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  • Why is there no autorelease pool when I do performSelectorInBackground: ?

    - by Thanks
    I am calling a method that goes in a background thread: [self performSelectorInBackground:@selector(loadViewControllerWithIndex:) withObject:[NSNumber numberWithInt:viewControllerIndex]]; then, I have this method implementation that gets called by the selector: - (void) loadViewControllerWithIndex:(NSNumber *)indexNumberObj { NSAutoreleasePool *arPool = [[NSAutoreleasePool alloc] init]; NSInteger vcIndex = [indexNumberObj intValue]; Class c; UIViewController *controller = [viewControllers objectAtIndex:vcIndex]; switch (vcIndex) { case 0: c = [MyFirstViewController class]; break; case 1: c = [MySecondViewController class]; break; default: NSLog(@"unknown index for loading view controller: %d", vcIndex); // error break; } if ((NSNull *)controller == [NSNull null]) { controller = [[c alloc] initWithNib]; [viewControllers replaceObjectAtIndex:vcIndex withObject:controller]; [controller release]; } if (controller.view.superview == nil) { UIView *placeholderView = [viewControllerPlaceholderViews objectAtIndex:vcIndex]; [placeholderView addSubview:controller.view]; } [arPool release]; } Althoug I do create an autorelease pool there for that thread, I always get this error: 2009-05-30 12:03:09.910 Demo[1827:3f03] *** _NSAutoreleaseNoPool(): Object 0x523e50 of class NSCFNumber autoreleased with no pool in place - just leaking Stack: (0x95c83f0f 0x95b90442 0x28d3 0x2d42 0x95b96e0d 0x95b969b4 0x93a00155 0x93a00012) If I take away the autorelease pool, I get a whole bunch of messages like these. I also tried to create an autorelease pool around the call of the performSelectorInBackground:, but that doesn't help. I suspect the parameter, but I don't know why the compiler complains about an NSCFNumber. Am I missing something? My Instance variables are all "nonatomic". Can that be a problem? UPDATE: I may also suspect that some variable has been added to an autorelease pool of the main thread (maybe an ivar), and now it trys to release that one inside the wrong autorelease pool? If so, how could I fix that? (damn, this threading stuff is complex ;) )

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  • Is it possible to execute a function in Mongo that accepts any parameters?

    - by joshua.clayton
    I'm looking to write a function to do a custom query on a collection in Mongo. Problem is, I want to reuse that function. My thought was this (obviously contrived): var awesome = function(count) { return function() { return this.size == parseInt(count); }; } So then I could do something along the lines of: db.collection.find(awesome(5)); However, I get this error: error: { "$err" : "error on invocation of $where function: JS Error: ReferenceError: count is not defined nofile_b:1" } So, it looks like Mongo isn't honoring scope, but I'm really not sure why. Any insight would be appreciated. To go into more depth of what I'd like to do: A collection of documents has lat/lng values, and I want to find all documents within a concave or convex polygon. I have the function written but would ideally be able to reuse the function, so I want to pass in an array of points composing my polygon to the function I execute on Mongo's end. I've looked at Mongo's geospatial querying and it currently on supports circle and box queries - I need something more complex.

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  • How do tools like Hiphop for PHP deal with heterogenous arrays?

    - by Derek Thurn
    I think HipHop for PHP is an interesting tool. It essentially converts PHP code into C++ code. Cross compiling in this manner seems like a great idea, but I have to wonder, how do they overcome the fundamental differences between the two type systems? One specific example of my general question is heterogeneous data structures. Statically typed languages don't tend to let you put arbitrary types into an array or other container because they need to be able to figure out the types on the other end. If I have a PHP array like this: $mixedBag = array("cat", 42, 8.5, false); How can this be represented in C++ code? One option would be to use void pointers (or the superior version, boost::any), but then you need to cast when you take stuff back out of the array... and I'm not at all convinced that the type inferencer can always figure out what to cast to at the other end. A better option, perhaps, would be something more like a union (or boost::variant), but then you need to enumerate all possible types at compile time... maybe possible, but certainly messy since arrays can contain arbitrarily complex entities. Does anyone know how HipHop and similar tools which go from a dynamic typing discipline to a static discipline handle these types of problems?

