black; text-align: center; } Javascript: $(function() { for (var i=0; i<15; i++) { sleep(100); $("div").append("<span>--- " + i + " ---<br /></span>"); } function sleep(milliseconds) { var start = new Date().getTime(); for (var i = 0; i < 1e7; i++) { if ((new Date().getTime() - start) > milliseconds){ break; } } } });

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  • What is the fastest method to calculate substring

    - by Misha Moroshko
    I have a huge "binary" string, like: 1110 0010 1000 1111 0000 1100 1010 0111.... It's length is 0 modulo 4, and may reach 500,000. I have also a corresponding array: {14, 2, 8, 15, 0, 12, 10, 7, ...} (every number in the array corresponds to 4 bits in the string) Given this string, this array, and a number N, I need to calculate the following substring string.substr(4*N, 4), i.e.: for N=0 the result should be 1110 for N=1 the result should be 0010 I need to perform this task many many times, and my question is what would be the fastest method to calculate this substring ? One method is to calculate the substring straight forward: string.substr(4*N, 4). I'm afraid this one is not efficient for such huge strings. Another method is to use array[N].toString(2) and then wrap the result with zeros if needed. I'm not sure how fast is this. May be you have any other ideas ?

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  • Fractional y-var in ggplot

    - by Misha
    How can I easily create a fractional y-value when using ggplot? t <- as.factor(test=sample(seq(0,100,10),1000,rep=T)) d <- as.factor(sample(c(0,1),1000,rep=T) p <- data.frame(t,d) My best shot was: ggplot(p,aes(x=t,y=prop.table(table(t,d),1)[,1])) + geom_point() However this doesnt work and I guess there is an easier way around this...

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  • Long task in Javascript / jQuery

    - by Misha Moroshko
    I have a long task in Javascript that should be performed before the web page content is displayed. During the execution of this task I would like to show an image whose opacity will grow up to 100% (when the task is done). How this can be achieved ?

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  • Javascript for loop efficiency

    - by Misha Moroshko
    Is for (var i=0, cols=columns.length; i<cols; i++) { ... } more efficient than for (var i=0; i<columns.length; i++) { ... } ? In the second variant, is columns.length calculated each time the condition i<columns.length is checked ?

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  • How to change file contents in PHP ?

    - by Misha Moroshko
    I save in a file some info about users (like number of times user passed the login page, last visited time, and so on). I want to read this info from the file, and update it (add 1 to the counter, and change the last visited time). My question is: can I do it without opening the file twice ? I open the first time to read the contents, and then open it again to overwrite the contents with the updated ones. Thanks !

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  • Referring to a specific place on page

    - by misha-moroshko
    I know that in Javascript document.location.href = "#my_id" tells the browser to display the same page starting from element with id="my_id". In this case, the address that appears in the address bar is in the following format: my_page_address#my_id Is this the only method to refer to a specific place on a page ? I'm looking for a method that will not show my_id in the address bar.

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