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  • Our GUI Situation

    - by shawn-harrison
    These days, any decent Windows desktop application must perform well and look good under the following conditions: 1) XP and Vista and Windows 7. 2) 32 bit and 64 bit. 3) With and without Themes. 4) With and without Aero. 5) At 96 and 120 and perhaps custom DPIs. 6) One or more monitors (screens). 7) Each OS has it's own preferred Font. Oh My! What is a lowly little Windows desktop application developer to do :(. I'm hoping to get a thread started with suggestions on how to deal with this Gui dilemma. First off, I'm on Delphi 7. a) Does Delphi 2010 bring anything new to the table to help with this situation? b) Should we pick an aftermarket component suite and rely on them to solve all these problems? c) Should we go with an aftermarket skinning engine? d) Perhaps a more html type gui is the way to go. Can we make a relatively complex gui app with html that doesn't require using a browser? (prefer to keep it form based) e) Should we just knuckle down and code through each one of these scenarios and quit bitching about it? f) And finally, how in the world are we supposed to test all these conditions? thanks, shawnH

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  • How to use the same element name in different purposes ( in XML and DTD ) ?

    - by BugKiller
    Hi, I Want to create a DTD schema for this xml document: <root> <student> <name> <firstname>S1</firstname> <lastname>S2</lastname> </name> </student> <course> <name>CS101</name> </course> </root> as you can see , the element name in the course contains plain text ,but the element name in the student is complex type ( first-name, last-name ). The following is the DTD: <!ELEMENT root (course|student)*> <!ELEMENT student (name)> <!ELEMENT name (lastname|firstname)> <!ELEMENT firstname (#PCDATA)> <!ELEMENT lastname (#PCDATA)> <!ELEMENT course (name)> When I want to validate it , I get an error because the course's name has different structure then the student's name . My Question: how can I make a work-around solution for this situation without changing the name of element name using DTD not xml schema . Thanks.

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  • De-normalization alternative to specific MYSQL problem?

    - by Booker
    I am facing quite a specific optimization problem. I currently have 4 normalized tables of data. Every second, possibly thousands of users will pull down up-to-date info from these tables using AJAX. The thing is that I can predict relatively easily which subset of data they need... The most recent 100 or so entries in those 4 normalized tables. I have been researching de-normalization... but feel that perhaps there is an easier solution. I was thinking that I could somehow every second run one sql query to condense the needed info, store it in a temp cached table and then have all of the user queries just draw from this. This will allow the complex join of 4 tables to only be run once, and then from there the users just need to do a simple lookup from the cached table. I really don't know if this is feasible. Comments on this or any other suggestions would be much appreciated. Thanks!

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  • Rhino Mocks Partial Mock

    - by dotnet crazy kid
    I am trying to test the logic from some existing classes. It is not possible to re-factor the classes at present as they are very complex and in production. What I want to do is create a mock object and test a method that internally calls another method that is very hard to mock. So I want to just set a behaviour for the secondary method call. But when I setup the behaviour for the method, the code of the method is invoked and fails. Am I missing something or is this just not possible to test without re-factoring the class? I have tried all the different mock types (Strick,Stub,Dynamic,Partial ect.) but they all end up calling the method when I try to set up the behaviour. using System; using MbUnit.Framework; using Rhino.Mocks; namespace MMBusinessObjects.Tests { [TestFixture] public class PartialMockExampleFixture { [Test] public void Simple_Partial_Mock_Test() { const string param = "anything"; //setup mocks MockRepository mocks = new MockRepository(); var mockTestClass = mocks.StrictMock<TestClass>(); //record beahviour *** actualy call into the real method stub *** Expect.Call(mockTestClass.MethodToMock(param)).Return(true); //never get to here mocks.ReplayAll(); //this is what i want to test Assert.IsTrue(mockTestClass.MethodIWantToTest(param)); } public class TestClass { public bool MethodToMock(string param) { //some logic that is very hard to mock throw new NotImplementedException(); } public bool MethodIWantToTest(string param) { //this method calls the if( MethodToMock(param) ) { //some logic i want to test } return true; } } } }

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  • spring.net proxy factory with target type needs property virtual ?

    - by Vince
    Hi all, I'm creating spring.net proxy in code by using ProxyFactory object with ProxyTargetType to true to have a proxy on a non interfaced complex object. Proxying seems ok till i call a method on that object. The method references a public property and if this property is not virtual it's value is null. This doesn't happen if i use Spring.Aop.Framework.AutoProxy.InheritanceBasedAopConfigurer in spring config file but in this case i can't use this because spring context doesn't own this object. Is this normal to have such behavior or is there a tweak to perform what i want (proxying object virtual method without having to change properties virtual)? Note that i tried factory.AutoDetectInterfaces and factory.ProxyTargetAttributes values but doesn't help. My proxy creation code: public static T CreateMethodCallStatProxy<T>() { // Proxy factory ProxyFactory factory = new ProxyFactory(); factory.AddAdvice(new CallMonitorTrackerAdvice()); factory.ProxyTargetType = true; // Create instance factory.Target = Activator.CreateInstance<T>(); // Get proxy T proxiedClass = (T)factory.GetProxy(); return proxiedClass; } Thanks for your help

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  • Stuck on Object scope in Java

    - by ivor
    Hello, I'm working my way through an exercise to understand Java, and basically I need to merge the functionality of two classes into one app. I'm stuck on one area though - the referencing of objects across classes. What I have done is set up a gui in one class (test1), and this has a textfield in ie. chatLine = new JTextField(); in another class(test2), I was planning on leaving all the functionality in there and referencing the various gui elements set up in test1 - like this test1.chatLine I understand this level of referencing, I tested this by setting up a test method in the test2 class public static void testpass() { test1.testfield.setText("hello"); } I'm trying to understand how to implement the more complex functionality in test2 class though, specifically this existing code; test1.chatLine.addActionListener(new ActionAdapter() { public void actionPerformed(ActionEvent e) { String s = Game.chatLine.getText(); if (!s.equals("")) { appendToChatBox("OUTGOING: " + s + "\n"); Game.chatLine.selectAll(); // Send the string sendString(s); } } }); This is the bit I'm stuck on, if I should be able to do this - as it's failing on the compile, can I add the actionadapter stuff to the gui element thats sat in test1, but do this from test2 - I'm wondering if I'm trying to do something that's not possible. Hope this makes sense, I'm pretty confused over this - I'm trying to understand how the scope and referencing works. Ideally what i'm trying to achieve is one class that has all the main stuff in, the gui etc, then all the related functionality in the other class, and target the first class's gui elements with the results etc. Any thoughts greatly appreciated.

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  • jQuery Accordion

    - by Fuego DeBassi
    Just wondering if anyone can provide some basic advice on an accordion I'm trying to simplify. Got a working version, but it seems way overly complex. Here is my new JS. $(document).ready(function() { $("#themes li ul").hide(); $("#themes li").hover(function() { $("ul").show(); }, function() { $("li ul").hide(); }); The markup looks like this: <ul> <li>Tier 1 <ul> <li>Tier 2</li> <li>Tier 2</li> </ul> </li> <li>Tier 1 <ul> <li>Tier 2</li> <li>Tier 2</li> </ul> </li> </ul> My script works alright. But it shows all of the child ul's when any parent li is hovered, and it hides all the child ul's when unhovered. Just not sure how I can get it to A.) Only .show the li ul when that specific li is hovered. And B.) Hide the shown li ul only when another one is hovered (not itself). Example + explanation would be especially helpful! Thanks!!

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  • Save XML directly to Database with C#

    - by LifeH2O
    Here is a part of my xml file <teams> <team-profile> <name>Australia</name> <id>1</id> <stats type="Test"> <span>1877-2010</span> <matches>721</matches> <won>339</won> <lost>186</lost> <tied>2</tied> <draw>194</draw> <percentage>47.01</percentage> </stats> <squad> <player id="135" fullname="Shane Warne"/> <player id="136" fullname="Damien Martyn"/> <player id="138" fullname="Michael Clarke"/> </squad> </team-profile> </team> I have read somewhere that there is a way to save this XML directly to database. I am using VS2010. I have created the dataset, for the data i need from this xml. Is there any way to map this XML directly on dataset? Any other idea? I also have to save some other more complex XML files to database. I have tried xsd.exe to create xsd schema for this XML.

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  • C Run-Time library part 2

    - by b-gen-jack-o-neill
    Hi, I was suggested when I have some further questions on my older ones, to create newer Question and reffer to old one. So, this is the original question: What is the C runtime library? OK, from your answers, I now get thet statically linked libraries are Microsoft implementation of C standart functions. Now: If I get it right, the scheme would be as follow: I want to use printf(), so I must include which just tels compiler there us functio printf() with these parameters. Now, when I compile code, becouse printf() is defined in C Standart Library, and becouse Microsoft decided to name it C Run Time library, it gets automatically statically linked from libcmt.lib (if libcmt.lib is set in compiler) at compile time. I ask, becouse on wikipedia, in article about runtime library there is that runtime library is linked in runtime, but .lib files are linked at compile time, am I right? Now, what confuses me. There is .dll version of C standart library. But I thought that to link .dll file, you must actually call winapi program to load that library. So, how can be these functions dynamically linked, if there is no static library to provide code to tell Windows to load desired functions from dll? And really last question on this subject - are C Standart library functions also calls to winapi even they are not .dll files like more advanced WinAPI functions? I mean, in the end to access framebuffer and print something you must tell Windows to do it, since OS cannot let you directly manipulate HW. I think of it like the OS must be written to support all C standart library functions same way across similiar versions, since they are statically linked, and can differently support more complex WinAPI calls becouse new version of OS can have adjustements in the .dll file.

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  • How can I superimpose modified loess lines on a ggplot2 qplot?

    - by briandk
    Background Right now, I'm creating a multiple-predictor linear model and generating diagnostic plots to assess regression assumptions. (It's for a multiple regression analysis stats class that I'm loving at the moment :-) My textbook (Cohen, Cohen, West, and Aiken 2003) recommends plotting each predictor against the residuals to make sure that: The residuals don't systematically covary with the predictor The residuals are homoscedastic with respect to each predictor in the model On point (2), my textbook has this to say: Some statistical packages allow the analyst to plot lowess fit lines at the mean of the residuals (0-line), 1 standard deviation above the mean, and 1 standard deviation below the mean of the residuals....In the present case {their example}, the two lines {mean + 1sd and mean - 1sd} remain roughly parallel to the lowess {0} line, consistent with the interpretation that the variance of the residuals does not change as a function of X. (p. 131) How can I modify loess lines? I know how to generate a scatterplot with a "0-line,": # First, I'll make a simple linear model and get its diagnostic stats library(ggplot2) data(cars) mod <- fortify(lm(speed ~ dist, data = cars)) attach(mod) str(mod) # Now I want to make sure the residuals are homoscedastic qplot (x = dist, y = .resid, data = mod) + geom_smooth(se = FALSE) # "se = FALSE" Removes the standard error bands But does anyone know how I can use ggplot2 and qplot to generate plots where the 0-line, "mean + 1sd" AND "mean - 1sd" lines would be superimposed? Is that a weird/complex question to be asking?

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  • Creating Emulated iSCSI Target in a Lab/Testing Environment using Windows Server 2008 R2

    - by Brian McCleary
    We have a single server running Windows Server 2008 with Hyper-V installed running 5 virtual machines. I have purchased a second DELL R805 Server so that we can create a fail-over cluster to our current R805 that is currently in production. Right now, our R805 connects via iSCSI to a MD3000i iSCSI SAN. Before we try to roll out the second server and clustering to our production environment, I want to be able to test and "play with" the clustering features in our lab before rolling it out. The problem is that I don't want to spend a couple thousand dollars on another iSCSI SAN server just for testing. I already have two servers in my lab that are installed with Windows Server 2008 R2 64bit (one is the R805 and another spare desktop that was laying around) and with the Hyper-V roll enabled that should be ready to test with, but I don't have an iSCSI target to use as the Cluster Shared Volume. Is there anyway to install, either on a Hyper-V image or on a external spare computer that we have some sort of emulated iSCSI target? In our lab, we obviously don't need a real SAN, just something that we can test out how to setup the clustering properly outside of our production environment. Any advise is appreciated. FYI - I have read Jose Barret's blog on WUDSS at http://blogs.technet.com/josebda/archive/2008/01/07/installing-the-evaluation-version-of-wudss-2003-refresh-and-the-microsoft-iscsi-software-target-version-3-1-on-a-vm.aspx, but it seems awfully complex. I'm hoping for an easier solution.

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  • Three20 TTSectionedDataSource row height

    - by Ward
    Hey there, I'm using Three20 to create a table with several textfields for user registration. I've found two possible methods using Three20. The first uses the TTSectionedDataSource's tableDidLoadModel method to manually add UI components and the second adds custom items that contains pre formatted UI components. The second option seems way more complex and I'm having a difficult time accessing the individual fields. So if one field is a textfield for the username, I need to access the field to submit the username and it doesn't seem like there's an easy answer. The first option gives me a lot of flexibility, but I can't figure out how to set the individual row heights. One row may have a label above a text field, another may have an image, etc. Is there a method that can be used in TTSectionedDataSource that will allow me to set the height for each row? Thus far, I'm using method one and creating UIViews to hold a label field and a text field. I've tried changing the frame of the uiview before it is added to the items array, but it has no affect. Any ideas?

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  • Web application architecture, and application servers?

    - by seanieb
    Hi, I'm building a web application, and I need to use an architecture that allows me to run it on two servers. The application scrapes information from other sites periodically, and on input from the end user. To do this I'm using Php+curl to scrape the information, Php or python to parse it and store the results in a MySQLDB. Then I will use Python to run some algorithms on the data, this will happen both periodically and on input from the end user. I'm going to cache some of the results in the MySQL DB and sometimes if it is specific to the user, skip storing the data and serve it to the user. I'm think of using Php for the website front end on a separate web server, running the Php spider, MySQL DB and python on another server. As you can see I'm fairly clueless. I'm familiar with using Php, MySQL and the basics of Python, but bringing this all together using something more complex than a cron job is new to me. How do go about implementing this? What frame work(s) should I use? Is MVC a good architecture for this? (I'm new to MVC, architectures etc.) Is Cakephp a good solution? If so will I be able to control and monitor the Python code using it?

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  • How do I get a ComboBox SelectionChanged event to fire from a nested ListBoxItem?

    - by Stephen McCusker
    This is a rather complex problem that has me really confused right now. Any help would be greatly appreciated. The Setup: ListBox of Type A UserControls -ListBoxItem of Type A UserControl --ListBox of Type B UserControls ---ListBoxItem of Type B UserControl ----ListBox of Type C UserControls -----ListBoxItem of Type C UserControl (contains the ComboBox) In other words, the Type A control has a ListBox of Type B controls that has a ListBox of Type C controls. All of the controls are hierarchical in nature. Type A contains the data that's needed to load the Type B controls and the Type B contains the data that's needed to load the Type C controls. The Type C control has a standard ComboBox in it for changing the values of the present items. In addition to the above structure, I have drag and dropping tied to the PreviewMouseLeftButtonDown event on both the Type A and Type B UserControl levels to handle reordering/deleting/etc commands in the GUI. All of this is working as intended. The Problem: When I attempt to change the value in the ComboBox, the SelectionChanged event never fires on the Type C "level" unless I'm careful enough to click on the borders/spacing in between any Type A or B controls. This happens when my ComboBox popout menu overlaps on either a Type A or B control located below itself. The selection events for Type A or B are firing instead of the Type C events, so the ComboBox is never changing its value reliably. In the debugger, the code for handling the drag and drop is triggering on the next ListBoxItem that's located underneath the ComboBox. Thoughts: Is there a way I can make my ComboBox popup take prevalence over the items behind it while double-nested in a ListBox (ie, ignore anything behind it while it's open)? Is there some way to reroute the incorrectly firing SelectionChanged events down to the ComboBox that's supposed to be triggering them?

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  • Sharing storage between servers

    - by El Yobo
    I have a PHP based web application which is currently only using one webserver but will shortly be scaling up to another. In most regards this is pretty straightforward, but the application also stores a lot of files on the filesystem. It seems that there are many approaches to sharing the files between the two servers, from the very simple to the reasonably complex. These are the options that I'm aware of Simple network storage NFS SMB/CIFS Clustered filesystems Lustre GFS/GFS2 GlusterFS Hadoop DFS MogileFS What I want is for a file uploaded via one webserver be immediately available if accessed through the other. The data is extremely important and absolutely cannot be lost, so whatever is implemented needs to a) never lose data and b) have very high availability (as good as, or better, than a local filesystem). It seems like the clustered filesystems will also provide faster data access than local storage (for large files) but that isn't of vita importance at the moment. What would you recommend? Do you have any suggestions to add or anything specifically to look out for with the above options? Any suggestions on how to manage backup of data on the clustered filesystems?

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  • Advantage Database Server ORDER BY behaviour

    - by ie
    I'm using ADS v10 beta. I'm trying to numerate ordered resultset. 1) ORDER BY in nested queries. I need to use nested SELECT for some calculations: SELECT Name, Value, ROWNUM() FROM (SELECT * FROM MainTable WHERE Value > 0 ORDER BY Value) a And I'm getting Expected lexical element not found: ) There was a problem parsing the table names after the FROM keyword in your SELECT statement. Everything is working well when the ORDER BY is removed. Although, I found the sample in the Help, it looks like my query (more complex, indeed): SELECT * FROM (SELECT TOP 10 empid, fullname FROM branch1 ORDER BY empid) a UNION SELECT empid, fullname FROM branch2 ORDER BY empid 2) ORDER BY + ROWNUM(). I used the nested query in the example above, to numerate ordered rows. Is there are any chance to avoid nested query? In the SQL Server I can do something like this: SELECT Name, Value, ROW_NUMBER() OVER(ORDER BY Value) FROM MainTable WHERE Value > 1 ORDER BY Value Please advice. Thanks.

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  • Special technology needed for browser based chat?

    - by orokusaki
    On this post, I read about the usage of XMPP. Is this sort of thing necessary, and more importantly, my main question expanded: Can a chat server and client be built efficiently using only standard HTTP and browser technologies (such as PHP and JS, or RoR and JS, etc)? Or, is it best to stick with old protocols like XMPP find a way to integrate them with my application? I looked into CampFire via LiveHTTPHeaders and Firebug for about 5 minutes, and it appears to use Ajax to send a request which is never answered until another chat happens. Is this just CampFire opening a new thread on the server to listen for an update and then returning a response to the request when the thread hears an update? I noticed that they're requesting on a specific port (8043 if memory serves me) which makes me think that they're doing something more complex than just what I mentioned. Also, the URL requested started with /tcp/ which I found interesting. Note: I don't expect to ever have more than 150 users live-chatting in all the rooms combined at the same time. I understand that if I was building a hosted pay for chat service like CampFire with thousands of concurrent users, it would behoove me to invest time in researching special technologies vs trying to reinvent the wheel in a simple way in my app. Also, if you're going to do it with server polling, how often would you personally poll to maximize response without slamming the server?

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  • Rolling back file moves, folder deletes and mysql queries

    - by Workoholic
    This has been bugging me all day and there is no end in sight. When the user of my php application adds a new update and something goes wrong, I need to be able to undo a complex batch of mixed commands. They can be mysql update and insert queries, file deletes and folder renaming and creations. I can track the status of all insert commands and undo them if an error is thrown. But how do I do this with the update statements? Is there a smart way (some design pattern?) to keep track of such changes both in the file structure and the database? My database tables are MyISAM. It would be easy to just convert everything to InnoDB, so that I can use transactions. That way I would only have to deal with the file and folder operations. Unfortunately, I cannot assume that all clients have InnoDB support. It would also require me to convert many tables in my database to InnoDB, which I am hesitant to do.

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  • Ajax heavy JS apps using excessive amounts of memory over time.

    - by Shane Reustle
    I seem to have some pretty large memory leaks in an app that I am working on. The app itself is not very complex. Every 15 seconds, the page requests approx 40kb of JSON from the server, and draws a table on the page using it. It is cheaper to draw the table over because the data is usually always new. I am attaching a few events to the table, approx 5 per line, 30 lines in the table. I used jQuery's .html() method to put the new html into the container and overwrite the existing. I do this specifically so that jQuery's special cleanup functions go in and attempt to detach all events on the elements in the element that it is overwriting. I then also delete the large variables of html once they are sent to the DOM using delete my_var. I have checked for circular references and attached events that are never cleared a few times, but never REALLY dug into it. I was wondering if someone could give me a few pointers on how to optimize a very heavy app like this. I just picked up "High Performance Javascript" by Nicholas Zakas, but didn't have much time to get into it yet. To give an idea on how much memory this is using, after 4~ hours, it is using about 420,000k on chrome, and much more on Firefox or IE. Thanks!

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  • Validating collection elements in WPF

    - by Chris
    I would like to know how people are going about validating collections in WPF. Lets say for example that I have an observable collection of ViewModels that I am binding to the items source of a grid, and the user can add new rows to the grid and needs to fill them. First of all I need to validate on each row to ensure that required fields of each ViewModel are filled in. This is fine and simple to do for each row. However, the second level of validation is on the collection as a whole. For example i want to ensure that no two rows of the collection have the same identifier, or that no two rows have the same name. Im basically checking for duplicate properties within different rows. I also have more complex conditions where I must ensure that there is at least one item within the collection that has some property set. How do I get a validation rule that would allow me to check these rules, validating on the whole collection rather than the individual items. I also want to print any validation error above the datagrid so that the user can fix the problem and the message will update or disappear as the user fixes each different rule. Anyone have any experience of the proper way to do this? Thanks Chris

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  • Nested parsers in happy / infinite loop?

    - by McManiaC
    I'm trying to write a parser for a simple markup language with happy. Currently, I'm having some issues with infinit loops and nested elements. My markup language basicly consists of two elements, one for "normal" text and one for bold/emphasized text. data Markup = MarkupText String | MarkupEmph [Markup] For example, a text like Foo *bar* should get parsed as [MarkupText "Foo ", MarkupEmph [MarkupText "bar"]]. Lexing of that example works fine, but the parsing it results in an infinite loop - and I can't see why. This is my current approach: -- The main parser: Parsing a list of "Markup" Markups :: { [Markup] } : Markups Markup { $1 ++ [$2] } | Markup { [$1] } -- One single markup element Markup :: { Markup } : '*' Markups1 '*' { MarkupEmph $2 } | Markup1 { $1 } -- The nested list inside *..* Markups1 :: { [Markup] } : Markups1 Markup1 { $1 ++ [$2] } | Markup1 { [$1] } -- Markup which is always available: Markup1 :: { Markup } : String { MarkupText $1 } What's wrong with that approach? How could the be resolved? Update: Sorry. Lexing wasn't working as expected. The infinit loop was inside the lexer. Sorry. :) Update 2: On request, I'm using this as lexer: lexer :: String -> [Token] lexer [] = [] lexer str@(c:cs) | c == '*' = TokenSymbol "*" : lexer cs -- ...more rules... | otherwise = TokenString val : lexer rest where (val, rest) = span isValidChar str isValidChar = (/= '*') The infinit recursion occured because I had lexer str instead of lexer cs in that first rule for '*'. Didn't see it because my actual code was a bit more complex. :)

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  • general learning methodology

    - by momo
    just wanted to hear on the different general learning paths people embark on when learning a new language/framework. the one i currently use, which is how i learned bash and am currently learning python, is: instant hacking tutorial (very short tutorial introducing the basic syntax, variable declaration, loops, data types, etc. and how they are generally used) in depth tutorial with good programming style and slightly topic-specific (e.g. Mark Pilgrim's Dive into Python), important topics for me personally are regex methods, file IO, and ways the different data types are utilized best (i wrote a very primitive bayesian spam filter using python's dictionaries to keep track of word occurrences) spaced-repition of syntax or short recipes (i use anki, with questions like 'create dictionary with filename and filesize metadata, human-readable' or simpler ones like 'match 0 - 3 occurences of the letter M in a string', or 'return/create an iterator from two sequences') the use of spaced-repitition has been invaluable, and i credit it with the ease that i can recall/create python algorithms. however, i've recently started looking into django, and i've found that spaced-repitition, at least in my case, doesn't work very well for learning a framework, it works best with short code recipes (either that or i should start looking into more basic django framework tutorials). the problem i'm encountering is that since framework programming is not only algorithms, but actually learning the API, which can be quite complex since you have to learn all the methods, modules, the places where they are stored, and the sequence of which things have to be done. for ex. in django to start a project that deals with polls (from the django tutorial), one has to create the project, edit the settings.py file, create the polls app, edit the models.py file (which requires knowing the classes that are present in the module models), edit the urls.py file, etc. i found that my spaced-repition method didn't work very well for this type of learning, so i wanted to ask you guys what method(s) you use for learning the different frameworks/APIs.

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